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From Greenland to Green Lakes: cultural eutrophication and the loss of benthic pathways in lakes
Limnology and Oceanography
Abstract
Benthic community responses to lake eutrophication are poorly understood relative to pelagic responses. We compared phytoplankton and periphyton productivity along a eutrophication gradient in Greenland, U.S., and Danish lakes. Phytoplankton productivity increased along the phosphorus gradient (total phosphorus (TP) 5 2-430 mg m 23 ), but whole-lake benthic algal productivity decreased, substantially depressing increases in primary productivity at the whole-lake scale. In shallow, oligotrophic Greenland lakes, periphyton was responsible for 80-98% of primary production, whereas in Danish lakes with TP . 100 mg m 23 , phytoplankton were responsible for nearly 100% of primary production. Benthic contributions ranged from 5 to 80% depending on morphometry and littoral habitat composition in lakes with intermediate phosphorus concentrations. Thus, eutrophication was characterized by a switch from benthic to pelagic dominance of primary productivity. Carbon stable isotope analysis showed that the redistribution of primary production entailed a similar shift from periphyton to phytoplankton in the diets of zooben- thos. Benthic and pelagic habitats were energetically linked through food web interactions, but eutrophication eroded the benthic primary production pathway.
... The relative abundance of sand, mud, rocks, and submerged aquatic vegetation in nearshore, littoral habitats depends upon interactions among erosional forces (e.g., wind-waves and currents), the structural complexity imparted by variation in geologic parent material, and basin slope. Littoral attached (benthic) algae grow on submerged surfaces from the lake edge to a depth below 1% surface irradiance, and light and nutrients strongly influence the distribution and productivity of benthic algae (Ask et al., 2009;Vadeboncoeur et al., 2003Vadeboncoeur et al., , 2001. However, our understanding of the spatial variation in attached algal biomass imparted by physical disturbance is rudimentary (Kahlert et al., 2002;Vadeboncoeur et al., 2014), which is concerning because climate change will increase the frequency of extreme weather events (Jabbari et al., 2021) and reduce lake ice cover . ...
... Wave-influenced cobble erosional habitats are a small fraction of total habitat for benthic algae in the Laurentian Great Lakes, and both resource availability and physical stressors differ from what algae in the more extensive depositional habitats experience. Decreases in light with depth overwhelmingly influence the distribution and productivity of benthic algae growing on nutrient-rich soft sediments (Ask et al., 2009;Godwin et al., 2014;Vadeboncoeur et al., 2014Vadeboncoeur et al., , 2008Vadeboncoeur et al., , 2003, but benthic algae on rocky wave-washed shores experience saturating light intensities. However, the algae that colonize these rocky habitats do not benefit from the substratum-associated nutrients typical of soft, unconsolidated sediments in depositional zones (Vadeboncoeur et al., 2003). ...
... Decreases in light with depth overwhelmingly influence the distribution and productivity of benthic algae growing on nutrient-rich soft sediments (Ask et al., 2009;Godwin et al., 2014;Vadeboncoeur et al., 2014Vadeboncoeur et al., , 2008Vadeboncoeur et al., , 2003, but benthic algae on rocky wave-washed shores experience saturating light intensities. However, the algae that colonize these rocky habitats do not benefit from the substratum-associated nutrients typical of soft, unconsolidated sediments in depositional zones (Vadeboncoeur et al., 2003). In large oligotrophic lakes, algal assemblages in erosional littoral habitats are often dominated by taxa that grow closely appressed to the substrate (e.g., adnate diatoms) or short turfs of nitrogen-fixing cyanobacteria or filamentous green algae with strong holdfasts (Cantonati and Lowe, 2014;Higgins et al., 2006;Reuter et al., 1983). ...
... The sources of sedimentary OM in lakes include both within-lake production (autochthonous) and terrestrial materials from surrounding catchments (allochthonous) that are transported to the lake via runoff or eolian deposition. Autochthonous production includes primary production and heterotrophic bacterial production in benthic and pelagic habitats, which are limited primarily by light and nutrients, respectively (Vadeboncoeur et al. 2003;Ask et al. 2009). For autochthonous materials, their relative contribution to surface sediment OC increases with the mean light irradiation in both arctic and boreal lakes . ...
... Depth and transparency can affect three aspects of lacustrine OM dynamics-generation/input, sedimentation, and preservation, which eventually influence the quantity of organic materials preserved in lacustrine sediments. Autochthonous OM can be produced in the benthic habitat, where primary production and heterotrophic bacterial production are mostly limited by light, or in the pelagic habitat, where production is limited largely by nutrients (Vadeboncoeur et al. 2003). Benthic production usually dominates in clearwater lakes (Ask et al. 2009), while the contribution of pelagic primary productivity increases with nutrient availability (Vadeboncoeur et al. 2003). ...
... Autochthonous OM can be produced in the benthic habitat, where primary production and heterotrophic bacterial production are mostly limited by light, or in the pelagic habitat, where production is limited largely by nutrients (Vadeboncoeur et al. 2003). Benthic production usually dominates in clearwater lakes (Ask et al. 2009), while the contribution of pelagic primary productivity increases with nutrient availability (Vadeboncoeur et al. 2003). To evaluate the relative importance of benthic vs. pelagic primary productivity, we estimated the depth of euphotic zone of the study lakes based on the relationships between transparency and euphotic zone (Kalff 2002). ...
Identifying primary environmental drivers mediating the quantity and quality of sedimentary organic matter (OM) in climate‐sensitive alpine lakes is crucial to understanding the role of alpine lakes in greenhouse gas emissions and Earth's climate system. Here, we characterized various pools of OM of 20 alpine lakes across the Tibetan Plateau, including bulk OM, water‐soluble OM and alkaline‐extracted OM from surface sediments, and dissolved OM (DOM) from surface water. The total organic carbon (TOC) content in sediments was low (< 3%), and δ13C of TOC and C : N ratios indicated limited allochthonous carbon inputs. Sedimentary water‐soluble OM and alkaline‐extracted OM were both dominated by low‐molecular‐weight, low‐aromaticity compounds with low contributions of terrestrial humic substances, suggesting that sedimentary leachable OM was primarily regulated by in‐lake sources and processes. Redundancy analysis showed that water depth, water transparency, and total phosphorus concentration in water column explained ~ 50% variance of sedimentary bulk and leachable OM, substantiating the importance of autochthonous sources and primary productivity in regulating the quantity and quality of sedimentary OM. Compared with lake surface water DOM, water‐soluble OM and alkaline‐extracted OM from sediments had higher proportions of terrestrial humic‐like substances, suggesting preferential preservation of allochthonous materials in sediments. Our results are the first to demonstrate a clear link between physical attributes and sedimentary OM in Tibetan lakes. The associated relations predict that the amount of total OM and autochthonous carbon preserved in sediments would increase due to the lake enlargement under the scenarios of climate warming and precipitation enhancement, which may amplify greenhouse gas emissions from Tibetan lakes.
... Consequently, lake browning and eutrophication will alter algal and invertebrate community composition, which has negative impacts on the availability and trophic transfer of EPA and DHA in lake food webs (Strandberg et al. 2015;Taipale et al. 2016;Kesti et al. 2021). By suppressing benthic primary and secondary productivity due to lower light and oxygen, darker water, and intensified stratification, a decline in the relative importance of benthic trophic pathways is expected (Vadeboncoeur et al. 2003;Solomon et al. 2015). The impacts of browning on PUFA occur at community levels and within species. ...
... We analyzed fatty acid-specific stable carbon isotope values (δ 13 C FA ) of macroinvertebrates and these basal resources to test the hypothesis that macroinvertebrates in humic and eutrophic lakes have lower total fatty acid and EPA contents, but higher contents of bacterial fatty acids (BCFA) compared to those in clear and oligotrophic lakes. We based this hypothesis on the assumption that increasing nutrient and DOC concentrations lower the periphyton biomass due to shading and consequently the periphyton availability to macroinvertebrate diets (Vadeboncoeur et al. 2003;Ask et al. 2009;Butkas et al. 2011). In eutrophic lakes, we also expected to find lower EPA content in macroinvertebrates due to higher proportions of the cyanobacteria in the water column and loss of benthic algal energy pathways (Vadeboncoeur et al. 2003). ...
... We based this hypothesis on the assumption that increasing nutrient and DOC concentrations lower the periphyton biomass due to shading and consequently the periphyton availability to macroinvertebrate diets (Vadeboncoeur et al. 2003;Ask et al. 2009;Butkas et al. 2011). In eutrophic lakes, we also expected to find lower EPA content in macroinvertebrates due to higher proportions of the cyanobacteria in the water column and loss of benthic algal energy pathways (Vadeboncoeur et al. 2003). Nevertheless, we predicted strong relationships between δ 13 C values of periphyton and invertebrate EPA, because algal-derived EPA is required and readily used for somatic growth (Karlsson 2007;Brett et al. 2017;Grieve and Lau 2018), and because motile benthic invertebrates can selectively feed on different periphyton assemblages (Devlin et al. 2013). ...
We studied how physiologically important long-chain polyunsaturated fatty acids (PUFA) in benthic macroinvertebrates (Asellus aquaticus, Chironomidae, and Oligochaeta) were related to those in periphyton and terrestrial organic matter (tree leaves), collected from littoral areas of 17 boreal lakes that differed in their dissolved organic carbon (DOC) and nutrient (phosphorus and nitrogen) concentrations. We also analyzed fatty acid (FA)-specific stable carbon isotopes (δ 13 C FA) to investigate the dietary origin (periphyton vs. terrestrial organic matter) of PUFA in the consumers. In contrast to periphyton, terrestrial organic matter was deprived of long-chain PUFA, such as eicosapentaenoic acid (EPA), but rich in short-chain PUFA. The FA composition of macroinvertebrates was primarily taxon-specific despite the large differences in DOC and nutrient concentrations of the lakes. An increase in DOC concentration had a negative impact on the EPA content of Asellus, chi-ronomids, and oligochaetes as well as the total FA content of chironomids and oligochaetes. However, the FA content of macroinvertebrates was not related to lake total phosphorus concentrations, although the total FA and EPA content of periphyton increased with the trophic status of the study lakes. The δ 13 C PUFA values of macroinvertebrates were positively related with the δ 13 C PUFA of periphyton and weakly with δ 13 C PUFA of terrestrial leaf material. The results indicate that EPA in the studied macroinvertebrate taxa was mainly derived from an algal-based diet and not via biosynthesis from allochthonous precursor FA. Thus, macroinvertebrate production in lakes may be limited by the available algae-based food sources.
... Benthic primary production and oxygen consumption are important components of lake biogeochemical cycling. Early studies paid similar attention to planktonic and benthic producers (Forbes, 1887;Lindeman, 1942;Hutchinson, 1957), however, in the late 20th century, theoretical and experimental limnology focused mainly on pelagic habitats and only scarcely were data of benthic processes integrated into the whole-lake dynamics (Vadeboncoeur et al., 2001;Vadeboncoeur et al., 2003;Cantonati and Lowe, 2014;Vander Zanden and Vadeboncoeur, 2002). In the past few decades, researchers have renewed their recognition of the importance of benthic pathways. ...
... A substantial body of studies has specifically delved into the production and the role of the phytobenthos, along with its interactions with phytoplankton (Vadeboncoeur and Vadeboncoeur and Steinman, 2002;Reynolds, 2008;Vadeboncoeur et al., 2008;Genkai-Kato et al., 2012;Vadeboncoeur et al., 2014;Rodríguez and Pizarro, 2015;Daniels et al., 2015;Steinman et al., 2016;Vesterinen et al., 2016;Vander Zanden and Vadeboncoeur, 2002). The starting point of this progress was the recognition of the significance of a compensatory trade-off between benthic and pelagic primary producers across a trophic gradient (Vadeboncoeur et al., 2003;Daniels et al., 2015). In other words, re-oligotrophicationwhich occurs in many lakes worldwide since the end of the 20th century as a result of largescale efforts to reduce nutrient inputdoes not necessarily imply a decrease in whole-lake primary production because of a transition from pelagic primary productivity towards benthic dominance (Genkai-Kato et al., 2012;Steinman et al., 2016;Vander Zanden and Vadeboncoeur, 2002). ...
... resources (i.e., leaf litter) (Fig. 3), which verifies our hypothesis. The effect of nutrient enrichment on the diets of macroinvertebrates has been extensively studied, with many studies reporting an increase in the contribution of autochthonous resources to their diets (Price et al., 2019;Vadeboncoeur et al., 2003). Our study supports these findings, demonstrating a significant increase in the consumption of primary producers by macroinvertebrates in response to nutrient enrichment. ...
... Moreover, moderate nutrient inputs have the potential to amplify this effect on stream algal productivity (de Guzman, 2022). Many studies have shown that nutrient enrichment under conditions without light intensity limitation can increase the importance of primary producers in stream food webs and reduce the importance of upstream food chains (Cummins et al., 2005;Vadeboncoeur et al., 2003). This can lead to a reduction in trophic redundancy as fewer resources come from different trophic levels, thus reducing the resilience of the ecosystem to environmental changes (Layman et al., 2007b). ...
Riparian deforestation, which leads to increase in light intensity and excessive nutrient loading in waterways, are
two pervasive environmental stressors in the stream ecosystems. Both have been found to alter basal resource
availability and consequently stream food webs. However, their interactive effects on trophic structure in stream
food webs are unclear. Here, we manipulated light intensity and nutrient availability in three headwater streams
to evaluate their effects on consumer diet composition and food web characteristics (i.e., trophic diversity and
redundancy) with stable isotope analysis. Dietary analysis revealed that the relative contribution of stream
periphyton to the diets of macroinvertebrates increased, while that of allochthonous resources, specifically leaf
litter from the terrestrial ecosystems in the catchment, decreased in response to open canopy and nutrient
enrichment in the streams. The trophic diversity also increased with the elevated light intensity and nutrient
availability, while the trophic redundancy decreased, suggesting a reduced ability of the stream ecosystems to
resist environmental changes. Nutrient enrichment also increased the δ15N ratios of periphyton and macroinvertebrates,
indicating potential δ15N enrichment of stream benthos by nitrogen pollution. Our results suggested
that an increase in light intensity due to riparian canopy openness and stream water nutrient enrichment
primarily from human activities have interactive effects on resource flow and trophic structure in stream food
webs.
... Further reductions in light availability can be deduced from increasing particle resuspension in shallow areas related to increased storminess and dredging activity (Fettweis et al. 2011, Forsberg et al. 2019. Finally, also changes in autotrophic biomass and community composition itself alter light absorption, contributing to temporal trends of light availability (Opdal et al. 2019) with consequences for the relative role of benthic and pelagic primary producers (Vadeboncoeur et al. 2003, Griffiths et al. 2017. ...
... This can easily be explained by the interdependency of categorizations as all plankton are microalgae, but some microalgae are benthic. We had expected that benthic and pelagic organisms respond differently to light attenuation given the strong role of vertical light profile in the interaction between phytobenthos and phytoplankton (Vadeboncoeur et al. 2003). Moreover, Duarte (1991) showed that the distribution depth of seagrasses is highly light limited and their strong response to light reduction might reflect a high sensitivity of these marine angiosperms to underwater light attenuation (Williams andRuckelshaus 1993, Carr et al. 2010). ...
The availability of underwater light, as primary energy source for all aquatic photoautotrophs, is (and will further be) altered by changing precipitation, water turbidity, mixing depth, and terrestrial input of chromophoric dissolved organic matter (CDOM). While experimental manipulations of CDOM input and turbidity are frequent, they often involve multiple interdependent changes (light, nutrients, C‐supply). To create a baseline for the expected effects of light reduction alone, we performed a weighted meta‐analysis on 240 published experiments (from 108 studies yielding 2500 effect sizes) that directly reduced light availability and measured marine autotroph responses. Across all organisms, habitats, and response variables, reduced light led to an average 23% reduction in biomass‐related performance, whereas the effect sizes on physiological performance did not significantly differ from zero. Especially, pigment content increased with reduced light, which indicated a strong physiological plasticity in response to diminished light. This acclimation potential was also indicated by light reduction effects minimized if the experiments lasted longer. Nevertheless, the performance (especially biomass accrual) was reduced the more the less light intensity remained available. Light reduction effects were also more negative at higher temperatures if ambient light conditions were poor. Macrophytes or benthic systems were more negatively affected by light reduction than microalgae or plankton systems, especially in physiological responses were microalgae and plankton showed slightly positive responses. Otherwise, the effect magnitudes remained surprisingly consistent across habitats and aspects of experimental design. Therefore, the strong observed log–linear relationship between remaining light and autotrophic performance can be used as a baseline to predict marine primary production in future light climate.
... The results presented here demonstrate that three of the four environmental parameters commonly used to measure trophic level; light penetration (Secchi disk depth), TN, and TP, are important in controlling the structure of lake diatom communities, and that diatom community structure and life-history traits differ among trophic levels. These findings are consistent with trends common to lakes undergoing eutrophication (Jeppesen et al., 2000;Vadeboncoeur et al., 2003), and with diatom ecology. For example, diatoms are photosynthetic organisms, and their growth and reproduction are inherently linked to light and nutrients (Battarbee et al., 2001). ...
... For example, the shift in the Rototoa diatom community profile beginning at approximately 1980 CE was primarily due to the rapid increase in one species, Fragilaria crotonensis, and a consequent shift to a predominantly pelagic assemblage . While this shift does not translate to a change in the TLI3 of the lake, it does have important environmental implications; Fragilaria crotonensis is considered an indicator of increasing nitrogen concentrations in Rototoa and shifts to pelagic dominance are frequently associated with decreasing light availability and increasing eutrophication, in this and other studies (Vadeboncoeur et al., 2003;Vadeboncoeur et al., 2001). This information strongly suggests that Rototoa is undergoing eutrophication despite there being no change in the TLI3. ...
Lakes provide crucial ecosystem services and harbour unique and rich biodiversity, yet despite decades of research and management focus, cultural eutrophication remains a predominant threat to their health. Our ability to manage lake eutrophication is restricted by the lack of long-term monitoring records. To circumvent this, we developed a bio-indicator approach for inferring trophic level from lake diatom communities and applied this to sediment cores from two lakes experiencing eutrophication stress. Diatom indicators strongly predicted observed trophic levels, and when applied to sediment cores, diatom predicted trophic level reconstructions were consistent with monitoring data and land-use histories. However, there were significant recent shifts in diatom communities not captured by the diatom-based index or monitoring data, suggesting that conventional trophic level indices obscure important ecological change. New approaches, such as the one in this study, are critical to detect early changes in water quality and prevent the decline of lake ecosystems worldwide.
... Changes in optical properties and nutrient status of the water are major factors regulating GPP and autotrophic structuring, and drivers of these factors differ across regions (Kosten et al., 2009;Krause-Jensen et al., 2012). In temperate, nutrient rich landscapes, eutrophic conditions promote pelagic GPP, resulting in increased turbidity and shading of the benthic habitat (Krause-Jensen et al., 2012;Scheffer & Jeppesen, 2007;Vadeboncoeur et al., 2003). Such lakes can, through complex feedback loops, abruptly shift into clear-watered states in the presence of macrophytes Kosten et al., 2009;Scheffer, 2004;Schindler & Scheuerell, 2002). ...
... In addition, considering the dominance of benthic processes in many northern shallow lakes (Karlsson & Säwström, 2009), it would take considerable increases in pelagic GPP in response to CO 2 and/or nutrients (Bergström & Karlsson, 2019;Vadeboncoeur et al., 2003) to decrease autotrophic structuring. Indeed, while experimental studies are needed to test these mechanisms, results from the subarctic lakes suggest that increasing the supply of CO 2 may instead increase autotrophic structuring through stimulating effects on benthic GPP. ...
Global change affects gross primary production (GPP) in benthic and pelagic habitats of northern lakes by influencing catchment characteristics and lake water biogeochemistry. However, how changes in key environmental drivers manifest and impact total (i.e., benthic + pelagic) GPP and the partitioning of total GPP between habitats represented by the benthic share (autotrophic structuring) is unclear. Using a dataset from 26 shallow lakes located across Arctic, subarctic, and boreal northern Sweden, we investigate how catchment properties (air temperature, land cover, hydrology) affect lake physico‐chemistry and patterns of total GPP and autotrophic structuring. We find that total GPP was mostly light limited, due to high dissolved organic carbon (DOC) concentrations originating from catchment soils with coniferous vegetation and wetlands, which is further promoted by high catchment runoff. In contrast, autotrophic structuring related mostly to the relative size of the benthic habitat, and was potentially modified by CO2 fertilization in the subarctic, resulting in significantly higher total GPP relative to the other biomes. Across Arctic and subarctic sites, DIC and CO2 were unrelated to DOC, indicating that external inputs of inorganic carbon can influence lake productivity patterns independent of terrestrial DOC supply. By comparison, DOC and CO2 were correlated across boreal lakes, suggesting that DOC mineralization acts as an important CO2 source for these sites. Our results underline that GPP as a resource is regulated by landscape properties, and is sensitive to large‐scale global changes (warming, hydrological intensification, recovery of acidification) that promote changes in catchment characteristics and aquatic physico‐chemistry. Our findings aid in predicting global change impacts on autotrophic structuring, and thus community structure and resource use of aquatic consumers in general. Given the similarities of global changes across the Northern hemisphere, our findings are likely relevant for northern lakes globally.
... Nutrients tend to be higher near the bottom of the lake because of exchanges from the sediment, and benthic producers such as macrophytes and periphyton are better positioned to use these resources in the littoral zone, when not limited by light availability. In oligotrophic lakes, periphyton can be responsible for greater than 80% of primary productivity, while phytoplankton increasingly dominates productivity as total phosphorus increases (Vadeboncoeur et al. 2003). Shifting producer dominance from the benthos to phytoplankton can impact the structure of the food web in the littoral zone, with more zoobenthos relying on phytoplankton prey over benthic algae (Vadeboncoeur et al. 2003). ...
... In oligotrophic lakes, periphyton can be responsible for greater than 80% of primary productivity, while phytoplankton increasingly dominates productivity as total phosphorus increases (Vadeboncoeur et al. 2003). Shifting producer dominance from the benthos to phytoplankton can impact the structure of the food web in the littoral zone, with more zoobenthos relying on phytoplankton prey over benthic algae (Vadeboncoeur et al. 2003). This variability can drive differences in the ecological community as depth increases (Ali et al. 2002;Hämäläinen et al. 2003). ...
Lakes are currently facing multiple anthropogenic stressors impacting their ecological communities. The best way to understand how these systems will be affected by the changing environment is by modeling community dynamics. Models of lake food webs have tended to focus on pelagic organisms and treat lakes as if they contain single, uniform communities. However, heterogeneity in environmental conditions and resource availability generates within‐lake compartmentalization in food web structure. Turnover among species and their interactions resulting from differences in depth and substrate type creates unique food webs in different regions of lakes. Food webs within lakes can therefore be represented as a three‐dimensional meta‐ecosystem, where food web compartments are connected by flows of nutrients, materials, and consumers with variable degrees of mobility within the lake. We review how food webs are spatially structured within lakes and the processes that connect different parts of the ecosystem. We then discuss how current modeling approaches address the spatial heterogeneity of lake communities, highlighting key methods and some of the constraints preventing more spatially explicit representation of food webs. Finally, we recommend the use of allometric trophic networks to make spatially explicit food web modeling easier. By capitalizing on empirically described allometric relationships to parameterize trophically complex food webs, we can balance generalizable model approaches with system‐specific needs. Given the spatially explicit nature of many current threats to freshwater lakes, building an understanding of how space structures the community is imperative to create better approaches for freshwater management and conservation.
... The changes in water N:P ratios can affect epipelon growth in shallow lakes and reservoirs (Lambert et al. 2008), as widely observed in phytoplankton. The epipelon can substantially contribute to primary productivity and total biomass in lakes and reservoirs (Vadeboncoeur et al. 2003, Cano et al. 2016. Additionally, epipelon can oxidize the surface layer of the sediment and immobilize P, which contributes to the decreased P concentrations in the water column (Wetzel 2001, Dodds 2003. ...
Nitrogen and phosphorus are essential elements for the growth and performance of organisms, and the environmental N:P ratio can determine the biomass and structure of algal communities. We investigated the effects in the N:P molar ratio changes on epipelon and phytoplankton chlorophyll-a under eutrophic conditions. An enrichment experiment was performed in open-bottom mesocosms to simulate P limitation, N limitation, and good N and P availability. Under eutrophic conditions, the combined availability of N and P enhanced phytoplankton bloom, while an increase in P limitation resulted in the loss of phytoplankton biomass. Under conditions of high P limitation, there was significantly loss of epipelon biomass. No change in the N:P ratio led to a significant increase in algal biomass in the epipelon. In conclusion, changes in the N:P molar ratio can affect the growth of phytoplankton and epipelic algae under eutrophic conditions. Our results suggest that photosynthetic biomass increase in the epipelon depends on an optimal relationship between light and P.
Keywords:
enrichment; eutrophic reservoir; N and P limitation; mesocosm experiment
... Moreover, compartmentalization and the loss of natural ecotones can significantly reduce the inflow of allochthonous organic matter (OM) from the catchment into coastal reservoir lakes, an important component of secondary productivity in natural lake systems (Cole et al., 2006;Tanentzap et al., 2017). Subsequently, changes in the availability of food sources in such coastal reservoir lakes are expected to influence trophic transfer and trophic links in the food web, which may potentially have cascading effects on higher trophic levels (Genkai-Kato et al., 2012;Vadeboncoeur et al., 2003) and large consequences for ecosystem functioning (Thébault and Loreau, 2003;Mulder et al., 2012). However, to our knowledge, a thorough understanding of the food-web structure of enclosed coastal reservoir lakes is still lacking. ...
... Aquatic metabolism, and thus C cycling, are responsive to human activities including ongoing climatic and hydrological changes, eutrophication, and increased catchment disturbances that modify the transport of solutes into lakes (Oleksy et al., 2021;Solomon et al., 2015;Vadeboncoeur et al., 2003). Within this framework, the most commonly described controls of metabolic processes are nutrient and dissolved organic C (DOC) availability, light, and water temperature Bergstrom & Karlsson, 2019;Staehr et al., 2010). ...
The Arctic is the fastest warming biome on the planet, and environmental changes are having striking effects on freshwater ecosystems that may impact the regional carbon cycle. The metabolic state of Arctic lakes is often considered net heterotrophic, due to an assumed supply of allochthonous organic matter that supports ecosystem respiration and carbon mineralization in excess of rates of primary production. However, lake metabolic patterns vary according to regional climatic characteristics, hydrological connectivity, organic matter sources and intrinsic lake properties, and the metabolism of most Arctic lakes is unknown. We sampled 35 waterbodies along a connectivity gradient from headwater to downstream lakes, on southern Victoria Island, Nunavut, in an area characterized by low precipitation, organic‐poor soils, and high evaporation rates. We evaluated whether lakes were net autotrophic or heterotrophic during the open water period using an oxygen isotopic mass balance approach. Most of the waterbodies were autotrophic and sites of net organic matter production or close to metabolic equilibrium. Autotrophy was associated with higher benthic primary production, as compared to its pelagic counterpart, due to the high irradiance reaching the bottom and efficient internal carbon and nutrient cycling. Highly connected midstream and downstream lakes showed efficient organic matter cycling, as evidenced by the strong coupling between gross primary production (GPP) and ecosystem respiration, while decoupling was observed in some headwater lakes with significantly higher GPP. The shallow nature of lakes in the flat, arid region of southern Victoria Island supports net autotrophy in most lakes during the open water season. Ongoing climate changes that lengthen the ice‐free irradiance period and increase rates of nutrient evapoconcentration may further promote net autotrophy, with uncertain long‐term effects for lake functioning.
... Studies of lake ecosystems have focused predominantly on macroscopic pelagic processes as humans were most interested in the stock of edible fish (Reynolds, 2008). Yet, the abundant communities of benthic organisms producing or recycling organic matter are a vital trophic pathway supporting fish biomass directly or indirectly by remineralizing organic matter for renewed autochthonous primary production (Vadeboncoeur et al., 2003). The role of benthic macroinvertebrates in this process has been extensively studied (Schindler and Scheuerell, 2002;Weidel et al., 2008;Zanden and Vadeboncoeur, 2002). ...
... Studies comparing phytoplankton and periphyton behavior under eutrophic conditions are scarce and have generally been conducted in temperate and subtropical regions (e.g., Vadeboncoeur et al., 2003;Crossetti et al., 2013;Rimet et al., 2015;Sánchez et al., 2016;Kolada et al., 2016;Ovaskainen et al., 2019;Pećić et al., 2023). Knowledge of these algal communities at high-altitude tropical lakes is even more limited (Lazzaro, 1981;Fontúrbel and Castaño-Villa, 2011;Komárková et al., 2016;Lanza et al., 2017). ...
Eutrophication is a global environmental problem in aquatic ecosystems, mainly caused by increased nutrient loads (nitrogen and phosphorus). Phytoplankton and periphyton responses to the nutrients increase and temporal variation may be related to mutual seeding and/or variable environmental constraints. Each of these communities may be useful for characterizing and monitoring eutrophication processes. However, little information exists about the simultaneous responses or interactions between such communities during eutrophication, even less in high-altitude tropical lakes such as Lake Titicaca. Here, we first established a eutrophication gradient with stable isotopes (δ15N and δ13C) and physicochemical variables in a shallow bay of Lake Titicaca. Later, we analyzed the shifts in taxonomic and morphological forms of phytoplankton and periphyton colonizing the underwater stems of totora (Schoenoplectus californicus ssp. tatora), an emergent aquatic macrophyte, along the eutrophication gradient. There is a clear turnover (groups, genera, and morphological forms) in phytoplankton and periphyton and decreased biodiversity along the eutrophication gradient. Gomphonema genus relative abundance increase with eutrophication in both communities, while Achnanthidium abundance decreases. However, other genera behave differently in each community, allowing for the identification of specific bioindicators of eutrophication for phytoplankton (Oscillatoria, Spirogyra, and Euglena) and periphyton (Oedogonium, Stigeoclonium, and Characium). They share genus composition with some taxa showing similar behaviors, thus interactions between phytoplankton and periphyton may exist. We also believe that each compartment can act as a seeding reservoir for the other, though remaining independent to some extent.
... It is also possible that primary production in the openwater season can play a role in the seasonal CO 2 exchange dynamics. While these lakes are nutrient-poor, favorable light conditions can maintain high growth rates by benthic algae that have access to nutrients in sediments (Hansson 1992;Vadeboncoeur et al. 2003). Published values of summer gross primary production in the lakes are similar to the CO 2 evasion at ice-melt presented in this paper. ...
Current estimates of carbon dioxide (CO2) evasion from Arctic lakes are highly uncertain because few studies integrate seasonal variability, specifically evasion during spring ice-melt. We quantified annual CO2 evasion for 14 clear-water Arctic lakes in Northern Sweden through mass balance (ice-melt period) and high-frequency loggers (open-water period). On average, 80% (SD: +-18) of annual CO2 evasion occurred within 10 d following ice-melt. The contribution of the ice-melt period to annual CO2 evasion was high compared to earlier studies of Arctic lakes (47% +-32%). Across all lakes, the proportion of ice-melt : annual CO2 evasion was negatively related to the dissolved organic carbon concentration and positively related to the mean depth of the lakes. The results emphasize the need for measurements of CO2 exchange at ice-melt to accurately quantify CO2 evasion from Arctic lakes.
... been an important source of primary production in Lake Manitoba throughout the past 200 years. Interestingly, most phytobenthic diatoms (by abundance) did not decline during initial fertilisation of Lake Manitoba, in contrast to patterns seen in other lakes undergoing cultural eutrophication (Vadeboncoeur et al., 2003). Before c. 1890, assemblages were composed mainly (c. ...
Evaluation of large lake response to centennial changes in land use and climate can be complicated by high spatial and hydrological complexity within their catchments, particularly in regions of low relief. Furthermore, large lakes can exhibit abrupt changes in structure and function that obscure causes of eutrophication.
We provide the first quantification of historical trends in lake production, cyanobacterial abundance, sediment geochemistry and diatom composition since c. 1800 in Lake Manitoba, the 29th largest lake in the world, and compared them to Lake Winnipeg, a morphologically similar, adjacent basin with a 10‐fold larger catchment and an abrupt increase in production around 1990.
Before 1900, Lake Manitoba was mesotrophic, with low sedimentary concentrations of carbon, phosphorus, nitrogen, cyanobacteria and algal pigments, as well as assemblages of low‐light‐adapted benthic diatoms. Analysis of pigment time‐series with hierarchical generalised additive models revealed that Lake Manitoba eutrophied during 1900–1930 as a consequence of the development of intensive agriculture within its local catchment, but thereafter exhibited stable cyanobacterial densities with limited expansion of N 2 ‐fixing cyanobacteria despite persistent eutrophication.
Lake Manitoba did not undergo an abrupt change as seen in Lake Winnipeg.
These findings suggest that catchment size had little influence on water quality degradation and that nutrient influx from proximal agricultural sources was sufficient to initially degrade these large prairie lakes. The abrupt change in Lake Winnipeg around 1990 required additional intensification of local land use that did not occur in the Lake Manitoba catchment.
... With this in mind, any factors that limit production of macrophytes and their epiphytes may ultimately hinder fish production (Karlsson et al. 2009;Jardine et al. 2013) and affect the livelihood of people that rely on the ecosystem services provided by one of the last large free-flowing rivers in the tropics and its surrounding floodplain. Alterations in hydrological connectivity, introduction of non-native herbivorous fish (e.g., grass carp), and eutrophication of water bodies in this region are of great concern, as they may trigger shifts in the equilibrium between periphytic and planktonic algal production in the lakes (Scheffer et al. 1993;Vadeboncoeur et al. 2003;Phillips et al. 2016;Castillo 2020). Efforts of environmental conservation and management programs in this region and from other large floodplain ecosystems should focus on preventing the loss of macrophytes and their attached algal pathways to preserve the biological diversity and fishery yield of these vital ecosystems. ...
Floodplain lakes are highly productive and biodiverse ecosystems whose food webs depend on a variety of autochthonous and allochthonous resources. Thus far, the role of attached algae, and epiphytes in particular has been understudied, although often high densities of macrophytes in these lakes may provide extensive substrate for attached algal growth. Our goal was to evaluate spatial and temporal variability in food web dynamics of three floodplain lakes permanently connected to the Usumacinta River, with emphasis on the role of epiphytes as a carbon source for upper trophic levels. To achieve this, we analyzed the physicochemical properties of water and stable isotopes of fish and invertebrate consumers and potential autochthonous (macrophytes, phytoplankton, epiphytes, epipelon) and allochthonous (terrestrial organic matter) basal resources during the rainy and dry seasons. The mixing model output highlighted the crucial role of epiphytes as the main energy pathway supporting secondary production year-round, while aquatic macrophytes were of secondary importance. The contribution of terrestrial organic matter to consumers was low, mostly limited to invertebrates, and overall increased from the rainy to the dry season, countering expectations of higher allochthony following strong seasonal flow pulses. Community-wide metrics further revealed higher trophic diversity among invertebrates as compared to fish. Our findings highlight the importance of preserving epiphytic energy pathways and macrophyte-periphyton linkages, as they provide key support to food webs of these vital fishery ecosystems.
... This strongly suggests that the fish density is lower in the open waters of larger, deeper lakes. This could be caused by a higher food availability in the more productive littoral environment [27], while in smaller and more elongated lakes, the habitats are so closely connected that fish move freely between them. The char catches decreased over the study period in both lakes. ...
Arctic char (Salvelinus alpinus) is a top predator and the most widespread fish in Arctic lakes. The presence of Arctic char affects the predator-prey dynamics of the key species in the food webs in these lakes. This study sought to elucidate the effects of habitat (littoral, pelagic, or profundal) and lake morphometry on the trophic position of this char in the food web. Using stomach content and stable isotope analyses, we investigated the effect of fish length, habitat, and time (individual survey years: 2008, 2013, 2018, and 2019) on the dietary niches of landlocked Arctic char populations during summer in two west Greenland lakes: Badesø (area 0.8 km 2 , mean depth 9.2 m) and Langesø (area 0.3 km 2 , mean depth 5.0 m). The small char (<20 cm fork length) in Badesø generally foraged less littoral macroinvertebrates than those from Langesø. The large chars were mainly piscivorous in both lakes. In Badesø, there was a shift from relying on littoral to pelagic invertebrates by the small char from 2008-2013 to 2018-2019. The proportionally larger size of the littoral habitat in the smaller Langesø led to an increased reliance on littoral-derived macroinvertebrates in the diet of the small char, more so than in the larger Badesø, where the predominant reliance was on pelagic sources.
... High inputs of colored humic compounds also lead to less available light in the water column, which can become limiting for photosynthesis and thus promote further oxygen depletion (Golosov et al., 2007;Kirillin et al., 2012;Modenutti et al., 2001;Rose et al., 2014;Walsh et al., 2003). This is particularly the case for benthic photosynthetic organisms, which are more affected by light attenuation in water and account for the majority of the primary production in shallow oligotrophic lakes (Karlsson et al., 2009;Vadeboncoeur et al., 2003). Thermokarst lakes and ponds, therefore, have several characteristics that make them particularly prone to O 2 deficiency; (a) low total O 2 contents; (b) prolonged ice and snow covers that impede light penetration and gas exchange; (c) cold waters that are more vulnerable to O 2 depletion due to warming that stimulates respiration; (d) organic rich sediment; and (e) high concentrations of dissolved organic matter attenuating the light available for photosynthesis and providing more substrates for respiration (Rautio et al., 2011). ...
Polar amplification of climate change has the potential to cause large‐scale shifts in the dissolved oxygen (DO) dynamics of Arctic lakes, with implications for fish survival, greenhouse gas production, and drinking water quality. While DO is also a sentinel of environmental changes of physical, chemical, and biological nature (e.g., ice cover, temperature, dissolved organic carbon, photosynthesis, and respiration), no synthesis exists of current knowledge of DO dynamics across the diverse freshwater systems of the Arctic. We thus conducted a systematic review of the literature that yielded DO data from 167 sites north of the Subarctic limit (based on vegetation zones), spanning 76 years and including 40 sites with time series. The compilation revealed insufficient observations for adequate representativeness of oxygen dynamics over Arctic ecosystem gradients. We described the main processes controlling DO budgets of Arctic lakes and tested relationships of summer oxygen depletion with maximum depth and latitude. The meta‐analysis showed that most sites with low O2 concentrations were shallow (<10 m) and situated toward the southern end of the latitudinal gradient. Permanently stratified lakes with deep, perennially anoxic basins were located toward the northern end of the gradient. By way of a conceptual model, we identified the direct and indirect drivers and mechanisms that lead to changes in oxygen budgets in the context of the warming Arctic. This comprehensive update on available data allowed us to suggest future research directions and recommend the use of moored instruments for continuous all‐season observations, combined with modeling, remote sensing, and paleo‐reconstructions.
... Increased pelagic primary production can also reduce light penetration and inhibit benthic primary production (Vadeboncoeur et al., 2003), leading to overall declines in food availability for consumers at all levels of the food web (Paerl et al., 1998;Rasconi et al., 2017;Schabhüttl et al., 2013). Furthermore, if increases in water temperature exceed consumers' thermal tolerances, declines in species abundances can be expected, with a shift toward more heat-tolerant species (Giersch et al., 2015;Jourdan et al., 2019;Strecker et al., 2004). ...
Globally, lakes are warming and browning with ongoing climate change. These changes significantly impact a lake's biogeochemical properties and all organisms, including invertebrate consumers. The effects of these changes are essential to understand, especially during critical periods after and before the growing season, that is, autumn and spring, which can determine the composition of the invertebrate consumer community.
In this study, we used a large‐scale experimental pond system to test the combined effect of warming (+3°C) and increased input of terrestrial and coloured dissolved organic carbon (gradient of 1.6–8.8 mg/L in the ambient and 1.6–9.3 mg/L in the warm)—which causes browning—on zooplankton and benthic macroinvertebrate biomass and composition during the autumn and the following spring.
Total zooplankton biomass decreased with warming and increased with browning, while total zoobenthos did not respond to either treatment. Warming and browning throughout the autumn had no overall interactive effects on zooplankton or zoobenthos. Autumnal warming decreased total pelagic consumer biomass, caused by a decrease in both Rotifera and Copepoda. In contrast, there was no effect on overall benthic consumer biomass, with only Asellus sp. biomass showing a negative response to warming. An autumnal increase in dissolved organic carbon led to increased total pelagic consumer biomass, which was related to increases in Daphnia sp. biomass but did not affect zoobenthos biomass. While we expected zooplankton and zoobenthos biomass to follow responses in primary and bacterial production to treatments, we did not find any relationship between consumer groups and these estimates of resource production.
Our results suggest that consumer responses to warming and browning during autumn may lead to less overarching general changes in consumer biomass, and responses are mostly taxon‐specific.
This study gives novel insights into the effects of warming and browning on consumer biomass during autumn and spring and increases the understanding of the effects of climate change on invertebrate community biomass in the different habitats.
... The size of the littoral zone determines the relative benthic vs. pelagic contribution to whole lake primary production (Vadeboncoeur et al. 2002). Consumer diets switch from periphyton to phytoplankton as water clarity decreases and the littoral zone diminishes (Vadeboncoeur et al. 2003). Some organisms also utilize littoral resources more in some seasons than others (Hayden et al. 2014;Stewart et al. 2017). ...
Lake water clarity is an indicator of water quality, trophic status, and habitat condition. Changes in clarity impact lake ecosystems and may reflect land use changes or presence of invasive species. Quantifying temporal changes in water clarity can be challenging because clarity varies seasonally, annually, and spatially within and among lakes. We developed a hierarchical generalized additive model to quantify trends in water clarity (Secchi depth) from 1979 to 2018 for 909 Minnesota lakes, accounting for seasonal and spatial variability. Water clarity increased by 0.41 m across lakes from 1984 to 1988 and 2014 to 2018. Lake‐specific clarity trends varied: clarity did not change significantly in 59.0% of lakes, increased in 34.5% of lakes, and decreased in 6.5% of lakes. Water clarity dynamics caused considerable variability in littoral area between seasons and years. Our results have wide applications in aquatic ecology, including understanding changes to food webs, assessing fish habitat, and evaluating impacts of invasive species.
... Benthic periphyton (algae) ecosystem functions include significant contributions to gross primary production (Velasco et al. 2003, trophic interactions (Moulten et al. 2004), ecosystem engineering (e.g., biostabilization of sediments; Dodds 2003;Droppo et al. 2007;Spears et al. 2007b) and regulation of nutrient cycling across the sedimentwater interface (Dodds 2003, Poulickova et al. 2008, Vadeboncoeur et al., 2003. Benthic algae are also vastly underappreciated contributors to pelagic fisheries and also increase retention of nutrients. ...
Utah Lake is a small remnant of ancient Lake Bonneville. The lake’s ecosystem has been severely degraded over the past 150 years or so, since first settled by Americans of European decent, including a shift from a clearer water stable state to a highly turbid unstable state, loss of native species including loss of aquatic vegetation, mollusks and fishes, introduction of nonnative species (particularly carp), nutrient addition, water level and flow regulation, and other pollutants, to name a few. Utah Lake’s water quality, foodweb, and ecosystem have been degraded to such a state that by many ecosystem measures, its resilience to future perturbation and resistance to improvement (restoration) appears to be compromised.
There is much concern as to the future of Utah Lake and what can be done to improve its condition (i.e., health, integrity), including the reduction of algal blooms. However, the focus of concern has been almost exclusively on nutrient reduction (bottom-up) and to a lesser extent invasive carp control. There has been little to no effort expended to examine or understand the importance of the lake’s food web and how top-down, trophic cascades directly and indirectly effect and respond to current conditions or how biomanipulation including restoring native aquatic vegetation and mollusks and a more balanced fishery may help restore its ecosystem. Restoring Utah Lake to reduce algal blooms, improve its fisheries and ecosystem function cannot proceed without this understanding.
The overall goal of this study was to understand factors that influence nutrient cycling, algal blooms, food web dynamics, and ecosystem functioning that contribute to the impairment of the health of Utah Lake’s ecosystem via in-lake mesocosm (limnocorral) experiments. Results of these ongoing studies will help direct managers to develop a holistic restoration program essential for improving the lake’s health using integrated and adaptive management strategies.
We examined the direct and indirect effects of application of nutrients, carp, pelagic fishes, aquatic plants (macrophytes), and bivalves, and in particular reduction in wave action using a series of limnocorrals (mesocosms) on:
1. Phytoplankton assemblages,
2. Benthic algae (periphyton) assemblages,
3. Zooplankton assemblages and,
4. Benthic invertebrate assemblages.
We postulated that the application of these treatments would have measurable direct and indirect effects on these four assemblages and that these non-target effects needed to be addressed. In addition, we expected that treatment effects would alter nutrient cycling and water quality in complicated interactions within the food web.
Ten large limnocorrals (mesocosms) were installed in Utah Lake near the outfall of Timpanogos Special Service District near Lindon, UT in Spring/early Summer 2022. Treatments included, macrophytes, bivalves, carp, and a combination of these, zooplanktivorous fish, nutrient additions, control corrals, and lake controls. In addition to regular weekly nutrient and chemistry data collection, we collected detailed phytoplankton, zooplankton, benthic invertebrate, and periphyton data on three occasions, start (May), middle (August), and end (October) of experiments.
Our results confirmed our hypotheses that intentional modifications of top-down, trophic cascade effects can help improve and restore Utah Lake’s ecosystem function. Specifically, wind and wave, and to a lesser extent carp, induced turbidity, as well as zooplanktivorous fish predation had direct and indirect effects on:
• Phytoplankton,
• zooplankton,
• benthic invertebrates,
• benthic algae and periphyton, and
• light availability.
Reduced wave action and zooplanktivorous fish predation allowed for increased zooplankton abundance particularly larger sized individual taxa such as daphniids and copepods to prosper. Increased abundance of large-sized zooplankton likely reduced phytoplankton biovolume and likely altered the phytoplankton assemblage’s relative abundances and dynamics. Wave and carp induced turbulence was mostly responsible for nutrient flux from easily suspended fine sediments. Subsequently, turbulence reduction increased light penetration to the substrate allowing benthic algae and the periphyton community to increase in biovolume and compete with phytoplankton, including potential reduction of harmful algal blooms.
All results in this study were consistent with over a century of aquatic ecological findings from other ecosystems worldwide, Utah Lake was not expected to be an exception. These findings also show that restoration of Utah Lake is straight forward and not beyond are capability. Successful science based aquatic ecosystem restoration is being conducted worldwide and a detailed discussion on the relevance of our mesocosm findings in relation to aquatic ecosystem science and restoration is included in this progress report.
Based on this study we recommend:
• Future mesocosm treatments need to be replicated focusing on wave, juvenile carp, and mollusk effects.
• More detailed analyses of response variables such as
o mollusk growth, diets, fitness,
o zooplankton size distributions, diets, and diversity,
o fish fitness, diets, growth,
• Initiation of reestablishment of native aquatic macrophytes, particularly emergent vegetation throughout the lake.
• Installation of temporary wave breaks at select locations until native aquatic plants can be fully established.
• Consideration of top-layer nutrient rich sediment removal.
• Reintroduction of native mollusks.
• Management of the lake towards a more balanced fishery.
We conclude that restorative measures based on these findings especially native aquatic plant reestablishment, and implementation of what is known and currently practiced throughout the world can be prudently and expeditiously used to improve Utah Lake’s foodweb, health, integrity, and resilience to future perturbation.
... Periphyton includes algae growing on submerged surfaces with nutrient contents ranging from nutrient-poor rocks (epilithic algae) to nutrient-rich sediments (epipelic algae) from which it derives nutrients for its growth (Vadeboncoeur and Lodge 2000). Because of the relatively nutrient-rich sediment conditions, epipelic algae in northern lakes are primarily light-and not nutrient-limited (Vadeboncoeur et al. 2003;Ask et al. 2009;Puts et al. 2022). However, positive responses to in situ inorganic nutrient (Myrstener et al. 2018;Fork et al. 2020) and nutrients combined with cDOM additions (Vinebrooke and Leavitt 1998), as well as field studies (Hansson 1992), indicate that epipelic algae can also be nutrient limited, especially in nutrient-poor systems. ...
We tested interactive effects of warming (+2°C) and browning on periphyton accrual and pigment composition when grown on a synthetic substrate (plastic strips) in the euphotic zone of 16 experimental ponds. We found that increased colored dissolved organic matter (cDOM) and associated nutrients alone, or in combination with warming, resulted in a substantially enhanced biomass accrual of periphyton, and a comparatively smaller increase in phytoplankton. This illustrates that periphyton is capable of using nutrients associated with cDOM, and by this may affect nutrient availability for phytoplankton. However, warming weakened the positive impact of browning on periphyton accrual, possibly by thermal compensation inferred from altered pigment composition, and/or changes in community composition. Our results illustrate multiple impacts of climate change on algal growth, which could have implications for productivity and consumer resource use, especially in shallow areas in northern lakes.
... Because benthic primary production is difficult to measure (Puts I. et al., 2022), whole-lake productivity measurements are uncommon, and so our compilation contains nearly three times more lakes than the next largest, allowing us to potentially describe novel patterns like this quarter-power relationship. Even global studies have a small number of lakes compared to what is compiled here (Puts I. C et al., 2022); (Vadeboncoeur et al., 2003); (Seekell et al., 2015). Table 1 shows the basic characteristics of the lakes in our compilation, which is also included as a supplemental file. ...
Kleiber’s 3/4-scaling law for metabolism with mass is one of the most striking regularities in biological sciences. Kleiber’s law has been shown to apply not only to individual organisms but also to communities and even the whole-ecosystem properties such as the productivity of estuaries. Might Kleiber’s law also then apply to lake ecosystems? Here, we show that for a collection of whole-lake primary production measurements, production scales to the 3/4 power of lake volume, consistent with Kleiber’s law. However, this relationship is not explicable by analogy to theories developed for individual organisms. Instead, we argue that dimensional analysis offers a simple explanation. After accounting for latitudinal gradients in temperature and insolation, whole-lake primary production scales isometrically with lake area. Because Earth’s topography is self-affine, meaning there are global-scale differences between vertical and horizontal scaling of topography, lake volume scales super-linearly with lake surface area. 3/4 scaling for primary production by volume then results from these other two scaling relationships. The identified relationship between the primary production and temperature- and insolation-adjusted area may be useful for constraining lakes’ global annual productivity and photosynthetic efficiency. More generally, this suggests that there are multiple paths to realizing the 3/4 scaling of metabolism rather than a single unifying law, at least when comparing across levels of biological organization.
... ecosystems 34 . Here, we demonstrate that, as the time-window of observation lengthens, shallow lakes generally undergo a gradual change in response to eutrophication, which has been shown to involve a slow erosion of benthic habitats and pathways of production 55 and that nutrient levels overwhelmingly dictate chlorophyll-a concentrations. Whilst abundant macrophytes alter trophic interactions and nutrient to chlorophyll-a relationship in the short-term 27 , the year-to-year variation evens out and bottom-up forces prevail in the longer term. ...
Since its inception, the theory of alternative equilibria in shallow lakes has evolved and been applied to an ever wider range of ecological and socio-ecological systems. The theory posits the existence of two alternative stable states or equilibria, which in shallow lakes are characterised by either clear water with abundant plants or turbid water where phytoplankton dominate. Here, we used data simulations and real-world data sets from Denmark and northeastern USA (902 lakes in total) to examine the relationship between shallow lake phytoplankton biomass (chlorophyll-a) and nutrient concentrations across a range of timescales. The data simulations demonstrated that three diagnostic tests could reliably identify the presence or absence of alternative equilibria. The real-world data accorded with data simulations where alternative equilibria were absent. Crucially, it was only as the temporal scale of observation increased (>3 years) that a predictable linear relationship between nutrient concentration and chlorophyll-a was evident. Thus, when a longer term perspective is taken, the notion of alternative equilibria is not required to explain the response of chlorophyll-a to nutrient enrichment which questions the utility of the theory for explaining shallow lake response to, and recovery from, eutrophication.
... Conceptual models postulate that periphyton will dominate in oligotrophic lakes because low densities of phytoplankton in clear lakes allow enough light to reach the bottom for periphyton to maintain high productivity. In eutrophic or turbid lakes, massive phytoplankton and suspended particulate matter may impose a light limitation on periphyton (Vadeboncoeur et al. 2003); in contrast, low nitrogen conditions promoted periphyton due to more efficient use of nutrients and improved light conditions resulting from lower phytoplankton biomass (Pacheco et al. 2021b). However, some studies have shown that epipelon such as Oscillatoria amphibia can obtain large amounts of nutrients to compensate for the impact of insufficient light on their growth (Vadeboncoeur et al. 2008;Kazemi-Dinan et al. 2014). ...
It has been well documented that periphyton communities play a key role in primary productivity, nutrient cycling, and food web interactions. However, a worldwide overview of research on the key themes, current situation, and major trends within the field is lacking. In this study, we applied the machine learning technique (latent Dirichlet allocation, LDA) to analyze the abstracts of 6690 publications related to periphyton from 1991 to 2020 based on the Web of Science database. The relative frequency of classical and basic research on periphyton related to colonization, biomass, growth rate, and habitats has been clearly decreasing. The increasing trends of research on periphyton are embodied in the periphyton function in freshwater ecosystems (e.g., application as ecological indicators, function in the removal of nutrients, and application in paleolimnology), the research at macroscales (e.g., spatial–temporal variation, and functional and taxonomic diversity), and the anthropogenic themes (e.g., climate warming, response to multiple stressors, and land use type). The keyword and title analysis showed that the periphyton studies are concentrated mainly on diatom aspects, especially with respect to streams relative to lakes. The thematic space based on non-metric multidimensional scaling (NMDS) showed that the classical themes such as growth rate, colonization, and environmental factors (e.g., multiple stressors and climate warming) were most linked to other research themes. We proposed that future trends in the periphyton should focus on the function of periphyton in lakes and their response to multiple environmental pressures with the increasingly extensive eutrophication in lakes and the increasingly significant change in the climate.
... The documented increase in pelagic productivity resulting from excess nutrients as the primary driver of ecosystem change is consistent with global patterns of anthropogenic lake ecosystem degradation. 99,100 The effects of nutrient enrichment in lakes can override the influence of other anthropogenic and natural perturbations. 101,102 However, because many anthropogenic nutrient inputs originate from diffuse sources and can accumulate in lakes over long periods of time before prompting ecological change (as measured by monitoring), they can remain unrecognized until after large and often irreversible changes in ecosystem structure and function have occurred. ...
Interactions among multiple stressors, legacies of past perturbations, and the lack of historical information make it difficult to determine the influence of individual anthropogenic impacts on lakes and separate them from natural ecosystem variability. In the present study, we coupled paleolimnological approaches, historical data, and ecological experiments to disentangle the impacts of multiple long-term stressors on lake ecosystem structure and function. We found that the lake structure and function remained resistant to the impacts of catchment deforestation and erosion, and the introduction of several exotic fish species. Changes in ecosystem structure and function were consistent, with nutrient enrichment being the primary driver of change. Significant and sustained changes in the lake diatom community structure (and their nutrient requirements), bacterial community function, and paleolimnological proxies of ecosystem function coincided with nitrogen and phosphorus fertilizers in the catchment. The results highlight that the effects of increased nutrient inputs are much stronger than the influence of other, potentially significant, drivers of ecosystem change, and that the degree of nutrient impact can be underestimated by environmental monitoring due to its diffuse and accumulative nature. Delineating the effects of multiple anthropogenic drivers requires long-term records of both impacts and lake ecosystem change across multiple trophic levels.
... In eutrophic conditions, increased light availability can favor the growth of the phototrophic epipelon (Amaral et al. 2020; Tavares et al. 2019), with light being a determining factor (Vadeboncoeur et al. 2014). Although the effect of light on the epipelon may be less noticeable in shallow lakes (Vadeboncoeur et al. 2014), primary production of epipelon is negatively affected by phytoplankton bloom (Vadeboncoeur et al. 2003). Although our findings were unexpected, some studies reported a weak or no epipelon response under low light availability (Rober et al. 2015;Tavares et al. 2019). ...
We evaluated the effects of a periphyton bioreactor on phytoplankton by experimentally simulating oligotrophication in a shallow eutrophic system. The experiment had two 50% diluted treatments with and without a periphyton bioreactor. Sampling was performed on days 6, 9, 12, 15, and 20 of the experimental period. The periphyton bioreactor accumulated biomass (chlorophyll-a, AFDM) and TP during the experimental period. Despite the biomass and TP loss due to periphyton detachment from the substrate after community reaching the algal biomass peak, the gains exceeded the losses, and the net rate was positive for all attributes in the bioreactor. Based on the average, our findings suggest that periphyton bioreactors negatively affected the phytoplankton total biovolume. Cyanobacteria were the most abundant phytoplankton group. However, the periphyton bioreactor caused the biomass loss of the Raphidiopsis raciborskii in phytoplankton. Our results suggest that bioreactor influenced the phytoplankton structure, reducing cyanobacterial biomass, especially Raphidiopsis raciborskii. However, the bioreactor did not reflect a significant increase in the epipelon biomass during the experimental period. We conclude that the periphyton bioreactor has the potential to assist in the maintenance of restored shallow lakes and reservoirs, especially in controlling phytoplankton growth.
... Benthic algae and biofilms are dominant energy sources for food webs in many Arctic lakes (Vadeboncoeur et al., 2003;Chételat et al., 2010;Rautio et al., 2011). In the eastern Canadian Arctic, MeHg concentrations ranged from 2 to 12 ng/g dw for rocky shoreline biofilms (Chételat et al., 2018), 0.3 to 1.3 ng/g dw for microbial mats (Camacho et al., 2015), and 2 to 56 ng/g dw for periphyton and filamentous algae (van der Velden et al., 2013a). ...
Anthropogenic mercury (Hg) undergoes long-range transport to the Arctic where it is transformed into methylmercury (MeHg), potentially leading to high exposure in some Arctic inhabitants and wildlife. The environmental exposure of Hg is determined not just by the amount of Hg entering the Arctic, but also by biogeochemical and ecological processes occurring in the Arctic. These processes affect MeHg uptake in biota by regulating the bioavailability, methylation and demethylation, bioaccumulation and biomagnification of MeHg in Arctic ecosystems. Here, we present a new budget for pools and fluxes of MeHg in the Arctic and review the scientific advances made in the last decade on processes leading to environmental exposure of Hg. Methylation and demethylation are key processes controlling the pool of MeHg available for bioaccumulation. Methylation of Hg occurs in diverse Arctic environments including permafrost, sediments and the ocean water column, and is primarily a process carried out by microorganisms. While microorganisms carrying the hgcAB gene pair (responsible for Hg methylation) have been identified in Arctic soils and thawing permafrost, the formation pathway of MeHg in oxic marine waters remains less clear. Hotspots for methylation of Hg in terrestrial environments include thermokarst wetlands, ponds, and lakes. The shallow sub-surface enrichment of MeHg in the Arctic Ocean, in comparison to other marine systems, is a possible explanation for high MeHg concentrations in some Arctic biota. Bioconcentration of aqueous MeHg in bacteria and algae is a critical step in the transfer of Hg to top predators, which may be dampened or enhanced by the presence of organic matter. Variable trophic position has an important influence on MeHg concentrations among populations of top predator species such as ringed seal and polar bear distributed across the circumpolar Arctic. These scientific advances highlight key processes that affect the fate of anthropogenic Hg deposited in Arctic environments.
... crispus the water may become dominated by phytoplankton and risks being shifted into a turbid state. This might further impair benthic food webs, a key pathway in shallow water bodies, which has largely been ignored (Puche et al., 2021;Vadeboncoeur et al., 2003). ...
Submerged macrophytes play a key role in maintaining a clear‐water phase and promoting biodiversity in shallow aquatic ecosystems. Since their abundance has declined globally due to anthropogenic activities, it is important to include them in aquatic ecosystem restoration programs. Macrophytes establishment in early spring is crucial for the subsequent growth of other warm‐adapted macrophytes. However, factors affecting this early establishment of submerged macrophytes have not been fully explored yet. Here, we conducted an outdoor experiment from winter to early spring using the submerged macrophytes Potamogeton crispus and Vallisneria spinulosa to study the effects of shading, nutrient loading, snail herbivory (Radix swinhoei), and their interactions on the early growth and stoichiometric characteristics of macrophytes. The results show that the effects strongly depend on macrophyte species. Biomass and number of shoots of P. crispus decreased, and internode length increased during low light conditions, but were not affected by nutrient loading. P. crispus shoot biomass and number showed hump‐shaped responses to increased snail biomass under full light. In contrast, the biomass of the plant linearly decreased with snail biomass under low light. This indicates an interaction of light with snail herbivory. Since snails prefer grazing on periphyton over macrophytes, a low density of snails promoted growth of P. crispus by removing periphyton competition, while herbivory on the macrophyte increased during a high density of snails. The growth of V. spinulosa was not affected by any of the factors, probably because of growth limitation by low temperature. Our study demonstrates that the interaction of light with snail herbivory may affect establishment and growth of submerged macrophytes in early spring. Macrophyte restoration projects may thus benefit from lowering water levels to increase light availability and making smart use of cold‐adapted herbivores to reduce light competition with periphyton. Our study demonstrates that the interactions of light with snail herbivory, but not nutrient loading, may affect establishment and growth of submerged macrophytes in early spring. Our study thus has implications for recovery of submerged macrophytes in deteriorative water bodies.
... Browning affects the light atmosphere of the lakes, narrowing the water layer available to photosynthesis and primary production (Ask et al. 2012, Seekel et al. 2015. Lake eutrophication has been shown to shift primary production balance from benthic algae production towards pelagic production (Vadeboncoeur et al. 2003, Vadeboncoeur et al. 2008. Moreover, lake browning may impact the energy dynamics of the lake as the bacterial loop is able to transfer the humic substances to biomass further consumable by higher trophic levels (Creed et al. 2018, Blanchet et al. 2022. ...
Climate change and intense land-use activities are promoting lake eutrophication
and browning, affecting community structure and food web processes. In this
thesis, space-for-time approach was used to study the environmental change
impacts on food web structure, energy pathways, and organism nutritional
quality (defined with fatty acids and mercury content) in subarctic and boreal
regions. Only specific algal taxa can synthesize eicosapentaenoic acid (EPA) and
docosahexaenoic acid (DHA), which are important polyunsaturated fatty acids
(PUFA) for consumer growth and reproduction. Mercury is a toxic heavy metal
that, bioaccumulates to organisms via diet. In subarctic lakes, increasing
temperature and productivity negatively affected EPA+DHA content of seston
and zooplankton. However, no such changes were observed from boreal regions.
Seston and cladoceran PUFA contents were uncorrelated in the boreal zone
where cladoceran preferred to feed on high-quality algae. European perch (Perca
fluviatilis (L.)) showed slight decreasing trends in their muscle DHA content from
more transparent lakes towards shallower and murkier ones in the boreal areas.
In subarctic climate–productivity gradient, the decreasing prey item quality
(zooplankton and profundal benthos) did not affect fish muscle EPA+DHA
content at community level. Perch in boreal low pH lakes and highly forested
catchments rely more on terrestrial energy sources than eutrophic lakes with
neutral pH. This likely resulted in higher mercury and omega-6 PUFA content in
perch muscle. Increasing temperature and productivity fundamentally alter
subarctic lake communities' structure and function, resulting in an increasing
share of cyanobacteria, smaller-bodied zooplankton, smaller benthos taxa, and
warmer-water-adapted cyprinid fishes. Positive trends in biomass at each second
trophic level (phytoplankton and invertivorous fish) were observed along with
climate-productivity gradient shaping biomass pyramids. Food web processes
and PUFA dynamics seem to differ between boreal and subarctic lakes. Future
studies with harmonized methodology and wide lake gradients are needed to
evaluate wheter methodology or ecology are driving these observed differences.
Global warming can affect biomass accumulation and the dynamics of periphytic communities, potentially altering their role in aquatic ecosystem functioning. We conducted a 38-day mesocosm experiment to investigate the effects of an increase in winter temperature on periphyton biomass accumulation under eutrophic conditions. We evaluated the warming effect on colonization phases, identifying the most affected phase. The experiment had two treatments (control: current winter temperature of 23.5 ℃, warming: + 5.7 ℃ under IPCC scenario). It was carried out in growth chambers under controlled temperature, light, and humidity. Periphyton and water samplings were performed on days 3, 6, 9, 13, 17, 21, 27, and 38. The increase in temperature did not affect the organic matter accrual rate of the periphyton. However, it negatively affected the net and gross accrual rate of the algal biomass. Ash-free dry mass and chlorophyll-a ratio in the periphyton increased at higher temperatures, indicating a decrease in autotrophic components in the periphyton in the warming treatment. We detected losses in algal biomass during the intermediate and advanced colonization phases. Our results showed a decrease in periphytic algal biomass with an increase in average temperature in winter. In conclusion, a warming scenario can negatively influence periphyton biomass in eutrophic ecosystems, where algal growth in the community is generally unfavorable.
Changing nutrient concentrations and introduction of non-native species affect the energy and nutrient fluxes in aquatic ecosystems. As a response, invertebrate communities could be altered, and ‘novel’ trophic communities could develop. Lake Constance (Europe) experienced pronounced nutrient variation caused by cultural eutrophication (prior 1980s) and oligotrophication (post-1980) and experienced many neobiota invasions. We used archived samples to investigate the impact of oligotrophication and invasive species on carbon and nitrogen isotope signatures of littoral macroinvertebrates during spring and autumn periods from 2000 to 2015 and of littoral fish species in 2018. Isotopic signatures of invertebrate and fish species were in the same range and showed similar seasonal differences and clear patterns in respect to littoral vs pelagic food sources and trophic level. Oligotrophication did not strongly alter isotopic values and only δ¹⁵N values of invertebrates declined weakly with oligotrophication. In contrast, interannual variability of stable isotope signatures was related to abundances of the invasive Dreissena polymorpha suggesting interannual differences in the importance of benthic-pelagic coupling due to Dreissena pseudofaeces for the nutrition of littoral invertebrates. This study illustrates how stored samples can be used to detect the importance of oligotrophication and benthic-pelagic coupling on the stable isotope signatures of a benthic community.
Primary producers form the base of lake ecosystems and, due to their often short lifecycles, respond rapidly to changing conditions. As the Arctic is warming nearly four times faster than the global average, we see major shifts in environmental conditions, which impacts lake ecosystem functioning. Previous studies have found a general increase in primary productivity due to climate warming. However, few long‐term studies have included changes in phytoplankton community composition and biomass in relation to warming in Arctic lakes and it therefore remains unclear how different algal taxa and thus the community respond.
We investigated how climate warming affects phytoplankton community composition, taxon richness and biomass in High Arctic lakes, using a unique 23‐year data series on phytoplankton in two shallow lakes at Zackenberg, north‐east Greenland, one with Arctic charr ( Salvelinus alpinus ) and one without fish. We further elucidated the role of physico‐chemical variables and zooplankton grazers in the changes observed.
Few major changes were observed in phytoplankton community composition over time, but the year‐to‐year variation was large. Taxon richness did, however, increase throughout the monitoring period, and in both lakes there was a significant increase in diatom biomass coinciding with increasing conductivity. Additionally, phytoplankton biomass was greater during warmer years with earlier ice melt. We further found that nutrient levels were positively associated with the total phytoplankton biomass in both lakes, indicating that expected increased nutrient levels, due to climate change, may lead to a greater phytoplankton biomass in High Arctic lakes in the future.
The large year‐to‐year variability, in both climate and environmental conditions, makes it difficult to predict weather patterns and their consequences for lake ecosystems in the Arctic region. This underlines the importance of long‐term monitoring programmes across the circumpolar Arctic and collaboration across regions and institutes within large scale studies.
In this study, we quantify the differences in gross primary production (GPP), respiration (R), and algal nutrient limitation (nitrogen and phosphorus) in the littoral and pelagic habitats of an oligotrophic Patagonian lake (southern South America). We used submerged high frequency sensors that measure light, temperature, and dissolved oxygen and wind data to calculate GPP and R in both lake habitats. In addition, we carry out nutrient enrichment bioassays with nitrate, ammonium, and phosphate to determine which nutrient(s) limit algal growth in each lake habitat. On average, the productivity rate was 7.2 times higher at the epi-littoral (32.0 to 5.3 mmol O2 m−2 d−1) relative to the epi-pelagic (4.1 to 1.3 mmol O2 m−2 d−1). Algal growth in the littoral habitat was limited by nitrate and ammonium, while the pelagic habitat was co-limited by nitrogen (nitrate or ammonium) and phosphorus. Our work demonstrates that the littoral habitat of a Patagonian oligotrophic lake is more productive than the pelagic habitat and that the nutrients limiting algal growth in both habitats are different. These results underscore habitat variations and their significance in shaping the lake’s trophic dynamics for the first time in the southern hemisphere.
Young-of-the-year fish communities are widely used as bioindicators of various environmental disturbances. This study was conducted from 1997 to 2015 and aims to develop fish trait–based indices of changes in the temperature regime and eutrophication of water bodies in the Dnipro River basin. We identified fish traits that significantly correlate with both temperature and chlorophyll-a concentration optimum: reproduction habitat, oxygen tolerance, and toxicity tolerance. Compared to other ecological groups, lithophilic species exhibited the lowest degree of thermal and eutrophication optimum, indicating this species’ greater vulnerability to environmental alteration. Fish species that are intolerant to water quality and low oxygen concentration were the most sensitive to changes in temperature regime and eutrophication level. Salinity preferences and water quality tolerance emerged as reliable predictors of temperature optimum. Freshwater fish had an average temperature optimum that was 4.5% higher than that of freshwater-brackish and freshwater-brackish-marine fish. Species tolerance to the temperature factors and nutrient loads correlated only with rheophily, with rheophilic species having an average 13.8% higher temperature tolerance than other fish species and a 10.4% higher chlorophyll-a concentration tolerance. The fish temperature index increased over time during the study period in all the studied water bodies, consistent with ongoing warming affecting all sites. In contrast, the Fish Eutrophication Index showed greater temporal heterogeneity in studied water bodies, indicating various adaptative potentials of fish communities to eutrophication. These indices can be relevant for assessing disturbed situations caused by changes in climatic and anthropogenic impacts on water bodies.
Anthropogenic impacts on lake and stream water quality are well established but have been much less studied in wetlands. Here we use data from the 2016 National Wetland Condition Assessment to characterize water quality and its relationship to anthropogenic pressure for inland wetlands across the conterminous USA. Water samples obtained from 525 inland wetlands spanned pH from < 4 to > 9 and 3 to 5 orders of magnitude in ionic strength (chloride, sulfate, conductivity), nutrients (total N and P), turbidity, planktonic chlorophyll, and dissolved organic carbon (DOC). Anthropogenic pressure levels were evaluated at two spatial scales – an adjacent scale scored from field checklists, and a catchment scale indicated by percent agricultural plus urban landcover. Pressure at the two spatial scales were uncorrelated and varied considerably across regions and wetland hydrogeomorphic types. Both adjacent- and catchment-scale pressure were associated with elevated ionic-strength metrics; chloride elevation was most evident in road-salt using states, and sulfate was strongly elevated in a few sites with coal mining nearby. Nutrients were elevated in association with catchment-scale pressure but concomitant changes were not seen in planktonic chlorophyll. Acidic pH and high DOC occurred primarily in upper Great Lakes and eastern seaboard sites having low anthropogenic pressure, suggesting natural organic acid sources. Ionic strength and nutrients increased with increasing catchment-scale pressure even in Flats and closed Depression and Lacustrine sites, which indicates connectivity to rather than isolation from upland anthropogenic landuse even for wetlands lacking inflowing streams.
Allochthonous dissolved organic matter (DOM) structures many physical, chemical, and biological properties of lakes including key variables that control productivity at the base of freshwater food webs. A growing number of studies have documented increasing DOM concentrations within lakes across Europe and North America, including boreal lakes. Such increases are associated with the recovery of catchment soils from acid rain and rising precipitation linked to climate change.
We examined phytoplankton biomass, productivity, and their drivers across eight pristine boreal lakes with DOM ranging from 3.5 to 9.5 mg dissolved organic carbon/L. Physical and chemical properties were assessed using standard limnological methods. Phytoplankton biomass was assessed using both chlorophyll a (Chl‐ a ) and via microscopy. Phytoplankton productivity was assessed using change in partial pressure of carbon dioxide within in vitro incubations.
Increases in DOM were associated with significant increases in epilimnetic nitrogen, phosphorus and Chl‐ a concentrations suggesting that nutrients associated with DOM stimulated phytoplankton biomass and productivity. Such results were misleading; there was no significant relationship between Chl‐ a and phytoplankton biomass. Chl‐ a :biomass and Chl‐ a :carbon ratios indicated that increases in Chl‐ a with DOM were driven by photo‐acclimation to declining light availability. Further, results presented as epilimnetic concentrations would not account for concurrent declines in thermocline depth or euphotic depth driven by DOM.
Increases in DOM led to large declines in thermocline ( c. 50%) and euphotic ( c. 75%) depths, and depth‐integrated phytoplankton biomass ( c. 70%) and primary production ( c. 70%).
Our results indicate that DOM plays a structuring role for key physical, chemical, and biological properties of lakes, including productivity, at a landscape level. Further, practitioners should be cautious when using Chl‐ a as an indicator of phytoplankton biomass in studies using DOM or water clarity gradients, report results using depth integrated units due to changes in volumes of thermal layers induced by DOM, and incorporate estimates of sub‐epilimnetic productivity when evaluating DOM effects.
High-frequency data from dissolved oxygen (DO) loggers were obtained during and before a massive summer fish kill event in the oxbow lake Doubka in the Elbe river basin, Czech Republic, and evaluated in the context of meteorological data. In the period from 3 June to 1 September 2020, extreme fluctuations of DO in the surface layer of water were recorded (values in the range of 0–25.48 mg l−1). The DO concentrations were affected by phytoplankton photosynthesis and fluctuated within 12 h from more than 100% saturation (in the afternoon) to zero (at dawn). DO values near the bottom were less variable (0–9.67 mg l−1) and after mid-July, zero values prevailed. A huge fish kill associated with windy weather occurred between 26 and 28 August 2020, resulting in more than 800 kg of dead fish. High percentages of dead fish were of the northern pike (Esox lucius), the pikeperch (Sander lucioperca) and the European catfish (Silurus glanis). Wind-induced water mixing (when oxygenated water containing phytoplankton moved from the surface to the anoxic bottom) and subsequent depletion of oxygen by decomposition processes in the organic substrate of the bottom, in combination with limited sunshine in the same period, resulted in a 2-day lack of oxygen both in the surface layer of water and near the bottom. Repeated fish kills probably contribute to the massive occurrence of the resistant and invasive topmouth gudgeon (Pseudorasbora parva) at the locality.
Benthic primary production varies among lakes from 1 to 2000+ mg C m− 2 d− 1, in part owing to variations in basin shape. First principles predict an inverse correlation between benthic primary production and mean to maximum depth ratio, an index of basin shape, but reports of positive correlations suggest that current understanding is incorrect or incomplete. We develop a hypsometric (area–depth) model for littoral area that accounts for habitat disruption due to ice scouring at the lake margin. When this disruption is incorporated, the direction of the relationship between benthic primary production and depth ratio depends on water clarity—regions with clear lakes should have positive correlations, whereas regions with less water clarity should have inverse correlations. Empirical analysis of benthic primary production measurements from four eco-regions characterized by different levels of water clarity supports this prediction. Collectively, our analyses demonstrate how first principles can be used to explain heterogeneous patterns of benthic primary production at broad geographic scales.
Some biological invasions can result in algae blooms in the nearshore of clear lakes. We studied if an invasive crayfish (Pacifastacus leniusculus) modified the biomass and community composition of benthic macroinvertebrates and therefore led to a trophic cascade resulting in increased periphyton biomass, elevated littoral primary productivity, and benthic algae bloom in a lake with remarkable transparency [Crater Lake, Oregon, USA]. After quantifying the changes in the spatial distribution of invasive crayfish over a 13-year period, we compared biomass and community composition of littoral–benthic macroinvertebrates, periphyton biovolume, community composition, nutrient limitation, and the development of benthic algae bloom in locations with high and low crayfish density. In addition, we determined if the alteration in community structure resulted in directional changes to gross primary production and ecosystem respiration. The extent of crayfish distribution along the shoreline of Crater Lake doubled over a 13-year period, leaving less than 20% of the shoreline free from crayfish. At high crayfish density sites, benthic macroinvertebrate biomass was 99% lower, and taxa richness was 50% lower than at low crayfish areas. High crayfish sites show tenfold greater periphyton biovolume, sixfold higher periphyton biomass (chlorophyll a), twofold higher metabolic productivity, and the presence of large filamentous algae (Cladophora sp.). The invasion of crayfish had negative consequences for a lake protected under the management of the USA National Park Service, with direct impacts on many levels of ecological organization.
With the retreat of glaciers, new ponds and lakes are often formed. These are gradually col-onised and become more productive as vegetation develops in their catchments, creating more complex food webs. Near the Jakobshavn Isbrae in West Greenland, we studied trophic structure and food web complexity using stable isotopes in 26 lakes belonging to two different age groups (19 new lakes and 7 nearby older (> 150 years) ones). The older lakes had significantly higher total nitrogen and pelagic chlorophyll-a concentrations, as well as a higher organic matter content in the surface sediment. The biomass and richness of cladocerans, copepods and rotifers were higher in the older lakes and so was the zooplankton:phytoplankton biomass ratio. Multi-variate analyses showed a marked difference between the zooplankton communities of new and older lakes. Layman food web metrics indicated higher food chain length and width of invertebrates (zooplankton and benthic macroinvertebrates) in the older lakes, being significantly higher in lakes with fish. Our findings highlight a potential sequence of succession occurring in lakes created by glacial retreat in the Arctic, implying an increase in food web complexity and higher taxonomic (and likely also functional) diversity following ageing and increased nutrient state.
While the sentinel nature of freshwater systems is now well recognized, widespread integration of freshwater processes and patterns into our understanding of broader climate-driven Arctic terrestrial ecosystem change has been slow. We review the current understanding across Arctic freshwater systems of key sentinel responses to climate, which are attributes of these systems with demonstrated and sensitive responses to climate forcing. These include ice regimes, temperature and thermal structure, river baseflow, lake area and water level, permafrost-derived dissolved ions and nutrients, carbon mobilization (dissolved organic carbon, greenhouse gases, and radiocarbon), dissolved oxygen concentrations, lake trophic state, various aquatic organisms and their traits, and invasive species. For each sentinel, our objectives are to clarify linkages to climate, describe key insights already gained, and provide suggestions for future research based on current knowledge gaps. We suggest that tracking key responses in Arctic freshwater systems will expand understanding of the breadth and depth of climate-driven Arctic ecosystem changes, provide early indicators of looming, broader changes across the landscape, and improve protection of freshwater biodiversity and resources.
Shallow mountain lakes and ponds may function as reference systems for monitoring the effects of global climate change. A survey of phytobenthos and phytoplankton communities was conducted along an altitudinal gradient of Canadian Rocky Mountain lakes and ponds to relate patterns in algal abundance and community composition to catchment and climate-related variables. Algal abundance and community composition were quantified using pigments as analyzed by high performance liquid chromatography (HPLC). Regression analyses revealed that the abundance of rock-attached algae (epilithon) was negatively correlated (r2 = 0.54, p 2 = 0.52, pcond.DOC
Cyprinids (Margariscus margarita, Phoxinus spp., Pimephales promelas) have resumed reproduction in a boreal headwater lake (Lake 302S, Experimental Lakes Area, northwestern Ontario) that is recovering from experimental acidification. Concomitant changes to the littoral food web suggested that these omnivorous minnows suppressed the development of green algal mats, termed metaphyton. We tested this hypothesis by conducting an experiment using minnow enclosures, minnow exclosures, and open control plots in the shallow littoral zone of Lake 302S. Minnows significantly suppressed zooplankton biomass, and altered community composition by disproportionally reducing large daphnids and chydorids. Epiphytic chironomids were also significantly less abundant in the presence of minnows. Minnows had a significant time-dependent, negative effect on benthic invertebrate biomass and community composition because chironomids and anisopterans were suppressed during the second half of the 6-wk experiment. However, minnows did not reduce the abundance of the dominant primary producer, namely metaphyton. Stable isotope analyses revealed that minnows did not suppress metaphyton because these algae were not the primary C source for the food web. Instead, our findings suggest that the littoral food web depended mainly on sedimentary C, which resulted in the foodweb effect of minnows being truncated at the level of invertebrates. Therefore, metaphyton appears to be regulated primarily by abiotic factors (e.g., availability of dissolved inorganic C) and not herbivory in recovering acidified lakes.
Periphyton nitrate uptake and denitrification, not phytoplankton assimilation, accounted for -90% and 73% of the depletion of - 35 pg N03-N liter-l added as whole-epilimnion enrichments of ammonium nitrate to Castle Lake, California, in midsummer 1980 and 198 1. The importance of benthic processes is suggested by similar rates of depletion for nitrate and ammonium in the whole-lake experiments; these rates are inconsistent with previous microcosm studies of phytoplankton that showed strong preferential uptake of ammonium and low uptake rates of nitrate. The importance of the benthic pathways was confirmed by an NH,15N03 mesocosm experiment, which simulated the whole-epilimnion experiments. Less than 9% of the 15N transformed was associated with water-column pools; the remainder was incorporated into epipelic periphyton and sediments (56%) or attributed to 15Nz J5Nz0 loss via denitrification. Historical analysis of nitrate depletion in the epilimnion during spring suggests that periphyton may outcompete phytoplankton for water-column nutrients.
Lakes are complex ecosystems composed of distinct habitats coupled by biological, physical and chemical processes. While the ecological and evolutionary characteristics of aquatic organisms reflect habitat coupling in lakes, aquatic ecology has largely studied pelagic, benthic and riparian habitats in isolation from each other. Here, we summarize several ecological and evolutionary patterns that highlight the importance of habitat coupling and discuss their implications for understanding ecosystem processes in lakes. We pay special attention to fishes because they play particularly important roles as habitat couplers as a result of their high mobility and flexible foraging tactics that lead to inter-habitat omnivory. Habitat coupling has important consequences for nutrient cycling, predator-prey interactions, and food web structure and stability. For example, nutrient excretion by benthivorous consumers can account for a substantial fraction of inputs to pelagic nutrient cycles. Benthic resources also subsidize carnivore populations that have important predatory effects on plankton communities. These benthic subsidies stabilize population dynamics of pelagic carnivores and intensify the strength of their interactions with planktonic food webs. Furthermore, anthropogenic disturbances such as eutrophication, habitat modification, and exotic species introductions may severely alter habitat connections and, therefore, the fundamental flows of nutrients and energy in lake ecosystems.
Previous studies of freshwater eutrophication have shown that algal biomass tends to increase with the supply of dissolved phosphorus. This concept has been condensed into empirical relationships between chlorophyll a and total phosphorus concentrations (convenient measures of algal biomass and phosphorus availability) which have become essential tools in theoretical and applied limnology. With few exceptions, ecologists accept the idea that chlorophyll concentration rises linearly with phosphorus concentration among lakes. Such a suggestion runs counter to Liebigian principles of fertilization however, and contradicts laboratory and field research indicating the influence of other nutrients. Our analysis of two large independent phosphorus–chlorophyll data sets from temperate-zone lakes shows that log phosphorus–log chlorophyll relationships are sigmoid in shape and that a second nutrient, nitrogen, has a significant impact on chlorophyll concentrations when phosphorus availability is high. Our new empirical relationships indicate that mechanisms regulating algal biomass change with enrichment, and suggest new management strategies for polluted lakes.
Estimates of macrozoobenthos from the literature were regressed against a series of limnological variables to yield empirical models for zoobenthic biomass in the profundal, sublittoral, and littoral zones of lakes. Variables indicative of phytoplankton biomass (chlorophyll concentration, total phosphorus concentration, and Secchi disk transparency) explained between 14 and 57% of the variance of zoobenthic biomass ((g/m2)0.1). Other factors such as humic colour, morphometry (slope, mean depth, ratio of mean to maximum depth, and lake area), and mean annual air temperature substantially increased the amount of explained variance. In the profundal and sublittoral zones, the best models explain 70% of the variance in zoobenthic biomass. Littoral zone models explained less than 50%, and this deficiency was attributed to sampling difficulties and to high local variability of slope and wave exposure in the littoral zone.
A primary focus of coastal science during the past 3 decades has been the question: How does anthropogenic nutrient enrichment cause change in the structure or function of nearshore coastal ecosystems? This theme of environmental science is recent, so our conceptual model of the coastal eutrophication problem continues to change rapidly. In this review, I suggest that the early (Phase I) conceptual model was strongly influenced by limnologists, who began intense study of lake eutrophication by the 1960s. The Phase I model emphasized changing nutrient input as a signal, and responses to that signal as increased phytoplankton biomass and primary production, decomposition of phytoplankton-derived organic matter, and enhanced depletion of oxygen from bottom waters. Coastal research in recent decades has identified key differences in the responses of lakes and coastal-estuarine ecosystems to nutrient enrichment. The contemporary (Phase II) conceptual model reflects those differences and includes explicit recognition of (1) system-specific attributes that act as a filter to modulate the responses to enrichment (leading to large differences among estuarine-coastal systems in their sensitivity to nutrient enrichment); and (2) a complex suite of direct and indirect responses including linked changes in: water transparency, distribution of vascular plants and biomass of macroalgae, sediment biogeochemistry and nutrient cycling, nutrient ratios and their regulation of phytoplankton community composition, frequency of toxic/harmful algal blooms, habitat quality for metazoans, reproduction/growth/survival of pelagic and benthic invertebrates, and subtle changes such as shifts in the seasonality of ecosystem functions. Each aspect of the Phase II model is illustrated here with examples from coastal ecosystems around the world. In the last section of this review I present one vision of the next (Phase III) stage in the evolution of our conceptual model, organized around 5 questions that will guide coastal science in the early 21st century: (1) How do system-specific attributes constrain or amplify the responses of coastal ecosystems to nutrient enrichment? (2) How does nutrient enrichment interact with other stressors (toxic contaminants, fishing harvest, aquaculture, nonindigenous species; habitat loss, climate change, hydrologic manipulations) to change coastal ecosystems? (3) How are responses to multiple stressors linked? (4) How does human-induced change in the coastal zone impact the Earth system as habitat for humanity and other species? (5) How can a deeper scientific understanding of the coastal eutrophication problem be applied to develop tools for building strategies at ecosystem restoration or rehabilitation?
Top predators and nutrient loading in lakes were manipulated to assess the influence of food web structure on carbon flux
between lakes and the atmosphere. Nutrient enrichment increased primary production, causing lakes to become net sinks for
atmospheric carbon (Catm). Changes in top predators caused shifts in grazers. At identical nutrient loading, Catm invasion was greater to a lake with low grazing than to one with high grazing. Carbon stable-isotope distributions corroborated
the drawdown of lake carbon dioxide and traced Catm transfer from algae to top predators. Thus, top predators altered ecosystem carbon fixation and linkages to the atmosphere.
Studies of lake ecosystems generally focus on pelagic food chains and pro- cesses. Recently, there has been an emerging recognition of the importance of benthic production and processes to whole-lake ecosystems. To examine the extent to which zoo- benthos contribute to higher trophic level production in lakes, we synthesized diet data from 470 fish populations (15 species) and stable isotope data from 90 fish populations (11 species), all of which are common inhabitants of north-temperate lakes. Across all species considered, zoobenthos averaged 50% of total prey consumption. Indirect consumption of zoobenthos (i.e., feeding on zoobenthos-supported fishes) contributed another 15%, for a total of 65% reliance on benthic secondary production. Stable isotopes provided estimates of mean zoobenthivory ranging from 43% to 59%. For most fish species, consumption of zoobenthos was highly variable among populations. The overwhelming concern of ecol- ogists with pelagic food chains and processes contrasts sharply with our finding that benthic secondary production plays a central role in supporting higher trophic level production. This extensive zoobenthivory can subsidize fish populations, leading to apparent compe- tition and otherwise altering trophic dynamics and ecosystem processes in the pelagic zone. We argue for a more integrated view of lake ecosystems that recognizes the duality of benthic and pelagic production pathways. Food web models that explicitly consider energy flow from pelagic and benthic sources will provide a more realistic energy flow template for understanding the regulation of lake ecosystem functioning.
1. The physiological characteristics of nitrogen uptake by sublittoral and eulittoral (splash zone) epilithic periphyton as well as epipelic periphyton in N-deficient Castle Lake, California were determined by evaluating the half-saturation constants (Kt) and initial slopes (Vmax/Kt) of uptake kinetics curves. These results were compared to similar studies of phytoplankton nitrogen uptake in this lake.
2. The strategies of nitrogen uptake differed among the various communities and were largely determined by the proximity of each to pools of available dissolved inorganic N (DIN).
3. The sublittoral algae did not have a high biological affinity for either NH4 or NO3 and depended on nitrogen fixation for their N supply. The eulittoral community showed an increased capacity for DIN uptake at low substrate concentration, but not as high as measured for the phytoplankton community. Epipelic algae live immediately adjacent to a large pool of interstitial sediment NH4 and showed no physiological adaptations for surviving in a N-deficient environment.
4. Kt values for all benthic communities were approximately two orders of magnitude greater than ambient substrate levels. In contrast, the half-saturation constants for NH4+ NO3 uptake by phytoplankton were very similar to in situ levels of these nutrients.
The importance of Chironomus plumosus larvae onbenthic metabolism and nutrient exchange across thesediment–water interface
was evaluated in a shalloweutrophic lake (Lake Arreskov, Denmark) following aphytoplankton sedimentation. Chironomus plumosuslarvae
were added to laboratory sediment microcosms,corresponding to a density of 2825 larvae m−2.Non-inhabited microcosms served as controls. Asedimentation pulse of organic matter was simulated byadding fresh algal material
(Chlamydomonasreinhardii) to sediment cores (36 g dryweight m−2). The mineralization was followed bymeasuring fluxes of O2, CO2, dissolvedinorganic nitrogen and phosphate. A rapid clearance ofalgae from the water column in faunated microcosmssuggested
that chironomids may be of major importancein controlling phytoplankton concentrations in shalloweutrophic lakes. Chironomids
increased the sedimentO2 uptake ≈ 3 times more than what wouldbe expected from their own respiration, indicating astimulation of microbial activity
and decomposition oforganic matter in the sediment. Addition of algaeenhanced the release of CO2, NH+
4 ando-P. The excess inorganic C, N and P released inamended non-inhabited sediment after 36 dayscorresponded to 65, 31 and
58% of the C, N and P inthe added algae. In sediment inhabited by Chironomus plumosus the corresponding numbers were147, 45
and 73%, indicating that mineralization oforganic matter also from the indigenous sediment poolwas stimulated by chironomids.
One of our goals as ecologists involved in basic research, should be to contribute knowledge that will enhance management of natural resources (Peterson 1993). As C. J. Krebs (1994:8) defines it, “ecology should be to environmental science as physics is to engineering.” But the manner in which ecologists conduct research determines the extent of its usefulness to resource management and conservation efforts.
One frequent mismatch between basic research and resource management arises because the small spatial and temporal scale of much basic research does not provide information relevant to resource management (Kitchell et al. 1988, Cullen 1990, Hall et al. 1994, Naiman et al. 1995). Whereas basic research is often conducted at small temporal and spatial scales in simplified systems, management often operates on the whole-ecosystem scale and over many years. Even if only one species of economic interest is directly managed, the whole ecosystem is often affected because many indirect and feedback effects exist that cannot be adequately addressed in small-scale, short-term studies. Large-scale issues that require long-term research and management include acidic deposition, lake eutrophication and biomanipulation, fisheries management, forest management, role of large mammalian predators in affecting prey populations, invasion by exotic species, role of iron in controlling oceanic productivity, stratospheric ozone depletion, and global warming (Carpenter et al. 1995b). For many aspects of these topics, large-scale, long-term research (augmented by small-scale mechanistic experiments) can offer appropriate guidance to manage resources and mitigate anthropogenic effects (Fisher 1994, Brown 1995, Franklin 1995, Lubchenco 1995, Schindler 1995).
Ecologists have recently focused much attention on quantifying the strengths and relative importance of resource-based (bottom-up) and predator-based (top-down) forces in food webs (e.g., Hunter and Price (1992), Power (1992), and Strong (1992)). Resource abundance and quality can have strong effects on the composition and dynamics of food webs, particularly primary producer assemblages (Tilman, 1982). Predators also have strong influences on lower trophic levels. Top predators in food webs may regulate the abundance of species at lower trophic levels; when the effects of top predators extend through the food web all the way to the primary producers the result is called a trophic cascade effect (Paine, 1980; Carpenter et al., 1985, 1987; McQueen et al., 1986; Power, 1990; Vanni et al., 1990).
Littoral zone primary production can be expressed as the summation of the integral production of its phytoplanton and benthic components:$$littoral prod.(mgC \cdot {m^{ - 1}}tim{e^{ - 1}}) = \mathop \smallint \limits_0^z \mathop \smallint \limits_0^x phyto prod, dzdx + \mathop \smallint \limits_0 benthic prod. dx.$$.
This expression represents a ‘wedge’ of the littoral zone, 1 m wide, extending from the shore a distance, x, to where the depth of the water, z, is equal to the maximum depth of the littoral zone (i.e. 1% of surface light intensity). The periphyton community contributed 63% of the total littoral production (0–60 m) in Lake Tahoe at a site where the benthic substratum was rock.
Evaluation of littoral productivity on a water column basis (i.e. m-2 of lake surface) illustrated that periphyton contributed varying amounts to the total productivity depending upon the depth of the water column, the time of year, the degree bottom of slope, and the benthic substratum type. Periphyton (epilithic) contributed its maximum to 2, 8 and 16 m littoral water column productivity at Lake Tahoe during the spring (>84%) and its minimum during the summer and winter (>60%). A survey of five oligotrophic lakes indicated that periphyton often contributed the majority of the littoral zone production when the substrata were rocks or organic sediments.
The relative influence of riparian vegetation and geomorphology on trophic structure was examined at three streams in adjacent catchments of the French Massif Central Mountains. The study sites differed mainly by the degree of anthropogenic alteration of riparian and watershed vegetation, and by valley geomorphology. Fishes, benthic macroinvertebrates (grouped into functional feeding groups: FFG), macrophytes and periphyton were sampled seasonally between July 1991 and April 1992. At the riffle-pool (100m) scale, instream morphological units appear to control the spatial partitioning of trophic resources and their consumers. For example, depositional zones supported a specialized trophic structure based on coarse organic matter consumption, whereas in erosional zones (subdivided into lotic and lentic units) periphyton and fine organic matter were the main food source. At the reach-segment scale (101 to 10²m),valley morphology was the primary factor controlling the stream ecosystem, but anthropogenic alteration of riparian vegetation seems to override geomorphological controls on the trophic structure. For example, the open-canopied Triouzoune Creek (gentle plateau valley), characterized by scrapers (
Food webs of tropical, temperate, and arctic lakes can be characterized by the carbon and nitrogen stable isotope ratios of their constituent organisms. After assigning trophic levels using δ 15N, a broad range of δ 13C is observed at the primary consumer level in nearly all lakes. The range of δ 13C is on the order of 20 ‰ in tropical lakes Kyoga and Malawi and lakes with low dissolved inorganic carbon in temperate Canada, but is narrower in shallow lakes of the Canadian arctic. This broad range exists in ecosystems in which terrestrial inputs and/or aquatic macrophytes are often minimal. The isotopically light end of the range results from phytoplankton photosynthesis whereas the isotopically heavy end represents benthic algae photosynthesizing within an unstirred boundary layer. This range is successfully predicted by an application of a simple isotopic model for photosynthetic fractionation, originally developed for aquatic macrophytes, which uses boundary layer thicknesses reported for benthic algal communities. When benthic photosynthesis becomes light-limited in very turbid lakes of the Mackenzie Delta, then phytoplanktonic carbon dominates the diet of the primary consumers. The organisms on the primary consumer trophic level appear from their δ 13C values to harvest preferentially either planktonic or benthic algal carbon but, in temperate and arctic lakes, higher consumer levels are increasingly omnivorous. Therefore top aquatic predators often have a narrow range of δ 13C. In temperate and arctic lakes these top predators have a δ 13C near the midpoint of the range at the primary consumer level, which would result from nearly equal dependence on planktonic and benthic algal carbon. This equal dependence would not be predicted from the relative magnitude of planktonic and benthic algal photosynthesis as currently estimated in these systems.
Substratum heterogeneity is a large source of variability in periphyton production, but the influence of substratum on periphyton response to experimental manipulations is rarely measured. Using laboratory and whole-lake experiments, we compared area-specific primary production of periphyton on wood (epixylon) and sediment (epipelon), and tested whether periphyton on the 2 substrata responded differently to water-column fertilization. In the laboratory, natural periphyton assemblages on wood or sediment were exposed to 1 of 6 treatments in a fully factorial (light [250, 70, or 10 μmol m−2 s−1] × nutrient [control or + N and P]) experiment. We measured 14C primary production on both substrata after 25 to 30 d. We also measured epipelic and epixylic production in a reference and an experimentally fertilized lake. We constructed photosynthesis-irradiance curves for epipelon from 3 depths in each lake, and used the curves to predict primary production at average in situ light intensities for each lake and depth.Production response to fertilization was substratum-specific, and area-specific epipelic production was 10× that of epixylon at both experimental scales. Both epixylon (ANOVA, p
Interactions between benthic predators and pelagic prey, such as larval odonates and Daphnia, are often used to describe classic predator–prey relationships in laboratory studies. However, few field studies explore the potential impact of benthic predators on pelagic prey. Recent studies of cladocerans document diel horizontal migration (DHM), where large-bodied zooplankton (i.e., Daphnia) decrease their exposure to pelagic predators by seeking refuge among macrophytes. However, daphnids undergoing DHM may simultaneously increase their likelihood of encountering benthic predators that commonly occur in littoral zones. In laboratory experiments, we showed that dragonfly nymphs (Epitheca cynosura) effectively eliminated all Daphnia within 24 h, regardless of macrophyte presence or architecture. We also tested whether additions of larval damselflies (Ischnura elegans, Coenagrion puella, C. pulchellum) and dragonflies (Somatochlora flavomaculata) (total odonate density of 35–55/m2) significantly reduced total zooplankton or benthic invertebrate abundance in field enclosures with different macrophyte densities (20, 40, 80% volume infested [PVI]). Odonates significantly reduced Daphnia abundance at 20 PVI. However, the magnitude of the influence of odonates on daphnids, as well as Ceriodaphnia and Polyphemus, decreased with increasing macrophyte density. Odonate predation did not significantly affect benthic taxa abundance. Thus, daphnids undergoing DHM may lower predation from pelagic predators, but our results suggest that mortality from littoral predators may be significant. The net benefit of DHM may, therefore, differ among lakes as a function of the relative threats posed by pelagic and littoral predators.
Foodchain models predict strong positive response of algal biomass to total phosphorus (TP) in odd-link ecosystem where grazers are controlled by planktivores and no significant response of algal biomass in even-link ecosystem where grazers are released from planktivore predation. On the other hand, resource- or ratio-dependent models predict proportional increase in algal biomass with increasing TP. These predictions were tested with field data from a large number of north temperature lake ecosystems exhibiting a wide range of TP. Instead of using the traditional approach of the number of trophic links present in an ecosystem, I used the presence vs. absence or near absence of large Daphnia and planktivorous fish to indicate the function dominance of odd vs. even links. Results showed that algal biomass response to TP is stronger in dominant odd-link ecosystems than in dominant even-link ecosystems, which is consistent with the predictions of foodchain models. The significant positive slope of the relationship of algal biomass to total phosphorus for dominant even-link ecosystems is not consistent with foodchain models. In addition, a nonlinear response pattern of algal biomass to total phosphorus appears to be inconsistent with both foodchain and ratio-dependent models. Results also showed that even-link ecosystems produce proportionately lower algal biomass, demonstrating that grazers can modify ratio dependence of algal biomass. Overall, algal biomass appears to be both predator and ratio dependent because grazers are capable of modifying algal response to nutrients, and algae show positive response to nutrients even in the presence of larger grazers.
Phytodetrital sedimentation, bacterial activity in sediments, and benthic macro‐ and meiofauna abundance were measured to calculate a carbon budget for pelagic‐benthic coupling in Lake Erken. Bacterial activity in surficial sediment was limited by temperature in spring, although a significant correlation with the input of spring‐bloom phytodetritus was noted. Population dynamics of benthic meiofauna during a period of increased food availability in spring were highly taxon‐specific and closely correlated to feeding behavior. Abundances of ostracods and nematodes rapidly increased when phytodetritus became available in hypolimnetic water and surficial sediment, respectively. Considerable time lags (months) were found between phytodetritus deposition and population development of harpacticoid copepods and chydorids.
Carbon budget calculations based on sedimentation data (traps) and surficial sediment C content showed that during spring between 1.1 and 7.2% of deposited phytodetritus is assimilated by benthic meiofauna, whereas the dominant macroinvertebrates, sedentary chironomids, assimilated between 2.4 and 6.0%. On average, between 1.9 and 12.4% of the deposited phytodetritus was mineralized by sediment bacteria. A significant negative correlation was found between abundances of benthic meiofauna and bacteria in the sediment. Chlorophyll a analysis of surficial sediment was a necessary, complementary tool to detect sedimentation that was not detected by the traditional, cylindric sediment traps.
The impact of grazing and nutrient supply on epilithic periphyton was investigated in factorial field experiments in four seasons at three Swedish sites of different productivity and herbivore composition (Lake Limmaren, Lake Erken, and Vaddo ¨, a low salinity coastal site). Nutrient supply was enhanced by a granulose fertilizer containing nitrogen (N) and phosphorus (P), and grazer density was manipulated by exclusion cages. Algal biomass was increased by nutrient enrichment and reduced by grazer presence, but effects were highly variable between sites and seasons. Generally, grazers had stronger effects on algal biomass than nutrient enrichment, but there was no overriding effect of either grazing or nutrients. This indicated a simultaneous top-down and bottom-up control of algal biomass. Taxonomic composition of the periphyton was more affected by grazer presence than by nutrients. Internal nutrient ratios of the algae indicated N limitation at two of the sites. At all sites, the content of N and P in the periphytic assemblage was enhanced by the experimental nutrient enrichment, resulting in decreased C : N and C : P ratios. The presence of herbivores also increased periphytic nutrient content (decreased N : P and C : P ratios) in some experiments, suggesting an increase in algal P due to excretion. The effect strength of grazers and nutrients on periphyton was affected by different abiotic characteristics such as light availability, nutrient concen- trations, and temperature. However, single environmental characteristics were not sufficient to explain the relative importance of grazing and nutrients.
Previous studies utilizing oxygen‐sensitive microelectrodes have demonstrated that as a result of epipelic algal photosynthesis and microbial metabolism, and regardless of the oxygen concentration of the overlying water, sediments within the euphotic zone of lakes undergo marked diel fluctuations in the extent of oxygen penetration. This investigation utilized oxygen‐sensitive microelectrodes, ³² PO 4 ³⁻ radiotracer, and a novel flow‐through system to examine the effect of epipelic algal photosynthesis on sediment oxygen dynamics and the concomitant pattern of phosphorus release from lake sediments. Epipelic algae mediated release of phosphorus from sediments to overlying water via daily formation and breakdown of the oxidized microzone. During illumination, surficial sediments rapidly became oxygenated, and release of phosphorus diffusing from deeper sediment layers was inhibited. During darkness the microzone became anoxic, and phosphorus was released to overlying water at an accelerated rate, producing marked diel fluctuation in efflux rate. Observed patterns of release are consistent with recent evidence for a mechanism consisting of rapid uptake or release of dissolved phosphate by sediment microorganisms in response to respective oxic or anoxic conditions.
Phosphate uptake kinetics of periphyton were evaluated by addition of carrier‐free radiophosphate under controlled laminar flow conditions. In most cases, excluding only poorly colonized substrata, tracer fluxes were found to be limited by boundary‐layer mass transfer. Tracer flux could be described as a power function of flow velocity and as a negative power function of distance from the leading edge of the communities, as expected from mass transfer calculations. Observed deviations from theoretical functions were interpreted as effects of community patchiness and of internal water flow in the periphyton matrix. Phosphate turnover by periphyton in suspension was within the range of values for lake plankton, when related to biomass. Kinetic calculations based on these turnover measurements indicated that internal recycling of phosphate and recycling from the boundary layer, rather than external uptake, accounted for most phosphate turnover within intact periphyton films. This situation is likely typical under oligotrophic conditions. Boundary‐layer thickness was within the range of published estimates from littoral systems. The results indicate that chemical conditions within periphyton communities differ considerably from the immediate surroundings and that boundary‐layer development is a key factor affecting the metabolism of periphyton communities.
We sampled periphyton in dominant habitats at oligotrophic and eutrophic sites in the northern Everglades during the wet and
the dryseasons to determine the effects of nutrient enrichment on periphytonbiomass, taxonomic composition, productivity,
and phosphorus storage. Arealbiomass was high (100–1600 g ash-free dry mass [AFDM]m−2) in oligotrophic sloughs and in stands of the emergentmacrophyte Eleocharis cellulosa, but was low in adjacent stands of
sawgrass,Cladium jamaicense (7–52 g AFDM m−2). Epipelon biomasswas high throughout the year at oligotrophic sites whereas epiphyton andmetaphyton biomass varied seasonally
and peaked during the wet season.Periphyton biomass was low (3–68 g AFDM m−2) and limitedto epiphyton and metaphyton in open-water habitats at eutrophic sites andwas undetectable in cattail stands (Typha
domingensis) that covered morethan 90% of the marsh in these areas. Oligotrophic periphytonassemblages exhibited strong seasonal
shifts in species composition and weredominated by cyanobacteria (e.g., Chroococcus turgidus, Scytonema hofmannii)during the
wet season and diatoms (e.g. Amphora lineolata, Mastogloiasmithii) during the dry season. Eutrophic assemblages were dominated
byCyanobacteria (e.g., Oscillatoria princeps) and green algae (e.g., Spirogyraspp.) and exhibited comparatively little seasonality.
Biomass-specific grossprimary productivity (GPP) of periphyton assemblages in eutrophic openwaters was higher than for comparable
slough assemblages, but areal GPP wassimilar in these eutrophic (0.9–9.1 g C m−2d−1) and oligotrophic (1.75–11.49 g C m−2d−1) habitats. On a habitat-weighted basis, areal periphytonGPP was 6- to 30-fold lower in eutrophic areas of the marsh due to
extensiveTypha stands that were devoid of periphyton. Periphyton at eutrophic siteshad higher P content and uptake rates than
the oligotrophic assemblage, butstored only 5% as much P because of the lower areal biomass.Eutrophication in the Everglades
has resulted in a decrease in periphytonbiomass and its contribution to marsh primary productivity. These changesmay have
important implications for efforts to manage this wetland in asustainable manner.
In a study of 10 lakes in the Eastern Townships (Quebec) periphyton biomass correlated less well with total P (TP) concentration in the water than did phytoplankton biomass. The relationship with TP was improved somewhat when periphyton biomass was estimated as cell volume rather than as chlorophyll or organic material. When the community was divided among various groups according to taxa, life form, and size, only the biomasses of greens, filamentous algae, and algae exceeding 10 000 μm3 were correlated with TP. The biomass of the smaller algae, which are more readily grazed by benthos, was about the same in all lakes whereas nuisance forms increased significantly with P enrichment. At more eutrophic sites, maximal periphyton biomasses were observed in midsummer, coinciding with peak recreational use of lakes, whereas at the other sites, maxima appeared earlier in the season.
We compiled 414 studies from the literature to test if general relationships exist between chlorophyll concentration, light attenuation, and gross photosynthesis across phytoplankton communities, macrophyte stands, and attached microalgal mats. We also evaluated the upper limit to photosynthesis in the various communities. Along with increasing chlorophyll concentration, the photic zone diminishes from > 100 m in sparse phytoplankton communities to centimeters-meters in macrophyte stands to < 1 mm in dense microalgal mats. This compression of the photic zone is paralleled by a marked increase in volumetric photosynthesis (mmol O2 m-3 h-1). In contrast, integral photosynthesis (mmol O2 m-2 h-1) remains relatively constant, depending on both the photic zone and volumetric photosynthesis. A similar upper limit (~60 mmol O2 m-2 h-1) is attained in dense macrophyte and phytoplankton communities when most of the irradiance is captured by plants. Integral photosynthesis, however, is often far below this upper limit because background light attenuation by particles and dissolved organic matter restrict photosynthesis in many aquatic plant communities. Moreover, limitation of CO2 and O2 exchange may constrain integral photosynthesis in dense plant communities, which are often subject to severe CO2 depletion and O2 supersaturation.
The biomass and species composition of epilithic periphyton in oligotrophic Lake Taupo was measured over a full year. Measurements of photosynthetic carbon uptake were made during summer and early winter. The lake supported a high biomass of epilithic periphyton throughout the year, averaging 100–600 mg m over the 0–35 m water depth and peaking in early summer. Periphyton extended to at least 40 m depth. Depth‐integrated carbon fixation rates of 242–362 mg m h were measured. Periphyton constituted more than 90% of the algal biomass and carbon fixation within the littoral zone, but less than 2% of production on a whole‐lake basis. Based on taxonomic composition, periphyton could be divided into three zones, surface (0–2 m), mid water (2–20 m) and deep (> 20 m). The diatoms Aulacosira granulata, Rhopalodia novae zealandiae, Epithemia sorex, and Fragilaria spp. dominated the deep assemblage, Tolypothrix tenuis and Mastogloia elliptica the mid water, and Scytonema, Dichothrix, and filamentous chlorophytes the shallow zone. Indicator pigments, analysed by high‐performance liquid chromatography, confirmed these groupings. Biomass‐specific rates of photosynthesis were low in shallow water (assimilation number ≤ 1 at 1 m depth) and at depths of 20 m and below, photosynthesis was light‐limited. We hypothesise that the periphyton community was slow‐growing and that the high biomass seen at all depths resulted from gradual accrual with low rates of loss.
Responses of zooplankton, pelagic primary producers, planktonic bacteria, and CO2 exchange with the atmosphere were measured in four lakes with contrasting food webs under a range of nutrient enrichments during a seven-year period, Prior to enrichment, food webs were manipulated to create contrasts between piscivore dominance and planktivore dominance. Nutrient enrichments of inorganic nitrogen and phosphorus exhibited ratios of N:P > 17:1, by atoms, to maintain P limitation. An unmanipulated reference lake, Paul Lake, revealed baseline variability but showed no trends that could confound the interpretation of changes in the nearby manipulated lakes. Herbivorous zooplankton of West Long Lake (piscivorous fishes) were large-bodied Daphnia spp., in contrast to the small-bodied grazers that predominated in Peter Lake (planktivorous fishes). At comparable levels of nutrient enrichment, Peter Lake's areal chlorophyll and areal primary production rates exceeded those of West Long Lake by factors of approximately three and six, respectively. Grazers suppressed pelagic primary producers in West Long Lake, relative to Peter Lake, even when nutrient input rates were so high that soluble reactive phosphorus accumulated in the epilimnions of both lakes during summer. Peter Lake also had higher bacterial production (but not biomass) than West Long Lake. Hydrologic changes that accompanied manipulation of East Long Lake caused concentrations of colored dissolved organic carbon to increase, leading to considerable variability in fish and zooplankton populations. Both trophic cascades and water color appeared to inhibit the response of primary producers to nutrients in East Long Lake. Carbon dioxide was discharged to the atmosphere by Paul Lake in all years and by the other lakes prior to nutrient addition. During nutrient addition, only Peter Lake consistently absorbed CO2 from the atmosphere, due to high rates of carbon fixation by primary producers. In contrast, CO2 concentrations of West Long Lake shifted to near-atmospheric levels, and net fluxes were near zero, while East Long Lake continued to discharge CO2 to the atmosphere.
Primary productivity of algal epiphytes on the surfaces of Phragmites, Potamogeton, and Nuphar was measured seasonally from June 1978, through June 1979, in the littoral zone of Lake Ohrid, using 14C methodology. Surface areas of individual macrophytes were determined throughout the study period through the use of a non-miscible surfactant and a calibration curve of surfactant weight versus known, calculated surface areas.
Mean total surface area available for epiphytic colonization during the study period was 1.032 m2 macrophyte surface per m2 of littoral zone for Phragmites, 0.810 m2 for Potamogeton, and 0.167 m2 for Nuphar. Seasonal rates of mean primary productivity of algal epiphytes on Phragmites from the surface to the light-compensation depth ranged from 84–1406 mg C m−2 littoral zone d−1; ranges for epiphytes on Potamogeton and Nuphar were 77–586 and 69–268 mg C m−2 littoral zone d−1, respectively. Maximum rates were observed typically during June; minimum rates were observed typically during August to December. Mean daily productivity rates over the 12 month period were for epiphytes on Potamogeton 167.0, on Nuphar 100.4 and on Phragmites 671.2 mg C m−2 littoral zone d−1. Calculated annual production for epiphytes on Nuphar was 36.65, on Potamogeton 60.95 and on Phragmites 245.0 g C m−2 littoral zone yr−1. Epiphytic production data were typically considerably higher than production data obtained for littoral and pelagial planktonic algae and compare favorably with published data for epiphytic and periphytic production in Lawrence Lake, Marion Lake, and Borax Lake.
SUMMARY 1. Pelagic and epipelic microalgal production were measured over a year in a pre-defined area (depth 0.5 m) in each of two lakes, one turbid and one with clear water. Further estimates of epiphytic production within reed stands were obtained by measuring production of periphyton developed on artificial substrata.
2. Total annual production of phytoplankton and epipelon was 34% greater in the turbid lake (190 g C m−2 year−1) than in the clearwater lake (141 g C m−2 year−1). However, the ratio of total production to mean water column TP concentration was two fold greater in the clearwater lake.
3. Phytoplankton accounted for the majority of the annual production (96%) in the turbid lake, while epipelic microalgal production dominated (77%) in the clear lake. The relative contribution of epipelic algae varied over the year, however, and in the turbid lake was higher in winter (11–25%), when the water was relatively clear, than during summer (0.7–1.7%), when the water was more turbid. In the clearwater lake, the relative contribution of epipelon was high both in winter, when the water was most clear, and in mid-summer, when phytoplankton production was constrained either by nutrients or grazing.
4. Compared with pelagic and epipelic primary production, epiphytic production within a reed stand was low and did not vary significantly between the lakes.
5. The study supports the theory of a competitive and compensatory trade-off between primary producers in lakes with contrasting nutrient concentrations, resulting in relatively small differences in overall production between clear and turbid lakes when integrating over the season and over different habitats.
The suspension feeding of Bithynia tentaculata was tested in laboratory experiments. The animals were fed in 1-1 aerated glass beakers, and filtration rates were calculated from changes in cell concentrations during the 6-h experiment. Temperature influenced the filtering rate, with minimum values of 5ml ind–1 h–1 at 5 C and maxima of 17.2 ml ind–1 h–1 at 18 C. Three food species of different size, motility and cell surface characteristics (Chlamydomonas reinhardii, Chlorella vulgaris and Chlorogonium elongatum) did not affect filtration rates. Suspension feeding increased with increasing food concentrations up to 12 nl ml–1, above which feeding rate was kept constant by lowering the filtering rates. Even the smallest animals tested (–1 h–1, and increasing rates up to 8.4 ml were found in the 6–7 mm size class. All size classes of Bithynia showed a circannual fluctuation of their filtration rates. The ecological consequences of Bithynia's ability to switch between two feeding modes, grazing and suspension feeding, are discussed.
Within a certain nutrient level shallow lakes may alternate between two states, a clearwater and a turbid state. To obtain more information on the characteristics of these two states, we compared seasonal variations in trophic structure and physico-chemical variables of two clear and two turbid lakes studied during seven or eight years. The clearwater lakes were characterised by a high abundance of submerged macrophytes, high piscivorous:planktivorous fish ratios, high zooplankton:phytoplankton ratios and low chlorophyll aduring summer. Submerged macrophytes were almost absent from the turbid lakes, planktivorous fish dominated, the zooplankton:phytoplankton ratio was low and summer chlorophyll awas high. While total phosphorus (TP) was almost constant throughout the season in the clearwater lakes, TP was substantially higher during summer in the turbid lakes reflecting high internal loading. In the clearwater lakes, mean summer chlorophyll awas only 45–51% of winter values, while summer chlorophyll awas 118–259% of winter values in the turbid lakes. Our data suggests that zooplankton, by grazing on phytoplankton, play a major role in maintaining clearwater conditions in eutrophic macrophyte-rich lakes, in particular during summer. In addition, results from a multiple regression on data from 37 lakes and the analyses of the seasonal dynamics in suspended solids provide some evidence that zooplankton grazing diminishes concentrations of detritus and inorganic suspended solids either directly by grazing or more indirectly. Using information also from literature, we argue that the role of zooplankton grazing for water clarity in macrophyte-rich lakes may increase from mesotrophic to eutrophic lakes.
Benthic food web dynamics and carbon flow were examined in the littoral zone of Lake Coleridge, a large deep oligotrophic lake, using radioactive and stable isotope techniques in conjunction with analyses of stomach contents of the fauna. We specifically address two hypotheses: (1) that macrophytes only contribute to the carbon flow to higher trophic levels when they have decayed; and (2) that epiphytic algae is the major source of carbon for macroinvertebrates, and thus fish, with only minor contributions from phytoplankton or terrestrial sources. Epiphytic diatoms were a major component of the stomach contents of the gastropod snail Potamopyrgus antipodarum, and of chironomids. Animal remains were also common in the diet of some chironomids, while amorphous organic matter predominated in the stomachs of oligochaetes. A variety of epiphytic algal taxa was found in trichopteran larvae. Feeding rate of P. antipodarum measured with radioactive tracers increased by 10 on decayed macrophytes (Elodea) compared with live material, while feeding rates on characean algae increased by a factor of 3 when decayed material was presented. However, assimilation rates were less than 20% on decayed material compared with 48–52% on live material. Potential carbon sources were easily distinguished based on their 13C values, although isotopic ratios showed significant variation among sites. Epiphytic algae showed less variation among sites than macrophytes and were depleted by 4–5 compared with macrophytes. Detrital material, organic matter in the sediments and plankton were significantly depleted in 13C relative to macrophytes and slightly depleted relative to epiphytic algae. Most macroinvertebrate taxa showed a similar pattern among sites to macrophytes and epiphytic algae. P. antipodarum and chironomids were slightly enriched compared with epiphytic algae. Ratios for the common bully (Gobiomorphus cotidianus) were generally consistent with a diet dominated by chironomids, while there was some evidence for terrestrial inputs for koaro (Galaxias brevipinnis) and juvenile brown trout. Epiphytic algae appear to underpin much of the production in the littoral zone of this oligotrophic lake, with trichopteran and chironomid larvae mediating carbon flows from algae to fish. Macrophytes do not make a major contribution directly to carbon flow to higher trophic levels even when decayed. The lack of a direct link between macrophytes and higher trophic levels is due to the faunal composition, including a lack of large herbivores.
Stable isotope ratios of carbon and nitrogen were used successfully to elucidate the biogeochemical and ecological frameworks of the trophic structure of benthic organisms in Lake Baikal, Siberia. Analysis of the benthic animals showed a considerable variance in both carbon and nitrogen stable isotope ratios. Two main primary producers of benthic plants and planktonic organic matter were clearly differentiated by 13C, and thus the diets of these two primary producers' groups could be analyzed with the use of a two source mixing model. The trophic position of each benthic animal was estimated by the analysis of 15N. Contrasting characteristics between food webs in shallow and deep benthic areas were clearly observed on the 13C – 15N map. Food webs in shallow benthic areas were complex, and many primary producers and various animals were present with diverse isotope distributions. In contrast, food webs in deep benthic areas were composed of single organic matter origin exhibiting simple predator and prey relationships. Both 13C and 15N values of benthic gammarids were correlated with the sampling water depth. A trend of 13C decrease and 15N enrichment was observed with increasing water depth. The stable isotope ratios of the benthic animals indicated that the complexity of the food web structure in their ecosystem decreased as the depth of the water increased.
The physico-chemical environment and the resource needs of phytoplankton, periphyton and macrophytes are markedly different. In this paper we compare the characteristics of the different phototrophs with respect to water movements and diffusive boundary layers, nutrient demands, carbon and oxygen dynamics, and light climate and light requirements. We discuss how these characteristics affect growth dynamics, biomass limitation and biotic interactions of phototrophs in natural habitats, and, finally, we discuss how plant community dominance can be predicted from ecosystem size, depth and nutrient loading.Phytoplankters live in a stirred environment with thin diffusive boundary layers, low nutrient availability and a highly variable light climate. They grow fast and have high nutrient requirements but their biomass is often nutrient limited. Diffusive boundary layers of benthic microalgae and rooted macrophytes are thicker and reduce the exchange of gases and nutrients. Sessile organisms live in a more predictable light climate but may experience severe self-shading and generally grow more slowly than phytoplankters. The nutrient requirements of rooted macrophytes are lower than those of microalgae because of low growth rates, high internal C:N:P ratios and the existence of nutrient conserving mechanisms, and nutrient limitation is less important because the plants exploit the rich nutrient pools of the sediment.The phototrophs compete for light, nutrients and inorganic carbon, and the balance among phototrophs changes with size, depth and nutrient richness of the ecosystem. Phytoplankters dominate in deep lakes and oceanic waters and may also, together with periphyton, dominate in nutrient-rich shallow waters because of shading effects on macrophytes and benthic microalgae. However, shallow lakes and estuaries with low nutrient availability in the water column are dominated by benthic phototrophs because of their lower nutrient requirements and contact to sediment nutrient pools.
1. The biomass of the different primary producers, and their relative contributions to the total, were measured quarterly from July 1997 to September 1998 in a tropical reservoir (Brobo, Côte‐d'Ivoire). The study period was marked by an exceptional decrease in the water level as a result of a long drought with only one significant rainfall in June 1998.
2. In July 1997, at the beginning of the usual rainy season, the level of the lake was normal and the ecosystem was in a moderately clear water state dominated by littoral macrophytes, mostly Potamogeton octandrus (more than 55% of the 6.4 tons of carbon of the total primary biomass). The microphytobenthos (19%) and the phytoplankton (25%) were secondary contributors, whereas the periphyton on macrophytes (0.5%) and the epixylon (periphyton on dead flooded trees, 0.3%) were negligible.
3. As a result of the steady decline in water level due to a lack of rain, the macrophytes were progressively stranded on the shores and had disappeared by March 1998. From this time, microalgae (microphytobenthos and phytoplankton) became dominant. Their combined biomass increased slowly from 2.8 tons of carbon in July 1997 to 3.7 tons in September 1998. The microphytobenthic biomass contributed 78% to the total in March, 55% in June and 60% in September, while other contributions were mainly due to the phytoplankton. The epixylon remained negligible throughout the study (≤0.5% of the whole primary biomass).
4. The distribution and temporal changes in the biomass during each survey were mainly linked to hydrology and to interactions between primary producers.
5. The effect of water level changes on free (planktonic) and fixed primary producers (periphytic microalgae and rooted macrophytes) is discussed.
The turbidity of lakes is generally considered to be a smooth function of their nutrient status. However, recent results suggest that over a range of nutrient concentrations, shallow lakes can have two alternative equilibria: a clear state dominated by aquatic vegetation, and a turbid state characterized by high algal biomass. This bi-stability has important implications for the possibilities of restoring eutrophied shallow lakes. Nutrient reduction alone may have little impact on water clarity, but an ecosystem disturbance like foodweb manipulation can bring the lake back to a stable clear state. We discuss the reasons why alternative equilibria are theoretically expected in shallow lakes, review evidence from the field and evaluate recent applications of this insight in lake management.
