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Ephemeral Floodplain Habitats Provide Best Growth Conditions for Juvenile Chinook Salmon in a California River
Abstract and Figures
We reared juvenile Chinook salmon for two consecutive flood seasons within various habitats of the Cosumnes River and its
floodplain to compare fish growth in river and floodplain habitats. Fish were placed in enclosures during times when wild
salmon would naturally be rearing in floodplain habitats. We found significant differences in growth rates between salmon
reared in floodplain and river enclosures. Salmon reared in seasonally inundated habitats with annual terrestrial vegetation
experienced higher growth rates than those reared in a perennial pond on the floodplain. Growth of fish in the non-tidal river
upstream of the floodplain varied with flow in the river. When flows were high, there was little growth and high mortality,
but when the flows were low and clear, the fish grew rapidly. Fish displayed very poor growth in tidally influenced river
habitat below the floodplain, a habitat type to which juveniles are commonly displaced during high flow events due to a lack
of channel complexity in the main-stem river. Overall, ephemeral floodplain habitats supported higher growth rates for juvenile
Chinook salmon than more permanent habitats in either the floodplain or river. Variable responses in both growth and mortality,
however, indicate the importance of providing habitat complexity for juvenile salmon in floodplain reaches of streams, so
fish can find optimal places for rearing under different flow conditions.
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... For example, flooding facilitates the dispersal of nutrients, seeds and other vegetative propagules, and eggs, larvae, juveniles, and adults of many animals (Fischer et al. 2021 ). For many organisms located in channels and on the floodplain, flooding cues reproduction, makes nursery habitat available, and is conducive for survival and growth of early life stages (Sommer et al. 2001 , Ahearn et al. 2006, Jeffres et al. 2008, Yarnell et al. 2010. It can also lead to seed germination (Mahoney andRood 1998 , Brock et al. 2003 ) and the hatching of desiccation-resistant eggs in floodplain soils (Nielsen et al. 2000 ). ...
Societal perceptions of river floods are typically negative because of the death and destruction they may cause, although scientists and natural resource managers have long recognized the critical ecological role of floods. Like fire and some other ecological disturbances, river flooding intersects many aspects of ecology and society. But unlike fire, flooding receives relatively little attention in the disturbance ecology literature. We call for more focused recognition of flood ecology as a discipline to help river science better inform societal perceptions through developing a better understanding of the ecological roles of flooding. We contend that the absence of a discipline of flood ecology has constrained progress in our understanding of how rivers function and that a formal conceptualization could help reveal the positive aspects of flooding. Finally, we propose a series of questions that we believe a discipline of flood ecology should address.
... We do note that periodic connectivity is an inherent property of floodplains, and the riskreward trade-off of using floodplain habitat has existed during the evolution of salmon using floodplains (e.g. Jeffres et al. 2008). Thus, occasional disconnect from the mainstem does not necessarily mean that these habitats are ecological traps. ...
Cool‐water habitats provide increasingly vital refuges for cold‐water fish living on the margins of their historical ranges; consequently, efforts to enhance or create cool‐water habitat are becoming a major focus of river restoration practices. However, the effectiveness of restoration projects for providing thermal refuge and creating diverse temperature regimes at the watershed scale remains unclear. In the Klamath River in northern California, the Karuk Tribe Fisheries Program, the Mid‐Klamath Watershed Council, and the U.S. Forest Service constructed a series of off‐channel ponds that recreate floodplain habitat and support juvenile coho salmon ( Oncorhynchus kisutch ) and steelhead ( O. mykiss ) along the Klamath River and its tributaries. We instrumented these ponds and applied multivariate autoregressive time series models of fine‐scale temperature data from ponds, tributaries, and the mainstem Klamath River to assess how off‐channel ponds contributed to thermal regime diversity and thermal refuge habitat in the Klamath riverscape. Our analysis demonstrated that ponds provide diverse thermal habitats that are significantly cooler than creek or mainstem river habitats, even during severe drought. Wavelet analysis of long‐term (10 years) temperature data indicated that thermal buffering (i.e. dampening of diel variation) increased over time but was disrupted by drought conditions in 2021. Our analysis demonstrates that in certain situations, human‐made off‐channel ponds can increase thermal diversity in modified riverscapes even during drought conditions, potentially benefiting floodplain‐dependent cold‐water species. Restoration actions that create and maintain thermal regime diversity and thermal refuges will become an essential tool to conserve biodiversity in climate‐sensitive watersheds.
... This amalgamation of land parcels, known as the Cosumnes River Preserve (CRP), is protected by a combination of ownership and conservation easements, and has also been the focus of several major restoration efforts, including experimental floodplain reconnection treatments ( Table 1). Given these unique characteristics, CRP has served as an experimental test bed to investigate the multiple ecosystem service benefits of floodplain reconnection, including enhanced biodiversity (e.g., birds, fish) [66,[85][86][87], carbon sequestration [69,88,89], and groundwater recharge [90,91]. The underlying fundamental drivers of the observed ecosystem service benefits have also been extensively studied, including hydrologic dynamism and geomorphic response [35,51,52,68]. ...
In this study, we examine a novel levee breach experiment that reconnected a floodplain along the Cosumnes River, California to determine the decadal impact of removing 250 meters of levee and assess the recruitment of large wood. This is the latest study in an ongoing series of investigations 40 years in the making along the largest river on the western slope of the Sierra Nevada without a major dam. We present the findings of this multi-modal investigation here by first measuring the geomorphic alteration of the floodplain surface to quantify the depletion and accretion of sediment across the excavated site. We then identify and quantify the deposition of large wood. Results indicate initiation of anastomosing channel formation and distinct areas of large wood recruitment supporting a naturally evolving lateral levee. Accretion resulted in more than 25,000 m ³ of sediment deposition within the original excavation site, the development of multiple sand splays, and natural recruitment of native riparian tree species. We conclude by discussing implications following other approaches to floodplain restoration as a Nature-based Solution. In episodic flow regimes, like in California’s Mediterranean-montane hydroclimatic regime, restoring lateral hydrologic connectivity facilitates ecosystem function. Large flood pulse events drive sediment dynamics and geomorphic heterogeneity while enriching biodiversity through biogeochemical fluxes and habitat creation on reconnected floodplains that store floodwaters and reduce peak discharge. These findings support the importance of long-term monitoring efforts of floodplain restoration.
... Previous studies have indicated that the highly productive food web coupled with prey availability during inundation on the Yolo Bypass confers significant benefits in terms of growth and survival for rearing juvenile Chinook Salmon (Jeffres et al. 2008;Sommer et al. 2001). However, it is possible that the benefits of floodplain habitat could be further enhanced if the higher risk of contaminant bioaccumulation and its potential effects on floodplain-rearing fish could be reduced. ...
Stable isotopes (SI) and fatty acid (FA) biomarkers can provide insights regarding trophic pathways and habitats associated with contaminant bioaccumulation. We assessed relationships between SI and FA biomarkers and published data on concentrations of two pesticides [dichlorodiphenyltrichloroethane and degradation products (DDX) and bifenthrin] in juvenile Chinook Salmon (Oncorhynchus tshawytscha) from the Sacramento River and Yolo Bypass floodplain in Northern California near Sacramento. We also conducted SI and FA analyses of zooplankton and macroinvertebrates to determine whether particular trophic pathways and habitats were associated with elevated pesticide concentrations in fish. Relationships between DDX and both sulfur (δ³⁴S) and carbon (δ¹³C) SI ratios in salmon indicated that diet is a major exposure route for DDX, particularly for individuals with a benthic detrital energy base. Greater use of a benthic detrital energy base likely accounted for the higher frequency of salmon with DDX concentrations > 60 ng/g dw in the Yolo Bypass compared to the Sacramento River. Chironomid larvae and zooplankton were implicated as prey items likely responsible for trophic transfer of DDX to salmon. Sulfur SI ratios enabled identification of hatchery-origin fish that had likely spent insufficient time in the wild to substantially bioaccumulate DDX. Bifenthrin concentration was unrelated to SI or FA biomarkers in salmon, potentially due to aqueous uptake, biotransformation and elimination of the pesticide, or indistinct biomarker compositions among invertebrates with low and high bifenthrin concentrations. One FA [docosahexaenoic acid (DHA)] and DDX were negatively correlated in salmon, potentially due to a greater uptake of DDX from invertebrates with low DHA or effects of DDX on FA metabolism. Trophic biomarkers may be useful indicators of DDX accumulation and effects in juvenile Chinook Salmon in the Sacramento River Delta.
... Conversely, marsh-and delta-derived autochthonous organic matter such as phytoplankton, diatoms, algae, and eelgrass contributed considerably to the diets of insects with aquatic life stages and to some crustaceans and polychaetes that were sampled in riverine habitats. Proximity to marsh-adjacent habitat and other areas with high primary productivity and abundant prey resources can provide measurable benefits for juvenile salmon in terms of growth and survival [89][90][91]. Thus, this study joins others in underscoring the importance of connectivity, and conservation of multiple estuarine habitat types for salmon and other estuary-dependent fishes. ...
Terrestrial organic matter is believed to play an important role in promoting resilient estuarine food webs, but the inherent interconnectivity of estuarine systems often obscures the origins and importance of these terrestrial inputs. To determine the relative contributions of terrestrial (allochthonous) and aquatic (autochthonous) organic matter to the estuarine food web, we analyzed carbon, nitrogen, and sulfur stable isotopes from multiple trophic levels, environmental strata, and habitats throughout the estuarine habitat mosaic. We used a Bayesian stable isotope mixing model (SIMM) to parse out relationships among primary producers, invertebrates, and a pelagic and demersal fish species (juvenile Chinook salmon and sculpin, respectively). The study was carried out in the Nisqually River Delta (NRD), Washington, USA, a recently-restored, macrotidal estuary with a diverse habitat mosaic. Plant groupings of macroalgae, eelgrass, and tidal marsh plants served as the primary base components of the NRD food web. About 90% of demersal sculpin diets were comprised of benthic and pelagic crustaceans that were fed by autochthonous organic matter contributions from aquatic vegetation. Juvenile salmon, on the other hand, derived their energy from a mix of terrestrial, pelagic, and benthic prey, including insects, dipterans, and crustaceans. Consequently, allochthonous terrestrial contributions of organic matter were much greater for salmon, ranging between 26 and 43%. These findings demonstrate how connectivity among estuarine habitat types and environmental strata facilitates organic matter subsidies. This suggests that management actions that improve or restore lateral habitat connectivity as well as terrestrial-aquatic linkages may enhance allochthonous subsidies, promoting increased prey resources and ecosystem benefits in estuaries.
... Mussen et al. 2023) can aid in the management and restoration of carbon (C) flow to higher trophic levels in such systems (Cloern et al. 2021). To support the recovery of threatened and endemic and migratory fish species in the Delta, a major goal is to restore and expand tidal marshes, wetlands, and floodplains based on the premise that these habitats support higher phytoplankton productivity and biomass than the deeper channel habitats (Sommer et al. 2001, Schemel et al. 2004, Jeffres et al. 2008, Lehman et al. 2008. ...
Shallow-water habitats are being restored in the Sacramento-San Joaquin River Delta with the goal of enhancing phytoplankton production and food availability for higher trophic levels. However, elevated grazing pressure from the non-native freshwater clam Corbicula fluminea and localized depletions of dissolved inorganic nitrogen may limit phytoplankton biomass accumulation in restored habitats. To evaluate interactions between nutrients and grazing on phytoplankton productivity and biomass accumulation, Sacramento River water high or low in phytoplankton biomass was amended with wastewater effluent, presence of C. fluminea , or both, in 48 h in situ incubations. We measured changes in chl a concentration, phytoplankton community composition, and photosynthetic efficiency as well as carbon and nitrogen uptake rates as indicators of phytoplankton responses. Diatoms dominated phytoplankton communities before and after incubation. Chl a concentrations increased 0.7 and 7.4 times in the high and low phytoplankton biomass controls, respectively, and 4.5 and 14 times in the high and low phytoplankton biomass effluent-added treatments, respectively. In the clam treatments, chl a accumulation was suppressed to near zero regardless of effluent additions or initial phytoplankton biomass. In treatments with clams and effluent combined, phytoplankton photosynthetic efficiency was nearly 50% lower than in the effluent-only treatments, suggesting phytoplankton were stressed in the presence of clams. This experiment demonstrated that the presence of clams can prevent the accumulation of phytoplankton biomass, both directly by clam filtering and indirectly by depressing phytoplankton photosynthetic efficiency and rate of growth. We recommend that future wetland restoration projects promoting increased phytoplankton biomass assess clam settlement likelihood as well as nutrient availability.
... In general, many studies showed that more complex habitat types provide favorable condition for fish, such as growth substrate, spawning sites as well as food and protection from predation (Cucherousset et al., 2007;Jeffres et al., 2008;Pusey & Arthington, 2003), contributing to biotic community structure (richness and abundance distribution). Different species of fish exhibit particular preferences for different habitat types, thus creating local patterns of composition of species assemblages (Junqueira et al., 2016) as predicted by the Niche Theory (Hutchinson, 1957). ...
Aim To understand the distribution of fish species and their use of habitat, a range of environmental variables were evaluated as predictors of fish assemblage composition and richness in tropical semiarid aquatic systems. Methods We surveyed the species composition of fish assemblages in semiarid aquatic systems and established their degree of association with the structure of the aquatic habitat. Sites consisted of stream reaches with surface water flow, isolated temporary pools, and man-made reservoirs. Fish sampling was conducted on four occasions during the wet (April and June 2006) and dry seasons (September and December 2006). The correlation between richness and abundance with the habitat structure was evaluated using stepwise multiple regression. Patterns of variation in fish assemblage composition across sites were evaluated using Nonmetric Multidimensional Scaling, and the Indicator Species Analysis was used to determine which species were significant indicators of sites. To establish multivariate correlations and test the hypothesis of local fish composition being associated with the environmental variables we used a Canonical Correspondence Analysis. Results Morphometric variables, stream reach width, stream length and elevation explained 75.6% of the variation in fish richness. Macrophyte cover and overhanging vegetation added to the predictive power of the model equation, where the final model explained 86.9% of the variation in fish richness. Canonical Correspondence Analysis showed a significant relationship between fish composition data and site morphology (altitude, bank slope and littoral depth). Among the water quality, habitat composition and substrate variables, temperature, sand, and gravel showed higher correlation with the CCA axes. Conclusions These results indicated that fish communities assume different structures and compositions across different habitat types following the environmental heterogeneity in dryland aquatic systems.
... These conditions can be important for nutrient cycling in the floodplain sediments and soils (Opperman et al., 2010) and for ecological connectivity (Tockner et al., 2000). For example, juvenile salmonids use inundated floodplains, tracking warm waters (Baldock et al., 2016) and food resources to support rapid growth (Jeffres et al., 2008). The examples provided above are only a few of the ecologically relevant physical processes that play out mostly outside the brief temporal windows of discrete extreme events that would fall under the typical definition of disturbance. ...
I argue that the dynamic nature of contemporary, landscape‐shaping (geomorphic) processes deserves more consideration in conservation science and practice. In an analysis of a sample of fundamental terms related to geomorphology and area‐based conservation in the Web of Science, I found that the terms co‐occurred in <2% of the analyzed entries (titles, abstracts, and keywords) from 2000 to 2020. This result is indicative of the rather peripheral attention that, more broadly, landscape‐shaping processes seem to receive in the conservation literature. Among conservation scientists and practitioners, landforms that define the physical structure of habitat are often perceived as largely static, whereas the consideration of their dynamic adjustments to geomorphic processes is often limited to extreme events. I use examples derived from river‐floodplain environments to illustrate strong, multifaceted, and reciprocal interactions between biota and various erosional and depositional processes. These ubiquitous interdependencies clearly demonstrate that geomorphic processes are an integral part of ecosystem dynamics at time scales relevant for conservation. Crucially, erosional and depositional processes modulate many environmental impacts of past and current anthropogenic activities. I conclude that the absence of a more explicit and widespread consideration of geomorphic processes in conservation science and practice is surprising and detrimental to their effectiveness. I call for bolstered efforts among the conservation and geoscience communities to better integrate landscape dynamics within the field of conservation. The rise of the ecosystem‐based and social‐ecological systems approaches to conservation and the growth of interdisciplinary geoscience branches (e.g., biogeomorphology, ecohydraulics, and geoconservation) will facilitate such an integration.
Alluvial rivers that exhibit multi-thread patterns are common in nature and can be the dominant channel
morphology in large rivers. However, their ecological properties in response to diverse and dynamic channel
morphology has gained limited attention and remained poorly understood. In this study, we adopted an ecohydraulic
model by integrating a hydrodynamic, a sediment-transport, and a habitat-suitability model to
assess habitat quality for fish species (Schizopygopsis pylzovi and Platypharodon extremus) in three anabranching
reaches with each exhibiting a distinct anabranching morphology in the Upper Yellow River, eastern Qinghai-
Tibet Plateau. Based on the hydrologic data and actual channel morphology, we modeled the hydrodynamic
and sediment-transport conditions for a period spanning ten years, and simulated habitat conditions under a
potentially changing environment with different flow magnitudes and frequencies. The results indicated that the
average flow velocity in the low and mid-order anabranching reaches is higher than that in the high-order,
complex anabranching reaches. Meanwhile, the bedload transport rate was higher in the high and mid-order anabranching reaches than that in the low-order anabranching reach, demonstrating a greater transport efficiency
of multi-thread systems with a greater multiplicity. Consequently, the habitat suitability shows a deteriorating
trend over the ten-year modeling period and Schizopygopsis pylzovi shows better habitat status than
Platypharodon extremus. The flow magnitudes and frequency also have a significant impact on the distribution of
high habitat suitability index among the different river patterns in Upper Yellow River. This study can provide
valuable information to optimize ecological outcomes and provide valuable insights for future dam operation
strategies and consideration efforts aimed at preserving and restoring riverine ecosystems.
Relocating levees further back from river channels to increase river–floodplain connection can reduce flood stages and provide a host of co‐benefits. Modeling case studies show the significant potential of large levee setbacks for reducing flood stages; however, the difficulty of comparing between these case studies limits our understanding of how the hydraulic effects of setbacks vary in different settings. We filled this research gap by systematically modeling the hydraulic effects of setbacks across a range of river and flood conditions. We used unsteady, 1D Hydrologic Engineering Center‐River Analysis System models to quantify changes in flood stage, channel velocity, and sediment transport capacity for various setback sizes with different river slopes, widths, floodplain roughness, and flood sizes (peak flows) and durations. Setbacks reduce flood stages within the setback, as well as up‐ and downstream. Channel velocity and sediment transport capacity both increased upstream and decreased within the setback. Channel slope, flood size, and flood duration had the largest influence on hydraulic changes. There are diminishing returns in hydraulic effects with increasing setback size. These results can help guide the design and prioritization of levee setback projects and help set reasonable expectations for the scale of changes to flood hydraulics relative to the size of the reconnected floodplain.
Abstract
JUNK, W. J., P. B. BAYLEY, AND R. E. SPARKS, 1989. The flood pulse concept in river-floodplain
systems, p. 110-127. In D. P. Dodge [ed.] Proceedings of the International Large River
Symposium. Can. Spec. Publ. Fish. Aquat. Sci. 106.
The principal driving force responsible for the existence, productivity, and interactions of the major biota in river—floodplain systems is the flood pulse. A spectrum of geomorphological and hydrological conditions produces flood pulses, which range from unpredictable to predictable and from short to long duration. Short and generally unpredictable pulses occur in low-order streams or heavily modified systems with floodplains that have been leveed and drained by man. Because low-order stream pulses are brief and unpredictable, organisms have limited adaptations for directly utilizing the aquatic/terrestrial transition zone (ATTZ), although aquatic organisms benefit indirectly from transport of resources into the lotic
environment. Conversely, a predictable pulse of long duration engenders organismic • adaptations and strategies that efficiently utilize attributes of the ATTZ. This pulse is coupled with a dynamic edge effect, which extends a "moving littoral" throughout the ATTZ. The moving littoral prevents prolonged stagnation and allows rapid recycling of organic matter and nutrients, thereby resulting in high productivity. Primary production associated with the ATTZ is much higher than that of permanent water bodies in unmodified systems. Fish yields and production are strongly related to the extent of accessible floodplain, whereas the main river is used as a migration route by most of the fishes. In temperate regions, light and/or temperature variations may modify the effects of the pulse, and anthropogenic influences on the flood pulse or floodplain frequently limit production. A local floodplain,
however, can develop by sedimentation in a river stretch modified by a low head dam. Borders of slowly flowing rivers turn into floodplain habitats, becoming separated from the main channel by levées. The flood pulse is a "batch" process and is distinct from concepts that emphasize the continuous processes in flowing water environments, such as the river continuum concept. Flooclplains are distinct because they do not depend on upstream processing inefficiencies of organic matter, although their nutrient pool is influenced by periodic lateral exchange of water and sediments with the main channel. The pulse
concept is distinct because the position of a floodplain within the river network is not a primary determinant of the processes that occur. The pulse concept requires an approach other than the traditional limnological paradigms used in lotic or lentic systems.
Résumé
JUNK, W. J., P. B. BAYLEY, AND R. E. SPARKS. 1989. The flood pulse concept in river-floodplain
systems, p. 110-127. In D. P. Dodge [cd.] Proceedings of the International Large River
Symposium. Can. Spec. Publ. Fish. Aquat. Sci . 106.
Les inondations occasionnées par la crue des eaux dans les systèmes cours d'eau-plaines inondables constituent le principal facteur qui détermine la nature et la productivité du biote dominant de même que les interactions existant entre les organismes biotiques et entre ceux-ci et leur environnement. Ces crues passagères, dont la durée et la prévisibilité sont variables, sont produites par un ensemble de facteurs géomorphologiques et hydrologiques. Les crues de courte durée, généralement imprévisibles, surviennent dans les réseaux hydrographiques peu ramifiées ou dans les réseaux qui ont connu des transformations
importantes suite à l'endiguement et au drainage des plaines inondables par l'homme. Comme les crues survenant dans les réseaux hydrographiques d'ordre inférieur sont brèves et imprévisibles, les adaptations des organismes vivants sont limitées en ce qui a trait à l'exploitation des ressources de la zone de transition existant entre le milieu aquatique et le milieu terrestre (ATTZ), bien que les organismes aquatiques profitent indirectement des éléments transportés dans le milieu lotique. Inversement, une crue prévisible de longue durée favorise le développement d'adaptations et de stratégies qui permettent aux organismes d'exploiter efficacement 1 'ATTZ. Une telle crue s'accompagne d'un effet de bordure dynamique qui fait en sorte que l'ATTZ devient un « littoral mobile'<. Dans ces circonstances, il n'y a pas de stagnation prolongée et le recyclage de la matière organique et des substances nutritives se fait rapidement, ce qui donne lieu à une productivité élevée. La production primaire dans l'ATTZ est beaucoup plus élevée que celle des masses d'eau permanentes dans les réseaux hydrographiques non modifiés. Le rendement et la production de poissons sont étroitement reliés à l'étendue de la plaine inondable, tandis que le cours normal de la rivière est utilisé comme voie de migration par la plupart des poissons.
Fishes were sampled on the restored floodplain of the Cosumnes River in Central California in order to determine patterns of floodplain use. The floodplain was sampled for seven years (1998-2002, 2004-2005) during the winter-spring flooding season. The fishes fell into five groups: (1) floodplain spawners, (2) river spawners, (3) floodplain foragers, (4) floodplain pond fishes, and (5) inadvertent users. Eight of the 18 abundant species were natives, while the rest were aliens. There was a consistent pattern of floodplain use, modified by timing and extent of flooding. The first fishes to appear were floodplain foragers, inadvertent users, and juvenile Chinook salmon (river spawners). Next were floodplain spawners, principally Sacramento splittail and common carp. At the end of the season, in ponds of residual water, non-native annual fishes, mainly inland silverside and western mosquitofish, became abundant. Adult spawners left when inflow decreased; their juveniles persisted as long as flood pulses kept water levels up and temperatures low. Juvenile splittail and carp quickly grew large enough to dominate floodplain fish samples, along with smaller numbers of juvenile Sacramento sucker and pikeminnow (river spawners). Such juveniles left the Relatively few fishes that used the floodplain for spawning or rearing became stranded, except late season alien fishes. Most alien fishes had resident populations in adjacent river, sloughs, and ditches and were not dependent on the floodplain for persistence. This indicates that Central Valley floodplains managed to favor native fishes should have the following char-acteristics: (1) extensive early season flooding, (2) complete drainage by the end of the flooding season, (3) few
The Flood Pulse Concept in River—Floodplain Systems
Wolfgang J. Junk
Max Planck Institut für Limnologie, August Thienemann Strasse 2,
Post fach 165, D-2320 Pion, West Germany
Peter B. Bayley and Richard E. Sparks
Illinois Natural History Survey, 607 E. Peabody Dr., Champaign, IL 61820, USA
Abstract
JUNK, W. J., P. B. BAYLEY, AND R. E. SPARKS, 1989. The flood pulse concept in river-floodplain
systems, p. 110-127. In D. P. Dodge [ed.] Proceedings of the International Large River
Symposium. Can. Spec. Publ. Fish. Aquat. Sci. 106.
The principal driving force responsible for the existence, productivity, and interactions of the major biota in river—floodplain systems is the flood pulse. A spectrum of geomorphological and hydrological conditions produces flood pulses, which range from unpredictable to predictable and from short to long duration. Short and generally unpredictable pulses occur in low-order streams or heavily modified systems with floodplains that have been leveed and drained by man. Because low-order stream pulses are brief and unpredictable, organisms have limited adaptations for directly utilizing the aquatic/terrestrial transition zone (ATTZ), although aquatic organisms benefit indirectly from transport of resources into the lotic
environment. Conversely, a predictable pulse of long duration engenders organismic • adaptations and strategies that efficiently utilize attributes of the ATTZ. This pulse is coupled with a dynamic edge effect, which extends a "moving littoral" throughout the ATTZ. The moving littoral prevents prolonged stagnation and allows rapid recycling of organic matter and nutrients, thereby resulting in high productivity. Primary production associated with the ATTZ is much higher than that of permanent water bodies in unmodified systems. Fish yields and production are strongly related to the extent of accessible floodplain, whereas the main river is used as a migration route by most of the fishes. In temperate regions, light and/or temperature variations may modify the effects of the pulse, and anthropogenic influences on the flood pulse or floodplain frequently limit production. A local floodplain,
however, can develop by sedimentation in a river stretch modified by a low head dam. Borders of slowly flowing rivers turn into floodplain habitats, becoming separated from the main channel by levées. The flood pulse is a "batch" process and is distinct from concepts that emphasize the continuous processes in flowing water environments, such as the river continuum concept. Flooclplains are distinct because they do not depend on upstream processing inefficiencies of organic matter, although their nutrient pool is influenced by periodic lateral exchange of water and sediments with the main channel. The pulse
concept is distinct because the position of a floodplain within the river network is not a primary determinant of the processes that occur. The pulse concept requires an approach other than the traditional limnological paradigms used in lotic or lentic systems.
Résumé
JUNK, W. J., P. B. BAYLEY, AND R. E. SPARKS. 1989. The flood pulse concept in river-floodplain
systems, p. 110-127. In D. P. Dodge [cd.] Proceedings of the International Large River
Symposium. Can. Spec. Publ. Fish. Aquat. Sci . 106.
Les inondations occasionnées par la crue des eaux dans les systèmes cours d'eau-plaines inondables constituent le principal facteur qui détermine la nature et la productivité du biote dominant de même que les interactions existant entre les organismes biotiques et entre ceux-ci et leur environnement. Ces crues passagères, dont la durée et la prévisibilité sont variables, sont produites par un ensemble de facteurs géomorphologiques et hydrologiques. Les crues de courte durée, généralement imprévisibles, surviennent dans les réseaux hydrographiques peu ramifiées ou dans les réseaux qui ont connu des transformations
importantes suite à l'endiguement et au drainage des plaines inondables par l'homme. Comme les crues survenant dans les réseaux hydrographiques d'ordre inférieur sont brèves et imprévisibles, les adaptations des organismes vivants sont limitées en ce qui a trait à l'exploitation des ressources de la zone de transition existant entre le milieu aquatique et le milieu terrestre (ATTZ), bien que les organismes aquatiques profitent indirectement des éléments transportés dans le milieu lotique. Inversement, une crue prévisible de longue durée favorise le développement d'adaptations et de stratégies qui permettent aux organismes d'exploiter efficacement 1 'ATTZ. Une telle crue s'accompagne d'un effet de bordure dynamique qui fait en sorte que l'ATTZ devient un « littoral mobile'<. Dans ces circonstances, il n'y a pas de stagnation prolongée et le recyclage de la matière organique et des substances nutritives se fait rapidement, ce qui donne lieu à une productivité élevée. La production primaire dans l'ATTZ est beaucoup plus élevée que celle des masses d'eau permanentes dans les réseaux hydrographiques non modifiés. Le rendement et la production de poissons sont étroitement reliés à l'étendue de la plaine inondable, tandis que le cours normal de la rivière est utilisé comme voie de migration par la plupart des poissons.
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Chinook salmon are considered, nonnally, to spend from a few months to a year rearing in freshwater before migrating to sea. Although large downstream movement offry, recently emerged from spawn ing gravels, has been observed in several river systems, it has been suggested that most of these migrant fry are lost to the population. This report describes the fate of downstream migrant chinook salmon fry in the Nanaimo River, British Columbia. In 1975 and 1976 most of the potential fry production from the river system was estimated to have passed by a trapping location near the river mouth. Many of these fry were subsequently found rearing in the intertidal area at the river mouth where salinity was commonly above 20%0. Very few chinook salmon fry were captured at other sampling sites within a 10 km radius ofthe river mouth. Juvenile chinook salmon were present in the intertidal area of the estuary from March to July each year, but peak numbers occ.urred in April and May. Peak estuary population was estimated to be 40,000-50,000 in 1975 and 20,000-25,000 in both 1976 and 1977. While in the estuary, chinook salmon grew about 1.32 mm per day or 5.8% oftheir body weight per day. Individual fish probably spent an average ofabout 25 days rearing in the estuary and left the estuary when about 70 mIDfork length. While in the estuary,juvenile chinook salmon fed on harpacticoid copepods, amphipods, insect larvae, decapod larvae, and mysids. After leaving the es tuary, they fed mainly on juvenile herring. The stomach content of chinook salmon captured in the estuary averaged 5% ofbody weight or less, and varied seasonally and between years. It appears that in the Nanaimo and probably in other systems with well-developed estuaries, that the estuary is an important nursery for chinook salmon fry.
A tenet of the flood pulse concept, the highway analogy, states that the main channel of large floodplain rivers is used by fishes mainly as a route for gaining access to floodplain habitats. We examined this proposition by analyzing habitat use for freshwater fishes in 4 large rivers in the United States (Colorado, Columbia, Mississippi, Missouri) and 4 in Europe (Danube, Rhine, Rhon e, Volga). Fish species from floodplain segments of each river were classified as fluvial specialist, fluvial dependent, and macrohabitat generalist based on literature and expert opinion. We also summarized the proportion of imperiled and introduced fishes present in each of these categories. The high proportion (mean 6 1S D5 29 6 17.5%) of fluvial specialist fishes inhabiting north- temperate large rivers was inconsistent with the highway analogy. Most members of the families Petromyzontidae, Acipenseridae, Hiodontidae, Osmeridae, Salmonidae, and Gobiidae require flowing water during some life stage. Between 29 and 100% of the native fish assemblage was of conservation concern, and from 50 to 85% of these fishes required riverine habitats to complete their life cycles. Macrohabitat generalists are adapted to capitalize on floodplain habitats and composed from 44 to 96% of introduced fishes in the rivers studied. Habitat diversity inherent in main-channel complexes of unaltered large rivers and reestablished in regulated large rivers is essential to meet life-history needs of native fluvial fishes while discour- aging expansion of introduced species. Restoration of north-temperate large rivers and their native fish fauna should incorporate the dynamic interplay among main channel, floodplain, and tributary habitats and processes.
Riparian and floodplain ecosystems are shaped and sustained by the river's hydrologic processes, such as flooding. The Cosumnes River Preserve is a multi-partner effort to protect and restore natural habitats within the floodplain of the Cosumnes River. This landscape-scale project protects over 40,000 acres of riparian forest, wetlands, and vernal pool grasslands. Early restoration efforts relied on active measures, such as hand planting of oaks and willows. This method, however, was expensive and labor intensive, and sometimes plantings failed. In the last several years we have focused on restoring natural processes that sustain and create habitat, such as flooding. Natural process restoration is now an integral part of the restoration program and central to our planning for property acquisition. Intentional levee breaches have restored the hydrologic connection between the lower Cosumnes River and its floodplain. Floods passing through levee breaches created in 1995 and 1997 have deposited sediment, seeds and plant cuttings on former farm fields, and stimulated natural recruitment of cottonwood and willow riparian forests. This method also provided valuable habitat for chinook salmon and Sacramento splittail. Creating seasonally flooded habitat rather than permanent ponds benefits native fishes more than non-native fishes. Monitoring by the Cosumnes Research Group and others is providing feedback for adaptive management.
Declining fall flows are limiting the ability of the Cosumnes River to support large fall runs of Chinook salmon. Management scenarios linking surface water and groundwater alternatives to provide sufficient fall flows are examined using groundwater flow and channel routing models. Results show that groundwater overdraft in the basin has converted the river to a predominantly losing stream, practically eliminating base flows. Management alternatives to increase net recharge ~for example, pumping reductions! were examined along with surface water augmentation options. Using a minimum depth standard for fish passage, average surface water flow deficits were computed for the migration period of Chinook salmon. Groundwater deficits were evaluated by comparing simulated current groundwater conditions with conditions under various scenarios. Increases in net recharge on the order of 200 to 300 million m 3/year would be required to reconnect the regional aquifer with the channel and in turn reestablish perennial base flows. Options that combine surface water augmentation with groundwater management are most likely to ensure sufficient river flows in the short term and to support long-term restoration of regional groundwater levels. DOI: 10.1061/~ASCE!0733-9496~2004!130:4~301! CE Database subject headings: Surface waters; Ground water; Restoration; California; Rivers; Base flow.
Ten percent of the juvenile coho salmon Oncorhynchus kisutch rearing in the main channel of Carnation Creek during the summer moved into intermittent tributaries and ephemeral swamps (off channel winter habitats) during the autumn of 1983. The number of juveniles residing within specific off channel sites during winter was governed by the magnitude of water levels associated with the first fall storms relative to the flooding levels required for adequate access to these sites (P < 0.05). Off channel habitats contributed 15.3% of the watershed's coho salmon smolts in 1983 and 23.1% in 1984. A 25-year flood event (65 m/s) occurred in January 1984 and may have reduced the main-channel contribution for that year. The inability of coho salmon smolts to emigrate from off channel habitats and return to the main channel in spring may have reduced the off-channel contribution in 1983. April–May water levels were 37% below the 13-year mean water level in 1983 and 55% above it in 1984.
In this study, we provide evidence that the Yolo Bypass, the primary floodplain of the lower Sacramento River (California, U.S.A.), provides better rearing and migration habitat for juvenile chinook salmon (Oncorhynchus tshawytscha) than adjacent river channels. During 1998 and 1999, salmon increased in size substantially faster in the seasonally inundated agricultural floodplain than in the river, suggesting better growth rates. Similarly, coded-wire-tagged juveniles released in the floodplain were significantly larger at recapture and had higher apparent growth rates than those concurrently released in the river. Improved growth rates in the floodplain were in part a result of significantly higher prey consumption, reflecting greater availability of drift invertebrates. Bioenergetic modeling suggested that feeding success was greater in the floodplain than in the river, despite increased metabolic costs of rearing in the significantly warmer floodplain. Survival indices for coded-wire-tagged groups were somewhat higher for those released in the floodplain than for those released in the river, but the differences were not statistically significant. Growth, survival, feeding success, and prey availability were higher in 1998 than in 1999, a year in which flow was more moderate, indicating that hydrology affects the quality of floodplain rearing habitat. These findings support the predictions of the flood pulse concept and provide new insight into the importance of the floodplain for salmon.
We describe six habitat types for large rivers (>100 m bank-full width), including pools, riffles, and glides in midchannel and bank edges, bar edges, and backwaters along channel margins. Midchannel units were deeper and faster than edge units on average. Among edge habitat types, backwater units had the lowest velocities and contained complex cover consisting mainly of wood accumulations and aquatic plants. Banks and bars had similar velocity distributions, but banks had more complex cover such as rootwads and debris jams. Because sampling of juvenile salmonids was ineffective in the midchannel units (electrofishing capture efficiency was low, and the units were too deep and fast to snorkel), we focused our sampling efforts on juvenile salmonid use of edge habitats during winter, spring, and late summer. Densities of juvenile Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch were highest in bank and backwater units in winter, whereas age-0 and age-1 or older steelhead densities were highest in bank units in winter. In summer, only coho salmon densities were significantly different among edge unit types, densities being highest in banks and backwaters. Microhabitat selection (velocity, depth, and cover type) by juvenile salmonids mirrored that in small streams, most fish occupying areas with a velocity less than 15 cm/s and wood cover. Among ocean-type salmon, Chinook and chum salmon fry were captured in large numbers in all edge units and exhibited only slightly higher densities in low-velocity areas (