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A modeling study of discontinuous biological irrigation
Abstract
Irrigation of infaunal dwellings can lead to significant alteration of solute distributions in sediments. As a result, sediment-seawater fluxes of nutrients and dissolved carbon are greatly enhanced, and the biology of benthic communities is affected. The most realistic mathematical representation of irrigation and its effect on sediment geochemistry is Aller's (1980) cylinder model. One critical assumption of this model is that burrows are irrigated continually, and that burrow water solute concentrations are identical to overlying water concentrations at all times. However, the vast majority of infaunal tube- and burrow-dwelling organisms irrigate periodically, i.e. in an on/off cycle. During periodic irrigation, the solute concentration at the tube wall may vary between the limits imposed by the flux from the porewater and the concentration in the overlying water. We introduce modifications to the cylinder model which allow for periodic irrigation. We assess how periodic irrigation affects solute profiles and fluxes of two chemical constituents, silica and ammonium, for different population densities (distance between burrows) and organism sizes (burrow radii). Silica and ammonium follow first and zeroth order reaction kinetics, respectively, and illustrate the behavior of two general reaction classes. Model results show that the effects of periodic irrigation vary with the class of reaction considered. For silica, radially-averaged profiles during discontinuous irrigation varied less than 15% from those with continuous irrigation for nearly all burrow sizes, burrow distances and reaction rate constants considered. However, we observed large temporal changes (as much as a factor of 6) in the areally-averaged silica flux over the irrigation cycle. Despite this time-dependence, the time-averaged silica flux was similar to that calculated for the continuous case. For ammonia, radially-averaged solute profiles were extremely sensitive to the duration of irrigation. In this case, the differences between discontinuous and continuous irrigation were greatest when the duration of irrigation was short (e.g. 5 min), and when the inter-burrow distance was small. As with silica, there was a strong time-dependence in areally-averaged ammonia flux when irrigation was periodic. However, the time-averaged ammonia flux is identical to the flux calculated for continuous irrigation. Our results suggest that irrigation behavior can affect the local burrow environment and this imposes a time dependence on solute fluxes.
... as Pygospio enhance the irrigation of sediments (Kristensen, 1981;Boudreau & Marinelli, 1994;Marinelli, 1994;Mayer et. al., 1995). ...
... as Pygospio enhance the irrigation of sediments (Kristensen, 1981;Boudreau & Marinelli, 1994;Marinelli, 1994;Mayer et. al., 1995). ...
... gnify the sediment-water interface area by a factor of around x16, leading to proportionally greater overall diffusion rates.Sedentary, tube-dwelling macroinfauna typically irrigate their tubes. Ciliary action, coupled with muscular undulations of the body, produce CUlTents which import nutrient material and oxygen while removing waste metabolites.Marinelli (1994) demonstrated the threefold reduction of sediment ammonium concentration by burrow ventilation in the terebellid polychaete Eupolymnia heterobranchia; ventilation rate was increased in the presence of increased ammonium(Woodin & Marinelli, 1991), suggesting a toxin removal response by the worm. BUlTOW ventilation is a noncontinuous proce ...
p>The spionid polychaete Pygospio elegans Claparède 1863 is a small tube-building opportunist, commonly found in the benthic communities of organically enriched boreal estuaries. The species may reproduce both sexually and asexually; larvae may develop either planktonically or benthonically. Population densities of up to 100,000m<sup>-2</sup> have been recorded.
In the macrotidal Somme Bay, N. France, the Pygospio population regularly exceeds densities of 100,000m<sup>-2</sup>; an abundance of nearly 600,000m<sup>-2</sup> was noted in December 1993. Raised sedimentary structures are formed in the presence of dense arrays of Pygospio- built tubes: so-called "tube-beds". A multidisciplinary study was made of these structures and the Pygospio population that formed them.
An extended period of sexual activity was discovered in the Somme Bay Pygospio population; there was no asexual activity. All larvae developed planktonically, hatching at an early stage in development. This life-history provides a massive larval availability for tube-bed foundation and an optimal spatio-temporal vantage for the re-colonisation of defaunated areas in the strongly hydrodynamic Somme Bay. Laboratory experiments suggested that this reproductive mode in the Somme Bay population was fixed. A similarly non-poecilogonous response was observed in individuals taken from Ryde Sand (Isle of Wight), which exhibited extended larval brooding. Although no morphological variation was noted among Pygospio specimens from populations from Europe and the USA, this apparent reproductive inflexibility within Pygospio elegans populations suggested the possibility of cryptic, sibling speciation.
Sampling revealed that the approximate threshold tube-bed forming Pygospio density in the Somme Bay was 50,000 m<sup>-2</sup>. Pygospio had a significant effect on sediment physico-chemical characteristics and dense aggregations of the spionid stimulated the proliferation of the microbial and meiofaunal communities. Pygospio density affected the structure of the associated macrofaunal community: diversity peaked between Pygospio densities of 50,000m<sup>-2</sup> and 200,000m<sup>-2</sup> as tube-bed formation offered an attractive resource and refuge from erosion. Beyond Pygospio densities of 200,000m<sup>-2</sup>, the community became more dominated by species able to tolerate the spionid's spatial monopoly.</p
... Furthermore, if the burrow reached the zone where methane was available, the steep chemical gradient could have fostered methane diffusion from the sediment towards or into the burrow (cf. Boudreau and Marinelli 1994). In addition, the gradient in pressure from lithostatic in the sediment to hydrostatic in the tube could induce advection and have facilitated the formation of bubbles. ...
... Consequently, when the U-turn was slowly displaced downward and contained closely spaced mucous films, the spreite became enhanced during diagenesis; otherwise, it is hardly visible because the mucous lining was too thin to have diagenetic potential. The producer appears to have constructed the protrusive spreite in a stepwise manner because the redox gradient decreased with time as oxidizing seawater compounds diffused from the burrow into the surrounding sediment (e.g., Boudreau and Marinelli 1994;Shull et al. 2009;Meysman et al. 2010). The conditions for microbial activity deteriorated, and so the producer deepened its burrow to maintain a length sufficient to create an efficient ''microbial reactor''. ...
The type material of Tisoa siphonalisde Serres, 1840 is lost but nearly complete specimens occur at the herein designated type locality Hameau de Valz (Department of Gard, France), where Tisoa is present in dark Pliensbachian organic-rich mudrock. The upper part of the trace is encased in a concretion. The concretion's carbonate content implies 65% initial porosity, a value typical of soft mud. Such a consistency is also indicated by shallowly produced biodeformational structures that dominate the fabric; in association with small traces they are diagnostic of low-oxygenated bottom water and anoxic conditions just below the seafloor. At its type locality, Tisoa represents a nearly vertical protrusive spreite burrow, exceeding 2 m in length and having nearly parallel limbs 0.1–1.5 cm apart. The spreite is only weakly expressed; the inter-limb material was apparently not processed during deepening of the U-tube but placed directly in the spreite or pressed aside. Tisoa deviates slightly but consistently from a vertical orientation and commonly shows a low-amplitude helicoidal course. The U-tube exhibits a thick pyrite lining implying the former presence of mucus. The steep chemical gradient between oxygenated water in the U-tube and anoxic host sediment evidently fostered microbial activity. The extraordinary penetration depth of Tisoa suggests exploitation of extreme redox conditions such as could be found in the methanogenesis zone. The Tisoa producer probably deepened the U-tube incrementally, continuing when the chemical gradient between tube and host sediment declined due to circulation of the oxygenated water used for respiration. The Tisoa producers might have fed on suspended material, microbes flourishing along the tube wall, or acquired nutrition via chemosymbionts.
... Infauna ventilate their burrow structures to sustain their respiration and feeding (Boudreau & Marinelli 1994. This activity alters the physical and chemical properties of surface sediments and transforms the 1-dimensional, vertically layered distribution of biogeochemical processes into a 3-dimensional system , Aller 2014). ...
Coastal zones play an important role in the exchange of carbon and nutrients between the land and the open ocean, and typically comprise a mosaic of benthic habitats harbouring diverse faunal and plant communities. Seagrasses are the only vascular plants adapted to live in fully marine environments, and their presence in coastal habitats is associated with key ecosystem services. Most notably, seagrasses establish productive meadows in oligotrophic environments, thereby providing habitats for metabolically active and diverse benthic communities. Remarkable aspects of seagrass ecosystems include their impressive organic carbon binding capacity (blue carbon) and nutrient recycling efficiency. However, a recent surge in seagrass research and advances in the conceptual knowledge of coastal biogeochemistry have revealed a greater complexity of seagrass ecosystems than previously thought. In particular, there is growing consensus for better exploring the effects of site- and species-specific characteristics on seagrass biogeochemistry, rather than making generalized claims regarding their potential role as a sink or source for carbon and nutrients.
The aim of this thesis is to fill some of the crucial knowledge gaps on carbon and nitrogen cycling in seagrass ecosystems. The first component of this research investigated the effects of wave-induced sediment resuspension on benthic metabolism and carbon turnover of a temperate seagrass meadow (Finland). Resuspension largely stimulated reoxidation processes thus directly (instantaneous), and indirectly (following days), influencing benthic metabolism. These findings highlight the importance of accounting for the natural occurrence of resuspension events when assessing the carbon turnover in seagrass ecosystems. The second study investigated the influence of potent greenhouse gas (CH4 and N2O) evasion on seagrass blue carbon potential. Evasion of CH4 and N2O substantially offset seagrass blue carbon potential at the subtropical study site (Wallis Lake, Australia), thereby highlighting the importance of accounting for CH4 and N2O cycling in future seagrass blue carbon assessments. The third study targeted site- and species-specific effects on benthic nitrification and denitrification in the seagrass rhizosphere. The results indicated that coupled nitrification-denitrification, a key process in the removal of fixed nitrogen from the oceans, can be largely stimulated by seagrass species with high biomass, provided nitrogen is not rapidly immobilized. This research prompts to assess local hydrodynamic and benthic community characteristics to critically resolve carbon and nutrient cycling in seagrass ecosystems.
... Bioirrigation might also be misrepresented. Indeed, the term used in Eq. (2) to calculate this contribution, i.e., ϕα irrigation ([solute] tube − [solute]), is indeed an approximation of intricate 3-D processes variable in space and time (Meile et al., 2005;Boudreau and Marinelli, 1994;Forster and Graf, 1995;Gallon et al., 2008;Riisgård and Larsen, 2005). On the other hand, DIC production through HMW OM fermentation (Reaction R2; Corbett et al., 2013) was constrained by default in Lake Tantaré Basin A (Table 4). ...
The complexity of organic matter (OM) degradation mechanisms represents a significant challenge for developing biogeochemical models to quantify the role of aquatic sediments in the climate system. The common representation of OM by carbohydrates formulated as CH2O in models comes with the assumption that its degradation by fermentation produces equimolar amounts of methane (CH4) and dissolved inorganic carbon (DIC). To test the validity of this assumption, we modelled using reaction-transport equation vertical profiles of the concentration and isotopic composition (δ13C) of CH4 and DIC in the top 25 cm of the sediment column from two lake basins, one whose hypolimnion is perennially oxygenated and one with seasonal anoxia. Furthermore, we modelled solute porewater profiles reported in the literature for four other seasonally anoxic lake basins. A total of 17 independent porewater datasets are analyzed. CH4 and DIC production rates associated with methanogenesis at the five seasonally anoxic sites collectively show that the fermenting OM has a mean (± SD) carbon oxidation state (COS) value of -1.4±0.3. This value is much lower than the value of zero expected from carbohydrate fermentation. We conclude that carbohydrates do not adequately represent the fermenting OM in hypolimnetic sediments and propose to include the COS in the formulation of OM fermentation in models applied to lake sediments to better quantify sediment CH4 outflux. This study highlights the potential of mass balancing the products of OM mineralization to characterize labile substrates undergoing fermentation in sediments.
... The boundary conditions are time-dependent, as the animals ventilate their burrows periodically, not constantly. This approach has been shown to reproduce porewater profiles in the bioirrigated zone well (Aller, 1982;Boudreau and Marinelli, 1994;Boudreau, 2000;Gilbert et al., 2003). Shull et al. (2009) extended the model to include burrow ventilation by benthic fauna through injection of bottom waters, suggesting that burrow ventilation strongly influences the vertical profiles of porewater and fluxes. ...
Coastal seas are highly productive systems, providing an array of ecosystem services to humankind, such as processing of nutrient effluents from land and climate regulation. However, coastal ecosystems are threatened by human-induced pressures such as climate change and eutrophication. In the coastal zone, the fluxes and transformations of nutrients and carbon sustaining coastal ecosystem functions and services are strongly regulated by benthic biological and chemical processes. Thus, to understand and quantify how coastal ecosystems respond to environmental change, mechanistic modeling of benthic biogeochemical processes is required. Here, we discuss the present model capabilities to quantitatively describe how benthic fauna drives nutrient and carbon processing in the coastal zone. There are a multitude of modeling approaches of different complexity, but a thorough mechanistic description of benthic-pelagic processes is still hampered by a fundamental lack of scientific understanding of the diverse interactions between the physical, chemical and biological processes that drive biogeochemical fluxes in the coastal zone. Especially shallow systems with long water residence times are sensitive to the activities of benthic organisms. Hence, including and improving the description of benthic biomass and metabolism in sediment diagenetic as well as ecosystem models for such systems is essential to increase our understanding of their response to environmental changes and the role of coastal sediments in nutrient and carbon cycling. Major challenges and research priorities are (1) to couple the dynamics of zoobenthic biomass and metabolism to sediment reactive-transport in models, (2) to test and validate model formulations against real-world data to better incorporate the context-dependency of processes in heterogeneous coastal areas in models and (3) to capture the role of stochastic events.
... This, coupled with the biogenic habitat that sponges provide, explains the high benthic diversity associated with these grounds (Beazley et al., 2013(Beazley et al., , 2015. The sea pen habitats are important as structure formers (Baillon, Hamel, & Mercier, 2014;De Clippele, Buhl-Mortensen, & Buhl-Mortensen, 2015) and are also associated with bioturbation activity which can alter the physical and chemical properties of marine sediments (Boudreau & Marinelli, 1994), increasing sediment permeability, remineralization, or inorganic efflux, among others (Lohrer, Thrush, & Gibbs, 2004). Although their biomass is lower than the sponge grounds, they add important and different functions to areas with few other large taxa present. ...
Aim
To characterize the functional diversity and selected ecological functions of marine epibenthic invertebrate communities at the ecosystem scale and to evaluate the relative contributions of environmental filtering, including bottom‐contact fishing, and competitive interactions to benthic community assembly.
Location
Flemish Cap, an ecosystem production unit and fishing bank in the high seas of the north‐west Atlantic Ocean.
Methods
Through the use of Hierarchical Modelling of Species Communities (HMSC), we have explored seven community response traits to the environment applied to 105 epibenthic species and evaluated the influence of such traits on the community assembly processes. Assumed bioturbation, nutrient cycling and habitat provision functions, linked to individual or a combination of biological traits, were mapped using random forest modelling.
Results
Functional richness within benthic communities reached an asymptote for trawl sets with roughly more than 30 species. Assemblages on top of the Flemish Cap (<500 m depth) were characterized by higher biomass of small‐ and medium‐sized species with short life spans, whereas large species with longer life spans and broadcast spawners were dominant in the deeper assemblages (500–1,500 m depth). The amount of variation explained by the species’ responses to the covariates mediated by the traits was relatively high (25%) indicating their relevance to community assembly. Community‐weighted mean trait values changed with depth and physical oceanographic variables, indicating that environmental filtering was occurring. Interspecific interactions, as inferred from the random effect at the sample level, accounted for 16.3% of the variance in the model, while fishing effort explained only 5.2% of the variance but conferred strong negative impacts for most species.
Main conclusions
Our results suggest that while bottom‐contact fishing impacts have an effect on functional diversity, changes to the physical oceanography of the system are likely to have more profound impacts. The maps of benthic functioning can aid assessments of ecosystem impacts of fishing.
... Infauna ventilate their burrow structures to sustain their respiration and feeding (Boudreau & Marinelli 1994, Kristensen et al. 2012. This activity alters the physical and chemical properties of surface sediments and transforms the 1-dimensional, vertically layered distribution of biogeochemical processes into a 3-dimensional system (Kristensen 2000, Aller 2014). ...
It is well established that benthic infauna alter sediment biogeochemistry, but the importance of their behavioural patterns in biogeochemical processes has only recently been fully appreciated. Using arrays of O2 microoptodes, siphon imaging, accelerometer loggers and different incubation approaches, we investigated the importance of behavioural patterns of the soft-shell clam Mya arenaria for benthic O2 and nitrogen dynamics. The investigations resolved a new behavioural component of buried M. arenaria: pedal water ejection (PWE). During PWE, the clams contracted their valves while briefly closing the siphon to expel oxic water previously accumulated within the mantle cavity through the pedal gape. Consequently, an upward-moving oxic plume embedded
most of the shell, and oxia at the shell−sediment interface was observed for 15% of the total time of investigation. The buried clams displayed 2 additional behavioural stages: resting (R) and ventilation (V) that occurred for 57 and 28% of the time, respectively. During the V and PWE stages, the siphon of the clam was elongated above the sediment surface and surrounded by a dynamic oxic halo; both behavioural stages thus markedly increase the sediment oxygenation. The resolved irrigation patterns enhanced the benthic exchange of O2 and NH4+ as well as the benthic denitrification rate, presumably via increased benthic NO3− supply and production. Particularly, the extensive sediment irrigation induced by the PWE stage has important implications for benthic nutrient cycling as well as for sediment oxidation and biogeochemical function of coastal sediments.
... In these cases, the cores were bubbled with argon for 2 h and sealed tightly with the stirrer mounted through a rubber stopper. After the settling period, an excess 1 week when transient concentration gradients and fluxes associated with burrows are reduced (Boudreau and Marinelli, 1994). The presence of macrofauna in sieved (mm) sediment was noted but not measured quantitatively. ...
This study presents benthic data from 12 samplings from February to December 2010 in a 2 m deep channel in the southwest Baltic Sea. In winter, the distribution of solutes in the porewater was strongly modulated by bioirrigation which efficiently flushed the upper 1 cm of sediment, leading to concentrations which varied little from bottom water values. Solute pumping by bioirrigation fell sharply in summer as the bottom waters became severely hypoxic (
Abstract A simple,closure,scheme,for turbulent,transport,yields mean-velocity,and dissolved-substance,concen- trationjust above and solute fluxes across a sediment-water interface underlying uniform, steady flow. In the case of near-bed turbulence characterization, this approach retains both turbulent and viscous terms,in expressions,for important,structural aspects of the near-bed,regions of turbulent,boundary,layers. Moreover, a modified turbulent kinetic energy balance is used to define eddy viscosity in the viscous- dominated,region,of flow very,near,the bed. In the case of characterization,of mass,distribution,and diffusional transfer rate, the approach partitions important factors that control mass transfer rate: near- bed turbulent transport, interfacial-flux boundary condition, and reaction kinetics. Diffusive sublayers overlying smooth beds exposed to typical deep-sea conditions are predicted to be - 1 mm thick, a result in agreement,with,the,sublayer,thickness,observed,in situ and,the inferred,thickness,used,in many hydrodynamic,models. One application,of the new closure scheme,indicates that typical biogenic roughness in fine-sediment,marine,environments,enhances,solute exchange,rates threefold,over those,expected,for a smooth,bed. This increase,is due to enhanced,turbulent,transport,in the vicinity of the rough,bed,and occurs,in spite of viscous,ponding,of “dead water” among,roughness,elements. Diffusional transfer of dissolved,substances
In a recent letter to this journal, Smith and Mackenzie [1991]
emphasized the role of near-shore environments, such as bays and
estuaries, as being the principal locus for the enhanced burial of
organic matter due to anthropogenically derived nutrient inputs to the
oceans. I commend them for this because of the relative lack of
attention given to near-shore environments by much of the biogeochemical
and ocanographic community. It is along continental margins and not in
the pelagic ocean where most organic matter, as well as most sediment,
is buried. From an extensive review of the sediment literature I have
shown [Berner, 1982] that principal organic carbonburial on a global
basis occurs in deltas and other continental margin environments. (A
large proportion of the organic C may be of terrestrial origin.)
Although the average carbon content of the surficial portions of deltaic
and continental shelf muds is only about 0.75%C, the large mass of
sediment carrying this small carbon percentage adds up to a very large
burial rate. The riverine flux of suspended sediment to the oceans has
been estimated [e.g., Milliman and Meade, 1983; Milliman and Syvitski,
1992] to be between 12,000 and 25,000 Tg (102grams) per year,
and most of this sediment is deposited at present on or near the
continental shelves. At 0.75 % C this amounts to anannual carbon burial
rate of 90-190 Tg C. Burial rates in other environments such as offshore
upwelling zones of high productivity or the vast pelagic realms of the
oceans do not come close to matching these rates. If one is to look for
a locus for the burial of excess carbon from fossil fuel burning and
deforestation, the place to look is near the continents.