Bioturbation-induced phosphorous release from an insoluble phosphate source

The underestimated importance of fertilizer in aquacultural phosphorus budget: Case of Chinese mitten crab

China's reliance on aquaculture has intensified to satisfy the growing human demand for high-quality animal protein, making it the only country whose aquaculture production has greatly exceeded that of capture fishery for a long time. Previous studies have shown that phosphorus (P) is a limiting nutrient for freshwater eutrophication; therefore, the quantification of P flows in freshwater aquaculture is of great importance for improving aquaculture efficiency and reducing environmental pollution. In this study, life cycle assessment (LCA) and substance flow analysis (SFA) are combined to develop a life cycle P flow model for Chinese mitten crab (Eriocheir sinensis) culture and calculate the P inputs, outputs and net change in stock. The results show a relatively low P use efficiency (4 %) in Chinese mitten crab. Among all life-cycle stages, the maximum P input occurs during adult crab cultivation, when feed is continuously added to maintain appropriate nutrition levels and increase body weight. In addition, fertilizer is often neglected in the existing accounts but accounts for 24 % of the total P inputs. On the output side, approximately 86 % of the P accumulates in sediment, indicating the potential of sediment recycling as a nutrient source in agriculture. This study provides an updated quantitative method for describing nutrient flows within freshwater aquaculture systems and will contribute to decision-making in pollution control of intensive freshwater aquaculture activities.

Macroinvertebrates as engineers for bioturbation in freshwater ecosystem

Bioturbation is recognized as a deterministic process that sustains the physicochemical properties of the freshwater ecosystem. Irrigation, ventilation, and particle reworking activities made by biotic components on sediment beds influence the flow of nutrients and transport of particles in the sediment-water interface. Thus, the biogenic disturbances in sediment are acknowledged as pivotal mechanism nutrient cycling in the aquatic system. The macroinvertebrates of diverse taxonomic identity qualify as potent bioturbators due to their abundance and activities in the freshwater. Of particular relevance are the bioturbation activities by the sediment-dwelling biota, which introduce changes in both sediment and water profile. Multiple outcomes of the macroinvertebrate-mediated bioturbation are recognized in the form of modified sediment architecture, changed redox potential in the sediment-water interface, and elicited nutrient fluxes. The physical movement and physiological activities of benthic macroinvertebrates influence organic deposition in sediment and remobilize sediment-bound pollutants and heavy metals, as well as community composition of microbes. As ecosystem engineers, the benthic macroinvertebrates execute multiple functional roles through bioturbation that facilitate maintaining the freshwater as self-sustaining and self-stabilizing system. The likely consequences of bioturbation on the freshwater ecosystems facilitated by various macroinvertebrates - the ecosystem engineers. Among the macroinvertebrates, varied species of molluscs, insects, and annelids are the key facilitators for the movement of the nutrients and shaping of the sediment of the freshwater ecosystem.

Mussels can both outweigh and interact with the effects of terrestrial to freshwater resource subsidies on littoral benthic communities

Litterfall is an important resource subsidy for lake ecosystems that primarily accumulates in littoral zones. Bivalves are abundant within littoral zones and may modify the effects of terrestrial resource subsidies through trophic interactions and engineering their surrounding habitat. Leaf inputs to lakes and freshwater mussel abundances are changing throughout the boreal ecoregion so we set out to investigate how the co-occurring benthic community might respond. We set up an in situ mesocosm experiment in Ramsey Lake, Sudbury, ON, Canada. Mesocosms contained sediments of either 5% or 35% terrestrial organic matter (tOM), into which we placed mussels (Elliptio complanata) at differing densities (0, 0.4 and 2musselsm^-2, with a sham mussel treatment at 0.4musselsm^-2). Over one month we recorded the sediment chemistry (dissolved organic carbon, nitrogen and phosphorus), littoral organisms (benthic algae and zooplankton) and mussel growth. At high mussel densities we recorded a 90%, 80%, 45% and 40% reduction in phosphorus, dissolved organic carbon, nitrogen and benthic diatoms, respectively, whereas at low mussel densities we observed a 3-fold increase in zooplankton. We discuss that these results were caused by a combination of bioturbation and trophic interactions. Benthic diatom concentrations were also reduced by 20% in sediments of 35% tOM, likely due to shading and competition with bacteria. Mussel growth increased at high mussel densities but was offset at high tOM, likely due to the organic matter interfering with filter feeding. Our results suggest that mussels can alter the geochemical composition of sediments and abundances of associated littoral organisms, in some cases regardless of tOM quantity. Therefore, the dominant top-down control exerted by freshwater mussels may outweigh bottom-up effects of tOM additions. Generally, our study reveals the importance of considering dominant species when studying the effects of cross-ecosystem resource fluxes.

Effects of benthic macrofauna bioturbation on the bacterial community composition in lake sediments

Benthic macrofauna are considered to be an important part of the lacustrine ecosystem, and bioturbation may greatly affect the biogeochemical processes and microbial activities in sediments. In the present study, the bacterial community composition in sediments inhabited by 3 different types of benthic macrofauna (Corbicula fluminea, Chironomidae larvae, and tubificid worms) in the shallow and eutrophic Lake Taihu was studied to investigate the different effects of bioturbation on the composition of these communities. Microcosms were constructed, and culture-independent methods, including terminal restriction fragment length polymorphism (T-RFLP) and clone library analysis, were performed to evaluate the bacterial communities. Analysis of similarities (ANOSIM) and multidimensional scaling (MDS) analysis of T-RFLP patterns demonstrated that differences in the bacterial community composition between the control and the macrofauna-inhabited sediments were not as great as expected, although the chemical properties of the sediments changed remarkably. Nevertheless, the dominant bacterial group in each type of macrofauna-inhabited sediment was different. Acidobacteria, Betaproteobacteria, and Deltaproteobacteria were the dominant bacterial groups in sediments inhabited by C. fluminea, tubificid worms, and Chironomidae larvae, respectively. The data obtained in this study are helpful for understanding the effects of bioturbation in a shallow, eutrophic lake.

A coupled biogeochemical-Dynamic Energy Budget model as a tool for managing fish production ponds

The sustainability of semi-intensive aquaculture relies on management practices that simultaneously improve production efficiency and minimize the environmental impacts of this activity. The purpose of the present work was to develop a mathematical model that reproduced the dynamics of a semi-intensive fish earth pond, to simulate different management scenarios for optimizing fish production. The modeling approach consisted of coupling a biogeochemical model that simulated the dynamics of the elements that are more likely to affect fish production and cause undesirable environmental impacts (nitrogen, phosphorus and oxygen) to a fish growth model based on the Dynamic Energy Budget approach. The biogeochemical sub-model successfully simulated most water column and sediment variables. A good model fit was also found between predicted and observed white seabream (Diplodus sargus) growth data over a production cycle. In order to optimize fish production, different management scenarios were analysed with the model (e.g. increase stocking densities, decrease/increase water exchange rates, decrease/increase feeding rates, decrease phosphorus content in fish feeds, increase food assimilation efficiency and decrease pellets sinking velocity) to test their effects on the pond environment as well as on fish yields and effluent nutrient discharges. Scenarios were quantitatively evaluated and compared using the Analytical Hierarchical Process (AHP) methodology. The best management options that allow the maximization of fish production while maintaining a good pond environment and minimum impacts on the adjacent coastal system were to double standard stocking densities and to improve food assimilation efficiency.