Burrowing macroinvertebrates alter phosphorus dynamics in drainage ditch sediments

摘要

Consumptive and nonconsumptive interactions of benthic organisms play important roles in regulating rates of ecosystem services such as nutrient cycling in freshwater ecosystems. Studies of macroinvertebrate communities in drainage ditches have focused on documenting the biodiversity supported by these human-altered environments, but none have explored the ecosystem functions provided by those biological communities in ditches. Bioturbation by burrowing benthic invertebrates in ditch sediments may change rates of biogeochemical processes controlling fluxes of nutrients across the sediment-water interface. We used microcosms to test the effect of four species of burrowing invertebrates (Naididae: Ilyodrilus templetoni, Naididae: Limnodrilus hoffmeisteri, Gammaridae: Crangonyx sp., Chironomidae: Chironomus decorus S.G.) on exchanges of phosphorus between sediment and water from a drainage ditch. These effects were measured across a range of sediment and water characteristics, representing variability within ditches. All species reduced concentrations of P (as molybdenum-reactive phosphorus) in the surface water relative to controls under conditions were sediment porewater was not likely to contain higher concentrations of P than surface water. Decreases in P concentration were linked to changes in the sediment redox potential and water pH. Two species (L. hoffmeisteri and C. decorus) increased P concentrations under conditions where sediment porewater likely had higher concentrations of P than surface water. Increases in P concentrations were likely due to physical changes to the sediment from burrowing, and increased transport of dissolved P from sediment porewater to surface waters. Management of ditches should consider effects of burrowing benthic invertebrates on physical and biogeochemical processes at the sediment-water interface. Habitat manipulation in ditches could lead to unpredicted changes in nutrient dynamics mediated by changes to the burrowing benthic invertebrate community.