Aquatic invertebrates burrow into sediments and alter nutrient cycling by introducing oxygenated surface water into generally anoxic sediment. Oxygen introduction changes sediment redox conditions, which alters the biogeochemical processes occurring (i.e. facilitates phosphorus sorption and nitrification). Alternately, during bottom-water hypoxia, bioturbators deliver overlying water with very low dissolved oxygen into their burrows, likely changing how bioturbation influences nutrient fluxes. Many water bodies experience a variety of water oxygen conditions over time, including extended periods of oxia and/or hypoxia, and shorter fluctuations during storm events. To assess how the fluxes of nitrate (NO3-) , ammonium (NH4+), and soluble reactive phosphorus (SRP) change from bioturbation under different bottom water oxygen concentrations, we experimentally tested how two densities of chironomid larvae altered nutrient concentrations over two weeks using an intact flow-through core experiment under three different oxygen treatments (oxic, hypoxic, and variable oxygen (i.e., “storm-induced”) overlying water conditions) with sediments from Lake Erie’s Sandusky Bay. Surface water nutrients, porewater nutrients, and sediment oxygen penetration were measured in all cores.
Results/Conclusions
Preliminary results suggest that in all oxygen conditions, NO3- and NH4+ are released to the overlying water due to increase porewater-overlying water connectivity. Meanwhile, SRP is released to the overlying water in hypoxic treatments, removed from overlying water in oxic treatments, and “storm-induced” treatments show pulses of release and removal corresponding to the hypoxic and oxic periods. This suggests that bioturbator-driven nutrient fluxes can change direction and magnitude under different bottom-water oxygen conditions. Bioturbation-driven nutrient cycling is therefore an important factor regulating internal nutrient loading, especially in terms of reducing phosphorus in eutrophic shallow systems.