INVERTEBRATE ACTIVITIES IN WETLAND SEDIMENTS INFLUENCE OXYGEN AND NUTRIENT DYNAMICS AT THE SEDIMENT-WATER INTERFACE04/05/2018
Invertebrates living in aquatic sediments alter nutrient cycling by shaping oxygen penetration into sediments, influencing geochemical and microbial processes. Through the creation of burrows, bioturbating invertebrates rework sediment, which introduces oxygenated water to otherwise anoxic sediment. Invertebrate bioturbation can have critically important effects on sediment-surface water nutrient (i.e. nitrogen and phosphorus) exchange, but until recently these effects have been underappreciated. Nutrient release from benthic sediments into surface waters, or alternately nutrient immobilization, may influence rates of internal loading and eutrophication. To assess how bioturbators influence nutrient exchange from wetland sediments to surface waters, I experimentally tested the effects of two functionally different bioturbators (Ephemera mayfly larvae and Lumbriculus worms) in urban wetland and Lake Erie coastal wetland sediments. I analyzed surface water nutrients and measured sediment oxygen penetration using microelectrode sensors. Results show a stronger increase in sediment oxygen penetration into normally anoxic regions by Ephemera than Lumbriculus. With increasing densities of both bioturbators, I observed decreasing phosphorus and increasing nitrate surface water concentrations. Changes in surface water concentrations suggest that bioturbators simultaneously enhance sediment phosphorus sequestration while releasing nitrogen, consistent with expectations of oxidation processes.