Invertebrate Activities in Wetland Sediments Influence Oxygen and Nutrient Dynamics at the Sediment-water Interface

Abstract

Invertebrate activities at the sediment-water interface can facilitate nutrient retention, release, and transformation by changing the nature of oxygen penetration into anoxic sediments, influencing geochemical and microbial-mediated processes. By reworking sediment and conveying oxygenated surface water into deeper anoxic sediment through burrowing activities, bioturbating invertebrates influence nutrient cycling in wetlands sediments. To test the effects of bioturbators on oxygen introduction and nutrient fluxes, we investigated the impacts of two functionally different bioturbators at a range of four densities using a microcosm study. We measured sediment oxygen penetration depth at small-scale resolution using microelectrode sensors and analyzed surface water nutrients weekly over four weeks. Results indicate increased oxygen penetration in regions of normally anoxic sediment with the presence of each of the two bioturbation modes. In general, we observed negative phosphorus fluxes (i.e., into the sediment) with increasing bioturbator densities, indicating retention in the sediment due to bioturbation activities. These activities caused enough retention of phosphorus to counteract the phosphorus released by bioturbator excretion alone. There was a flux of nitrate into the surface water, likely driven by invertebrate excretion of ammonia followed by an oxidative process such as nitrification. This investigation contributes to the growing understanding of how organisms influence nutrient cycling in wetlands, which are hotspots for biogeochemical processing.