BIOLOGICAL VERSUS PHYSICAL CONTROLS ON SEABED ERODABILITLY IN A MUDDY, PARTIALLY MIXED ESTUARY IN THE CHESAPEAKE BAY

Sediment erodability has important implications for pollutant transport and burial, benthic communities, nutrient cycling, channel stability, and various other processes and systems within estuaries. We examined several characteristics of the York River seabed, which is a subestuary of the Chesapeake Bay, at a biologically dominated and a physically dominated site in order to better understand which factors most influence sediment erodability in a muddy estuarine environment. Physical factors affecting erodability include physical grain properties, water content, recent deposition or compaction of sediment, and recent erosion or disturbance by physical energy (waves, tides, currents). Stabilizing biological effects include extracellular polymeric substances (EPS) that are secreted by certain benthic invertebrates as well as microbial organisms. Destabilizing biological forces include bioturbation by macrobenthic organisms. Multiple box cores were taken in the York River estuary offshore Gloucester Point (a more biologically dominated site) and near Clay Bank (a more physically dominated site). We analyzed these cores for Eh, water content, total % organics, 7-Be, and grain size. Also, digital X-radiographs for each site allowed us to observe whether bioturbation or preserved physical layering of the sediment is more prominent. In addition, we measured EPS to quantify biostabilizing substances. Lastly, an erosion microcosm was used to directly measure the erosion rates at each site. In this presentation, the results of the erosion rate tests are compared with the observed sediment properties.