DETERMINING A PROXY FOR SEDIMENT OXYGEN DEMAND OF COASTAL ESTUARIES AND THE ROLE OF SEDIMENTARY IRON AND SULFUR

SOD (Sediment Oxygen Demand) plays an important role in O₂ availability in estuaries and is an indicator of bay health. Coastal managers must monitor SOD, because a high SOD demand indicates a high amount microbial activity, which can deplete oxygen levels in the water column, leading to eutrophication. During anoxic conditions, reduction of redox reactive species such as sulfate and iron (III) occurs through microbial respiration reactions, where the reduced by-products are eventually stored in sediment porewaters and solid phase components. Measurement of reduced species can provide valuable information about potential chemical oxygen demand that may contribute to the overall SOD. Obtaining SOD flux data requires expensive, time-consuming and labor-intensive field deployment, incubation, and monitoring efforts. As such, high spatial resolution is difficult to achieve in large bays. Quicker, easier-to-collect measures may yield suitable approximations for SOD. Geochemical proxies for SOD will be explored though correlating SOD values with concentrations of O₂, NO₃^-, PO₄^3-, Ortho-P, NH₄⁺, Mn²⁺, Fe²⁺, H₂S in dissolved sediment porewaters and solid phase total carbon, reactive iron, TRS (total reduced sulfides), and AVS (acid volatile sulfides) collected from Weeks Bay, AL and Tampa Bay, FL. Both bays are shallow Gulf Coast estuaries with varying levels of coastal urbanization, sediment types, nutrients and phytoplankton growth, and physical mixing – as such, they represent diverse case studies for this exploratory research. To better understand long-term accumulation of redox reactive species that may ultimately chemically enhance sediment oxygen uptake, we explore the sulfur and iron cycles within and between each case study through non-parametric statistical analyses. The results may potentially provide a viable alternative to the traditional, yet arduous SOD method, allowing researchers and managers greater opportunity to increase their capacity to measure SOD in estuarine systems. The results will also emphasize the geochemical role in two Gulf Coast estuaries in order to help coastal managers better estimate the sedimentary impacts on overall estuary health.