EVALUATING THE IMPORTANCE OF SEDIMENT RESUSPENSION AS A SOURCE OF PARTICULATE METHYLMERCURY TO COASTAL ECOSYSTEMS

Coastal sediments are a major repository for mercury and are known to be an active zone for net mercury methylation, specifically at the sediment oxic-anoxic interface. This zone is generally within millimeters of the sediment surface in organic rich coastal systems and slightly deeper when sediments are organic poor. Near surface methylmercury (MeHg) production suggests that sediment resuspension could be a significant source of MeHg to the water column. This study investigated the effect fine scale resuspension has on MeHg inputs to coastal waters of the Delaware Bay using Gust Microcosm erosion core chambers. This method also allowed us to measure MeHg distribution within the top cm of the sediment, which is not possible with other sampling approaches. The erosion chambers induce step-wise increases in critical shear stress to the water column which erodes the sediment surface. The stress levels simulated tidal resuspension up to storm-like stress conditions. Cores were collected at four sites in the Delaware Bay; two sites were characterized as having organic poor sediments and two organic rich sediments. The two sediment types were chosen to better understand the role of organic carbon (OC) on MeHg cycling, and to examine the importance of erodibility on MeHg flux. Particles were collected from the erosion effluent and analyzed for MeHg, total Hg, chlorophyll a, and C, N, S composition. The data indicate that the high OC cores were more erodible with increasing shear stress than the low OC cores, and resulted in higher MeHg fluxes to the water column. Comparing MeHg concentrations to other variables (C, N, S, Chl a) in the eroded sediments with co-sampled suspended particulate matter at the core sites provides insights to the importance of sediments as a source of MeHg to forage fish relative to other potential inputs. The presentation will focus on factors that control the distribution of MeHg in the sediment surface layer, and the importance of sediment resuspension as a source of water column MeHg.