The delivery, speciation and fate of trace elements in St. Louis Bay, Mississippi

Estuaries are dynamic regions in which there can be significant modification of the riverine flux of trace elements to the open ocean due to various geochemical, physical, and biological processes. Additionally, estuaries are often subject to anthropogenic inputs of trace elements. The first portion of this study investigated the source, behavior, and sediment interaction of anthropogenic stable cesium (Cs) in St. Louis Bay (SLB), MS. A consistent increase in stable Cs concentration was noticed in sediment cores starting from a period when a titanium dioxide refinery on SLB started operations. Weak correlation between Cs and clay percentage and strong correlations among Cs, silt percentage, and particulate organic carbon (POC) indicate non-specific adsorption of stable Cs. Evidence of non-specific adsorption of Cs also came from remobilization of Cs during sediment resuspension. Cs-enriched SLB waters can be tracked into the Mississippi Sound but not the Mississippi Bight.;In the second portion of this study, the impact of hurricanes on the trace element deposition history in marsh sediments of SLB was examined. Salt marsh sediments are widely used to reconstruct the depositional history of anthropogenic contaminants derived from atmospheric and fluvial sources. However, hurricanes can significantly affect the coastal landscape by eroding and re-distributing sediments. This study has found that metal (e.g. Cs) enrichment factors (EF) in sediment cores were much higher for event layers and, thus, indicate modification to their smooth deposition history in SLB marsh sediments.;St. Louis Bay is shallow and prone to wind-driven resuspension. The impact of geochemical processes associated with sediment resuspension on speciation and transport of trace elements was investigated. Seasonal and time series samples covering sediment resuspension events and normal periods of minimal resuspension were analyzed for trace metals. Additions of particulate iron or dissolved vanadium per sediment resuspension event were greater or comparable to riverine fluxes. Sediment resuspension also impacted rare earth elements and showed a higher percentage of removal of both dissolved and colloidal REE during resuspension. This leads to a more negative cerium anomaly and a more positive lanthanum anomaly in REEs during resuspension events.