TRACE AND MINOR ELEMENTS IN COASTAL SEDIMENTS AND NATURAL WATERS OF TAMPA BAY (FLORIDA, USA)

Tampa Bay is Florida’s largest open water estuary, receiving inputs from four small rivers, and having a large tidal connection to the Gulf of Mexico. Coastal development and urbanization have dramatically altered the natural landscape of many sub-tropical rivers and estuaries within Florida, including those in Tampa Bay. Such land-use modifications have also altered numerous biogeochemical processes, and a history of urbanization can be recorded in the elemental concentrations of coastal sediments. Concentrations of 15 trace elements were measured via inductively coupled plasma mass spectrometry in the waters of the tidal portion of the Little Manatee River (LMR) in eastern Tampa Bay. The same suite of trace and minor elements were also measured in salt marsh sediments cored adjacent to the main channel of the LMR. Trace and minor elements dissolved in the water column were grouped into three distinct mixing patterns: conservative, quasi-conservative, and non-conservative. However, many anthropogenically derived elements, including Cr, Pb, Ni, and V exhibited strong non-conservative mixing, with higher concentrations typically found in the zero-salinity (riverine) end-member. Concentrations of the same four elements were three orders of magnitude larger in the sediments, with a major increase in the concentrations of all elements above 9 cm depth. Based on age models derived from both ²¹⁰Pb and ¹⁴C, the 9 cm core depth is equivalent to the onset of urbanization in the LMR (1950 – 1955). The role of past, present, and future land cover and other anthropogenic environmental change in the coastal catchments of Tampa Bay exerts control on the quantity and flux of trace elements found in these systems. Despite low ambient concentrations of anthropogenically derived elements in the water column, the sedimentary chemistry of coastal marsh peats reveals a history of urbanization in Tampa Bay.