PATTERNS OF EARLY DIAGNESIS OF METALS IN LAKES

Sediment cores were obtained to better understand the spatial and historical loadings of trace inorganic (e.g., Hg, Pb) and organic (e.g., PCBs, PAHs) chemicals in a large region of the Great Lakes watershed. The project afforded the opportunity to collect vertical porewater chemical profiles in over 20 lakes. Lakes represent a range of landuse characteristics (e.g., urban, agricultural) and lake bottom conditions (e.g., oxic, cyclic oxic/anoxic). Samples were extracted from cores using a whole core squeezing system. They were imediately filtered, acidified and kept on ice until analysis (ICPMS). Thus, the concentrations are for total concentrations and not specific species (e.g., P not PO4). The overarching hypothesis is that if the porewater-sediment system is in steady state then 1) the vertical profiles of the dissolved redox sensitive species (e.g., Fe, U) should reflect patterns relative to those predicted from thermodynamic constrains and 2) non redox metals influenced by redox processes (e.g., Cu sorption on iron oxyhydroxides) should reflect patterns expected for sequestrate and release. Early diagenetic conditions in lakes can great differ causing different profiles for the same element among lakes. For example As profiles can be consistent with the steady state hypothesis or follow those of Fe or Mn. Profiles of certain elements (e.g., Fe, U, Cu) are often similar among lakes and consistent with the steady state process. Diagenetic release of P appears to influence the mobility of elements (e.g., U through sequestration). The relationship of porewater profiles to sediment profiles (e.g., formation of Fe enrichment layers) appears to be influenced by the stability of bottom oxidizing conditions. Although some similarities in the diagenetic patterns among lakes is evident, in general they are complex, and related to various environmental factors (e.g., bottom conditions, nutrient release). Diagentic release of metals (e.g., Pb, U) to the overlying water can be seen. Understanding the fate, magnitude, and relative imporance of environmental factors causing this release is needed