TRACE METAL TRANSPORT AND DEPOSITION IN THE GREAT BAY ESTUARY, NH: A JULY 2008 UPDATE

The Great Bay Estuary in southeastern New Hampshire receives the influx of seven rivers which drain almost 100 square miles of highly developed coastal land and mixes it twice daily with ocean water from the Gulf of Maine. Previous studies have documented human influence in the estuary through the introduction of agricultural runoff, automobile and pavement contaminants, industrial (including tannery) effluent, sewage, and runoff from an adjacent military installation. The distribution of rare earth elements (REEs) and transition metals in the water column and sediment can begin to answer questions regarding the role of anthropogenic activities in the source of these metals, as well as how they are stored and transported through the estuarine environment. Water column samples were collected in July 2008 just south of Adams Point at the surface and depths of 7 and 13 m. These samples, as well as recent rain water and water from the Lamprey River, were analyzed for REE and Pb concentration. A 1.3 m sediment core also collected in July 2008 near Adams Point was analyzed for concentrations of extractable transition metals (Cr, Ni, Zn, Fe, Pb, and Cu). As expected the surface estuary waters were in general more depleted in REEs and Pb than their inputs from the precipitation and riverwaters. Interestingly, the Lamprey water may also be elevated in Gd, an increasingly observed marker of river waters passing through industrialized areas (cf. Bau and Dulski, 1996). Though estuary waters were in general more depleted in REEs and Pb than their river water and precipitation inputs, Great Bay deep waters showed a relative enrichment in light and medium-mass rare earth elements and Pb. These elevated concentrations, including an Eu enrichment, could result from mineral dissolution. In the core, extractable metals were relatively enriched near the sediment-water boundary and, with the exception of several excursions, become less abundant with depth. This pattern is consistent with enhanced contributions of these metals during historical times. Forthcoming integration of trace metal geochemical data with sediment organic content and size fraction will elucidate the variability of metal concentrations within the sediment column and provide insight into the degree of post-depositional metal remobilization.