THE ORGANIC GEOCHEMISTRY OF SEBAGO LAKE SEDIMENTS

Sebago Lake is a relatively large (surface area of 117 km²) and deep lake (>100 m) located in southern Maine. Sebago Lake serves as the water supply for the city of Portland, ME and therefore monitoring water quality and lake trophic status is of much interest. Today the watershed of Sebago Lake is mostly forested and contains numerous residential dwellings, but has been deforested in the past, and currently the lake is heavily used for recreational activities including boating. Here we examine the organic geochemistry of Sebago Lake surface sediments and catchment soils. We identify and determine the concentrations of numerous compound classes present in modern soil and lake sediments including polycyclic aromatic hydrocarbons (PAHs), which largely result from human activities. Although Sebago Lake water quality has been extensively monitored by the Portland Water District since the late 1970s, a longer record is required to evaluate potential impacts of human activities in and around Sebago Lake. Here we examine a short gravity core, collected from the deep central lake basin, and use a suite of algal biomarkers, including sterols, diols and glycolipids, to examine changes in the algal community structure of Sebago Lake through time. Additionally, we reconstruct past temperatures using branched and isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) to gain insights into the temperature history of New England.