The eutrophication of Lake Champlain's northeastern arm: Insights from paleolimnological analyses

The trophic history of Lake Champlain's northeastern arm was assessed using a multi-proxy paleolimnological approach to provide sub-basin specific information for restoration planning. Sediment cores collected from Missisquoi Bay, St. Albans Bay, and the central Northeast Arm (Inland Sea) were analyzed for nutrients, organic carbon, carbon stable isotopes, biogenic silica, pigments, diatoms and soft algae microfossils. Results indicate that this arm of Lake Champlain was oligotrophic when Europeans arrived in 1609, and that clearance of > 70% of catchment forest cover had minor impact on algal production. Instead, eutrophication of St. Albans Bay was concurrent with sewer installation and expansion in early 20th century, and again with urban development in the 1960–70s. In contrast, less urbanized Missisquoi Bay remained mesotrophic until agriculture intensified after 1970. Interpretation of central Northeast Arm trophic history is complicated because road and railroad causeways built in 19th century reduced sediment input to this basin for several decades. Nevertheless, high surface-sediment concentrations of nutrients, pigments and organic matter along with replacement of Cyclotella bodanica with more eutrophic Fragilaria crotonensis suggest substantial eutrophication in deep as well as shallow water after 1970. We conclude that effective restoration of the northeastern arm is possible, but will require stringent control of animal and human wastes and reduced use of crop fertilizers.