UVM Theses and Dissertations
Format:
Print
Author:
Schwarting, Lindsay L.
Dept./Program:
Natural Resources
Year:
2011
Degree:
MS
Abstract:
Since European settlement of its watershed in the 18th century, Lake Champlain has been subjected to combined excessive nutrient supply from land-based activities, and food web disturbances associated with commercial fishing and introduced nonnative fish. Because routine monitoring of the lake began only in 1992, evaluation of the relative impacts of top-down trophic cascades and eutrophication on food webs and water quality has been nearly impossible. This study uses a variety of paleolimnological proxies for productivity and food-web structure (algal pigments, zooplankton microfossils, and organic matter) to construct a long-term history of Lake Champlain's food web and trophic status from sediment records. While largely exploratory in nature, it provides preliminary data for two widely-separated and ecologically dissimilar locations in the lake, far northern Missisquoi Bay, and the southern Main Lake near Elm Point.
Evidence of eutrophication at both study sites included increasing rates of algal pigment, organic carbon and phosphorus accumulation, declining C:N ratios, and greater representation of cyanobacteria and the cladoceran Chydorus sphaericus in plankton communities. Both sites were oligo-mesotrophic between the 18th century and the 1960s then underwent accelerated eutrophication up until the mid-1990s, when Elm Point entered a recovery phase related to point-source phosphorus reduction. Missisquoi Bay continued to degrade, likely due to increased agricultural activity. Canonical correspondence analysis (CCA) revealed that top-down cascades also were active, especially the impact of invasive white perch and alewife on the zooplankton assemblage. In accordance with size-selective theory, the arrival of these nonnative planktivores yielded a decline in the representation of large-bodied Leptodora kindti and Bosmina spp. The results showed promise for paleolimnology as a useful tool for studying long-tenn processes in Lake Champlain and elsewhere.
Evidence of eutrophication at both study sites included increasing rates of algal pigment, organic carbon and phosphorus accumulation, declining C:N ratios, and greater representation of cyanobacteria and the cladoceran Chydorus sphaericus in plankton communities. Both sites were oligo-mesotrophic between the 18th century and the 1960s then underwent accelerated eutrophication up until the mid-1990s, when Elm Point entered a recovery phase related to point-source phosphorus reduction. Missisquoi Bay continued to degrade, likely due to increased agricultural activity. Canonical correspondence analysis (CCA) revealed that top-down cascades also were active, especially the impact of invasive white perch and alewife on the zooplankton assemblage. In accordance with size-selective theory, the arrival of these nonnative planktivores yielded a decline in the representation of large-bodied Leptodora kindti and Bosmina spp. The results showed promise for paleolimnology as a useful tool for studying long-tenn processes in Lake Champlain and elsewhere.