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Carr, Helen

Natural Resources

2011

MS

Paleolimnological records show that since Europeans began settling in the Lake Champlain Basin approximately 250 years ago, the lake has become progressively eutrophic. Eutrophication of freshwater bodies through excess nutrient input has been a major water quality issue worldwide for the past half century (Codd et al., 2005). Certain land use changes, such as the commercialization of agriculture, urbanization, as well as deforestation in the 19th century, may explain some of the observed variability in nutrient and algal biomass accumulation rates in sediments since settlement began. While the underlying causes of productivity rise in Lake Champlain have been inferred from anecdotal evidence, quantitative inferences based on modeled nutrient fluxes are lacking.
A computer simulation model has been developed using Simile that estimates phosphorus (P) loading, from four land uses (cropland, pasture, urban and forested), as well as from discrete point sources. In addition to loading, the model evaluates P accumulation in the sediments and phosphorus and chlorophyll a concentrations. Its goal is to better understand causality between historical landscape changes and the trophic state of Lake Champlain and to aid in the development of effective management strategies. The simulation of phosphorus input and algal response by the model was validated against trends in sediment cores and monitoring data. Model simulations explore the effects of deforestation, the intensification of agriculture, urbanization and phosphorus export reduction needed to meet TMDL (total maximum daily load) requirements. Results indicate a need to focus phosphorus mitigation efforts in urban areas.