Abstract

Lake Champlain is one of the largest bodies of freshwater in the United States, stretching almost 200 km long yet only 19 km wide. Its drainage basin of 10450 km2 includes portions of Vermont, NewYork, and Quebec. As with many other water bodies, man's presence on and around the lake and in its drainage basin has had negative impacts. The most pressing water quality problem today is excess phosphorus loading which contributes to eutrophication and subsequent degradation of lake water quality.

The water quality model described here was developed to study the dynamics and kinetics of the distribution and concentration of nutrients in the lake. The development focused on the phosphorus cycle, including phytoplankton population simulation, and the estimation of lake response to phosphorus loadings. A comprehensive water, chloride, (as a conservative tracer) and phosphorus mass balance dataset developed through the joint effort of the Vermont Department of Environmental Conservation (VTDEC) and the New York State Department of Environmental Conservation (NYSDEC), for the two year period between March 1990 and February 1992, is used to provide flow and loading information for model input, and mean in-situ concentration information for comparison with model calculations.

The model conservation of mass equations are solved using a multiply-connected control volume approach in three dimensions and in time. This is a sophisticated version of the standard segment model approach. The model development also presents a unique approach to the determination of inter-segment mixing exchange, based entirely on a conservative tracer data set, chloride in this case. The method presented eliminates the trial-and-error and tuning necessary in other modelling approache

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