The effect of terrigenous inputs on spatial patterns of water quality indicators in South Lake, Lake Champlain

Spatial patterns of measures of trophic stare, optical properties and parti cle composition are documented for Lake Champlain, with particular emphasis on the southernmost shallow section (< 10 m deep, <similar to> 55 km in le ngth) known as South Lake, to depict the impacts of terrigenous inputs. The analysis is supported by two surveys conducted in 1998 for South Lake (thi rteen sites) following typical and unusually high runoff intervals, and for selected deep-water sires (thirteen) for the typical runoff interval. Terr igenous inputs, particularly as clays, cause light penetration to be lower, turbidity (T-n) and phosphorus (P) concentrations to be higher by a wide m argin, and particle composition to differ greatly in South Lake relative to deeper portions of the lake. Generally progressive gradients are documente d within South Lake for Secchi disc transparency (SD), the light attenuatio n coefficient, T-n, particulate organic carbon, total P, and particulate P, that demonstrate diminishing impacts of the terrigenous inputs with the ap proach to the deeper portions of the lake. Increased loadings associated wi th high runoff impart greater, and a wider array of impacts in South Lake, that appear to be relatively short-lived (less than 1 month). The high leve ls of inanimate particles (tripton) that prevail in South Lake systematical ly compromise total P concentration and SD as measures of trophic stare. De spite lower levels, this terrigenous material also influences these measure s in deep-water areas. Management strategies that focus on reductions in P loading will not result in substantive increases in SD in South Lake, as ph ytoplankton biomass is unimportant in regulating the prevailing clarity con ditions. Erosion control may be a more promising alternative to pursue impr oved clarity in this portion of the lake.