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 particle composition are documented for Lake Champlain, with particular emphasis on the southernmost shallow section (< 10 m deep, 55 km in length) known as South Lake, to depict the impacts of terrigenous inputs. The analysis is supported by two surveys conducted in 1998 for South Lake (thirteen sites) following typical and unusually high runoff intervals, and for selected deep-water sires (thirteen) for the typical runoff interval. Terrigenous inputs, particularly as clays, cause light penetration to be lower, turbidity (T-n) and phosphorus (P) concentrations to be higher by a wide margin, and particle composition to differ greatly in South Lake relative to deeper portions of the lake. Generally progressive gradients are documented within South Lake for Secchi disc transparency (SD), the light attenuation coefficient, T-n, particulate organic carbon, total P, and particulate P, that demonstrate diminishing impacts of the terrigenous inputs with the approach to the deeper portions of the lake. Increased loadings associated with 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 levels of inanimate particles (tripton) that prevail in South Lake systematically compromise total P concentration and SD as measures of trophic stare. Despite lower levels, this terrigenous material also influences these measures 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 phytoplankton biomass is unimportant in regulating the prevailing clarity conditions. Erosion control may be a more promising alternative to pursue improved clarity in this portion of the lake.