Scale-dependent landscape effects on north temperate lakes and rivers
Land use and land cover can have a significant impact on water chemistry, but the spatial scales at which landscape attributes exert a detectable influence on aquatic systems are not well known. This study quantified the extent of the landscape influence using the proportion of wetlands in the watershed measured at different distances to predict dissolved organic carbon (DOC) concentrations in Wisconsin lakes and rivers, and to determine whether the watershed influence varied with season and hydrology. The proportion of wetlands in the total watershed usually explained the most variability in DOC when stepwise regression was used. However, best model techniques revealed that r2 values often only varied from 1-3\% between models using the proportion of wetlands in the total watershed versus the proportion of wetlands in nearshore riparian areas (25-lOOm) for lakes. In rivers, the proportion of wetlands in watershed always explained considerably more of the variability in DOC versus considering only the wetlands in the riparian zone. The watershed influence also varied seasonally in rivers, as the proportion of the watershed in wetlands explained more of the variability in DOC in the fall than in the spring. Overall, the proportion of wetlands in the landscape was a much better predictor of DOC concentrations in rivers than in lakes.