Using a Landscape Approach to Interpret Diffuse Phosphorus Pollution and Assist with Water Quality Management in the Basins of Lake Champlain (Vermont) and Lac Léman (France)

Abstract

Diffuse pollution should be recognized as a landscape-level phenomenon. As such, it requires an observational approach consistent with the complex structure and function of the landscape system. We developed a landscape-level approach to study the transfer of phosphorus in rural areas of the Lake Champlain and Lac Leman basins. We began by developing a concept of P dynamics that captured some of the diversity and complexity of P movement through the land (transfer system). Given this initial concept of the diffuse pollution in the landscape, we adopted a synoptic watershed sampling strategy to begin the quantitative description of diffuse P pollution. Data from these types of studies were then analyzed using multiple regression to infer connections between activities on the land and phosphorus flux to surface waters. Our inferences include: 1) land cover determines phosphorus flux during high flow but not during low flows periods, 2) during high flow events, natural wetlands are a significant sink for diffuse phosphorus in surface waters, 3) fluxes and concentrations are higher when the basins are intensively plowed, 4) in the context of plowed areas, agricultural practices as opposed to land cover is a more important determinant of phosphorus flux in watersheds, and 5) the position of elements in the landscape is an important factor controlling diffuse phosphorus pollution. The method and basis for arriving at these conclusions are discussed. We suggest that synoptic sampling of water quality over extensive areas in a landscape, coupled with multiple regression to analyze relationships among P fluxes and landscape variables, is an appropriate tool for determining driving factors, analyzing the diversity of processes, and finding generality in complex landscape systems.