Quantifying Watershed-Based Influences on the Gulf of Maine Ecosystem: The Saint John River Basin

Estuarine and coastal ecosystems of the Gulf of Maine continue to be degraded by excessive loadings of sediments, nutrients, and contaminants derived from surrounding watersheds. The Saint John River basin is the largest basin in the Gulf of Maine, and within it there are a significant number of major industries along the main stem of the river and vast expanses of land-based activities of forestry and potato production along many of the river valleys and floodplains. Water quality and loading of sediments and nutrients have changed over the past few hundred years, with the most important changes coming with the expansion of agriculture and pulp and paper processing operations since the 1950s. Several studies are discussed in this chapter that outline the identification and quantification of watershed-based activities that influence the Saint John River ecosystem. Using export coefficient modeling, nonpoint sources of nitrogen and phosphorus to the Bay of Fundy are shown to be three to four times that of point sources. Few studies explicitly couple river dynamics to estimates of load to the Saint John River estuary and the Bay of Fundy. With high-quality geographic information on land coverage, land usage and human activities, and robust water quantity and quality monitoring programs, analytical models can be developed to help evaluate policy options and chart pathways towards a more integrated understanding and management of the basin and its receiving waters.