Background/Question/Methods Excess loading of nitrogen and phosphorus to the nation’s waters has had devastating impacts on downstream lakes, estuaries, and coastal zones. The Long Island Sound is one such waterbody that suffers from low dissolved oxygen and excessive algal blooms due to nutrient loading from surrounding areas. Here we present results of work performed with stakeholders in the Upper Connecticut River to help them reduce their nutrient exports from the watershed. The Upper Connecticut River is a 16,000 km2 watershed, of which 5% is urban land, 2% is in row crop, and the remainder is primarily forested land with some hay fields. The nutrient inputs to the watershed are varied, and reductions in export may be accomplished by grey infrastructure upgrades to Waste Water Treatment Plants, through combinations of Best Management Practices (BMPs) and green infrastructure creation for urban and agricultural land, or through the conversion of riparian areas to grassland or forests with intact soil structures than can effectively retain and remove nutrients entering a stream reach. We combined published estimates of nutrient inputs from spatially resolved water quality models, estimates of BMP nutrient reduction efficiencies based on hydrologic-hydraulic-biogeochemical models, and regional and national cost analyses to create an optimization model that identifies a suite of BMPs that will reduce annual loading from the watershed for the least financial cost to stakeholders.
Results/Conclusions For the Upper Connecticut River, simultaneously reducing total nitrogen export from the watershed by 10%, and phosphorus export into 2 in-river-network lakes by 2-12% can be accomplished through a combination of agricultural BMPs, urban green infrastructure, upgrades to Waste Water Treatment Plants, and the creation of riparian buffers along a fraction of river banks. We show the likelihood of reducing nutrient export from the watershed based on different decisions, such as favoring agricultural practices that are most familiar in the region or implementing green infrastructure over grey infrastructure. Our case study demonstrates how ecological processes of nutrient retention and transformation in green infrastructure and bioreactors can be effectively coupled with economic and social data to inform human decisions that will determine ecosystem states and water quality downstream. Our work models nutrient retention across a large area using soil, topography and land cover use information, and from our case study we have created a tool that synthesizes the results of these ecological processes into simple metrics that watershed planners from around the region can use.
