Strategies for Alleviating Estuarine Eutrophication in the Northeast United States

The watersheds of estuaries of the Northeast region are some of the most densely populated coastal areas in the United States. These dense populations result in high loadings of nutrients to waters with high value for recreational and commercial use. Controlling nitrogen input to coastal waters has been a priority following the passage of the Clean Water Act in 1972, and specifically within many of the individual programs of the National Estuary Program (NEP) since the establishment of this program in 1987. Much of the coastline stretching from New Jersey to Southern Maine falls within the domain of an NEP. The main source of nitrogen continues to be from sewer and septic systems in the Northeast estuaries, unlike the highly agricultural Mississippi basin where fertilizer and animal waste dominate. The sources of nitrogen within a watershed determine the approaches used to reduce nitrogen loads. Northeast estuaries have focused on sewer inputs and substantial reductions have been achieved throughout the region. The symptoms of eutrophication (e.g. hypoxia, algal blooms) have been reduced in many of these systems, but not to the level predicted by the nitrogen reductions. The timescale of recovery from eutrophic conditions can be long and many of these systems have only achieved reduced nitrogen inputs from point sources within the last ten years or less. Modeling of hypoxia dynamics is key to understanding the effect of management responses on the anthropogenic pressures acting on these estuarine systems. Results indicate further nitrogen load reductions are required to achieve a greater reduction in eutrophication. As reductions of nitrogen input from point sources are reduced to target goals, assessment of ways to reduce nitrogen from non-point sources have become the focus for many communities. At a local level, modeling of nitrogen sources on a subwatershed level allows for targeting of sources specifically relevant to the watershed. Assessing success of management responses requires monitoring of key state variables which are sensitive to improvement in water quality. Spatial extent and duration of hypoxia and seagrass extent are good indicators. In highly eutrophied estuaries, reduction in the abundance of nuisance macroalgae is also a sensitive indicator. Increasing pressures of climate change on estuaries, including increasing temperatures and ocean acidification, compound the impact of eutrophication. Increasing efforts to address eutrophication in coastal waters is critical to maintaining the ecosystem services provided by these environments in a changing world.