address chronic water-quality deterioration, but it has proved elusive even there.
Nutrient (nitrogen and phosphorus) pollution is one of the more persistent and pervasive environmental problems in the United States, and it is worsening in many locations (Howarth 2008). The volume of nutrients reaching surface water and groundwater has increased substantially since the middle of the 20th century as a result of a complex of factors, including population growth, changes in land cover, increased fossil fuel combustion, and changes in the structure of agricultural production (Selman et al. 2008). Providing the scientific foundations for the development of policies that can reduce nutrient-pollution problems will require innovative economic, social-science, and natural-science research. The challenges are particularly difficult because the hydrologic, ecologic, economic, and social processes affecting the magnitude and scope of nutrient pollution and its consequences are complex, multi-scaled, and spatially variable. To deal effectively with this complex problem, a framework for incorporating human and environmental interactions, such as the Millennium Ecosystem Assessment framework (see Chapter 1) would prove useful. Nutrient pollution should be approached from a broad perspective that uses systems thinking (see Chapter 4) and there are examples in which EPA is already taking steps in this direction with the Chesapeake Bay Program and the New York—New Jersey Harbor Estuary Program. The problem may not be getting progressively worse, but there are still many challenges to attaining further improvements. The prospects are that eutrophication will continue to be a challenge until policies to control nutrients are made more effective (Cary and Migliaccio 2009; Spiertz 2009).