ABSTRACT
Despite advances in our understanding of agriculturally derived nonpoint source (NPS) pollution and the development of best management practices (BMPs) intended to reduce NPS pollution (USDA SCS 1994), aquatic ecosystems linked to agricultural regions in the United States continue to receive high loadings of agricultural pollutants. The mechanisms associated with these increased loadings are complex. It is well established, however, that they result from a combination of increased inputs of nutrients through soil amendments and fertilization and a decreased potential for nutrient immobilization and loss through improved land surface drainage related to wetland conversion, tile drainage, and channelization (Menzel et al. 1984; Mitsch et al. 2001). The effects of these human-induced changes are relevant on a wide variety of scales, from small watersheds (Becher et al. 2000; Schilling and Thompson 2000) to large basins such as the Mississippi River Basin (MRB; see Chapters 2 and 15). These effects extend into coastal waters such as the Gulf of Mexico, where nutrient-rich discharge from the Mississippi River significantly increases the potential for eutrophication and oxygen depletion. Many of the most effective remediation strategies for reducing NPS pollution, including improved nutrient management, off-field buffers, crop selection and rotation, and conservation set-asides, are implemented at the farm and local watershed scale. The cumulative effect of implementing the locally appropriate sets of these alternative strategies (see Brezonik et al. 1999), combined with basin-scale land use and management practices such as extensive restoration of riverine riparian wetlands and floodwater management structures (Chapter 15), could ultimately lead to the level of reductions in nutrient loadings necessary to substantially reduce eutrophication rates in the Mississippi River and the Gulf. For this reason, small watershed studies have significant potential to inform decisionmaking and planning across much larger areas, including the MRB and the Gulf of Mexico.
