Wetlands at your service: reducing impacts of agriculture at the watershed scale

Midwest by converting upland and wetland habitats to crops and pastures, simultaneously changing hydrologic conditions and water quality, and threatening the region’s biodiversity (Table 1). Where corn is the dominant crop (in Iowa, Illinois, and Indiana, in particular), extensive networks of perforated pipes and drainage ditches were installed to drain wetlands. As a result, surface and ground waters flow directly into rivers, and cultivation and fertilization release sediments, phosphorus (P), and nitrogen (N) into downstream waters (Howarth et al. 2002). About 43% of the nation’s N fertilizer is applied to the corn fields that cover only 21% of the agricultural land, and at least 35% runs off into streams, lakes, and ultimately coastal waters (Crumpton et al. 1993; Howarth et al. 2002). Excess P causes algal blooms in inland lakes, and excess N causes seasonal hypoxia (low oxygen levels) in coastal waters. Although farming practices have improved since the 1930s Dust Bowl years, serious problems remain. Even where farmers reduce fertilizer applications, agricultural fields discharge more surface runoff and nutrients than do undisturbed soils (Woltemade 2000; Howarth et al. 2002). In the large Mississippi drainage basin, agricultural activities contribute up to 65% of the nutrients that reach the Mississippi River (NSTC 2000). Aquatic and wetland species, in turn, are affected by the poor water quality caused by the plowing of habitat and the channelization of streams. In Missouri and Illinois, for example, 10–11% of fish species are endangered (Stein and Flack 1997). Low water quality can threaten the survival of rare plant communities, such as those found in wetlands; The Nature Conservancy lists several types of wetland as “rare” in 12 Midwestern states (Grossman et al. 1994). As a result of runoff from urban and agricultural 65