Environmental Effects of Agricultural Practices (EEAP) Initiative


Environmental Effects of Agricultural Practices (EEAP) Initiative

Sediments are considered among the most significant agricultural pollutants (Lowrance and others, 2006) because sediment runoff physically degrades aquatic habitat, carries excess nutrients (especially phosphorus, P) and may carry a wide array of chemical pollutants, including pesticides. Riparian buffers, including those retired from agricultural production, are a key agricultural practice used to control runoff of sediment and associated pollutants, reduce streambank erosion, dissipate stream energy, trap sediment and associated pollutants, and enhance terrestrial and aquatic wildlife habitat (NRCS, 2010; Sharpley and others, 2006; USEPA, 2003). Most studies of riparian buffer effectiveness have been conducted at the edge-of-field, have focused only on changes in water quality, and have not addressed larger questions of aquatic ecological responses (Lowrance and others, 2006). In addition, few such studies have examined the effects of buffers at the watershed scale (Lowrance and others, 2006), where discontinuities in riparian buffers, tile drains that route sediment and water past the buffers, and stream bank erosion, may play a larger role than immediate farm runoff.

In the Minnesota River Basin, MN, retirement of agricultural land has been actively pursued at the state and federal level and includes removal of tile drains and planting of retired riparian corridors (RRC) with native grasses (Christensen and others, 2009). These authors observed that suspended sediment as well as nitrite plus nitrate and total nitrogen decreased with increasing percentages of retired land in a basin. In addition, although biological indicators varied in their response to percentage of retired land, most, including algal biovolume, abundance of tolerant invertebrate and fish species, and Fish Index of Biotic Integrity (IBI) scores improved as a function of the amount of retired land within 50 to 100 meters of the stream. In contrast, total phosphorus concentrations showed no clear link to percentage of retired land. This observed inconsistent relation between various water quality and biological indicators led to questions of how the distribution and history of retired agricultural land impacted ecological outcomes.

A project was initiated in the Fall of 2011 that builds on the initial findings of Christensen and others (2009) to further address the linkages between riparian buffer extent, age, and continuity, and stream water and biotic quality, with a specific emphasis on sediment and phosphorus.

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