However, agricultural impacts on water quality go beyond the concerns for drinking water-the aquatic ecosystem of the plateau also has been significantly affected. "Very little surface water is used for drinking water in this area, but fish are harmed by decreased stream-water quality," said Mark Munn, the biologist for the USGS study. "Pesticides and habitat degradation are the main concerns." He noted that stream sampling by the USGS showed seven currently used pesticides at concentrations above the limits recommended for protecting aquatic life.
Soil erosion, a long-term problem for farmers in the Palouse River Basin, transports some soil to streams, degrading habitat and carrying with it older pesticides and their breakdown products. A breakdown product of the banned insecticide DDT was found in both streambed sediment and bottom fish at concentrations exceeding guidelines for the protection of aquatic life.
"Another problem for fish habitat is excessive plant growth caused by high levels of nutrients in streams," said Munn, who explained that these nutrients enter streams in runoff from agricultural fields and discharge from urban wastewater treatment plants.
Some agricultural practices, such as allowing cattle to graze near streams, are associated with higher rates of erosion. However, increased use of BMPs may improve water quality of the plateau. The USGS study showed that use of sprinkler or drip rather than furrow irrigation has decreased soil erosion in the CBIP area. In the Palouse, erosion has also decreased, which may be due to BMPs such as no-till seeding. And lower rates of fertilizer application may account for the fact that nitrate concentrations are leveling off in some areas.
A new, 35-page color report by the USGS summarizes the results of the study, which included three years of
intensive sampling and data analysis. The Central Columbia Plateau is a 13,100-square mile area between t
Contact: Mr. Sandy Williamson
United States Geological Survey