Water-quality characteristics in runoff for three discovery farms in North Dakota, 2008-12

The U.S. Geological Survey, in cooperation with North Dakota State University Agriculture Research Extension and in collaboration with North Dakota State Department of Health, North Dakota State Water Commission, U.S. Environmental Protection Agency, and several agricultural producers, helped organize a Discovery Farms program in North Dakota in 2007. Discharge measurements and water-quality samples collected at the three Farms (Underwood, Dazey, and Embden) were used to describe water-quality characteristics in runoff, and compute estimates of annual loads and yields for selected constituents from spring 2008 through fall 2012.

Consistent patterns in water quality emerged at each individual farm, but similarities among farms also were observed. Suspended sediment, total phosphorus, and ammonia concentrations generally decreased downstream from feeding areas, and were primarily affected by surface runoff processes such as dilution, settling out of sediment, or vegetative uptake. Because surface runoff affects these constituents, increased annual surface runoff volume tended to result in increased loads and yields. No significant change in nitrate plus nitrite concentration were observed downstream from feeding areas because additional processes such as high solubility, nitrification, denitrification, and surface-groundwater interaction affect nitrate plus nitrite. For nitrate plus nitrite, increases in annual runoff volume did not consistently relate to increases in annual loads and yields. It seems that temporal distribution of precipitation and surface-groundwater interaction affected nitrate plus nitrite loads and yields. For surface drainage sites, the primary form of nitrogen was organic nitrogen whereas for subsurface drainage sites, the primary form of nitrogen was nitrate plus nitrite nitrogen.