U.S. Geological Survey U.S. Geological Survey
The Pudding River Basin encompasses 1400 square kilometers of the Willamette River Basin and includes Oregon's leading agricultural region in terms of gross sales. Water samples collected from 18 stream sites throughout the Pudding Basin during a 4-day peak-runoff period in April 1993 yielded nitrate-nitrogen concentrations as high as 10 mg/L. Atrazine and simazine were the most frequently detected of 11 pesticides, with maximum concentrations of 3.0 and 1.4 µg/L, respectively. The highest measured nitrate, atrazine, and simazine concentrations occurred at the same site. Concentrations of dissolved organic carbon were significantly correlated with atrazine concentrations, but not with simazine concentrations. Sampled tributaries contributed about 50 percent of the measured instantaneous loads of nitrate, atrazine, and simazine in the Pudding River; the highest nitrate, atrazine, and simazine loads per unit area were from subbasins in the more intensely farmed mid-basin region.