Factors affecting nutrient concentrations in the White River Basin, Indiana

ABSTRACT: Nutrient concentrations in rivers and streams in the White River basin are affected by land use, agricultural practices, seasonal changes in nutrient uptake, point-source discharges, and variations in precipitation and runoff. Median concentrations of dissolved nitrate and phosphorus were 0.66 and 0.02 milligrams per liter, respectively, in a small urban watershed, but median concentrations were 1.5 to 10 times greater for nitrate and 1.5 to 3 times greater for phosphorus in six small agricultural watersheds. The lowest nutrient concentrations in the small agricultural watersheds were measured in a watershed where conservation tillage was extensively used. Median concentrations of ammonia and nitrite were more than 2 times and more than 5 times greater, respectively, in an agricultural watershed affected by waste from farm animals than in the other small agricultural watersheds. Nitrate concentrations were highest during the winter and spring when vegetation was dormant and uptake was reduced. High nitrate concentrations in late spring in some agricultural watersheds seem to correspond to the application and runoff of nitrogen fertilizers. Nondetectable concentrations of nitrate, ammonia, and phosphorus in the White River during extreme summer low flows were caused by nutrient uptake during periods of intense algal productivity.