Nitrate in ground and surface waters in the vicinity of a concentrated animal feeding operation

Abstract

Non-point source pollution by nitrates (NO 3 ) from fertilizers and animal wastes has potential effects on human health and eutrophication of surface waters. Until now one problem in determining sources of NO 3 has been the difficulty of identifying origin. Stable isotopes of nitrogen can be used as a signature of NO 3 to identify origin from animal wastes. NO 3 derived from animal waste has a δ 15 N signature of +10 +20‰, which is uniquely high compared to δ 15 NO 3 from other sources. The purpose of this research was to describe the distribution of δ 15 NO 3 , NO 3 and Cl in wells, springs, seeps and lakes in the vicinity of a concentrated animal feeding operation (CAFO), which was the suspected source of contamination. Nitrate concentrations and δ 15 NO 3 were higher in wells just below the waste spray area of the CAFO than above it. Chloride ion concentrations in wells confirmed a contaminated area below the waste spray area. Surface water samples had a wide range of NO 3 concentrations and were uncontaminated, except for samples from one seep and one spring. However, the mean δ 15 NO 3 in samples from springs were +3.9 to +5.0‰, values that are in a range reported for soil NO 3 . Thus, although data are not available on groundwater movement, both stable isotope signatures and chloride concentrations indicate that animal wastes were the source of NO 3 contamination.