Nitrate concentrations in surface and groundwater from a livestock farm with manure management in Cajamarca, Peru

Abstract

Manure slurry is a liquid mixture of feces, urine, wash water and organic residues generated in livestock systems; it contains organic and ammoniacal nitrogen that can be transformed into nitrate and mobilized toward surface water or groundwater. This study aimed to evaluate nitrate concentrations in surface water and groundwater from a livestock farm with manure slurry management in Cajamarca, Peru. Ten sampling sites (eight surface water sites and two wells) were evaluated over two days, one week apart, yielding twenty determinations. Nitrate was determined using a sodium-salicylate colorimetric procedure with absorbance measured at 410 nm, and the results were expressed as mg/L NO₃-N. In surface water samples, nitrate concentrations ranged from 1.24 to 11.44 mg/L NO₃-N during the first sampling event and from 1.51 to 15.41 mg/L NO₃-N during the second, with no significant differences between the two events (p>0.05). Twenty-five percent of the surface water determinations in the first event and 12.5% in the second exceeded the US EPA drinking water reference value of 10 mg/L NO₃-N. No well samples exceeded this value. Surface water samples showed greater variability and localized higher concentrations than the well samples. Limitations in the study design and analytical control are discussed.