Chemical and bacteriological quality of pasture runoff

Abstract

ABSTRACT: Natural background characteristics and grazing cattle both influence the chemical and bacteriological quality of pasture runoff in south central Nebraska. The chemical quality of runoff from unstocked grassland was poorer than that from grazed pasture. The chemical quality of pasture runoff, which was better than runoff from cultivated cropland and urban areas, was within recommended water quality criteria. Cattle grazing increased fecal coliform (FC) counts 5- to 10-fold; however, FC counts in rainfall runoff from both grazed and ungrazed pasture, which were comparable to FC counts in runoff from cropland and urban areas, exceeded the water quality criterion of 200 organisms per 100 milliliters more than 90 percent of the time. The FC/fecal streptococci (FS) ratio of runoff from both grassland and ungrazed pasture was characteristic of wildlife feces, suggesting that the natural background level for bacteriological inputs may be large. Recommended bacteriological water quality criteria may be inappropriate for characterizing pasture runoff and other nonpoint sources of potential pollution.