Ground-water quality and effects of poultry confined animal feeding operations on shallow ground water, upper Shoal Creek basin, Southwest Missouri, 2000

Abstract

Forty-seven wells and 8 springs were sampled in May, October, and November 2000 in the upper Shoal Creek Basin, southwest Missouri, to determine if nutrient concentrations and fecal bacteria densities are increasing in the shallow aquifer as a result of poultry confined animal feeding operations (CAFOs). Most of the land use in the basin is agricultural, with cattle and hay production dominating; the number of poultry CAFOs has increased in recent years. Poultry waste (litter) is used as a source of nutrients on pasture land as much as several miles away from poultry barns. Most wells in the sample network were classified as “P” wells, which were open only or mostly to the Springfield Plateau aquifer and where poultry litter was applied to a substantial acreage within 0.5 mile of the well both in spring 2000 and in several previous years; and “Ag” wells, which were open only or mostly to the Springfield Plateau aquifer and which had limited or no association with poultry CAFOs. Waterquality data from wells and springs were grouped for statistical purposes as P1, Ag1, and Sp1 (May 2000 samples) and P2, Ag2, and Sp2 (October or November 2000 samples). The results of this study do not indicate that poultry CAFOs are affecting the shallow ground water in the upper Shoal Creek Basin with respect to nutrient concentrations and fecal bacteria densities. Statistical tests do not indicate that P wells sampled in spring 2000 have statistically larger concentrations of nitrite plus nitrate or fecal indicator bacteria densities than Ag wells sampled during the same time, at a 95-percent confidence level. Instead, the Ag wells had statistically larger concentrations of nitrite plus nitrate and fecal coliform bacteria densities than the P wells. The results of this study do not indicate seasonal variations from spring 2000 to fall 2000 in the concentrations of nutrients or fecal indicator bacteria densities from well samples. Statistical tests do not indicate statistically significant differences at a 95-percent confidence level for nitrite plus nitrate concentrations or fecal indicator bacteria densities between either P wells sampled in spring and fall 2000, or Ag wells sampled in spring and fall 2000. However, analysis of samples from springs shows that fecal streptococcus bacteria densities were statistically smaller in fall 2000 than in spring 2000 at a 95-percent confidence level. Nitrite plus nitrate concentrations in spring 2000 samples ranged from less than the detection level [0.02 mg/L (milligram per liter) as nitrogen] to 18 mg/L as nitrogen. Seven samples from three wells had nitrite plus nitrate concentrations at or larger than the maximum contaminant level (MCL) of 10 mg/L as nitrogen. The median nitrite plus nitrate concentrations were 0.28 mg/L as nitrogen for P1 samples, 4.6 mg/L as nitrogen for Ag1 samples, and 3.9 mg/L as nitrogen for Sp1 samples. Fecal coliform bacteria were detected in 1 of 25 P1 samples and 5 of 15 Ag1 samples. Escheri-