Relationships between stream phosphorus concentrations and drainage basin characteristics in a watershed with poultry farming

Abstract

In the Illinois River watershed (Arkansas and Oklahoma) poultry litter is routinely applied to pasture lands as fertilizer supplements. The objective of this study was to quantify the impacts of this practice on water quality in small streams in the watershed. Total phosphorus concentrations in small streams were quantified during a 15 month intensive sampling program for small tributaries, un-impacted by point sources, and covering a range of upstream poultry farming intensities throughout the watershed. Base flow samples were also collected from the tributaries during multiple dry weather sampling events. Correlation analysis was performed for various measurable drainage basin characteristics and phosphorus concentrations. Results show significant positive correlations between total phosphorus concentrations and the intensity of poultry farm operations upstream of sample sites. This relationship is supported by a supplemental synoptic sampling event upstream and downstream of a field applied with poultry litter and by a watershed-scale mass balance analysis. The latter identifies poultry as the single largest contributor of phosphorus inputs to the basin, accounting for over 76 % of the total watershed load. Study results also show significant, but generally weaker, positive correlations between phosphorus and upstream density of septic tanks and soil conservation service curve number of the drainage basin, but these appear likely to be primarily due to cross-correlations with poultry farm presence. This study demonstrates the use of readily-observed basin characteristics in simple water quality predictive tools and has implications for management of poultry-dominated watersheds.