PHOSPHORUS LOADING IN SOILS CAUSED BY SWINE WASTEWATER LAGOON OVERFLOW IN BEREA, KENTUCKY

Phosphorus loading in soil associated with intensive agricultural practices can alter freshwater ecosystems by releasing excess nutrients and causing eutrophication and hypoxia. In agricultural watersheds, increased soil P loading can be linked to the expansion of confined animal feeding operations. Increased loading is caused by land application of animal waste and by failure of wastewater retention lagoons, resulting in P enrichment of overland flow. The movement of P from enriched soil to large water bodies, along with related biogeochemical interactions and sequestration is poorly understood. The purpose of this study is to further the understanding of P sequestration and movement in an agricultural watershed by studying a watershed receiving swine wastewater effluent in Berea, KY. The P concentration of the watershed receiving swine wastewater effluent was compared to an adjacent watershed receiving no effluent. Soil samples were collected from the watershed receiving swine wastewater effluent (n=55) and the watershed receiving no effluent (n=37). Sediment and suspended sediment samples were collected from the two retention lagoons (n=2, n=2) and Big Lake (n=7, n=1) which receives runoff from the two watersheds. Concentrations of Mehlich III extractable P (M3P) of soil and combusted sediment samples, and concentrations of 6M sulfuric acid-extractable phosphorus of combusted suspended sediment samples were determined using the molybdate blue method. Within the 4m drainage buffer, mean soil P concentration of the treated watershed (M3P=288±183 mgP/kg) was significantly greater than the soil P in the control watershed (M3P= 94±42 mgP/kg). However, outside the 4m drainage buffer the soil P in the treated watershed (M3P=63±93 mgP/kg) was not significantly greater than soil P in the control watershed (M3P= 44±42 mg P/kg). The M3P concentration of combusted sediment samples from Big Lake and the lagoons averaged 1500±300 mgP/kg and 19000±6700 mgP/kg respectively. Acid-extractable P concentration of suspended sediment samples averaged 22±16 mgP/L from the lagoons and 0.33 mgP/L from Big Lake. The results suggest that deposition of P rich suspended sediment during overflows accumulates in the soil, creating a significant sink of P that may continue to affect the lake for a substantial amount of time.