NUTRIENT IMPACT OF SWINE CAFO WASTE ON SURFACE WATER AND GROUNDWATER IN EASTERN NORTH CAROLINA

Abstract

Eastern North Carolina (ENC) is a significant pork producer in the United States, with most swine raised in concentrated animal feeding operations (CAFOs). Swine wastewater typically contains elevated nutrient concentrations and is stored in lagoons (LG) until land application occurs. Periodically, nutrient-rich wastewater is applied to spray fields (SFs) to facilitate plant uptake by crops; however, nitrogen and/or phosphorus may leach into groundwater or run off into streams, potentially degrading water quality located hydraulically downgradient of SFs. The goal of this study was to analyze nutrient concentrations, transport, and physiochemical parameters of wastewater and water resources located hydraulically downgradient from SFs at a swine farm in ENC. Piezometers were installed to monitor groundwater quality in the surficial aquifer upgradient and downgradient of spray fields. Additionally, surface water quality was evaluated for streams upgradient and downgradient of the CAFO. Monthly samples were collected between July 2023 and February 2024, which were analyzed for nitrogen and phosphorus. Results revealed that wastewater irrigation from the LG influenced nutrient concentrations in water resources. Wastewater in the LG had a median Total Dissolved Nitrogen, TDN (1651.12 mg/L) and a phosphate concentration (7.48 mg/L), which was greater than all other groundwater sampling locations. Groundwater beneath the SF contained the next highest nutrient, and background concentrations were low. Streams located hydraulically downgradient from SF also tended to contain nutrient concentrations that were significantly greater than stream nutrient concentrations upstream of the farm (median TDN and phosphate of 1.25 mg/L and < 0.001, respectively). Stream discharge was substantially lower than expected, likely due to drought conditions that occurred before and during the study period. Median discharge at the downstream sampling location was 54.4 L/min, while the streams that drain the farm (East Creek and Seep) had a median discharge ranging from 11.29 to 163.37 L/min. Thus, drought conditions also likely influenced nutrient mass transport, particularly for TDN. The median mass transport for nitrogen and phosphate was 1.01 kg-N/day and 0.04 g-P/day respectively. The mass transport at the UP and DW locations was not statistically significant (p > 0.05) for nitrogen and phosphorus, respectively. These results differed from a previous study at the same farm during normal conditions, where stream discharge (median: 2,150 L/min) and nutrient exports were substantially greater (median TDN: 21.4 kg-N/day; median phosphate: 3 g-P/day) than the current study. Results from this study indicated that nutrient concentrations and mass transport typically decreased as distance from the CAFO increased. However, nutrient concentrations suggest that eutrophication could still occur, but mass transport was likely underestimated due to drought. Thus, CAFOs can be a significant source of nutrients to nearby water resources, possibly contributing to environmental and/or public health challenges. Episodic weather patterns (e.g., regional drought) can also substantially influence nutrient mass transport in surface water. More research is recommended to evaluate how drought can influence nutrient mass transport from swine CAFOs.