Fecal Contamination Source Tracking and Forecasting to Support Recreational and Cultural Development in the Black River Watershed

Abstract

The Coharie Tribe expressed interest in learning more about specific CAFO and human impacts on water quality along the Great Coharie River, with special attention to spatial and temporal variability of these impacts. The Tribe’s interest also aligns with opportunities to answer fundamental research questions about water quality in North Carolina’s Coastal Plain and areas similarly impacted by industrialized agriculture. We proposed research questions and objectives intended to help meet these needs while also advancing fundamental science concerning biological water quality. What are the dominant sources of fecal contamination at 3 sites in the watershed? How do these sources vary across base flow and storm flow conditions, and warm and cold seasons? Can forecasting tools be developed to capture elevated levels of fecal contamination in the watershed to support Tribal decision-making related to the use of river? To address these questions, low frequency and high frequency (determined by base and storm flow) sampling events were conducted at three sites in the Great Coharie River watershed from March 2022 to March 2023. Each sample was evaluated for total coliforms, Escherichia coli, molecular microbial source tracking (MST) targets, Total suspended solids, Total Kjeldahl Nitrogen, the sum of Nitrate and Nitrite, Ammonia, Total Phosphorus, Orthophosphate, Temperature, pH, dissolved oxygen, specific conductivity, and turbidity. An automated DNA extraction kit was optimized for use with surface water filters and nucleic acid was extracted from each sample. Following DNA extraction, samples were analyzed using polymerase chain reaction microbial source tracking targets including LA35, Pig2bac and hCYTB484 which is sensitive and specific to swine and poultry combined, swine, and human fecal contamination, respectively. Results from the MST assays indicate that the watershed likely suffers from fecal contamination from the three target hosts. Escherichia coli data collected throughout the study indicate that the three sites have contamination levels that would deem the Great Coharie River as impaired per the United States Environmental Protection Agency’s Recreational Water Quality Criteria. An explanatory model using multiple linear regression was developed with the available data. The preliminary model revealed that 2-day total rainfall is an important covariate to help explain E. coli concentrations in the watershed. In addition to the explanatory model, a random forest predictive model was constructed to predict whether the water was at an E. coli concentration above or below the EPA recommended threshold (i.e., 126 MPN/100 mL). When performing covariate importance analysis, it was determined that 2-day total rainfall was the most important covariate of any examined in this study when predicting E. coli. Lastly, a generalized estimating equation was developed, and this model also found 2-day total rainfall to be an important covariate. It is recommended that caution be used during primary contact recreation, which includes activities that involve increased likelihood of water ingestion or immersion like swimming, at each of the three sites due to elevated levels of E. coli- especially following an intense rainfall event. We also recommend that a land use study be undertaken to determine potential management strategies to minimize fecal contamination at the Marsh Swamp site, which experienced higher levels of E. coli contamination than other sites. Additionally, further studies into the human contributions to the watershed could be performed to help identify if further interventions related to human waste management need to be made.