QUANTIFYING NUTRIENT TRANSPORT FROM WATERSHEDS SERVED BY ONSITE WASTEWATER SYSTEMS, CENTRALIZED SEWER, AND A FORESTED AREA IN THE PIEDMONT OF NORTH CAROLINA

Excessive concentrations of nutrients can negatively influence water resources, which may affect aquatic ecosystems and human health. A recent watershed plan for the nutrient sensitive Falls Lake in central North Carolina has suggested that malfunctioning septic systems may be a significant source of nutrients to two tributaries of the Lake (Lick Creek and Little Lick Creek). The objective of this study is to determine if nutrient concentrations were higher in subwatersheds served by septic systems relative to centralized sewer, and relative to a forested subwatershed. We are monitoring six streams downgradient from active septic systems, one stream in a forested area, and one stream downgradient from a sewer system. Preliminary results show that median concentrations and loads of total dissolved nitrogen (TDN) and phosphate (PO₄) in streams draining watersheds downgradient from the septic systems (TDN: 1.92 mg/L, PO₄: 0.05 mg/L; TDN load: 4.79 kg-TDN/yr/ha, PO₄ load: 0.16 kg-PO₄/yr/ha) were elevated relative to a stream draining a forested watershed (TDN: 1.03 mg/L, PO₄: 0.01 mg/L; TDN load: 1.80 kg-TDN/yr/ha, PO₄ load: 0.01 kg-PO₄/yr/ha) and a stream draining a watershed served by a sewer system (TDN: 0.69 mg/L, PO₄: 0.01 mg/L; TDN load: 1.62 kg-TDN/yr/ha, PO₄ load: 0.04 kg-PO₄/yr/ha). There are high densities of surface discharge sand filter septic systems in Lick and Little Lick Creek watersheds. The specific influence on stream water quality of these septic system technologies will be investigated. Once the study is completed, the information may aid in developing nutrient management strategies for nutrient-sensitive lakes.