Nutrient Concentrations in the Water Column at University Lake, Carrboro, NC (2006)

Undergraduate: Colter Chitwood

Faculty Advisor: Tom Shay
Department: Environmental Studies

---

University Lake, in Carrboro, NC, is an important water resource to the communities of Carrboro, Chapel Hill, and the University of North Carolina. The distributions of methane, carbon dioxide, and nutrients in the lake are seasonally influenced. Physical properties control the structure of the water column resulting in summer stratification and winter mixing, and in the hypolimnion these compounds are in high concentration. The seasonal buildup of methane in the hypolimnion indicates that its primary source of production is the sediment. Calculations of flux concentrations from the sediment suggest that University Lake is a significant source of methane to the atmosphere. University Lake is supersaturated with carbon dioxide, therefore the lake is also a source of CO2 to the atmosphere. It was found that carbon and nitrogen are in accordance with the Redfield ratio in the hypolimnion while the same ratio in the epilimnion is altered due to preferential stripping of ammonium by phytoplankton. The depletion of ammonium and corresponding accumulation of nitrate suggests that nitrification is the dominant process during winter mixing.