An Evaluation of Water Quality Parameters and Flow Dynamics in High Rock Lake, North Carolina to Assist in the Development of Nutrient Criteria for Lakes and Reservoirs in the State

High Rock Dam, located in Rowan and Davidson Counties in North Carolina, was constructed on the Yadkin River in 1927. High Rock Lake (HRL) is primarily fed by the Yadkin River and several smaller tributaries, draining a total area of 3974 square miles. HRL has been on the 303d list of impaired waters since 2004 due to elevated levels of turbidity, chlorophyll-a, and pH. North Carolina currently has surface water standards for chlorophyll-a (40 µg/L), turbidity (25 NTU- lakes), and pH (<6 or >9), but not for nutrients. NC DEQ chose HRL as a pilot study to help develop nutrient criteria for lakes throughout the state. There is a high degree of spatial variability in water quality in HRL. Turbidity, total nitrogen, and total phosphorus decrease with increasing proximity to the dam, whereas chlorophyll-a is most elevated within the mid-section of the lake. Phytoplankton taxonomic assemblage varies according to lake section, with the lower-section of the lake experiencing the most elevated levels of cyanobacteria. Riverine discharge appears to influence chlorophyll-a and biovolume, and future studies should aim to identify the impact of discharge on phytoplankton assemblage. An improved understanding of discharge-water quality relationships can help guide nutrient criteria development for the state’s reservoirs, particularly for reservoirs with short residence times (days-weeks).