The concentration of organic matter (i.e., naturally or anthropogenic-derived carbon-based compounds) is an important water quality metric for drinking water managers because of its numerous effects on water quality, necessitating new and improved strategies for monitoring our freshwaters. Here, we studied two types of organic compounds in a Virginia drinking water reservoir. First, pharmaceutical and personal care products (PPCPs) are anthropogenically-derived organic contaminants that can negatively alter ecosystem health and water quality. Second, naturally-occurring dissolved organic matter (DOM) compounds play important roles in ecosystem function but can react with chlorine in drinking water treatment to form carcinogenic disinfectant by-products.

To improve our understanding of organic matter cycling and inform water quality management, we implemented a new water quality monitoring program at Carvins Cove Reservoir (CCR) in Roanoke, VA, using high-frequency sensors and manual monitoring. CCR is the primary supply reservoir for the Western Virginia Water Authority, which provides water to ~300,000 southwestern Virginians. Two years of high-frequency data revealed seasonal variation in fluorescent DOM concentrations, with increases during spring and fall mixing. The sensor data were complemented by monthly measurements of DOM in the reservoir’s inflows. Data from our samples reveal increases in terrestrial-associated compounds during fall and spring.

We expanded water quality monitoring at CCR during and after Ironman triathlons in June 2021 and 2022. Swimming was not allowed in CCR before or between the Ironmans, providing a unique opportunity to track the effects of ~1600 swimmers on water quality. We sampled for several PPCPs (acetaminophen, triclosan, and caffeine) within a month of the race. We found PPCP concentrations to vary both spatially and temporally (range: <0.1 – >50 ug/L). We saw increases in acetaminophen the day of the race, and detectable caffeine throughout the sampling period. We hypothesize swimmers may introduce some of these compounds to the reservoir through urine or soap residues on skin or clothing. Despite increases in PPCPs, concentrations remained below levels of concern to human health. Altogether, our work demonstrates the importance of monitoring organic matter to understand the effect of these compounds on drinking water quality and ecosystem functioning.