Assessment of Drivers of Water Clarity in Virginia Reservoirs

Water clarity is ecologically important in aquatic ecosystems, as reduced light penetration is associated with submerged aquatic vegetation declines and algal abundance increases. Clarity is often impaired by excess sediments associated with land disturbance, or increased algal presence due to nutrient overabundance. We measured total suspended solids (TSS), chlorophyll-a (CHLa), and chromophoric dissolved organic matter (CDOM) in seven Virginia reservoirs to better understand their roles in regulating light attenuation (kd). Among study sites, there was an average kd of 1.85 m^-1 with values in the range of 0.57 to 4.04 m^-1. The photic depths of sites were between 1.14 and 8.10 m with an average of 2.48 m across sites. CDOM was the best predictor of kd across sites (R² = 0.66), accounting for 35.4% ± 0.03% of attenuation on average. Residual variation after removing CDOM effects, was strongly correlated with TSS (R² = 0.96). We estimate that, on average, TSS accounts for 52.8% ± 0.01% of light attenuation across sites. CDOM accounts for 33.3% more attenuation in Coastal Plain sites when compared to Piedmont lakes. Conversely, TSS accounts for 26.1% more attenuation in Piedmont sites than in Coastal Plain lakes. Greater topographic variation and sediment yields in Virginia's Piedmont region may explain the strong influence of TSS on lake clarity in this region. In contrast, CHLa has insignificant effects on attenuation across sites, suggesting clarity is primarily driven by natural processes like organic leaching, and by sediment transport, rather than algae abundance.

Presentation Preference: Oral

Primary Presenter: Jackson Barnett, Virginia Commonwealth University (barnettj8@vcu.edu)

Authors:

Paul Bukaveckas, Virginia Commonwealth University  (pabukaveckas@vcu.edu)