Contributions of suspended particulate matter and dissolved color to light attenuation and trends in water clarity among mid-latitude reservoirs

Bukaveckas PA, Barnett J, Cameron A. 2026. Contributions of suspended particulate matter and dissolved color to light attenuation and trends in water clarity among mid-latitude reservoirs. Lake Reserv Manage. XXX–XXX.Reservoirs account for almost half of all lakes in the conterminous United States and are the dominant lake type in the southeastern United States. Reservoirs are optically complex systems in which diverse factors affect water clarity, including both algal and non-algal suspended particulate matter, as well as dissolved color. Data obtained from 7 reservoirs in central Virginia were used to partition the effects of suspended particulate matter and dissolved color on light attenuation. Their relative importance differed among ecoregions as dissolved color was the dominant component of light attenuation in Coastal Plain lakes, whereas suspended particulate matter was the largest contributor to light attenuation among Piedmont lakes. Multidecadal Secchi data from over 100 Virginia reservoirs were used to assess status and trends in water clarity. Although phytoplankton were a minor component of suspended particulate matter, chlorophyll a (Chl-a) was an important predictor of interlake, seasonal, longitudinal and long-term variation in water clarity. Our findings show that although algae are a small contributor to suspended particulate matter, the large spatial and temporal variation in Chl-a (relative to chromophoric dissolved organic matter and total suspended solids) increases their importance in explaining variability in light attenuation.