Water clarity is a key parameter for monitoring water quality and often used to assess habitat suitability for submerged aquatic vegetation (SAV). Light attenuation, a measure of water clarity, is impacted by colored dissolved organic matter (CDOM), and by suspended particulates which include living and non-living components. We anticipated that the relative importance of these factors in regulating light attenuation would vary among the upper portions of three sub-estuaries differing in morphometry, hydrology, and degree of human influence. The James is characterized by eutrophic conditions and high algal abundance, whereas the Mattaponi and Pamunkey exhibit lower phytoplankton production. The Mattaponi and Pamunkey have extensive floodplains, which likely serve as sources for CDOM. We measured light attenuation, turbidity, total suspended solids (TSS), chlorophyll a (CHLa), dissolved organic carbon (DOC), and CDOM over a 3-year period at sites within each estuary. These parameters, along with discharge, were analyzed to identify factors regulating light attenuation. The Mattaponi and Pamunkey exhibited greater light attenuation than the James. Turbidity and TSS were the strongest predictors of variation in light attenuation at all sites. CHLa was not found to be a significant predictor of light attenuation at any of the sites. Light scattering per unit of suspended particle mass was twice as high in the James compared to the other rivers despite similarities in suspended particle size and mass. Linear statistical models based on suspended solids and dissolved organic matter accounted for 64-93% of the range of variation in light attenuation. Understanding factors that regulate light attenuation is important when considering management activities intended to improve estuarine water clarity and SAV habitat
