The relative importance of chlorophyll and colored dissolved organic matter (CDOM) to the prediction of the diffuse attenuation coefficient in shallow estuaries

The availability of underwater tight is a critical factor in the growth and abundance of primary producers in shallow embayments. The goal of this study was to examine the relative importance of factors influencing tight availability in this type of water body. Many simulation models of aquatic ecosystems predict tight attenuation from chlorophyll or phytoplankton stock. In the three southern New England sites studied here, no useful relationship was found to exist between chlorophyll and K-PAR (the diffuse attenuation coefficient of photosynthetically active radiation; Kirk 1994; Mobley 1994). In 40 of 53 cases, a regression of chlorophyll versus K-PAR was not statisticatly significant. Variation in K-PAR did demonstrate a correlation to salinity, implicating a freshwater source of light attenuating material. This was true even in a system with little freshwater inflow. Colored dissolved organic matter (CDOM) is one such terrestrial input that enters estuaries from their watersheds and can strongly influence the availability of light to aquatic primary producers. This study demonstrated that over 70% of the variability in the K-PAR coefficient can be attributed to CDOM in the shallow estuaries studied. This illustrates the need for improved model formulations that include CDOM in the prediction of light attenuation in shallow coastal systems. A new equation has been developed to predict K-PAR with CDOM.