MODELING SPECTRAL DIFFUSE ATTENUATION, ABSORPTION, AND SCATTERING COEFFICIENTS IN A TURBID ESTUARY

Spectral diffuse attenuation coefficients were measured in the Rhode River and Chesapeake Bay, Maryland, on 28 occasions in 1988 and 1989. The model of Kirk was used to extract scattering and absorption coefficients from the measurements in waters considerably more turbid than those in which the model was previously applied. Estimated scattering coefficients were linearly related to mineral suspended solids. Estimates of total absorption coefficients were decomposed as the sum of contributions by water, dissolved organic matter, phytoplankton chlorophyll, and particulate detritus, each having a characteristic spectral shape. The 1988 data were used to develop a model of scattering and absorption coefficients based on the specific curves regressed against water-quality parameters. Diffuse attenuation coefficients in the 1989 data ranging from 1 to 10 m-1 and photic depths ranging from < 1 to 4.5 m were predicted with a C.V. of about 25%. The problem of estimating concentrations of water-quality constituents from optical measurements was indeterminate due to the similarity in shape of the specific curves of dissolved substances and depigmented particulates. Chlorophyll concentration could be estimated because it was strongly related to water-corrected absorption in the 670-nm waveband, but several outliers occurred due to biological variability in specific absorption of pigments.