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 coefftcients 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. Diffise attenuation coefficients in the 1989 data ranging from 1 to 10 m-l 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.

Characterization of both the source materials and the bottom sediments of an estuary by magnetic characters, on a particle size basis, allows the source of the bottom sediments to be determined and indicates a shift in sediment sources, corresponding to changing land-use patterns. The major source of the sediments in the lower part of cores from the middle of the estuary is eroding shorelines. Soil-derived particulates, from the uplands, dominate the upper part of the cores. This change in source occurred in the early part of the 19th century. The magnetic character of the most recent sediments suggests a progressive depletion, through time, of the upland soils in the finest fractions.

There was a net influx of suspended particulate matter to the uppermost part of the Rhode River estuary during the several years of this study. Most of the influx was due to episodic discharges of suspended sediment from the watershed during heavy rains. In contrast, tidal exchange of particulate matter was not related to rainstorms. Sediment composition data and historical records indicate that marsh accretion accounts for only 13% of the sediment trapping although marshes occupy 60% of the study area. Influx of particulate matter to the marshes is directly related to the amount of time they are submerged during tidal cycles.

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