MODELING, MEASUREMENTS, AND SATELLITE REMOTE-SENSING OF BIOLOGICALLY-ACTIVE CONSTITUENTS IN COASTAL WATERS

We examine ways of addressing coastal environmental quality concerns t hrough the use of modeling, measurements, and in the future, satellite remote sensing. In a summary of historical trace-metal concentrations in the waters of Narragansett Bay, we partitioned the estuary into se ctors that reflect the morphology of the Bay and the transition betwee n freshwater inputs and offshore coastal waters. We constructed a 24-b ox two-layer model of the Bay. A convenient summary of the chemical va riations in the Bay was provided by a schematic diagram which for a co nstituent such as copper or other metals displays the average concentr ation, the range, the standard deviation, and the number of observatio ns in our database for each sector. This diagram shows the spatial gra dients through the Bay and the variability within a sector. Using a si mple two-layer box model with seven transport terms we computed the ph ysical exchanges between boxes using freshwater input and salinity dat a The box model approach was applied in greater detail to the upper po rtion of Narragansett Bay to provide transport terms for use in an oxy gen water quality evaluation. A digital bathymetric map of the estuary was compiled to enable volume-weighted calculations of physical and c hemical properties. A seasonally variable data set was available to de termine the effects of summer/winter and high-/low-runoff conditions o n the oxygen concentrations of the waters. Using the freshwater input rates and the observed salinity distribution in the estuary we calcula ted the transport of waters between boxes and the residence times of w ater within each box. The model was applied to oxygen concentrations i n the estuary incorporating estimates of the effects of air-sea exchan ge, of sediment oxidation demand, of photosynthetic production and res piratory consumption, and of biochemical oxygen demand from sewage tre atment effluents. The model provides a basis to estimate the relative importance of various processes that may cause low oxygen conditions i n the waters. An investigation of oxygen variations in coastal waters was conducted with an Endeco/YSI rapid-pulse dissolved oxygen electrod e. A 30-day time series was obtained at a depth of 1-2 m in Narraganse tt Bay. Measurements of oxygen, temperature, and salinity were obtaine d every 30 min during October 1993. Fourier analyses were used to dete rmine the frequencies in the oxygen, temperature, and meteorological ( wind speed and sunlight levels) variables. There was a strong diel sig nal in oxygen with smaller amplitude variations at the semidiurnal tid al frequency and a large amplitude variation with a period of 3-5 days . High temporal resolution data are needed to detect the events in coa stal waters that result in substantial chemical variations of biologic ally active constituents such as oxygen. In anticipation of possible a pplications of the next generation ocean color satellite sensor, SeaWi FS, we have been examining the historical CZCS data from the region of f the northeastern U.S.A. We have worked with both the 4-km and the l- km horizontal resolution CZCS data. The scales of variability that are evident are in the range of 5-50 km. For quantitative use of the ocea n color data attention must be given to spatial variations in the atmo spheric attenuation of the visible radiation, and to the separation of chlorophyll, suspended matter, and possibly blue-absorbing organic ma tter in the ocean color signal.