Assessing freshwater inflows to the hypersaline lower Laguna Madre Estuary of Texas using spectral radiometry, aerial videography, and in situ physicochemistry

Abstract

The Lower Laguna Madre is a biologically productive, subtropical, hypersaline estuary on the southern Texas Coast. Its shallow waters tend to be relatively clear, over extensive seagrass beds that serve as important nursery areas for many Gulf of Mexico species and as food for the largest wintering population of redhead ducks (Aytha americana) in North America. The Arroyo Colorado and its distributary arm, the North Floodway, are the only two freshwater streams entering the Lower Laguna Madre. Both streams are turbid and deliver significant particulate, nutrient, and chlorophyll/pheophytin loads to the estuary. Water reflectance, airborne videography, and in situ physicochemical data were acquired from two above-tidal and two tidal stations in the Arroyo Colorado and from one station in the estuary, at the confluence of the Arroyo Colorado with the Gulf Intracoastal Waterway, during the summer of 1995. Analysis of the spectral data, collected imagery, and physicochemistry confirm that near-surface chlorophyllous aggregates (chlorophyll a and pheophytin) can be imaged, yielding both qualitative and quantitative results. Correlation coefficients greater than 0.90 were obtained when digital data from specified spectral bands and band ratios were compared to chlorophyll a, total suspended solids and total dissolved solids concentrations. Results demonstrate the potential of rapid airborne video image acquisition for detecting and mapping effluent discharges into rivers and estuaries. Video remote sensing could be used for environmental monitoring by government agencies, managers, planners, and others making decisions about land and water use, disposition, and development.