Hypoxia Formation Along Coastal Texas Due to Brazos River Flooding: Summer 2007
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Record setting rainfall over Texas during MayaAugust 2007 led to unseasonably large summer freshwater discharge of the Brazos River into the Gulf of Mexico. A National Marine Fisheries Service cruise in late June 2007 showed a plume of hypoxic near-bottom oxygen concentrations (less than 2.0 mg/l) extending from the Brazos River mouth southwestward along the Texas coast to Matagorda Bay. Subsequent nearshore observations along the Texas coast in July showed persistently low dissolved oxygen and highly stratified conditions. In August, a four-vessel survey was conducted to provide estimates of the spatial distribution of water column stability, dissolved oxygen, organic material, particulate, chlorophyll, and nutrient concentrations between Galveston and Matagorda Bay, Texas. Low dissolved oxygen concentrations were correlated with freshwater capping. High surface silicate was coincident with large diatom numbers. Bottom nutrient concentrations were consistent with remineralization processes. Coastal observations on 18 September show the Texas hypoxic region was dissipated by mixing resulting from winds associated with Hurricane Humberto. Analysis of recent water quality data indicates that Texas coastal hypoxia may be more frequent than previously thought.