Globally, hypoxic areas (\63 mmol O 2 m -3 ) in coastal waters are increasing in number and spatial extent. One of the largest coastal hypoxic regions has been observed during the summer in the bottom-water of the Louisiana continental shelf. The shelf receives the sediments, organic matter, and nutrients exported from the Mississippi River watershed, and much of this material is ultimately deposited to the sea floor. Hence, quantifying the rates of sediment-water dissolved inorganic carbon (DIC), oxygen (O 2 ), and nutrient fluxes is important for understanding how these processes relate to the development and maintenance of hypoxia. In this study, the sediment-water fluxes of DIC, O 2 , nutrients, and N 2 (denitrification) were measured on the Louisiana shelf during six cruises from 2005 to 2007. On each cruise, three to four sites were occupied in or directly adjacent to the region of the shelf that experiences hypoxia. DIC fluxes, a proxy for total sediment respiration, ranged from 7.9 to 21.4 mmol m -2 day -1 but did not vary significantly either spatially or as a function of bottom-water O 2 concentration. Overall, sediment respiration and nutrient flux rates were small in comparison to water-column respiration and phytoplankton nutrient demand. Nitrate fluxes were correlated with bottomwater O 2 concentrations (r = 0.69), and there was evidence that decreasing O 2 concentrations inhibited coupled nitrification-denitrification. Denitrification rates averaged 1.4 mmol N m -2 day -1 . Scaled to the area of the shelf, the denitrification sink represented approximately 39% of the N load from the Mississippi River watershed. The sediment-water fluxes reported from this study add substantial information on the spatial and temporal patterns in carbon, O 2 , and nutrient cycling available for the Louisiana continental shelf and, thus, improve the understanding of this system.

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Land use and land cover (LULC) can affect the watershed exports of optically active constituents such as suspended particulate matter and colored dissolved organic matter, and in turn affect estuarine optical properties. We collected optical data from six estuaries in the northeastern Gulf of Mexico with different watershed LULC characteristics and investigated how estuarine optical properties varied across these systems. Differences in LULC corresponded with significant differences in the estuarine inherent optical properties and specific inherent optical properties (SIOPs), which are known surrogates for phytoplankton cell size, organic particle concentration, and the amount of terrigenous dissolved organic carbon. The results indicated that increasing proportions of developed land use (urban 1 agriculture) in the watersheds resulted in a linear increase in light attenuation in the estuaries primarily through increased absorption by phytoplankton. Estuarine SIOPs were also linearly related to the proportion of developed land. These findings were used to demonstrate how improved knowledge of the factors regulating estuarine SIOPs may be used to increase the accuracy of semianalytical ocean color remote sensing algorithms in optically complex estuaries.