River Discharge and Environmental Stress in Galveston Bay and the Guadalupe Estuary, Texas

Loading of nutrients and organic carbon affect many aspects of plankton communities, which include primary production, community respiration and microbial loop interactions. Furthermore, manipulation of inflows may serve as a management tool designed to influence lower food web interactions. The purpose of this study was to understand the freshwater inflow impact on the spatial and temporal plankton dynamics. To achieve this we examined spatial and temporal characterizations of the pelagic environment in two bay systems of Texas, Galveston Bay and the Guadalupe Estuary. Characterizations included water quality parameters (temperature, salinity, oxygen saturation and turbidity etc.), nutrients, dissolved organic carbon, net productivity and respiration. All of these parameters were measured monthly (from Jan 2005 to Aug 2006) at 6 stations in Galveston Bay and 7 stations in the Guadalupe Estuary. Our preliminary analyses showed that light penetration was positively correlated with freshwater discharge, where the relationship became stronger at stations located closer to the point of river discharge. Also correlated with discharge was dissolved inorganic nitrogen and phosphate concentrations, where the N:P ratio was ~10. Dissolved organic carbon, however, showed no obvious temporal variation throughout these two ecosystems, but the spatial variations related to the distance from the point of river discharge. In addition, primary productivity showed no relationship with river discharge or nutrients, which suggests that other factors might be important, such as temperature. We are currently analyzing plankton community shifts in response to discharge.