Effects of Freshwater Inflow and Tides on Water Quality of the Brazos River Estuary

The State of Texas is currently in the process of validating environmental flow recommendations in an effort to maintain sound ecological environments in rivers and estuaries.  It is assumed that the primary mechanism regulating production in estuaries is the discharge of freshwater which creates an optimal salinity gradient influenced by freshwater inflow and tidal forces.  The objectives of this study were to 1) characterize the flow regime and 2) assess the influence of freshwater inflow and tidal movement on water quality in the lower Brazos River.  Continuous and opportunistic samples were collected from November 2014 to May 2015.  Nine sampling events were distributed across the hydrograph during base flow conditions with several events occurring following high flow pulses.  Broad-scale patterns in water quality gradients depended upon the timing, magnitude and duration of freshwater inflow events.  Salinity levels were inversely related to freshwater inflow and predictable trends in the tidal wedge location relative to the size of the inflow event were defined.  Continued monitoring of water quality and flow along with the integration of biological community data will help resource managers better understand the influence of freshwater inflow on biota and plan for the freshwater needs of the Brazos River estuary.