Monitoring Mid-Coastal Estuaries - 2016

In recognition of the importance that the ecological soundness of our riverine, bay, and estuary systems and riparian lands has on the economy, health, and well-being of our state, the 80th Texas Legislature enacted Senate Bill 3 (SB3, 2007), which requires an ecosystem management approach to provide environmental flows “adequate to support a sound ecological environment and to maintain the productivity, extent, and persistence of key aquatic habitats.” Thus, there is a continued need for monitoring information about freshwater inflow effects on water and sediment quality and biological indicator communities to provide adaptive management of environmental inflow standards for Texas estuaries. The purpose of the present study is to extend the long-term biological collection of benthic data in San Antonio Bay (Guadalupe Estuary), Lavaca and Matagorda Bays (Lavaca-Colorado Estuary), and Nueces and Corpus Christi Bays (Nueces Estuary). Bottom-dwelling organisms are ideal bioindicators of freshwater inflow effect on bays and estuaries because they are fixed in space, and integrate ephemeral processes in the over-lying water column over long periods of time. Only benthic samples from the Guadalupe Estuary have been analyzed, and the benthic data has demonstrated that long-term hydrological cycles, which affect freshwater inflow and water quality, also regulate benthic abundance, productivity, diversity, and community structure. In addition, changes in water quality due to inflow variability were measured in all three estuaries, including chlorophyll (as an indicator of primary production), inorganic nutrients, dissolved and particulate organic matter (DOM and POM), and the carbonate system variables alkalinity, dissolved inorganic carbon (DIC), and pH. The estuaries respond rapidly to freshwater inflow variability, displaying higher inorganic nutrient and chlorophyll concentrations during high inflow, low salinity conditions. Dissolved organic carbon and nitrogen concentrations were consistently high in the estuaries, providing an important source of matter fueling microbial growth. The dissolved organic matter concentration was influenced by freshwater inflow variability in Lavaca-Colorado and Nueces Estuaries, but not in the Guadalupe Estuary. Carbonate saturation state, an important indicator for the suitability of calcifying organisms (shellfish etc.), changed with both river endmember chemical composition and the extent of freshwater inflow. The northern Lavaca-Colorado Estuary showed carbonate undersaturation following a significant freshwater discharge period, although the southern estuaries were less influenced by the hydrological change.