Benthic infaunal long term response to wastewater diffuser discharge in Lavaca Bay, Texas

The Lavaca-Colorado Estuary (LCE) is one of seven major estuarine systems located on the Texas coast. As the second largest estuary in Texas, the LCE provides local and statewide residents with industrial, recreational, and agricultural benefits and historically known to be an abundant and diverse ecosystem for marine organisms. Previous studies have shown there has been long-term decline in benthic abundance, biomass, and diversity in the LCE since 1988. A more recent study found that in fact there was a long-term increase in benthic abundance, biomass, and diversity in the LCE since 1993. Multiple stressors, natural and anthropogenic in origin, are affecting biological community structure. Therefore, these stressors are transforming ecosystems. The purpose of this research is to continue the previous studies to determine if long-term diffuser discharge has any effect on benthic infauna communities in the sediment of Lavaca Bay. This thesis analyzes a 29-year long-term monitoring/time series dataset that was designed to evaluate the impact a discharge pipeline had on constituents of ecological and biological conditions in Lavaca Bay. The purpose of this study was to answer environmental questions about Lavaca Bay. The primary question is: Does the industrial discharge affect the ecological health of Lavaca Bay? If so, are the benthos being affected more near the diffuser site, or is the effect constant throughout the bay? The overall goal was to perform an analysis to determine which parts of the bay are being most affected and to reach conclusions about the overall bay health. Bay health can be indicated by a decline in benthic integrity (i.e., diversity), decreased survival rates of organisms exposed to sediments, and sediment chemical contaminant concentrations over threshold limits. The results revealed that industrial discharge does affect ecological health in localized areas near the outfall. Sediment characteristics closest to the outfall had higher combinations of silt and clay, possibly due to diffuser outflows disturbing the sediment and increasing turbidity. The water column had lower pH, temperature, and DO closer to the outfall. Survival predictions showed an increase over time suggesting that the diffuser does not negatively affect the survival rates of the benthic communities within the bay. However, benthic community diversity means were higher as distance increases away from the outfall. Therefore, even though the diffuser isn’t negatively affecting the overall benthic bay health, it has a negative local effect when compared to stations further away from the outfall area.