Influence of discharge on long-term dynamics of abiotic and biotic resources in Lavaca Bay, Texas




Harris, Elizabeth

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Long-term ecological condition monitoring studies have revealed benthic community dynamics (abundance, biomass, and diversity) to be in a state of decline in Lavaca Bay, Texas since 1988. Previous research has identified temporal variability (climate, inflow, and season) to best explain benthic community declines within Lavaca Bay, but researchers fear there may be more to the story than meets the eye. Researchers, stakeholders, and the public call for action to best determine possible mechanisms (i.e., anthropogenic and/or natural environmental stressors) that influence biological trends within Lavaca Bay, Texas. The current study aimed to use long-term environmental monitoring data to 1) identify possible anthropogenic and/or natural environmental stressors that may account for observed biological community trends and 2) determine if these ecological trends indicate an un-healthy environment. Data from Formosa Plastics Corporation (FPC) and the United States Geological Survey was used in the analyses for this thesis study. The FPC dataset is a long-term monitoring dataset with fixed point sampling at 19 stations with measures by four different primary contractors during their respective years of employment. Data collection occurred quarterly at each station for 27 years. Samples were collected for biological, hydrographical, porewater, and sediment parameters. All parameter trends changed over time due to climate, freshwater inflow events, and/or seasonal changes rather than the influence of distance from the discharge pipeline, except for sediment quality parameters. Presence of discharge effluent has been found as a driving force for sediment quality. Additionally, both reference stations (natural background) and impact stations (near the discharge point) presented similar hydrographical and biological trends, except for sediment trends. A total of 99.9% of 424,671 measurements of organic contaminants were non-detectable because the methods were insensitive to ambient concentrations. So, it is still not known if contaminants play a role in the long-term decline of benthos. Because a contamination “marker” was not identified in the FPC study and contractor methods changed or were inadequate to detect contaminants throughout the study, it is possible that trends at reference stations were insufficiently representing the overall natural background of Lavaca Bay. In addition to using chemical methods with high detection limits, only four reference stations were sampled, and were all 3,810 m from the discharge site. So, while there were no differences between discharge and reference stations, it is possible that ecological trends observed in the FPC study reference stations do not represent the natural background of Lavaca Bay.



abiotic, biotic, contamination, discharge, Lavaca Bay, long-term monitoring



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