Long-term Trends in Lavaca-Colorado and Guadalupe Estuaries




Montagna, Paul


Journal Title

Journal ISSN

Volume Title




The purpose of the current project was to determine if the long-term decline in bottom-dwelling invertebrates are still occurring and if pollution from the Formosa discharge into Lavaca Bay may be the cause of the decline if it is still occurring. The primary focus was on water and sediment quality of the Lavaca Bay ecosystem. Four tasks were performed: 1) Analyzed archived benthic samples. 2) Synthesized existing monitoring data from the Texas Parks and Wildlife Department, Coastal Fisheries Program (TPWD). 3) Synthesized existing water and sediment quality monitoring data of the Formosa Plastics Corporation discharge site into Lavaca Bay. 4) Data management, reporting, and outreach.

In the long-term benthic dataset, the bay systems have different long-term characteristic fauna that reflects the long-term average salinity conditions in each bay system. The Lavaca-Colorado Estuary has on average about 37% more inflow than the Guadalupe Estuary, and 11 times more than the Nueces Estuary. San Antonio Bay is small and limited exchange with the Gulf of Mexico, therefore it has lower long-term average salinity than Lavaca Bay. The San Antonio Bay community has a higher contribution of mollusks, which are freshwater indicators, than Lavaca Bay, and much higher than Nueces Bay. Within the estuary systems, the secondary bays have distinct communities compared to the primary bays. This is because secondary bays are closer to freshwater inflow sources and are more oligohaline and/or brackish in nature than primary bays, which are more marine influenced.

In the Formosa dataset, all parameter trends changed over time due to climate, freshwater inflow events, and/or seasonal changes. Biological community structure and sediment changed with distance from the discharge site. Dominance characterized community structure because three to four taxa comprised >70% of individuals for nekton (trawl and gill net), phytoplankton, zooplankton, and ichthyoplankton samples. Sediment became sandier over time (48% to 75%) and away from the discharge. Surface water and porewater at reference (R) stations and stations near the discharge site had similar hydrographical and biological trends over time, indicating no long-term impact due to the discharge. However, 99.9% of 424,671 measurements of organic contaminants were non-detectable because the methods were insensitive to ambient concentrations.

There is an inconsistency between the HRI and Formosa benthic data, in that the HRI data is still declining, but the Formosa data has remained constant over time. Similar trends are true for the TPWD trawl data and the Formosa trawl data. In conclusion, it is still not known if contaminants play a role in the long-term decline of ecosystem health in Lavaca Bay. Furthermore, only four R stations were sampled, and were all 3,810 meters from the discharge site, so it is possible that trends in R stations do not represent the natural background. Future studies should include more R stations and lower detection limits for contaminants.






Montagna, P.A. 2022. Long-term Trends in Lavaca-Colorado and Guadalupe Estuaries. Final Report to the Matagorda Bay Mitigation Trust, Contract 011. Texas A&M University-Corpus Christi, Corpus Christi, Texas, 15 pp.