Texas Natural Resource Damage Assessment (NRDA): Essex Bayou Habitat Restoration

Essex Bayou and the Slop Bowl marsh are part of the Brazoria National Wildlife Refuge in Brazoria County, Texas. The project site is located in the southwestern portion of the refuge near to the Gulf of Mexico and the community of Surfside, Texas. The tidal marsh systems within this region have historically high rates of relative sea level rise (RSLR). The project site exhibits several geological growth faults that are likely associated with nearby salt domes and/or activities related to oil and gas development. Additional hydrologic modifications associated with the marsh complex include man-made channels such as the Intracoastal Waterway and access channels which have modified hydrology and geomorphic processes. These wetlands experience wide swings in salinity and tidal reach. Initial assessments suggest that modifications to the watershed, flow restrictions in Essex Bayou, and diversions of tidal flow were responsible for extreme salinity conditions. Periods within these wide swings of salinity can produce high biological diversity and productivity, however swings into each extreme salinity condition causes changes to existing vegetation that biologically and structurally destabilize the system. High salinities cause considerable vegetation damage and allow for only a few species of estuarine organisms to survive. These high salinity levels cause high mortality of wetland plants, invertebrates, and fish species. These conditions result in poor foraging habitat for birds, fish, and other vertebrate species. In the drier, summer months, salinities of 150 parts per thousand, almost five times that of open ocean water, have been documented. To identify the best method to protect and/or restore these wetland habitats, this project will build on previous lessons learned by evaluating existing site conditions. Previous efforts have included an assessment of shoreline change as well as identification of pipeline rights-of-way, potential fault lines, grazing activity, tidal elevations, elevations at critical locations, and watershed diversions. This project will further evaluate the processes responsible and propose solutions to ameliorate extreme salinity conditions. Data collection will include bathymetric/topographical surveys, growth fault analyses, hydrologic and tidal flow evaluations, magnetometer surveys, and soil borings. The UK component will focus on the collection of sediment cores from 8-10 stations sampled in 2018. These stations will be selected to determine typical vertical accretion rates in these wetlands, and to investigate possible relationships between active growth faulting and surface elevation change. All cores will be characterized for fallout radionuclides (137Cs, 210Pb), sedimentological properties (grain size, POC), and will have a sub-set of samples dated using radiocarbon (14C). Specifically, the approach will provide information critical to address questions including: ~ How do typical vertical accretion rates in these wetlands compare to rates of RSLR? ~ Have any of the growth faults in these wetlands been historically active (~100 years)? ~ Is there evidence that recently or currently active growth faults are influencing rates of vertical accretion, subsidence and RSLR? This research will inform the design and possible implementation of a major coastal restoration program. It will support and provide research experiences to multiple undergraduate students, and research staff. Results will be widely disseminated to the scientific community and public via presentations at professional meetings and the development of peer-reviewed publications.