Geochemical and Sedimentary Record of Urbanization and Industrialization of the Galveston Bay Watershed

Galveston Bay (GB) is the second largest estuary in the Gulf of Mexico, with the watershed containing one of the largest concentrations of petroleum and chemical industries globally, particularly within the lower 15 km of the San Jacinto River/Houston Ship Channel (SJR/HSC). Throughout the last century, extensive groundwater extraction to support these industries and an expanding population has resulted in significantly enhanced land subsidence (0.6-3.0 cm yr^-1). In order to examine the impacts of these anthropogenic alterations to the system, 22 vibracores were collected throughout the bay and analyzed for ²¹⁰Pb and ¹³⁷Cs radioisotope geochronology, X-radiography, grain size, X-Ray Fluorescence, Hg concentration, lignin phenol concentrations, and stable isotopes (δ¹³C and δ¹⁵N). The sedimentation rates from these cores were used to determine historical input of trace metals and organic matter sources. Results indicate sedimentation rates are relatively higher (1.4-1.9 cm yr^-1) in areas with elevated Relative Sea Level Rise (RSLR). However, in general, sedimentation rates are lower (as much as 50%) than RSLR, indicating that sediment accumulation has not kept pace with land subsidence. Hg core profiles show significant input of Hg beginning around 1900, with peak concentrations in the 1960-70’s, and decrease thereafter. Surficial Hg concentrations were found to be significantly higher proximal to the SJR/HSC, and decrease seaward. Preliminary results of stable isotopes and lignin phenols show there is a significant terrestrial input of organic matter, and the provenance has shifted from being marine to terrestrial dominated. Due to the industrial and residential importance of the GB watershed, these results not only increase our knowledge of the fate and transport of organic biomarkers, Hg, and other particle bound contaminants under varying sedimentation regimes, but aid in local environmental management strategies to minimize impact to public health.