Enhanced Land Subsidence and Seidment Dynamics in Galveston Bay- Implications for Geochemical Processes and Fate and Transport of Contaminants

Galveston Bay is the second largest estuary in the Gulf of Mexico. The bay?s watershed and shoreline contains one of the largest concentrations of petroleum and chemical industries in the world, with the greatest concentration within the lower 15 km of the San Jacinto River/Houston Ship Channel (SJR/HSC). Extensive groundwater has been withdrawn to support these industries and an expanding population has resulted elevated land subsidence, with the highest land subsidence in the lower SJR/HSC, of over 3 m (3 cm yr^-1) and has decreased seaward throughout the bay to 0.6 cm yr^-1 near Galveston Island. Mercury (Hg) contamination is well documented throughout the bay?s sediments. Sediment vibra-cores were collected throughout the bay systems. 210Pb and 137Cs geochronologies from these cores was used to determine sedimentation rates and correlated to Hg profiles to estimate input histories. Relative Sea Level Rise (RSLR) is the sum of eustatic sea level rise and land subsidence. The results show sedimentation rates are high in areas with high rates of RSLR and the rates are of the same order of magnitude, however, in general, sedimentation rates are as much as 50% of RSLR, indicating that sedimentation has not kept pace with land subsidence, although they have the same relative order. Hg core profiles were correlated with radioisotope geochronologies and show significant input of Hg beginning around 1940, with a peak around 1971, and a dramatic drop off in concentration afterwards, demonstrating it to be a valuable geochronology tool. Hg concentrations were found to be dramatically higher proximal to the SJR/HSC and progressively decreasing seaward and to distal parts of the bay.