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Galveston Bay is the second largest estuary along the northern Gulf of Mexico coast, with a watershed containing one of largest concentrations of petroleum and chemical industries globally, as well as Houston, the fifth largest metropolitan area in the USA. 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 ). The highest subsidence rates observed in the bay are within the lower 15 km of the San Jacinto River/Houston Ship Channel region (SJR/HSC), with distal areas in East and West Galveston Bays having subsidence rates on the order of 0.2 cm yr −1 . In order to investigate the impacts of subsidence on sedimentation, a series of 22 vibracores were collected throughout the bay, and 210 Pb and 137 Cs radioisotope geochronologies and grain size distributions were determined. Sediment accumulation rates are highest (1.9 ± 0.5 cm yr −1 ) in the SJR/HSC, and decrease (<0.6 cm yr −1 ) both seaward and towards low subsidence regions. These results indicate sedimentation rates are significantly (p < 0.01) higher in areas with elevated Relative Sea Level Rise (RSLR). However, throughout most of Galveston Bay sedimentation rates are lower (as much as 50%) than estimated RSLR, indicating a sediment accretionary deficit. In areas (e.g., Scott Bay) within the SJR/HSC, the bay has deepened by more than 1.5 m, suggesting that sediment accumulation cannot keep pace with RSLR. Ultimately, this has resulted in a loss of coastal wetlands and a conversion of marine habitats from relatively shallow to deeper water settings. [ABSTRACT FROM AUTHOR]

Hurricane Harvey (Harvey), a slow-moving storm, struck the Texas coast as a category 4 hurricane. Over the course of 53 days, the floodwaters of Harvey delivered 14 × 109 m3 of freshwater to Galveston Bay. This resulted in record flooding of Houston bayous and waterways, all of which drained into the San Jacinto Estuary (SJE,) with its main tributaries being Buffalo Bayou and the San Jacinto River. The lower SJE and lower Buffalo Bayou has experienced up to 3 m of land subsidence in the past 100 years and, as a result, prior to Hurricane Harvey, up to 2 m of sediment within the upper seabed contained an archive of high concentrations of Total Hg (HgT) and other particle-bound and porewater contaminants. Within the SJE, Harvey eroded at least 48 cm of the sediment column, resulting in the transport of an estimated 16.4 × 106 tons of sediment and at least 2 tons of Hg into Galveston Bay. This eroded sediment was replaced by a Harvey storm deposit of 7.73 × 106 tons of sediment and 0.96 tons within the SJE, mostly sourced from Buffalo Bayou. Considering that the frequency of slow-moving tropical cyclones capable of delivering devastating rainfall may be increasing, then one can expect that delivery of Hg and other contaminants from the archived sediment within urbanized estuaries will increase and that what happened during Harvey is a harbinger of what is to come. Unlabelled Image • Hurricane Harvey caused massive flooding of the San Jacinto Estuary (SJE). • Harvey eroded/deposited 16.4 × 106/7.73 × 106 tons of sediment from SJE. • Eroded sediment sourced at least 2/3.9 tons of Hg from SJE/Buffalo Bayou. • Main source of Hg is an industrial wastewater outfall in Patrick Bayou. • The Harvey deposit in the SJE contains ~1 ton of Hg sourced from Buffalo Bayou. [ABSTRACT FROM AUTHOR]