Spatial distribution and historical trends of mercury in Matagorda Bay sediment

Matagorda Bay, a shallow, microtidal estuarine system, located along the northwestern Gulf of Mexico/Texas coast, faces considerable challenges due to natural events and anthropogenic activities, leading to the resuspension and dispersal of sediment and pollutants within the water column. Here, we reconstructed historical trends and the spatial distribution of total mercury (T-Hg) concentrations in surface and subsurface sediment across the bay using 49 vibra-cores collected between 2021 and 2023. Bulk and clay-normalized T-Hg concentrations revealed a localized contamination hotspot near the ALCOA-Point Comfort chloralkali facility in Lavaca Bay with peak concentrations reaching 983.7 ng g^-1. T-Hg concentrations decreased with increasing distance from Cox Bay, identifying the chloralkali facility as the dominant point source, though additional inputs from wastewater discharge and agricultural runoff contribute to Hg enrichment in other parts of the bay. Downcore trends suggest that industrial point sources are the dominant contributor to T-Hg loading in the region, with limited influence from fluvial sources. Despite a fast recovery time and recent cleanup efforts, portions of the bay continue to contain significant T-Hg concentrations. While recent declines in T-Hg concentrations and fish tissue levels suggest gradual recovery, continued navigational dredging activities, shrimp trawling, oyster dredging and storm-driven sediment resuspension threaten to remobilize legacy contaminants. These findings underscore the need for regionally informed management strategies to mitigate the ecological and public health risks associated with sediment-bound Hg.