A time-series of heavy metal geochemistry in sediments of Galveston Bay estuary, Texas, 2017-2019

Abstract

Galveston Bay is an anthropogenic-influenced estuary where industrial runoff, wastewater, and shipping vessel discharges enter the bay alongside natural freshwaters. Here, heavy metal concentrations in Galveston Bay surface sediment (2-year quarterly time-series) and a single sediment core are presented to explore the anthropogenic and geochemical controls on the spatiotemporal distributions, fluxes, sources, and potential toxicity of metals within this estuary. Samples were leached to distinguish authigenic sediment coatings from geogenic crystalline material. Spatial differences dominate the observed concentration variability, with higher metal concentrations in eastern vs. western bay sediments, as the eastern bay is where metals are flocculated from the dissolved phase and/or sediments are hydrodynamically trapped. Temporal variations are a secondary controlling factor, with sediment metal concentrations positively correlated with Trinity River discharge. Core data indicate stable Fe, Pb Ni, Cd and Hg levels during the 20th century but increasing Cu and Zn levels in recent years. Galveston Bay sediments are potentially toxic for As, Cd, Cr, Cu, Ni, Sb, Zn and Hg, based on federal toxicity standards. Enrichment factors and statistical analyses suggest that Ni and Cr originate from natural sources, while anthropogenic sources dominate supply of As, Cd, Hg, Ni, Pb, Sb, and Zn. This unique time-series shows that major flooding events, such as Hurricane Harvey in 2017, affect surface sediment metal distributions in Galveston Bay, but not any more than the natural geochemical controls on spatiotemporal distributions of metals in anthropogenic-influenced estuaries.