Historical and seasonal patterns of Hg accumulation: A comparative study of Pb-dated sediment cores and sediment trap records in a large coastal lagoon, southern Gulf of Mexico.

Sedimentary processes, ecological risks, and historical trends of mercury (Hg) contamination were assessed through Pb-dated sediment cores and sediment traps (period 2017-2019) in Términos Lagoon (TL), a critical coastal ecosystem in the southern Gulf of Mexico. Hg natural background levels in TL cores widely varied (7-153 ng g), and Hg concentrations were higher in the cores (median 32 ng g, range 6-4240 ng g) than in the sediment traps (median 54 ng g, range 44-1311 ng g). In most cores, enrichment factors ranged from null to moderate, except for very severe levels found in core LT01, indicating the presence of an Hg hotspot. Enrichments (minor to severe) were confined to river discharge areas in the sediment traps. Low to very high ecological risks were observed across the sampling areas. The factor analyses, for the core and trap samples, indicated fine-grained terrigenous sediments and high organic matter content as major drivers of Hg accumulation, with river discharges playing a central role. The sediment records displayed increasing Hg fluxes after the 1970s, coinciding with the local urban-industrial boom, while peak values in recent decades corresponded with population growth around the lagoon. Sediment trap data suggested that Hg fluxes are somewhat independent of rainfall, as peak values were observed during dry and winter storm seasons. These findings highlight the interplay of natural and anthropogenic factors promoting Hg accumulation in TL, offering insights to mitigate the effects of global change in one of Mesoamerica's most important coastal ecosystems.