COMPARISON OF MICROBIAL COMMUNITIES IN SOIL SEDIMENTS IMPACTED BY MERCURY CONTAMINATION ALONG A GRADIENT IN THE TRINITY RIVER, TEXAS

Heavy metal contamination in the freshwater ecosystem has become a serious global issue impacting ecological, environmental, and human health. Over decades, the Trinity River in Texas has become polluted with several toxic heavy metals, including mercury (Hg), due to intensive anthropogenic activities and natural sources. The combustion of coal in power plants to generate electricity and several other Hg sources have led to mercury pollution in this river system. This study aims to i) determine the concentration of mercury in soil sediments along the gradient of the Trinity River, ii) investigate the soil microbial communities in the sites along the Trinity River that are impacted by mercury contamination, iii) examine the soil sediments to find whether the sites closer to coal-fired industries have higher mercury concentrations compared to the sites that are distantly located from coal-fired industries along the Trinity River, and iv) to determine if the soil sediments of the sites contaminated with high mercury concentration were enriched with mercury methylating genera compared to the non-contaminated sites leading to shift in microbial composition and diversity. The findings of the study supported our hypothesis that there is a relatively higher concentration of mercury in the downstream site of the river, but it remained inconclusive that the sites closer to coal power plants have higher mercury concentrations, since most tributaries carries the industrial waste effluents generated by these power plants flow into the main channel of Trinity River farther from the sites where soil sediments were sampled. On the other hand, the result of the microbial diversity analysis showed that statistically, there is no significant difference in microbial composition (alpha diversity and beta diversity) between the uncontaminated upstream locations and contaminated downstream locations. While certain groups of mercury methylating genera were present in relatively higher abundance in sites with the increased level of mercury. The study suggests that; besides mercury, several other physicochemical factors of river water and soil sediment might contribute to emerging a synergistic microbiome composition at these sites, and while only small microbial differences lead to affect mercury metabolism.