RAPID: Hurricane-mediated alteration of microbial mercury methylation in coastal wetlands

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Forested wetlands in the coastal plain of the southeastern United States are important sinks of atmospheric mercury but also represent active sites of mercury methylation and production of highly toxic methylmercury, which can contaminate regional water bodies. On October 8, 2016, Hurricane Matthew had a final landfall at Winyah Bay, South Carolina, and resulted in torrential rain and extensive flooding in a short period of time. This extreme weather event flooded an extensive area of the coastal plain, inundating the coastal wetland for a prolonged period that could potentially have stimulated many oxygen-deficient processes including microbial mercury methylation. This research will investigate if and how microbial mercury methylation is stimulated during the prolonged flooding period in these coastal wetlands. This study represents a new and unique collaboration between four investigators with different specialties from three institutions including two assistant professors from a minority serving institution and an undergraduate institution, respectively. This study will also raise the awareness of the impacts of extreme weather events on toxic mercury cycling in low-lying coastal areas in the southeastern United States.This RAPID research is aimed at examining the influences of Hurricane Matthew on the dynamics of microbial mercury methylation in coastal forested wetlands near Winyah Bay, South Carolina, where Hurricane Matthew had a final landfall. Specifically, this study will integrate field sampling and laboratory experiments to investigate the impacts of this extreme weather event on microbial methylation of mercury in the coastal wetland soils over the course of variation in flooding levels. To evaluate the immediate impacts of Hurricane Matthew on mercury cycling, surface water and wetland soil samples have been collected by the research team since October 10, 2016 near Winyah Bay, South Carolina, where Hurricane Matthew had a final landfall on October 8, 2016. The sampling sites represent transects along with different degrees of seawater intrusion and flood severity impacted by Hurricane Matthew. Samples will be quantified for total mercury and methylmercury, and the abundance of mercury methylation genes (hgcA) associated with the wetland surface soils over time, to examine the temporal and spatial variations of mercury methylation and abundance of mercury methylation genes. Results will be used to evaluate the formation of hot spots and hot moments of mercury methylation in these wetland soils under prolonged inundation. Moreover, controlled laboratory experiments will be employed to examine the effects of different environmental factors on microbial methylation of mercury in these wetland soils, including duration of inundation, addition of fresh litter, increase of water salinity, and a combination of these factors. The proposed work will provide a better understanding of how microbial mercury methylation, the key biogeochemical step making mercury toxic, is impacted in coastal wetlands by extreme weather events.