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

美国东南部沿海平原的森林湿地是大气汞的重要汇，但也是汞甲基化和产生剧毒甲基汞的活跃场所，这可能会污染区域水体。2016年10月8日，飓风马修在南卡罗来纳州温亚湾最后登陆，并在短时间内造成暴雨和大范围洪灾。这一极端天气事件淹没了沿海平原的大片地区，淹没了沿海湿地很长一段时间，这可能会刺激许多缺氧过程，包括微生物汞的甲基化。这项研究将调查在这些沿海湿地延长的洪泛期中，微生物汞甲基化是否以及如何受到刺激。这项研究代表了来自三个机构的四名不同专业的研究人员之间的一项新的、独特的合作，其中包括分别来自少数族裔服务机构和本科机构的两名助理教授。这项研究还将提高人们对极端天气事件对美国东南部低洼沿海地区有毒汞循环影响的认识。这项快速研究旨在研究飓风马修对飓风马修最后登陆的南卡罗来纳州温亚湾附近沿海森林湿地微生物汞甲基化动态的影响。具体地说，这项研究将结合现场采样和实验室实验，调查这一极端天气事件在洪水水位变化过程中对沿海湿地土壤中汞的微生物甲基化的影响。为了评估飓风马修对汞循环的直接影响，研究小组自2016年10月10日以来一直在南卡罗来纳州温亚湾附近收集地表水和湿地土壤样本，马修飓风于2016年10月8日在那里最后登陆。采样点代表了横断面以及受飓风马修影响的不同程度的海水入侵和洪水严重程度。将量化样品的总汞和甲基汞，以及与湿地表层土壤相关的汞甲基化基因(HGCA)随时间的丰度，以检查汞甲基化的时空变化和汞甲基化基因的丰度。结果将被用来评估这些湿地土壤在长期淹水条件下汞甲基化热点和热点时刻的形成。此外，还将通过对照实验室实验来研究不同环境因素对这些湿地土壤中汞的微生物甲基化的影响，包括淹没时间、添加新鲜凋落物、增加水的盐度以及这些因素的组合。拟议的工作将更好地了解微生物汞甲基化--使汞有毒的关键生物地球化学步骤--如何在沿海湿地受到极端天气事件的影响。

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.