Role of the deep brine layer in the production of methylmercury in the Great Salt Lake

犹他州的大盐湖是每年数百万候鸟的主要停留地。 这些鸟类以生活在湖中的卤虫和卤蝇为食，由于大盐湖中甲基汞的浓度非常高，它们面临汞中毒的风险。 甲基汞是有毒重金属汞的一种形式，也是唯一一种容易在食物链中积累并增加浓度的形式。 目前还不清楚为什么大盐湖的甲基汞浓度是有史以来在天然水体中测得的最高浓度。 这项研究的目的是确定大盐湖中甲基汞生产的主要地点。 这些信息可以帮助科学家和政府监管机构找到减少大盐湖人类和动物汞暴露的方法。 这项研究将支持来自地球科学背景的多名学生，特别是多名女性。 该项目还将支持高中和大学教师制定新的科学课程。高盐度的大盐湖（GSL）是每年数百万候鸟的主要停留地。 它也是有史以来天然水体中甲基汞（MeHg）浓度最高的地方。最高浓度的甲基汞被发现在南臂的缺氧深盐水层，这是由密度更大，更咸的水从北臂流入南臂。虽然整个生态系统中的甲基汞含量很高，但甲基汞的主要来源和甲基汞浓度异常升高的根本原因尚不清楚。关闭分隔GSL北臂和南臂的堤道上的两个涵洞导致了最近深层盐水层的消失，而2016年下半年堤道上一座新桥的完工预计将导致南湾深层卤水层的重新开发。这一独特的短暂事件为意外的区域性-大规模的自然实验和机会，以跟踪甲基汞的可能来源（缺氧深层盐水层或该层下的沉积物）。研究人员将使用多方面的方法来测试这些假设，包括测量甲基汞浓度，汞甲基化和去甲基化率，以及在深层卤水层重建之前，期间和之后收集的水和沉积物中自然发生的稳定汞同位素比率。

The Great Salt Lake in Utah is a major stop over for millions of migratory birds each year. These birds feed on brine shrimp and brine flies that live in the Lake, putting them at risk of mercury toxicity due to the very high concentrations of methylmercury in the Great Salt Lake. Methylmercury is one form of the toxic heavy metal mercury, and it is the only form that is readily accumulated to increasing concentrations moving up the food chain. It is currently unknown why the Great Salt Lake has some of the highest methylmercury concentrations ever measured in a natural water body. The goal of this research is to determine the primary locations of methylmercury production in the Great Salt Lake. Such information could help scientists and government regulators to develop ways to decrease mercury exposure to humans and animals at the Great Salt Lake. This research will support multiple students from backgrounds underrepresented in the geosciences, in particular multiple women. This project will also support the development of new science curriculum by teachers at both the high school and university levels.The hypersaline Great Salt Lake (GSL) is a major stop over for millions of migratory birds each year. It is also home to some of the highest concentrations of methylmercury (MeHg) ever reported for a natural water body. The highest concentrations of MeHg are found in the South Arm's anoxic deep brine layer, which is created by the flow of denser, more saline water from the North Arm into the South Arm. While the high levels of MeHg throughout this ecosystem have been well documented, the primary source of MeHg and the underlying reasons for the exceptionally elevated concentrations of MeHg here are not known. The closure of two culverts in the causeway separating the North Arm and South Arm of the GSL has resulted in the recent disappearance of the deep brine layer, while the completion of a new bridge on the causeway in the second half of 2016 is expected to lead in the redevelopment of the deep brine layer in the South Arm. This unique and transient event provides the conditions for an unintended regional-scale natural experiment and opportunity to track the possible sources of MeHg (either the anoxic deep brine layer or sediment underlying this layer). The investigators will use a multifaceted approach to test these hypotheses, including the measurement of MeHg concentrations, Hg methylation and demethylation rates, and naturally occurring stable Hg isotope ratios in water and sediment collected before, during, and after the reestablishment of the deep brine layer.