Ecological processes controlling methylmercury cycling in prairie wetlands

我的研究项目探讨了汞（Hg）和碳(C)如何在北美大平原的草原坑区（PPR）的水生系统内移动。小反刍兽兽区数以百万计的湿地在地下水补给、防洪、碳和养分封存以及野生动物生物多样性方面发挥着至关重要的作用。这些有价值的系统受到农业的威胁，很容易受到预测的气候变化情景的影响。人们对草原生态系统中汞的循环知之甚少，但湿地具有许多特征，为高速率的神经毒性甲基汞（MeHg）生产提供了理想的条件。湿地产生甲基汞的速度取决于控制微生物种群生长的因素(例如：提供高质量的溶解有机碳（DOC）和微生物可利用的无机汞的来源；两者都受各种环境条件和过程的控制。我提出的研究的总体目标是利用生物地球化学方法（质量平衡预算（MBB），稳定的汞同位素孵育）和分子（16S rRNA基因扩增子测序）技术来研究湿地中甲基汞产生的地球化学和微生物控制。

My research program explores how mercury (Hg) and carbon (C) move within aquatic systems in the Prairie Pothole Region (PPR) of the North American Great Plains. Millions of wetlands in the PPR provide vital roles in groundwater recharge, flood control, C and nutrient sequestration, and wildlife biodiversity. These valuable systems, threatened by agriculture, are vulnerable to projected climate change scenarios. Hg cycling in prairie ecosystems is poorly understood, but wetlands possess many characteristics offering ideal conditions for high rates of neurotoxic methylmercury (MeHg) production. The rate of MeHg produced in wetlands depends on factors that control microbial population growth (eg. supply of high quality dissolved organic carbon [DOC]) and sources of inorganic Hg bioavailable to microbes; both are controlled by various environmental conditions and processes. The overall goal of my proposed research is to investigate the geochemical and microbial controls on MeHg production in wetlands using both a biogeochemical approach (mass balance budgets (MBB), stable Hg isotope incubations) and molecular (16S rRNA gene amplicon sequencing) techniques. My overall hypothesis is that production of MeHg in PPR ponds is controlled by geochemical and bacterial constraints that are heavily influenced by the chemical nature of DOC, Hg bioavailability, and microbial community composition. Further, net methylation rates will be influenced by hydrologic variability that may result from drought and deluge anticipated under climate change and results in sediment drying and rewetting. Whole-ecosystem MBBs on PPR ponds with differing DOC and sulphate water concentrations, and small scale microcosm and incubation experiments will be used to elucidate processes impacting MeHg sources and sinks. The chemical characterization of DOC, bioavailability of Hg in sediments, and potential MeHg production rates will be measured using advanced methods. Once we characterize the microbial community in ponds with varying DOC and sulphate concentration using 16S rRNA gene amplicon sequencing and resulting OTU values of known methylators, we can measure changes in microbial community compositions over time. As ponds dry out over the course of the summer, we will compare net methylation rates, substrate availability, and changes in microbial community in wet and dry sediments. Similar comparisons will be made in the following summer after ponds are rewetted due to snowpack contributions. This research will provide new insights on regulatory mechanisms controlling biological production of MeHg. My work will improve understanding of how these pathways may change with future climate change allowing us to make informed predictions on how changes will impact aquatic organisms. This study will also contribute to the long-term objective of my research program, which is to identify changes in the biogeochemical cycling of contaminants in the environment resulting from human impacts.