Ecological processes controlling methylmercury cycling in prairie wetlands

草原湿地甲基汞循环的生态过程控制

• 批准号: RGPIN-2019-05566
• 负责人: Hall, Britt
• 金额: $ 2.19万
• 依托单位: University of Regina
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=765034
• 关键词: Ecological; processes; controlling; methylmercury; cycling

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.

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洼区（PPR）的水生系统中移动。PPR中的数百万湿地在地下水补给，洪水控制，C和营养物封存以及野生动物生物多样性方面发挥着重要作用。这些宝贵的系统受到农业的威胁，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的汞循环知之甚少，但湿地具有许多特性，为高比率的神经毒性甲基汞（甲基汞）生产提供了理想条件。湿地中产生甲基汞的速率取决于控制微生物种群增长的因素（例如：高质量溶解有机碳（DOC）的供应）和微生物可生物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调查的地球化学和微生物控制甲基汞生产的湿地使用的地球化学方法（质量平衡预算（MBB），稳定的汞同位素孵育）和分子（16 S rRNA基因扩增子测序）技术。我的总体假设是，生产的甲基汞在PPR池塘控制的地球化学和细菌的限制，在很大程度上受DOC的化学性质，汞的生物利用度，和微生物群落组成。此外，净甲基化率将受到水文变化的影响，这可能是由于气候变化下预期的干旱和洪水造成的，并导致沉积物干燥和再湿润。全生态系统MBBs PPR池塘不同DOC和硫酸盐水浓度，和小规模的微观和孵化实验将被用来阐明影响甲基汞源和汇的过程。DOC的化学特性，沉积物中汞的生物利用度，以及潜在的甲基汞生产率将使用先进的方法进行测量。一旦我们使用16 S rRNA基因扩增子测序和已知甲基化剂的OTU值表征具有不同DOC和硫酸盐浓度的池塘中的微生物群落，我们就可以测量微生物群落组成随时间的变化。随着池塘在夏季干涸，我们将比较净甲基化率、底物可用性以及湿沉积物和干沉积物中微生物群落的变化。类似的比较将在下一个夏天后，池塘重新湿润，由于积雪的贡献。这项研究将为控制甲基汞生物生产的调节机制提供新的见解。我的工作将提高对这些途径如何随着未来气候变化而变化的理解，使我们能够对变化将如何影响水生生物做出明智的预测。这项研究也将有助于我的研究计划的长期目标，这是确定人类影响造成的环境中污染物的地球化学循环的变化。