Climate change and catchment controls on the mercury cycle of northern lakes

尽管几十年来汞在环境中的循环一直是科学界关注的焦点，但许多控制过程仍然没有得到很好的描述，这仍然使我们无法预测鱼类体内的汞浓度。最近关于植被在向集水区土壤供应汞方面的作用以及从集水区向湖泊输送甲基汞的重要性的发现表明，我们对环境中的汞的了解仍然不完整。由于缺乏相关知识，我们无法将气候变化因素纳入对生物群汞含量的预测。由于气候变化已经对加拿大北部产生了影响，对于以鱼类为主食的北部居民来说，了解高纬度集水区和湖泊中鱼类中汞的控制是极其紧迫的。这一建议有三个目标，旨在显著提高我们对北方亚北极集水区和湖泊汞循环的理解。第一个目标侧重于植被在汞从大气向土壤转移中的作用，这将采取一种令人兴奋的方法，在实验室内使用汞的稳定同位素来确定来自大气和土壤的植物叶片中的汞含量。一项实地研究还将评估森林火灾后北方从云杉林到白杨林的转变将如何改变土壤中汞的供应。第二个目标侧重于集水区在甲基汞生产方面的作用，甲基汞是在鱼类体内积累的有毒形式的汞。我们将使用一套实验室仪器对有机物质和稳定汞同位素的来源进行指纹识别，以测量生物地球化学过程。我们将验证以下假设：北部湖泊沉积物主要是来自集水区的有机物质，集水区是北部湖泊中甲基汞的最重要来源，以及冻土融化是环境中甲基汞的一个特定且不断增长的来源。一旦甲基汞和溶解的有机物进入湖泊，它就需要进入食物链，在生物群中积累。拟议工作的最终目标是评估未来溶解有机物数量和质量的变化将如何改变汞被水生食物链最底部的藻类吸收的方式。该建议解决了我们对北部流域汞循环的理解中三个最重要的知识空白：对大气沉积的控制；控制物种形成和流域运输的过程；水生食物网基础的生物利用度控制。这些进展将极大地提高我们预测北部湖泊和鱼类中汞的当前和未来模式的能力。

Although the cycling of mercury in the environment has been the focus of scientific attention for decades, many governing processes remain poorly described which still prevent us from being able to predict mercury concentrations in fish. Very recent discoveries about the role of vegetation in supplying mercury to catchment soils, and the importance of the delivery of methyl mercury from the catchment to lakes reveal that our understanding about mercury in the environment remains incomplete. The lack of knowledge contributes to our inability to factor climate change into predictions of mercury in biota. Since climate change is already having an impact in Canada's north, understanding the controls on mercury in fish in higher latitude catchments and lakes is extremely urgent for northern residents who rely on fish as a dietary staple. This proposal has three objectives which seek to significantly advance our understanding of the mercury cycle in boreal sub-arctic catchments and lakes. The first objective focusing on the role of vegetation in the transfer of mercury from the atmosphere to soils will take an exciting approach using stable isotopes of mercury in experimental chambers to determine the fractions of mercury in plant leaves that come from the atmosphere and soils. A field study will also evaluate how the shift from spruce to aspen forests in the north after forest fires will change the supply of mercury to soils. The second objective focusses on the role of the catchment on the production of methylmercury, the toxic form of mercury that accumulates in fish. Using a suite of laboratory instruments to fingerprint' the sources of organic matter and stable mercury isotopes to measure biogeochemical processes, we will test the hypotheses that northern lake sediments are dominated by organic matter from the catchment, that the catchment is the most important source of methylmercury to northern lakes, and that thawing permafrost is a specific and growing source of methylmercury in the environment. Once this methylmercury and the dissolved organic matter that it is bound to gets to the lake, it needs to enter the food chain to be accumulated in biota. The final objective of the proposed work will evaluate how future changes in dissolved organic matter quantity and quality will change the way that mercury is assimilated by algae which is at the very base of the aquatic food chain. This proposal addresses three of the most important knowledge gaps in our understanding of mercury cycling in northern catchments: controls on atmospheric deposition; processes governing speciation and transport from catchments, and; controls on bioavailability at the base of aquatic food webs. These advances will dramatically improve our ability to predict current and future patterns of mercury in northern lakes and fish.