Geography of Air Pollution: Tree Rings as Spatial and Temporal Proxies for Atmospheric Mercury Concentrations

这项研究项目将探索使用年轮作为汞空气污染随时间的监测，以及大气中汞浓度与年轮中汞浓度之间的关系。该项目将寻求加强对空气污染过程的基本了解，克服汞空气污染数据在空间上是不连续的，它只涵盖很短的时间段，而且是零星收集的。此外，使用仪器收集数据的成本很高，而且偏向环境监管机构特别感兴趣的地点。由于树木在其木质生物量中加入了汞等大气污染物，树轮化学(树枝化学)科学在开发良好复制的连续空气质量数据集方面大有可为，并允许在空间上详细重建与环境变化和工业活动相关的长期趋势。该项目将测试使用年轮测量汞空气污染的有效性，从而扩大关于年轮作为大气汞监测仪的用途的知识。这些知识将促进未来的研究，将树木年轮汞浓度的变化与地方、区域和全球范围内的工业实践和土地利用变化联系起来。这些知识将产生一系列积极的、更广泛的影响。该项目将提高利用年轮分析作为监测大气汞的手段的能力，从而为那些寻求减少大气汞的人提供新的信息和见解。在项目实施期间开发的信息、见解和方法也将在博物馆展览中展示，重点是空气污染、汞和树枝化学。该项目将为研究生和本科生提供令人兴奋的教育和培训机会，调查人员和学生将与小学教师合作，帮助开发动手操作的科学学习单元。调查人员将探索汞树枝化学的用途，他们将通过一系列野外和实验室实验来校准树木年轮和大气中汞浓度之间的关系。他们还将对之前采样的树木进行重新采样，以检测年轮中的汞浓度。他们将测试一些假设，以评估树轮浓度可以在多大程度上作为跨越空间和时间的大气汞浓度的代用品。他们将寻求通过测试树轮汞浓度是否是大气汞污染的良好指标来确定环境大气汞的浓度。他们将通过测试树轮汞浓度是否在多年间保持稳定来探索随着时间的推移的一致性，因为移位和化学降解最小)。他们将通过测试同一地点同一物种的树木是否记录树轮中类似的汞浓度来评估种群内是否存在一致性，并将通过测试大气和树轮汞浓度之间的函数关系中的物种特定差异是否可以通过校正方程来检查物种之间的一致性。研究人员将采用操纵性实验，在受控条件下将树苗(整个植物)和木质部组织暴露在已知汞浓度下。他们还将进行实地观测研究，在直接测量或已经测量到大气汞的地点，每年重复为树木取芯，以及使用盆栽树苗进行操纵性田间实验，在盆栽树苗中收获全部植物。因此，该项目将量化树木年轮汞数据的可靠性，并改进采样、校准和外推的方法。

This research project will explore the use of tree rings as a monitor of mercury air pollution over time and the relationship between mercury concentrations in the atmosphere and mercury concentrations in tree rings. The project will seek to enhance basic understanding of air pollution processes by overcoming the fact that data on mercury air pollution is spatially discontinuous, that it covers only short time periods, and that it is collected sporadically. Furthermore, data collection using instruments is expensive and is biased towards locations of particular interest to environmental regulators. Because trees incorporate atmospheric pollutants like mercury in their woody biomass, the science of tree-ring chemistry (dendrochemistry) holds great promise for developing well-replicated air-quality datasets that are continuous and allow for a spatially detailed reconstruction of long-term trends associated with environmental change and industrial activity. The project will test the efficacy of using tree rings to measure mercury air pollution, thereby expanding knowledge about the utility of tree rings as a monitor of atmospheric mercury. Such knowledge will facilitate future research relating variations in tree-ring mercury concentrations to industrial practices and land-use changes at local, regional, and global scales. Such knowledge will have a range of positive broader impacts. The project will improve capabilities to use analysis of tree rings as a means of monitoring atmospheric mercury, thereby providing new information and insights for those seeking to reduce atmospheric mercury. Information, insights, and approaches developed during the conduct of the project also will be displayed in museum exhibits focusing on air pollution, mercury, and dendrochemistry. The project will provide exciting education and training opportunities for graduate and undergraduate students, and both the investigators and students will work with elementary school teachers to assist in the development of hands-on science learning units.The investigators will explore the utility of mercury dendrochemistry, and they will calibrate the relationship between mercury concentrations in tree rings and in the atmosphere using a series of field and laboratory experiments. They also will resample trees that had been sampled previously for mercury concentration in tree rings. They will test a number of hypotheses to assess the degree to which tree-ring concentrations can be applied as proxies for atmospheric mercury concentrations across space and time. They will seek to determine the consistency of environmental atmospheric mercury by testing whether tree-ring mercury concentrations are good indicators of atmospheric mercury pollution. They will explore consistency over time by testing whether tree-ring mercury concentrations are stable across years because translocation and chemical degradation are minimal). They will assess whether there is consistency within populations by testing whether trees of the same species at the same site record similar mercury concentrations in tree rings, and they will examine consistency among species by testing whether species-specific differences in the functional relationship between atmospheric and tree-ring mercury concentrations can be corrected through calibration equations. The investigators will employ manipulative experimentation through which tree saplings (whole plants) and xylem tissues are exposed to known mercury concentrations under controlled conditions. They also will engage in field observational studies in which trees are cored repeatedly at annual intervals at locations where atmospheric mercury is or has been measured directly as well as manipulative field experiments involving potted saplings where whole plants are harvested. The project therefore will quantify the reliability of tree-ring mercury data and refine approaches for sampling, calibration, and extrapolation.