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

Board Of Regents, Nshe, Obo University Of Nevada, Reno, Reno NV

Investigators

Abstract

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.