Collaborative Research: Investigating tree rings as archives for atmospheric Hg concentrations using Hg, carbon isotopes, and comparisons to other proxies

In addition to recording atmospheric conditions, trees also take up atmospheric pollutants, such as mercury, and store them in the wood they produce each year. Thus, tree rings are a promising archive of historic mercury pollution, however there remains a lot unknown about how trees take up and then store mercury in their rings. This research project aims to address this by studying how tree physiology influences how trees capture mercury from the air.

Other archives of mercury (e.g. ice cores) often have high uncertainty in their dating and record mercury deposition. Comparing tree rings and other records will improve understanding of historic mercury pollution. There are very few records of mercury in the environment that are older than a few hundred years.

One of the aims of this project is to develop records of up to 2000-years of atmospheric mercury, improving our understanding of natural atmospheric mercury, including how mercury is influenced by volcanic activity, wildfire and past climate changes. The knowledge and data generated in this project will be of immense value to future research projects on mercury pollution related to historic industrial practices and land-use changes, and will assist in our research into the nature and scale of industrial era mercury pollution and provide new insights to those seeking to further reduce atmospheric mercury.

New reliable records of pre-industrial atmospheric mercury are also extremely important for current efforts to monitor and assess changes in mercury emissions as part of the United Nations Minamata Convention. Information, insights and approaches developed in this project will be used in exciting education and training opportunities for undergraduate and graduate students, including those from underserved groups, and in hands-on science modules for K-12 educators.

Although tree-rings are a promising high-resolution archive for reconstructing past concentrations of atmospheric mercury (Hg) there remain factors that need to be further investigated. This research project aims to improve the utility of tree-rings as an Hg archive by 1) using concurrent stable carbon isotope measurements to better understand how within-tree processes related to stomatal conductance influence the incorporation of Hg into tree rings; 2) comparing concentrations of Hg in tree rings to measurements from small-catchment lake sediment and ice cores to test the fidelity of the Hg signals observed; and 3) develop long-term records of Hg concentrations derived from tree rings to investigate important natural drivers of atmospheric Hg (e.g. volcanic activity, wildfire & climate).

Through the unique combination of Hg concentrations and stable carbon isotope measurements, the biotic influences on the incorporation of Hg into tree rings will be better understood. By comparing concentrations of Hg in tree rings to Hg deposition measurements from small-catchment lake sediment and ice cores, the differences and similarities between these two types of records will improve understanding of how Hg is preserved in these different archives, providing important information on post-depositional processes in depositional archives.

Finally, a long-term (up to 2000-year) record of Hg concentration from tree rings will improve our understanding of natural variability in atmospheric Hg.

This project is jointly funded by the Geobiology and Low-Temperature Geochemistry Program, and the Established Program to Stimulate Competitive Research (EPSCoR).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.