Assessment of the Suitability of Tree Rings as Archives of Global and Regional Atmospheric Mercury Pollution

Abstract

This study investigated the methodology and utility of dendrochemistry in the assessment of spatial and temporal concentrations of gaseous elemental mercury. Tree cores from the Pinus species in California and Nevada, U.S.A. were collected from previously sampled areas to test the stability of tree ring concentrations over time. Cores were collected from 2 new locations to assess spatial variability among trees within and between stands located at two elevations in the same watershed. Results indicated that using 2 to 3 cores from ∼10 or more trees provided the best framework for understanding tree ring concentrations within a population of trees located in uncontaminated areas. At the least 2 sides of a tree should be cored to account for radially asymmetric variations associated with growing conditions or injury. An agreement of concentrations and trends measured in trees cored with previous research indicated that tree rings are suitable proxies for historical air mercury concentrations and that mercury concentrations have increased since the Industrial Revolution. Data collected demonstrate that tree rings record regional gradients in GEM concentrations. In addition, temporal consistency may vary within a geographic location due to differing biotic and abiotic factors influencing ring growth since trees are active samplers of atmospheric Hg.

Mercury Accumulation in Tree Rings: Observed Trends in Quantity and Isotopic Composition in Shenandoah National Park, Virginia

“…Tree ring Hg concentrations measured in Shenandoah National Park (from below detection to 4.4 ng/g) are within the range of previously reported Hg concentrations in tree woody tissue, based on the literature review of Wright et al () and subsequent studies. Concentrations are very similar to the mean concentrations measured in pine species in California and Nevada (0.4 to 5.8 ng/g) by Wright et al () and Peckham et al () and white spruce in northwestern Canada (0.3 to 3.2 ng/g) by Clackett et al (). They were also similar to bulk bole wood concentrations in hardwood and conifer species in the northeastern United States (0.4 to 2.8 ng/g) reported by Yang et al ().…”

“…A limited number of prior studies have used dendrochemistry to estimate historical levels of ambient atmospheric Hg. For studies that were conducted in the absence of known local sources, trends in tree ring Hg have generally shown gradual increases since the time of the Industrial Revolution (Clackett et al, ; Peckham et al, ; Wright et al, ). Such behavior might be expected in Shenandoah National Park, but similar trends were not observed (Figure ).…”

“…Previous studies that have quantified Hg in tree rings have either documented post‐Industrial Revolution increases corresponding with gradually increasing Hg concentrations in the atmosphere (Clackett et al, ; Peckham et al, ; Wright et al, ) or peaks in tree ring Hg corresponding with the timing of local industrial sources (Hojdová et al, ; Maillard et al, ; Navratil et al, ; Navratil et al, ). The present study differs in that the main feature of the measured tree ring Hg time series derives from a previously unidentified source.…”

“…Sediment cores have also documented regional atmospheric Hg signals in the Great Lakes region (Pirrone et al, 1998) and from major fires and volcanic eruptions (Daga et al, 2016). An emerging approach to reconstruct trends in atmospheric Hg is through the use of dendrochemistry (Clackett et al, 2018;Navratil et al, 2018;Peckham et al, 2019;Wright et al, 2014). With careful sampling strategies, tree cores may provide a regionally integrated atmospheric Hg archive while avoiding problems associated with other methods, such as uncertain geochemical dating of peat (Biester et al, 2007) and diagenetic remobilization in sediments (Sunderland et al, 2008).…”

A coumarin‐based fluorescent probe for Hg2+ and its application in living cells and zebrafish

“…Mercury (Hg) is one of the most important global pollutants because of its high toxicity and easy migration. [1][2][3][4] Mercury can be transported through both air and water, and then enriched in the food chain. [5][6][7][8] Aquatic products are the most important source of Hg ingested by humans.…”