ASSESSING ANTHROPOGENIC IMPACT THROUGH TREE RINGS USING MERCURY CONCENTRATION TRENDS IN CENTRAL MASSACHUSETTS

As trees grow, they form annual growth bands (rings) where the element composition of their surrounding environment is captured. This provides a promising history of past environmental and assimilated pollution records. The methodology and variation among species, however, are being tested for suitability. In this study, we assessed spatial patterns of mercury concentration (Hg) between trees growing near a former fossil fuel-fired power station. Three types of tree samples were collected; 1) Acer rubrum (Red Maple), 2) Quercus rubra (Red Oak), and 3) Pinus strobus (Eastern White Pine) to test how these different trees responded to the emission of anthropogenic pollutants throughout the history of fossil-fuel combustion. The tree samples were collected within an 8 km radius of the former Mount Tom Power Plant in Holyoke, MA a 5.15 mm diameter increment borer. The Mount Tom Power Plant operated from 1960 to 2014. This power plant generated electricity using oil during the 1960s and 1970s, and then coal during the 1980s through the 2000s.

Measurement of annual growth bandwidths of the samples was taken using Project J2X software. An ITRAX XRF core scanner was used to examine the elemental composition of individual growth bands and to establish a time series of multiple tree samples within similar species. Hydra C was used on those samples to measure Hg concentration within growth rings. During the same time period, meteorological data from local weather stations were collected to assess changes in tree growth related to climate conditions.

Based on Hydra C analysis, Hg concentration contained within was generally lower than found in White pine. White retained a peak concentration of around 8 ng/g, recorded in 1972, and declined after. Oak peaked at around 3 ng/g, recorded in 1965, and decreased thereafter. Red oak Hg concentration recorded in 2010 increased and closely corresponded with concentrations found in pine recorded through 2017, which is a few years after the closure of the power plant. The ITRAX data pattern for Hg does not correspond with concentrations from Hydra C in either of the trees. Red oak and trees showed similar trends in concentrations while the power plant was active, demonstrating sensitivity to the detection of mercury emission.