Mercury Deposition Network Monitoring at VT99
Mercury is a persistent pollutant that can accumulate in organisms as it moves up the food chain, leading to neurological damage, lowered reproductive success, motor skill impairment and hormonal changes in humans and animals (Driscoll et al. 2007, Evers et al. 2004). Human activities such as fossil fuel burning and waste incineration elevate levels of atmospheric mercury, which is later transferred to forests and water bodies through both dry and wet (in precipitation) deposition. Since 1992, FEMC has been collecting data on both wet and dry mercury deposition, making it one of the longest records in the U.S. In 2004, the FEMC joined the Mercury Deposition Network (MDN, part of the National Atmospheric Deposition Program) as one of over 120 sites in the U.S. and Canada. The FEMC air quality site serves as a sentinel site for the northeastern U.S. – it is high enough in elevation to detect regional mercury transport events that are not detected by other stations. This very long record has provided context to many shorter-duration studies, including the way mercury cycles through the forest canopy 1, how mercury bioaccumulates in birds 2 and amphibians 3, how mercury levels are influenced by elevation 4, and how falling leaves contribute to deposition 5. FEMC and its partners have committed to this long-term monitoring in order to document and better understand the input of mercury into Vermont's forested ecosystems and the inhabitants of those ecosystems, including birds, fish, bobcats and human beings.
FEMC conducts year-round sampling of precipitation chemistry at the air quality monitoring site at the Proctor Maple Research Center in Underhill, Vermont. Weekly composites of precipitation are gathered in an automated wet-only precipitation collector at the site. The collector opens automatically when rain or snow is detected, capturing precipitation through a funnel and tube sampling train into a bottle charged with hydrochloric acid (to preserve the sample). The collector is heated in the winter and vented in the summer as needed. Samples are collected every Tuesday and shipped to the Mercury Analytical Laboratory at Eurofins Frontier Global Science, Inc. in Bothell, WA for analysis of mercury concentration and cleaning of the sampling train. Data are submitted to NADP for quality control and posted on the NADP/MDN website (http://nadp.isws.illinois.edu/data/MDN/).
2016 in Summary
Mercury monitoring at FEMC's air quality site (VT99) for 2016 shows slightly lower deposition than average for the 11-year record, higher than 2015 and roughly equal to 2014 (Table 2). Over the entire record for VT99, total mercury deposition fluctuated from a high of 11.6 µg/m2 in 2007 to a low of 6.1 µg/m2 in 2012 and 2015. Similarly, the precipitation-weighted mean mercury concentration and the maximum mercury concentrations measured at VT99 are quite variable. In 2016, precipitation-weighted mean concentration was roughly average for the record, while the maximum recorded concentration in a single sample was well below historical average. In 2016, Vermont registered lower concentration and deposition averages that most sites elsewhere in the United States (Figure 12).
Long Term Trends
Over 10 years of monitoring at VT99 prior to the current year, mean annual deposition was higher than 41% of national MDN sites (Table 3). The VT99 monitoring station has fallen from the high end of measured values (2007, with higher total Hg deposition than 85% of other MDN sites) and climbed from the low end of measured values (2012, with higher total Hg deposition than only 14% of other MDN sites). During most years of monitoring, the VT99 site typically falls in the middle of reported Hg deposition values across the Mercury Deposition Network.
Mercury deposition has decreased in VT in recent years, but still remains among the highest deposition rates in the region (Figure 13).
Indeed, a recent regional trends analysis using NADP MDN data (Figure 14) provides further signs of regional differences for VT99. Different periods were analyzed, including the years 1997-2013 as well as several shorter portions of the record. The shorter time period analyses were a way to incorporate the changing spatial pattern into the trends analysis as the MDN network expanded. This period from 2008 to 2013 shows VT99 having a statistically significant positive slope in increased mercury concentrations. Five years is too short for a definitive trend, but it might suggest that VT99 is more influenced by global sources than are surrounding lower altitude MDN sites due to its relatively high altitude and the absence of nearby coal utility boilers (Weiss-Penzias et al. 2016).
In the long term, mercury deposition levels decreased dramatically with the enactment of clean air legislation in the late 20th century (Kamman and Engstrom 2002). The atmosphere is the main pathway for mercury into Vermont's ecosystems. It is estimated that more than half of this atmospheric deposition is dry. Dry deposition is difficult to measure but the NADP is committed to expanding its network of mercury dry deposition sites. Unfortunately, the FEMC had to terminate its Atmospheric Mercury Network (AMNet) site on Dec. 31, 2015 so dry deposition rates going forward will have to be inferred rather than measured.
Mercury persists in the environment and continues to be cycled through the various storage pools (soils, air, and biota). The continued low-level input and occasional spikes will likely drive cumulative increases in mercury in Vermont's forests, which are particularly sensitive to these inputs (Driscoll et al. 2007, Gay 2016, pers comm, Weiss-Penzias et al. 2016). Fish mercury burdens are one way to track these trends and in Vermont, fish advisories are still being issued (Chalmers et al. 2014, Vijayaraghavan et al. 2014). Until fish tissue, sampling shows a long-term negative trend, the need to monitor mercury is critical. Mercury cycling is complex and not completely understood, also highlighting the need to track concentration and deposition rates.
Historically, sulfate emissions have been strongly correlated with mercury emissions because they shared the same primary source, coal-fired utility boilers, but with the impressive reduction in sulfates mandated by the Clean Air Act, sulfates are no longer well correlated. In the northeastern region mercury concentrations are up, suggesting that mercury measured here is not associated with regional S emissions. It is possible that the mercury falling on Vermont is from foreign or at least not from regional sources. As of March 2016, The U.S. Supreme Court denied a stay of the Environmental Protection Agency's Mercury and Air Toxics Standards ("MATS") which would implement emissions reductions of toxic air pollutants from existing and new coal and oil-fired power plants. Although the rule is under review by the EPA at the urging of the Trump administration, if it survives, we should see a downward trend in mercury deposition from regional sources in Vermont and the Northeast in the coming years.
More emission to the atmosphere from a global pollutant could mean more deposition for everyone, and potentially higher fish concentrations and therefore higher concentrations in VT humans. This underscores the need to curtail anthropogenic contributions in Vermont and worldwide.
Regionally, Vermont's precipitation-borne mercury has not been decreasing as quickly as in neighboring states, highlighting the role of Vermont's monitoring for identifying global patterns of mercury pollution.
- AMAP/UNEP, 2015. Global Mercury Modelling: Update of Modelling Results in the Global Mercury Assessment 2013. Arctic Monitoring and Assessment Programme, Oslo, Norway/UNEP Chemicals Branch, Geneva, Switzerland. iv + 32 pp. Available online at: https://wedocs.unep.org/bitstream/handle/20.500.11822/11440/Report-ModellingupdateoftheGMA2013.pdf.pdf?sequence=1&isAllowed=y
- Chalmers, A.T., Krabbenhoft, D.P., Van Metre, P.C. and Nilles, M.A., 2014. Effects of urbanization on mercury deposition and accumulation in New England. Environmental Pollution, 192, pp.104-112.
- Driscoll, C. T., Han, Y. J., Chen, C. Y., Evers, D. C., Lambert, K. F., Holsen, T. M., and R.K. Munson. (2007). Mercury contamination in forest and freshwater ecosystems in the Northeastern United States. Bioscience, 57(1), 17-28. doi: 10.1641/b570106.
- Gay, D. 2016. Pers comm.
- Evers, D.C., Lane, O.P., Savoy, L. and W. Goodale. 2004. Assessing the Impacts of Methylmercury on Piscivorous Wildlife Using a Wildlife Criterion Value Based on the Common Loon, 1998–2003. Gorham (ME): Maine Department of Environmental Protection, BioDiversity Research Institute. Report no. BRI 2004-05.
- Kamman, N.C., and D.R. Engstrom. 2002.Historical and present fluxes of mercury to Vermont and New Hampshire lakes inferred from 210Pb dated sediment cores. Atmospheric Environment 36: 1599–1609.
- Mahaffey KR. 2005.Update on recent epidemiologic mercury studies. Pages 31–33 in Proceedings of the 2004 National Forum on Contaminants in Fish; 25–28 January 2004, San Diego, California. Report no. EPA-823-R-05-006.
- National Atmospheric Deposition Program (NADP). 2015. National Atmospheric Deposition Program 2014 Annual Summary. NADP Data Report 2015-01. Illinois State Water Survey, University of Illinois at Urbana-Champaign, IL.
- Rimmer, C.C., E.K. Miller, K.P. McFarland, R.J. Taylor, S.D. Faccio. 2010. Mercury bioaccumulation and trophic transfer in the terrestrial food web of a montane forest. Ecotoxicology 19(4):697-709. doi: 10.1007/s10646-009-0443-x.
- Vijayaraghavan, K., Levin, L., Parker, L., Yarwood, G. and Streets, D., 2014. Response of fish tissue mercury in a freshwater lake to local, regional, and global changes in mercury emissions. Environmental toxicology and chemistry, 33(6), pp.1238-1247.
- Weiss-Penzias, P.S., Gay, D.A., Brigham, M.E., Parsons, M.T., Gustin, M.S. and ter Schure, A., 2016. Trends in mercury wet deposition and mercury air concentrations across the US and Canada. Science of The Total Environment. Available online at http://dx.doi.org/10.1016/j.scitotenv.2016.01.061
- Vermont Health Department Fish Consumption Recommendations: http://healthvermont.gov/enviro/fish_alert/documents/fish_alert.pdf
- Global Sources of Local Pollution: An Assessment of Long-Range Transport of Key Air Pollutants to and from the United States. 2009. National Academy of Sciences. Chapter 4, Mercury: Atmospheric Mercury Primer. https://www.nap.edu/read/12743/chapter/6#99
FEMC Project Database Link
- Wet Deposition of Mercury at Proctor Maple Research Center (Mercury Deposition Network-MDN) https://www.uvm.edu/femc/data/archive/project/wet-deposition-mercury-proctor-maple-research
- 1Mercury Flux at PMRC - https://www.uvm.edu/femc/data/archive/project/mercury-flux-pmrc
- 2Bicknell's Thrush Population Demographics and Ecology: Assessing levels of methylmercury in montane forest bird community on Mount Mansfield - https://www.uvm.edu/femc/data/archive/project/bicknells-thrush-population-demographics-ecology-assessing
- 3Mercury Burdens in Amphibians - https://www.uvm.edu/femc/data/archive/project/mercury-burdens-amphibians
- 4Cloudwater Chemistry on Mount Mansfield - https://www.uvm.edu/femc/data/archive/project/cloudwater-chemistry-mount-mansfield
- 5Litterfall Mercury Dry Deposition in the Eastern USA - https://www.uvm.edu/femc/data/archive/project/litterfall-mercury-dry-deposition-eastern-usa