Emission and Long-Range Transport of Gaseous Mercury from a Large-Scale Canadian Boreal Forest Fire

Abstract

Field observations made at Harvard Forest [Petersham, MA, U.S.A. (42 degrees 54' N, 72 degrees 18' W)] during early July 2002 show clear evidence of long-range transport of gaseous mercury (Hg) in a smoke plume from a series of boreal forest fires in northern Quebec. These measurements indicated significant and highly correlated increases in Hg and CO during the plume event. The Hg:CO emissions ratio determined from the data (8.61 x 10(-8) mol mol(-1)) was combined with previously published information on CO emissions and biomass burned to determine a mean area-based Hg emission flux density for boreal forest fires (1.5 g Hg ha(-1)), annual Hg emissions from Canadian forest fires (3.5 tonnes), and annual global Hg emissions from boreal forest fires (22.5 tonnes). Annual Hg emissions from boreal fires in Canada may equal 30% of annual Canadian anthropogenic emissions in an average fire year and could be as high as 100% during years of intense burning. The Hg:CO emissions ratio of this study was much lower than those reported for a temperate forest in Ontario and a pine/shrub vegetation in South Africa, suggesting that fire emission is dependent on biome/species and that any extrapolation from a single fire event to determine the global fire emission is speculative.

Mercury concentrations and pools in four Sierra Nevada forest sites, and relationships to organic carbon and nitrogen

“…A combined linear regression showed a slope of 15.2 µg Hg g −1 N and indicates that soil N contents alone explained a full 92% of the Hg variability observed across all sites and soil horizons. The affinity of Hg to organic matter has been attributed to complexation of Hg with reduced S and O or N groups abundantly present in organic molecules (Schuster, 1991;Skyllberg et al, 2000;Xia et al, 1999). Our results showing strong relationships between Hg and N in soils and similar relationships in litter (see above) suggest that nitrogen groups may be key ligands for retention of Hg in terrestrial ecosystem compartments.…”

Modelling the sensitivity of soil mercury storage to climate-induced changes in soil carbon pools

“…In general, Hg depth distributions in soils follow those of soil organic matter, with the highest concentrations found in near-surface layers and decreasing concentrations with depth (Aastrup et al, 1991;Andersson, 1979;Meili, 1991;Obrist et al, 2009). Studies also show corresponding spatial distribution patterns of organic matter and Hg in top soils and litter across multiple sites (Grigal, 2003;Skyllberg et al, 2000;Obrist et al, 2009;. For example, Lag and Steinnes (Lag and Steinnes, 1978) reported positive correlations between organic matter and Hg (with r 2 of 0.58 and 0.55, respectively) content across Eastern and Northern Norway humus layers, and showed regressions between soil organic C and Hg content with coefficient of determination, r 2 , up to 47 % across 14 US forest sites.…”

“…We must, however, put strong limitations on the magnitude of predicted changes in soil Hg densities because using direct (i.e., linear) relationships between soil Hg and C changes that result from our model implementation are highly unlikely in reality. For example, linear responses between Hg and C changes might be expected upon complete loss of both Hg and organic C pools (e.g., that may occur in surface organic horizons during wildfires) where significant Hg losses have in fact been observed (Artaxo et al, 2000;Brunke et al, 2001;Friedli et al, 2001;Sigler et al, 2003;Turetsky et al, 2006;. In contrast, however, the few experimental studies that correspondingly measured the fate of Hg upon C mineralisation indicate that only a small fraction of Hg may be subject to volatilisation losses upon evasion of CO 2 (Fritsche et al, 2008;Obrist et al, 2010b), which would indicate a much smaller magnitude of soil Hg losses compared to that of C. The biogeochemistry of terrestrial Hg is very complex, including various deposition and emission pathways (Graydon , 2008b;Gustin et al, 2008), redox transformations between volatile and non-volatile Hg forms (Lalonde et al, 2001;Obrist et al, 2010a), and methylation and demethylation processes (Ullrich et al, 2001).…”

Concentration-weighted trajectory approach to identifying potential sources of speciated atmospheric mercury at an urban coastal site in Nova Scotia, Canada

“…In comparison, residential oil combustion is even a larger source of Hg compared to wood combustion and natural gas in the US northeast ranging from 0.04 kg in Delaware to 265 kg in Ohio annually (USEPA, 2012b). Forest fires in Quebec have always been persistent sources of Hg, PM 2.5 , and carbon, impacting sites in Massachusetts (Sigler et al, 2003), Baltimore (Sapkota et al, 2005), Philadelphia (Begum et al, 2005), and northern New York (Wang et al, 2010). From 2010-2011, there were 1019 forest fires across central to southern Quebec, which had burned a total area of ∼ 3300 km 2 (NFD, 0.9 % 0.9 % 1.4 % 1.8 % 0.9 % 0.9 % 0.9 % 5.0 % 0.5 % 2.8 % 1.4 % 3.7 % ≥ 118.1 0.5 % 1.4 % 0.0 % 1.8 % 2.8 % 1.4 % 0.0 % 1.8 % 2.3 % 3.2 % 0.5 % 2.3 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 2012; SOPFEU, 2012).…”