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To assess the role of salt-marsh plants on the vegetation-atmospheric Hg0 fluxes, three salt marsh plant species, Halimione portulacoides, Sarcocornia fruticosa and Spartina maritima were selected from a moderately contaminated site in the Tagus estuary during May 2012. Total mercury in stems and leaves for each plant as well as total gaseous mercury and vegetation-air Hg0 fluxes were measured over two continuous days. Mercury fluxes were estimated with a dynamic flux Tedlar® bag coupled to a high-resolution automated mercury analyzer (Tekran 2537A). Other environmental parameters such as air temperature, relative humidity and net solar radiation were also measured aside. H. portulacoides showed the highest total mercury concentrations in stems and leaves and the highest average vegetation-air Hg0 flux (0.48 ± 0.40 ng Hg m−2 h−1). The continuous measurements converged to a daily pattern for all plants, with enhanced fluxes during daylight and lower flux during the night. It is noteworthy that throughout the measurements a negative flux (air-vegetation) was never observed, suggesting the absence of net Hg0 deposition. Based on the above fluxes and the total area occupied by each species we have estimated the total amount of Hg0 emitted from this salt-marsh plants. A daily emission of 1.19 mg Hg d−1 was predicted for the Alcochete marsh and 175 mg Hg d−1 for the entire salt marsh area of the Tagus estuary.

Intertidal sediments of Tagus estuary regularly experiences complex redistribution due to tidal forcing, which affects the cycling of mercury (Hg) between sediments and the water column. This study quantifies total mercury (Hg) and methylmercury (MMHg) concentrations and fluxes in a flooded mudflat as well as the effects on water-level fluctuations on the air-surface exchange of mercury. A fast increase in dissolved Hg and MMHg concentrations was observed in overlying water in the first 10min of inundation and corresponded to a decrease in pore waters, suggesting a rapid export of Hg and MMHg from sediments to the water column. Estimations of daily advective transport exceeded the predicted diffusive fluxes by 5 orders of magnitude. A fast increase in dissolved gaseous mercury (DGM) concentration was also observed in the first 20-30min of inundation (maximum of 40pg L-1). Suspended particulate matter (SPM) concentrations were inversely correlated with DGM concentrations. Dissolved Hg variation suggested that biotic DGM production in pore waters is a significant factor in addition to the photochemical reduction of Hg. Mercury volatilization (ranged from 1.1 to 3.3ngm-2h-1; average of 2.1ngm-2h-1) and DGM production exhibited the same pattern with no significant time-lag suggesting a fast release of the produced DGM. These results indicate that Hg sediment/water exchanges in the physical dominated estuaries can be underestimated when the tidal effect is not considered.

Depth variations of total mercury (Hg) and methylmercury (MeHg) concentrations were studied in cores from non-colonized sediments, sediments colonized by Halimione portulacoides, Sarcocornia fruticosa and Spartina maritima and belowground biomass, in a moderately contaminated salt marsh (Tagus Estuary, Portugal). Concentrations in belowground biomass exceeded up to 3 (Hg) and 15 (MeHg) times the levels in sediments, and up to 198 (Hg) and 308 (MeHg) times those found in aboveground parts. Methylmercury in colonized sediments reached 3% of the total Hg, 50 times above the maximum values found in non-colonized sediments. The absence of correlations between total Hg concentrations in sediments and the corresponding MeHg levels suggested that methylation was only dependent on the environmental and microbiological factors. The analysis of belowground biomass at high-depth resolution (2 cm) provided evidence that Hg and MeHg were actively absorbed from sediments, with higher enrichment factors at layers where higher microbial activity was probably occurring. The results obtained in this study indicated that the biotransformation of Hg to the toxic MeHg could increase the toxicity of plant-colonized sediments.

Mercury (Hg) contamination in tundra region has raised substantial concerns, especially since the first report of atmospheric mercury depletion events (AMDEs) in the Polar Regions. During the past decade, steady progress has been made in the research of Hg cycling in the Polar Regions. This has generated a unique opportunity to survey the whole Arctic in respect to Hg issue and to find out new discoveries. However, there are still considerable knowledge gaps and debates on the fate of Hg in the Arctic and Antarctica, especially regarding the importance and significance of AMDEs vs. net Hg loadings and other processes that burden Hg in the Arctic. Some studies argued that climate warming since the last century has exerted profound effects on the limnology of High Arctic lakes, including substantial increases in autochthonous primary productivity which increased in sedimentary Hg, whereas some others pointed out the importance of the formation and postdeposition crystallographic history of the snow and ice crystals in determining the fate and concentration of mercury in the cryosphere in addition to AMDEs. Is mercury re-emitted back to the atmosphere after AMDEs? Is Hg methylation effective in the Arctic tundra? Where the sources of MeHg are? What is its fate? Is this stimulated by human made? This paper presents a critical review about the fate of Hg in the Arctic tundra, such as pathways and process of Hg delivery into the Arctic ecosystem; Hg concentrations in freshwater and marine ecosystems; Hg concentrations in terrestrial biota; trophic transfer of Hg and bioaccumulation of Hg through food chain. This critical review of mercury fates and contamination in the Arctic tundra ecosystem is assessing the impacts and potential risks of Hg contamination on the health of Arctic people and the global northern environment by highlighting and "perspectiving" the various mercury processes and concentrations found in the Arctic tundra.

Mercury contamination in the Great Lakes continues to have important public health and wildlife ecotoxicology impacts, and atmospheric deposition is a significant ongoing loading pathway. The objective of this study was to estimate the amount and source-attribution for atmospheric mercury deposition to each lake, information needed to prioritize amelioration efforts. A new global, Eulerian version of the HYSPLIT-Hg model was used to simulate the 2005 global atmospheric transport and deposition of mercury to the Great Lakes. In addition to the base case, 10 alternative model configurations were used to examine sensitivity to uncertainties in atmospheric mercury chemistry and surface exchange. A novel atmospheric lifetime analysis was used to characterize fate and transport processes within the model. Model-estimated wet deposition and atmospheric concentrations of gaseous elemental mercury (Hg(0)) were generally within ∼10% of measurements in the Great Lakes region. The model overestimated non-Hg(0) concentrations by a factor of 2–3, similar to other modeling studies. Potential reasons for this disagreement include model inaccuracies, differences in atmospheric Hg fractions being compared, and the measurements being biased low. Lake Erie, downwind of significant local/regional emissions sources, was estimated by the model to be the most impacted by direct anthropogenic emissions (58% of the base case total deposition), while Lake Superior, with the fewest upwind local/regional sources, was the least impacted (27%). The U.S. was the largest national contributor, followed by China, contributing 25% and 6%, respectively, on average, for the Great Lakes. The contribution of U.S. direct anthropogenic emissions to total mercury deposition varied between 46% for the base case (with a range of 24–51% over all model configurations) for Lake Erie and 11% (range 6–13%) for Lake Superior. These results illustrate the importance of atmospheric chemistry, as well as emissions strength, speciation, and proximity, to the amount and source-attribution of mercury deposition.

An intensive survey of mercury speciation was performed at a site on the Upper St. Lawrence River near Cornwall, Ontario, Canada with a history mercury contamination in sediments. Surface sediments were collected every 1.50 h. Total mercury (Hgtotal), methylmercury (MeHg), organic carbon, inorganic and organic sulphur were determined in the solid fraction. Dissolved Hgtotal, MeHg and dissolved organic carbon (DOC) were measured in pore waters. Concentrations of Hgtotal in the upper layers (first 5 cm) were high, ranging from 1.42 to 25.8 nmol g−1 in solids and from 125 to 449 pM in pore waters. MeHg levels were also high, ranging from 4.34 to 34.1 pmol g−1 in solids and from 40 to 96 pM in pore waters. This amounts to up to 1.4% of Hgtotal present as MeHg in solids and 64% in pore waters. A daily pattern for Hgtotal was observed in the solid fraction. The MeHg distribution in solids and pore waters was not correlated with Hgtotal or DOC, suggesting that the concentrations of MeHg are probably more influenced by the relative rates of methylation/demethylation reactions in the sediment–water interface. Acid volatile sulphide levels and DOC were inversely correlated with organic sulphur (Sorg) levels suggesting that both parameters are involved in the rapid production of Sorg. A positive correlation was also observed between Hgtotal and Sorg in solids (R = 0.87, p < 0.01) illustrating the importance of organic sulphur in the retention and distribution of Hg in the solid fraction of the sediments. The results suggest that variations of Hgtotal concentrations in Upper St. Lawrence River surface sediments were strongly influenced by the formation/deposition/retention of organic sulphur compounds in the sediment–water interface.

This paper reports the first ebullitive fluxes of hydrogen (H2), carbon monoxide (CO), methane (CH4), carbon dioxide (CO2) and total gaseous mercury (TGM) from the Cornwall Area of Concern (CAC). Although sediments were contaminated with mercury, bubbling was a negligible source of mercury for the global atmosphere. Indeed, the average emission of TGM through ebullition was 0.04 pg m(-2) h(-1). Measurements of H2, CO, CH4 and CO2 trapped gas concentrations and fluxes were used as indicators of diagenesis processes. The CAC represented a significant regional source of CH4 since the estimated ebullitive fluxes (3.5 mg m(-2) h(-1)) were similar to the CH4 emissions measured above typical flooded freshwater wetlands. As molecular diffusion is known as the main pathway of CO2 transport from water to the atmosphere, CO2 ebullitive fluxes were weak (0.39 mg m(-2) h(-1)). Bubbling of CO (1.6 microg m(-2) h(-1)) was 10 folds less important than CO fluxes measured over flooded freshwater wetlands. Finally, H2 emissions (0.001 microg m(-2) h(-1)) were negligible since the level of this trace gas is tightly regulated by microorganisms in anaerobic environments.

Long-term monitoring data of total gaseous mercury (TGM) concentrations from the Canadian Atmospheric Mercury Measurement Network (CAMNet) were analysed for temporal trends, seasonality and comparability within the network and compared to other network and model results. Data collected from 11 Canadian measurement sites between 1995 and 2005 were analysed. Sites within CAMNet were characterized by principle component analysis (PCA) into four main categories. For the first time since automated TGM measurements have been made within CAMNet, this paper reveals statistically significant decreasing TGM concentrations from rural locations in Canada during this time period. The largest declines were observed close to the urban areas of Toronto and Montreal, where levels fell by 17% at Point Petre, and 13% at St. Anicet, respectively. Many of the TGM changes are comparable with the overall trends observed in total mercury concentrations in precipitation, for similar time periods, at co-located or nearby National Atmospheric Deposition programme's Mercury Deposition Network (NADP-MDN) sites. The results show that these changes are mostly driven by local or regional changes in mercury emissions. Other sites within CAMNet reflect reported changes in hemispherical global background concentrations of airborne mercury, where slight decreases or no statistically significant trend in TGM concentrations exist over the same time period.

Porewater samples were obtained on five occasions during spring, summer and fall by in situ dialysis from three sites of a large freshwater wetland situated along the St. Lawrence River. These samples were analysed for total dissolved mercury ([Hg] T ) and methylmercury ([MeHg]) concentrations and for complementary variables including dissolved sulfate, sulfide and elemental sulfur concentrations. Sediment cores were obtained on three occasions from one of these sites for the determination of total mercury ({Hg} T ) and methylmercury ({MeHg}) concentration as well as mercury methyltransferase (HgMT) activity profiles. {MeHg} and HgMT activity varied with time and sediment depth. The porewater [Hg] T and [MeHg] depth profiles varied with time and among sites. Modeling the porewater [MeHg] profiles with a one-dimensional reaction-transport equation allowed identification of the sediment depths where MeHg is produced or consumed, as well as an estimate of the net in situ MeHg production rates in the sediments. The model-predicted depths of MeHg production, as well as the sulfate concentration and the HgMT activity depth distributions are all consistent with the involvement of sulfate reducing bacteria in the production of MeHg.

One fate of gaseous elemental mercury (GEM) in the Arctic has been identified as gas phase oxidation by halogen-containing radicals, leading to abrupt atmospheric mercury depletion concurrent with ozone depletion. Rapid deposition of oxidized mercury leads to snow enrichment in mercury. In this report, we describe experiments that demonstrate the ability of snow to directly scavenge atmospheric mercury. The study was conducted at Kuujjuarapik, Québec, Canada (latitude 55 degrees 17'N). A mercury depletion event (MDE) caused the mercury concentration in the surface snow of the coastal snowpack to double, from (9.4+/-2.0) to (19.2+/-1.7) ng/L. Independent of the MDE, mercury concentrations increased five-fold, from (10.0+/-0.1) to (51.4+/-6.0) ng/L, upon spiking the snow with 500 microM hydrogen peroxide under solar irradiation. Total organic carbon in the spiked irradiated snow samples also decreased, consistent with the formation of strongly oxidizing species. The role of the snowpack in releasing GEM to the atmosphere has been reported; these findings suggest that snow may also play a role in enhancing deposition of mercury.

An intensive field study quantifying total gaseous mercury (TGM) and mercury speciation fluxes in a wetland ecosystem (Bay St. Franc - ois wetlands, Quebec, Canada) was conducted in summer 2003. This study is one of the first attempts to design and develop an innovative approach—dynamic flux bag (DFB) technique to measure in situ mercury air-vegetation exchange with a monoculture of river bulrush (Scirpus fluviatilis). Air-vegetation flux measurements were conducted under dry condition at site 1 and flood condition at site 2. TGM fluxes fluctuated from � 0.91 to 0.64 ng/m 2 (leaf area)/h with an average value of -0.2670.28 ng/m 2 (leaf area)/h at site 1 and ranged from � 0.98 to 0.08 ng/m 2 (leaf area)/h with a mean flux of � 0.3370.24 ng/m 2 (leaf area)/h at site 2 (positive sign means volatilization, and negative sign indicates deposition). The data indicated that TGM air-vegetation exchange is bidirectional. However, the net flux is primarily featured by dry deposition of TGM from atmosphere to the vegetation. In mercury speciation study using the DFB approach, particulate mercury (PM) and reactive gaseous mercury (RGM) represented less than 1% of total mercury. Ambient ozone concentrations had significant influences on RGM concentrations (r ¼ 0.54, po0.05), implicating oxidation of gaseous elemental mercury (GEM) by ozone to form RGM. A discussion about the similarities and discrepancies between the DFB and other approaches (dynamic flux chamber and modified Bowen ratio) is presented. During the course of this study, some operational effects associated with the bag design, mainly the emergence of condensation within the bag, were encountered. Several improvements relating to the DFB design were recommended. Upon improvement, the DFB method could be one of the most promising techniques to study the role of a single plant in air-vegetation exchange of mercury. r 2005 Elsevier Ltd. All rights reserved.

Eight years of gaseous elemental mercury (GEM) concentration measurements from Alert, Nunavut, Canada (between 1995 and 2002) is presented. The annual time series shows a distinct repeating seasonal pattern with an overall annual median concentration for this time period of 1.58 (S.D.=0.04 ng m(-3)). Strong seasonal variation was observed throughout the years with springtime displaying strong variability in the GEM and overall lower median concentrations due to the so-called mercury depletion events (MDEs). Summer concentrations are higher than the annual average and show a decrease in variability. Fall and winter concentrations are distributed around the annual median concentrations and show little variability. The relationship between the springtime depression and the summer increase shows a change in the behaviour of mercury between 1995 and 2002. Preliminary results suggest that during this period an increasing amount of the mercury lost from the atmosphere in the spring is not returned to atmosphere in summer. A comparison of GEM concentration data from three sites--Alert (Canada), Amderma (Russia) and Kuujjuarapik (Canada)--demonstrated similar monthly distribution of GEM between Alert and Amderma, with the latter not showing as high summer concentrations. Monthly distribution of GEM at Kuujjuarapik varied considerably from the other two sites. MDEs were found to occur at each site in the spring yet displayed different characteristics. MDEs appear to start at Alert shortly after polar sunrise but in Amderma their initiation is delayed approximately 2 months following polar sunrise. MDEs occur in Kuujjuarapik in the springtime despite an incomplete development of the polar day-night cycle. In spring, as soon as air temperature attained temperatures consistently above 0 degrees C, MDEs ended immediately at all three sites. Continued studies into MDEs are warranted, but clearly an important component of future studies must focus on the origins of the variation of GEM behaviour at different sites.

An intensive field campaign was conducted from 1 January to 31 December 2003 in St. Anicet (Quebec, Canada) using a set of Automatic Atmospheric Mercury Speciation Analyzers (Tekran 2537A with 1130 and 1135 units) for the measurements of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (Hg p ). This study is one of the first attempts to present the most extensive data sets of a year of continuous measurements of atmospheric mercury species. Average concentrations of GEM, RGM and Hg p in 2003 were 1.65±0.42 ng m −3 , 3±11 and 26±54 pg m −3 (mean±SD), respectively. On an average, the atmospheric mercury apportioned as follows: GEM (98.4%)>Hg p (1.4%)>RGM (0.2%). Regional atmospheric mercury sources contributed to the Southern Quebec atmospheric mercury contamination. The results showed large seasonality of GEM, RGM and Hg p (GEM: 0.37–10.4 ng m −3 ; RGM: 0–386 pg m −3 and Hg p : 0–1528 pg m −3 ). As a whole, mercury speciation concentrations are larger in wintertime than in summertime. RGM and Hg p concentrations showed the sharpest seasonal variations. Hourly variations were observed for the mercury species. Maximum RGM and Hg p concentrations were measured normally during mid-day with a Gaussian shape whereas GEM showed a bimodal shape with minimum values early in the morning. The backward trajectory model showed that atmospheric mercury speciation might be transported from local or regional sources. Also, it was observed that atmospheric mercury transformation times converting GEM to Hg p were short (∼4 h). However, atmospheric kinetics involving O 3 and OH radicals do not support such fast oxidation processes with normal concentrations.

Data from 13 National Atmospheric Deposition Program Mercury Monitor Network (NADP/ MDN) monitoring stations (1996-2002) and the Underhill (VT) event-based monitoring site (1993-2002) were evaluated for spatial and temporal trends. More precipitation and mercury deposition occurred in the southern and coastal MDN sites, except for the Underhill site, which received more mercury deposition than surrounding sites. Precipitation patterns varied. Regionally, higher concentrations of mercury were recorded during the late spring and summer months. Several sub-regional clusters of MDN sites were evident, based on mercury deposition patterns. In general, more mercury was deposited during the summer months. "Enhanced" weekly deposition (250 ng/m2) and distinct seasonal deposition patterns were evident at all MDN sites. Regionally, high depositional periods contributed significantly to annual loads (20%- approximately 60%). Southern and coastal sites measured more frequent periods of high deposition than inland sites. Spring and summer "enhanced" deposition may be important contributing factors to mercury bioaccumulation during the growing season. Recent regional reductions of mercury emissions were not reflected in the regional mercury concentration or deposition data. Few sites showed linear relations between the concentration of mercury in precipitation and acid rain co-contaminants (sulfates and nitrates).

In order to evaluate and understand the mercury gas exchange processes in fluvial wetlands, related researches were initiated in a St. Lawrence River wetland (Bay St. Francois, Que., Canada). Mercury fluxes were measured using dynamic flux chamber methods, coupled with an automatic mercury vapor analyzer (namely, Tekran, Model 2537A). Mercury air–surface gas exchanges as well as meteorological conditions were measured during two intensive field campaigns from August to September, 1999 and May, 2000, respectively. The field studies in 1999 were performed under bare soil (unvegetated portions) dry wetland conditions whereas the studies in 2000 were conducted under flooded conditions. Both field measurements were performed at the same location in the aim to study the impact of the water levels on the mercury fluxes. The water-level effect was simply to provide either a dry or a flooded site. Water-level fluctuations in fluvial wetland can result in a conversion between a standing water environment and an environment in which sediments are exposed to air. Mercury flux dynamics and processes would alter accordingly to changing environmental conditions. The average concentration of total Hg in the soil and water were ∼0.06 ng mg−1 (dry weight basis) and ∼1 ng l−1, respectively. The predominant flux of Hg° over both bare soil and water was emission. Median Hg flux under dry conditions was 0.83 ng m−2 h−1 in comparison with 0.50 ng m−2 h−1 under flooded conditions. Correlations between Hg flux, net radiation and temperature (bare soil or water) indicated that the main process involved in air–soil gas exchange under dry conditions is the enthalpy of volatilization; whereas photoreduction predominates under flooded conditions. This paper discusses the Hg flux results under both conditions in the perspective of water-level fluctuations and their impacts on the air–surface exchange of mercury.

In order to better understand MDE chemistry, which are thought to happen in the presence of halogenated (chloride and bromide) species, we have led several kinetic experiments with gaseous mercury, ozone and chlorine in Teflon bags under polar atmospheric conditions. The chlorine was expected to produce, with natural solar radiation, the reactive chloride species assumed to play a role in the MDE mechanism. The aim of the first experiment was to study the reactivity between ozone and gaseous mercury: we obtained a rate constant of (13±6)x10 -20 cm 3 /molec/s, which is roughly comparable to constants given in the literature. Concerning the second experiment, for which chlorine has been introduced, a rate constant of (6.2 ±2.2))x10 -17 cm 3 /molec/s for the reactivity of gaseous mercury was obtained. This constant is too weak to recover the atmospheric lifetime of gaseous mercury during MDE. This difference is in discussion in this paper.

During a field experiment at Kuujjuarapik/Whapmagoustui (55°31N, 77°75W), Quebec, we have pointed out modifications in the size distribution of particles during a Mercury Depletion Event (MDE). We observed an increase of atmospheric particles concentrations in the ambient air, correlated with depletions of ozone and atmospheric mercury. These increases were followed by a change in the size particles distribution. Assuming that the divalent mercury species formed during the MDE could be adsorbed onto particles, this is likely to contribute to higher deposition fluxes of oxidised mercury on the snow pack.

This study reported the first synchronized automated high-time resolution mercury species fluxes over plant canopy. It is suggested that plants can uptake reactive gaseous mercury and release elemental gaseous mercury during daytime. This can be environmentally significant due to the bio-transfer (conversion) from a short transported mercury species (Hg (II)) to a long transport mercury species (Hg°).

The snowpack is a medium that greatly interacts with a variety of atmospheric gases. Its role in the mercury depletion events in arctic and sub-arctic regions seems to be crucial though it is poorly understood. We studied an environmental component of mercury that is interstitial gaseous mercury (IGM) present in the air of the snowpack at Kuujjuarapik (55°N, 77°W), Quebec in April 2002. Our data demonstrate that the snow-pack plays a major role in the global mercury cycle. Indeed, IGM concentrations exhibit a well-marked diurnal cycle with uninterrupted events of Hg° depletion and production within the snowpack. During snowmelt episode, high IGM concentrations (∼20 ng/m 3 at a depth of 37 cm) have been recorded. This study gives us the confirmation that Hg° is involved in oxidation processes occurring in the snowpack. Additionally, we assume that the impressive production of Hg° during the daytime may be the results of photoreduction and photo-initiated reduction of Hg(II) complexes.

The combined effect of light and hydrogen peroxide on the ability of surface snow to scavenge atmospheric mercury was investigated in Kuujjuarapik, Nunavik, Canada (latitude 55°N). Mercury concentrations in the snowpack increased five-fold upon spiking with hydrogen peroxide under solar irradiation. Anion analysis of the snow revealed the presence of chloride, which may stabilize Hg(II). Measurements of total inorganic and organic carbon showed that both kinds of carbon content decreased in the spiked irradiated snow samples.

Mercury may be one of the best-documented hazardous substances utilised by man. Still the uncovering of the global human impacts on the environment through the use and mobilisation of mercury cannot be considered complete. Recent mercury depletion events observed in the Arctic have opened the horizon to numerous new aspects on mercury fate and cycling in the environment. This chapter browses various aspects of the extremely complex cycling and fate of mercury in the perspective of mercury as a global pollutant and discusses some new emerging research fields in mercury.

Volatilization of elemental Hg represents an important Hg flux for many aquatic systems. In order to model this flux accurately, it is necessary to measure elemental Hg concentrations in air and water, as well as meteorological variables. Up to now, temporal resolution of elemental Hg analysis has been low (0.5–1 h between data points) compared to other variables used in models (5 min between data points). Here we present an analytical system that allows for the near-real time measurement (every 5 min) of dissolved gaseous mercury (DGM). This system is automated and has a detection limit of 8.5 pg l−1. By using solar radiation as a predictor of DGM concentrations in aquatic systems, we demonstrate the fast response time of the analytical system to fluctuations in ambient DGM in the St. Lawrence river, at sunrise. Complete covering of the purge apparatus and tubing resulted in a 2.6-fold decrease in the slope of the DGM versus light relationship, revealing the importance of light shielding the instrumentation to obtain realistic values.

The main objectives of this paper were to report total gaseous mercury (TGM) concentrations at four stations along the St. Lawrence River in 1998 and to give some insights regarding their fate. The TGM network stretches from latitudes 45 degrees N to 50 degrees N. TGM and ozone concentrations (used as complementary pollutant) were presented. The median TGM concentrations throughout the network varied from 1.62 to 1.79 ng/m3. Sites close to Montreal had larger TGM concentrations. Montreal surroundings appeared to be a source of TGM. The TGM concentrations were maximum in wintertime and minimum in summertime throughout the sites. However, the diurnal variations were site specific. St. Anicet and L'Assomption were more variable in terms of large concentrations, whereas Mingan and Villeroy were more variable in terms of low concentrations. Ozone and TGM concentrations were positively correlated at some sites (Villeroy, Mingan and St. Anicet) whereas they were not at L'Assomption (closest site to Montreal). Local TGM and ozone precursor sources would affect the correlation.

The paper presents an analysis of a set of data that includes both Hg profiles and modeled fluxes over water surface (using the two-layer model) and develops some insights regarding mercury water−air exchanges in Lake Ontario and the Upper St. Lawrence River (USLR). This paper presents the first in situ estimation of the water−air Hg gas exchange in Lake Ontario. It shows that water−air exchange fluxes over Lake Ontario and the Upper St. Lawrence River contributed to atmospheric mercury built-up over water bodies. TGM concentrations over Lake Ontario were significantly higher on the South shore than on the North shore, whereas the degree of saturation was higher on the North shore. Moreover TGM concentrations over water bodies were significantly higher than the reference station located on the ground surface (St. Anicet) indicated. TGM gradient measurements suggested that the South shore of Lake Ontario was mostly in evasion mode, whereas on the North shore and the Upper St. Lawrence River, both evasion a...

Abundances of heavy metals and Pb and Sr isotope ratios have been determined in precipitation collected between December 1997 and June 1999 at St. Anicet and L'Assomption, near Montreal, Canada. Median enrichment factors for the heavy metals, relative to upper crustal abundances, are all »10 indicative of an anthropogenic origin. The 206Pb/207Pb values exhibit a large variation at both stations, with values of 1.170–1.190 and 1.130–1.150 recorded during the winter and summer seasons, respectively. The Pb isotope systematics defined by most of the samples from both stations may be explained by mixing of anthropogenic emissions from U.S. and Canadian sources. Comparison of Pb isotope ratios and heavy metal abundances between the same, individual precipitation events from both stations, however, do not systematically yield similar values and may be attributable to significant, local anthropogenic sources. The 87Sr/86Sr values for precipitations also exhibit a seasonal variation at both stations with the least radiogenic values being recorded, in general, during the winter months (

Elemental Hg (Hg0) is a volatile species that is responsible for water-to-air transfer of Hg in Lake Ontario and the St. Lawrence River. We conducted two cruises in 1998 to identify spatial and temporal patterns in Hg0 levels in these systems and performed field and laboratory experiments on redox transformations of Hg. Elemental Hg concentrations were higher in Lake Ontario than in the St. Lawrence River. At stations in Lake Ontario, Hg0 levels were higher at the bottom of the water column than at the surface, whereas they were homogeneous throughout the water column of the river. Elemental Hg concentrations were generally higher in July than in September and, in contrast with experiments on inland lakes, were relatively constant during the day except for a narrow peak at sunrise. Field and laboratory experiments showed that photoreduction of Hg(II) in St. Lawrence River water was substrate limited and was influenced by visible and ultraviolet radiation. Pseudo first-order kinetics best described photoreduction, with k values between 1 and 2·h-1.

The potential source contribution function (PSCF) has been used to study the source–receptor relationships for total gaseous mercury (TGM) found in air collected at two sites along the St. Lawrence River valley, namely at St. Anicet and Mingan. TGM concentrations have been measured with high time-resolution analysers (Tekran instrument). The source–receptor analyses have been applied with regards to the seasonality of TGM. Median TGM concentrations are significantly less (χ2: α=0.01) during the summertime than other periods at both sites. A total of 12 225 trajectory end-points for St. Anicet and 4480 trajectory end points for Mingan have been used to create potential source area maps. This study identifies preferred potential sources of TGM at St. Anicet during wintertime with strongest probability stretching from the Gulf of Mexico to the southern tip of Greenland. This pattern mimics, the North American anthropogenic Hg emission inventory. Furthermore, some Eurasian mercury air mass intrusions are suggested at Mingan during wintertime. The summertime period at Mingan points out some potential sources stretching from the american mid-west to the St. Lawrence River valley as well as areas around the southern tip of the Hudson Bay.

The paper presents one year of results (1995–1996) of an on-going research study in southern Quebec with regard to mercury in precipitation. A modified rain water collector (MIC-B1) coupled to a data logger is used, in order to be able to select individual events from a remote site. A peristaltic pump coupled with an enclosed Teflon system train separates `in situ' the particulate and the dissolved phases of mercury. QA/QC sampling protocol including memory effect, percentage of recovery as well as field blanks are applied to maintain the high standards of quality. Total mercury concentrations in both phases are measured by Cold Vapour Atomic Fluorescence Spectrophotometry (CVAFS). The volume-weighted mean of total Hg concentration is 6.98 ng.l−1 (the median concentration is 6.58 ng.l−1 and the arithmetic mean is 8.26 ng.l−1). The annual total mercury deposition is about 7.6 μg.m−2. The particulate fraction accounts for a median of 26% of the total mercury concentration. According to Henry's Law, the truly dissolved mercury accounts for less than 0.5% whereas most of the dissolved fraction is expected to be in molecular complexes or colloidal form (

In order to evaluate and understand the processes of water-air and soil-air exchanges involved at background sites, an intensive field measurement campaign has been achieved during the summer of 1995 using high-time resolution techniques (10 min) at two sites (land and water) in southern Quebec (Canada). Mercury flux was measured using a dynamic flux chamber technique coupled with an automatic mercury vapour-phase analyser (namely, Tekran®). The flux chamber shows that the rural grassy site acted primarily as a source of atmospheric mercury, its flux mimicked the solar radiation, with a maximum daytime value of ∼ 8.3 ng m−2 h−1 of TGM. The water surface location (St. Lawrence River site located about 3 km from the land site) shows deposition and evasion fluxes almost in the same order of magnitude (−0.5 vs 1.0 ng m−2 h−1).The latter is influenced to some extent by solar radiation but primarily by the formation of a layer of stable air over the water surface in which some redox reactions might promote evasion processes over the water surface. This process does not appear over the soil surface. As a whole, soil-air exchange rate is about 6–8 fold greater than the water-air exchange.

Total Gaseous Mercury (TGM) data (n = 5125) measured from September 9 to November 30, 1994 in Southern Quebec with an automatic TGM analyser (Tekran®) are used to study the behaviour of TGM with ozone and the water vapour mixing ratio. Results show, as a whole, no straight-forward correlation between TGM and ozone concentrations. A significant correlation between TGM and water vapour mixing ratio was measured. Some back reduction of Hg(II) to Hgo in the aqueous phase and subsequent evaporation of Hg0 according to Henry's Law is expected. The latter correlation seems to be partly ozone dependent since under ‘clean conditions’ (ozone > 30 ppbv) the slope of TGM vs the water vapour mixing ratio is twice that during ‘polluted conditions’ (ozone > 30 ppbv) which suggests some compensation effects under polluted conditions (counteracting the back-reduction of Hg(II) to Hgo in the aqueous phase). Oxidation of TGM by ozone during high moisture conditions (water vapour mixing ratio ∼14g/kg) seems to appear at the threshold ozone concentration ⩾ 30 ppbv.

Global emissions of mercury continue to change at the same time as the Arctic is experiencing ongoing climatic changes. Continuous monitoring of atmospheric mercury provides important information about long-term trends in the balance between transport, chemistry, and deposition of this pollutant in the Arctic atmosphere. Ten-year records of total gaseous mercury (TGM) from 2000 to 2009 were analyzed from two high Arctic sites at Alert (Nunavut, Canada) and Zeppelin Station (Svalbard, Norway); one sub-Arctic site at Kuujjuarapik (Nunavik, Québec, Canada); and three temperate Canadian sites at St. Anicet (Québec), Kejimkujik (Nova Scotia) and Egbert (Ontario). Five of the six sites examined showed a decreasing trend over this time period. Overall trend estimates at high latitude sites were: −0.9% yr−1 (95% confidence limits: −1.4, 0) at Alert and no trend (−0.5, +0.7) at Zeppelin Station. Faster decreases were observed at the remainder of the sites: −2.1% yr−1 (−3.1, −1.1) at Kuujjuarapik, −1.9% yr−1 (−2.1, −1.8) at St. Anicet, −1.6% yr−1 (−2.4, −1.0) at Kejimkujik and −2.2% yr−1 (−2.8, −1.7) at Egbert. Trends at the sub-Arctic and mid-latitude sites agree with reported decreases in background TGM concentration since 1996 at Mace Head, Ireland, and Cape Point, South Africa, but conflict with estimates showing an increase in global anthropogenic emissions over a similar period. Trends in TGM at the two high Arctic sites were not only less negative (or neutral) overall but much more variable by season. Possible reasons for differences in seasonal and overall trends at the Arctic sites compared to those at lower latitudes are discussed, as well as implications for the Arctic mercury cycle. The first calculations of multi-year trends in reactive gaseous mercury (RGM) and total particulate mercury (TPM) at Alert were also performed, indicating increases from 2002 to 2009 in both RGM and TPM in the spring when concentrations are highest.

Using inductively coupled plasma-mass spectrometry (ICP-MS), 24 inorganic elements were analysed for about 65 station-events during the summer of 1989, at Montreal Island (Canada). Enrichment factors indicate that numerous elements are enriched as compared to the Earth's crust, since only six elements (titanium, iron, rubidium, yttrium, zirconium, and cerium) can be considered natural. A comparison with results from a rural area indicates that most elements are affected by urbanization. For the majority of the elements, scavenging below the cloud (wash-out) seems to be a significant atmosphere cleansing mechanism, although one element, lead, appears to be rather governed by long-range transportation and rain-out (in-cloud scavenging). Correlation between elements indicates that some elements have similar behaviour, which can be partly explained by sorption phenomena or chemical bonding in the same compound.

Contaminated sediments in the St. Lawrence River remain a difficult problem despite decreases in emissions. Here, sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and diffusion from the sediment to the overlying water was 17.5 + or - 10.6 SE ng cm(-2) yr(-1) for THg and 3.8 + or - 1.7 SE ng cm(-2) yr(-1) for MeHg. These fluxes were very small when compared to the particle-bound mercury flux accumulating in the sediment (183 + or - 30 SE ng cm(-2) yr(-1)). Studies have reported that fish from the westernmost site have higher Hg concentrations than fish collected from the other two sites of the Cornwall Area of Concern, which could not be explained by differences in the Hg flux or THg concentrations in sediments, but the highest concentrations of sediment MeHg, and the greatest proportions of MeHg to THg in both sediment and pore water were observed where fish had highest MeHg concentrations.

This chapter presents a review of atmospheric mercury measurements (as total and as speciated mercury) conducted at terrestrial sites during the last decade. A large number of activities have been carried out in different regions of the world aiming to assess the level of mercury in ambient air and precipitation, and its variation over time and with changing meteorological conditions. Recent studies have highlighted that in fast developing countries (i.e., China, India) mercury emissions are increasing in a dramatic fashion due primarily to a sharp increase in energy production from the combustion of coal (Chapter-2 by Street et al.; Chapter-3 by Feng et al. in this report). The large increase in mercury emissions in China over the last decade are not currently reflected in the long-term measurement of total gaseous mercury at Mace Head, Ireland between 1996 to 2006, nor in the precipitation data of the North American Mercury Deposition Network (MDN). There are documented recent increases in the oxidation potential of the atmosphere which might account, at least in part, for the discrepancy between observed gaseous mercury concentrations (steady or decreasing) and global mercury emission inventories (increasing). This chapter provides a detailed overview of atmospheric measurements performed at industrial, remote and rural sites during the last decade with reference to the monitoring techniques and location of monitoring sites in most of the continents.

Distribution of total mercury (THg), gaseous elemental Hg(0) (GEM), monomethyl Hg (MMHg), and dimethyl Hg (DMHg) was examined in marine waters of the Canadian Arctic Archipelago (CAA), Hudson Strait, and Hudson Bay. Concentrations of THg were low throughout the water column in all regions sampled (mean +/- standard deviation; 0.40 +/- 0.47 ng L(-1)). Concentrations of MMHg were also generally low atthe surface (23.8 +/- 9.9 pg L(-1)); however at mid- and bottom depths, MMHg was present at concentrations sufficient to initiate bioaccumulation of MMHg through Arctic marine foodwebs (maximum 178 pg L(-1); 70.3 +/- 37.3 pg L(-1)). In addition, at mid- and bottom depths, the % of THg that was MMHg was high (maximum 66%; 28 +/- 16%), suggesting that active methylation of inorganic Hg(II) occurs in deep Arctic marine waters. Interestingly, there was a constant, near 1:1, ratio between concentrations of MMHg and DMHg at all sites and depths, suggesting that methylated Hg species are in equilibrium with each other and/or are produced by similar processes throughout the water column. Our results also demonstrate that oceanographic processes, such as water regeneration and vertical mixing, affect Hg distribution in marine waters. Vertical mixing, for example, likely transported MMHg and DMHg upward from production zones at some sites, resulting in elevated concentrations of these species in surface waters (up to 68.0 pg L(-1)) where primary production and thus uptake of MMHg by biota is potentially highest. Finally, calculated instantaneous ocean-atmosphere fluxes of gaseous Hg species demonstrated that Arctic marine waters are a substantial source of DMHg and GEM to the atmosphere (27.3 +/- 47.8 and 130 +/- 138 ng m(-2) day(-1), respectively) during the ice-free season.

An open-bottom and a closed-bottom mesocosm were developed to investigate the release of mercury from sediments to the water column in a frozen freshwater lake. The mesoscosms were deployed in a hole in the ice and particulate mercury (Hg(P)) and total dissolved mercury (TDHg) were measured in sediments and in water column vertical profiles. In addition, dissolved gaseous mercury (DGM) in water and mercury water/airflux were quantified. Concentrations of TDHg, DGM, and mercury flux were all higher in the open-bottom mesocosm than in the closed-bottom mesocosm. In this paper we focus on the molecular diffusion of mercury from the sediment in comparison with the TDHg accumulation in the water column. We conclude that the molecular diffusion and sediment resuspension play a minor role in mercury release from sediments suggesting that solute release during ebullition is an important transport process for mercury in the lake.

[1] This paper presents mercury (Hg) concentrations and foliage/atmosphere fluxes in a maple forest ecosystem in southern Quebec, Canada. The average total gaseous mercury (TGM) concentration measured at an open field site was significantly (p < 0.001) higher than that measured at an adjacent maple forest site, some 300 m away (1.40 ng m−3 versus 1.03 ng m−3, respectively). Foliage/atmosphere flux of TGM, measured with a dynamic flux bag device, indicated an average deposition flux of 0.39 ± 0.38 ng m−2 h−1 in the maple tree foliage. Although, bi-directional Hg fluxes were observed, the compensation point in the maple forest was low (∼0.6 ng m−3) explaining a net Hg deposition process at TGM background levels. Foliage mercury concentrations increased from 8.7 ± 1.5 ng g−1 to 30.8 ± 3.0 ng g−1 during the leaf-growing season. The average Hg deposition flux was in a similar range to the Hg accumulation rate in the maple tree foliage assuming a foliage productivity rate of 220 g m−2 a−1 (i.e., 0.39 versus 0.55 ng m−2 h−1). Although significant Hg accumulated in foliage, its transport to non-organic surface topsoil was not significant. When the uptake of mercury measured in this experiment was extrapolated to include all of the maple forest in North America (12.5 million ha), it amounted potentially to more than 600 kg of mercury per year. This represents approximately 0.5% of mercury emissions in Canada and the United States (approximately 120 metric tons).

[1] Snow samples were collected in the seasonal snow cover of the low arctic tundra (Whapmagoostui-Kuujjuarapik, Quebec) during episodic atmospheric mercury depletion events (AMDEs) and in the snowmelt period, long after AMDEs had occurred. Total and methyl mercury analyses were done in order to investigate the critical factors influencing the fate of mercury once deposited in the snowpack. Following AMDEs, snow total mercury (THg) concentrations increased and were inversely proportional to the distance from Hudson Bay. The correlations between MeHg, sulfate (SO42−), and chlorine (Cl−) snow concentrations implicated marine aerosols as a significant source of MeHg, independent of AMDEs. However, the newly deposited MeHg was unstable in the snow cover as 15–56% of the MeHg was demethylated or otherwise “lost” during the nighttime period. In contrast, during the snowmelt period, marine aerosols were not a significant source of MeHg. MeHg snow concentrations higher than 200 pg L−1 were observed when snow's heterotrophic plate counts, total suspended volatile solids, and total suspended solids were higher than 5.0 × 105 CFU L−1, 25 mg L−1, and 90 mg L−1, respectively. During the snowmelt, although the THg snow concentrations remained at 8–9 ng L−1, the proportion of MeHg increased from 2.7 to 7.6%. This is the first report suggestive of the presence of mercury methylation activities within the snow cover of the low arctic tundra.

[1] Total gaseous mercury (TGM) air-water flux measurements were taken using a dynamic flux chamber (DFC) coupled with a gaseous mercury (Hg) analyzer at the Bay St. Francois (BSF) wetlands (Quebec, Canada) in summer 2003. The measured TGM fluxes over water exhibited a consistent diurnal pattern, with maximum emissions during daytime and minimum fluxes occurring at night. Pearson correlation analysis showed that solar radiation was the most influential environmental parameter in TGM air-water exchange. Significant correlations were also found between TGM fluxes and 1 hour time-lagged water temperature, indicating the enhancement of fluxes by bacterial activities or chemical reactions. The concentrations of dissolved gaseous mercury (DGM) in water were measured during the 2003 sampling period and indicated that DGM was always supersaturated, which implied that the water body acted primarily as a source of mercury to the atmosphere. Several empirical models of mercury air-water gas exchange were developed and evaluated. Compared to the published models, these proposed models were capable of producing good results, leading to a better agreement between the measured and modeled fluxes (improvements by 48–98%). Among these empirical models, the ones linking TGM fluxes with net radiation were superior because of their strong predictive capability. Two preferred models were selected for air-water TGM flux estimation from Lake St. Pierre's surrounding wetlands. These two models yield a mean emission of 0.19–0.24 kg mercury during May–September each year from 1999 to 2003.

Whereas many ecosystem characteristics and processes influence mercury accumulation in higher trophic-level organisms, the mercury flux from the atmosphere to a lake and its watershed is a likely factor in potential risk to biota. Atmospheric deposition clearly affects mercury accumulation in soils and lake sediments. Thus, knowledge of spatial patterns in atmospheric deposition may provide information for assessing the relative risk for ecosystems to exhibit excessive biotic mercury contamination. Atmospheric mercury concentrations in aerosol, vapor, and liquid phases from four observation networks were used to estimate regional surface concentration fields. Statistical models were developed to relate sparsely measured mercury vapor and aerosol concentrations to the more commonly measured mercury concentration in precipitation. High spatial resolution deposition velocities for different phases (precipitation, cloud droplets, aerosols, and reactive gaseous mercury (RGM)) were computed using inferential models. An empirical model was developed to estimate gaseous elemental mercury (GEM) deposition. Spatial patterns of estimated total mercury deposition were complex. Generally, deposition was higher in the southwest and lower in the northeast. Elevation, land cover, and proximity to urban areas modified the general pattern. The estimated net GEM and RGM fluxes were each greater than or equal to wet deposition in many areas. Mercury assimilation by plant foliage may provide a substantial input of methyl-mercury (MeHg) to ecosystems.

[1] Field measurements of mercury air-surface exchange from natural settings were made in various Canadian landscapes. Soil and water samples were analyzed for mercury concentrations, and air-surface exchange fluxes from these substrates were determined using dynamic chamber, micrometeorological, or modeling methods. Environmental variables, including air and soil/water temperature, solar radiation, humidity, and wind speed, were monitored concurrently with the air-surface exchange to better understand the processes affecting the environmental cycling of mercury. Average mercury fluxes from aquatic landscapes ranged from 0.0 to 5.0 ng m−2 h−1 with total mercury concentration in water ranging from 0.3 to 6.5 ng L−1. A significant correlation (R2 = 0.47) was found between gaseous Hg fluxes and total Hg concentration in water. Mean gaseous Hg fluxes from forest soils varied from −0.4 to 2.2 ng m−2 h−1, while those from agricultural fields ranged from 1.1 to 2.9 ng m−2 h−1. Non-mineralized bedrock, sand, and till sites yielded fluxes ranging from −0.03 to 5.9 ng m−2 h−1. Mean fluxes from mercuriferous geological substrates at various locations were large compared to non-mercuriferous sites, ranging from 9.1 to 1760 ng m−2 h−1, and represent natural emissions. The corresponding total mercury substrate concentrations ranged from 0.360 to 180 ppm. A significant correlation (R2 = 0.66) was found between Hg fluxes and total Hg concentrations in mineralized and non-mineralized substrates. These gaseous Hg flux measurements represent a significant contribution to understanding natural mercury cycling, but there are still insufficient data and knowledge of processes to properly scale up fluxes from natural sources in Canada.

[1] Atmospheric mercury speciation and deposition are critical to understanding the fate of mercury in the environment. The importance of atmospheric mercury speciation and deposition was investigated during an intensive field campaign in the Bay St. Francois wetlands in late summer 2002. Measured gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and particulate mercury (PM: 0.1–2.5 μm) concentrations were 0.85–2.16 ng/m3 (average 1.38 ng/m3), 0–22 pg/m3 (average 3.63 pg/m3), and 0.5–18 pg/m3 (average 6.44 pg/m3), respectively. PM and RGM represented

An extensive mercury study was conducted in April 2002 prior to and during the annual melting of a snowpack in a sub-arctic site along the Hudson Bay (Canada). Gas-phase measurements show that the snowmelt coincides with an elemental mercury (Hg°) pulse in the snowpack air far above ambient levels. Additional measurements of inorganic mercury (Hg2+) and methylmercury (MeHg+) in snow pits, in surface snow and in a meltwater sample clearly reveal that most of Hg is removed from the snow during the first days of snowmelt. We estimate that gas-phase exchanges contribute poorly to remove Hg from the snowpack; consequently during a snowmelt day more than 90% of Hg present in the snow surface is likely released with the meltwater. In arctic areas, where Hg accumulates at an accelerated rate in the snow surfaces [Lu et al., 2001] during mercury depletion events (MDE), the discharge of this toxic and bio-accumulating pollutant in water systems could be a threat to ecosystems and local indigenous populations.

The objective of this paper is to give an overview of the findings of the Canadian chapter of the Northeast States and Eastern Canadian Provinces Mercury Study, which was conducted between 1995 and 1998. The Canadian chapter provided information on mercury emissions, sources and levels in air, water, biota and humans. Industry, governments and universities provided information for the Canadian chapter. The study showed that the Northeast States and Eastern Canadian Provinces (NES/ECP) is a region impacted by airborne mercury. Annual mercury emissions for the NES/ECP region are estimated to be approximately 19 t (12%) of the combined Canadian and US national anthropogenic mercury emissions of 155 t/year. 210 Pb-dated lake sediment cores from Atlantic Canada showed a mercury enrichment factor of 2.5 for coastal sites with mercury increases starting in 1860. Regional mercury wet deposition for the NES/ECP region was 7–11 μg/m 2 /year. Provincial and federal fish health advisories have been updated in the ECP for children and women of child-bearing age limiting the consumption of freshwater fish, as well as fresh or frozen shark, tuna or swordfish.

Recent mercury depletion events observed in the Arctic have opened the horizon to numerous new aspects on mercury fate and cycling in the environment. Total Gaseous Mercury and other Atmospheric Mercury speciations are measured in Kuujjuarapik/Whapmagoostui (Lat.: 55.30°N; Long.: 77.73°O) along the Hudson Bay (Quebec) with Tekran 2537A, 1130 and 1135 units. The former is measured since August 1999 whereas the latter are measured during springtime periods over the last three years. Mercury Depletion Events are observed at this low latitude region. MDEs are observed between February and April and are occurring during both the day and nighttime periods. Typically, MDE in Kuujjuarapik are related to air temperature. During MDEs, a significant speciation conversion from Hg 0 to RGM and TPM is operating. However, ratios of TPM to RGM conversion are variable in time.

Diffuse anthropogenic and naturally mercury-enriched areas represent long- lived sources of elemental mercury to the atmosphere. The Nevada Study and Tests of the Release of Mercury From Soils (STORMS) project focused on the measurement of mercury emissions from anaturally enriched area. During the project, concurrent measurements of mercury fluxes from naturally mercury-enriched substrate were made September 1-4, 1997, using four micrometeorological methods and seven field flux chambers. Ambient air mercury concentrations ranged from 2 to nearly 200 ng m- 3 indicating that the field site is a source of atmospheric mercury. The mean day time mercury fluxes, durin p conditions of no precipitation, measured with field chambers were 50 to 360 ng m -2 h - , and with the micrometeorological methods we re 230 to 600 ng m- 2 h -1. This wide range in mercury emission rates reflects differences in method experimental designs and local source strengths. Mercury fluxes measured by many field chambers were significantly different (p < 0.05) but linearly correlated. This indicates that field chambers responded similarly to environmental conditions, but differences in experimental design and site heterogeneity had a significant influence on the magnitude of mercury fluxes. Data developed during the field study demonstrated that field flux chambers are ideal for assessment of the physicochemical processes driving mercury flux and development of an understanding of the magnitude of the influence of individual factors on flux. In general, mean mercury fluxes measured with micrometeorological methods during day time periods were nearly 3 times higher than me an fluxes measured with field flux chambers. Micrometeorological methods allow for derivation of a representative mercury flux occurring from an unconstrained system and provide an assessment of the actual magnitude and variability of fluxes occurring from an area.

An international intercomparison of micrometerological techniques and dynamic flux chamber methods applied to measure mercury fluxes was conducted from September 1 to 4, 1997, during the Nevada Study and Tests of the Release of Mercury From Soils (STORMS) in Reno, Nevada. Nine research groups from four countries met in the Steamboat Springs, Nevada Geothermal Area, to participate in the first international flux intercomparison ever attempted for mercury. The highly heterogeneous soil Hg concentrations and complex landscape within the study area (4 ha) were unfavorable for spatial intercomparison of Hg fluxes between the research groups. However, reliable and correlated Hg fluxes were measured between our micrometerological technique and a dynamic flux chamber method (r2 = 0.29), run side by side (5 m). Hg fluxes and their relationships with environmental factors were complex. After ∼90 days of dry condition, a series of storm events impacted the site and increased the soil moisture from