Search

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.

Microbial-mediated soil uptake accounts for approximately 80% of the global tropospheric dihydrogen (H(2)) sinks. Studies conducted over the last three decades provide indirect evidences that H(2) soil uptake is mediated by free soil hydrogenases or by unknown microorganisms that have a high affinity for H(2). The exact nature of these hypothetical free soil enzymes or of H(2)-consuming microorganisms remains elusive because the activity has never been observed in pure culture. Here, we present the first aerobic microorganism able to consume tropospheric H(2) at ambient levels. A dynamic microcosm chamber was developed to enrich a microbial consortium with a high affinity for H(2), from which selected bacterial and fungal strains were isolated and tested for H(2) uptake. Strain PCB7 had a H(2) consumption activity that followed a Michaelis-Menten kinetics, with an apparent K(m) of 11 p.p.m.v. and a H(2) threshold concentration0.100 p.p.m.v., corresponding to the high-affinity uptake of tropospheric H(2) observed in soil. 16S ribosomal RNA gene sequences showed that strain PCB7 is highly related to several Streptomyces species. H(2) consumption occurred during the sporulation period of the bacterium. Addition of nickel increased the activity, suggesting that the enzymes involved in H(2) consumption belong to the NiFe uptake class of hydrogenases. Because this is the first microorganism showing a high-affinity uptake of tropospheric H(2), we anticipate that Streptomyces sp. PCB7 will become a model organism for the understanding of the environmental factors influencing H(2) soil uptake.

The industrialization and the demographic expansion have both influenced the biogeochemical cycle of hydrogen (H 2 ), carbon monoxide (CO) and carbon dioxide (CO 2 ). In the actual context, knowledge about the spatial distribution of the natural sources and sinks of these trace gases is then crucial to infer possible effects of climate and land use changes on their global budget. This article reports the H 2 , CO and CO 2 concentrations and micrometeorological fluxes measured during 1 year in a rural area of the mixed wood ecozone of Canada. Land use represents a critical issue in the control of trace gas natural sources or sinks of that region, which is the most densely habited in Canada. On average, the site emitted CO 2 at a rate of 7.7 g m −2 d −1 and consumed H 2 and CO at 0.34 and 5.1 mg m −2 d −1 , respectively. Temperature was the most important factor affecting the H 2 and CO surface to air exchanges. The strength of the soil sink was maximal at the end of the summer, while H 2 and CO emissions were observed at the snow-melting period. In winter, H 2 and CO depositions were attributed to their oxidation by photochemically active compounds within the snow cover. When soil temperature was above 10 °C, trace gas fluxes followed a well-defined diurnal cycle. H 2 and CO 2 deposition rates were positively correlated with H 2 O fluxes, while CO followed the inverse trend. CO 2 diurnal variations resulted from a balance between photosynthesis and soil respiration, while some biotic and abiotic factors were proposed to explain the trend observed for H 2 . In the case of CO, emissions originating from heat- and photo-induced reactions were involved in the attenuation in the strength of the soil sink during daytime. Measured fluxes were compared with the literature to show the relative importance of the rural areas in the studied trace gases budget.

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.

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.

The Canadian Pesticide Air Sampling Campaign was initiated in 2003 to assess atmospheric levels of pesticides, especially currently used pesticides (CUPs) in agricultural regions across Canada. In the first campaign during the spring to summer of 2003, over 40 pesticides were detected. The spatial and temporal distribution of pesticides in the Canadian atmosphere was shown to reflect the pesticide usage in each region. Several herbicides including triallate, bromoxynil, MCPA, 2,4-D, dicamba, trifluralin and ethalfluralin were detected at highest levels at Bratt's Lake, SK in the prairie region. Strong relationships between air concentrations and dry depositions were observed at this site. Although no application occurred in the Canadian Prairies in 2003, high air concentrations of lindane (γ-hexachlorocyclohexane) were still observed at Bratt's Lake and Hafford, SK. Two fungicides (chlorothalonil and metalaxyl) and two insecticides (endosulfan and carbofuran) were measured at highest levels at Kensington, PEI. Maximum concentrations of chlorpyrifos and metolachlor were found at St. Anicet, QC. The southern Ontario site, Egbert showed highest concentration of alachlor. Malathion was detected at the highest level at the west coast site, Abbotsford, BC. In case of legacy chlorinated insecticides, high concentrations of DDT, DDE and dieldrin were detected in British Columbia while α-HCH and HCB were found to be fairly uniform across the country. Chlordane was detected in Ontario, Quebec and Prince Edward Island. This study demonstrates that the sources for the observed atmospheric occurrence of pesticides include local current pesticide application, volatilization of pesticide residues from soil and atmospheric transport. In many instances, these data represent the first measurements for certain pesticides in a given part of Canada.

This paper, and its companion (that dealt with lindane and endosulfan) review available data on the presence of currently used pesticides (CUPs) in air and precipitation in Canada, since the late 1980s. Pesticides usage/sales are also given when available. Data from local studies/initiatives, region-wide monitoring networks and remote locations are compiled to summarize atmospheric levels of different CUP classes (e.g. acid herbicides, organophosphates, “new” organochlorines, triazines, etc.) and how this varies among regions and with time. Based on this information, and other parameters not specific to Canada, knowledge gaps are identified and ideas for further research work are proposed.

This paper, and its companion, review available data on the presence of currently used pesticides (CUPs) in air and precipitation of Canada, since the late 1980s. Pesticides usage/sales are also given when available. Two older CUPs—lindane, which shows a wealth of data, and endosulfan, one of the most abundant and ubiquitous organochlorine pesticides in the North American atmosphere today—are the focus of this first part. Data from local process studies, monitoring work in source and receptor regions, and modelling efforts are compiled to give an overall picture of the atmospheric levels and deposition and how this varies between regions and with time.

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.

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.

Atmospheric concentrations of α - and γ -hexachlorocyclohexane (HCH) were measured during 1993–1995 along the St. Lawrence River in Quebec, Canada. Average α - and γ -HCH concentrations (pg/m 3 ) were St. Anicet: 93–101; Villeroy: 92–42; Mingan: 96–20, respectively. α -HCH mean concentrations were similar in all sites and appeared to be more influenced by long-range transport than local sources. γ -HCH mean levels in St. Anicet were 2 and 5 times higher than in Villeroy and Mingan, respectively. The time-series of γ -HCH air concentrations at St. Anicet and Villeroy were characterised by highly elevated springtime episodes, which are in agreement with the γ -HCH usage in Quebec as corn seed dressing pesticide. No temporal trend was observed for the α -HCH in air. Clausius–Clapeyron plots (log conc. vs. 1/ T ) showed a stronger correlation between temperature and measured γ -HCH concentrations at St. Anicet and Villeroy than Mingan. On a regional scale, the influence of the local sources of γ -HCH implied a seasonal variability in air concentrations due to its short transport, while at the background site (Mingan), the observed α - and γ -HCH concentrations in air were the result of its long-range transport and/or water/air gas exchanges.

An efficient linear Kalman filter has been combined with a coupled atmospheric transport and soil–air exchange model to determine organochlorine pesticides emissions on the regional scale. In this study, results of γ-HCH emissions from the Great Lakes–St. Lawrence ecosystem, estimated from the coupled model, are presented and discussed. A source receptor technique is used to identify a priori the locations of emission sources of γ-HCH, the emissions are then updated through a Kalman filtering procedure which minimizes the weighted difference between the predicted mixing ratios from the coupled model and the measured concentrations over the Great Lakes–St. Lawrence river region. Two experiments using the inverse algorithm are carried out. In the first experiment, the coupled atmospheric transport and soil–air exchange model is implemented to predict γ-HCH air and soil concentrations. Emissions are then updated every 12 days using the updated soil concentrations and emission factors. However, the updated emissions are not input into the coupled atmospheric transport and soil–air exchange model. On the other hand, in the second experiment the updated emissions are fed back to the coupled model, so that the model is reinitialized in each 12 days. The results from the inverse technique for the year 1995 have been compared with grided γ-HCH emission inventory in Canada, generated by emission factors. It is shown that the estimated emissions of γ-HCH are consistent with the measured emissions. It is found that the St. Lawrence valley has larger emissions of γ-HCH than the Great Lakes region, indicating an opposite distribution to the emission usage inventory, but in agreement with the measured γ-HCH concentration.

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.

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 (

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.

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.

This paper presents a year of data on certain persistent organic pollutants and heavy metals in the atmosphere over a St.Lawrence River valley site (Villeroy) in 1992. These results are compared with other sites in North America: most of the concentration levels found here are characteristic of a rural site. The specific behaviours of certain species are presented and discussed with regard to physical and chemical laws as well as with the potential source and transport in the atmospheric compartment of the environment.

The southern Ontario oxidant study (SONTOS) is one of the scientific responses to the problem of ozone exceedences in the Windsor/Quebec City corridor, the strip extending from Windsor in the extreme southwest of Ontario, along the north shores of Lake Erie and Lake Ontario and down the St Lawrence valley. This corridor includes the two major metropolitan areas of Toronto and Montreal and experiences more exceedences of the Canadian ozone guideline per year than any other part of the country. The overall objective of SONTOS is to elucidate the factors which lead to these high levels. The study design is based on intensive measurements made at a site to the NNW of Toronto, with supplementary measurements at other sites and on board an aircraft. This paper, and the seven which follow, describe and interpret the measurements made in the summer of 1992. Although this summer was noteworthy for generally very low ozone concentrations, a number of interesting observations have been made which have a bearing on the oxidant phenomenon in southern Ontario. In particular, this paper describes two specific events. In one, which occurred on 6 August 1992, the intensive measurement site experienced the impact of a polluted air mass, which had apparently travelled to the site from Toronto, by way of Lake Ontario. This case has been contrasted with an event in the last week of August, in which large-scale, organised southwesterly flow led to the conditions which more typically give rise to widespread ozone episodes in the province. Events similar to the 6 August episode occurred on several occasions during the study period, and underline the very important role of the Great Lakes in ozone transport and delivery in southern Ontario.

Statistical analysis of observations made between 7 and 31 August 1992 at a rural site in Southern Ontario, Canada, is presented using principal component analysis (PCA), as well as rank and partial correlation analyses. Data for ozone, CO, SO 2 , NO, NO y (NO + NO 2 including NO x , PAN and HNO 3 ), ethane, ethylene, propane, acetylene and isoprene are employed, as well as such meteorological information as temperature, relative humidity, wind speed and direction. The analysis involved several scenarios classifying the data according to daytime, nighttime and wind direction. A normal correlation analysis suggests that isoprene might be important in the build-up of ozone in the S-W sector, whereas it is not important in the N-E wind sector. PCA show that the chemical and the meteorological variables interact differently within the different scenarios. Finally, the relationships between ozone and isoprene for both wind sectors are found to be the same when the data are subjected to a partial correlation analysis including the meteorological parameters and it is concluded that the S-W ozone-isoprene relationship might be biased by temperature.

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.

Environmental contextMercury, in its methylated form, is a neurotoxin that biomagnifies in marine and terrestrial foodwebs leading to elevated levels in fish and fish-eating mammals worldwide, including at numerous Arctic locations. Elevated mercury concentrations in Arctic country foods present a significant exposure risk to Arctic people. We present a detailed review of the fate of mercury in Arctic terrestrial and marine ecosystems, taking into account the extreme seasonality of Arctic ecosystems and the unique processes associated with sea ice and Arctic hydrology. AbstractThis review is the result of a series of multidisciplinary meetings organised by the Arctic Monitoring and Assessment Programme as part of their 2011 Assessment ‘Mercury in the Arctic’. This paper presents the state-of-the-art knowledge on the environmental fate of mercury following its entry into the Arctic by oceanic, atmospheric and terrestrial pathways. Our focus is on the movement, transformation and bioaccumulation of Hg in aquatic (marine and fresh water) and terrestrial ecosystems. The processes most relevant to biological Hg uptake and the potential risk associated with Hg exposure in wildlife are emphasised. We present discussions of the chemical transformations of newly deposited or transported Hg in marine, fresh water and terrestrial environments and of the movement of Hg from air, soil and water environmental compartments into food webs. Methylation, a key process controlling the fate of Hg in most ecosystems, and the role of trophic processes in controlling Hg in higher order animals are also included. Case studies on Eastern Beaufort Sea beluga (Delphinapterus leucas) and landlocked Arctic char (Salvelinus alpinus) are presented as examples of the relationship between ecosystem trophic processes and biologic Hg levels. We examine whether atmospheric mercury depletion events (AMDEs) contribute to increased Hg levels in Arctic biota and provide information on the links between organic carbon and Hg speciation, dynamics and bioavailability. Long-term sequestration of Hg into non-biological archives is also addressed. The review concludes by identifying major knowledge gaps in our understanding, including: (1) the rates of Hg entry into marine and terrestrial ecosystems and the rates of inorganic and MeHg uptake by Arctic microbial and algal communities; (2) the bioavailable fraction of AMDE-related Hg and its rate of accumulation by biota and (3) the fresh water and marine MeHg cycle in the Arctic, especially the marine MeHg cycle.

This paper gives a practical demonstration that the receptor models based on the absolute PCA techniques, to apportion atmospheric contaminants to sources, might bias results. The demonstration is done with two simple examples. Results show in both cases that the mean of ζ j (APCS jk ∗ ) is in fact closer to the absolute PC 0 ∗ than the source distribution ( S j ). These three terms being not, as previously stated, always equal. In this circumstance, elements concentrated in the sources are not accurately reproduced.

A rainwater quality model based on a scavenging coefficient parameterized with rainfall intensity and calibrated on sequential sampling data has been developed. The model can predict ratio to maximum concentration for different species during events at each rainfall amount step. Once calibrated, this model needs as input simple hydrological data, namely instantaneous rainfall intensity and cumulative rainfall depth. These limited and easily available data make it particularly suitable for stormwater control purposes.

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.

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] 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.

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.

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.

Le mercure est l'un des metaux les plus toxiques de l'environnement Meme en faible concentration, il peut avoir des effets importants sur les ecosystemes. La methode de mesure utilisee lors de celte etude permet des mesures en continu automatique a une frequence quart horaire (aux 15 minutes) avec une limite de detection de 0,2 ng/m3. Le train analytique de la mesure automatique du mercure est base sur l'amalgame de celui-ci sur une trappe garnie d'or suivie d'une desorption thermique et d'une analyse par fluorescence a froid (γ=253,7 nm). Des mesures effectuees en milieu rural (Saint-Anicet, Quebec, Canada) entre le 13 septembre et 30 novembre 1994, nous indiquent que des episodes de sources locales ou regionales s'ajoutent au bruit de fond estime ici a environ 1,4ng/m3. Des apports locaux et regionaux en provenance des secteurs des vents N-E et S-E s'ajoutent par episode au bruit de fond pour atteindre des pointes de concentrations maximales de 5,50 ng/m3. La grande region de Montreal pourrait enrichir d'environ 20 % les valeurs moyennes seuil de base. Un leger cycle diurne est mesure avec des maxima observes lors de la periode de jour, illustrant une certaine concomitance avec l'activite economique. Une relation entre le logarithme de la concentration de la vapeur mercurielle et la reciproque de la temperature mesuree au sol (Log Hg = A/T + K) est significative pour le secteur des vents S-O (R = - 0,37). Cette observation indiquerait que des phenomenes de volatilisation/condensation ou absorption/desorption du mercure a l'interieur de ce secteur de vent sont possibles entre les surfaces (particules, sol, eau, vegetation, etc.) et l'atmosphere. En contrepartie, la relation pour le secteur N-O est moins evidente laissant presumer que les concentrations mercurielles atmospheriques seraient plutot representatives du bruit de fond atmospherique et moins influence par des phenomenes locaux.

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

Le but de la présente étude était d'étudier l'impact de la variation des niveaux d'eau d'un marais d'eau douce (Baie Saint-François, Québec) sur l'évolution des concentrations et des flux d'hydrogène, monoxyde de carbone, méthane et dioxyde de carbone. Une approche originale impliquant l'association d'un gradient de concentration de ces composés sur un profil vertical de 1,5 m au transfert de flux turbulent micrométéorologique fut utilisée pour la détermination des flux. L'étude démontre qu'une hausse du niveau d'eau d'un bassin versant alimentant une zone humide influence les flux de méthane, de monoxyde de carbone d'hydrogène et de dioxyde de carbone. En conditions submergées, le marais émettait du méthane et du monoxyde de carbone et consommait moins d'hydrogène troposphérique. Ainsi, cette étude démontre que des mesures in situ peuvent servir à inférer des scénarios d'impacts possibles des changements climatiques et des variations des niveaux d'eau sur les émissions des gaz à effets de serre dans l'écosystème du fleuve Saint-Laurent., Wetlands are known for their great biodiversity and the important carbon reservoir that they represent. Moreover, in the global warming context, these ecosystems represent net sources or sinks for different greenhouse gases depending of their conditions. For instance, flooded conditions favour methane production whereas they prevent hydrogen and carbon monoxide soil consumption. Baie Saint-François is a freshwater wetland that opens onto Lake Saint-Pierre (St. Lawrence River) where water levels are subject to important fluctuations due to natural processes and human activities (hydroelectricity and navigation). This study was done in order to assess the impact of the Lake Saint-Pierre water level variations on the tropospheric methane, carbon monoxide, hydrogen and carbon dioxide dynamics over the wetland. Knowledge of these dynamics should provide indications about the possible effects of the decreasing or increasing water level associated with the global warming on the production or consumption of these trace gases.Studies were carried out between June and August 2003 in Baie Saint-François where soil was subjected to successions of flooded and dry conditions. Water and carbon dioxide fluxes were obtained with a Bowen ratio micrometeorological station including a high frequency single infrared gas analyser. Hydrogen, carbon monoxide and methane fluxes were estimated with the modified Bowen method, their vertical concentration gradients (1.5 m) were measured over the plant canopy. The Bowen Ratio station was equipped with different probes to measure parameters such as net radiations, soil heat fluxes and vertical temperature gradients. The turbulent transfer coefficient (k) obtained every 20 min was assumed equal for heat, water vapour and trace gases. Hence, fluxes calculations were done by the multiplication of the turbulent transfer coefficients with the vertical concentration gradients of hydrogen, carbon monoxide and methane.The instrument used to detect hydrogen, carbon monoxide and methane was a RGA5. This analyser has two detectors: the reductive gas detector (RGD) for hydrogen and carbon monoxide and a flame ionisation detector (FID) for methane. The RGD contains an HgO bed wherein oxygen reacts with reductive gases resulting in Hg° releases detectable by differential UV absorbance. Chemicals were detected continuously in 10 min cycles with an analytical reproducibility of ±0.2, 0.3 and 2% for hydrogen, carbon monoxide and methane. Generally, vertical concentration gradients measured were greater than these limits. A calibration gas containing hydrogen, carbon monoxide and methane at 4940, 1000 and 1000 ppbv respectively in nitrogen was analysed daily to verify calibration. To ensure data integrity, linearity of the instrument was assayed by several dilutions of the standard gas and the integration of the curves gave a correction factor for hydrogen (18%) and carbon monoxide (13%). An intercomparison with NOAA (National Oceanic and Atmospheric Administration) was done to corroborate these correction factors.Background carbon monoxide, methane and carbon dioxide levels were in agreement with literature values. However, hydrogen was low, as observed by other investigators in summertime, since this season is related to minimal concentrations. Methane followed a diurnal cycle where maximum levels were observed during nighttime. In wet conditions, these nocturnal peaks reached occasionally 4000 ppbv and could be explained by specific production mechanisms and diurnal changes of vertical mixing in the boundary layer. Sensitivity of the processes responsible for methane and carbon monoxide cycling was seen between July 21st and 26th where a rain episode (total precipitation of 33.2 mm) increased their background concentrations. It seems that this precipitation was enough to favour methanogenesis and inhibit tropospheric CO and CH4 consumptions by a reduction of the diffusion of these chemicals into the soil.Our results demonstrated that four to eleven days following a variation of the Lake Saint-Pierre water level, a change in the tropospheric hydrogen, carbon monoxide and methane concentrations was observed. This lag might be explained by the distance between the lake and the research station (about 1.5 km) and the required time for the adaptation of soil microorganisms to the disruption of their environment. The concentration variations of these chemicals resulted from the inhibition of the processes responsible for their consumption or the activation of the processes accountable for their production.In June, the wetland was flooded and the CO2 median flux was -56.5 g m-2 d-1. Fluxes increased significantly (Mann-Whitney, α=0.01) in July to 5.30 g m-2 d-1, possibly due to dry conditions. Indeed, absence of water favours the activity of soil aerobic microorganisms which might produce more carbon dioxide than the quantity used by plants during photosynthesis.Methane was produced in June where the median flux was 54 mg m-2 d-1. These emissions were caused by the presence of water which maintained anaerobic conditions in the sediments, a suitable environment for methanogenic microorganisms. July was characterised by dry conditions, which generated aerobic environments in soils, an unfavourable microniche for methanogens. Therefore, methane median fluxes decreased significantly (Mann-Whitney, α=0.05) to 0.011 mg m-2 d-1 in July. In August, before the end of the investigation period, water levels had increased but methane fluxes were not significantly higher than in July. Moreover, in this period, methane concentrations tended to increase, showing that after an augmentation of the Lake Saint-Pierre water level, Baie Saint-François flooding area could represent a methane source.During summer 2003, Baie Saint-François acted as a net source of carbon monoxide. In June, the median flux was 21 µg m-2 d-1 due to presence of water which inhibited consumption by soil. Emissions were significantly (Mann-Whitney, α=0.05) lower in July (15 µg m-2 d-1) due to the absence of water, which represented a suitable environment for microorganisms consuming tropospheric carbon monoxide. In August, the median carbon monoxide flux attained 65 µg m-2 d-1 due to an increase of the Lake Saint-Pierre water level. Net carbon monoxide emissions observed in wet and dry conditions might be due to the high organic content in soil and water in addition to the presence of plants since all of these are subjected to photooxidation, generating this pollutant. Therefore, an increase of the Lake Saint-Pierre water level is associated with an augmentation of tropospheric carbon monoxide due to the inhibition of the processes responsible of its consumption.A decline in the water level might result in the activation of the soil microorganisms (or abiotic hydrogenases) able to consume tropospheric hydrogen. At the beginning of the campaign (June), the median hydrogen flux was weak (-1.37 g m-2 d-1) due to the presence of water. However, a net soil consumption was seen in July, where the median hydrogen flux decreased to -125 g m-2 d-1. The Lake Saint-Pierre water level increase observed in August was associated with a significant (Mann-Whitney, α=0.05) augmentation of the hydrogen median flux to 299 g m-2 d-1. Consequently, a rise in the Lake Saint-Pierre water levels induced an inhibition of the processes responsible of the tropospheric hydrogen consumption.This study illustrated that the water level fluctuations of the Lake Saint-Pierre have an impact on the H2, CO, CH4 and CO2 dynamics over the surrounding wetlands. When the Lake Saint-Pierre water level decreased, the wetlands acted as a carbon monoxide and carbon dioxide source, but as a consumer of tropospheric hydrogen and a minor source of methane.