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.

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.

Methylmercury [MeHg(I) in the aerobic surface water of lakes is thought to be rapidly degraded, but contrary to expectations, we show that MeHg(I) concentrations often increase during sunlight hours or remain relatively constant. We hypothesized that there were water column processes that generated MeHg(I) and that these processes were linked to dissolved organic matter (DOM) and solar radiation. A 2-day diurnal pattern of MeHg(I) in surface water with corresponding bottled controls was assessed for two contrasting lakes in Kejimikujik, Nova Scotia, Canada. Following this study, a tangential ultrafiltrator was used to size-fractionate and generate a concentration gradient of DOM from four different lakes located near Lac Berthelot, Quebec, Canada. The watersheds of two of these lakes were not substantially logged whereas the other two had been extensively logged. Different size fractions of DOM as well as different concentrations of DOM were exposed to sunlight for varying periods of time. We observed that, in Keiimikujik, the concentration of MeHg(I) in surface waters peaked in the early afternoon. Furthermore, this also occurred in bottled water for one of the lakes, Puzzle, eliminating the possibility that in-lake mixing played a role in this pattern. The formation of MeHg(I) was found to be dependent on the size fraction and amount of DOM present in the water. Specifically, DOM less than 5 kDa or between 30 and 300 kDa generated MeHg(I) when exposed to sunlight, but larger fractions did not. Furthermore, although data are limited, we found that water from lakes with logged watersheds generated MeHg(I) when exposed to sunlight, whereas water from lakes with low levels of logging in the undisturbed watersheds did not. Our results demonstrate that MeHg(I) can be formed in freshwaters of certain lakes in response to solar radiation. This photoproduction of MeHg(I) is dependent on DOM concentrations and type, with the importance of water chemistry not yet clear. The significance of this process to freshwater lakes and the mechanism responsible for MeHg(I) photoproduction is still unclear, but a correction in the conventional wisdom that MeHg(I) is rapidly photodegraded is timely.

While sources of gaseous mercury (natural and anthropogenic) are well known, studies on atmospheric mercury concentrations in Mexico are new. In order to assess the total gaseous mercury (TGM) levels at some characteristic Mexican sites, four locations were selected to start an exploratory survey and begin to asses the TGM behavior. This paper presents data obtained at an urban site (Mexico City), a rural site (Huejutla, Hidalgo), a coastline site (Puerto Angel, Oaxaca) and a closed mining site (Zacatecas City, Zacatecas). The highest TGM average values were found at this last site (71.82ngm−3) together with the urban site (9.81ngm−3). At the rural and coast line sites the lowest TGM values (1.32 and 1.46ngm−3, respectively) were found. According to the ANOVA test, there were significant differences for the TGM values among all the studied sites, except between the coastline and the rural place. A multiple correlation test performed between TGM and some meteorological parameters showed that in sites without anthropogenic mercury sources influence (rural and coast line), the TGM levels are correlated with the temperature and relative humidity, while for the other two sites no clear correlation was found.

Precipitation samples were collected from July 2001 through June 2002 to determine sources of anthropogenic heavy metal pollutants to Kejimkujik National Park, Nova Scotia using Pb isotope ratios. Generally, Mean annual Pb concentrations (0.116 μg l−1) and depositional fluxes (151 μg m−2) are lower than other reported mid-Atlantic coastal regions. Pb isotope compositions may be explained by binary mixing of anthropogenic emissions from US and Canadian sources, indicating long-range atmospheric transport of pollutants from populated and industrial regions of northeastern US and southeastern Canada. The 206Pb/207Pb ratios in precipitation ranged from 1.165 to 1.201, with an annual weighted mean 206Pb/207Pb ratio of 1.181, indicating that on an annual basis, US and Canadian sources contribute 61% and 39%, respectively, of the anthropogenic Pb (and likely other similarly behaved metal pollutants) reaching Kejimkujik Park. These results differ from those estimated by using epiphytic lichens due to one or a combination of the following possibilities: (1) some of the Pb in the lichens reflects more radiogenic local bedrock sources; (2) there has been an overall increase in the proportion of Canadian inputs since the early 1990s; (3) there was an unusually higher proportion of Pb inputs from Canadian sources during the study period; or (4) possible shifts in the isotopic composition of the Canadian and US sources that may have occurred due to increased international trade in lead and a lesser dependency on national production. As well, seasonal variations in the sources were observed, with summer and fall months having a lower mean 206Pb/207Pb ratio of 1.178 (more Canadian) than the winter and spring months with 206Pb/207Pb of 1.185 (more American).

Continuous measurements of total gaseous mercury (TGM) concentration were taken during 1997–1999 at 10 rural sites across Canada, ranging from 43° to 82°N and from 62° to 123°W. Overall median TGM concentrations ranged among the sites from 1.32 to 1.83ng m−3. The spatially averaged median concentration among all sites was 1.60±0.15ng m−3. Maximum hourly average concentrations, on the order of 10ng m−3, were observed at several sites located near major sources of anthropogenic emissions. Minimum hourly average concentrations were observed in springtime at the arctic site where concentrations dropped below the detection limit of the analyzer (50pg m−3) on several occasions. Seasonal variability in TGM concentrations was observed at all sites. At most sites monthly median concentrations were highest in late winter and lowest in fall. Diurnal variations in TGM concentration were also observed at most sites. The most common pattern of diurnal variability was a diel cycle of minimum concentrations just before sunrise and maximum concentrations around solar noon. The diel cycle was seasonally modulated, reaching maximum amplitude during spring or summer at all sites.

Diurnal patterns for dissolved gaseous mercury (DGM) concentration, mercury flux, several water variables (pH, oxidation reduction potential (ORP), water temperature), and meteorological variables (wind speed, air temperature, % relative humidity, solar radiation) were measured in two lakes with contrasting dissolved organic carbon (DOC) concentrations in Kejimkujik Park, Nova Scotia. A continuous analysis system made it possible to measure quick changes in DGM over time. Consistently higher DGM concentrations were found in the high DOC lake as compared to the low DOC lake. An examination of current mercury flux models using this quantitative data indicated some good correlations between the date and predicted flux (r ranging from 0.27 to 0.83) but generally poor fit (standard deviation of residuals ranging from 0.97 to 3.39). Cross-correlation analysis indicated that DGM dynamics changed in response to solar radiation with lag-times of 65 and 90 min. This relationship with solar radiation was used to develop new predictive models of DGM and mercury flux dynamics for each lake. We suggest that a generalized approach using time-shifted solar radiation date to predict DGM can be incorporated into existing mercury flux models. It is clear from the work presented that DOC and wind speed may also play important roles in DGM and mercury flux dynamics, and these roles have not been adequately accounted for in current predictive models.

The Caribou gold-mining areas in Nova Scotia, Canada were in full production from 1869 to 1927. Abandoned waste rocks and fine-grained tailings from Hg-amalgamation processes have weathered into Long Lake, part of the Moose River system. Metal burdens in tailings and lake sediments, as well as the biological community structure above and below the processing site, were investigated. Surface tailings were found to contain (in μ g g −1 ): As (5000–28 000), Cd (0.1–0.6), Cu (6–37), Mn (50–600), Ni (600–2000), Hg (0.3–0.7), Pb (70–120), Tl (0.03–0.06), V (3–10) and Zn (20–100). Lake sediments below the tailing field were found to be highly enriched with As, Ni, Pb and, to a lesser extent, Hg, Cu and Mn. Air–surface exchange from tailings (preliminary results, 48 h cycle) exhibit Hg-flux rates from 20 to >100 times greater than those of natural soils in Nova Scotia. Stream water and sediments below the mine were toxic to the benthic community.

Understanding the relative importance of various sources of mercury within ecosystems and their subsequent impact on biota requires a thorough understanding of the biogeochemical cycling of mercury. An important component of the biogeochemical mercury cycle involves the exchange of gas-phase mercury between the atmosphere and various landscape surfaces. This study examines air–surface exchange (flux) of gaseous elemental mercury in selected undisturbed and anthropogenically impacted aquatic and terrestrial landscape settings. The objective of this study was to quantify air–surface mercury exchange rates in these contrasting landscape settings, to put constraints on these rates and provide insight into physical processes controlling mercury flux. Mean daily mercury flux was typically low over natural forest soils varying from −0.4 (net deposition) to 2.2 ng m −2 h −1 (net evasion). Minimum and maximum flux rates measured at these sites over the diurnal cycle ranged from a minimum of −1.3 to a maximum of 5.7 ng m −2 h −1 . Low flux rates from forest soils was partially due to poor light penetration through the forest canopy. Average daily mercury flux over undisturbed glacial till soil at an open field site with full sun exposure was also low (0.9 ng m −2 h −1 ) compared to the same soil mixed over a depth of 2 m (8.0 ng m −2 h −1 ). Mean daily mercury flux rates measured over pristine freshwater lake surfaces were also low (0.7–6.5 ng m −2 h −1 ), although the overall range in flux varied more widely (−0.3 to 44 ng m −2 h −1 ). Total mercury concentrations in marine water at a moderately polluted coastal harbour site (mean c. 0.8 ng l −1 ) and mean daily mercury flux rates over salt water (0.7 ng m −2 h −1 ) were similar to those measured over freshwater lakes. The highest daily average and diurnal range in mercury flux rates were measured at two abandoned gold mine tailings sites (130 and 237 ng m −2 h −1 ). The abandoned mine sites comprised tailings high in mercury content due to the past use of the mercury amalgamation process in gold extraction from the ore. Flux rates from tailings were two orders of magnitude higher than those observed over undisturbed native soils of similar parent material. Higher flux rates at the mine tailings sites were accompanied by ambient air concentrations 5–10 times background levels at 20 cm above the tailings. Mercury flux from vegetation has not been widely considered. A preliminary study of mercury flux from a white pine tree ( Pinus strobus ) indicated that actively growing trees might play a role in the atmospheric mercury cycle.

Mercury flux measurements were conducted at two lakes and three soil sites in Kejimkujik National Park, located in the eastern Canadian province of Nova Scotia. One of the lakes had high levels of both mercury and Dissolved Organic Carbon (DOC). Two of the soil sites were located under the forestcanopy, while the other was in a small clearing surrounded by forest. Flux measurements were performed using the dynamic chamber method. Mercury concentrations in the air were measured with a TEKRAN mercury analyzer. Mercury fluxes over the two lakes were most strongly correlated with solar radiation, although the flux was also significantly correlated with water temperature, air temperature, and negatively correlated with relative humidity. The flux from the high DOC lake (Big Dam West) was especially high when the conditions were both sunny and windy (wind speed greater than 1.3 m s-1) and the average flux measured was 5.4 ng m-2 h-1. The mercury flux from this lake was wellparameterized in terms of a simple expression involving solar radiation and a nonlinear dependence on wind speed. The flux measured from the low DOC lake (North Cranberry) tended to be lower than from the high DOC lake. The averageflux measured was 1.1 ng m-2 h-1, but was again strongly correlated with solar radiation. The flux was low during windy conditions in the absence of sunlight, suggesting that wind enhances mercury evasion from lakes only in the presence of solar radiation. Mercury fluxes measured over the soil sites tended to be smaller than those over water (a range of –1.4–4.3 ng m-2 h-1). At one of the forest sites, mercury flux was very strongly correlated with 0.5 cm soil temperature, and this dependence was well described by an Arrhenius-typeexpression with an activation energy of 14.6 kcal-1 mole, quite close to the heat of vaporization of mercury (14.5 kcal-1 mol-1 at 20 °C). At the clearing, where there was direct exposure to the sun, the mercury flux was most strongly correlated with solar radiation.

Southwestern Nova Scotia receives acidic precipitation (average pH 4.5 to 4.6), and there are many waterbodies that are susceptible to acidification. This study characterizes the physical and chemical features of three remote, oligotrophic lakes and their watersheds in this region, in order to provide baseline information against which assessments can be made of changes caused by atmospheric depositions. Two of the lakes are small (<0.5 km2) and on headwater watersheds: Beaverskin Lake has an almost completely forested watershed and is moderately acidic and clear (pH 5.3, 5 Hazen units), while the watershed of Pebbleloggitch Lake is about 2/3 forested and 1/3 covered by a Sphagnum-heath bog, and its water is very acidic and highly colored (pH 4.3, 87 Hazen units). Kejimkujik Lake is much larger, its watershed is mostly forested but also contains some boggy terrain, its water is intermediate in acidity and color (pH 4.9, 65 Hazen units), and because it drains a much larger area of watershed it has relatively large concentrations of Ca, Mg, Na, Cl, and SO4.

Solar insolation impinging upon and penetrating the surface of a water body undergoes a variety of changes depending on the physical and chemical characteristics of the water column. Photosynthesis and phototrophic responses of organisms are related to the number of quanta of light of specific frequencies impinging on biochemical receptor systems. Colored waters with high concentrations of dissolved organic carbon (DOC), primarily in the form of humic and fulvic acids, predominate in certain areas of the Atlantic region. These high molecular weight organic compounds strongly influence spectral quantity and quality in waterbodies receiving land drainage. This paper discusses optical properties in clear and colored inland waters and their effects on autotrophic production with reference to problems related to underwater research diving activities.

Dilute waters (Ca = 0, 3 to 0.8 mg L-1) respond by depressed pH levels throughout the year to existing atmospheric wet deposition of sulphate (20 kg ha-1yr-1). This occurs in southwest Nova Scotia particularly during the cold, wet season when runoff is high. Colored waters of similar Ca levels receiving runoff from peaty catchments exhibit pH values one unit lower (4.7 to 4.1) than those of catchments of similar Ca levels but free from peat deposits (pH > 5.3). In colored streams sulphate and organic anions show opposing cyclic patterns while the negative gran alkalinity is the near mirror image of sulphate. Sulphate anion peaks during the high spring discharge when the organic anion concentration is lowest. Sulphate suddenly drops during the summer months during periods of high evapotranspiration, low water table and runoff, when the concentration of organic anions is highest. Both Al and Fe follow cyclic patterns similar to that of the organic anions while H+ reflects that of the sulphate anion. Hydrogen ion concentration is always higher than that of sulphate in very colored waters, particularly during the summer months when organic anion concentrations are very high. Analysis of data in the tributaries in the Kejimkujik watersheds indicates that while considerable organic acidity is present in colored waters, anthropogenic sulphate further increases the free acidity of these waters, particularly at times of high discharge.

There is a declining gradient of wet SO4 deposition from south to north in Nova Scotia with the highest values being in the south, along with a localized increase around the Halifax metropolitan area, due to local SO4 emission. Edaphic conditions such as drainage from soils containing gypsum or drainage on disturbed rocks containing pyrite, provide additional SO4 to surface waters.Acidity is usually absent in the former (pH > 7.0) and very high in the latter (as low as pH 3.6). By contrast peaty, organic drainages release water low in SO4 during the growing season but they release high amounts of organic anions (A−), consequently, these waters maintain decreased pH values, usually < 4.5. A study of over 80 wetlands and lakes during the ice free period in Nova Scotia showed that sea salt corrected SO4 concentrations range from 45 ueq L−1 in the south end of the province, ∼30 ueq L−1 in the Kejimkujik area and < 17 ueq L−1 in the northern areas with values > 85 ueq L−1 in the Halifax area, reflecting the atmospheric deposition pattern of SO4 The SO4 concentrations may be > 2000 ueq L−1 in drainages containing gypsum, > 700 ueq L−1 in drainages over pyrite bearing socks but < 20 ueq/L−1 in streams draining bogs. The SO4 concentrations change considerably during the non-growing season when the ground is saturated with water or frozen, and the runoff is high (snow and rain often alternate in winter). Under such conditions SO4 concentration drops in the two former cases and increases in bog drainages, accompanied with a considerable drop in (A−) concentrations. Care should be taken when interpreting SO4 concentrations in surface waters in Nova Scotia with respect to atmospheric SO4 deposition.