Mercury Fluxes Research Articles

Mercury emissions from soils and fumaroles of Nea Kameni volcanic centre, Santorini (Greece)

There have been limited studies to date targeting mercury emissions from volcanic fumarolic systems, and no mercury flux data exist for soil or fumarolic emissions at Santorini volcanic complex, Greece. We present results from the first geochemical survey of Hg and major volatile (CO2, H2S, H2O and H2) concentrations and fluxes in the fumarolic gases released by the volcanic/hydrothermal system of Nea Kameni islet; the active volcanic center of Santorini. These data were obtained using a portable mercury spectrometer (Lumex 915+) for gaseous elemental mercury (GEM) determination, and a Multi-component Gas Analyzer System (Multi-GAS) for major volatiles. Gaseous Elemental Mercury (GEM) concentrations in the fumarole atmospheric plumes were systematically above background levels (~4 ng GEM m-3), ranging from ~4.5 to 121 ng GEM m-3. Variability in the measured mercury concentrations may result from changes in atmospheric conditions and/or unsteady gas release from the fumaroles. We estimate an average GEM/CO2 mass ratio in the fumarolic gases of Nea Kameni of approximately 10-9, which falls in the range of values obtained at other low-T (100°C) volcanic/hydrothermal systems (~10-8); our measured GEM/H2S mass ratio (10-5) also lies within the accepted representative range (10-4 to 10-6) of non-explosive volcanic degassing. Our estimated mercury flux from Nea Kameni’s fumarolic field (2.56 × 10-7 t yr-1), while making up a marginal contribution to the global volcanic non-eruptive GEM emissions from closed-conduit degassing volcanoes, represents the first available assessment of mercury emissions at Santorini volcano, and will contribute to the evaluation of future episodes of unrest at this renowned volcanic complex.

Pluriannual Watershed Discharges of Hg into a Tropical Semi-Arid Estuary of the Jaguaribe River, NE Brazil

Mercury fluxes were measured during the dry and rainy seasons (2005 to 2009) at the Jaguaribe River estuary, which discharges into the Equatorial Atlantic Ocean in NE Brazil. During rainy periods, the water masses exhibited a short residence time within the estuary (0.8 days). During dry periods, seawater choked the fluvial discharge, resulting in longer residence times (3.1 days). Dissolved (< 0.7 µm) and particulate Hg concentrations and fluxes were greater from the river to the estuary than from the estuary to the sea, producing accumulated particulate Hg in the estuary. Particulate Hg export (1.8 to 12.6 mg s-1) to the ocean occurred during extremely rainy periods, while dissolved Hg export was practically nonexistent during rainy periods and increased up to 0.45 mg s-1 during dry periods. Because continental runoff in semi-arid regions is affected by land use and global climate changes, the increasing accumulation of particulate Hg in the estuaries and increasing export of dissolved Hg to the ocean are expected.

A comparison of recent methods for modelling mercury fluxes at the air-water interface

The atmospheric pathway of the global mercury flux is known to be the primary source of mercury contamination to most threatened aquatic ecosystems. Notwithstanding, the emission of mercury from surface water to the atmosphere is as much as 50% of total annual emissions of this metal into the atmosphere. In recent years, much effort has been made in theoretical and experimental researches to quantify the total mass flux of mercury to the atmosphere. In this study the most recent atmospheric modelling methods and the information obtained from them are presented and compared using experimental data collected during the Oceanographic Campaign Fenice 2011 (25 October - 8 November 2011), performed on board the Research Vessel (RV) Urania of the CNR in the framework of the MEDOCEANOR ongoing program. A strategy for future numerical model development is proposed which is intended to gain a better knowledge of the long-term effects of meteo-climatic drivers on mercury evasional processes, and would provide key information on gaseous Hg exchange rates at the air-water interface.

Comparison of two measurement methods of dissolved gaseous mercury concentrations and estimations of supersaturation grade and mercury fluxes during a research campaign at the Mediterranean Sea

Dissolved gaseous mercury (DGM) concentrations and gaseous elemental mercury (GEM) concentrations were measured during an oceanographic campaign in the Mediterranean Sea. The DGM concentrations were measured using two different methods, a manual-and an automated method. The manual method was used to obtain DGM depth profiles at several stations throughout the campaign. The automated device measured DGM concentrations continuously at a depth of 4 m. Gaseous elemental mercury (GEM) concentrations in air were measured continuously at the bridge deck. The objectives were to achieve DGM depth profiles, compare the manual-and automated DGM measurement methods, to calculate the supersaturation grades of the sea and the evasional fluxes from the sea surface. Depth profiles of the four measured stations show no diurnal variations. The manual-and the automated method show good compliance. Supersaturation grades are high due to high DGM values and low GEM concentrations. Fluxes of Hg from the sea surface are more dependent on the wind speed than on the supersaturation grade according to the flux models used.

Mercury emissions from flooded soils and sediments in Germany are an underestimated problem: challenges for reliable risk assessments and management strategies

Environmental pollution by mercury is a world-wide problem. Particularly floodplain ecosystems are frequently affected. One example is the Elbe River in Germany and its catchment areas; large amounts of Hg from a range of anthropogenic and geogenic sources have been accumulated in the soils of these floodplains. They serve as sink for Hg originating from the surface water of adjacent river. Today, the vastly elevated Hg contents of the floodplain soils at the Elbe River often exceed even the action values of the German Soil Conservation Law. This is especially important as Hg polluted areas at the Elbe River achieve several hundred square kilometres. Thus, authorities are coerced by law to conduct an appropriate risk assessment and to implement practical actions to eliminate or reduce environmental problems. A reliable risk assessment particularly with view to organisms (vegetation as green fodder and hay production, grazing and wild animals) to avoid the transfer of Hg into the human food chain, requires an authentic determination of Hg fluxes and their dynamics since gaseous emissions from soil to atmosphere are an important pathway of Hg. However, reliable estimates of Hg fluxes from the highly polluted floodplain soils at the Elbe River and its tributaries, and its influencing factors are scarce. For this purpose, we have developed a new method to determine mercury emissions from soils at various sites. Our objectives were i) to quantify seasonal variations of total gaseous mercury (TGM) fluxes for floodplain soils at the Elbe River, ii) to provide insights into physico-chemical processes regulating these TGM fluxes, and iii) to quantify the impacts of the controlling factors soil temperature and soil water content on Hg volatilization from a typical contaminated floodplain soil within soil microcosm experiments under various controlled temperature and moisture conditions. Our study provides insight into TGM emissions from highly Hg-polluted floodplain soils in Germany and that those emissions are an underestimated problem. Current needs for reliable risk assessments, the induced implications for authorities, and future challenges will be discussed. The presented data will contribute to a better understanding of seasonal dynamics of Hg fluxes and its controlling factors. This presentation should be of large interest for a wide international audience, such as environmental scientists and managers, applied ecologists, and authorities.

Mercury emissions in equilibrium: a novel approach for the quantification of mercury emissions from contaminated soils

Mercury emissions from soil samples with different mercury contents have been estimated using a closed circuit array. The samples were collected from the Almaden mercury mining district. The emissions confirmed that temperature and light radiation favour mercury desorption due to the increase in the mercury vapour pressure. An additional positive factor could be the photocatalytic reduction of soluble Hg2+ to volatile Hg0 at the soil surface. A physicochemical model based on mass transfer and equilibrium was developed and was used to reproduce the mercury emissions at the laboratory scale. The use of this model allowed us to obtain the unknown mass transfer coefficient (KL) and adsorption parameters required to quantify the possible gaseous mercury fluxes from these contaminated soils. Experimental results indicate that an equilibrium between the solid and gas phases was established. The proposed kinetic model reproduced perfectly the experimental data, with KL found to be proportional to the inverse of temperature and independent of the radiation. The concentration of mercury in the gas phase was mainly dependent on the soluble mercury content (HgS). Equilibrium data were fitted by Langmuir and Freundlich models and the best fit was obtained using the multi-layer model attending to the convex shape of the curves, which is characteristic of non-porous or possibly macroporous materials having a low adsorption energy. The Freundlich constant (KF) was also fitted as a polynomial function with temperature and this gave a straight line for the light radiation and a second grade equation for dark conditions. Once the parameters had been obtained, the Hg emission fluxes from contaminated soils were estimated and the values were between two and three orders of magnitude higher than those published in the literature for non-contaminated soils.

Dissolved gaseous mercury and mercury flux measurements in Mediterranean coastal waters: A short review

There is a general agreement in the scientific community that the marine ecosystem can be a sink and/or source of the mercury that is cycling in the global environment, and current estimates of the global mercury budget for the Mediterranean region are affected by high uncertainty, primarily due to the little progress made so far in evaluating the role of chemical, physical and biological processes in the water system and in the lower atmosphere above the sea water (air-water interface). The lack of knowledge of the magnitude of the air-sea exchange mechanisms is, therefore, one of the main factors affecting the overall uncertainty associated with the assessment of net fluxes of Hg between the atmospheric and marine environments in the Mediterranean region. Results obtained during the last 15 years in the Mediterranean basin indicate the quantitative importance of such emission in the biogeochemical cycle of this element, highlighting the need for thorough investigations on the mechanisms of production and volatilization of dissolved gaseous mercury in waters.

222Rn calibrated mercury fluxes from terrestrial surfaces of southern Africa derived from observations at Cape Point, South Africa

Gaseous elemental mercury (GEM) and 222 Rn, a radioactive gas of primarily terrestrial origin with a half-life of 3.8 days, have been measured simultaneously at Cape Point, South Africa, since March 2007. Between March 2007 and December 2009 altogether 59 events with high 222 Rn concentrations were identified. GEM correlated with 222 Rn in 41 of the events and was constant during the remaining events without significant correlation. The average GEM/ 222 Rn emission ratio of all events was -0.0047 ± 0.0054 pg mBq -1 , with ± 0.0054 being the standard error of the average. With an emission rate of 1.1 222 Rn atoms cm -2 s -1 and a correction for the transport duration, this emission ratio corresponds to a radon calibrated flux of about -0.53 ± 0.62 ng m -2 h -1 which is statistically not distinguishable from zero. With wet deposition, which is not included in this estimate, the terrestrial surface of southern Africa appears to be a net mercury sink.

Significance of submarine groundwater discharge in the coastal fluxes of mercury in Hampyeong Bay, Yellow Sea

Submarine groundwater discharge (SGD) and various solutes released with SGD have received particular attention recently; however, understanding of the impact of SGD on trace metal fluxes in the coastal ocean is limited. To understand the contribution of SGD to the coastal Hg input, the Hg mass fluxes associated with SGD were estimated from Hampyeong Bay, a coastal embayment in the Yellow Sea. Hg concentrations in filtered groundwater and seawater ranged from 1.3 to 4.4pM and from 0.83 to 2.0pM, respectively, and Hg concentrations in unfiltered seawater ranged from 1.7 to 4.6pM. The Hg flux estimation showed that SGD was the prime input source of Hg in the bay (18±12molyr−1), contributing 65% of the total input. Atmospheric deposition was the second dominant source of Hg (8.5±2.7molyr−1), contributing 31% to the total input. The results of the current study suggest that SGD can be a significant source of Hg in estuarine/coastal systems; therefore, estimating the coastal mass budgets of Hg must include SGD as a prime source of Hg.

안동호 퇴적물 중 수은 및 중금속의 분포특성 연구

본 연구에서는 안동호 퇴적물 중의 총 수은, 메틸수은, 중금속 농도를 조사하고 퇴적물과 수체간의 수은 이동량을 산정하였다. 안동호 퇴적물 중 수은 농도는 2009~2011 년에 각각 <TEX>$155.0{\pm}71.9$</TEX> ng/g, <TEX>$211{\pm}62$</TEX> ng/g 및 <TEX>$198{\pm}6.88$</TEX> ng/g이었으며, 메틸수은은 2009 년 및 2011 년에 각각 <TEX>$1.85{\pm}1.09$</TEX> ng/g, <TEX>$3.49{\pm}1.79$</TEX> ng/g이었고, 총수은에 대한 메틸수은의 분율인 %메틸수은은 <TEX>$1.17{\pm}0.39%$</TEX> 및 <TEX>$1.77{\pm}0.94%$</TEX>로 나타났다. 퇴적물 중 아연, 카드뮴, 납, 구리의 농도는 644 mg/kg, 7.3 mg/kg, 67 mg/kg, 42 mg/kg 으로 모두 미국 국립해양대기청(NOAA, National Oceanic and Atmospheric Administration)에서 제시한 퇴적물 기준(SQGs, Sediment Quality Guidelines)중의 최소 무영향 농도(ERL, Effect Range Low) 수준을 초과하는 수준이었다. 안동호에서 퇴적물로의 수은 이동량은 83.7 <TEX>$ng/cm^2{\cdot}$</TEX>년, 퇴적물에서부터 수체로의 수은 확산속도는 1.24 <TEX>$ng/cm^2{\cdot}$</TEX>년으로 추정되었다. In this study, mercury, methylmercury and heavy metals in sediment from the lake Andong were analyzed, along with the estimation of mercury flux between sediments and water in the lake Andong. Average mercury concentrations in sediments sampled in 2009~2011 were <TEX>$155.0{\pm}71.9$</TEX> ng/g, <TEX>$211{\pm}62$</TEX> ng/g and <TEX>$198{\pm}6.88$</TEX> ng/g, respectively. The average methylmercury concentration were <TEX>$1.85{\pm}1.09$</TEX> ng/g (2009) and <TEX>$3.49{\pm}1.79$</TEX> ng/g (2011), and %methylmercury, the fraction of methylmercury in total mercury were <TEX>$1.17{\pm}0.39%$</TEX> and <TEX>$1.77{\pm}0.94%$</TEX>, respectively. Heavy metal (Zn, Cd, Pb, Cu) concentrations of the sediments exceeded ERL (Effect Range Low) level of US NOAA (National Oceanic and Atmospheric Administration)'s sediment quality criteria. Estimated mercury sedimentation flux was found to be 83.7 <TEX>$ng/cm^2{\cdot}yr$</TEX> and mercury diffusion flux was estimated as 1.24 <TEX>$ng/cm^2{\cdot}yr$</TEX>.

The cycling and sea–air exchange of mercury in the waters of the Eastern Mediterranean during the 2010 MED-OCEANOR cruise campaign

An oceanographic cruise campaign on-board the Italian research vessel Urania was carried out from the 26th of August to the 13th of September 2010 in the Eastern Mediterranean. The campaign sought to investigate the mercury cycle at coastal and offshore locations in different weather conditions. The experimental activity focused on measuring mercury speciation in both seawater and in air, and using meteorological parameters to estimate elemental mercury exchange at the sea–atmosphere interface. Dissolved gaseous mercury (DGM), unfiltered total mercury (UTHg) and filtered total mercury (FTHg) surface concentrations ranged from 16 to 114, 300 to 18,760, and 230 to 10,990pgL−1, respectively. The highest DGM, UTHg and FTHg values were observed close to Augusta (Sicily), a highly industrialized area of the Mediterranean region, while the lowest values were recorded at offshore stations. DGM vertical profiles partially followed the distribution of sunlight, as a result of the photoinduced transformations of elemental mercury in the surface layers of the water column. However, at some stations, we observed higher DGM concentrations in samples taken from the bottom of the water column, suggesting biological mercury production processes or the presence of tectonic activity. Moreover, two days of continuous measurement at one location demonstrated that surface DGM concentration is affected by solar radiation and atmospheric turbulence intensity. Atmospheric measurements of gaseous elemental mercury (GEM) showed an average concentration (1.6ngm−3) close to the background level for the northern hemisphere. For the first time this study used a numerical scheme based on a two-thin film model with a specific parameterization for mercury to estimate elemental mercury flux. The calculated average mercury flux during the entire cruise was 2.2±1.5ngm−2h−1. The analysis of flux data highlights the importance of the wind speed on the mercury evasion from sea surfaces.

Mercury release flux and its influencing factors at the air-water interface in paddy field in Chongqing, China

The exchange of mercury (Hg) across the air-water interface is an important part of Hg biogeochemical cycle. Mercury fluxes across the air-water interface in paddy fields were measured by a Dynamic Flux Chamber (DFC) coupled with a Lumex® multifunctional mercury analyzer RA-915+ at two sites (Chengjiang (CJ) and Caoshang (CS)) in Beibei, Chongqing, China in 2008. The results showed that mercury emission followed a power-law relationship with solar radiation and air temperature, and it increased exponentially with water temperature at both sites. Mercury emission was mainly influenced by the solubility of gaseous elemental Hg, photo-thermal effect, electron activity (Eh) and air Hg concentrations. Solar radiation made the greatest direct contribution to mercury emission during the daytime (0.80), with an 83.60% contribution, whereas at nighttime the water temperature (0.72) contributed to 71.65% of emissions. The temperature gradient between water and air might also influenced mercury emission across the air/water interface at nighttime. These findings suggest that paddy fields could act as a significant source of atmospheric mercury, and it can contribute significantly to the atmospheric mercury in a local region.

Gaseous mercury emissions from subtropical forested and open field soils in a national nature reserve, southwest China

Total gaseous mercury flux measurements of forested and open field soils in the subtropical forest zones, in Chongqing, Southwestern China were monitored from April 2011 to March 2012 to provide insight into the characteristics of gaseous mercury flux with and without vegetation covers. Samples were collected from surfaces of forest and open field as the most representative terrestrial surfaces in Jinyun Mountain. Simultaneously meteorological parameters at the soil level relating GEM fluxes to soil temperature, air humidity, solar radiation were analyzed and variations of atmospheric GEM concentration were examined. The results showed that annual averaged fluxes from soil in the forest and open-air site were 14.23 ng m2 h−1 and 20.74 ng m2 h−1 respectively, with a clear seasonal variation for each surface. The soil surface displayed the largest difference between evening and daytime flux, particularly in spring and summer in open field surface (i.e., with low flux in evening (1.93 ng m2 h−1) to high flux in daytime (97.86 ng m2 h−1) in summer). GEM fluxes in the open-air site were positively correlated with solar irradiation and soil temperature, and inversely correlated with air humidity. In the forest site, GEM fluxes showed weaker correlation with meteorological variables. Based on the whole year experiments and field tests, it can be found that in some season (especially fall), the mercury emission fluxes were more highly dependent on solar radiation and less dependent on temperature. The regression results demonstrated that each surface displayed similar responses to time series change in meteorological parameters. A comparison between one year periods in the two sites showed much larger emission from the open field with forest conversion to bare soil.

Evaluating the effects of sub-zero temperature cycling on mercury flux from soils

A number of mechanisms have been shown to facilitate the flux of mercury from soils, although at sub-zero temperatures, there is evidence to suggest that alternate mechanisms may exist. Field studies at sub-zero temperatures have observed spikes in flux under certain conditions however very little laboratory work has been done to characterize the specific effects or mechanisms. A Dynamic Flux Chamber (DFC) and Tekran Model 2537A were used to analyse mercury flux from a naturally enriched soil. Soil moisture contents were varied between 30%, 60%, and 75% of field capacity while temperatures were cycled between 0 and −25 °C. The results, which were compared to room temperature baseline runs, showed that, at sub-zero temperatures, the mercury flux was suppressed in general. However, during the temperature cycling runs, soil flux spikes were evident during positive temperature change or warming. A one-way ANOVA by ranks proved that statistically significant fluxes were occurring during the runs at 30% and 60% of field capacity for positive rates of temperature changes. Arrhenius plots showed that for positive soil temperatures flux and temperature correlated well with the Arrhenius relationship. At sub-zero conditions however, no relationship was present, indicating another mechanism was present. The proposed mechanism for this enhanced flux is the physical evacuation of interstitial pore space gaseous mercury by the expansion and contraction of the freeze–thaw cycle.

Benthic fluxes of mercury during redox changes in pristine coastal marine sediments from the Gulf of Trieste (northern Adriatic Sea)

Purpose The Gulf of Trieste (northern Adriatic Sea) is an example of a coastal environment contaminated with mercury (Hg). Contamination is a consequence of nearly 500 years of activity at the Idrija Mine (western Slovenia), which is the second largest Hg mine in the world. Oxygen depletion can be common in the Gulf of Trieste due to late summer stratification of the water column and accumulation of labile organic matter. Since changing redox conditions can have an impact on Hg transformations, we studied the effect of oxygen depletion, in parallel with sulphide, iron (Fe), manganese (Mn), fluorescent dissolved organic matter (FDOM) and nitrogen (N) and phosphorus (P) availability, on total Hg and methylmercury (MeHg) fluxes from sediments.

The impacts of land use changes in the mercury flux in the Madeira River, Western Amazon

Changes in hydrochemistry and Hg distribution in the Madeira River from Porto Velho to the confluence with the Amazon River were studied in two cruises in 1997 and 2002. Water conductivity was similar in both periods, but the pH was significantly higher in 2002, in particular along the middle reaches of the river. Total suspended matter concentrations also increased from 1997 to 2002 along the same river portion, which is a result of forest conversion to other land uses, in particular pastures and agriculture accelerated during the interval between the cruises. Dissolved Hg concentrations were similar along the river in both cruises, but particulate Hg concentrations increased significantly along the middle portion of the river, although the suspended matter from 2002 was relatively poorer in Hg compared to that from 1997. Since particulate Hg represents more than 90% of the total Hg present in the river water, there was a significant increase in the total Hg transport in the Madeira River. Although gold mining has nearly ceased to exist in the region, the remobilization of Hg from forest soils through conversion to other land uses is responsible for maintaining relatively high Hg content in the Madeira River environment.

Past and present mercury flux to a West African crater lake (Lake Bosomtwe/Bosumtwi, Ghana)

Lake sediment cores have been used to reconstruct mercury deposition patterns in many parts of the world; however, no studies to date have used these methods in West Africa, nor are there any published measurements of mercury deposition to this region. We measured mercury in a 210Pb dated sediment core from a meromictic crater lake in West Africa (Lake Bosomtwe, Ghana). Lake Bosomtwe has a very small catchment area to lake area ratio (1.1) and the sediment mercury profile is expected to reflect past and present atmospheric mercury deposition to the lake. Mercury concentrations in sediments as well as mercury flux to the sediments increased from the mid-1800s to latter half of the 1900s, however there has been a sharp decline in mercury flux to Lake Bosomtwe in recent decades. The recent decline in mercury flux to Lake Bosomtwe's sediments does not appear to be consistent with trends in local, regional or global mercury emissions, and may instead reflect declining global atmospheric mercury concentrations or declining European emissions, highlighting the importance of long-range atmospheric transport of mercury.

Tidally Driven Export of Dissolved Organic Carbon, Total Mercury, and Methylmercury from a Mangrove-Dominated Estuary

The flux of dissolved organic carbon (DOC) from mangrove swamps accounts for 10% of the global terrestrial flux of DOC to coastal oceans. Recent findings of high concentrations of mercury (Hg) and methylmercury (MeHg) in mangroves, in conjunction with the common co-occurrence of DOC and Hg species, have raised concerns that mercury fluxes may also be large. We used a novel approach to estimate export of DOC, Hg, and MeHg to coastal waters from a mangrove-dominated estuary in Everglades National Park (Florida, USA). Using in situ measurements of fluorescent dissolved organic matter as a proxy for DOC, filtered total Hg, and filtered MeHg, we estimated the DOC yield to be 180 (±12.6) g C m–2 yr–1, which is in the range of previously reported values. Although Hg and MeHg yields from tidal mangrove swamps have not been previously measured, our estimated yields of Hg species (28 ± 4.5 μg total Hg m–2 yr–1 and 3.1 ± 0.4 μg methyl Hg m–2 yr–1) were five times greater than is typically reported for terrestrial wetlands. These results indicate that in addition to the well documented contributions of DOC, tidally driven export from mangroves represents a significant potential source of Hg and MeHg to nearby coastal waters.

Historical flux of mercury associated with mining and industrial sources in the Marano and Grado Lagoon (northern Adriatic Sea)

The “MIRACLE” Project was established in order to assess the feasibility of clam farming and high levels of sediment mercury (Hg) contamination coexisting in the Marano and Grado Lagoon, Italy. This lagoon has been subjected to Hg input from both industrial waste (chlor-alkali plant) and long-term mining activity (Idrija mine, NW Slovenia). One of the subtasks of the “MIRACLE” Project was to determine the historical evolution of Hg accumulation in the lagoon’s bottom sediments. Thirteen 1-m deep sediment cores were collected from the subtidal and intertidal zones, plus one in a saltmarsh, all of which were then analyzed for total Hg content and several physicochemical parameters. Sedimentation rate assessments were performed by measuring short-lived radionuclides (excess 210Pb and 137Cs). For most of the analyzed cores, natural background levels of Hg were observed at depths of 50–100 cm. In the eastern area, Hg contamination was found to be at its maximum level at the core top (up to 12 μg g−1) as a consequence of the long-term mining activity. The vertical distribution of Hg was related to the influence of the single-point contamination sources, whereas the grain-size variability or organic matter content seemed not to affect it. In the western area, Hg content at the surface was found not to exceed 7 μg g−1 and contamination was recorded only in the first 20–30 cm. Geochronological measurements showed that the depositional flux of Hg was influenced by anthropogenic inputs after 1800, when mining activity was more intense. After 1950, Hg in the surface sediment, most remarkable in the central-western sector, seemed to also be affected by the discharge of the Aussa River, which delivers Hg from the chlor-alkali plant. In 1996, Hg mining at Idrija ceased, however the core profiles did not show any subsequent decreasing trend in terms of Hg flux, which implies the system retaining some “memory” of contamination. Thus, in the short term, a decrease in Hg inputs into the nearby Gulf of Trieste and the lagoon seems unlikely. A preliminary rounded-down gross estimate of total Hg “trapped” in the lagoon’s sediments amounted to 251 t. Such a quantity, along with the complexity of the lagoon ecosystem, suggests that an in toto reclamation of the sediments at the lagoon scale is unfeasible, both economically and environmentally.

Inter-annual and spatial variability in hillslope runoff and mercury flux during spring snowmelt

Spring snowmelt is an important period of mercury (Hg) export from watersheds. Limited research has investigated the potential effects of climate variability on hydrologic and Hg fluxes during spring snowmelt. The purpose of this research was to assess the potential impacts of inter-annual climate variability on Hg mobility in forested uplands, as well as spatial variability in hillslope hydrology and Hg fluxes. We compared hydrological flows, Hg and solute mobility from three adjacent hillslopes in the S7 watershed of the Marcell Experimental Forest, Minnesota during two very different spring snowmelt periods: one following a winter (2009-2010) with severely diminished snow accumulation (snow water equivalent (SWE) = 48 mm) with an early melt, and a second (2010-2011) with significantly greater winter snow accumulation (SWE = 98 mm) with average to late melt timing. Observed inter-annual differences in total Hg (THg) and dissolved organic carbon (DOC) yields were predominantly flow-driven, as the proportion by which solute yields increased was the same as the increase in runoff. Accounting for inter-annual differences in flow, there was no significant difference in THg and DOC export between the two snowmelt periods. The spring 2010 snowmelt highlighted the important contribution of melting soil frost in the timing of a considerable portion of THg exported from the hillslope, accounting for nearly 30% of the THg mobilized. Differences in slope morphology and soil depths to the confining till layer were important in controlling the large observed spatial variability in hydrological flowpaths, transmissivity feedback responses, and Hg flux trends across the adjacent hillslopes.