Mercury Loading and Methylmercury Production and Cycling in High-Altitude Lakes from the Western United States

Studies worldwide have shown that mercury (Hg) is a ubiquitouscontaminant, reaching even the most remote environments such ashigh-altitude lakes via atmospheric pathways. However, very fewstudies have been conducted to assess Hg contamination levels ofthese systems. We sampled 90 mid-latitude, high-altitude lakes from seven national parks in the western United States during afour-week period in September 1999. In addition to the synoptic survey, routine monitoring and experimental studies were conducted at one of the lakes (Mills Lake) to quantify MeHg fluxrates and important process rates such as photo-demethylation. Results show that overall, high-altitude lakes have low total mercury (HgT) and methylmercury (MeHg) levels (1.07 and 0.05 ng L^-1, respectively), but a very good correlation of Hg to MeHg (r²= 0.82) suggests inorganic Hg(II) loading is a primary controlling factor of MeHg levels in dilute mountain lakes. Positive correlations were also observed for dissolved organic carbon (DOC) and both Hg and MeHg, although to a much lesser degree. Levels of MeHg were similar among the seven national parks, with the exception of Glacier National Park where lowerconcentrations were observed (0.02 ng L^-1), and appear to berelated to naturally elevated pH values there. Measured rates ofMeHg photo-degradation at Mills Lake were quite fast, and thisprocess was of equal importance to sedimentation and stream flowfor removing MeHg. Enhanced rates of photo-demethylation are likely an important reason why high-altitude lakes, with typically high water clarity and sunlight exposure, are low in MeHg.     

Mobility and Methylation of Mercury in Forest Soils Development of an In-Situ Stable Isotope Tracer Technique and Initial Results

A method for investigating in-situmethylation and mobility of mercury has beendeveloped and applied to forest soil. The methodis based on additions of stable ¹⁹⁹Hgisotopes to forest soil plots followed bysampling and analysis of isotope ratios of totalmercury and MeHg using ICP-MS. Initial resultsindicate that a fraction (30%) of the mercuryadded to the forest soils is immobilised over atime scale of 16 months. A small but significantfraction of the mercury is methylated during thesame time scale. Higher methylation rates werefound in wetland soil than in dry forest podzolsoil.     

Comparisons of Measured and Modelled Ozone Deposition to Forests in Northern Europe

The performance of a new dry deposition module, developedfor the European-scale mapping and modelling of ozone flux to vegetation, was tested against micrometeorological ozone and water vapour flux measurements. The measurement data are for twoconiferous (Scots pine in Finland, Norway spruce in Denmark) and one deciduous forest (mountain birch in Finland). On average, themodel performs well for the Scots pine forest, if local inputdata are used. The daytime deposition rates are somewhat over-predicted at the Danish site, especially in the afternoon. The mountain birch data indicate that the generic parameterisationof stomatal responses is not very representative of this northernspecies. The module was also tested by using modelled meteorological data that constitute the input for a photochemical transport model.     

Novel Mercury Oxidant and Sorbent for Mercury Emissions Control from Coal-fired Power Plants

The authors have successfully developed novel efficient and cost-effective sorbent and oxidant for removing mercury from power plant flue gases. These sorbent and oxidant offer great promise for controlling mercury emissions from coal-fired power plants burning a wide range of coals including bituminous, sub-bituminous, and lignite coals. A preliminary analysis from the bench-scale test results shows that this new sorbent will be thermally more stable and cost-effective in comparison with any promoted mercury sorbents currently available in the marketplace. In addition to the sorbent, an excellent elemental mercury (Hg(0)) oxidant has also been developed, and will enable coal-fired power plants equipped with wet scrubbers to simultaneously control their mercury emissions as well as their sulfur oxides emissions. This will work by converting all elemental mercury to an oxidized form which will be removed by the wet scrubber. This will result in significant cost savings for mercury emissions control to the atmosphere, and will help in keeping electric costs low. The sorbent and oxidant will benefit from the utilization of a waste stream from the printed circuit board (PCB) industry, and would thus be environmentally beneficial to both of the utility and electronics industries. The sorbent also demonstrated thermal stability up to 350°C, suggesting a possibility of an application in pulverized coal-fired power plants equipped with hot-side electrostatic precipitators and coal gasification plants.     

我国氯碱行业汞污染现状与防治对策

介绍了汞污染的来源、危害及治理现状,分析了氯碱行业的高汞触媒污染严重、汞流失环节多、含汞废触媒回收处理中存在污染隐患等汞污染问题,提出了减少氯碱行业汞消耗与汞污染的对策和措施.     

A Chronology of Nitrogen Deposition in the UK Between 1900 and 2000

Measurements of the concentrations of nitrogen compounds in air and precipitation in the UK have been made since the mid-19th century, but no networks operating to common protocols and having traceable analytical procedures were established until the 1950s. From 1986 onwards, a high-quality network of sampling stations for precipitation chemistry was established across the UK. In the following decade, monitoring networks provided measurement of NO₂, NH₃, HNO₃ and a satisfactory understanding of the dry deposition process for these gases allowed dry deposition to be quantified. Maps of N deposition for oxidized and reduced compounds at a spatial scale of 5 km × 5 km are available from 1986 to 2000. Between 1950 and 1985, the more limited measurements, beginning with those of the European Air Chemistry Network (EACN) provide a reasonable basis to estimate wet deposition of NO ₃ ^– –N and NH ₄ ⁺ –N. For the first half of the century, estimates of deposition were scaled with emissions assuming a constant relationship between emission and deposition for each of the components of the wet and dry deposition budget at the country scale. Emissions of oxidized N, which dominated total nitrogen emissions throughout the century, increased from 312 kt N annually in 1900 to a peak of 787 kt for the decade 1980–1990 and then declined to 460 kt in 2000. Emissions of reduced N, largely from coal combustion were about 168 kt N in 1900, increasing to a peak of 263 kt N in 2000 and by now dominated by agricultural sources. Reduced N dominated the deposition budget at the country scale, increasing from 163 kt N in 1900 to 211 kt N in 2000, while deposition of oxidized N was 66 kt N in 1900 and 191 kt N in 2000. Over the century, 68 Mt (Tg) of fixed N was emitted within the UK, 78% as NO _x , while 29 Mt of nitrogen was deposited (43% of emissions), equivalent to 1.2 t N ha^–1, on average, with 60% in the reduced form. Deposition to semi-natural ecosystems is approximately 15 Tg N, equivalent to between 1 and 5 t N ha^–1, over the century and appears to be accumulating in soil. The N deposition over the century is similar in magnitude to the total soil N inventory in surface horizons.     

The Role of Cloud Processing in the Relationship Between Wet Deposited Sulphur and Sulphur Dioxide Emissions

It is well established that wet deposition of sulphate in the UKhas fallen by a much smaller fraction than have emissions of sulphur dioxide. Dry deposition of sulphur has decreased in proportion to the decline in emissions. A number of suggestionshave been made which offer possible explanations for this non-linearity between emissions and wet deposition. In this paper amodel of the processing of sulphur dioxide by aqueous phase cloudchemistry in a cloudy boundary layer is presented. This work doesnot simulate all the details of the mechanisms by which sulphate is incorporated into precipitation. It does, however, explorethe non-linearity of this oxidation process. It is shown that theoxidation of sulphur dioxide, in these conditions, over the UK isdominated by oxidation by ozone. The rate of sulphate productionis then controlled by the availability of the one basic trace gasin the atmosphere ammonia. Using realistic concentrations of thereacting species this is found to simulate well the observed non-linearity. The model predicts that sulphate and sulphur dioxideconcentrations will be uncorrelated in the cloudy boundary layerbut that ammonium and sulphate will be well correlated. Fieldobservations at a cloudy site in Northern England are consistentwith these predictions.     

Elemental Mercury Control by Novel Oxidant and Sorbent in an Entrained-Flow System

An entrained-flow system has been designed and constructed to simulate in-flight mercury capture by sorbents in ducts of coal-fired utility plants. The test conditions of 1.5 s residence time, 140°C temperature, 4.5 ppbv inlet Hg⁰ concentration, and 0–20 lb/MMacf sorbent injection rates were chosen to simulate conditions in the ducts. Novel oxidants developed in previous fixed-bed tests and novel sorbents derived from the novel oxidants were tested for their Hg⁰ capture in the entrained-flow system to examine the possibility of using those sorbents in a full-scale system. Darco-FGD and Darco Hg-LH served as benchmark sorbents with which mercury control capability of the novel oxidants and novel sorbents could be compared. The test results showed that the novel oxidants have remarkable Hg⁰ oxidation capability, and the novel sorbents showed a better performance in Hg⁰ removal than Darco Hg-LH.     

Mercury and Organochlorine Contamination in Brown Trout (Salmo Trutta) and Arctic Charr (Salvelinus Alpinus) from High Mountain Lakes in Europe and the Svalbard Archipelago

High concentration of Hg, less volatile PCB congeners and p,p-DDE in Arctic charr from an arctic lake was mainly causedby biomagnification in the food chain where cannibalism was thedriving force. We suggest that low sediment fluxes of Hg, low net production of methyl mercury, and short food chains excludingpiscivory explain the low levels of Hg in the invertebrate feeding fish population in five European high mountain lakes.Concentrations of less volatile PCB congeners in insectivorous fish populations from the European high mountain lakes were mainly influenced by fish age and atmospheric deposition, indicated by the sediment inventory. Atmospheric deposition influenced by local sources may explain the higher concentrationsof pesticides (p,p-DDT, p,p-DDE and -HCH) observedin fish from the Pyrenees compared to the other sites. Theconcentrations of Hg and organochlorines did not exceedthe guidelines for fish consumption, except for Hg levelsin the oldest fish from the arctic lake.     

A New Concept for Air Quality Modelling in Street Canyons

We present an analytical model that predicts concentrations in street canyons assuming a uniform distribution within a street, dimensioned by its length and width and the height of the surrounding built-up area. Using the Prandtl-Taylor hypothesis, the concentration in the street is determined from a mass flux balance between a horizontal advective flux, a turbulent diffusive vertical flux and a continuous road transport emission source. The model does not necessarily assume re-circulation of the flow in the street canyon, but rather considers the turbulent intermittency in the shear layer shed from the upwind roof level as the driving force. This concept is in agreement with recent measurements and observations. The model has been applied to compute benzene concentrations based on hourly emissions obtained for 1963 streets and road segments in the City of Antwerp, Belgium. The results are compared with diffusive sampler measurements carried out at 101 locations in several streets of Antwerp, during 4 periods of 5 days in 1998. When averaged over periods of 5 days, the calculated benzene concentrations show a very good agreement with the results obtained by the diffusive sampler measurements.     

Lowest Effect Levels of Lead and Mercury on Decomposition of Mor Layer Samples in a Long-Term Experiment

Indications of possible negative effects of lead (Pb) and mercury(Hg) on microbial respiration in Southern Swedish forest humus layers led to experiments on dose-response relationships by additions of metal salts in the laboratory. Respiration rates andweight loss due to decomposition of organic material were measured. For relevance to field situations metal doses were low,the time span was long, 550 days including freeze storage, and microbial activity was kept up by plant litter additions. We looked for effects of Pb and Hg at levels moderately elevated above the Southern Swedish reference, as well as combined effectsof Pb + Hg. A reduction in respiration and decomposition of10% was found at about 225–245 g g^-1 of total Pb, i.e. ata Pb level elevated 3.5 times. Although small effects of Hg werefound even at the lowest dose level, 10% inhibition of microbialactivity appeared temporarily at about 2–3 g g^-1 of total Hg, i. e. at 6–8 times the reference level. There were nolong-term additive effects of Pb and Hg on decomposition. Type of anion had a strong influence on the test, chlorides of Pbbeing more toxic than nitrates. Long-term monitoring and maintenance of microbial activity during the experiment were prerequisites for the occurrence of effects at low metal levels.     

Soil Respiration in Relation to Small-Scale Patterns of Lead and Mercury in Mor Layers of Southern Swedish Forest Sites

Pollution-related lead (Pb) andmercury (Hg) in mor layers of Southern Swedenmight have effects on soil biology, although inthe literature effect concentrations have beenidentified at much higher levels. Considerablesmall-scale spatial variability in heavy metalcontents and microbial respiration in mor layersof forest sites was used to calculatecorrelations that could reveal toxic effects.Negative correlations were always strongest atsites with high loads of Pb or Hg, which was considered to indicate metal toxicity. The highload sites were found in Southwestern Sweden,locally at a motorway and at a chlorine-alkalifactory. Other factors of possible influence,such as other pollutants, age of organic materialor climatic differences, would affect high andlow load sites alike. Negative correlations withrespiration were found for Pb at sites with 74 g g^-1 of mean Pb content in O_f-layer and for Hg at 0.25 g g^-1.     

GHG emission factors developed for the recycling and composting of municipal waste in South African municipalities

GHG (greenhouse gas) emission factors for waste management are increasingly used, but such factors are very scarce for developing countries. This paper shows how such factors have been developed for the recycling of glass, metals (Al and Fe), plastics and paper from municipal solid waste, as well as for the composting of garden refuse in South Africa. The emission factors developed for the different recyclables in the country show savings varying from ?290 kg CO₂ e (glass) to ?19 111 kg CO₂ e (metals – Al) per tonne of recyclable. They also show that there is variability, with energy intensive materials like metals having higher GHG savings in South Africa as compared to other countries. This underlines the interrelation of the waste management system of a country/region with other systems, in particular with energy generation, which in South Africa, is heavily reliant on coal. This study also shows that composting of garden waste is a net GHG emitter, releasing 172 and 186 kg CO₂ e per tonne of wet garden waste for aerated dome composting and turned windrow composting, respectively. The paper concludes that these emission factors are facilitating GHG emissions modelling for waste management in South Africa and enabling local municipalities to identify best practice in this regard.     

Accumulation of pollutant nitrogen in calcareous and acidic grasslands: Evidence from N flux and 15N tracer studies

Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0, +35 and +140 kg N ha^–1 year^–1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets—calculated from the N flux data—showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutant N in the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing ¹⁵N labelled ammonium nitrate (+35 kg N ha^–1 year^–1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of ¹⁵N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study.     

Model Evaluation of Dry Deposition to Vegetation for Volatile and Semi-Volatile Organic Compounds in a Multimedia Environment

Gas-phase atmospheric deposition wasevaluated in a screening level model of themultimedia environmental distribution of toxics(MEND-TOX). Algorithmic additions to MEND-TOXfor the estimation of gas-phase depositionvelocity over vegetated surfaces were analyzedusing recently published dry deposition fluxmeasurements for nitric acid. Model outputs arecompared to similar estimates from the NOAAmultilayer dry deposition model. Results of theevaluation indicate that MEND-TOX performs wellas a screening level model for the estimation ofgas-phase dry deposition velocity of nitric acidover soybeans. The present study expandsprevious laboratory results for organic speciesto include an inorganic species and open fieldand dry leaf, conditions.(On assignment to the National Exposure Research Laboratory, U.S. Environmental Protection Agency); (author for correspondence, e-mail     

Emission Models and Inventories for Local Greenhouse Gas Emissions Assessment: Experience in the East Midlands Region of the Uk

This paper considers how regional greenhouse gas emissioninventories can be determined. It presents a greenhousegas emissions inventory, by source, for the East Midlandsthat has been compiled as part of a regional study intoclimate change impacts in the United Kingdom. This hasused available local data, and national emissions datawith appropriate scaling factors. Total greenhouse gasemissions for the region are estimated to be 59 milliontonnes of carbon dioxide equivalent (CO₂ equivalent)for 1997. Of these emissions, approximately 86% werecarbon dioxide emissions, 7% methane emissions, and 5%were nitrous oxide, with emissions of hydrofluorocarbons(HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride(SF₆) contributing less than 2% of total emissions.     

The importance of chemical buffering for pelagic and benthic colonization in acidic waters

In poorly buffered areas acidification may occur for two reasons: through atmospheric deposition of acidifying substances and – in mining districts – through pyrite weathering. These different sources of acidity lead to distinct clearly geochemistry in lakes and rivers. In general, the geochemistry is the major determinant for the planktonic composition of the acidified water bodies, whereas the nutrient status mainly determines the level of biomass. A number of acidic mining lakes in Eastern Germany have to be neutralized to meet the water quality goals of the European Union Directives and to overcome the ecological degradation. This neutralization process is limnologically a short-term maturation of lakes, which permits biological succession to overcome two different geochemical buffer systems. First, the iron buffer system characterizes an initial state, when colonization starts: there is low organismic diversity and productivity, clear net heterotrophy in most cases. Organic carbon that serves as fuel for the food web derives mainly from allochthonous sources. In the second, less acidic state aluminum is the buffer. This state is found exceptionally among the hard water mining lakes, often as a result of deposition of acidifying substances onto soft water systems. Colonization in aluminum-buffered lakes is more complex and controlled by the sensitivity of the organisms towards both, protons and inorganic reactive aluminum species. In soft-water systems, calcium may act as antidote against acid and aluminum; however, this function is lost in hard water post mining lakes of similar proton concentrations. Nutrient limitations may occur, but these do not usually control qualitative and quantitative plankton composition. In these lakes, total pelagic biomass is controlled by the bioavailability of nutrients, particularly phosphorus.     

Evidence for biodegradation and volatilisation of dissolved petroleum hydrocarbons during in situ air sparging in large laboratory columns

Laboratory column experiments run for up to 13 days compared air sparging of groundwater contaminated by dissolved petroleum hydrocarbons in sterile and non-sterile aquifer sediments as well as uncontaminated sediments and groundwater. Loss of dissolved BTEX compounds in the contaminated columns was very rapid, occurring through volatilisation. The majority of the dissolved total organic carbon (TOC) persisted for much longer periods however. A direct comparison between losses from sterile and non-sterile columns suggested a negligible contribution of biodegradation to the removal of TOC. This was difficult to confirm through examination of O₂ utilisation because oxidation of a small amount of reduced sulphur in the aquifer materials was the dominant sink for O₂. Despite this, it was possible to conclude that less than 22% of the removal of TOC was through biodegradation during the first three days of air sparging.     

What Anthropogenic Radionuclides (90Sr and 137Cs in Atmospheric Deposition, Surface Soils and Aeolian Dusts Suggest for Dust Transport over Japan

Currently, atmospheric anthropogenic radionuclides (particulate) are controlled by suspension of the surface dust containing those radionuclides (resuspension). We have found, therefore, that such radionuclides can be used as tracers of the surface dust suspension, transport and its subsequent deposition in distant areas. The ¹³⁷Cs/⁹⁰Sr activity ratios in the atmospheric deposition, without the direct influence of nuclear tests and accidents, at the Meteorological Research Institute (MRI, Tsukuba, Japan) during the 1990s were fairly low (average: 2.1). This value is not in agreement with the ratios in Japanese surface soils (range of averages: 4–7), which had been considered as the primary source of the deposited dust. This suggests that the current atmospheric dust deposition in Japan is a mixture of local and remote components. The remote component could be an aeolian dust that has been transported long distances from arid areas. The major component is most likely to be Asian dust. It was further hypothesized that other remote source may exist beyond the Asian domain, based on accumulated observations and model results. To obtain more information about the dust transport, Sahara dust deposited in Monaco in 2002 and a suspended dust collected in the Taklamakan area in 2001 were analyzed for ⁹⁰Sr and ¹³⁷Cs. The Taklamakan dust exhibited a ¹³⁷Cs/⁹⁰Sr ratio of about 4, which is within the range of atmospheric deposition observed at the MRI, while the Sahara dust exhibited a higher ¹³⁷Cs/⁹⁰Sr ratio (about 13). Although the present Sahara datum was negative for our hypothesis of ‘hyper-range transport’, the seasonal change of the ¹³⁷Cs/⁹⁰Sr ratio in the atmospheric deposition observed at the MRI requires an aeolian dust source having a low ¹³⁷Cs/⁹⁰Sr ratio, other than Asian dust.     

High Immobilization of NH4+ in Danish Heath Soil Related to Succession,Soil and Nutrients: Implications for Critical Loads of N

During recent decades heathlands havechanged into grasslands in regions with high atmosphericnitrogen deposition. In regions with intermediatedeposition level (e.g., Denmark) changes have been lesspronounced which may be due to delay or decrease inresponse of the ecosystem. The mor layer (O horizon) mayplay an important role for this delay due to high sinkstrength for N. In this study, the capacity for netNH₄ ⁺ immobilization and mineralization wasstudied during short- and long-term incubations (2–36 days)of mor samples from Danish dry inland heaths. High short-term capacity for net NH₄ ⁺ immobilization wasfound to be a general characteristic of Danish heath morlayers both under heather (Calluna vulgaris) andcrowberry (Empetrum nigrum ssp nigrum), the latterdominating late stages in heathland succession. The netNH₄ ⁺ immobilization was higher under youngcompared to old or dead vegetation, and higher on lessnutrient poor soils than on extremely nutrient poor soils.The addition of N, P and C stimulated CO₂ productionand net NH₄ ⁺ immobilization, but not net Nmineralization. The immobilization of ¹⁵NH₄ ⁺caused release of dissolved organic N, increased N anddecreased C/N ratio in the microbial biomass, and indicatedgrowth of microorganisms with other metabolic abilitiesthan the indigenous population. No evidence was obtained ofstabilization of immobilized ¹⁵NH₄ ⁺ intosoil organic matter during the experiment. On background ofthe results and current knowledge it was concluded that therecognition of the high capacity for net NH₄ ⁺immobilization in mor layers does not allow for a raiseof critical loads for N for northern dry inland heaths.