Temporal Trends in Mercury Accumulation in Lake Sediments in Sweden

Lake sediment cores were analyzedto study the history of mercury (Hg) pollution andparticularly to determine whether recent sedimentconcentrations have declined in response todeclining atmospheric deposition of Hg. Sedimentcores from 6 forest lakes distributed fromsouthern to northern Sweden and 3 northernmountain lakes were analyzed for Hg using CVAAS. A400 cm sediment profile from Måkevatten insouthwest Sweden indicates that the onset of Hgpollution occurred in the 18th century. Anindisputable increase in Hg concentrationsoccurred concurrent with the appearance ofspheroidal carbonaceous flyash particles (SCP)derived from fossil-fuel combustion, in themid-19th century. There is a strong correlationbetween Hg and SCP concentrations in the sedimentcores (r=0.67 to 0.91), which suggests a strongrelationship between historical Hg pollution andfossil fuel burning. In contrast to sediment corestaken in 1979, maximum Hg concentrations are nowobserved below the sediment surface and declinetowards the sediment surface. This study confirmsthat reductions in atmospheric deposition of Hgover Sweden have resulted in a decreased transferof total Hg to aquatic environments as reflectedby lake sediments, and that lake sediment profilesof Hg concentrations reflect relative trends inthe atmospheric deposition of Hg rather thanpost-depositional diagenetic processes.     

Long-term Trends in Surface Water Quality of Five Lakes in Japan

Since 1983, the Ministry of the Environment of Japan has conducted nation-wide acid deposition surveys. To investigate the effects of acid deposition on surface water, we used the nonparametric Mann–Kendall test to find temporal trends in pH, alkalinity, and electrical conductivity (EC) in more than 10 years of data collected from five lakes and their catchments (Lake Kuttara: northernmost; Lake Kamakita: near Tokyo; Lake Ijira: central; Lake Banryu: western; and Lake Unagiike: southernmost). The pH of Lake Ijira water has declined slightly since the mid-1990s, corresponding with the downward trends seen in the pH and alkalinity of the river water flowing into the lake. There were significant upward trends in the EC of both the lake and stream water; the same trends were also found for concentrations. These trends show evidence of acidification due to atmospheric deposition, and this is the first such finding in Japan based on significant long-term trends. Lake Ijira is located about 40 km north of the Chukyo industrial area near Nagoya. The annual depositions of H⁺, nss-, and in Lake Ijira were among the highest of all deposition monitoring sites, suggesting that this is the main cause of the significant acidification observed in Lake Ijira. No significant trends suggesting acidification were observed in any of the other lake catchments in spite of the significant upward trends in EC. Upward trends in pH and alkalinity at Lake Banryu and upward trends in alkalinity at Lake Kamakita were detected, but no change in pH or alkalinity at Lake Kuttara and Lake Unagiike was observed.     

Temporal Trends of Non-sea Salt Sulfate and Nitrate in Wet Deposition in Japan

Temporal trends of non-sea salt (nss-) sulfate and nitrate were analyzed from nationwide precipitation chemistry measurements provided by the Ministry of the Environment (MOE) for the 1988–2002 fiscal years (April–March). The concentrations and deposition of nss-sulfate were found to be decreasing, and those of nitrate were stable or slightly increasing at most sites. These deposition trends were discussed from the viewpoint of emissions of SO₂ and NO_X during the period of interest. Because monitoring techniques have changed in the number of active sites, samplers, and analytical methods during the operation period, the median of all annual depositions measured in Japan in a specific year was selected as the annual representative. The contribution of specific emission sources was also calculated for 1990 on the basis of the nss-sulfate and nitrate deposition in Japan obtained with a model simulation in which the model did not include volcanic emissions from Mt. Oyama, Miyakejima Island, which began to erupt suddenly and violently in 2000. For nss-sulfate, the calculated deposition agrees well with the intensity and trends of the median up to 1999. After 2000, a higher deposition than calculated in the preceding years was evident, which is attributable to the volcanic SO₂ from Mt. Oyama. For nitrate, both the calculated and observed depositions were slightly increasing; however, the calculation was found to exceed the observation.     

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.     

Recent Recovery of Lake Water Quality in Southern Québec Following Reductions in Sulfur Emissions

Since 1985, monitoring activities have been conducted in a networkof 43 lakes comprising the Québec portion of the Long-Range Transport of Airborne Pollutants (LRTAP) program. The results to date indicate that Québec lakes generally are responding positively to the generalized decline in precipitation sulfate (SO₄ ^2-), with 40 of the 43 lakes now showing steep declines in SO₄ ^2- concentrations. The drop in SO₄ ^2- was associated with a significant decrease in Ca²⁺ concentrations in 77% of the lakes (67% for Mg²⁺ concentrations). Overall, the acid-neutralizing capacity was increasing in 19 lakes and decreasing only in three, while 21 lakes showed no temporal trends. Compared with previous trend studies of the LRTAP-Québec network for the period of 1985–1993, the longer period (1985–1999) shows a clear improvement, with the proportion of lakes that were acidifying changing from 24 to 7% and with the proportion of lakes that were recovering changing from 16 to 35%. These observations suggest that the recent drop in SO₄ ^2- deposition in the northeastern U.S. and eastern Canada was significant enough to allow chemical recovery for a significant proportion of Québec lakes.     

Application of Static Critical Load Models for Acidity to High Mountain Lakes in Europe

Critical load models for acidityprovide a measure of the sensitivity of surfacewaters to acid deposition, and can be used todetermine critical load exceedance and potentiallong-term harmful effects. Three static models,the Steady-State Water Chemistry model, diatommodel and First-order Acidity Balance model, arehere applied to 11 high mountain lakes in Norway,Scotland, the Alps, the Pyrenees and the Tatras.Between five and seven of the lakes show criticalload exceedance, depending on the model used.Nitrogen as well as sulphur deposition isimportant in causing exceedance. Since soil andvegetation cover are generally sparse, geologyand lake retention time appear to be key factorsin the determination of critical load. Retentionof nitrogen is observed, but it is unclearwhether this occurs within the lake or theterrestrial part of the catchment.     

Chemistry of Selected High-Elevation Lakes in Seven National Parks in the Western United States

A chemical survey of 69 high-altitude lakes in seven national parks in the western United States was conducted during the fallof 1999; the lakes were previously sampled during the fall of 1985, as part of the Western Lake Survey. Lakes in parks in the Sierra/southern Cascades (Lassen Volcanic, Yosemite, Sequoia/Kings Canyon National Parks) and in the southern RockyMountains (Rocky Mountain National Park) were very dilute; medianspecific conductance ranged from 4.4 to 12.2 S cm^-1 andmedian alkalinity concentrations ranged from 32.2 to 72.9 eqL^-1. Specific conductances and alkalinity concentrations were substantially higher in lakes in the central and northernRocky Mountains parks (Grand Teton, Yellowstone, and GlacierNational Parks), probably due to the prevalence of more reactivebedrock types. Regional patterns in lake concentrations of NO₃ and SO₄ were similar to regional patterns in NO₃ and SO₄ concentrations in precipitation, suggestingthat the lakes are showing a response to atmospheric deposition.Concentrations of NO₃ were particularly high in Rocky Mountain National Park, where some ecosystems appear to be undergoing nitrogen saturation.     

Speciation and Seasonal Variations of Dissolved Inorganic Arsenic in Jiaozhou Bay,North China

The distributions and biogeochemical cycles of arsenic in the aquatic environment have captured the interest of geochemists due to arsenic’s multiple chemical forms, the toxicity of certain arsenic species and large anthropogenic input. Seasonal variations in the dissolved inorganic arsenic concentration and speciation in Jiaozhou Bay, which is located on the west coast of the Yellow Sea in northern China, are presented here. Three cruises were carried out in Jiaozhou Bay under varying tidal regimes, one at neap tide and one at spring tide in August and one at spring tide in October of 2001. In addition to the transect surveys, the main sources of dissolved inorganic arsenate and arsenite in Jiaozhou Bay, including riverine input from five major tributary rivers, atmospheric dry and wet depositions, and groundwater and wastewater input, were collected in different seasons to estimate arsenic transport through different sources. The mean concentrations of total dissolved inorganic arsenic (TDIAs, As (V+III)) in Jiaozhou Bay were statistically comparable between summer and autumn, with higher concentrations at the northwest and northeast parts of the bay, reflecting human activities. The As (III)/TDIAs ratio ranged between 0.045 and 0.68, with an average of 0.16, implying that arsenate was the dominating species in Jiaozhou Bay. A preliminary box model was established to estimate the water-mass balance and arsenic budgets for Jiaozhou Bay, which demonstrated that river inputs and atmospheric depositions were the main sources of arsenic into Jiaozhou Bay. The concentrations of dissolved inorganic arsenic in Jiaozhou Bay have decreased in the last two decades. Compared with other areas in the world, the concentration of arsenic in Jiaozhou Bay remains at the natural level and this region can be characterized as a less disturbed area.     

Spatial and Temporal Comparison of Polycyclic Aromatic Hydrocarbons and Spheroidal Carbonaceous Particles in Remote European Lakes

Spheroidal carbonaceous particles (SCP) and polycyclicaromatic hydrocarbons (PAH) have been measured in the dated sediment cores of 10 remote lakes distributed across Europe. The geographic trends were evaluated by examination of the superficial sediment fluxes and total sediment inventories. The highest levels of both markers were observed in the Eastern European lakes whereas the minimal values corresponded to the lake located in the Arctic. However, this SCP-PAH correlation was not observed after exclusion of the end member lakes from the series. The temporal trends of both pollutant markers are consistent with the history of pyrolytic emissions over Europe. However, the downcore SCP distributions are shorter than the PAH profiles in nearly all lakes. The differences are probably related to the different size particle fractions involved in the measurement of each marker, >5 and >1 m for SCP and PAH, respectively. Thus, the two proxies probably reflect pollution inputs from closer (SCP) and more distant sites (PAH).     

A Comparison of Loch Chemistry from 1955 and 1999 in the Cairngorms,N.E. Scotland

The Cairngorms in north-east Scotland is remote from pollutant sources although it currently receives ca. 10 kg ha¹ yr¹ S and ca. 11 kg ha¹ yr¹ N deposition from the atmosphere.In 1955, 15 lochs (lakes) at a range of altitudes were sampled and analysed for major ion concentrations. A new survey of these and an additional 23 lochs and their catchment soils was conducted in 1999 to determine the impact of acid deposition, and the changes in loch chemistry since the 1955 survey. The bedrock geology of this region has a strong influence on the loch chemistry. Surface waters were generally more acidic in high altitude areas due to predominantly poorly buffered, thin alpine soils developed on granitic parent material (mean acid neutralising capacity (ANC) for 23 lochs = 30 eq L¹). At lower altitudes where the geology is dominated by Dalradian metamorphic rocks surface waters are comparatively base rich and have higher ANC (mean ANC for 15 lochs = 157 eq L¹). Surface water nitrate concentrations show a negative relationship with soil C:N status, in that higher nitrate only occurs at low soil C:N ratios. A comparison of data for 1955 and 1999 shows that sulphate concentrations are significantly lower (67.8 and 47.5 eq L¹, respectively), and pH has improved (pH 5.6 and 5.9) in response to decreased S deposition since the mid 1970s. However, mean nitrate concentrations were found to increase from 2.48 >eq L¹ in 1955 to 5.65 eq L¹ in 1999. Differences in the sampling and laboratory methods from 1955 and 1999 are acknowledged in the interpretation of data.     

大气环境立法新动向

大气环境法是随大气环境的变化而发展的。通过分析美、日、中等国家近年来的大气环境立法状况，概括出目前大气环境立法的五大趋势。这些趋势反映了人们对大气污染防治问题认识的深入和对大气环境污染防治法律观念的转变。     

Biological Pollutants: Alien Fishes in Mountain Lakes

Many lakes in the national parks of the Canadian Rockies were stocked with alien fish species in the early to mid 20th century. Changes to Parks Canada's mandate require the original communities of these lakes to be restored. We document the changes to invertebrate communities caused by the stocking of alien fishes into three fishless alpine lakes, and describe the results of two restoration experiments, one the reintroduction of Hesperodiaptomus arcticus, a planktonic predator that had been eliminated from Snowflake Lake by stocked fish, and the other the removal of brook trout (Salvelinus fontinalis) from Bighorn Lake. In both cases, there were great changes to the zooplankton communities, which required several years to complete, probably because of the cold water and unproductive nature of the lakes. Many of the invertebrate species extirpated by stocked alien fishes co-exist with native fish species in nearby lakes. Possible reasons are discussed.     

Critical Loads of Acidity for Surface Waters in South-Central Ontario, Canada: Regional Application of the First-Order Acidity Balance (FAB) Model

Major sulphur emission control programs have been implemented in North America, resulting in current emissions being ～30% less than those in 1980. However, the level of acidic deposition remaining is still unlikely to promote widespread recovery of aquatic ecosystems. The First-order Acidity Balance (FAB) model has been applied to south-central Ontario (285 lakes in the Muskoka River Catchment) to evaluate the need for further reductions in emissions. As a result of the past decline in deposition, the proportion of lakes with critical loads exceedance has dropped substantially; however, further reductions in sulphur and nitrogen emissions are required to eliminate critical loads exceedance. Based on bulk deposition of sulphate and nitrogen (41.1 mmol_c m^-2 yr^-1 and 62.5 mmol_c m^-2 yr^-1, respectively) for the period 1995–1999, 166 lakes (58.3%) exceedcritical loads. Even with full implementation of SO₂ abatementprograms in Canada (achieved in 1994) and the United States (legislated for 2010), critical loads will be exceeded in a large proportion (46.6%) of the study lakes.     

Volumetric changes in landfill gas flux in response to variations in atmospheric pressure

This paper develops a quantitative model which attempts to relate volumetric changes in landfill gas emissions to variations in the surface atmospheric pressure. The model considers gas emissions as the sum of two terms, one constant over a period of weeks, and the other able to vary on a scale of hours. Results from computer simulations are given which indicate that the magnitude of the variable factor is proportional to the rate at which surface pressure is changing, rather than the actual value of the surface pressure.     

Atmospheric Budget of Non-Seasalt Chlorine in the Kanto District,Japan

To evaluate the influence of anthropogenic emission of HCl on the air quality in the Kanto district of Japan, the atmospheric budgetof non-seasalt Cl (nssCl) was analyzed. The Kanto district, which consists of the Tokyo metropolis and the six surrounding prefectures, is the most densely populated region in Japan. The emission intensity of HCl is extremely high compared with those in other regions and most western countries. In this study, the annual wet and dry depositions of nssClwere estimated on a 0.25 × 0.25° grid over the Kanto district based on the concentration monitoring resultsand meteorological data. The budget analysis was conducted by comparing the estimated deposition with the emission of HCl. As a result, the annual total (wet + dry) deposition of nssCl was estimated to be 32 kt yr^-1, which closely agreed with HCl emission (36 kt yr^-1) from waste incineration in this area. The result suggested that the anthropogenic emission of HCl had a significant influence on the air quality and the deposition of acidity in this area.     

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.     

Recovery of Acidified Streams in Forests Treated by Total Catchment Liming

Reduced emissions of acidifying pollutants have changed the acidification process, and as a result, forest soils and surface waters are slowly recovering in Sweden. However, model calculations show that some areas may never recover completely unless further measures, such as liming, are undertaken. Liming of surface waters (lakes, rivers and wetlands) has been successfully practised in Sweden since the 1970s, but repeated treatments are necessary. A full recovery of acidified lakes and streams without frequent liming is however not possible until soil acidification is reversed in the most strongly affected areas. In this study, the recovery of acidified streams was examined using ‘the total catchment approach’ i.e. treatment of both recharge and discharge areas. The aim was to compare the quantitative effect of different treatments on run off chemistry and the recovery of brown trout. Catchments in southwest Sweden were treated with a combination of 2 tons of wood ash and 4, 6 or 12 tons of crushed limestone per hectare in 1998/1999. Treatment of both recharge and discharge areas resulted in fast and significant changes in stream water quality, e.g. increased concentrations of calcium, higher pH and ANC and a decreased concentration of inorganic aluminium. The initial changes were dependent on the distribution of the applied lime between discharge and recharge areas rather than the average dose on the total catchment. Treatment of recharge areas only, resulted in smaller but still significant effects on calcium, pH and ANC in stream water. Furthermore, there was an initial leaching of nitrate but it was only minor compared with the elevated leaching that occurs after a clear-cut. As a result of the treatments, brown trout is now successfully reproducing. Olle Westling (deceased).     

Passive landfill gas emission - Influence of atmospheric pressure and implications for the operation of methane-oxidising biofilters

A passively vented landfill site in Northern Germany was monitored for gas emission dynamics through high resolution measurements of landfill gas pressure, flow rate and composition as well as atmospheric pressure and temperature. Landfill gas emission could be directly related to atmospheric pressure changes on all scales as induced by the autooscillation of air, diurnal variations and the passage of pressure highs and lows. Gas flux reversed every 20 h on average, with 50% of emission phases lasting only 10h or less. During gas emission phases, methane loads fed to a connected methane oxidising biofiltration unit varied between near zero and 247 g CH4 h(-1)m(-3) filter material. Emission dynamics not only influenced the amount of methane fed to the biofilter but also the establishment of gas composition profiles within the biofilter, thus being of high relevance for biofilter operation. The duration of the gas emission phase emerged as most significant variable for the distribution of landfill gas components within the biofilter.     

Effects of Climate Events on Elemental Fluxes from Forested Catchments in Ontario, Canada: Modelling Drought-Induced Redox Processes

One of the principal influences on elemental fluxes from forestedcatchments in south-central Ontario is the atmospheric deposition rate of strong acids. While sulphate deposition has decreased by ～40% in the past two decades, nitrate deposition has remained unchanged and is now equivalent to sulphate deposition. Sulphate concentrations in headwater lakes and their inflows have decreased, but much less than expected based on the anticipated direct response of the catchments. Reduction-oxidation (redox) processes occurring in wetlands have been identified as the reasonfor delayed recovery, and climate events as controlling these redoxprocesses. A new version of the biogeochemical model MAGIC (modelof acidification of groundwater in catchments) with a wetland compartment that incorporates redox processes driven by climate events has been generated. The application of MAGIC to a subcatchmentof Plastic Lake in south-central Ontario indicates that the basic structure of the model appears to be consistent with the observeddata. Moreover, the wetland component was essential in reproducingthe observed trends, which include sulphate retention in non-droughtyears and re-oxidation of previously stored (reduced) sulphur in drought years.     

FLUENT在燃煤电厂大气污染控制领域的应用研究进展

介绍了FLUENT软件的基本原理、方法及主要特点,综述了其在燃煤电厂大气污染控制、大气污染扩散、大气污染物生成模拟方面的研究进展和实际应用情况,在此基础上,总结了FLUENT软件在燃煤电厂大气污染领域应用中存在的问题,并提出了今后的研究方向和发展趋势。