Critical Loads of Acidity for Forest Ecosystems of North Asia

Critical loads of acidity were calculated using the PROFILE model to assess the forest ecosystem sensitivity to acid deposition in the Asian part of Russia — Siberia. The main input parameters and the output were mapped. At present atmospheric inputs of acid forming pollutants to the study territory are mainly related to transregional and transboundary pollution from Europe. It was shown that the most sensitive to acid loading are ecosystems of the Tundra zone and of the East Sayan mountains' coniferous forests with dystric cambisols and gleysoils, critical loads of actual acidity (CL(Ac)) = 0–0.3 keq/ha/yr. The most tolerant ecosystems are ecosystems of deciduous forests with podsoluvisols, luvisols and humic luvisols of South Taiga zone in West Siberia, CL(Ac) = 3.5–7.0 keq/ha/yr. Generally the values of critical loads are increasing from the North to the South and from the East to the West following the bioproductivity, annual soil temperature and alkalinity of deposition increases.     

Quantifying Uncertainty in Critical Loads: (B) Acidity Mass Balance Critical Loads on a Sensitive Site

This paper reports an uncertainty analysis of critical loads for acid deposition for a site in southern England, using the Steady State Mass Balance Model. The uncertainty bounds, distribution type and correlation structure for each of the 18 input parameters was considered explicitly, and overall uncertainty estimated by Monte Carlo methods. Estimates of deposition uncertainty were made from measured data and an atmospheric dispersion model, and hence the uncertainty in exceedance could also be calculated. The uncertainties of the calculated critical loads were generally much lower than those of the input parameters due to a “compensation of errors” mechanism – coefficients of variation ranged from 13% for CL_maxN to 37% for CL(A). With 1990 deposition, the probability that the critical load was exceeded was > 0.99; to reduce this probability to 0.50, a 63% reduction in deposition is required; to 0.05, an 82% reduction. With 1997 deposition, which was lower than that in 1990, exceedance probabilities declined and uncertainties in exceedance narrowed as deposition uncertainty had less effect. The parameters contributing most to the uncertainty in critical loads were weathering rates, base cation uptake rates, and choice of critical chemical value, indicating possible research priorities. However, the different critical load parameters were to some extent sensitive to different input parameters. The application of such probabilistic results to environmental regulation is discussed.     

Calculation and Mapping of Critical Loads for S, N and Acidity in China

Critical loads of nutrient and acidifying nitrogen, as well as of sulphur and acidity, were derived for various ecosystems in China using the steady state mass balance (SSMB) equations. The weathering rates of major soils necessary for applying SSMB were calculated through the PROFILE model on the basis of mineralogical data from experimental analysis. The growth uptakes of nitrogen and base cations were also derived by multiplying the annual increases in biomass with the element contents of the vegetation. Using a geographical information system (GIS), 1°(latitude)×1°(longitude) critical load maps of China with different percentiles were compiled. Results indicate that low critical loads of S (< 0.5 keq·ha^?1·a^?1) occurred predominately in southwest and northeast China, and the critical loads of southeast China were intermediate and in the range of 0.5～1.0 keq·ha^?1·a^?1. In addition, the critical loads of N were very low for desert ecosystems in northwest China and high for agricultural ecosystems in east China. Among the ecosystems with intermediate critical load of N, coniferous forests may be more sensitive to N deposition than broad-leaf forests and temperate steppes.     

Crown Condition and Needle Chemistry of Norway Spruce in Relation to Critical Loads of Acidity in South-East Norway

This study shows that it is questionable if critical load modelling can contribute in the search for harmful effects of acid deposition on forest health at present. Critical loads forS and N deposition were calculated using the MAGIC and PROFILE models for more than 100 monitoring plots in Norway spruce forestin south-east Norway. The two models gave different results, likely due to differences in the models, including differences in the time spans applied. The PROFILE model gave considerably more plots with exceedance than the MAGIC model.At plots where the CL was exceeded, calcium/aluminium (Ca/Al) ratios in the soil solutions were low. However, very few of theseplots had possible harmful values of the Ca/Al-ratio. More than 50 yr seems in most cases to be needed to bring Ca/Al ratios below 1.0. Present deposition was better correlated with measured forest condition variables such as crown condition and needle chemistry,than with modelled exceedance according to any of the two methods. The deposition of S and N was weakly, negatively correlated to foliar concentrations of P and Ca, and positivelyto foliar N concentrations and crown density.     

Determination and Mapping Critical Loads of Acidity and Exceedances for Upland Forest Soils in Eastern Canada

Critical loads of acidity were estimated for upland forests in Eastern Canada using the steady-state Simple Mass Balance (SMB) Model. A consistent methodology was applied to the entire region, although critical loads were estimated separately for the Atlantic provinces (New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland), Quebec and Ontario using different data sources. In this project, critical load estimates and steady-state exceedance values did not include the effect of forest fire and forest harvesting, which could have a considerable impact on critical loads in Eastern Canada. The observed soil pH – base saturation relationship for forest soils indicated that the constants used into the calculation of alkalinity leaching should be set to 10 (M/M) for the molar Bc/Al ratio in soil leachate and 10⁹ (mol L^?1)² for the gibbsite dissolution constant. The area-weighted median critical load for each province varied between 519 (Quebec) and 2063 eq ha^?1 y^?1 (Prince Edward Island), with a median critical load value for Eastern Canada of 559 eq ha^?1 y^?1. It is estimated that approximately 52% of the mapped area is exceeded in terms of acidity according to the 1994–1998 average total (wet + dry) atmospheric deposition. Greatest exceedances occurred in Ontario and Quebec and in the south of Nova Scotia, due to low critical loads and high loads of acid deposition.     

Acidification and Prognosis for Future Recovery of Acid-Sensitive Streams in the Southern Blue Ridge Province

This study applied the Model of Acidification of Groundwater in Catchments (MAGIC) to estimate the sensitivity of 66 watersheds in the Southern Blue Ridge Province of the Southern Appalachian Mountains, United States, to changes in atmospheric sulfur (S) deposition. MAGIC predicted that stream acid neutralizing capacity (ANC) values were above 20???eq/L in all modeled watersheds in 1860. Hindcast simulations suggested that the median historical acidification of the modeled streams was a loss of about 25???eq/L of ANC between 1860 and 2005. Although the model projected substantial changes in soil and stream chemistry since pre-industrial times, simulated future changes in response to emission controls were small. Results suggested that modeled watersheds would not change to a large degree with respect to stream ANC or soil % base saturation over the next century in response to a rather large decrease in atmospheric S deposition. Nevertheless, the magnitude of the relatively small simulated future changes in stream and soil chemistry depended on the extent to which S emissions are reduced. This projection of minimal recovery in response to large future S emissions reductions is important for designing appropriate management strategies for acid-impacted water and soil resources. Exploratory analyses were conducted to put some of the major modeling uncertainties into perspective.     

Cellular Distribution of Metals in a Liverwort and a Moss Transplanted to Two Streams of Differing Acidity

To investigate the consequences of acidification and metal accumulation on the biology of aquatic bryophytes, the acid-tolerant liverwort Scapania undulata (L.) Dum. and the acid-sensitive moss Rhynchostegium riparioides (Hedw.) Cardot were transplanted from one stream to two other streams of differing acidity (pH 5.20 and 6.38). The bryophytes were collected in a circumneutral (pH 6.57) stream in the Vosges Mountains. Metal accumulation was semi-quantitatively measured in shoots by energy dispersive TEM X-ray spectroscopy (EDXS). After 1 month, the two species remained green without alteration signs. Although no marked ultrastructural damage was observed in either species, some cells seemed to be necrotic, with flattened chloroplasts, in R. riparioides. Lipid droplet accumulation was observed in some leaf cells of S.undulata when transplanted to the most acidic stream. Metal was mostly localised in the cell wall, and was only sometimes detected in small vacuoles. Under acidic conditions, R. riparioides showed the highest relative amount of Al and the lowest amount of Fe, whereas the acid-tolerant bryophyte species S. undulata contained more Fe and less Al. The capability to limit the uptake of metals into the cytoplasm varies according to the bryophyte species. This could be an explanation of the tolerance of S. undulata to acidification.     

Deposition and Critical Loads of Nitrogen in Switzerland

Many ecosystems in Switzerland suffer from eutrophication due to increased atmospheric nitrogen (N) input. In order to get an overview of the problem, critical loads for nutrient N were mapped with a resolution of 1×1 km applying two methods recommended by the UN/ECE: the steady state mass balance method for productive forests, and the empirical method for semi-natural vegetation, such as natural forests, (sub-)alpine or species-rich grassland and raised bogs. The national forest inventory and a detailed atlas of vegetation types were used to identify the areas sensitive to N input. The total N input was calculated as the sum of NO₃ ^?, NH₄ ⁺, NH₃, NO₂ and HNO₃ wet and dry deposition. Wet deposition was determined on the basis of a precipitation map and concentration measurements. Dry deposition was calculated with inferential methods including land-use specific deposition velocities. The concentration fields for NH₃ and NO₂ were obtained from emission inventories combined with dispersion models. Reduced N compounds account for 63% of total deposition in Switzerland. As indicated by exceeded critical loads, the highest risk for harmful effects of N deposition (decrease of ecosystem stability, species shift and losses) is expected on forests and raised bogs in the lowlands, where local emissions are intense. At high altitudes and in dry inner-alpine valleys, deposition rates are significantly lower.     

Estimation of Point and Diffuse Contaminant Loads to Streams by Non-Parametric Regression Analysis of Monitoring Data

In this study, point and diffuse contaminant loads to a stream are estimated using stream monitoring data. Regression analysis is conducted to separate point source loads and background contaminant loads using water quality and flow time series. Non-parametric methods are utilized for regression and auxiliary statistical tests to eliminate the effects of outliers in the data and to avoid restrictions posed by assumptions of normality. Point source loads and background concentrations are estimated directly by regression of data from a station. A second station is needed to estimate diffuse load contributions. The method is exemplified using data from a polluted stream in Turkey, the Porsuk Stream. Point and diffuse loads are estimated for six water quality parameters, chloride, dissolved solids, ammonia, nitrate, biochemical oxygen demand and total phosphorus. It is found that for many water quality parameters, contaminant loads to a stream can be estimated with reasonable accuracy.     

Effects of Afforestation on Acidity and Invertebrates in Danish Streams and Implications for Freshwater Communities in Denmark

The relationship between acidity and benthic invertebrate communities was investigated in two small streams in coniferous forests in central Jutland, Denmark, during 1992 and 1993. Stream pH was acid (mean pH 4.8 and 5.4) and alkalinity fluctuated greatly with mean values around zero. During rain events, water from springfed reaches upstream were mixed downstream with brown humic acid water with high aluminium content, and pH declined from circumneutral near the springs down to pH below 4 over a very short distance (0.5–1.5 km). The benthic invertebrate communities in the most acidic downstream reaches of both streams were dominated by filipalpian stoneflies, mainly Leuctra nigra (Olv.). Community composition remained very similar throughout the sampling period despite variations in pH. In the upper (neutral) reaches invertebrates intolerant of low pH such as Gammarus pulex L. were found. The concentrations of chloride and sulphate in the streams were more than double the concentrations in a nearby moorland stream indicating a strong impact of acidifying atmospheric deposition on the two forest streams. Results of this study indicate that afforestation with conifers on sandy Danish soils with low buffering capacity (about 25% of the total Danish land area) may lead to an increased acidification of surface waters and thereby also to an impoverished aquatic fauna.     

Carbon dynamics in Appalachian peatlands of West Virginia and Western Maryland

Abundant production of organic matter that decomposes slowly under anaerobic conditions can result in substantial accumulation of soil organic matter in wetlands. Tedious means for estimating production and decomposition of plant material, especially roots, hampers our understanding of organic matter dynamics in such systems. In this paper, I describe a study that amended typical estimates for both production and decomposition of organic matter by measuring net flux of carbon dioxide (CO₂) over the peat surface within a conifer swamp, a sedge-dominated marsh, and a bog in the Appalachian Mountain region of West Virginia and western Maryland, USA. The sites are relatively productive, with net primary production (NPP) of 30 to 82.5 mol C m^?2 yr^?1, but peat deposits are shallow with an average depth of about 1 m. In summer, all three sites showed net CO₂ flux from the atmosphere to the peat during the daytime (?20.0 to ?30.5 mmol m^?2 d^?1), supported by net photosynthesis, which was less than net CO₂ flux from the peat into the atmosphere at nighttime (39.2 to 84.5 mmol m^?2 d^?1), supported by ecosystem respiration. The imbalance between these estimates suggests a net loss of carbon (C) from these ecosystems. The positive net CO₂ flux seems to be so high because organic matter decomposition occurs throughout the peat deposit — and as a result concentrations of dissolved inorganic carbon (DIC) in peat pore waters reached 4,000 Μmol L^?1 by late November, and concentrations of dissolved organic carbon (DOC) in peat pore waters reached 12,000 Μmol L^?1. Comparing different approaches revealed several features of organic matter dynamics: (i) peat accretion in the top 30 cm of the peat deposit results in a C accumulation rate of about 15 mmol m^?2 d^?1; however, (ii) the entire peat deposit has a negative C balance losing about 20 mmol m^?2 d^?1.     

Critical Loads of Acid Deposition on Soil in China

Critical loads of acid deposition havebeen mapped for Chinese soils using a modifiedsemi-quantitative method, which is based on theminerals controlling weathering and soil development,and corrected by introducing an Arrhenius relationshipto describe the effect of temperature and a weightedaveraging approach to evaluate the effect of soiltexture, land use and precipitation. As a consequenceof these modifications, the method has been quantifiedand can be more widely used. Results from this studyshow that the lowest critical loads of acid depositionin China, i.e., those areas most sensitive to aciddeposition, occur in the Podzolic soils in theNortheast, followed by Latosol, Dark brown forest soiland Black soil areas. The Ferralsol areas in SouthChina are intermediate, tolerating about 0.8–1.6 g m^-2 yr^-1 sulfur deposition. The highestcritical loads of acid deposition are mainly locatedin the Alpine soil areas on the Plateau of Tibet andareas of Xerosol and Podocal soil in Northwest China.The reason for lower critical loads in the Northeastrelative to South China can be attributed to thedifference of temperature, soil moisture and soiltexture. Comparison of critical loads with the sulfurdeposition in 1995 identifies almost one fourth of theland area in southeast China to be subject to risk of acidification.     

土壤污染物临界负荷研究进展

随着城市化进程与工农业的快速发展,土壤污染形势也越来越严峻。土壤污染物临界负荷的研究,可获取土壤可持续发展质量指标,是一条实现土壤可持续管理的有效途径。我国土壤污染临界负荷研究不足,为了推动其发展,本文讨论了其研究进展、指导原则、应用、存在问题与发展趋势。动态的和基于风险的土壤污染物临界负荷估算已是国际发展趋势。当前,缺乏完善的动态临界负荷估算模型,估算过程具有较大不确定性。为了准确地估算土壤污染物的临界负荷,在未来研究中需要加强对临界浓度制定和动态模型构建的研究,主要包括土壤中污染物的迁移传输规律、污染物的剂量-效应关系等。     

Multi-Effect Critical Loads Used in Multi-Pollutant Reduction Agreements in Europe

The scientific support of negotiations on emission reductions under the framework of the Convention on Long-range Transboundary Air Pollution of the UN Economic Commission for Europe has been based during the last decade on the integrated assessment of sources, including abatement costs, and risks to receptors (e.g. forests, lakes) quantified by critical loads. The shift from a single-pollutant (sulfur) protocol in 1994 to a multi-pollutant protocol in 1999 necessitated an extension of the methods by which critical loads were computed and mapped. Instead of a single critical load for acidification, methods were now developed to assess the risk of acidifying effects of both sulfur and nitrogen deposition as well as the eutrophying effects of nitrogen on sensitive elements of the environment. Collaboration with a scientific network of 24 national institutions ensured a successful implementation of the proposed methodology across countries. This paper summarizes the methodology, describes the latest input data and presents critical load maps on the basis of which about 98% and 78% of European ecosystems would be protected against acidification and eutrophication, respectively, by the year 2010 according to the multi-pollutant multi-effect protocol.     

Effects of liming on water quality of two streams in West Virginia

In an effort to improve the fisheries potential of many West Virginia mountain streams by increasing the alkalinity and pH, the West Virginia Department of Natural Resources (DNR) is conducting research into the feasibility of a point source limestone application technique. This research was to provide data that would assist in the design of future projects and the selection of appropriate methodology. Thirteen metric t and 33.3 t of 0.64 cm crusher run ground limestone aggregate were applied as a single deposition to Crouch and Yokum Runs, respectively. Limestone was applied to Crouch Run a year prior to treatment of Yokum Run. The point source treatment produced discharge dependent changes in the downstream water chemistry. The pH increased from an average of 4.73 above the application point to 5.70 below. At high stream discharges, the pH dropped, but never to the pretreatment background level. Increases in Ca concentrations and ANC were also observed downstream of the limestone application site. Sediment analysis was performed to determine the calcite concentration within the stream bed by both an instrumental technique (x-ray fluorescence (XRF)) and an HC1 leach technique to indicate the extent of downstream movement and distribution of limestone. The analysis showed both a limited downstream transport and a variable spread of limestone across the stream channel. The XRF and wet laboratory methods of quantifying the calcite content of the sediments were compared. Although statistical analysis indicated a difference in precision between the x-ray fluorescence and HC1 leach methods, the acid leach method can be considered an economical alternative to x-ray fluorescence. Recommendations are made on methods to increase the effectiveness of the point source treatment and the design of future research.     

Critical Loads of SO2 Dry Deposition and Their Exceedance in South China

The critical loads of SO₂ dry deposition in South China,which is transferred from critical level, as well the excess ofcritical loads are computed and mapped. The areas with thelowest critical load and the highest excess are, respectively,identified. The research is complementary to the previousresearches on critical loads for soils, and expected to beintegrated with them to make efficient sulfur emission abatement strategy.     

Critical Loads of Trace Metals in Soils: a Method of Calculation

Critical load of trace metals in soils is a function of biological uptake, leaching by percolating water, input of the trace metals due to bedrock weathering, and the norms set to protect soils from metal pollution. The exceedance of the critical load is a difference between the calculated load and the measured input of the metals by atmospheric deposition and by application of agrochemicals. A critical time is the time when the concentration of a trace metal in soil, which is the result of all inputs and outputs of the metal in the soil, reaches the value of the norm. Data on biologically important trace metals in a small agricultural catchment in the Czech Republic indicate that the soil concentrations of As, Cd and Pb will reach the norms set for the soils after 4.5, 61, and 980 years, respectively. The present mass balances of Cu and Zn in the soils indicate that their steady-state concentrations will be below the norms so that the atmospheric and agricultural inputs will never overshoot the calculated critical load.     

Quantifying Uncertainty in Critical Loads: (A) Literature Review

Critical loads are the basis for policies controlling emissions of acidic substances in Europe. The implementation of these policies involves large expenditures, and it is reasonable for policymakers to ask what degree of certainty can be attached to the underlying critical load and exceedance estimates. This paper is a literature review of studies which attempt to estimate the uncertainty attached to critical loads. Critical load models and uncertainty analysis are briefly outlined. Most studies have used Monte Carlo analysis of some form to investigate the propagation of uncertainties in the definition of the input parameters through to uncertainties in critical loads. Though the input parameters are often poorly known, the critical load uncertainties are typically surprisingly small because of a “compensation of errors” mechanism. These results depend on the quality of the uncertainty estimates of the input parameters, and a “pedigree” classification for these is proposed. Sensitivity analysis shows that some input parameters are more important in influencing critical load uncertainty than others, but there have not been enough studies to form a general picture. Methods used for dealing with spatial variation are briefly discussed. Application of alternative models to the same site or modifications of existing models can lead to widely differing critical loads, indicating that research into the underlying science needs to continue.     

Calculation and Mapping of Sulfur Critical Loads for Terrestrial Ecosystems of Thailand

The essential parameters needed for the calculation of critical load of sulfur, CL(S), are base cation weathering rate, base cation uptake, acid neutralizing capacity leaching and base cation deposition. These parameters are estimated and mapped for the most area of terrestrial ecosystems of Thailand using data of national data soil survey. The values of CL(S) range from <200 to 2,225 eq.ha^?1yr^?1 and about 70% of terrestrial ecosystems are characterized by low values (<200 eq.ha^?yr^?1). These CL values reflect the sensitivity of Thai ecosystems to sulfur deposition.     

Assessment of the bacteriological quality of rural groundwater supplies in Northern West Virginia

A bacteriological survey was performed on 155 untreated, individual, rural groundwater supplies which included drilled wells, dug wells, and springs. Of these, 105 exceeded the Environmental Protection Agency (EPA) maximum contaminant level of one total coliform per 100 mL. Repeat sampling for 87 of the unacceptable 105 supplies indicated that 76 again exceeded the EPA standard limit. Masked coliforms were detected through confirmation tests in 11 water supplies that exhibited excessive noncoliform colonies (> 50 CFUs/membrane filter). Also, 48% of the supplies contained fecal coliforms and 62% contained fecal streptococci. Bacterial densities were related to the type of water supply with drilled wells containing fewer total coliforms, fecal coliforms, fecal streptococci, and heterotrophic plate count bacteria than dug wells or springs. Water supplies that were shallower, older, and lacking adequate casing characteristically were more heavily contaminated with sanitary indicator bacteria than supplies that were deeper, of more recent construction, and with sufficient casing.