Soil Acidification in Loess and Clay Soils in The Netherlands

To assess the impact of acid deposition on forestedloess and clay soils in the Netherlands, changes inbase saturation and soil solution concentrations weresimulated with the dynamic soil acidification modelReSAM for 38 loess soils and 16 clay soils. Theselected locations represent the range in geographicalposition and diversity in parent material occurring inforested loess and clay soils in the Netherlands. Twodeposition scenarios were used for the period1992–2050: a business as usual scenario (BAU) and ascenario in which deposition was reduced according topresent Dutch policy plans (MV-3). A comparison ofsimulated and measured soil solution concentrationsand base saturation in 1992/1993 showed that the modelsimulated concentrations and base saturation in theloess soils quite good. However, the model tended tooverestimate acidification in the top (0–10 cm) of theclay soils. Despite the reasonable agreement betweenmeasured and simulated data some uncertainty in thevalidity of the model predictions remains because timetrends to validate the model were not available. Themodel predicted a small but ongoing acidificationduring the BAU scenario in the loess soils asindicated by a decline in median base saturation andpH in the topsoil in 2050. Present policy plans (MV-3)lead to a slight recovery of the base saturation in2050 and a decline in Al concentrations. In the claysoils a strong decline in base saturation is simulatedin the topsoil, whereas an increase in base saturationis predicted for the subsoil.     

Simulation of the long-term soil response to acid deposition in various buffer ranges

A soil acidification model has been developed to estimate long-term chemical changes in soil and soil water in response to changes in atmospheric deposition. Its major outputs include base saturation, pH and the molar Al/BC ratio, where BC stands for divalent base cations. Apart from net uptake and net immobilization of N, the processes accounted for are restricted to geochemical interactions, including weathering of carbonates, silicates and Al oxides and hydroxides, cation exchange and CO₂ equilibriums. First, the model's behavior in the different buffer ranges between pH 7 and pH 3 is evaluated by analyzing the response of an initially calcareous soil of 50 cm depth to a constant high acid load (5000 mol_c ha^?1 yr^?1) over a period of 500 yr. In calcareous soils weathering is fast and the pH remains high (near 7) until the carbonates are exhausted. Results indicate a time lag of about 100 yr for each percent CaCO₃ before the pH starts to drop. In non-calcareous soils the response in the range between pH 7 and 4 mainly depends on the initial amount of exchangeable base cations. A decrease in base saturation by H/BC exchange and Al/BC exchange following dissolution of Al³⁺ leads to a strong increase in the Al/BC ratio near pH 4. A further decrease in pH to values near 3.0 does occur when the A1 oxides and/or hydroxides are exhausted. The analyses show that this could occur in acid soils within several decades. The buffer mechanisms in the various pH ranges are discussed in relation to Ulrich's concept of buffer ranges. Secondly, the impact of various deposition scenarios on non-calcareous soils is analyzed for a time period of 100 yr. The results indicate that the time lag between reductions in deposition and a decrease in the Al/BC ratio is short. However, substantial reductions up to a final deposition level of 1000 mol_c ha^?1 yr^?1 are needed to get Al/BC ratios below a critical value of 1.0.     

A Global Analysis of Acidification and Eutrophication of Terrestrial Ecosystems

This paper presents an explorative, quantitative analysis of acidification and eutrophication of natural terrestrial ecosystems caused by excess sulfur (S) and nitrogen (N) deposition. The analysis is based on a steady-state approach, involving the comparison of deposition fluxes with critical loads to identify areas where critical loads are exceeded. Deposition fields for sulfur and nitrogen were obtained from the STOCHEM global chemistry-transport model, and they were combined with estimated base cation deposition to derive net acid deposition fluxes. The results indicate that the critical loads for acidification are exceeded in 7–17% of the global area of natural ecosystems. In addition, comparison of nitrogen deposition with critical loads for eutrophication yielded an exceedance in 7–18% of the global natural ecosystems. Apart from serious problems in the heavily industrialized regions of eastern USA, Europe, the former Soviet Union, and large parts of Asia, risks are also found in parts of South America, and West, East and Southern Africa. Both acidification and eutrophication risks could significantly increase in Asia, Africa and South America in the near future, and decrease in North America and Western Europe. Accounting for the effects of N in the analysis of acidification significantly enlarges the potentially affected areas and moves them away from highly industrialized areas compared to studies considering S deposition alone. Major uncertainties in the approach followed are associated with upscaling, the estimates of S, N and base cation emission and deposition fluxes, the critical loads to describe ecosystem vulnerability and the treatment of soil N immobilization and denitrification.     

Critical deposition levels for nitrogen and sulphur on dutch forest ecosystems

Critical loads for N and S on Dutch forest ecosystems have been derived in relation to effects induced by eutrophication and acidification, such as changes in forest vegetation, nutrient imbalances, increased susceptibility to diseases, nitrate leaching, and Al toxicity. The criteria that have been used are N contents in needles, nitrate concentrations in groundwater (drinking water), and NH₄/K ratios, Ca/Al ratios, and Al concentrations in the soil solution. Assuming an equal contribution of N and S, all effects seem to be prevented at a total deposition level below 600 mol_c ha^?1 yr^?1 due to N uptake by stemwood and acid neutralization by base cation weathering. The most serious effects will probably be prevented at total deposition levels between 1500 and 2000 mol_c ha^?1 yr^?1. The current average deposition in the Netherlands is 4900 mol_c ha^?1 yr^?1.     

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.     

Tiefengradienten der Bodenversauerung

Depth gradients of soil acidification In dystric Cambisols, developed from diabas and clay schist/greywacke in the Sösemulde (Harz), the depth gradient of the acid/base status has been assessed by measuring pH and the composition of exchangeable cations. After the soil in the root zone has acidified to within the aluminum buffer range, a marked acidification front is formed below the rooting zone. Strong acids (protons, Mn, Al ions) are buffered completely above the acidification front. Long-term measurements of the input and output of acids and bases in nine forest ecosystems in NW-Germany show that the acid input due to acid deposition into soil horizons in the Al- or Al/Fe- buffer range appears almost quantitatively as output in the seepage water from these horizons. The kind of acid responsible for the soil acidification can be identified by the anion composition of the seepage water. The deep reaching acidification is traced back to acid deposition.     

土壤风化速率研究及其应用

土壤矿物风化是土壤、也是整个生态系统中无机矿质养分的最重要来源,不仅为植物长期提供养分和保持土壤的化学平衡稳定性,并缓冲土壤和地表水的酸化,还影响全球气候变化。风化速率在全球碳循环、酸临界负荷和土壤侵蚀等研究中都是非常重要的参数。土壤化学风化是一个不断进行的自然释放过程,气候是最主要的驱动力,而矿物本身的稳定性也影响了风化速率的快慢。由于人为影响下的大气酸沉降和农业活动已经非常普遍,目前的土壤风化速率也因此而改变。本文从风化速率的研究方法、风化速率的影响因素以及风化速率在全球变化中的应用3个方面介绍了近年来在风化速率方面的研究进展,并探讨了相关研究未来的发展趋势。     

Natural and anthropogenic components of soil acidification

The following 8 theses are theoretically founded and experimentally quantified. 1. Rocks contain only bases and no acid precursors. Therefore, with the exception of sulfide containing rocks, soils cannot acidify as a result of atmospheric rock weathering. 2. A consumption of protons in rocks and soils results in a decrease of their acid neutralizing capacity (ANC) and can result in the buildup of a base neutralizing capacity (BNC). Strong soil acidification leads to the formation of stronger acids from weaker acids in the solid phase; this may be connected with a decrease in the BNC. 3. Weak acids (carbonic acid) lead in geological times to the depletion of bases without a larger accumulation of labile cation acids. Strong acids (HNO₃, organic acids, H₂SO₄) can lead within a few decades to soil acidification, i.e. to leaching of nutrient cations and the accumulation of labile cation acids. 4. The acid input caused by the natural emission of SO₂ and NO_x can be buffered by silicate weathering even in soils low in silicates. 5. The cause of soil impoverishment and soil acidification is a decoupling of the ion cycle in the ecosystem. 6. Acid deposition in forest ecosystems which persists over decades leads to soil acidification. 7. Formation and deposition of strong acids with conservative anions (SO₄, NO₃) shifts soil chemistry into the Al or Al/Fe buffer range up to great soil depth. In such soils eluvial conditions prevail throughout the solum and even in upper part of the C horizon: in connection with the decomposition of clay minerals, Al and eventually Fe are being eluviated. The present soil classification does not include this soil forming process. 8. In the long run, soil acidification by acid deposition results in the retraction of the root system of acid tolerant tree species from the mineral soil, and in water acidification.     

Long-Term Soil Acidification Model (LTSAM) Development and Application for Analyzing Soil Responses to Acidic Deposition

A long-term soil acidification model (LTSAM) which can describe calcareous and non-calcareous soil responses to acidic deposition is developed based on the conservation of alkalinity and Ulrich buffer ranges. The model which considers nine major ions of armospheric deposition, has focused on certain soil processes (weathering of carbonates, silicates, and aluminum (Al) oxides or hydroxides, cation exchange, anion retention, and CO2 solubility). After comparing the model design and simulation results with the SMART, the paper describes several numerical experiments on the sensitivity of calcareous drab soil in Beijing and red earth (nearly dystric cambisol) in Wenzhou of Zhejiang Province in Southern China to acidic deposition scenarios. The modelling results indicate that increase or decrease in atmospheric deposition of base cations and not only changes in deposition of sulfate (S) and H+ must be considered in assessment of critical loads both for red earth and calcareous drab soil.     

Variability in Mapping Acidification Risk Scenarios for Terrestrial Ecosystems in Asian Countries

Acidification has the potential to become a widespread problem in parts of Asia. Just how widespread this risk may be is discussed by comparing sulphur deposition to critical load estimates, taking into account neutralising base cation deposition from soil dust. Two scenarios for the sulphur emission in 2025 are used as inputs to the MATCH atmospheric transfer model to estimate sulphur deposition scenarios. Net acidic deposition using a low and high base cation deposition input is compared to a map of sensitivity of terrestrial ecosystems to acidic deposition. Two ranges of critical loads assigned to this sensitivity map are used. The variability in the maps showing risks of acidification using low and high estimates for critical loads and base cation deposition for two different development pathways is discussed. Certain areas are shown to be at risk in all cases whereas others are very sensitive to the values used to estimate risk.     

Uncertainty in predicting weathering rate and environmental stress factors with the profile model

The PROFILE model is a steady state soil chemistry model which is used to calculate soil weathering rate. The model has also been used to calculate critical loads of acidity and N to forest soils, using the ratio of Ca+Mg+K to total inorganic aluminium in the soil solution as criterion, and to surface waters, using the ANC leached from the soil column as criterion. An uncertainty analysis of the PROFILE model was performed by Monte Carlo analysis, varying input parameter errors individually and simultaneously in ranges of ±10–100%, depending on parameter. The uncretainty in calculation of weathering rate, ANC leaching and ratio of Ca+Mg+K to inorganic Al in the soil solution was studied for three Nordic sites. Furthermore, the effect of uncertainty in estimates of critical load for forest soils was assessed. The analysis shows that the weathering rate can be calculated with high precision, provided that the errors of input parameter are within the range that has been reported in the literature. The model tend to be less sensitive to errors in input parameters for the range of conditions where forest damage is most likely to occur. Critical loads of acid deposition for one site calculated on the basis of the model varies within a largest range of ±40%. A study of one geographical grid included in the Swedish critical loads assessment shows that with the number of calculation points in the grid, the distribution of critical loads will stay stable independently of stochastic errors.     

Effects of Acid Deposition on Forest Soils in Northernmost Russia: Modelled and Field Data

In addition to strong natural stresses forest ecosystems in the Kola Subarctic, Russia, receive high loads of sulphur and heavy metals from the nickel smelter. To estimate soil response to acid deposition we compared the soil field data along a pollution gradient and simulated time effects. Multivariate technique was applied to investigate spatial distribution of soil field data. Time response of soils to acid deposition was evaluated with the SMART model. According to field observations there is no evidence for strong soil acidification effects close to the smelter. Concentrations of exchangeable Ca and base saturation increase, while acidity decrease in lower soil mineral horizons towards the pollution source. However, some features seem to reflect the early stages of the started acidification. Most soil profiles have low pH values. Despite increasing of exchangeable Ca and Mg towards the smelter in lower mineral horizons due to geological inheritance, they do not reveal the same trends in the upper ones. Concentration of exchangeable K in organic horizons decreases towards the smelter, thus confirming the starting acidification. As result, exchangeable base cations are depleted in the considerable part of shallow soil profiles. According to model simulation the present acid load does not effect considerably on forest soils in background areas, however, dramatic shift in soil chemistry near the smelter is expected within several decades. Due to low pool of exchangeable base cations and low weathering rate continued acid deposition can lead to increased soil acidification and nutrient imbalance.     

Modelling Acidification Effects on Coniferous Forest Soils

Two submodels for simulating the leaching of forest soils are described. SOILORG is used for O, E, and top B layers where Al(OH)₃ is absent and organic matter is the major base cation storage. SOILMIN cares for the rest of the profile where Al(OH)₃ control of Al is assumed and goethite provides most of the sulphate storage, clay mineral surfaces providing base cation storage. Results are presented from a test run for the period 1911 to 2030, based on data from a 260 cm deep soil profile in the SW of Sweden investigated 1990 and on a likely deposition scenario. Considering that the deposition of base cations exceeded the removal by stemwood in 1911 when the simulation started, the biologic acidification of the soil profile had reached a steady state before 1911 so that no additional acidification took place before 1930 and very little before 1950. After 1950 it was strongly enhanced by the increased acid deposition. In the mineral soil a considerable resistance against acidification is offered both by base cation exchange and sulphate adsorption, creating an acidification front which moved slowly down the B-horizon then accelerated, reaching the bottom of the profile in 1990. A deposition reduction by 2/3 during 1990–2010 will cause a partial recovery of pH, particularly in the deeper parts of the profile.     

Alberta油砂地区在两种水文流域森林土壤酸化敏感性研究

Input of large amounts of N and S compounds into forest ecosystems through atmospheric deposition is a significant risk for soil acidification in the oil sands region of Alberta. We evaluated the sensitivity of forest soils to acidification in two watersheds （Lake 287 and Lake 185） with contrasting hydrological regimes as a part of a larger project assessing the role of N and S cycling in soil acidification in forest ecosystems. Fifty six forest soil samples were collected from the two watersheds by horizon from 10 monitoring plots dominated by either jack pine （Pinus banksiana） or aspen （Populus tremuloides）. Soils in the two watersheds were extremely to moderately acidic with pH （CaCl2） ranging from 2.83 to 4.91. Soil acid-base chemistry variables such as pH, base saturation, Al saturation, and acid-buffering capacity measured using the acetic acid equilibrium procedure indicated that soils in Lake 287 were more acidified than those in Lake 185. Acid-buffering capacity decreased in the order of forest floor 〉 subsurface mineral soil 〉 surface mineral soil. The most dramatic differences in percent Ca and Al saturations between the two watersheds were found in the surface mineral soil horizon. Percent Ca and Al saturation in the surface mineral soil in Lake 287 were 15% and 70%, respectively; the percent Ca saturation value fell within a critical range proposed in the literature that indicates soil acidification. Our results suggest that the soils in the two watersheds have low acid buffering capacity and would be sensitive to increased acidic deposition in the region.     

Average critical loads for nitrogen and sulfur and its use in acidification abatement policy in the Netherlands

Atmospheric deposition of N and S on terrestrial and aquatic ecosystems causes effects induced by eutrophication and acidification. Effects of eutrophication include forest damage, NO₃ pollution of groundwater and vegetation changes in forests, heathlands and surface waters due to an excess of N. Effects of acidification include forest damage, groundwater pollution, and loss of fish populations due to Al mobilization. Critical loads (deposition levels) for N and S on terrestrial and aquatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Critical loads of N generally vary between 500 and 1500 mol _c ha^?1 yr^?1 for forests, heathlands and surface waters and between 1500 and 3600 for phreatic groundwaters. Critical loads of total acid (S and N) vary between 300 to 500 mol _c ha^?1 yr^?1 for phreatic groundwaters and surface waters and between 1100 to 1700 mol ha^?1 yr^?1 for forests. On the basis of the various critical loads a deposition target for total acid of 1400 mol _c ha^?1 yr^?1 has been set in the Netherlands from which the N input should be less than 1000 mol _c ha^?1 yr^?1. This level, to be reached in the year 2010, implies an emission reduction of 80–90% in SO₂, NO _x and NH₃ in the Netherlands and of about 30% in neighboring countries compared to 1980 emissions.     

Pyrite and siderite oxidation in swamp sediments

Differences in the processes of pyrite and siderite oxidation, in reclaimed swamp sediments of the Skjernå delta (Denmark), are described from sediment chemistry, mineralogy and pore water chemistry. Pyrite oxidation leads to extreme soil acidification, with pH dropping to about 2, the release of large amounts of weathering products to the pore water, and the precipitation ofiron oxides, jarosite and gypsum. Siderite oxidation results only in moderate soil acidification where the pH does not drop below 3.5, while part of the acidification is due to the oxidation of small amounts of sulphur compounds together with siderite. The release of weathering products to the pore water is limited and only iron oxide is precipitated. Calculations indicate that equilibrium with amorphous FeOOH, gypsum and amorphous Al(OH)₃ sets an upper limit to the Fe³⁺, SO₄ and Al concentrations in the pore water.     

Changes in soil chemistry accompanying acidification over more than 100 years under woodland and grass at Rothamsted Experimental Station, UK

We have examined the effect that acid deposition and other sources of acidity have had over the last 110–140 years on soil under woodland (Broadbalk and Geescroft Wildernesses) and grassland (Park Grass) comprising some of the Classical Experiments at Rothamsted Experimental Station. Changes in soil chemistry have been followed by analysing some of the unique archive of stored samples for pH, water-soluble and exchangeable base cations, aluminium, iron and manganese, exchangeable acidity, cation exchange capacity (CEC) and soluble anions. Proton balances and historical data show the importance of acid deposition to acidification and concomitant changes in the chemistry of the soil. The pH of the surface soil of Geescroft Wilderness has fallen from 6.2 to 3.8 since 1883. The decrease in the pH of the unlimed, unfertilized plot on Park Grass was less over a similar period (from pH 5.2 to 4.2), illustrating the significant effect of the woodland canopy on the interception of acidifying pollutants. The effect of increasing acidity on the soil chemistry of Geescroft Wilderness is seen in its decreasing base saturation and CEC, with base cations moving down the soil profile. Clay minerals are being irreversibly weathered, and Mn and Al progressively mobilized, so that today Al occupies 70% of the exchange complex in the surface soil. Even with present reductions in sulphur deposition critical loads for sulphur, nitrogen and acidity are still exceeded. Such semi-natural ecosystems are unsustainable under the current climate of pollution.     

Modeling acidification and recover in the roofed catchment at Lake Gårdsjön

The dynamic, biogeochemical model SAFE was applied to a roofed subcatchment G1 at Gårdsjön, Sweden. The roof was installed in 1991, and deposition of anthropogenic S and N reduced by ca. 90%. Initiated from pre-industrial steady-state conditions, SAFE predicts present levels of biologically relevant chemical properties (pH, inorganic Al and base cations). SAFE overestimates the short-term effects of the manipulation on runoff pH, while the modeled decline in inorganic Al and and base cations are comparable to observations. Temporal variability and too few years of measured data make model to data comparison difficult. Sulfate desorption, which is not included in SAFE, may introduce a time lag between modeled and measured data. Reductions of S and N inputs by 90% will lead to a recovery in pH, low A1 but extremely low base cations concentrations due to replenishment of exchange sites.     

Magic,Safe and Smart Model Applications at Integrated Monitoring Sites: Effects of Emission Reduction Scenarios

Three well-known dynamic acidification models (MAGIC, SAFE, SMART) were applied to data sets from five Integrated Monitoring sites in Europe. The calibrated models were used in a policy-oriented framework to predict the long-term soil acidification of these background forest sites, given different scenarios of future deposition of S and N. Emphasis was put on deriving realistic site-specific scenarios for the model applications. The deposition was calculated with EMEP transfer matrices and official emissions for the target years 2000, 2005 and 2010. The alternatives for S deposition were current reduction plans and maximum feasible reductions. For N, the NOx and NHy depositions were frozen at the present level. For NOx, a reduction scenario of flat 30% reduction from present deposition also was utilized to demonstrate the possible effects of such a measure. The three models yielded generally consistent results. The ‘Best prediction’-scenario (including the effects of the second UN/ECE protocol for reductions of SO2 emissions and present level for NOx-emissions), resulted in many cases in a stabilization of soil acidification, although significant improvements were not always shown. With the exception of one site, the ‘Maximum Feasible Reductions’ scenario always resulted in significant improvements. Dynamic models are needed as a complement to steady-state techniques for estimating critical loads and assessing emission reduction policies, where adequate data are available.