酸沉降影响下近20年来衡山土壤酸化研究

对不同时期采自衡山东坡垂直带谱上6个典型土壤剖面Ah层和AB层的样品分析,土壤酸化指标研究结果表明,近2 0年来,由于酸沉降的影响,由花岗岩风化物发育的各类土壤,都有不同程度的酸化,表现在pH值下降,交换性酸,尤其是交换性Al3 增加,交换性盐基总量减少,盐基饱和度下降,特别是土壤酸缓冲性能和土壤酸害容量降低。相比之下,山顶的常湿淋溶土和山麓的湿润富铁土酸化更明显,而山体中部的常湿富铁土酸化进程较慢,山体上部的常湿雏形土酸化进程更慢,表明土壤酸化除了与土壤酸沉降量有关外,还与土壤类型有关     

Forest soil chemical changes between 1949/50 and 1987

Soil profiles from the Alltcailleach Forest in north-east Scotland originally sampled in 1949/50 were resampled in 1987. Soil pH, exchangeable Ca, Mg, K and Na, extractable Al and cation exchange capacity were measured on the original stored and resampled soils. Chemical changes were characterized by decreases in pH, base cations, base saturation and cation exchange capacity. Extractable amounts of Al increased. Sequential leaching experiments showed a significant increase in the amount of extractable sulphate in mineral soil horizons. Changes in soil chemistry were interpreted to result from a combination of nutrient depletion caused by tree growth, natural pedogenic processes and atmospheric pollution effects.     

Effects of acid deposition on acidity and exchangeable cations in podzols of the Kola Peninsula

Response of soil and soil water of podzols in the Kola Peninsula to acid deposition was estimated under both field and laboratory conditions. A significant increasing trend of exchangeable acidity in organic (O) horizons and exchangeable Al in podzolic (E) horizons of podzols with distance from the nickel smelter was observed. The simulated rain at pH 4.5 did not alter chemical properties of soils and soil solutions. As much as 95–99% of the applied H⁺ ions were retained by soils and appeared in the percolates after a treatment period that depended on acid load and soil thickness. Ca and Mg in soil solutions were highly sensitive to acid loading. Simulated acid rain enhanced the leaching of exchangeable base cations out of root zone. Acid inputs resulted in decreased pH, amount of exchangeable base cations and base saturation, in elevated exchangeable acidity and it's Al fraction in soil solid phase. The most significant changes occurred in O and E horizons. Substantial amounts of both Ca and Mg can be lost from the root zone of podzols in the north-western Kola, subjected to acid deposition, thus leading to forest productivity damage.     

Mechanisms controlling the mobility of dissolved organic matter, aluminium and iron in podzol B horizons

The processes governing the (im)mobilization of Al, Fe and dissolved organic matter (DOM) in podzols are still subject to debate. In this study we investigated the mechanisms of (im)mobilization of Al, Fe and organic matter in the upper and lower B horizons of two podzols from the Netherlands that are in different stages of development. We equilibrated batches of soil material from each horizon with DOM solutions obtained from the Oh horizon of the corresponding soil profiles. We determined the amount of (im)mobilized Al, Fe and DOM after addition of Al and Fe at pH 4.0 and 4.5 and initial dissolved organic carbon (DOC) concentrations of 10 mg C litre^?1 or 30 mg C litre^?1, respectively. At the combination of pH and DOC concentrations most realistic for the field situation, organic matter was retained in all horizons, the most being retained in the lower B horizon of the well‐developed soil and the least in the upper B horizon of the younger profile. Organic matter solubility seemed to be controlled mainly by precipitation as organo‐metal complexes and/or by adsorption on freshly precipitated solid Al‐ and Fe‐phases. In the lower B horizons, at pH 4.5, solubility of Al and Fe appeared to be controlled mainly by the equilibrium with secondary solid Al‐ and Fe‐phases. In the upper B horizons, the solubility of Al was controlled by adsorption processes, while Fe still precipitated as inorganic complexes as well as organic complexes in spite of the prevailing more acidic pH. Combined with a previous study of eluvial horizons from the same profiles, the results confirm the important role of organic matter in the transport of Al and Fe to create illuvial B horizons initially and subsequently deepening and differentiating them into Bh and Bs horizons.     

Modelling pH buffering and aluminium solubility in European forest soils

The pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation acidity. The chemistry of soil organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Nevertheless, models of humic substance chemistry have been developed, one of which is WHAM–S, which contains a model (Model V) of proton and metal binding at discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAM–S to model solution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting the amounts of soil aluminium and humic substances within defined limits, taking the contents of copper chloride‐extractable Al and the base‐extractable organic matter as starting values. The model simulated both pH and dissolved Al well with optimized amounts of aluminium and humic substances within the defined limits (root mean squared error for pH from 0.01 to 0.22, for p[Al]_aq (total dissolved Al) from 0.03 to 0.49, five data points). Control of dissolved Al by dissolved organic matter was important particularly at above‐ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)₃. The optimized model also gave reasonable predictions of pH and dissolved Al in supernatants obtained by repeated leaching of the soil horizons. The results show that humic substances dominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)₃ occurs but is the exception.     

Relationships between the High Aluminum Concentration and Other Components in Soil Solution of Acidic Soil in Kumagaya, Central Japan

A plot with a high aluminum (Al) concentration in soil solution was found in Kumagaya, central Japan; the maximum was 4.0 mg L⁻¹ as total dissolved Al (TD-Al) at a depth of 10 cm in August 2000. The soil type was Dystric Andosols with three horizons, A/Bw1/Bw2, which contained a considerable quantity of Al extracted by dithionite-citrate and acid-oxalate extractants. The upper two horizons were acidic with soil pH (H₂O) of 4.4 and 4.6. The fundamental cause of the high TD-Al concentration was the low pH with a very low base saturation of less than 2%. The seasonal change in TD-Al concentrations in soil solution at a depth of 10 cm was significantly and positively correlated with the nitrate concentrations but weakly and rather negatively correlated with the sulfate concentrations. Nitrification functioned as the direct acid source to cause the TD-Al concentrations to fluctuate strongly, whereas sulfate adsorption onto the soil at the research plot functioned as a sink of proton.     

Use of a chemical equilibrium model to understand soil chemical processes that influence soil solution and surface water alkalinity

A chemical equilibrium model was applied to soil chemistry data (Spodosols) collected from 30 and 21 forested watersheds in New York and Maine, respectively, during the EPA Pilot Soil Survey. Chemistry data were evaluated between states using lumped series and within New York using three series (Adams, Becket, and Canaan). All New York horizons had soil characteristics that tend to cause lower solution alkalinity in comparison to Maine horizons. Negative alkalinities were produced in all E horizons (? 69 to ? 37 μmol LU^?1) at each of the pCO₂ levels used (0.3 to 2%). All B horizons had negative alkalinities at low PCO₂ levels, which became positive at higher levels, except for the Canaan B and New York Bh horizons, which were negative at all pCO₂ levels. C horizons generated positive alkalinities (1 to 67 μmol L^?1) at most pCO₂ levels. Results indicate the importance of water contact with different horizons and soil series in determining solution alkalinity. Because of degassing effects, solutions with a positive alkalinity will increase in pH after leaving the soil, whereas solutions with a negative alkalinity will remain at low pH (pH < 5.5) and cause the surface water to be acidic. Application of the model to soil chemistry data collected in the northeastern U.S. illustrates the importance of various factors such as pCO₂, Al solubility, base saturation, and exchange coefficients in determining surface water chemistry.     

Cation exchange properties of acid forest soils of the northeastern USA

Negative correlations between soil pH and cation exchange capacity (CEC) or base saturation in soils of the northeastern USA and Scandinavia have raised questions regarding the nature of cation exchange in acid forest soils. Using data from three small‐catchment studies and an extensive regional survey of soils in the northeastern USA, I examined relationships among total carbon, effective CEC (CEC_e), soil pH_s (in 0.01 m CaCl₂) and base saturation. Organic matter is the predominant source of soil surface charge in these coarse‐grained, glacially derived soils. Correlation coefficients (r) between total carbon and CEC_e ranged from 0.43 to 0.74 in organic horizons and from 0.46 to 0.83 in mineral horizons. In all cases, the intercepts of functional relations between CEC_e and total C were near zero. In O horizons, the CEC_e per unit mass of organic carbon (CEC_e:C) was positively correlated with pH_s in three of the four data sets, consistent with the weak‐acid behaviour of the organic matter. However, CEC_e:C was negatively correlated with pH_s in mineral soils in two data sets, and uncorrelated in the other two. The CEC_e in mineral soils represents the portion of total CEC not occupied by organically bound Al. The negative correlations between CEC_e:C and pH_s can therefore be explained by increased Al binding at higher pH_s. Aluminium behaves like a base cation in these soils. When Al was considered a base cation, the relation between base saturation and pH_s could be effectively modelled by the extended Henderson–Hasselbalch equation. When modelled without Al as a base cation, however, there were no consistent relationships between pH_s and base saturation across sites or soil horizons. Because of the non‐acidic behaviour of Al, it is difficult to predict the effect of ongoing reductions in acid deposition on the base status of soils in the northeastern USA.     

Cation exchange capacity variations in acidic forest soils from Sutton,Québec,Canada

Abstract

Single values of the cation exchange capacity (CEC) are widely used in modeling soil solution chemistry in soil and water ecosystems. Our aim was to determine the CEC as a function of pH and ionic strength in an acidic forest soil. We examined the cation exchange of two Humo‐Ferric Podzols (Haplorthods) equilibrated with artificial soil solutions of different concentrations. Aliquots of acid (HC1) or base (NaOH) were added to generate a pH range of 3 to 6. The CEC, determined by displacement with BaCl₂ showed little or no increase with increasing pH and a definite increase with lower pH. This anomalous behavior was attributed to the precipitation of aluminum (Al) at high pH and to its dissolution at low pH.     

西藏酸性土壤的酸度特征

根据西藏7个土类6 6个土壤剖面2 5 7层土样的分析资料,探讨酸性土的酸度特征。西藏酸性土面积约占1/ 5 ,主要为山地湿润森林型和高山灌丛草甸型土壤,集中分布于藏东南地区。土壤pH主要决定于其潜性酸中的交换性酸,特别是其中占优势的交换性Al3 ,而受非交换性酸的影响较小。交换性酸中Al3 的相对比例随交换性酸总量增加而增大,随有机质增加而减小,H 的相对比例则呈相反的变化。非交换性酸主要来源于有机质(腐殖质酸性功能团缔合H和络合Al的解离)。土壤pH与交换性酸、非交换性酸饱和度分别呈近线性、非线性负相关,而与盐基饱和度呈非线性正相关,且主要受优势的交换性Ca2 制约。     

Classification schemes for the acidity,base saturation,and acidification status of forest soils in Switzerland

Soil chemical parameters related to soil acidity were determined for 1450 soil samples taken from individual mineral soil horizons in 257 forest soils in Switzerland, 196 developed from carbonate‐containing and 61 from carbonate‐free parent material. The distribution of pH values and exchangeable base cations in corresponding pH ranges were related to the capacity and rate of buffer reactions in the soil. Based on this, five acidity classes for individual soil samples were defined. To describe and classify the status of soil acidity and base saturation (BS) of an entire soil body, the pH and the BS of the total fine earth in the soil were calculated from the pH and BS, respectively, of the individual soil horizons and the estimated volumetric content of fine earth. The status of soil acidification of soil profiles was assessed primarily using the total amount of exchangeable acidic cations in percent of the CEC of the fine earth in the entire soil profile. As a second factor, the gradient between the acidity class of the most acidic soil horizon and the estimated acidity class at the beginning of soil formation was used. The application of these classification schemes to our collection of soil profiles revealed the great influence played by the type of parent material. The acidification status of most soils on carbonate‐containing parent material was classified as very weak to weak, whereas soils on carbonate‐free parent material were found to be strongly to very strongly acidified. In terms of parent rock material, microclimate, and natural vegetation, the results of this study and the proposed classification schemes can be considered appropriate for large parts of Europe.     

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.     

The sensitivity of Swiss forest soils to acidification and the risk of aluminum toxicity

In the context of pollution‐control strategies to minimize the detrimental effects of soil acidification, there is a need to know how and to what extent soils respond to acidifying substances. The purposes of this study were to assess the sensitivity of soil to acidification, in particular to a decrease in pH and in base saturation (BS), and the risk of Al toxicity for vulnerable plants using chemical indicators. These indicators were derived from soil data (pH, exchangeable cations, amount of fine earth) measured in the mineral horizons of 257 soil profiles throughout Switzerland. Based on the analysis of the distribution of pH and BS values in the soil collective, we assessed the sensitivity of soils to a decrease in pH and in BS. Soils that were considered sensitive to a decrease in pH had pH values between 4.8 and 7.0. The degree of sensitivity was estimated with the proportion of fine earth in the critical pH range to a depth of 100 cm. Soils that were considered sensitive to a decrease in BS had pH values between 3.6 and 5.5 and a BS between 10% and 95%. Since the effective cation‐exchange capacity (CEC_eff) of the fine earth might dampen the decrease in BS when acidity is added, the disposition for a decrease in BS was related to the relative amount of fine earth in the sensitive BS and to the mean CEC_eff of this fine‐earth fraction. The risk of Al toxicity for vulnerable plants was estimated using the ratio of base cations to Al at the cation‐exchange sites (BC : Al_exc). A BC : Al_exc of 0.2 was taken as a threshold value below which the risk for sensitive plants increases. The degree of risk was based on the proportion of fine earth in the critical BC : Al range (≤0.2) in the soil profile. These indicators taking into account the various aspects of soil acidification are derived from usually available data and represent therefore a cost‐effective tool to assess the sensitivity of soils to an input of acidity.     

Long-Term Evaluation of Acidic Atmospheric Deposition on Soils and Soil Solution Chemistry in the Daniel Boone National Forest,USA

Combustion of fossil fuels has contributed to many environmental problems including acid deposition. The Clean Air Act (CAA) was created to reduce ecological problems by cutting emissions of sulfur and nitrogen. Reduced emissions and rainfall concentrations of acidic ions have been observed since the enactment of the CAA, but soils continue to receive some acid inputs. Many soils sensitive to acid deposition are found to have low pH, a loss of base cations, and a shift in the mineral phase controlling the activity of Al³⁺ and/or SO₄ ^2?. If inputs continue, soil may be depleted of base cations and saturated with Al and could cause low forest productivity. Soil samples and soil solutions from pan lysimeters were taken on ridge-tops in the Daniel Boone National Forest to evaluate potential impacts of acid deposition recently and in the future. Sample results were compared to historical data from identical locations. Physicochemical characteristics of the soils revealed that sites were very low in base saturation and pH and high in exchangeable acidity, illustrating change since previously sampled. Soil solution data indicated that sites periodically received high acid inputs leading to saturation of Al in soils and the formation of Al-hydroxy-sulfate minerals. Given these conditions, long-term changes in soil chemistry from acid deposition are acknowledged.     

Cation exchange in forest soils: the need for a new perspective

The long‐term sustainability of forest soils may be affected by the retention of exchangeable nutrient cations such as Ca²⁺ and the availability of potentially toxic cations such as Al³⁺. Many of our current concepts of cation exchange and base cation saturation are largely unchanged since the beginnings of soil chemistry over a century ago. Many of the same methods are still in use even though they were developed in a period when exchangeable aluminium (Al) and variable charge were not generally recognized. These concepts and methods are not easily applicable to acid, highly organic forest soils. The source of charge in these soils is primarily derived from organic matter (OM) but the retention of cations, especially Al species, cannot be described by simple exchange phenomena. In this review, we trace the development of modern cation exchange definitions and procedures, and focus on how these are challenged by recent research on the behaviour of acid forest soils. Although the effective cation exchange capacity (CECe) in an individual forest soil sample can be easily shown to vary with the addition of strong base or acid, it is difficult to find a pH effect in a population of different acid forest soil samples. In the very acidic pH range below ca 4.5, soils will generally have smaller concentrations of adsorbed Al³⁺. This can be ascribed to a reduced availability of weatherable Al‐containing minerals and a large amount of weak, organic acidity. Base cation saturation calculations in this pH range do not provide a useful metric and, in fact, pH is modelled better if Al³⁺ is considered to be a base cation. Measurement of exchangeable Al³⁺ with a neutral salt represents an ill‐defined but repeatable portion of organically complexed Al, affected by the pH of the extractant. Cation exchange in these soils can be modelled if assumptions are made as to the proportion of individual cations that are non‐specifically bound by soil OM. Future research should recognize these challenges and focus on redefining our concepts of cation retention in these important soils.     

Simulation of solution chemistry in an acidic forest soil

The computer simulation model SOILEQ was used to estimate soil solution chemistry over a 7 week period from October 3 to November 14, 1988 in the soils of a sugar maple forest located near St. Hippolyte, Quebec, Canada. Model parameters for pH-dependent CEC and exchangeable cations were calculated from laboratory measurements while soil solution chemistry, including Al solubility, at the start of the simulation was taken from values obtained from lysimeter samples. Model predictions were compared with values obtained from 12 sets of soil solution collectors over the same time period. Predicted values of Ca, Mg and K in the mineral soil horizons at 25-, 75- and 125-cm depths generally fall within the 95% confidence interval of the median for the measured values. Simulated values of pH and inorganic Al are not as close to the measured values. Some error due to drift is apparent, most notably for base cations in solutions leaving the organic surface horizons, and may be attributable to decomposition of organic matter, not included in the simulation model. The results indicate that other mechanisms that release H* (nitrification, for example) and base cations (mineral weathering or mineralization of organic matter) need to be considered.     

Occurrence of polymerized silicic acid and aluminum species in two forest soil solutions with different acidity

Silica species were determined in soil solutions from different soil horizons of acidic Dystric Cambisols in Austria and France. In general, more acid pH and elevated concentrations of Al, Si, and DOC were found in solutions of the upper soil horizons and in particular in the Austrian soil solutions. Aqueous Al speciation was dominated by complexes with respect to DOC and sulphate and by free Al³⁺, whereas dissolved Si was dominated by monosilicic acid. The average proportion of low molecular weight polymerized silicic acid (PS) is about 10 mol% of total dissolved Si. However, PS proportions sporadically reached up to 23 mol%. The origin of polymers is most likely due to weathering of soil silicates and polymerization of silicic acid by freezing or evaporation events.

We found a positive relationship between the occurrence of PS and the saturation degree with respect to secondary Al-silicates. Thus, we suggest that PS may even indicate precursors for the formation of secondary Al-silicates. In accordance with this concept, our results show that PS preferentially occurred in the upper B1 horizons, where low pH and high Al content may prevent its destruction.     

Soil Aluminum Distribution in the Near-Stream Zone at the Bear Brook Watershed in Maine

Near-stream and upslope soil chemical properties were analyzed to infer linkages between soil and surface water chemistry atthe Bear Brook Watershed in Maine [BBWM]. Organic and mineral soil samples were collected along six 20 m transects perpendicular to the stream and one 200 m transect parallel tothe stream. O horizon soils immediately adjacent to the streamhad a significantly higher pH (4.20) and lower soil organic matter percentage (54%) than upslope O horizons (3.84 and 76%,respectively). Additionally, near-stream O horizon soils hadsignificantly higher concentrations of water-soluble Al (2.7 ×),exchangeable Al (2.3 ×), and organically-bound Al (3.9 ×) andsignificantly lower concentrations of exchangeable Ca (0.4 ×) than O horizons upslope. These results suggest that Al can accumulate in non-hydric near-stream zone soils at this site. Mobilization of labile Al from near-stream zone soils duringhydrologic events could play a key role in explaining controls on Al in stream water at BBWM.     

Aluminium chemistry in two contrasted acid forest soils and headwater streams impacted by acid deposition,Vosges mountains,N.E. France

Al chemistry was studied in two acidic watersheds, one with a podzol, the other with an acid brown soil, in the Vosges mountains (N.E. France), by analysing both leaching and centrifugation soil solutions and spring waters over 3 yr. In the podzol, Al was mobilized in the eluvial horizons under the predominant influence of organic acidity, then leached down the profile as organic and F-bound Al. Strong undersaturation with respect to proto-imogolite and imogolite showed that the proto-imogolite theory of podzolization could not apply. Al was transferred from the soil to spring water mostly as Al³⁺ and Al-F. Al³⁺, as well as additional minor species (AlOH²⁺, AlSO₄ ⁺), originated from the redissolution of the top of the spodic horizons under the influence of both soil solution acidity and the occurrence of mobile anions derived from atmospheric deposition. Conversely, in the acid brown soil, Al mobilization was regulated by nitrate and occurred mainly as Al³⁺. Most of Al was retained in the deep soil and only traces of monomeric Al reached spring water. In the podzol eluvial horizons, soil solutions were undersaturated with respect to all relevant mineral phases and their chemical composition agree with the concept of a mobilization of Al from the solid soil organic Al and a control of Al³⁺ activity by complexation reaction with the solid and soluble soil organic matter and F. In the acid brown soil, soil solutions were found to be in equilibrium with natural alunite, and the formation of this mineral, if confirmed, would account for the occurrence of 'open' vermiculites instead of the expected hydroxy-Al interlayered vermiculites. Al solubility control in surface water of both watersheds remains unclear. The Al-F species in both watersheds and the likely control of Al solubility by alunite in the acid brown soil emphasize the influence of acid deposition on Al chemistry in acid watersheds.     

Factors affecting snowmelt streamwater chemistry in the black forest (West Germany)

Site conditions such as parent material, soils, but also vegetation cover and elevation explain the varying snowmelt streamwater chemistry in the Black Forest. The results are derived from multiple statistical analysis of a regional survey of 104 small mountain streams in the first phase of snowmelt in spring 1984. Cluster analysis classifies the snowmelt streams into three groups which are clearly linked to bedrock geology. Factor analysis finds podsolization, weathering and mineralization processes in the soils of the catchments to have most impact even under snowmelt conditions. There is no evidence that acidic atmospheric deposition directly affects the acidity of the investigated streams. However, the deposition rates are low compared to certain other regions in Central Europe. In areas with podsolic soils the organic soil layer plays a key role in the acidity and mobilization of Al and heavy metals. This is shown in the high correlations between pH, DOC, UV-extinction, color and metal concentrations. Because the concentrations of DOC are low (<10 mg.L^?1) and an anion deficit cannot be found, it is assumed that water acidity is not caused by dissolved humic acids, but by cations exchanged in the organic layer of acidic soils. Streamwater chemistry in areas with brown earth soil types is mainly affected by leaching of basic cations in the mineral soil horizons and mineral weathering.