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1.
Cation exchange properties of acid forest soils of the northeastern USA   总被引：2，自引：0，他引：2  
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 (CECe), soil pHs (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 CECe 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 CECe and total C were near zero. In O horizons, the CECe per unit mass of organic carbon (CECe:C) was positively correlated with pHs in three of the four data sets, consistent with the weak‐acid behaviour of the organic matter. However, CECe:C was negatively correlated with pHs in mineral soils in two data sets, and uncorrelated in the other two. The CECe in mineral soils represents the portion of total CEC not occupied by organically bound Al. The negative correlations between CECe:C and pHs can therefore be explained by increased Al binding at higher pHs. Aluminium behaves like a base cation in these soils. When Al was considered a base cation, the relation between base saturation and pHs 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 pHs 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.  相似文献   

2.
Conventional wisdom states that the source of negative charge in organic soil horizons is pH dependent and, therefore, acidification will decrease charge and the ability to retain nutrient cations. Using a variety of methods, we found that the native cation exchange capacity (CEC) of northeastern US forest soils varied with the amount of soil carbon (about 0.5 cmol per %C), independent of field pH. However, individual soil samples exhibited dramatic charge variability if the pH was adjusted during CEC measurement, as much as 20 cmolc kg? per pH unit change. These last two statements appear to be mutually exclusive. Extrapolating from pH-adjusted samples, the point of zero “base” cation capacity was consistently about 1.5 pH units below the native pH. We hypothesize the amount of charge is at a steady state with humification and decomposition processes. Response of soils to long-term acidification may be much different than that of short-term laboratory adjustments.  相似文献   

3.
In Saxony‐Anhalt, Germany, an area of about 6000 ha is covered by lignite‐ash‐derived substrates. In some cases, pollutants like heavy metals or toxic organic compounds had been disposed of together with the lignite ashes. For this reason, we assessed factors influencing the cation exchange capacity (CEC) of lignite‐ash substrates exposed to natural weathering. We chose four research sites reflecting the different methods of disposal: two dumped landfills and two lagooned ashes of different ages. After determining the CEC at pH 8.1 (CECpot), we evaluated the influence of the content of silt and clay and the content of total organic C. As lignite‐ash‐derived substrates are rich in oxalate‐extractable Si, Al, and Fe, we performed an oxalate extraction and determined afterwards the CECpot to assess the contribution of oxalate‐soluble compounds to the CECpot. Moreover, we determined the variable charge of selected samples at pH values ranging from 4 to 7. The lignite‐ash‐derived soils had a high CECpot with means ranging from 25.1 cmolc kg–1 to 88.8 cmolc kg–1. The influence of the parent material was more important than the degree of weathering. The content of total organic C consisting of pedogenic organic matter and coked lignite particles together with the content of silt and clay played a statistically significant role in determining the CEC. Another property that influenced the amount of CEC in medium textured lignite ashes was the content of oxalate‐soluble silica and aluminum. After oxalate extraction, they lost about 30% of their CEC due to the dissolution of oxalate‐soluble compounds. In coarse textured lignite ashes, oxalate extraction led to higher amounts of CEC, probably due to an increase of surface area resulting either from the disintegration of particles or from etching caused by insufficient dissolution of magnetite and maghemite. Moreover, lignite‐ash‐derived substrates exhibit a high amount of pH‐dependent charge. The CEC decreased by 40% in a topsoil sample and by 51% in a subsoil sample as the pH declined from 7 to 4.  相似文献   

4.
Acid soils in some mediterranean forests were investigated for the composition of the adsorption complex and the gradients in soil pH. The effective CEC (235–838 mmolc kg?1) and base saturation (93–98 %) are highest in ectorganic horizons. In the mineral horizons the effective CEC (23–52 mmolc kg?1) and base saturation (11–40 %) are much lower. The exchange complex of mineral horizons consists for 90 (AEh) to 40 percent (Bw2) of organic matter. The effective CEC of the mineral clay fraction is low (60 mmolc kg?1 clay). The clear trends in soil pH within the ectorganic layer of deciduous and sclerophyllous oak forests are attributed to vertical spatial separation of nitrogen mineralization (ammonification and strongly impeded nitrification) and nutrient uptake by roots (mainly NH4). This leads to a high effective CEC in the fermentation layer and acidification of the uppermost part of the mineral soil. In contrast to the situation in temperate forests this process is impeded in mediterranean coniferous forests, where litter decomposition is extremely slow and both proton production and consumption take place in the organic rich mineral horizon.  相似文献   

5.
Selected horizons from six New Zealand soils under permanent natural vegetation, four of which form a development sequence, were chosen to provide variations in organic matter, phyllosilicate clay mineral and short-range ordered aluminosilicate (allophane) contents. The ionic strength of the soil solution (μ) extracted from the soils of the development sequence was low, being always less than 0.005. For all horizons of the six soils, the negative charge changes linearly with μ1/2 within the ionic strength range of 0.001 to 1. The change was negligible for the least weathered and leached soil, indicating that it contained mainly permanently charged colloids. As soil development increased and/or the components carrying variable charge increased in amount, the change in charge with ionic strength increased. A regression equation showed a strong relationship between change in negative charge with ionic strength and organic carbon and oxalate-extractable A1 (R2=0.976). This equation was tested by predicting observed changes in charge with ionic strength for a second selection of soils. The change in positive charge with ionic strength was correlated with oxalate-extractable A1 (r2=0.914). The results are discussed in relation to measurement of soil charge and iron movement in soils.  相似文献   

6.
The electric charge characteristics of four Ando soils (A1 and μA1) and a Chernozemic soil (Ap) were studied by measuring retention of NH4+ and Cl– at different pH values and NH4Cl concentrations. No positive charge appeared in the Ando soils at pH values 5 to 8.5 except for one containing allophane and imogolite. The magnitude of their negative charge (CEC; meq/l00g soil) was dependent on pH and NH4Cl concentration (C; N) as represented by a regression equation: log CEC =a pH +b log C +c, where the values of a and b were 0.113–0.342 and 0.101–0.315, respectively. Unlike the Chernozemic soil, Ando soils containing allophane, imogolite, and/or 2:1–2:1:1 layer silicate intergrades and humus showed a marked reduction of cation retention as pH decreased from 7 to 5. This was attributed to the charge characteristics of the clay minerals and to the carboxyl groups in humus being blocked by Al and Fe.  相似文献   

7.
Starting from the basic equations of chemical equilibrium, an analytical mathematical expression is derived that relates pH to base saturation, concentration of acid anions (SO42?, NO3?, etc.) and other properties of the soil and soil solution. The equation is particularly valid in acid soils (low base saturation and relatively large, >100 μmolc dm?3, concentration of acid anions) in the range in which cation exchange is the buffering mechanism. Values of pH, alkalinity and degassed pH calculated with the aid of this equation compared well to values measured in three forest-floor horizons; calculated pH values also compared well to values measured on a number of acid soils. The equation is also used to derive analytical mathematical expressions for alkalinity, soil leaching sensitivity (a measure of the sensitivity of a soil solution to become dominated by A13+), and other variables of interest in the context of acidification.  相似文献   

8.
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.  相似文献   

9.
本工作研究了阴离子吸附和ＰＨ对恒电荷土壤（黄棕壤和黑土）和可变电荷土壤（砖红壤）动电性质的影响。结果表明,砖红壤吸附不同阴离子后的ζ电位随ＰＨ升高由正电位移至负电位,在ζ电位－ＰＨ曲线上均有一个等电点（ＩＥＰ）在ＰＨ３．５～８之间,相同ＰＨ升高由正电红壤的ζ电位随吸附阴离子的负移顺序是ＨＰＯ４＾２－〉Ｆ＾－〉ＳＯ４＾２－〉Ｃｌ＾－〉ＮＯ３＾－。作为恒电荷土壤的黄棕壤和黑土,在不同电解发质溶液中的ε  相似文献   

10.
In northernmost Fennoscandia there is concern about the possible environmental effects of the sulphur emissions from Russian nickel smelters on the Kola Peninsula. The purpose of this study was to investigate to what extent the soils of this region may delay the response to pH changes through sulphate adsorption, and whether there are evidence for strong soil acidification effects. To this end 26 spodic B horizons were collected along a transect from northernmost Sweden to north-easternmost Norway, only 10 km from the Pechenganikel smelter. As the pH(H2O) was > 4.8 in all soils, and as the exchangeable Ca/Al ratio was high, there were no evidence for strong soil acidification effects. Water-extractable SO4 was clearly affected by the S deposition and thus SO4 was at least partly mobile in the soils; it is therefore possible that soil solutions close to the smelter may have been acidified. In spite of this, sulphate adsorption was found to be more important than cation exchange reactions as a delaying process against soil acidification, at least in the top 10 cm of the B horizon. For the top 20 cm of the B horizon it was estimated that S04 adsorption can neutralize, on average, 700 mmolc, m?2 of acid before the pH is decreased to 4.4. Thus if the S deposition remains unchanged, decades are required to severely acidify most soils in the affected parts of Norway and Finland.  相似文献   

11.
The potential for sulfate retention is an important soil feature for buffering of atmospheric acid deposition. We studied the effects of increasing additions of different neutral salts and acids on mobilization and retention of SO4 2- in acid forest soils. Soils containing up to 11 mmol SO4 2- kg-1 were equilibrated with H2O, NaCl, MgCl2, and HCl. Release of SO4 2- was highest with H2O and NaCl additions and lowest when HCl was used. Increasing the ionic strength of the added solutions caused decreasing SO4 2- concentrations in equilibrium solution. Decreasing pH in equilibrium solution was found to be the reason for the decrease in release. Even when the pH was < 4, the SO4 2- release decreased. We assume that this finding resulted from the fact that in the soils studied the SO4 2- sorption was controlled by the high contents of Fe oxides/hydroxides. Experiments with Na2SO4, MgSO4, and H2SO4 demonstrated that the B horizons already containing high amounts of SO4 2- were still able to retain SO4 2-. Sulfate retention increased in the order Na2SO4 < MgSO4 < H2SO4, which corresponds to increasing H+ availability. The higher SO4 2- retention along with MgSO4 compared to Na2SO4 may be caused by higher potential of Mg to mobilize soil acidity compared to Na.  相似文献   

12.
Extractability and adsorption of sulphate in soils   总被引：8，自引：0，他引：8  
Virtually all of the indigenous sulphate (SO4) in a range of UK soils with moderately high pH values (> 6) was found to be present in the soil solution and, as a consequence, was highly susceptible to leaching. For acid soils containing adsorbed SO4, the extractability of SO4 in NaCl and CaCl2 solutions was dependent on both the ionic strength and cation species. Addition of small amounts (<～ 10?2M) of either NaCl or CaCl2 actually decreased the amount of SO4 extracted, but SO4 extractability increased sharply with concentrations of NaCl or CaCl2 higher than about 0.1 M. At a similar ionic strength, more SO4 was extracted by NaCl than CaCl2. Sequential extraction with 1 M NaCl removed essentially all of the absorbed SO4. The release characteristics of SO4 were very different to those of phosphate and this difference in behaviour is not easily reconciled with the view that SO4 is chemisorbed, as is phosphate. Except for a few acid soils with high oxide contents, the capacity of the soils to adsorb added SO4 was quite small. None of the soils with pH values higher than 6 adsorbed a significant amount SO4. The results raise questions regarding the efficiency of SO4-containing fertilizers in correcting and preventing S deficiency in situations where leaching is important.  相似文献   

13.
Mean NH3 losses after nine days incubation at 18°C and 60% FC were 3.1±2.9% and 7.6±6.0% of applied urea-N from the pasture and tillage counterparts of 10 soil series. These losses were highly correlated with buffered CEC and maximal pH values (pHm) generated three days after urea application. NH3 volatilization was apparently controlled by buffered CEC and initial pH (R2= 72–87%) and was related to variations in soil organic matter and texture (R2= 77–81%). Losses in the acid pasture soils were attributed largely to initial pH differences, and in the tillage soils to buffered CEC only. Evolution was greater from the tillage than from the pasture equivalent in eight series. This was attributed to differences in CEC, including buffered CEC and pH-dependent charge, caused by differences in OM content primarily but also in texture between the two soil groups. Differences in NH3 evolution from urea in pasture and tillage soils, in general, are not related to pH differences.  相似文献   

14.
Abstract

Cation exchange capacity (CEC) of the 0–5 cm depth of forest soils increased with the square root of solution ionic strength over the experimental range of 6 to 96 mM. Percentage increases in CEC were positively correlated with percentage organic carbon; for mixed hardwood forest soils, increases were 38% for soils with 3.3% carbon, and 105% for soils with 7.4% carbon when ionic strength was varied over the full experimental range. When analyzing soils with constant‐potential surfaces, both pH and ionic strength must be controlled, preferably at or near levels found in the field, in order to provide interpretable measures of CEC.  相似文献   

15.
The Gaines–Thomas selectivity coefficient, K, was used to express the relation between the cations in solution and the cations in exchange sites in podzolic forest soils. Soil solution was obtained by centrifuging a fresh bulked soil sample. Exchangeable cations HX, AlX, CaX, MgX and KX and effective cation-exchange capacity, CECe, were determined with 0.1 m BaCl2. Apparent values of K indicated a preference of Ca2+ over Mg2+ and over Al3+ in O, A and B horizons (log KAl–Ca < 0 and log KMg–Ca < 0), whereas log KK–Ca and log KH–Ca exceeded zero. The horizons were similar with respect to log KH–Ca, and the differences in log KMg–Ca were small. Log KK–Ca and log KAl–Ca increased in the horizons in the order O < A < B. Log KAl–Ca was not significantly correlated with the fraction AlX/CECe. Log KMg–Ca was positively correlated with the fractions HX/CECe and AlX/CECe, and negatively correlated with log (CaX/MgX). The selectivity coefficient of binary cation exchange seemed to be applicable to in situ soil solutions. However, the fraction of each cation on exchange sites should be based on the CECe rather than on the sum of the two cations. The latter, also, seemed to be acceptable in cases of exchangeable cations with a large relative content in soil, e.g. in Al3+–Ca2+ exchange in A and B horizons, and in H+–Ca2+ exchange in O and A horizons.  相似文献   

16.
Two Oxisols (Mena and Malanda), a Xeralf and a Xerert from Australia and an Andept (Patua) and a Fragiaqualf (Tokomaru) from New Zealand were used to examine the effect of pH and ionic strength on the surface charge of soil and sorption of cadmium. Adsorption of Cd was measured using water, 0.01 mol dmp?3 Ca(NO3)2, and various concentrations of NaNO3 (0.01–1.5 mol dm?3) as background solutions at a range of pH values (3–8). In all soils, the net surface charge decreased with an increase in pH. The pH at which the net surface charge was zero (point of net zero charge, PZC) differed between the soils. The PZC was higher for soils dominated by variable-charge components (Oxisols and Andept) than soils dominated by permanent charge (Xeralf, Xerert and Fragiaqualf). For all soils, the adsorption of Cd increased with an increase in pH and most of the variation in adsorption with pH was explained by the variation in negative surface charge. The effect of ionic strength on Cd adsorption varied between the soils and with the pH. In Oxisols, which are dominated by variable-charge components, there was a characteristic pH below which increasing ionic strength of NaNO3 increased Cd adsorption and above which the reverse occurred. In all the soils in the normal pH range (i.e. pH>PZC), the adsorption of Cd always decreased with an increase in ionic strength irrespective of pH. If increasing ionic strength decreases cation adsorption, then the potential in the plane of adsorption is negative. Also, if increasing ionic strength increases adsorption below the PZC, then the potential in the plane of adsorption must be positive. These observations suggest that, depending upon the pH and PZC, Cd is adsorbed when potential in the plane of adsorption is either positive or negative providing evidence for both specific and non-specific adsorption of Cd. Adsorption of Cd was approximately doubled when Na rather than Ca was used as the index cation.  相似文献   

17.
PONETTE  Q.  DUFEY  J. E.  WEISSEN  F. 《Water, air, and soil pollution》1997,95(1-4):353-379
Liming and fertilization are important tools for improving the chemical status of acid, base poor forest soils. The downward movement of dolomite, kieserite and a mixture of CaCO3 and kieserite was investigated by monitoring the leachates and exchangeable cation composition from single and combined horizon columns, reconstructed from an acid brown forest soil profile (0–15 cm). Upon entering the soil, Mg ions from kieserite displaced base cations and acidity (H and Al ions) from exchange sites, which subsequently moved down with the mobile SO4 2- anions. Total leaching during the initial SO4 2- pulse was similar with the CaCO3 + kieserite mixture. Compared to the single kieserite treatment, the joint application of CaCO3 greatly increased the proportion of Ca in the leachates from all horizons. It also decreased the leaching of acidity from the surface Oe horizon and prevented pH from dropping under this layer. With both treatments, the redistribution of magnesium with SO4 2- anions resulted in a rapid increase in exchangeable Mg contents throughout the studied columns. Due to the important charge increase in the Oe horizon and to kinetic restraints imposed on dissolution, downward movement of Ca and Mg ions from dolomite was very limited. Mg was however much more mobile than Ca. In the CaCO3 + kieserite and dolomite treatments, the migration of alkalinity and base cations with time was associated with a decrease in exchangeable acidity and an increase in ECEC in the two upper soil layers. By the end of the monitoring period, overall net Mg retention in the 0–15 cm columns increased in the order kieserite < CaCO3 + kieserite << dolomite with respectively 20, 35 and 85% of cumulated inputs remaining in the columns. The corresponding net Ca retention amounted to 82 and 96% of cumulated inputs for the CaCO3 + kieserite and dolomite treatments, respectively. Results from this study complement those obtained in the field by clearly demonstrating the mechanisms involved in the downward movement of some fertilizers commonly used to increase the base saturation of acid forest soils.  相似文献   

18.
On the depletion of magnesium in soils of high altitudes of the Inner Bavarian Forest A widespread magnesium deficiency in stands of Norway spruce, growing at high altitudes of the Bavarian Forest, was the reason for an extensive soil survey and for hydrological-hydrochemical studies of these areas. The prevailing soils are Fragiorthods and Fragiumbrepts (great soil groups after US Soil Taxonomy). Total element contents of soils show clear relation to the respective parent rock. These relations are missing for exchange capacity (CECe) and exchangeable elements. This fact can be explained by a consolidated layer in the upper soil and high annual precipitations, which favor episodic interflow with low pH (about 4,0) and high SO4- respectively NO3-concentrations. Water of the deeper ground (baseflow) however, shows high pH-values (about 6,5) and low SO4-concentrations. Increased concentrations of SO4 and NO3 in seepage water (interflow) show relation to considerable atmospheric S- and N-input. Furthermore the qualitative evaluation of the nutrient balance in these forest ecosystems revealed a release of SO4 and NO3 in soils of the high elevations, which must be followed by an equivalent removal of cations. The balance of element translocations in soil profiles shows, that magnesium is mostly affected by these depletion processes.  相似文献   

19.
Soil chemical properties affecting NH4+ sorption in forest soils   总被引：2，自引：0，他引：2  
Fourteen European forest soils from the boreal to the mediterranean climate on different parent materials were investigated with respect to their ability to store NH4+ in exchangeable form, using sorption isotherms. Distribution coefficients for NH4+ sorption per unit weight of soil were in the range of 0.02 to 0.77. NH4+ sorption coefficients were usually highest in the forest floor of a given soil. NH4+ sorption behaviour of mineral soil horizons was correlated to soil parameters that are determined during routine soil analysis. A combination of CEC and base saturation explained up to 95% of the variability Of NH4+ sorption. In the forest floors, variability in NH4+ sorption could not be explained quantitatively from independent soil parameters. The affinity of the sorption sites for NH4+ was the most important factor for explanation of the variability in NH4+ sorption in the forest floors but was of low importance in mineral soil horizons. As NH4+ exchanges predominantly base cations, susceptibility of NH4+ to transport through the soil profile increases with Iowbase saturation of a soil as well as with low CEC values.  相似文献   

20.
A series of batch experiments were conducted to assess the effects of pH, temperature, and ionic strength on mercury adsorption by black and red soils. The results showed that the mercury adsorption increased when the temperature increased from 5 to 15 °C for red soil, whereas for black soil, the amount of adsorption was greater at 25 °C than at other temperatures. At the same temperature, the adsorption capacity of the black soil was greater than that of the red soil. The adsorption capacity of mercury by soils was not influenced by initial pH, sodium nitrate (NaNO3),or sulfate ion (SO4 2–). However, the change of chloride ion (Cl?) concentrations had a great effect on mercury adsorption. When the concentration was increased from 10?3to 10?1mol L?1, the adsorption capacity of mercury on both soils (especially for the red soil) decreased sharply.  相似文献   

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