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1.
Long‐term monitoring data from eastern North America and Europe indicate a link between increased dissolved organic carbon (DOC) concentrations in surface waters over the last two decades and decreased atmospheric pollutant and marine sulphur (S) deposition. The hypothesis is that decreased acidity and ionic strength associated with declining S deposition has increased the solubility of DOC. However, the sign and magnitude of DOC trends have varied between sites, and in some cases at sites where S deposition has declined, no significant increase in DOC has been observed, creating uncertainty about the causal mechanisms driving the observed trends. In this paper, we demonstrate chemical regulation of DOC release from organic soils in batch experiments caused by changes in acidity and conductivity (measured as a proxy for ionic strength) associated with controlled SO42? additions. DOC release from the top 10 cm of the O‐horizon of organo‐mineral soils and peats decreased by 21–60% in response to additions of 0–437 µeq SO42? l?1 sulphuric acid (H2SO4) and neutral sea‐salt solutions (containing Na+, Mg2+, Cl?, SO42?) over a 20‐hour extraction period. A significant decrease in the proportion of the acid‐sensitive coloured aromatic humic acids (measured by specific ultra‐violet absorbance (SUVA) at 254 nm) was also found with increasing acidity (P < 0.05) in most, but not all, soils, confirming that DOC quality, as well as quantity, changed with SO42? additions. DOC release appeared to be more sensitive to increased acidity than to increased conductivity. By comparing the change in DOC release with bulk soil properties, we found that DOC release from the O‐horizon of organo‐mineral soils and semi‐confined peats, which contained greater exchangeable aluminium (Al) and had lower base saturation (BS), were more sensitive to SO42? additions than DOC release from blanket peats with low concentrations of exchangeable Al and greater BS. Therefore, variation in soil type and acid/base status between sites may partly explain the difference in the magnitude of DOC changes seen at different sites where declines in S deposition have been similar.  相似文献   

2.
Longitudinal and temporal variations in water chemistry were measured in several low-order, high-elevation streams in the Great Smoky Mountains to evaluate the processes responsible for the acid-base chemistry. The streams ranged in average base flow ANC from ?30 to 28 μeq L?1 and in pH from 4.54 to 6.40. Low-ANC streams had lower base cation concentrations and higher acid anion concentrations than did the high-ANC streams. NO3 ? and SO4 2? were the dominant acid anions. NO3 ? was derived from a combination of high leaching of nitrogen from old-growth forests and from high rates of atmospheric deposition. Streamwater SO4 2? was attributed to atmospheric deposition and an internal bedrock source of sulfur (pyrite). Although dissolved Al concentrations increased with decreasing pH in the study streams, the concentrations of inorganic monomeric Al did not follow the pattern expected from equilibrium with aluminum trihydroxide or aluminum silicate phases. During storm events, pH and ANC declined by as much as 0.5 units and 15 μeq L?1, respectively, at the downstream sites. The causes of the episodic acidification were increases in SO4 2? and DOC.  相似文献   

3.
Discharge to concentration relationships for eight streams studied by the U.S. Geological Survey (USGS) as part of the U.S. Environmental Protection Agency's (U.S. EPA) Long-Term Monitoring Project (1983–89) indicate acidification of some streams by H2SO4 and HNO3 in atmospheric deposition and by organic acids in soils. Concentrations of major ions in precipitation were similar to those reported at other sites in the northeastern United States. Average concentrations of SO4 2? and NO3 ? were similar among streams, but base cation concentrations differed widely, and these differences paralleled the differences in acid neutralizing capacity (ANC). Baseflow ANC is not a reliable predictor of stream acidity at high flow; some streams with high baseflow ANC (>150 Μeq L?1) declined to near zero ANC at high flow, and one stream with low baseflow ANC (<50 Μeq L?1) did not approach zero ANC as flow increased. Episodic decreases in ANC and pH during peak flows were associated with increased concentrations of NO3 ? and dissolved organic carbon (DOC). Aluminum concentrations exceeding 300 Μg L?1 were observed during peak flows in headwater streams of the Neversink River and Rondout Creek. Seasonal Kendall Tau tests for temporal trends indicate that SO4 2? concentrations in streamwater generally decreased and NO3 ? concentrations increased during the period 1983–1989. Combined acid anion concentrations (SO4 2? + NO3 ?) were generally unchanged throughout the period of record, indicating both that the status of these streams with respect to acidic deposition is unchanged, and that NO3 ? is gradually replacing SO4 2? as the dominant acid anion in the Catskill streams.  相似文献   

4.
Iodine-129 is an important radionuclide released from nuclear facilities because of its long radioactive half-life and its environmental mobility. Its retention in surface soils has been linked to pH, organic matter, and Fe and Al oxides. Its inorganic solution chemistry indicates I will most likely exist as an anion. Three investigations were carried out to provide information on the role of the inorganic and organic chemistry during sorption of I by soil. Anion competition using Cl? showed that anion exchange plays a role in I sorption in both mineral and organic soils. The presence of Cl decreased the loss of I? from solution by 30 and 50% for an organic and a carbonated sandy soil respectively. The I remaining in solution was associated primarily with dissolved organic carbon (DOC). The loss rate from solution appears to depend on two reactions of I with the soil solids (both mineral and organic) creating both a release to and a loss from solution, and the reaction of I with the DOC (from very low to high molecular weight). Composition analyses of the pore water and the geochemical modelling indicate that I sorption affects the double-charged anion species in solution the most, particularly SO4 ?. Iodide introduced to natural bog groundwater at three concentrations (10?3, 10?1 and 10 meq L?1) remained as I? and was not lost from solution quickly, indicating that the association of I with DOC is slow and does not depend on the DOC or I concentration. If sorption of I to soil solids or DOC is not sensitive to concentration, then stable I studies, which by necessity must be carried out at high environmental concentrations, can be linearly extrapolated to radioactive I at much lower molar concentrations.  相似文献   

5.
Abstract: In recent years, sulfur (S) deficiencies in winter wheat (Triticum aestivum L.) have become more common, particularly on coarse‐textured soils. In Study I, field experiments were conducted in 2001/2002 through 2003/2004 on Mississippi River alluvial soils (Experiment I) and an upland, loessial silt loam (Experiment II) to evaluate the influence of spring S rates of 0, 5.6, 11.2, and 22.4 kg ha?1 and a fall rate of 22.4 kg sulfate (SO4)‐S ha?1 on grain yield of three varieties. In Study II, field experiments were conducted in 2001/2002 and 2004/2005 on alluvial soils to evaluate the influence of spring S rates of 0, 5.6, 11.2, and 22.4 kg SO4‐S ha?1 in fields where S‐deficiency symptoms were present. Grain yield response to applied S occurred only on alluvial, coarse‐textured, very fine sandy loam soils (Study II) that had soil SO4‐S levels less than the critical level of 8 mg kg?1 and organic‐matter contents less than 1 g kg?1 in the 0‐ to 15‐, 15‐ to 30‐, and 30‐ to 45‐cm depths. Soil pH increased with soil depth. Optimum S rate was 11.2 kg SO4‐S ha?1 in 2001/2002 and 5.6 kg SO4‐S ha?1 in 2004/2005. On the upland, loessial silt loam soil, soil SO4‐S levels accumulated with depth, whereas organic‐matter content and pH decreased. In the loessial soils, average soil SO4‐S levels in the 15‐ to 30‐ and 30‐ to 45‐cm soil depths were 370% greater than SO4‐S in the surface horizon (0 to 15 cm).  相似文献   

6.
Equilibrium studies on soil require reliable estimates of ion concentrations in the soil solution under field conditions. We evaluated the previously described iterative method to approximate the equilibrium soil solution (ESS) with four acid forest soils. We examined for which ions the ESS is suitable, making use of the fact that concentrations in water extracts are functions of the soil: solution ratio. The electric conductivity, pH, and the concentrations of base cations, Mn2+, NO?3, SO42+, and dissolved organic carbon (DOC) were usually linear with the soil:solution ratio in water extracts, whereas no relation was observed for Al (with one exception) and Fe. Assuming that the ESS can be attributed the soil solution ratio of the field moist soil at the time of sampling, concentrations appeared as the continuation of the linear relation with the soil: solution ratio for base cations, pH, and the electric conductivity. This indicates that the ESS actually represents field conditions for these solution properties. For Al water extracts allowed no evaluation of the ESS result. The ESS underestimated SO42? concentrations under field conditions, presumably because the lack of DOC in the solutions added distorts the balance amongst anions.  相似文献   

7.
The adsorption of dissolved organic carbon (DOC) and sulfate was examined in mineral horizons of acid soils from damaged (Oberwarmensteinach) and healthy (Wülfersreuth) Norway spruce forested sites in the Fichtelgebirge (NE-Bavaria). The A horizons of both sites desorbed DOC at all levels added, whereas the B horizons (Bs and Bv) retained added DOC at levels > 5 mmol C kg?1. An initial mass isotherm used on the B horizon data indicated that these soils have a greater affinity for DOC than B horizons from Spodosols in the northeastern U.S. Sulfate was only retained at high solution levels, and retention was pH dependent. Nitrate and sulfate additions (1000 μeq L?1 anion) had minor effects on DOC adsorption. Overall, there was little difference in DOC or sulfate retention at the two sites, indicating atmospheric deposition inputs have not affected these processes.  相似文献   

8.
Kinetically controlled release of uranium from soils   总被引：1，自引：0，他引：1  
Although trade element uptake on and release from solid phases are fundamental controls on the migration of the elements in the environment, the controls are incompletely understood. The extraction of uranium from two soils, both of which have been labelled naturally with uranium, was therefore studied using a cation resin exchange technique. One soil was a peat from the Needle's Eye natural analogue site, Scotland, and the other was a calcareous brown earth from Derbyshire, England. The effects of different exchanging cations, solution pH and the presence of complexing anions (Cl?, CO32?, SO42?) in solution on uranium extraction were assessed. The extraction could be described by a simple, first-order kinetic model with up to three rate constants being identifiable in individual experiments. In both soils no single reaction pathway appeared to dominate, and extraction was slow, with rate constants of 10?3?10?4 h?1 in acid conditions and around 10?6 h?1 in neutral conditions. Half-times for uranium release in the experiments were in the range 30–60 days in acid and around 10 years in neutral conditions; in the field they are therefore expected to be several years at both sites. Incorporation of kinetic factors into a simple one-dimensional migration model illustrates that their overall effect is to retard migration. Ideally, therefore, reaction rates should be taken into account in predictive modelling of element transport.  相似文献   

9.
We investigated the potential effects of elevated water-column sulfate (SO4) levels on heterotrophic microbial respiration and net phosphorus (P) release for soils collected from impacted and unimpacted Everglades wetlands in south Florida. Soils from three sites, ranging from low P and low SO4 to high P and high SO4 environments, were examined under controlled laboratory conditions. The soils were subjected to anaerobic incubations to evaluate net P release and organic matter decomposition in response to SO4 amendments of 32 or 96 mg l−1 (0.33 and 1.0 mM).Three processes have been described in the literature to explain why SO4 enrichment may lead to P release from soils under anaerobic conditions. First, alkalinization can lead to a more favorable pH environment for decomposition. For the soils examined here, alkalinization due to the hydrogen ion-consuming reaction of SO4 reduction was not a prominent mechanism. We found that pH decreased in the incubation vessels, and that increases in alkalinity were more likely attributable to calcium carbonate dissolution than SO4 reduction. Moreover, all the soils exhibited near circum-neutral pH levels, with moderate to high concentrations of native alkalinity.Second, formation of iron sulfide (FeSx) compounds has been shown to mobilize iron (Fe)-associated P. Soils from only one of the study sites had Fe concentrations that would be expected to be high enough to influence P mobility. Relatively high porewater Fe:soluble reactive P (SRP) ratios (>83:1) were observed at this site, which suggests that Fe could theoretically exert control over the release of P from the soil. However, soil P levels at this site were too low to measure any substantial influence of Fe on net P mobilization.Finally, availability of electron acceptors such as SO4 is a major determinant of decomposition rate, and thus rate of organic P release. Amending the soils with SO4 did not result in either more heterotrophic microbial respiration as measured by carbon dioxide (CO2) and methane (CH4) production, or increased net P mobilization. In two of the SO4-amended soils where post-incubation total sulfide concentrations were as high as 23.4 mg l−1, SO4 addition reduced production of respiratory carbon end products, suggesting hydrogen sulfide inhibition. Moreover, limitations imposed by substrate quality and low P contributed to the lack of meaningful enhanced decomposition of organic matter with the addition of 32 or 96 mg SO4 l−1 to the oligotrophic wetland soils. Even though P release did occur under anaerobic conditions for the more enriched site, addition of SO4 did not enhance P release.  相似文献   

10.
不同浸提剂处理森林土壤溶解性有机碳含量比较   总被引：1，自引：0，他引：1  
丁咸庆  柏菁  项文化  侯红波  彭佩钦 《土壤》2020,52(3):518-524
为了解亚热带森林土壤溶解性有机碳(DOC)的特征规律,采用培养离心的方法获取土壤溶液测得DOC含量,对比传统水溶性有机碳(WSOC)提取法间的差异。选取湖南大山冲森林公园保存完好的3种亚热带典型次生林地,按10cm一层采集剖面土壤,采用不同方法提取测定土壤DOC和WSOC含量,分析与土壤理化指标的相关性及方法间的显著性关系。结果表明:①典型森林土壤DOC或WSOC含量随土壤剖面深度的增加,呈显著下降趋势。培养离心提取测得的土壤DOC含量明显较低,仅0.82～9.52 mg/kg,超纯水浸提的风干土WSOC含量达10.56～249.19 mg/kg,而0.5 mol/L K_2SO_4提取的鲜土WSOC含量达155.70～576.94 mg/kg,0.5mol/L K_2SO_4浸提的干土WSOC含量最高,达158.94～797.56 mg/kg,含量表现为:DOC干土超纯水浸提WSOC鲜土K_2SO_4浸提WSOC干土K_2SO_4浸提WSOC;②3种次生林土壤DOC或WSOC含量存在显著差异,不同方法测定的含量均表现为针叶林常绿阔叶林落叶林;③培养离心法测得土壤DOC含量与其他测定方法间存在极显著正相关(P0.01),并且土壤DOC和WSOC均与土壤pH、总有机碳、胡敏酸、富啡酸、全氮、全磷、速效态氮以及微生物生物量碳氮达到极显著相关(P0.01),与土壤含水率和容重显著相关(P0.05)。培养离心法测得土壤DOC含量远低于水溶液提取WSOC含量,该方法下的测得值更接近于原位土壤溶解性有机碳实际值。  相似文献   

11.
Sulfate (SO4 2–) movement and transport in soils has received considerable attention in recent years. In most soils, SO4 2– coexists with a variety of natural organic compounds, especially organic acids. Studies were conducted to assess the effect of low-molecular-weight organic acids (eight aliphatic and five aromatic acids) on SO4 2– adsorption by variable charge soils from Chile and Costa Rica. The effects of type of organic acid, pH, type of soil, and organic acid concentration were investigated. In one experiment, a 1.0 g soil sample was equilibrated with 25 ml 0, 0.5, 1.0, 2.0, 4.0, or 6.0 mM K2SO4 in 1 mM NaCl in the presence or absence of 5 mM citric acid. In the second set of experiments, the adsorption of 2 mM SO4 2– in soils at pH 4 or pH 5 in the presence or absence of one of 13 organic acids at a concentration of 2 mM or 5 mM was studied. Results showed that citric acid significantly decreased SO4 2– adsorption by the two soils. Sulfate adsorption decreased with increasing pH of the equilibrium solution. Aliphatic acids, with the exception of cis-aconitic acid, decreased the amount of SO4 2– adsorbed by the two soils, with oxalic, tartaric, and citric acid showing the greatest effect. The differences in pH values of the equilibrium solutions in the presence and absence of organic acids were significantly, but negatively, correlated with the amount of SO4 2– adsorbed, suggesting chemisorption of SO4 2– and the release of hydroxide ions. The ionization fraction values of the organic acids at the equilibrium pH were correlated with the amounts of SO4 2– adsorbed, suggesting that the protonation of surface hydroxyl groups of the mineral phase increased as the strength of the ionization of the acid increased, thus creating more positively charged surfaces. Received: 12 February 1997  相似文献   

12.
A lake survey consisting of 987 randomly selected lakes was conducted in Finland in autumn 1987. The survey covered the whole country, and the water quality of the lakes can be considered as representative of the approximately 56 000 lakes larger than 0.01 km2 in Finland. The median TOC concentration is 12 mg L-1 and the median pH 6.3. The proportion of lakes with TOC concentrations > 5 mg L-1 in the whole country is 91 %. Organic anion is the main anion in the full data set (median 89 μeq L-1). The high organic matter concentrations in Finnish lakes are associated with catchment areas containing large proportions of peatlands and acid organic soils under coniferous forest. The survey demonstrated that organic matter strongly affects the acidity of lakes in Finland. The decreasing effect of organic matter on the pH values was demonstrated by both regression analysis and ion balances. At current deposition levels of *SO4 the pH of humic lakes in Finland is determined to a greater extent by high TOC concentrations than by *SO4 in most areas. In lakes with pH values lower than 5.5 the average organic anion contribution is 56 % and non-marine sulfate contribution 39 %. However, in the southern parts of the country, where the acidic deposition is highest, the minerogenic acidity commonly exceeds the catchment derived organic acidity.  相似文献   

13.
The dependency of the retention of dissolved organic carbon (DOC) on mineral phase properties in soils remains uncertain especially at neutral pH. To specifically elucidate the role of mineral surfaces and pedogenic oxides for DOC retention at pH 7, we sorbed DOC to bulk soil (illitic surface soils of a toposequence) and corresponding clay fraction (< 2 μm) samples after the removal of organic matter and after removal of organic matter and pedogenic oxides. The DOC retention was related to the content of dithionite‐extractable iron, specific surface area (SSA, BET‐N2 method) and cation exchange capacity (pH 7). The reversibility of DOC sorption was determined by a desorption experiment. All samples sorbed 20–40 % of the DOC added. The DOC sorption of the clay fractions explained the total sorption of the bulk soils. None of the mineral phase properties investigated was able to solely explain the DOC retention. A sorption of 9 to 24 μg DOC m–2 indicated that DOC interacted only with a fraction of the mineral surface, since loadings above 500 μg m–2 would be expected for a carbon monolayer. Under the experimental conditions used, the surface of the silicate clay minerals seemed to be more important for the DOC sorption than the surface of the iron oxides. The desorption experiment removed 11 to 31 % of the DOC sorbed. Most of the DOC was strongly sorbed.  相似文献   

14.
In northern Spain and elsewhere in the world, many vineyards are located on steep slopes and are susceptible to accelerated soil erosion. Contaminants, notably Cu, originating from repeated application of copper‐based fungicides to the vines to prevent mildew, are transported and stored in the sediments deposited close to valley bottoms. In this study, the contents and distribution of Cu in 17 soil samples and 21 sediment samples collected from vineyard stands were determined. In addition, the effect of pH on Cu release from vineyard soils and sediments was quantified. The total Cu content (CuT) in the soils varied between 96 and 583 mg kg?1, and was between 1.2 and 5.6 times greater in sediment samples. The mean concentration of potentially bioavailable Cu (CuEDTA) in the sediments was 199 mg kg?1 (46% of CuT), and was 80 mg kg?1 (36% of CuT) in the soils. Copper bound to soil organic matter (CuOM) was the dominant fraction in the soils (on average, 53% of the CuT), while in sediment samples CuOM values varied between 37 and 712 mg kg?1 and were significantly greater (P < 0.01) than in the soils. Copper associated with non‐crystalline inorganic components (CuIA) was the second most important fraction in the sediments, in which it was 3.4 times greater than in the soils. Release of Cu due to changes in the pH followed a U‐shaped pattern in soils and sediments. The release of Cu increased when the pH decreased below 5.5 due to the increased solubility of the metal at this pH. When the pH increased above 7.5, Cu and organic matter were released simultaneously.  相似文献   

15.
Dai  Zhaohua  Liu  Yunxia  Wang  Xingjun  Zhao  Dianwu 《Water, air, and soil pollution》1998,108(3-4):377-390
Soil acidification has been occurred in two locations in southern China. The changes in soil pH during a 35 yr period has been about 1.0 pH 2O) units, and about 0.58–0.71 pH (KCl) units at Wuming in Guangxi Zhuang Autonomous Region and Zhurongfeng of Mt. Heng in Hunan Province. A decrease in CEC and BS and an increase in hydrogen and aluminum ion concentrations were found in the acidified soils, and related to the acidification caused by acid deposition. Hydrogen ion concentration increased about 0.1–1.0 × 10-6 equivalent g-1 soil yr-1. Cation exchangeable capacity (CEC) and base saturation (BS) decreased to 53–76 and 30–59% in the acidified soils respectively, and an increase in exchangeable acidity also occurred. Acidification in the topsoil is higher than in the subsoil.  相似文献   

16.
Soil water at an acid-sensitive forested catchment in southwestern Poland has been studied for four years. Median base saturation (BS) is only 5% in the podzol B-horizons. Very low pH values in the soil water from the O-horizons (10- and 90 percentiles pH 3.5 and 4.3) increased to a typical median pH in the B-horizons of 4.4, mainly by release of inorganic labile aluminium (Ali). Median concentrations in the B horizons were 3.4mg Ali L?1. Al-soil/soilwater interactions were studied over a large span of sulphate concentrations resulting from both a generally decreasing S-deposition during the last decades and an increase in precipitation during the study period. These changes led sulphate to leach from the mineral soil. Aluminium mobilisation is better described by jurbanite- than by gibbsite solubility. For the soils with aluminium saturation (AlS) >90%, there is a tendency that the concentration of Al3+ decreases less than divalent base cations with a decrease in SO4 2? concentration. This causes the critical load molar ratio (RCL={Al3+}/{Ca2++Mg2+}) to increase with a decrease in the sulphate concentration in soil water, which is not in agreement with a simple cation-exchange model.  相似文献   

17.
Twenty-four low acid neutralizing capacity (ANC) lakes in Vermont have been monitored since 1980 to characterize their chemical variability, and to determine if they exhibit temporal trends in acid/base chemistry. Many of the lakes exhibit significant decreasing trends in SO4 2? and base cation (CB) concentrations, but few exhibit significant changes in pH or ANC. An examination of all trend results (significant and insignificant) suggests a tendency for ANC and pH values in these lakes to be increasing, but either the changes are too small, or the number of observations too small, for these trends to be significant. Data from these lakes suggest that the primary responses of surface waters in this region to declining rates of SO4 2? deposition are decreases in SO4 2? concentrations and rates of cation leaching from watershed soils. Decreasing rates of cb deposition may combine with lower rates of cation leaching to produce declines in cB that are very similar to measured declines in SO4 2? concentration. Vermont lakes exhibit their lowest ANC values in spring, attributable, for the most part, to dilution of cB concentrations during spring snow melt. Concentrations of SO4 2? are also more dilute in the spring, but cB decreases are greater, and the net effect is a lowering of ANC. One quarter of the Vermont lakes monitored exhibit strong seasonality in NO3 ? concentrations, with peak concentrations near 70 Μeq L?1. In these lakes, spring increases in NO3 ? concentrations are more important than CB dilution in producing minimal spring ANC values.  相似文献   

18.
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   

19.
In 1986 Lake Langedalstjenn in southern Norway was a weakly acidified lake with a pH of 5.2–5.6, and an average concentration of SO4 of 330 μeq L?1. The total Al concentration varied between 10 and 20 μeq L?1 (expressed as Al3+). The lake supported populations of brown trout and perch and had supplied about 100 people with drinking water until the late 1980's. During 1986–1989, a dramatic change in the water chemistry occurred because of blasting of and weathering of sulphidic gneisses in the watershed. The oxidation of sulphide to sulphate (sulphuric acid) caused an increase in the SO4 concentration of the draining stream of up to ≈ 4800 μeq L?1. Weathering and/or cation exchange of Ca and Mg neutralized approximately 52% of the protons from the sulphuric acid production, while about 46% were consumed by mobilization of aluminium and iron. Nevertheless, about 2% of the hydrogen ions from the sulfuric acid were still present, which resulted in a stream pH of 4.0. In the lake, the pH was 4.4, and the concentrations of all major cations and anions were significantly lower than in the heavily affected stream. Mixing of the stream water with lake water, formation of aluminium-sulphate complexes and coprecipitation of Ca may explain the resulting concentrations of major ions in the lake.  相似文献   

20.
Samples of three organic‐rich soils (ombrotrophic peat, podzol H‐horizon, humic ranker) were extensively washed with dilute nitric acid, dialysed against deionised water, and then subjected to acid‐base titrations over the pH range 3–10, in 0.3–300 mm NaNO3, and with soil concentrations in the range 2–150 g l?1. The results for the three soils were quantitatively similar. Comparison of the titration data with previously published results for humic acids isolated from the same soils showed the soil organic matter to have a greater ionic strength dependency of proton binding and to possess relatively greater buffering capacity at high pH, attributable to weak acid groups (c. 2–5 mmol g–1) in the humin fraction of the soils. To describe the soil titration data quantitatively, we modified Humic Ion‐Binding Model VI‐FD, which utilizes a fixed Donnan volume to describe counterion accumulation, by increasing the content of weak acid groups. When artefacts in pH measurement caused by the suspension effect were taken into account, the resulting Model VI‐FD2 provided good or fair simulations of all the titration data. The results suggest that soil structure, specifically aggregation, plays a significant role in cation binding by organic soils in situ. The lack of dependence of the titration results on soil suspension concentration suggests that the findings can be applied to soils in situ.  相似文献   

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