湿地土壤NH4+吸附解吸对冻融循环的响应

Nitrogen (N) cycling in boreal peatland ecosystems may be influenced in important ways by freeze-thaw cycles (FTCs).Adsorption and desorption of ammonium ions (NH + 4) were examined in a controlled laboratory experiment for soils sampled from palustrine wetland,riverine wetland,and farmland reclaimed from natural wetland in response to the number of FTCs.The results indicate that freeze-thaw significantly increased the adsorption capacity of NH + 4 and reduced the desorption potential of NH + 4 in the wetland soils.There were significant differences in the NH + 4 adsorption amount between the soils with and without freeze-thaw treatment.The adsorption amount of NH + 4 increased with increasing FTCs.The palustrine wetland soil had a greater adsorption capacity and a weaker desorption potential of NH + 4 than the riverine wetland soil because of the significantly higher clay content and cation exchange capacity (CEC) of the riverine wetland soil.Because of the altered soil physical and chemical properties and hydroperiods,the adsorption capacity of NH + 4 was smaller in the farmland soil than in the wetland soils,while the desorption potential of the farmland soil was higher than that of the wetland soils.Thus,wetland reclamation would decrease adsorption capacity and increase desorption potential of NH + 4,which could result in N loss from the farmland soil.FTCs might mitigate N loss from soils and reduce the risk of water pollution in downstream ecosystems.     

Adsorption and Desorption of Exogenous Rare Earth Elements in Soils:Ⅰ. Rate and Forms of Rare Earth Elements Sorbed

Adsorption and desorption of exogenous rare earth elements (REE) in soils were studied.Results showed that soils had strong adsorbability for REE and the rate of adsorption of REE was over 95% of the added REE in these tests.The characteristics of adsorption isotherms corresponded well with the both Freundlich and Temkin equations,but deviated from the Langmuir equation.The adsorption of REE tended to increase with the rising of soil pH.A sequential extraction method used for studing the desorption and distribution of REE sorbed in soils are also discussed.     

紫色水稻土的有机金属-矿物胶体复合物对磷的吸附、解吸特征

The kinetic characteristics of P adsorption and desorption by organo-mineral colloidal complexes (OMC) were studied using acid, calcareous and neutral purple paddy soils taken from Chongqing and Sichuan, China. The results showed that the P adsorption capacity of the organo-mineral colloidal complexes differed with the soil tyes, being higher for the acid and calcareous purple soils than for the neutral purple soils. Partial removal of the organic matter increased the adsorption capacity of the colloidal complexes. A very significant positive correlation was found between the amounts of P desorbed from OMC and the P saturation degrees. The P adsorption reaction was quick at the early stage and slowed later. The raise of temperature increased P adsorption capacity and P adsorption rate of the colloidal complexes. The adsorption processes could be described by the Elovich equation.     

Adsorption of Phosphate on Variable Charge Soils

The study about the adsorption of phosphate on four variable charge soils and some minerals revealed that two stage adsorption appeared in the adsorption isotherms of phosphate on 4 soils and there was a maximum adsorption on Al-oxide-typed surfaces between pH 3.5 to pH 5.5 as suspension pH changed from 2 to 9, but the adsorption amount of phosphate decreased continually as pH rose on Fe-oxide typed surfaces. The adsorption amount of phosphate and the maximum phosphate adsorption pH decreased in the order of yellow-red soil > lateritic red soil > red soil > paddy soil, which was coincided with the content order of amorphous Al oxide. The removement of organic matter and Fe oxide made the maximum phosphate adsorption pH rise from 4.0 to 5.0 and 4.5, respectively. The desorption curves with pH of four soils showed that phosphate desorbed least at pH 5. Generally the desorption was contrary to the adsorption with pH changing.     

可变电荷或永久电荷土壤上的电荷特征与土壤对Cu2+的吸附－解吸之间的交互作用

Charge characteristics and Cu^2 adsorption-desorption of soils with variable charge(latosol)and permanent charge(brown soil)and the relationship between them were studied by means of back-titration and adsorption equilibrium respectively.The amount of variable negative charge was much less in variable-charge soil than in permanent-charge soil and increased with the pH in the system,but the opposite trend occurred in the points of zero charge(PZCs).The amount of Cu^2 ions sorbed by permanent-charge soil was more than that by variable-charge soil and increased with the increase of Cu^2 concentration within a certain range in the equilibrium solution.The amount of Cu^2 ions desorbed with KCl from permanent-charge soil was more than that from variable-charge soil,but the amount of Cu^2 ions desorbed with de-ionized water from permanent-charge soil was extremely low whereas there was still a certain amount of desorption from variable-charge soil.The increase of PZC of soils with variable or permanent change varied with the increment of Cu^2 ions added.When the same amount of Cu^2 ions was added,the increments of PZC and variable negative surface chargc of permanent-charge soil were different from those of variable-charge soil.     

Adsorption of Potassium and Calcium Ions by Variable Charge Soils

Interactions of potassium and calcium ions with four typical variable charge soils in South China were examined by measuring pK-0.5pCa value with a potassium ion-selective electrode and a calcium ion-selective electrode,and pK value with a potassium ion-selective electrode.The results showed that adsorption of potassium and calcium ions increased with soil suspension pH,and the tendency of the pK-0.5pCa value changing with pH differed with respect to pH range and potassium to calcium ratio.Adsorption of equal amount of calcium and potassium ions led to release of an identical number of protons,suggesting similar adsorption characteristics of these two ions when adsorbed by variable charge soils.Compared with red soil,latosol and lateritic red soil had higher adsorption selectivities for calcium ion.The red soil had a greater affinity for potassium ion than that for calcium ion at low concentration,which seems to result from its possession of 2:1 type minerals,such as vermiculite and mica with a high affinity for potassium ion.The results indicated that adsorption of potassium and calcium ions by the variable charge soils was chiefly caused by the electrostatic attraction between the cations and the soil surfaces.Moreover,it was found that sulfate could affect the adsorption by changing soil surface properties and by forming ion-pair.     

Zero Point of Charge of Organo—Mineral Complexes

Five soil sapmles collected from China and two soil samples from Pakistan with widely different origin and characterstics were used to study the zero point of charge(ZPC) of soil colloids.The results showed that the value of zero point of charge of H-clay complexes was lower than that of H-clays in all the samples.Natural clay complexes had the highest ZPC as compared to -Hclay complex and H-clay in alfisol,closer to H-clays rather than H-clay complexes in oxisol and udult.The Delta Value of ZPT(zero point of titration )to ZPC was higher in H-Clay complexes than in H-Clays.     

亚热带土壤不同矿物组分中铬的吸附

Safe application of chromium (Cr)-containing organic industrial wastes to soil requires considering the ability of the soil to adsorb Cr.In this study,the maximum Cr adsorption capacity was assessed for the bulk samples and their clay and iron-free clay fractions of four subtropical soils differing in mineralogy.To this end,the samples were supplied with Cr(Ⅲ) nitrate solutions at pH 4.5 or 5.5.The results of Cr(Ⅲ) adsorption fitted to a Freundlich equation and the adsorption capacity was positively correlated with soil organic matter and iron oxide contents.The clay fractions adsorbed more Cr per unit mass than the bulk soils and the iron-free clay fractions.The Cr(Ⅲ) adsorption capacity increased with increasing soil pH due to more charges on adsorbing surfaces.Our results suggest that the soils rich in organic matter and iron oxides and having a pH above 4.5 are suitable for application of Cr(Ⅲ)-loaded industrial wastes.     

初始浓度对六氯苯在土壤中的吸附-解吸的影响及解吸

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of hexachlorobenzene (HCB) in soils. To examine the adsorption-desorption characteristics of HCB, equilibrium batch experiments were carried out using two soils (red soil and paddy soil) with different initial HCB concentrations (0.25, 0.50, 0.75, 1.00, 1.50, 2.50, 3.50, and 5.00 mg L^-1) by using 0.01 mol L^-1 calcium chloride as the background solution. The successive desorption experiments (48, 96, 144, 192, and 240 h) were conducted after each adsorption equilibrium experiment. The results revealed that adsorption and desorption isotherms of HCB on two soils were nonlinear, which can be best described by the Freundlich equation with the square of the correlation coefficient (r²) ranging from 0.97 to 0.99. Desorption of HCB from the two soils exhibited hysteresis at all HCB concentrations because the Freundlich desorption coefficients were always higher than the Freundlich adsorption coefficients. The hysteretic effect was enhanced with increasing initial HCB concentration, and positive hysteresis was observed at different concentrations.     

甲硫嘧磺隆在土壤中的吸附和解吸特性研究

Methiopyrsulfuron is a new low-rate sulfonylurea herbicide for weed control in wheat; however, there is a lack of published information on its behavior in soils. In this study, methiopyrsulfuron adsorption and desorption were measured in seven soils sampled from Heilongjiang, Shandong, Jiangxi, Sichuan, Anhui, and Chongqing provinces of China using a batch equilibrium method. The Freundlich equation was used to described its adsorption and desorption. Adsorption isotherms were nonlinear with the values of Kf-ads, the Freundlich empirical constant indicative of the adsorption capacity, ranging from 0.75 to 2.46, suggesting that little of this herbicide was adsorbed by any of the seven soils. Soil pH and organic matter content (OM) were the main factors influencing adsorption; adsorption was negatively correlated with pH and positively correlated with OM. Methiopyrsulfuron desorption was hysteretic on the soils with high OM content and low pH.     

不同类型土壤对汞和砷的吸附解吸特征研究

为了探明不同类型土壤对重金属汞和砷吸附、解吸的影响,以性质差异显著的红壤、黑土和潮土为供试土壤,采用批量平衡法,研究了Hg(Ⅱ)和As(Ⅴ)在不同土壤中的吸附-解吸行为。结果表明:(1)Freundlich方程和Langmuir方程均能较好地拟合这3种土壤对Hg(Ⅱ)和As(Ⅴ)的吸附,其中Hg(Ⅱ)的最大吸附量分别为451.33、1699.46和1635.21mg/kg,大小顺序为黑土>潮土>红壤,相关系数(R2)在0.8533～0.9911之间;As(Ⅴ)的最大吸附量分别为818.44、561.87和112.77mg/kg,大小顺序为:红壤>黑土>潮土,相关系数(R2)在0.9223～0.9949之间;而线性方程则不能较好地拟合这3种土壤对Hg(Ⅱ)和As(Ⅴ)的等温吸附。(2)Hg(Ⅱ)和As(Ⅴ)的解吸量随Hg(Ⅱ)和As(Ⅴ)吸附量的增加而增加,两者之间呈显著或极显著的线性正相关,Hg(Ⅱ)的相关系数(R2)分别为0.8668**、0.8971**、0.9969**,As(Ⅴ)的相关系数(R2)分别为0.9987**、0.9964**、0.9858**。研究结果对于探明土壤中汞和砷的环境行为具有重要意义。     

Translocation of 203Hg labelled HgCl2 and CH3HgCl in an iron-humus podzol studied by radio-analytical techniques

Since increased Hg-concentrations in fish in lakes and rivers in northern Europe, northern parts of the U.S.A. and Canada were found, environmental Hg research has focused intensively on the factors determining leaching of mercury from soil into water systems. This article presents the results of a leaching experiment with undisturbed soil columns treated with HgCI₂ and CH₃HgCl using radio-analytical techniques. The columns were irrigated with rain of different acidity, rain volumes and irrigation intensities. The leaching of mercury was traced by detecting the vertical distribution of ²⁰³Hg in the soil profiles. Advantages and disadvantages of radioanalytical scanning techniques are discussed. The results of Hg leaching in the soil columns indicate a considerably stronger leaching of monomethyl mercury compared to inorganic mercury. Leaching of the two Hg-species is ruled by competition of H⁺ induced soil-Hg desorption with DOM-Hg complex formation; both being affected by rain acidity. Rain intensity had no visible effect on leaching of Hg²⁺ and CH₃Hg⁺. An extended rain duration increased the leaching of CH₃Hg⁺.     

Geochemistry of mercury in pristine and flooded ferralitic soils of a tropical rain forest in French Guiana,South America

In ferralitic soils of the dense Guianese forest, mercury (Hg) concentrations of the surface horizons varied from 122 to 318 ng/g d.w. The behaviour and accumulation of Hg is not related to the accumulation of organic matter but to the penetration of humic substances and the progressive adsorption onto iron (Fe) oxy-hydroxydes in the mineral horizons. The flooding of such soils with the creation of a small reservoir has lead to a release of 20% of the Hg initially present. This observation is related to the reduction of the Fe oxy-hydroxydes and to the migration of the organo-metallic complexes to the water column. Although physico-chemical conditions are appropriate for bacterial methylation, methyl Hg (MeHg) levels of these soils are very low. The process regulating MeHg production and its possible loss from the soil are unknown.     

Effect of pH,Temperature, and the Role of Ionic Strength on the Adsorption of Mercury(II) by Typical Chinese Soils

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.     

The Effect of Fire on Mercury Cycling in the Soils of Forested Watersheds: Acadia National Park,Maine, U.S.A.

This study compares mercury (Hg) and methylmercury (MeHg) distribution in the soils of two forested stream watersheds at Acadia National Park, Maine, U.S.A. Cadillac Brook watershed, which burned in 1947, has thin soils and predominantly deciduous vegetation. It was compared to the unburned Hadlock Brook watershed, with thicker soil and predominantly coniferous vegetation. Soils in both watersheds were primarily well drained. The fire had a significant impact on the Cadillac watershed, by raising the soil pH, altering the vegetation, and reducing carbon and Hg pools. Total Hg content was significantly higher (P > 0.05) in Hadlock soils (0.18 kg Hg ha^-1) compared to Cadillac soils (0.13 kg Hg ha^-1). Hadlock O horizon had an average Hg concentration of 134±48 ng Hg g^-1 dry weight, compared to 103±23 ng Hg g^-1 dry weight in Cadillac O horizon. Soil pH was significantly higher in all soil horizons at Cadillac compared to Hadlock soils. This difference was especially significant in the O horizon, where Cadillac soils had an average pH of 3.41±0.22 compared to Hadlock soils with an average pH of 2.99±0.13.To study the mobilization potential of Hg in the O horizons of the two watersheds, batch adsorption experiments were conducted, and the results were modeled using surface complexation modeling. The results of Hg adsorption experiments indicated that the dissolved Hg concentration was controlled by the dissolved organic carbon (DOC) concentration. The adsorption isotherms suggest that Hg is more mobile in the O horizon of the unburned Hadlock watershed because of higher solubility of organic carbon resulting in higher DOC concentrations in that watershed.Methylmercury concentrations, however, were consistently higher in the burned Cadillac O horizon (0.20±0.13 ng Hg g^-1 dry weight) than in the unburned Hadlock O horizon (0.07±0.07 ng Hg g^-1 dry weight). Similarly, Cadillac soils possessed a higher MeHg content (0.30 g MeHg ha^-1) than Hadlock soils (0.16 g MeHg ha^-1). The higher MeHg concentrations in Cadillac soils may reflect generally faster rates of microbial metabolism due to more rapid nutrient cycling and higher soil pH in the deciduous forest. In this research, we have shown that the amount of MeHg is not a function of the total pool of Hg in the watershed. Indeed, MeHg was inversely proportional to total Hg, suggesting that landscape factors such as soil pH, vegetation type, or land use history (e.g., fire) may be the determining factors for susceptibility to high Hg in biota.     

Adsorption of mercury compounds by tropical soils

Mercury adsorption of HgCl₂ and 2-methoxyethylmercury chloride (Aretan) (100 mg Hg L^?1) was measured for three soil profiles from Morogoro, Arusha, and Dar es Salaam in Tanzania. The adsorption was investigated for the physical, chemical, and mineralogical properties of the soils. All soil samples showed greater capacity for adsorption of Aretan than for HgCl₂. In the Morogoro profile Hg adsorption decreased with depth but in the other two soils, the minimum adsorption occurred in the third horizon and increased both upwards and downwards. In the Morogoro profile, Aretan adsorption correlated well with pH. Adsorption of both Aretan and HgCl₂ correlated well with the distribution of organic C and with the cation exchange capacity of the soils. In the Arusha and Dar es Salaam profiles Hg adsorption was not significantly correlated with any of the soil properties tested.     

Adsorption of mercury compounds by tropical soils II. Effect of soil: Solution ratio,ionic strength,pH, and organic matter

Mercury adsorbed from HgCl₂ and 2-methoxy-ethylmercury chloride (Aretan) solutions by three contrasting soils showed a dependence on soil: solution ratio and initial Hg concentration in soil solution. Changing the soil solution ratio from 1: 10 to 1 : 100 but keeping the initial concentration constant resulted in an increase in Hg adsorption from both Hg compounds. A similar change in soil: solution ratio accompanied by a decrease in initial concentration, on the other hand, resulted in decrease in Hg adsorption. Upon manipulating of the pH of the surface soils, adsorption of HgCl₂ at 100 mg Hg L^?1 concentration increased from about 701 :o over 95 mg Hg kg^?1 when pH was raised from 5.0 to 8.0. Precipitation of Hg may also have contributed to this trend. Aretan adsorption by these soils, on the other hand, changed little with change in pH. Removal of organic matter from soil resulted in large reductions of Hg adsorbed, as much as 95 % from the HgCl₂ solutions, but only up to 31 % from Aretan solutions. This suggests that organic matter in soil played a mayor role in the adsorption of inorganic Hg whereas the soils' mineral fractions were involved more in the adsorption of the organic Hg compound.     

Oxalic Acid Effect on Potassium Release from Typical Rice Soils of Kashmir

Batch experiments were employed to examine the influence of oxalic acid on release kinetics of potassium (K) from soils along with adsorption and desorption of soil K⁺. The soils used were three rice soils from high-, mid-, and low-altitude zones. The results showed that soil K extracted using 0.2 mol L^–1 oxalic acid was similar to that of 1 mol L^–1 boiling nitric acid (HNO₃). The relation between K release (y) and concentrations of oxalic acid (c) could be best described as y = a + b log c, whereas the best-fit kinetic equation of K release was y = a + b √t. The K release for soils was in the order Bonbagh > Ganasthan > Kreeri. An oxalic acid solution with low pH was able to release more K. Oxalic acid decreased soil K⁺ adsorption and increased desorption, the effect of which tended to be greater at lower pH.     

Partitioning of Hg Between Solid and Dissolved Organic Matter in the Humus Layer of Boreal Forests

The mobility of mercury (Hg) deposited on soils controls the concentration and toxicity of Hg within soils and in nearby streams and lakes, but has rarely been quantified under field conditions. We studied the in situ partitioning of Hg in the organic top layer (mor) of podsols at two boreal forest sites differing in Hg deposition and climatic regime (S. and N. Sweden, with pollution declining to the north). Soil solution leaching from the mor layer was repeatedly sampled using zero-tension lysimeters over 2 years, partly in parallel with tension lysimeters. Concentrations of Hg and dissolved organic carbon (DOC) were higher while pH was lower at the southern site (means ± SD: Hg?=?44?±?15 ng L^?1, DOC?=?63.0?±?31.3 mg L^?1, pH?=?4.05?±?0.53) than at the northern site (Hg?=?22?±?6 ng L^?1, DOC?=?41.8?±?12.1 mg L^?1, pH?=?4.28?±?0.43). There was a positive correlation over time between dissolved Hg and DOC at both sites, even though the DOC concentration peaked during autumn at both sites, while the Hg concentration remained more constant. This correlation is consistent with the expected strong association of Hg with organic matter and supports the use of Hg/C ratios in assessments of Hg mobility. In the solid phase of the overlying O_f layer, both Hg concentrations and Hg/C ratios were higher at the southern site (means ± SD: 0.34?±?0.06 μg g^?1 dw and 0.76?±?0.14 μg g^?1 C, respectively) than at the northern site (0.31?±?0.05 μg g^?1 dw and 0.70?±?0.12 μg g^?1 C, respectively). However, concentrations in the solid phase differed less than might be expected from the difference in current atmospheric input, suggesting that the fraction of natural Hg is still substantial. At both sites, Hg/C ratios in the upper half of the mor layer were only about two thirds of those in the lower half, suggesting that the recent decrease in anthropogenic Hg deposition onto the soil is offset by a natural downward enrichment of Hg due to soil decomposition or other processes. Most interestingly, comparison with soil leachate showed that the average Hg/C ratios in the dissolved phase of the mor layers at both sites did not differ from the average Hg/C ratios in the overlying solid organic matter. These results indicate a simple mobilisation with negligible fractionation, despite differences in Hg deposition patterns, soil chemistry and climatic regimes. Such a straight-forward linkage between Hg and organic matter greatly facilitates the parameterisation of watershed models for assessing the biogeochemical fate, toxic effect and critical level of atmospheric Hg input to forest soils.     

Production of gaseous mercury in tropical hydromorphic soils in the presence of ferrous iron: a laboratory study

In this paper, we demonstrate that reduction of Hg(II) to Hg⁰ under anaerobic conditions, followed by volatilization of Hg⁰ to the atmosphere, might be responsible for the removal of Hg from tropical hydromorphic soils. We conducted a series of kinetic batch experiments in which we added Hg(II) to anoxic suspensions of a soil clay fraction and haematite nanoparticles. The clay fraction came from three depths in a hydromorphic soil by the Leblond River in French Guiana, South America: close to the upper and lower boundaries (30–40 cm and 90–100 cm) and within the central part (60–70 cm) of the frequently water‐saturated clay horizon. We prepared a second set of soil clay fraction suspensions with Fe(III) citrate, whose reduction acted as a source of dissolved Fe(II) to investigate the influence of Fe(II) on the production of Hg⁰. Reduction of Hg(II) to Hg⁰ occurred with all samples amended with Fe(III) citrate. Laboratory experiments with haematite suspensions demonstrated that adsorption of Fe(II) to the haematite surface created very reactive sites for the reduction of Hg(II), while in the absence of haematite particles, no production of Hg⁰ occurred. The greatest production of Hg⁰ was found for the depth intervals 30–40 cm and 90–100 cm, where the total mercury concentration exhibits a local minimum. The observed pseudo‐first order rate constants for the 90–100 cm depth sample were close to rate constants reported for abiotic reduction of Hg(II) by Fe(II) adsorbed on mineral surfaces. Significant production of Hg⁰ was found for the 90–100 cm depth interval sample, both with and without Fe(III) citrate. A biotic pathway as well as abiotic reduction by Fe(II) might be involved in the reduction of Hg(II) to Hg⁰.