Estimation of buffering capacity of mangrove soils by using hydrophobic organic compounds,atrazine and linuron

Samples of two soils and two sediments collected at sites originating from mangrove forests in Thailand, were examined in terms of buffering capacity to organic compounds. Atrazine and linuron were used as representative hydrophobic organic compounds for estimating the buffering capacity by observing their adsorptive and desorptive behavior. The buffering capacity could be represented by the distribution of the adsorption ratio (AR) and desorption ratio (DR) as follows: AR (%) = (amount of herbicide adsorbed per unit weight of soil)/(initial amount of herbicide) x 100, and DR (%) = (amount of herbicide desorbed per unit weight of soil after herbicide desorption experiments) / (initial amount of adsorbed herbicide on soil) x 100. The soil under mangrove forests displayed a larger buffering capacity to atrazine and linuron. Compared with 42 soils from Japan, in terms of the adsorption proparty of atrazine and linuron, the mangrove soil ranked in a higher category on the classification of the Japanese soils. Thus, the importance of maintaining or recovering the mangrove forests to promote environmental conservation was emphasized.     

Relationship between Freundlich isotherm Coefficients,log K F and 1 / n for atrazine desorption from soils in Japan

Desorption experiments were conducted on 21 soils at 3 atrazine concentrations. The Freundlich isotherm was used to estimate atrazine desorption. For the relationship between Freundlich isotherm coefficients, log K _F and 1 / n, 1 / n was also represented by a linear regression of log K _F as in the case of atrazine adsorption. All the linear regression lines of desorption exhibited larger slopes and intercepts than those of adsorption. When the atrazine concentration was high, the slope and intercept values were smaller than those for the desorption regression lines. The results showed that the larger the capacity of a soil to adsorb atrazine, the lesser the amount of atrazine desorbed. For the cultivated soils except for Andisols, the percentages of atrazine taken from solutions using the sequential exchange method after the first adsorption experiments, were the same as those desorbed from soils in relation to the initial amount adsorbed. Thus, reversible adsorption occurred in the soils due to weak physical adsorption.     

吸附反应时间对潮土中除草剂阿特拉津吸附行为的影响

A batch experiment was performed to investigate nonequilibrium adsorption behavior of atrazine （2-chloro-4-ethylamino-6-isopropylamlno-1,3,5-triazlne） on a fluvo-aquic soil. The amount of atrazine sorbed increased with increasing adsorption contact periods. For a range of initial atrazlne concentrations, the percentage of atrazine sorbed within 24 h ranged from 24% to 77% of the observed total amount sorbed for the longest contact period; when adsorption contact periods were more than 72 h, the deviations in curves fitted using a nonlinear Freundllch equation gradually became less. The opposite trend was observed for the atrazine concentrations in solution. The effect of adsorption contact periods on atrazine adsorption behavior was evaluated by interpreting the temporal variations in linear and nonlinear Freundlich equation parameters obtained from the phase-distribution relationships. As the adsorption contact period increased, the nonlinear Freundlich capacity coefficient kf showed a significant linear increase （r^2 = 0.9063, P 〈 0.001）. However, a significant negative linear correlation was observed for the nonlinear coefficient n, a dimensionless parameter （r^2 = 0.5666, P 〈 0.05）. Furthermore, the linear distribution coefficient kd ranged from 0.38 to 1.44 and exhibited a significant linear correlation to the adsorption contact period （r^2 = 0.72, P 〈 0.01）. The parameters kf and n obtained from a time-dependent isotherm rather than the distribution coefficient kd estimated using the linear Freundlich equation were more appropriate to predict the herbicide residue in the field and thus more meaningful for environmental assessment.     

Parameterization of Freundlich adsorption isotherms for heavy metals in soils from an area with intensive livestock production

Adsorption coefficients are valuable tools used to estimate the environmental relevance of heavy metal contamination. However, their determination with batch experiments is laborious. Thus, attempts have been made to deduce these coefficients from soil parameters. However, the application of the resulting parameterized equations to different sets of samples has often yielded poor results. Hence, the objectives of the present study were (1) to deduce basic soil properties governing the coefficients of Freundlich adsorption isotherms for Cd, Cu, Ni, Pb, and Zn, and (2) to derive parameterized isotherms and examine their accuracy. For this purpose, 30 topsoil and nine subsoil samples were investigated which represented one Podzol‐Cambisol‐Gleysol soilscape in an area with intensive livestock production in Lower Saxony, Germany. Total background concentrations (aqua regia digestion) of heavy metals in topsoils ranged from 0.290 (Cd) to 19.2 mg kg^—1 (Zn) and exhibited elevated mobilizable proportions (NH₄EDTA pH 4.6 extract) of 17 (Ni) — 66 % (Zn) from the total concentration. Background concentrations were higher in topsoils than in subsoils by factors of 1.7 (Ni) — 28 (Zn). These differences were assigned to the special situation of heavy metal input mostly originating from animal excrements. The isotherms obtained by batch experiments showed larger coefficients K_F for partition among soil solid phase and soil solution in topsoils than in subsoils by a factor of 3.5. The coefficients of the isotherms were significantly correlated with routinely determined soil properties such as cation exchange capacity and pH (R = 0.36—0.89). Parameterized isotherms were calculated for each metal by inserting the relevant parameters in multiple linear regression equations. Among these parameters were the soil pH, cation exchange capacity, total metal concentration, and the concentrations of organic carbon, clay, fine silt, and various pedogenic oxides. The K_F values, separately calculated for topsoils and subsoils, agreed well with those determined by batch experiments (R = 0.63—0.97). Therefore, parameterized isotherms are valuable tools for the prediction of heavy metal partition in soils from one soilscape and for a risk assessment in the investigated, densely stocked area and similar areas.     

Boron adsorption and desorption in some acid soils of West Bengal,India

Laboratory and greenhouse experiments were conducted to determine the influence of soil properties on adsorption and desorption of boron (B) as well as to estimate the degree of reversibility of adsorption reactions. The utility of Freundlich and Langmuir equations for characterizing the plant availability of applied B in soils was established using soybean [Glycine max (L.) Merr.] as a test crop. The adsorption-desorption study revealed that Fe₂O₃ and clay were primarily responsible for retaining added B in all the 25 different soils under investigation. Organic carbon, pH and cation exchange capacity (CEC) positively influenced the adsorption of B while free Fe₂O₃, organic carbon and clay retarded release of B from these soils. The degree of irreversibility (hysteresis) of B adsorption/desorption increased with increase in organic carbon and CEC of these soils. Freundlich isotherm proved more effective in describing B adsorption in soils as compared to Langmuir equation. The split Langmuir isotherm demonstrated that any of the adsorption maxima, calculated from lower, upper or entire isotherm, could be of practical use. Contrary, bonding energy coefficient, calculated either at lower or higher equilibrium concentration failed to show any practical benefit. Regression models as a function of B application rate and adsorption equation parameters to predict B uptake from applied B, demonstrated the utility of Langmuir and Freundlich equation parameters.     

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.     

Evaluation of water flux prediction with heat-pulse technique in saturated soils

Heat-pulse technique (HPT) has shown promise for predicting soil water flux (J_w). This study evaluated the accuracy of HPT in predicting J_w in packed saturated columns of quartz, sand, silt loam, and sandy clay loam. J_w was predicted using the maximum dimensionless temperature differences (MDTD), ratio of downstream to upstream temperature increases (T_d/T_u), and an improved T_d/T_u method. Results indicated that J_w predictions had a good linear relationship with measurements (R² > 0.93). The HPT underestimated J_w to varying degrees, and the underestimations increased as J_w increased and soil texture became fine. The T_d/T_u method outperformed the MDTD and the improved T_d /T_u because of its higher accuracy, fewer parameters, and simpler calculations. The MDTD exhibited the poorest performance. In coarse-textured soil materials (e.g. quartz and sand), J_w predictions by the T_d/T_u method were most accurate, and even with high J_w (up to 72.4 μm s^?1), relative errors still remained within 9.8%. However, in fine-textured soil materials, J_w was underestimated significantly by 16.9% in silt loam and by 23.3% in sandy clay loam. The lower J_w limits were 1.0, 2.3, 2.4, and 4.0 μm s^?1 for quartz, sand, silt loam, and sandy clay loam, respectively (P > 0.05).     

Studies on the release of adsorbed copper by soils and compost

Copper deficiency has been observed in soils rich in organic matter such as peat or in light mineral soils derived from silica and carbonate rich sediment. The deficiency can be corrected by adding copper sulphate in different doses. Also, the unavailable copper can be made available by increasing the acidity of soils by some means. It has been suggested that copper forms complexes with organic compounds present in the soil and gets fixed by the mineral exchange materials, thereby becomes unavailable to plants.     

基于模糊逻辑的北京城市边缘区土壤重金属污染空间预测

Fuzzy classification combined with spatial prediction was used to assess the state of soil pollution in the peri-urban Beijing area. Total concentrations of As, Cr, Cd, Hg, and Pb were determined in 220 topsoil samples （0-20 cm） collected using a grid design in a study area of 2 600 kin2. Heavy metal concentrations were grouped into three classes according to the optimum number of classes and fuzziness exponent using the fuzzy comean （FCM） algorithm. Membership values were interpolated using ordinary kriging. The polluted soils of the study area induced by the measured heavy metals were concentrated in the northwest corner and eastern part, especially the southeastern part close to the urban zone, whereas the soils free of pollution were mainly distributed in the southwestern part. The soils with potential risk of heavy metal pollution were located in isolated spots mainly in the northern part and southeastern corner of the study region. The FCM algorithm combined with geostatistical techniques, as compared to conventional single geostatistical kriging methods, could produce a prediction with a quantitative uncertainty evaluation and higher reliability. Successful prediction of soil pollution achieved with FCM algorithm in this study indicated that fuzzy set theory had great potential for use in other areas of soil science.     

An assessment of potential pesticide transmission,considering the combined impact of soil texture and pesticide properties: A meta-analysis

Pesticides are widely employed as a cost-effective means of reducing the impacts of undesirable plants and animals. The aim of this paper is to develop a risk ranking of transmission of key pesticides through soil to waterways, taking into account physico-chemical properties of the pesticides (soil half-life and water solubility), soil permeability, and the relationship between adsorption of pesticides and soil texture. This may be used as a screening tool for land managers, as it allows assessment of the potential transmission risks associated with the use of specified pesticides across a spectrum of soil textures. The twenty-eight pesticides examined were differentiated into three groups: herbicides, fungicides and insecticides. The highest risk of pesticide transmission through soils to waterways is associated with soils containing <20% clay or >45% sand. In a small number of cases, the resulting transmission risk is not influenced by soil texture alone. For example, for Phenmedipham, the transmission risk is higher for clay soils than for silt loam. The data generated in this paper may also be used in the identification of critical area sources, which have a high likelihood of pesticide transmission to waterways. Furthermore, they have the potential to be applied to GIS mapping, where the potential transmission risk values of the pesticides can be layered directly onto various soil textures.     

Irrigation with brackish water modifies the boron requirement of mungbean (Vigna radiata L.) on typic calciargid

The boron (B) sufficiency range for plant growth is narrow and its management is problematic under brackish irrigation water. This study was conducted to evaluate the B requirement of mungbean at different sodium adsorption ratios of irrigation waters (SAR_iw) [control, 8 and 16 (mmol_c L^?1)^1/2]. The boron adsorption characteristics of a loamy soil were first determined in the laboratory by equilibrating 2.5 g soil with 0.01 M CaCl₂ solution containing different B levels. Boron rates for a pot study were computed against different soil solution levels by fitting sorption data in a modified Freundlich model [x/m = K _f (EBC)^1/n ]. The maximum increase in shoot dry matter was 11.9% when B was applied at 1.29 mg kg^?1 soil at control SAR_iw. Visual leaf B toxicity symptoms appeared at higher B rates and became severe at higher SAR_iw. By contrast to Ca, shoot concentrations of B and Na increased significantly with B application and SAR_iw. For optimum shoot growth, internal and external B requirements were 25 mg B kg^?1 shoot dry matter and 0.39 mg B L^?1 soil solution, respectively, at control SAR_iw. At higher SAR_iw, a lower concentration of B in plant shoots and soil solution had an inhibitory effect on plant growth.     

纳米粘土矿物对阿特拉津的吸附-解吸特性研究

采用批量平衡实验,研究了纳米粘土矿物与原粘土矿物对除草剂阿特拉津的吸附解吸特陛。结果表明,粘土矿物对阿特拉津的吸附-解吸均能用Freundlich方程很好地拟合。随着溶液中阿特拉津浓度的增加,粘土矿物对阿特拉津的吸附量增加;粘土矿物粒径越小,吸附量越大,纳米粘土矿物的吸附量显著大于原粘土矿物。粘土矿物对阿特拉津吸附量大小顺序为：纳米SiO2）纳米蒙脱石〉凹凸棒石〉蒙脱石〉SiO2。粘土矿物对阿特拉津的解吸表现出一定的滞后效应,即粘土矿物吸附的阿特拉津越多,解吸的越少。粘土矿物对阿特拉津的解吸率大小顺序为：SiO2〉凹凸棒石〉纳米蒙脱石〉纳米SiO2〉蒙脱石。     

Effect of low-molecular-weight organic acids on Cl- adsorption by variable charge soils

Low-molecular-weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes.The objective of the present paper was to evaluate effect of two LMW organic acids, citric acid and oxalic acid, on Cl^- adsorption by three variable charge soils, a latosol, a lateritic red soil and a red soil, using a batch method. The results showed that the presence of citric acid and oxalic acid led to a decrease in Cl- adsorption with larger decreases for citric acid. Among the different soils Cl- adsorption in the lateritic red soil and the red soil was more affected by both the LMW organic acids than that in the latosol.     

土壤磷酸盐的吸收对Cu2+二次吸附动力学的影响

The effects of sorbed phosphate on the kinetics of Cu^2 secondary adsorption on three major types of soils in southern and Central China were studied using the batch method and flow (or miscible displacement) techniques.Both of the methods showed that diffusions were the ratedetermining steps in the Cu^2 adsorption by the soils.By the flow method,the course of Cu^2 adsorption kinetics consisted of two steps-sn initial rapid process and a later slow process of Cu^2 adsorption;while by the batch method,the 90% of Cu^2 adsorption reaction was found to finish within first 1 minute.The results obtained using the flow method also indicated that for red soil and yellow-brown soil ,Cu^2 adsorptions during the initial reaction periods were restrained when the soils sorbed phosphate,whereas the adsorption reactions were stimulated at the final time,For grey Chao soil,sorbed phosphate retarded the Cu^2 adsorption in the whole reaction period.The results obtained using the batch method and low techniques all implied that the different effects of sorbed phosphate would be attributed to its effects on Cu^2 ion diffusion in soil solution.     

土壤镉吸附的研究进展

综述了土壤镉吸附的机理和土壤pH、有机质含量、粘粒矿物类型及含量、土壤溶液中竞争性阳离子、共存阴离子、土壤温度等土壤性质对土壤镉吸附的影响；总结了土壤镉的吸附量随土壤pH增加、温度升高及有机质、铁锰氧化物和粘土矿物含量增加而增加的机理；竞争性阳离子的存在抑制镉的吸附，土壤溶液中共存阴离子对镉吸附的影响取决于阴离子种类和土壤类型。     

pH对针铁矿表面磷酸盐吸附的化学形态的影响

Chemical forms of the phosphate adsorbed on goethite surfaces and characteristics of the coordinate groups which exchange with P on goethite surfaces in solutions with different pll values were investigated.Results showed that the chemical forms of P on goethite surfaces changed from the dominance of monodentate corrdination to that of bidentate one with increasing pH of the solution.By influencing types of phosphate ions in solutions,pH affected the chemical forms of P on goethite surfaces,The amount of OH^- displaced by phosphae on goethite surfaces was the most at pH 7.0,the second at pH 9.0,and the least at pH 4.5.     

粘土土壤孔隙大小分布及其与土壤有机质的相关性

Soil pore size distribution(PSD) directly influences soil physical,chemical,and biological properties,and further knowledge of soil PSD is very helpful for understanding soil functions and processes.In this study,PSD of three clayey soils collected from the topsoil(0-20 cm) of Vertisols in Northern China was analyzed using the N_2 adsorption(NA) and mercury intrusion porosimetry(MIP) methods.The effect of soil organic matter(SOM) on the PSD of clayey soils was also evaluated.The differential curves of pore volume of clayey soils by the NA method exhibited that the pores with diameter 0.01 μm accounted for more than 50%in the pore size range of 0.001 to 0.1 μm.The differential pore curves of clayey soils by the MIP method exhibited three distinct peaks in pore size range of 60 to 100,0.3 to 0.4 and 0.009 to 0.012 μm,respectively.In the three clayey soils,the ultramicropores(5-0.1μm) were determined to be the main pore class(on average 35.5%),followed by macropores( 75 μm,31.4%),cryptopores(0.1-0.007μm,16.0%),micropores(30-5 μm,9.7%) and mesopores(75-30 μm,7.3%).The SOM greatly affected the pore structure and PSD of aggregates in clayey soils.In particular,SOM removal reduced the volume and porosity of 5-100 μm pores while increased those of 5 μm pores in the 5-2 and 2-0.25 mm aggregates of clayey soils.The increase in the volume and porosity of 5 μm pores may be attributed to the disaggregation and partial emptying of small pores caused by the destruction of SOM.