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基于小白菜Cd吸收推算土壤Cd安全阈值 总被引：3，自引：0，他引：3
LU Junhe YANG Xinping MENG Xuchao WANG Guoqing LIN Yusuo WANG Yujun ZHAO Fangjie 《土壤圈》2017,27(3):475-481
Cadmium(Cd), a common toxic heavy metal in soil, has relatively high bioavailability, which seriously threatens agricultural products. In this study, 8 different soils with contrasting soil properties were collected from different regions in China to investigate the Cd transfer coefficient from soil to Chinese cabbage(Brassica chinensis L.) and the threshold levels of Cd in soils for production of Chinese cabbage according to the food safety standard for Cd. Exogenous Cd(0–4 mg kg~(-1)) was added to the soils and equilibrated for 2 weeks before Chinese cabbage was grown under greenhouse conditions. The influence of soil properties on the relationship between soil and cabbage Cd concentrations was investigated. The results showed that Cd concentration in the edible part of Chinese cabbage increased linearly with soil Cd concentration in 5 soils, but showed a curvilinear pattern with a plateau at the highest dose of exogenous Cd in the other 3 soils. The Cd transfer coefficient from soil to plant varied significantly among the different soils and decreased with increasing soil p H from 4.7 to 7.5. However, further increase in soil pH to 8.0 resulted in a significant decrease in the Cd transfer coefficient. According to the measured Cd transfer coefficient and by reference to the National Food Safety Standards of China, the safety threshold of Cd concentration in soil was predicted to be between 0.12 and 1.7 mg kg~(-1) for the tested soils. The predicted threshold values were higher than the current soil quality standard for Cd in 5 soils, but lower than the standard in the other 3 soils. Regression analysis showed a significant positive relationship between the predicted soil Cd safety threshold value and soil p H in combination with soil organic matter or clay content. 相似文献
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A study was carried out on the transfer of native and added Ni towards plant both in different soils and at different time by using 63Ni tracer technique. The transfer of added Ni in soil was greater than native Ni and declined as time increased. The mobility was greater for soluble plus exchangeable fraction of soil Ni but very smaller for residual and Fe/Mn oxide bound fractions. These indicated that Ni was more mobile and more harmful in soils with a low pH and/or low content of Fe/Mn oxides. 相似文献
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施用污泥后石灰性土壤中铜、锌、镉的植物有效性 总被引：2，自引：0，他引：2
The toxicity of trace elements (TEs), such as copper (Cu), zinc (Zn), and cadmium (Cd), often restrict land application of sewage sludge (SS) and there was little information about soil-plant transfer of TEs in SS from field experiments in China. In this study pot and field experiments were carried out for 2 years to investigate the phytoavailability of TEs in calcareous soils amended with SS. The results of the pot experiment showed that the phytoavailability of Zn and Cu in the SS was equal to 53.4%-80.9% and 54.8%-91.1% of corresponding water-soluble metal salts, respectively. The results from the field experiment showed that the contents of total Zn, Cu, and Cd in the soils increased linearly with SS application rates. With increasing SS application rates, the contents of Zn and Cu in the wheat grains initially increased and then reached a plateau, while there was no significant change of Cd content in the maize grains. The bioconcentration factors of the metals in the grains of wheat and maize were found to be in the order of Zn > Cu > Cd, but for the straw the order was Cd > Cu > Zn. It was also found that wheat grains could accumulate more metals compared with maize grains. The results will be helpful in developing the critical loads of sewage sludge applied to calcareous soils. 相似文献
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A combined model of solute transport and water flow was developed to simulate the migration of methanol, a soluble organic chemical, in unsaturated soil zone. The solute transport equation considered convective-dispersive transport in the liquid phase as well as diffusion in the gas phase. The effect of rainfall and evapotranspiration on transport was considered at the boundary conditions of the governing equations. Data on the characteristics of a loam soil and the climatic conditions in southern California were also introduced to compare the results with those from a study in the USA in which the profiles of methanol distribution and water content in the soil zone at different times had been depicted. This comparison showed that there was good agreement between the two studies. The results showed that methanol contamination reached a depth of about 250 cm after 8 760 h. In contrast, if rainfall and evapotranspiration were not considered, the depth was only about 140 cm. The model therefore confirmed that rainfall strongly affected solute transport. 相似文献
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红壤中水热耦合转化的实验和数值模拟研究 总被引：1，自引：0，他引：1
Coupled transfer of soil water and heat in closed columns of homogeneous red soil was studied under laboratory conditions.A coupled model was constructed using soil physical theory,empirical equations and experimental data to predict the coupled transfer.The results show that transport of soil water was affected by temperaature gradient,and the largest net water transport was found in the soil column with initial water content of 0.148m^3m^-3,At the same time,temperature changes with the transport of soil water was in a nonlinear shape as heat parameters wre function of water content,and the changes of temperature were positively correlated with the net amount of water transported.Numerical modelling results show that the predicted values of temperature distribution were close to the observed values,while the predicted values of water content exhibited limited deviation at both ends of the soil column due to the slight temperature changes at both ends .It WAS indicated that the model proposed here was applicable. 相似文献
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Knowledge of the soil water characteristic curve is fundamental for understanding unsaturated soils. The objective of this work was to find scanning hysteresis loops of two fine textured soils at water potentials below wilting point. This was done by equilibration over NaCl solutions with water potentials of -6.6 to -18.8 MPa at 25 ℃. When cycled repeatedly through a series of potentials in the range noted previously both soils exhibited a hysteresis effect. The experimental differences in water content between the drying and wetting soils at the same water potential were much too large to be accounted for by failure to allow sufficient time to attain equilibrium as predicted by the exponential decay model. The wetting versus drying differences were relatively small, however, at only 4 mg g^-1 or less in absolute terms and about 3% of the mean of wetting and drying, in relative terms. Hysteresis should be a consideration when modeling biological and physical soil processes at water contents below the wilting point, where small differences in water content result in large potential energy changes. 相似文献
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A long term simulation test on salt-water dynamics in unsaturated soils with different groundwater depths and soil texture profiles under stable evaporation condition was conducted.Salinity sensors and tensiometers were used to monitor salt and water variation in soils.The experiment revealed that in the process of fresh groundwater moving upwards by capillary rise in the column,the salts in subsoil were brought upwards and accumulated in the surface soil,and consequently the salinization of surface soil took place.The rate of salt accumulation is determined mainly by the volume of capillary water flow and the conditions of salts contained in the soil profile.Water flux in soils decreased obviously when groundwater depths fell below 1.5m.When there was an interbedded clay layer 30cm in thickness in the silty loam soil profile or a clay layer 100cm in thickness at the top layer,the water flux was 3-5 times less than in the soil profile of homogeneous silty loam soil.Therefore,the rate of salt accumulation was decreased and the effect of variation of groundwater depth on the water flux in soils was weakened comparatively.If there was precipitation or irrigation supplying water to the soil,the groundwater could rarely take a direct part in the process of salt accumulation in surface soil,especially,in soil profiles with an interbedded stratum or a clayey surface soil layer. 相似文献
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A study was carried out on the transfer of native and added Ni towards plant both in different soils and at different time by using ^63 Ni tracer technique.The transfer of added Ni in soil was greater than native Ni and declined as time increased.The mobility was greater for soluble plus exchangeable fraction of soil Ni but very smaller for residual and Fe/Mn oxide bound fractions.These indicated that Ni was more mobile and more harmful in soils with a low pH and /or low content of Fe/Mn oxides. 相似文献
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在法国前铅和锌冶炼厂附近的城市土壤重金属的污染、分离和利用 总被引：1，自引：0，他引：1
smelters in Northern France were studied by analysing the chemical forms of these metals and evaluating their phytoavailability. These metals were determined using flame or electrothermal absorption atomic spectrometry （FAAS or ETAAS）, depending on their concentration levels. After optimisation of the ETAAS method, characteristic mass of In in water and aqua regia were 9.9 and 18 pg, respectively, showing the high sensitivity of the analytical Soil contamination by metals from anthropogenic activities （e.g., mining and smelting） is a major concern for the environment and human health. Environmental availability of cadmium （Cd）, lead （Pb）, zinc （Zn）, copper （Cu）, and indium （In） in 27 urban soils located around two former Pb and Zn smelters in Northern France were studied by analysing the chemical forms of these metals and evaluating their phytoavailability. These metals were determined using flame or electrothermal absorption atomic spectrometry （FAAS or ETAAS）, depending on their concentration levels. After optimisation of the ETAAS method, characteristic mass of In in water and aqua regia were 9.9 and 18 pg, respectively, showing the high sensitivity of the analytical procedure. Metal partitioning was conducted using a four-step sequential extraction procedure. The results showed that Cd and Zn were mainly in the acid-extractable and reducible forms in the urban soils studied. In contrast, Pb and In were largely in the reducible fraction. However, in some samples, the amount of In extracted in the residual or exchangeable fraction was higher than that in the reducible fraction. Copper was mainly found in the reducible and residual fractions. A pot experiment was conducted in a glasshouse with seven soils （six contaminated and one uncontaminated） and two plant species, ryegrass and lettuce. The results showed transfer of metals from the contaminated soils to the shoots of ryegrass and the edible part of lettuce. The metal bioconcentration factor was in the order of Cd Cu > In > Zn Pb for lettuce leaves, whereas for ryegrass shoots, three orders were found, Cd > Zn > Cu In > Pb, Cd ≥ In > Zn > Cu Pb, and Zn > Cd > Cu > In > Pb, depending on the physico-chemical properties of the soils, such as pH, cation exchange capacity, carbonates, and organic matter. It was established that the metal toxicity was related to the contamination levels and the physico-chemical properties, including pH, organic matter, and in a lesser extent, Ca, Mg, and phosphorus contents, of the soils. However, it was shown that lettuce could grow on soils having high Cd and CaCO3 contents. Cadmium was one of the most available metals while Pb was always the least available in the soils studied. 相似文献
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Water repellency （WR） is a phenomenon known from many soils around the world and can occur in arid as well as in humid climates; few studies, however, have examined the effect of soil WR on the soil-plant-atmosphere energy balance. The aim of our study was to estimate the effects of soil WR on the calculated soil-atmosphere energy balance, using a solely model-based approach. We made out evapotranspiration to have the largest influence on the energy balance; therefore the effect of WR on actual evapotranspiration was assessed. To achieve this we used climate data and measured soil hydraulic properties of a potentially water-repellent sandy soil from a site near Berlin, Germany. A numerical 1D soil water balance model in which WR was incorporated in a straightforward way was applied, using the effective cross section concept. Simulations were carried out with vegetated soil and bare soil. The simulation results showed a reduction in evapotranspiration of 30-300 mm year-1 （9%-76%） at different degrees of WR compared to completely wettable soil, depending on the severity degree of soil WR. The energy that is not being transported away by water vapor （i.e., due to reduced evapotranspiration） had to be transformed into other parts of the energy balance and thus would influence the local climate. 相似文献
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制冷系统不同表面能微通道的流动沸腾传热特性试验 总被引：3，自引：3，他引：0
为了研究微通道壁面特性对流动沸腾传热的影响,该文以具有不同表面能的微通道为研究对象,制冷剂R141b为试验工质,在不同热流密度、质量流率下对微通道内的沸腾传热特性进行了试验探究。结果表明:在该试验工况下,质量流率的增加有利于沸腾传热,但微通道内过冷段长度也相应增加;在微通道饱和沸腾区传热系数较稳定,但沿工质流动方向有缓慢降低的趋势;相比于表面能为23.93 m N/m的3#的微通道,表面能为60.03和49.54 m N/m的1#和2#微通道沸腾传热系数分别提高18.42%和9.28%;根据试验值与关联式预测值的对比情况,对Lazarek关联式进行修正,拟合得到能很好预测该试验各工况下的传热关联式,平均绝对误差为9.76%。该研究为微通道换热器的设计提供了参考。 相似文献
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对土壤中热和水分迁移过程进行了数值模拟及实验验证。理论上,通过对土壤内热和水分迁移机理分析,根据质量守恒和能量守恒原理,建立了土壤非饱和区热和水分迁移的理论模型。并对大气对流条件下土壤内热和水分迁移进行了数值模拟。实验上,对大气对流环境条件下土壤内热、水分迁移过程进行了研究。通过数值计算和实验测量,获得了不同大气对流速度作用下土壤中温度、含水率分布。 相似文献
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干燥现象是物系对应外部约束条件的自发过程,是各种因素同时作用的结果。多种传递行为并存,得不到严格意义的传递系数的数学解。基于扩散动力学建立的干燥机理函数,又存在活化能、指前因子和过程指数难以定量等问题。如何获得干燥过程的理论解是长期以来干燥研究领域的重要命题。该研究以水分活度统一特征,以自由能传递和转换为统一尺度,建立干燥特征函数,说明基于物料的最大汽化速率、初始态水分活度、相平衡条件下的水分活度和介质的相对湿度,揭示实际物系状态变化规律和获得理论解的方法;给出自由含水比、干燥速率比和干燥速率随时间变化的数学解。该理论及方法不仅可以基于物系中的一个状态点,揭示出任意外部条件下的理论解,同时,按照水汽化、混合过程压力变化特征及其发生的位置,能够完整地解析出干燥过程物料内部的含水率偏差和水分活度分布;摆脱了基于单一行为描述的传递定率中的传递系数,对揭示物系传递机理,评价工艺系统能效,制定科学评价标准具有较高的理论价值,对指导工程实践具有重要的现实意义。 相似文献
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粮食干燥传递和转换特征及其理论表达 总被引：5，自引：5，他引：0
干燥是不同物系间多场协同作用的复合系统,期间发生的?传递和转换特征尚未揭示,工程应用存在不同场间的耦合关系及其作用效果定量表达的理论空缺。为此,该文基于?分析法,解析粮食与干燥介质间的?传递和转换特征,给出热?、流动?,扩散?及其?效率定量评价理论表达式,基于焓-含湿量状态参数图,分析干燥系统状态参数间的内在联系及相互制约关系。研究结果表明,干燥是热?、扩散?和流动?同时作用的结果,热?是水分汽化必须的有用能;扩散?源于粮食中多余的水分,扩散?效率取决于水蒸气的状态,在扩散过程中,温度场和压力场同时存在,温度梯度与水蒸汽压差方向相反时,强化?效率,一致时则弱化?效率;流动?维持了热?和扩散?传递所需的势差,没有流动?的存在和消耗,热?和湿?的传递则不能有效进行;在通风干燥系统中,含湿粮食和干燥介质是两种不同物系,两种物系之间存在的不平衡势是干燥?传递和转换的动力;干燥可以归结为含湿粮食趋向系统介质状态点的?传递和转换的过程;指出了?及?效率都是状态函数,在工程应用时,引入时间坐标,依据环境状态参数和粮食在特定系统中的状态变化特性,可以揭示出?流密度及其?效率变化特征,进而对其能量利用效果做出评价;通过系统的?理论表达及其?效率分析,可以清晰地呈现干燥系统最大?损部位及环节,为评价干燥系统能量利用水平提供了科学的依据,为干燥工艺系统优化指明了能量合理利用的技术途径。 相似文献
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本文建立了一个冻土水盐热运动的数学模型。为了考虑土壤冻结和化冻时冰—液相变的影响,在传统土壤热传导方程中加入了溶化潜热运动项和存传统土壤水分运动方程中加入了相变项,从而推导出了三个相互关联的冻土水盐热运动方程,并提出了描述冻土未冻水含量随土壤冻结温度而变化的土壤冻结特征曲线及其实验测定方法。这个模型既可适应于冻土,也可适应于未冻土。 相似文献
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相对湿度作为干燥介质的重要参数,对干燥热质传质过程和干燥品质具有显著影响。但由于相对湿度对干燥过程的影响机理及优化调控机制尚不明确,导致相对湿度的调控方式多依靠经验,造成干燥效率低、品质差、能耗高等问题。对于传质过程,降低相对湿度能够增大对流传质系数,加快物料表面水分蒸发;而对于传热过程,升高相对湿度能够增大对流传热系数,加快物料升温速率。相对湿度较高时,物料升温速率快,内部水分迁移量增大,但表面水分蒸发量较小;而当相对湿度较低时,物料升温速率较慢,内部水分迁移量较小,但表面水分蒸发量较大。相对传热和传质过程的影响此消彼长,互相耦合。高相对湿度主要体现为对传热过程的影响,低相对湿度主要体现为对传质过程的影响。高相对湿度能够抑制物料表面的结壳,并能够提高复水性,降低收缩率。阶段降湿及多阶段降湿干燥方式下物料表面形成和保持了蜂窝状多孔结构,能够提高干燥效率和品质。基于监测物料温度的相对湿度调控方式被验证为较忧的相对湿度控制方式。阶段降湿干燥方式适用性的实质为：干燥过程中所体现出的对流传热热阻和内部导热热阻的相对大小,及对流传质阻力和内部传质阻力的相对大小,不同干燥条件和物料种类、厚度会影响以上传热传质阻力的大小,从而呈现出不同适应性的结果。当阶段降湿干燥过程中传热毕渥数>1且传热毕渥数>0.1时,说明阶段降湿干燥过程适用于此物料的干燥。该文综合论述了相对湿度对果蔬热风干燥过程中热质传递及干燥品质的影响,优化调控策略及适用性范围4个方面内容,明确了果蔬热风干燥过程中相对湿度的影响机理,为相对湿度的优化调控提供理论依据和技术支持。 相似文献