Agricultural sustainability in a sensitive environment--a case analysis of Loess Plateau in China

Loess Plateau,an arid and semi-arid region in Northwest China,is well-known for its most serious soil erosion in terms of sediment yield each year.Soil erosion,which is intensified by agricultural activities,is the major factor influencing sustainable agriculture development in this region.It reduces productivity by removing nutrients and especially reducing water availability that is essential for crop production in the area.It also brings about off-site costs by demanding more efforts for maintenance of banks and dame along Yellow River through raising the riverbed with sediment.Climate is capricious and extreme weather conditions occur frequently,which impairs normal agricultural production with erosion and also decrease of water availability.Extensive way of farming still dominates on the Loess Plateau,which canot produce satisfying economic results and needs to be improved or altered.Conventional agricultural production pattern needs to be reconsidered for husbandry has not been granted its due position.Agriculture is the backbone of economy.Poor agricultural production impedes economic development and vice versa,backward economy also influences the advancement of agriculture.Besides a large population,education status of farmers is another threshold that requires being resolved for a sustainable agriculture.Although conventional agriculture has been practiced there for more than 5000years,now it cannot meet the demand for food and fiber by the increasing population and some of its farming practices are contributing to environmental degradation directly or indirectly and can sustain no longer.Agriculture on Loess Plateau needs to find its own way of sustainability.To work toward a sustainable agriculture,chances and challenges both indwell on Loess Plateau.     

Phytoremediation and its models for organic contaminated soils

Soil pollution has been attracting considerable public attentions over the last decades.Sorts of traditional physiochemical methods have been used to remove th organic pollutants from soils.However,the enormous costs and low efficiencies associated with these remediation technologies limit their availabilities.Phytoremediation is an emerging technology that uses plants to cleanup pollutants in soils.As overwhelmingly positive results have been shown,phytoremediation is a most economical and effective remediation technique for organic contaminated soils.In this paper phytoremediation and its models for organic contaminated soils are viewed.The mechanisms of phytoremediation mainly include the direct plant uptake of organic pollutants,degradation by plant-derived degradative enzymes,and stimulated biodegradation in plat rhizosphere.Phytoremediation efficiency is close related to physicochemical properties of organic pollutants, environmental characteristics,and plant types.It is no doubt that soil amendments such as surfactants improve the solubilities and availabilities of organic pollutants in soils.However,little information is available about effects of soil amendments on phytoremediation efficiencies.Phytoremediation models have been developed to imulate and predict the environmental behavior of organic pollutants,and progress of models is illustrated.In many ways phytoremediation is still in its initial stage,and recommendations for the future for the future research on phytoremediation are presented.     

Study on the toxicity of acid rain to microbiota in soils

With simulated acid rain and acidification, the soils from both Nanning and Liuzhou municipalities, Guangxi Zhuang Nationality Autonomous Region have been studied to determine the counts of azotobacter, bacteria, actinomyces and the activity of urease in soils, and the changes in respiratory intensity of soil so as to identify the toxicity of acidic substances to microbiota and enzyme in such soils. The concept of the critical pH of toxicity has been developed and used to discuss the representation of the concept, the basis on which the soil treated with simulated acid rain can be taken as an object of study, and the criteria for the identification of toxicity. Based on that as mentioned above, it was found that acid rain behaved to have toxicity to the microbiota in soils from Liuzhou other than from Nanning. The findings may be regarded as an objective basis to study the toxicity of acidic substances to microbiota and enzyme in soils in this region.     

Changes in the sorption, desorption, distribution, and availability of copper, induced by application of sewage sludge on Chilean soils contaminated by mine tailings

The effect of mine tailings and sewage sludge was evaluated on sorption, desorption, availability and distribution of copper in two soils, one high (sandy soil) and one low in copper (clay soil). In both soils contaminated by mine tailings the copper sorption capacity and the affinity of the substrate for the metal decreased substantially compared to the uncontaminated soils, however, the sorption remained always high in the clay soil substrates. In the substrates with sandy soil, the high Cu content and lower clay content were determining factors in the lower magnitude of the sorption. Similarly, metal desorption was closely related to these two parameters, and it was higher in clay soil with lower pH. In general, the application of sewage sludge favored the sorption of Cu in soils contaminated and uncontaminated with mine tailings, and in all cases desorption decreased, an effect that remained for at least 30 days. Simple extraction of Cu with CaCl2 and diethylenetriaminepentaacetic acid gave contradictory results, so a careful choice of the procedure is required, depending on the level of metal in the soil and on the acting principle of the extracting agent. In that relation, more complete information on the changes in the metal forms was obtained by application of the sequential extraction procedure proposed by the European Community Bureau of Reference.     

MINTEQ modeling for evaluating the leaching behavior of heavy metals in MSWI fly ash

At present,all kinds of municipal solid waste incineration (MSWI) fly ash stabilization technology has been reported and successfully applied in many countries.However,leaching procedures are very different that the technologies lack uniform standard,and it is even impossible to predict the long-term stabilization.Geochemical model can explain the environmental stabilization based on chemical phase and thermodynamic crystal structure,and it is also able to guide the development of environment-friendly stabi...     

Substrate-induced changes in microbial community-level physiological profiles and their application to discriminate soil microbial communities

The addition of simple substrates could affect the microbial respiration in soils. This substrate-induced respiration is widely used to estimate the soil microbial biomass, but little attention has been paid to its influence on the changes of community-level physiological profiles. In this study, the process of microbial communities responding to the added substrate using sole-carbon-source utilization （BIOLOG） was investigated. BIOLOG is biased toward fast-growing bacteria; this advantage was taken to detect the prompt response of the active microbial communities to the added substrate. Four soil samples from agricultural fields adjacent to heavy metal mines were amended with L-arginine, citric acid, or D-glucose. Substrate amendments could, generally, not only increase the metabolic activity of the microbial communities, but also change the metabolic diverse patterns compared with no-substrate control. By tracking the process, it was found that the variance between substrate-induced treatment and control fluctuated greatly during the incubation course, and the influences of these three substrates were different. In addition, the application of these induced changes to discriminate soil microbial communities was tested. The distance among all samples was greatly increased, which further showed the functional variance among microbial communities in soils. This can be very useful in the discrimination of microbial communities even with high similarity.     

Impact of wastewater reuse on cobalt status in Egyptian environment

Cobalt is used in the manufacture of alloys,catalysts in the petroleum industry,catalytic converters,and paint pigments.Thus the potential for Co releases into the environment is highly increased.Use of waste sludges and sewage effluent to fertilize and irrigate soils has also increased soil Co concentrations.Total cobalt contents of alluvial delta soil of Egypt show considerable variation ranging from 13.1 to 64.7 ppm.The impact of either wastewater irrigation or industrial activities on soil total Co was obvious due to accumulation of organic matter and solid waste in the surface soil samples.Food crops and vegetables should not be grown on soil highly contaminated by Co.It is noteworthy that the delayed neutron activation analysis(DNAA)technique could be used successfully for total Co determination due to its high sensitivity.It is quit clearly that dust samples of Cairo City contains higher Co level.as compared to Suez Canal Region(Ismailia.Port Said and El-Suez cities).The high values in Cairo City may be due to the existence of industries around the city and the intensive traffic.To minimize Co environmental hazards,waste effluents should be treated on site.Thus,levels of potentially toxic Co needs to be continuously monitored and should be removed during several treatment processes before the disposal of these wastes.     

Effect of ionic strength on adsorption of As（Ⅲ） and As（Ⅴ） on variable charge soils

The study was to investigate the adsorption behavior of arsenite (As(Ⅲ)) and arsenate (As(Ⅴ)) on two variable charge soils, i.e., Haplic Acrisol and Rhodic Ferralsol at different ionic strengths and pH with batch methods. Results indicated that the amount of As(Ⅲ) adsorbed by these two soils increased with increasing solution pH, whereas it decreased with increasing ionic strength under the acidic condition. This suggested that As(Ⅲ) was mainly adsorbed on soil positive charge sites through electrostatic attraction under the acidic condition. Moreover, intersects of As(Ⅴ) adsorption-pH curves at different ionic strengths (a characteristic pH) are obtained for both soils. It was noted that above this pH, the adsorption of As(Ⅴ) was increased with increasing ionic strength, whereas below it the reverse trend was true. Precisely the intersect pH was 3.6 for Haplic Acrisol and 4.5 for Rhodic Ferralsol, which was near the values of PZSE (soil point of zero salt effect) of these soils. The effects of ionic strength and pH on arsenate adsorption by these soils were interpreted by the adsorption model. The results of zeta potential suggested that the potential in adsorption plane becomes less negative with increasing ionic strength above soil PZSE and decreases with increasing ionic strength below soil PZSE. These results further supported the hypothesis of the adsorption model that the potential in the adsorption plane changes with ionic strength with an opposite trend to surface charge of the soils. Therefore, the change of the potential in the adsorption plane was mainly responsible for the change of arsenate adsorption induced by ionic strength on variable charge soils.     

Adsorption–desorption behavior of atrazine on agricultural soils in China

Adsorption and desorption are important processes that affect atrazine transport,transformation,and bioavailability in soils.In this study,the adsorption–desorption characteristics of atrazine in three soils(laterite,paddy soil and alluvial soil) were evaluated using the batch equilibrium method.The results showed that the kinetics of atrazine in soils was completed in two steps:a"fast" adsorption and a "slow" adsorption and could be well described by pseudo-second-order model.In addition,the adsorption equilibrium isotherms were nonlinear and were well fitted by Freundlich and Langmuir models.It was found that the adsorption data on laterite,and paddy soil were better fitted by the Freundlich model;as for alluvial soil,the Langmuir model described it better.The maximum atrazine sorption capacities ranked as follows:paddy soil alluvial soil laterite.Results of thermodynamic calculations indicated that atrazine adsorption on three tested soils was spontaneous and endothermic.The desorption data showed that negative hysteresis occurred.Furthermore,lower solution pH value was conducive to the adsorption of atrazine in soils.The atrazine adsorption in these three tested soils was controlled by physical adsorption,including partition and surface adsorption.At lower equilibrium concentration,the atrazine adsorption process in soils was dominated by surface adsorption;while with the increase of equilibrium concentration,partition was predominant.     

Qualitative analysis and quantitative simulation on Yin-Huang water salinization mechanism in Bei-Da-Gang reservoir

Yellow River water transfer for Tianjin is important in solving the water shortage in Tianjin, which facilitate economic development and social progress for many years. Fresh water drawn from Yellow River（ i. e., Yin-Huang water） becomes saltier and saltier when being stored in the Bei-Da-Gang reservoir. We qualitatively analyze the water salinization mechanism based on mass transfer theory. The main factors are salinity transfer of saline soil, evaporation concentrating, and the agitation of wind. A simulative experimental pond and an evaporation pond were built beside the Bei-Da-Gang reservoir to quantitatively investigate the water salinization based on water and solute balance in the simulative pond. 80% of increased [Cl^-] is due to the salinity transfer of the saline soil and the other 20% is due to evaporation concentrating, so the former is the most important factor. We found that the salinization of Yin-Huang water can be described with a zero-dimension linear model.     

Agriculture sustainability in a sensitive environment--a case analysis of Loess Plateau in China

Loess Plateau, an arid and semi-arid region in Northwest China, is well-known for its most serious soil erosion in terms of sediment yield each year. Soil erosion, which is intensified by agricultural activities, is the major factor influencing sustainable agriculture development in this region. It reduces productivity by removing nutrients and especially reducing water availability that is essential for crop production in the area. It also brings about off-site costs by demanding more efforts for maintenance of banks and dams along Yellow River through raising the riverbed with sediment. Climate is capricious and extreme weather conditions occur frequently, which impairs normal agricultural production with erosion and also decrease of water availability. Extensive way of farming still dominates on the Loess Plateau, which cannot produce satisfying economic results and needs to be improved or altered. Conventional agricultural production pattern needs to be reconsidered for husbandry has not been granted its due position. Agriculture is the backbone of economy. Poor agricultural production impedes economic development and vice versa, backward economy also influences the advancement of agriculture. Besides a large population, education status of farmers is another threshold that requires being resolved for a sustainable agriculture.Although conventional agriculture has been practiced there for more than 5000 years, now it cannot meet the demand for food and fiber by the increasing population and some of its farming practices are contributing to environmental degradation directly or indirectly and can sustain no longer. Agriculture on Loess Plateau needs to find its own way of sustainability. To work toward a sustainable agriculture, chances and challenges both indwell on Loess Plateau.     

风蚀与环境若干问题及思考

本文从风蚀对植物生长环境的影响、风蚀与尘暴、人为活动与风蚀三个方面对风蚀与环境的关系进行了评述,并对今后的研究方向提出了建议.     

Soil erosion in Denmark: processes and politics

Denmark has been dealing seriously with wind erosion problems for the past 125 years whereas water erosion did not come into focus until serious euthrophication appeared in the coastal waters in 1986. This paper describes the problems and processes of soil erosion in Denmark and how these are inter-linked with the political system through subsidies, production systems, etc. The dominant soil erosion processes in Denmark are wind, sheet, rill, tillage and bank erosion. Whereas wind erosion is predominant on sandy soils with low soil fertility, sheet, rill and tillage erosion are mainly on till from the last glaciation and is largely caused by snowmelt events and prolonged rain on saturated and/or partly frozen soil. Danish laws and subsidies have played a major role in managing soil erosion. This has for instance been manifested by the extensive planting of windbreaks and the establishment of buffer zones along water courses. On the other hand, the focus on reducing nitrate leaching has led to increased sheet and rill erosion resulting from a larger number of fields with winter crops. When it comes to reducing phosphorous transport to the aquatic environment, soil erosion has been recognized as an important process but a thorough understanding of the mechanisms are lacking. Finally, the case study of the Water Environmental Protection Plan I shows that both the media and NGOs can play an important role in pushing environmental problems associated with soil erosion onto the political agenda and with the NGOs having a great say in the actual shaping of the laws.     

北京市平原区裸露地风蚀扬尘排放量

以北京市平原区为研究对象,基于美国国家航空航天局（NASA）的陆地卫星（Landsat系列）遥感资料,设计算法批量提取裸露地信息,并结合通用扬尘排放模型,计算估计北京市平原区的裸露地风蚀扬尘源中PM₁₀、PM_2.5的排放系数及年排放量,建立了北京市各区的裸露地风蚀扬尘排放清单.研究表明,1987~2016年间北京市平原区裸露地面积减小了约600km²;风蚀扬尘最严重的地区为大兴区,其次为通州区;以气候年均值为参数计算获得,2016年北京平原区裸露地由于风蚀扬尘效应产生的PM₁₀年排放量为7591.7t,这一排放量与前人研究估算的北京裸地风蚀扬尘PM₁₀排放量较为接近.在此基础上,进一步引入月和季度尺度气候参数,并对模型进行改进,探讨了逐月和季度累计的扬尘排放结果.进一步的研究表明：北京市平原区裸露地面积具有显著季节变化特征,2月裸露地面积最大,可达4500km²,8月最小为500km²;基于月气候参数和季度气候参数结合每月卫星资料反演获得的裸地面积估算,逐月累计的PM₁₀年排放量可达55175t,分季度累计PM₁₀年排放量为39294t.这说明当前常采用的裸地扬尘估算方法,由于扬尘排放模型的气候参数采用年均值,忽视了风蚀过程的季节差异,将会导致裸地风蚀扬尘的极大低估.     

高寒草地土壤保持功能的风洞模拟及其定量评估

青藏高原高寒草地的土壤保持功能对于保护生态环境具有重要的作用。为了研究人类活动不同干扰方式对高寒草地土壤保持功能的影响,利用大型风洞,对不同干扰方式下高寒草甸、草原化草甸和高寒草原3个类型的土壤保持功能定量评估,以侵蚀率作为土壤保持功能的测度指标。实验结果表明,随着风速的增大,3个样品的土壤侵蚀率均呈现增大趋势,但不同处理下侵蚀率的增幅不同。当植被根系破坏后,土壤侵蚀率大小为高寒草甸<草原化草甸<高寒草原,说明,高寒草甸土壤的可蚀性低,高寒草原土壤的可蚀性高,极易遭到破坏。从总体来看,土壤保持功能的强弱依次为高寒草甸>草原化草甸>高寒草原。风蚀前后土壤中有机质和养分含量的变化分析表明,土壤有机质和养分含量显著下降,其中速效K2O的养分含量下降幅度最大。对3个草地类型单位面积土壤保持经济价值进行计算,计算主要包括保持有机碳、保持养分和减少土壤流失对河流湖泊淤积3个方面的价值。结果表明,高寒草原化草甸单位面积的土壤保持价值最高,其次为高寒草甸,高寒草原单位面积土壤保持价值最低。     

基于WEPS模型的天津郊区土壤风蚀起尘及对中心城区迁移量估算

为了预测地表风蚀起尘,针对我国当前地表风蚀预测模型欠缺,相关开发滞后问题,借鉴美国风蚀预报系统(WEPS),研究典型地区地表风蚀预测模型的结构、参数体系以及各参数体系之间的关系,结合卫星遥感技术和实验数据,建立适合天津市的地表风蚀尘预测模型参数体系,开发适合天津市的地表风蚀尘预测模型系统.将天津市域划分为11080个分辨率为1×1 km²的地块,并从中筛选7778个起尘地块; 本地化各地块参数,包括地块经纬度、高程、方向等; 本地化各地块数据库文件,包括风文件、气象文件、土壤文件及管理文件; 编制weps.run文件.以Microsoft Visualstudio 2008为平台,利用C++语言完成WEPS的二次开发,循环计算7778块起尘地块的起尘量,包括蠕移质+跃移质平均损失量、悬移质平均损失量及PM₁₀平均损失量. 2009年,天津郊区各区县总(蠕移质+跃移质)损失量为2.54×10⁶ t,其中指向中心城区的为5.61×10⁵ t; 总悬移质损失量为1.25×10⁷ t,其中指向中心城区的为2.89×10⁶ t; 总PM₁₀损失量为9.04×10⁵ t,其中指向中心城区的为2.03×10⁵ t.     

137Cs示踪技术在滦河源区栗钙土风蚀速率估算中的应用

对采集于滦河源区3个栗钙土剖面中的27个土层样品的pH、有机碳含量、碳酸钙含量、密度及质地进行了化验分析,运用ADCOM100超低本底γ谱仪测定了土壤样品1377Cs的比活度.结果表明,自然栗钙土以及被风蚀土壤剖面中137Cs比活度随深度呈指数递减式分布,其最大渗透深度可达约30cm;利用137Cs示踪技术估算的研究区土壤风蚀速率在0.1842cm·a-1和0.2897cm·a-1之间;栗钙土不同粒径土壤颗粒中137Cs的比活度差异显著,即细粒(粒径≤0.10mm的极细砂、粉粒和黏粒)中137Cs比活度大于细砂(0.10～0.25mm)中137Cs比活度大于粗粒(0.25～2.00mm的中砂、粗砂和极粗砂)中137Cs比活度.可见,运用137Cs示踪法可以定量估算区域土壤风蚀速率,但需综合考虑137s在土壤中的分布、土壤有机质含量和质地等因素,以使其结果将更为准确.     

基于径向基函数神经网络（RBFN）的内蒙古土壤风蚀危险度评价

土壤风蚀是北方干旱和半干旱地区土地沙化和沙尘暴灾害的首要环节和主要动力过程之一. 选取影响内蒙古自治区土壤风蚀演化的相关指标,运用GIS技术提取各指标数据,构建径向基函数神经网络（Radial Basis Function Network,RBFN）;根据不同风蚀危险程度标准,选取12个市、县（旗）相关数据进行训练,确定网络模型参数,进而对内蒙古自治区88个市、县（旗）的土壤风蚀危险度进行了评价. 结果表明:内蒙古自治区西部为土壤风蚀发生的极强危险区,西北为强危险区,中部为中度危险区,而东部为轻度危险区;利用其他研究对该评价结论进行对比验证,结果较为理想.      

‘Tolerable’ hillslope soil erosion rates in Australia: Linking science and policy

This paper reviews water-borne soil erosion in Australia in the context of current environmental policy needs. Sustainability has emerged as a central tenet of environmental policy in Australia and water-borne hillslope soil erosion rates are used as one of the indicators of agricultural sustainability in State of the Environment reporting. We review attempts to quantify hillslope erosion rates over Australia and we identify areas at risk of exceeding natural baseline rates. We also review historical definitions of sustainable, or ‘tolerable’ erosion rates, and how to set these rates. There are many ways to estimate hillslope erosion and these can create confusing results. Moreover their application for land management purposes requires nuanced interpretations that ultimately depend on the desired objective of decision-makers. Soil is the earth surficial material that serves as a medium for plant growth and the notion of tolerable soil erosion arose historically to assess the impact of soil loss on agricultural uses. However now that the impact of erosion on aquatic ecosystems been recognized as a major concern for Australia, the concept of tolerable erosion needs to be revised. Here we discuss three definitions of tolerable soil erosion, following recent literature. We derive estimates of long-term agricultural sustainability based on natural soil production rates and discuss this in relation to other defined land-management objectives such as aquatic ecosystem health. We conclude that the desired objectives of land managers must be clearly articulated before questions of ‘where to invest to control erosion’ and ‘how to assess return-on-investment’ can be answered.