Agricultural Productivity Changes Induced by the Sloping Land Conversion Program: An Analysis of Wuqi County in the Loess Plateau Region

This paper examines the agricultural productivity change induced by the Sloping Land Conversion Program (SLCP) using the Malmquist index method and household data collected from Wuqi. We find that during the period of 1998–2004, the total factor productivity (TFP) grew by 15.8%. While numerous households suffered a TFP decline, the majority of them experienced a large gain. By decomposing the TFP, we further show that its increase is due exclusively to the improvement of technical efficiency rather than to technological change. To validate these findings and put them in perspective, we also estimated the TFP change with county-level aggregate data. It is revealed that driven by technological change and scale efficiency, the TFP grew slightly during the period of 1992–1998. Because of the tremendous cropland reduction and production mode shift caused by implementing the SLCP, the TFP declined substantially during the first three years of the program; due to continued improvement of technical efficiency; however, its growth accelerated later. Altogether, our evidence consistently suggests that implementing the SLCP has contributed to the agricultural TFP growth in the longer term and that the efficiency improvement has resulted mainly from the increased public expenditures for extension services and diffusion of technical knowledge. Wuqi’s experience proves that it is possible to achieve environmental conservation and increase productivity simultaneously, even when facing a cropland reduction and production mode alternation.     

A Value Orientation for Nature Preservation in Singapore

Over the past decade, the cause of nature preservation in Singapore had gained momentum through the efforts of the various non-governmental organisations. Tussles over disputed nature areas such as the Lower Peirce Forest, Marina South, Senoko, etc., had also garnered a great deal of publicity in the mass media. Many arguments for nature conservation were given by conservationists --- from the economic to the ecological --- without considering carefully their local relevance and impact. This paper provides an outline of a value orientation for nature preservation in Singapore --- taking into account the local context in terms of the economic, cultural, social and ecological conditions existing in this country. The major values usually associated with nature conservation are reviewed and prioritised in terms of local relevance and impact. The strategic thrust of the value orientation advocated is, in the final analysis, anthropocentric rather than non--anthropocentric in perspective.     

铀矿区周边水体典型核素污染特征及风险评价

为研究铀矿区周边水体中典型放射性核素分布特征及其潜在的健康风险,对该地区周边浅层地下水及河水中放射性活度浓度进行分析测定.运用改进内梅罗综合污染指数法和健康风险评价模型对放射性污染及不同年龄段人群健康风险进行评估.结果表明,地下水与河水中放射性核素²³⁸U、²²⁶Ra、²³²Th活度浓度（地下水：0.012~0.102,0.013~0.036,0.002~0.033Bq/L,河水：0.001~0.066,0.013~0.034,0.001~0.013Bq/L）均未超过WHO饮用水水质准则规定的标准限值,但远远高于江西省水体背景值.河水中各核素活度浓度随水流流向呈递减趋势,地下水中各核素空间分布无明显规律性特征.河水中综合污染指数高于地下水,最高值分别为9.21和6.83,属严重污染和中度污染.健康风险评价结果表明,幼儿和少儿致癌风险要高于成人,幼儿终身致癌风险均超过ICRP最大可接受风险值5.0×10^-5,少儿和成年超标率为33.3%和16.7%,即使未超标但也高于USEPA推荐可忽略风险水平10^-6,具有潜在致癌风险.各核素致癌风险水平呈现为²²⁶Ra > ²³²Th > ²³⁸U,因而对于铀矿区周边饮用水中²²⁶Ra和²³²Th要更加重视研究.     

膜、柱串联固相萃取-高效液相色谱法测定水中多环芳烃(PAHs)的研究

建立了用膜-柱串联固相萃取(SPE)技术,甲醇和水作为流动相进行梯度洗脱,紫外和荧光检测器串联的高效液相色谱法(HPLC)分析水中EPA优先监控的16种PAHs的方法.     

改进的QGA-BP模型在弥苴河总氮量预测中的应用

水质预测对水环境规划、评价和管理十分重要。构建一种改进的量子遗传算法（QGA）优化BP神经网络的模型,即在量子遗传算法中引入了旋转角的动态改进策略和遗传算法的交叉变异操作,并以改进的QGA作为进化操作准则优化BP模型的权值和阈值。以弥苴河复杂水环境水质预测为实例,选取一组历史观测数据作为训练样本,对其进行分析。将结果与BP模型、QGA-BP模型仿真结果进行了对比,改进后的QGA-BP模型在进化代数、收敛速度和预测结果的准确率有较大提高。对弥苴河水质的预测结果表明,将改进QGA-BP模型用于水质预测是可行、有效的预测方法。     

土壤中多环芳烃菲的自然降解特性

自然降解是去除环境中有机污染物的一种重要手段。为了解土壤中多环芳烃的自然降解规律,选择陕北风沙滩地区风积砂为典型土壤,多环芳烃菲为典型污染质,探讨了菲在风积砂中的自然降解规律;建立了菲的降解动力学模型;进一步考察了污染浓度、温度、pH值、含氧量等环境因素对降解的影响。结果表明,风积砂中菲的自然降解符合准一级反应动力学,降解半衰期为17 d;菲的降解率与生物量呈正相关;污染浓度对菲的自然降解影响不显著;25~35℃、中性条件能够促进风积砂中菲的降解;好氧微生物是降解的关键,氧的存在对于土壤中菲的降解具有重要的作用。     

Bio-drying and size sorting of municipal solid waste with high water content for improving energy recovery

Bio-drying can enhance the sortability and heating value of municipal solid waste (MSW), consequently improving energy recovery. Bio-drying followed by size sorting was adopted for MSW with high water content to improve its combustibility and reduce potential environmental pollution during the follow-up incineration. The effects of bio-drying and waste particle size on heating values, acid gas and heavy metal emission potential were investigated. The results show that, the water content of MSW decreased from 73.0% to 48.3% after bio-drying, whereas its lower heating value (LHV) increased by 157%. The heavy metal concentrations increased by around 60% due to the loss of dry materials mainly resulting from biodegradation of food residues. The bio-dried waste fractions with particle size higher than 45 mm were mainly composed of plastics and papers, and were preferable for the production of refuse derived fuel (RDF) in view of higher LHV as well as lower heavy metal concentration and emission. However, due to the higher chlorine content and HCl emission potential, attention should be paid to acid gas and dioxin pollution control. Although LHVs of the waste fractions with size <45 mm increased by around 2× after bio-drying, they were still below the quality standards for RDF and much higher heavy metal pollution potential was observed. Different incineration strategies could be adopted for different particle size fractions of MSW, regarding to their combustibility and pollution property.     

Greenhouse gas emissions from MSW incineration in China: Impacts of waste characteristics and energy recovery

Determination of the amount of greenhouse gas (GHG) emitted during municipal solid waste incineration (MSWI) is complex because both contributions and savings of GHGs exist in the process. To identify the critical factors influencing GHG emissions from MSWI in China, a GHG accounting model was established and applied to six Chinese cities located in different regions. The results showed that MSWI in most of the cities was the source of GHGs, with emissions of 25–207 kg CO₂-eq t^?1 rw. Within all process stages, the emission of fossil CO₂ from the combustion of MSW was the main contributor (111–254 kg CO₂-eq t^?1 rw), while the substitution of electricity reduced the GHG emissions by 150–247 kg CO₂-eq t^?1 rw. By affecting the fossil carbon content and the lower heating value of the waste, the contents of plastic and food waste in the MSW were the critical factors influencing GHG emissions of MSWI. Decreasing food waste content in MSW by half will significantly reduce the GHG emissions from MSWI, and such a reduction will convert MSWI in Urumqi and Tianjin from GHG sources to GHG sinks. Comparison of the GHG emissions in the six Chinese cities with those in European countries revealed that higher energy recovery efficiency in Europe induced much greater reductions in GHG emissions. Recovering the excess heat after generation of electricity would be a good measure to convert MSWI in all the six cities evaluated herein into sinks of GHGs.     

反渗透深度处理乳品加工业二级处理废水试验研究

采用砂滤、活性炭吸附和反渗透组合工艺深度处理乳制品加工废水。深度处理后出水指标CODcr、TP和硬度分别达到10、1 mg以下和20 mg/L以下,经反渗透组合工艺深度处理后的乳制品加工废水可以达到锅炉补水,冷却循环水等水质要求。     

β射线法与重量法监测环境空气PM_(2.5)的应用比较

重量法是测量PM_(2.5)的传统手工经典方法,而β射线法加动态加热系统联用光散射法作为自动在线监测技术的常用方法被广泛使用。将5030-SHARP型β射线法加动态加热系统联用光散射法PM_(2.5)自动监测设备监测结果与手工法测量结果进行比对、分析,结果表明:β射线法与重量法监测结果具有一致性,测量结果不存在显著性差异;β射线法与重量法相对偏差值与温度、相对湿度、风速等气象因子的相关性不明显;β射线法与重量法监测结果的差异性与PM_(2.5)质量浓度、季节等条件有关;随着PM_(2.5)质量浓度逐渐升高,β射线法与重量法相对偏差的绝对值|RD|也随之增大,不同季节的|RD|平均值差异较大,春季、冬季的|RD|平均值大于夏季、秋季。