Water‐Yield Reduction After Afforestation and Related Processes in the Semiarid Liupan Mountains,Northwest China1

Abstract: The increase of coverage of forest/vegetation is imperative to improve the environment in dry‐land areas of China, especially for protecting soil against serious erosion and sandstorms. However, inherent severe water shortages, drought stresses, and increasing water use competition greatly restrict the reforestation. Notably, the water‐yield reduction after afforestation generates intense debate about the correct approach to afforestation and forest management in dry‐land areas. However, most studies on water‐yield reduction of forests have been at catchment scales, and there are few studies of the response of total evapotranspiration (ET) and its partitioning to vegetation structure change. This motivates us to learn the linkage between hydrological processes and vegetation structure in slope ecosystems. Therefore, an ecohydrological study was carried out by measuring the individual items of water balance on sloping plots covered by different vegetation types in the semiarid Liupan Mountains of northwest China. The ratio of precipitation consumed as ET was about 60% for grassland, 93% for shrubs, and >95% for forestland. Thus, the water yield was very low, site‐specific, and sensitive to vegetation change. Conversion of grassland to forest decreased the annual water yield from slope by 50‐100 mm. In certain periods, the plantations at lower slopes even consumed the runon from upper slopes. Reducing the density of forests and shrubs by thinning was not an efficient approach to minimize water use. Leaf area index was a better indicator than plant density to relate ET to vegetation structure and to evaluate the soil water carrying capacity for vegetation (i.e., the maximum amount of vegetation that can be supported by the available soil water for an extended time). Selecting proper vegetation types and plant species, based on site soil water condition, may be more effective than the forest density regulation to minimize water‐yield reduction by vegetation coverage increase and notably by reforestation. Finally, the focuses in future research to improve the forest‐water relations in dry‐land areas are recommended as follows: vegetation growth dynamics driven by environment especially water conditions, coupling of ecological and hydrological processes, further development of distributed ecohydrological models, quantitative relation of eco‐water quota of ecosystems with vegetation structures, multi‐scaled evaluation of soil water carrying capacity for vegetation, and the development of widely applicable decision support tools.     

Particle-facilitated lead and arsenic transport in abandoned mine sites soil influenced by simulated acid rain

The role of acid rain in affecting Pb and As transport from mine tailings was investigated by pumping simulated acid rain at a infiltration rate of 10.2 cm/h through soil columns. Simulated acid rain with pH of 3.0, 4.5 and 5.6 were used as leaching solutions. Results showed that 86.9–95.9% of Pb and 90–91.8% of As eluted from the columns were adsorbed by particles in the leachates. Scanning electron microscopy (SEM) analysis showed that particles released from the columns were mainly composed of flocculated aggregates and plate or rod shaped discrete grains. Transmission electron microscopy (TEM) coupled with energy dispersive X-ray analysis (EDX) showed that these particles were predominantly silicate minerals. Results from our experiments demonstrated that when rapid infiltration conditions or a rainstorm exist, particle-facilitated transport of contaminants is likely to the dominant metal transport pathway influenced by acid rain.     

南京市典型地区可吸入颗粒物(PM10)中颗粒的微观形貌特征及其矿物组成

应用扫描电镜技术(SEM/EDX)对南京市两典型地区PM10中颗粒的微观形貌及其矿物组成进行了研究.结果表明,南京市大厂区(典型工业区)PM10中的颗粒多以形态规则矿物颗粒为主,山西路地区(典型商业区)PM10中的颗粒多以形态不规则出现,形态规则颗粒主要是碳酸盐、硫酸盐和铝硅酸盐矿物,形态不规则颗粒主要是烟尘结合体、生物质和原生矿物.     

新型除磷混凝剂的研制与应用＊

实验以处理金属表面所产生的磷化废水为研究对象,系统地分析了在新型混凝剂的使用过程中,pH值、温度、石灰投入量、沉降时间、助剂A等因素对脱磷效果的影响。结果表明,含磷量为18mg/L、COD为300mg/L、SS为150mg/L、pH值为5.7～6.5的废水,石灰投入量为300mg/L、沉降时间为10min左右、温度为25℃、pH值调节至9.0、加入5mL助剂A处理后,废水中磷含量为0.25～0.35mg/L、COD为80mg/L、SS为60mg/L,满足《污水综合排放标准》(GB8978—1996)中的一级标准。     

城市混凝土桥梁薄弱处分析

随着城市化进程的不断发展,包括高架桥、立交桥在内的大量混凝土桥梁在城市交通网络中扮演者极其重要的角色。但受环境侵蚀、交通量日益增加的影响,城市混凝土桥梁不可避免地出现一定损伤,严重甚至会导致桥梁倒塌等重大灾难事故。在分析城市混凝土桥梁的各种损伤及损伤演化过程的基础上提出运营桥梁薄弱处的概念。该薄弱处是指受环境侵蚀、材料老化、荷载变化等因素的影响,混凝土桥梁结构中最先发生破坏的构件或构件中的某一位置。对运营桥梁薄弱处的分析宜采用分析结构中各处的承载力下降及相应的荷载效应增加二者相结合的方法,通过比较获得桥梁中各处抗力与荷载效应最为接近的地方,即结构薄弱处。最后,总结了城市混凝土桥梁薄弱处分析研究的发展方向及亟待解决的关键技术。     

高校学生安全素质定量评价方法研究

本文通过运用层次分析法和发放调查问卷,对高校学生的安全素质进行分析,提出高校学生安全素质定量评价方法,并以首都经济贸易大学学生为实例进行应用研究,为高校的安全管理和校园安全文化建设提供参考。     

倒置A2/O工艺氮平衡与脱氮效率的分析

研究了倒置A^2／O工艺中的氮平衡和脱氮效率，并对影响脱氮效率的回流比和碳氮质量比进行分析。根据广州某城市污水处理厂水质特点，设计总回流比为3．0，其中污泥回流比为1．0，混合液回流比为2．0，理论总氮去除率为78．75％，实际运行总氮去除率达64．42％。     

钢铁工业含铁尘泥的资源化利用现状与发展方向

含铁尘泥是钢铁生产过程中从不同工艺流程的除尘系统中排出的含铁粉尘。这些尘泥回收后利用不当，不仅会造成环境污染，也是对含铁资源的巨大浪费。本文概述了钢铁工业含铁尘泥的综合利用现状，对瓦斯泥、转炉污泥、轧钢污泥、高锌含铁污泥、电炉粉尘等几类重点尘泥，提出了未来高附加值利用的方向。