坡地赤红壤物理退化及其机理研究──Ⅲ.土壤物理退化机理分析

主要通过相关统计和综合分析,探讨坡地赤红壤物理退化的内部和外部环境的影响因素．指出养分贫瘠化,尤其是贫有机质化是坡地赤红壤物理性状退化的主要内部原因,植被破坏则是坡地赤红壤物理性状退化的外部因素、而人类活动的影响对坡地赤红壤的物理退化有重要作用。     

Heavy metal characteristics in porewater profiles,their benthic fluxes,and toxicity in cascade reservoirs of the Lancang River,China

Environmental Science and Pollution Research - The construction of cascade reservoirs on the Lancang River (the upper Mekong) has an important influence on the distribution and accumulation of...     

New models for calculating the electrical resistivity of loess affected by moisture content and NaCl concentration

Environmental Science and Pollution Research - Saline loess is an important cause of environmental geo-issues in northwest China. In this research, electrical resistivity of loess with different...     

南亚热带丘陵土壤水分循环及其有效性的研究──Ⅰ.赤红壤水库容及其有效性

阐述了南亚热带低山、丘陵、台地赤红壤总库容、贮水库容、通透库容的占有情况。探讨了水库容的有效性以及不同利用方式的赤红壤有效水库容与无效水库容的差异,并对影响赤红壤水分有效性的因素作了分析．结果表明：赤红壤贮水库容小,尤其是有效水库容小;赤红壤水分有效性主要与土壤有机质相关。     

Ammonia production and kinetic properties of glutamate dehydrogenase in the sipinculid Phascolosoma arcuatum exposed to anoxia

The amounts of total NH ₄ ⁺ detected in the external media in which Phascolosoma arcuatum had been exposed to various periods of anoxia were significantly greater than those in which the worms were exposed to normoxia for a similar period. The increased NH ₄ ⁺ production by P. arcuatum during anoxic exposure was unlikely to be due to an increased catabolism of adenine nucleotides or urea. In contrast, there were significant decreases in the concentrations of several free amino acids in the coelomic plasma and body tissues of individuals during the 48 h of anoxic exposure. The amount of NH ₄ ⁺ produced by the anoxic P. arcuatum could be accounted for by the decreases in the concentrations of aspartate or glycine. Increases in the catabolism of free amino acids (FAA), leading to the increased production of NH ₄ ⁺ , in P. arcuatum during anoxia were supported by the detection of significant changes in the kinetic properties of glutamate dehydrogenase (GDH), in the deaminating direction, from worms exposed to anoxia for 48 h. The apparent increase in the affinity of GDH from the anoxic worm to glutamate would bring about a greater deaminating activity at physiological concentrations of ths substrate. P. arcuatum used in these experiments were collected from the mangrove swamp at Mandai, Singapore between 1990 and 1993.     

Why Singapore's land transportation energy consumption is relatively low

Since the early 1970s, Singapore has enacted a number of measures to tackle traffic congestion, including measures to restrain vehicle ownership. Although Singapore's per capita GDP is comparable to that of OECD countries, the present car-ownership level in Singapore (10 cars per 100 people) is only a fraction of levels in the OECD countries. Traffic flow in this city-State is relatively smooth, even during peak hours. Although the measures taken were aimed primarily at tackling traffic congestion, they have had other positive impacts, such as reducing energy consumption, air pollution and CO₂ emissions. This article presents an overview of the transportation measures and initiatives in Singapore, and analyses two of the transport demand management measures in detail: the vehicle restraint measure, in particular the unique vehicle quota system introduced in 1990; and the two road pricing systems, i.e. the area licensing scheme (ALS) that operated from 1974 to 1998, and the electronic road pricing system (ERP) that went into operation in 1998. Energy and environmental impacts are then discussed, and finally factors contributing to the success of these schemes. Although certain conditions are unique to Singapore, the experience shows that substantial energy and environmental benefits can be achieved through managing urban transportation system in an integrated and innovative way.     

完善我国森林立法势在必行

通过对1998年长江、嫩江特大洪水的反思,指出了目前森林立法中存在的种种弊端,从而提出了完善我国森林立法的建议。     

广西农业可持续发展的策略和措施

广西地处亚热带，光热水资源丰富，具有农业发展的良好条件。近年来，广西采取了一系列的改革措施，农业经济得到了较快发展。但在农业经济发展的同时，也面临着许多资源与环境问题。本文在分析广西农业经济发展的现状及其存在问题的基础上，提出了广西农业可持续发展的策略和措施     

Degradation and metabolism of hexazinone by two isolated bacterial strains from soil

Two hexazinone-degrading bacterial strains were isolated from soil by enrichment culture technique, and identified as Pseudomonas sp. and Enterobacter cloacap. The two purified isolates, designated as WFX-1 and WFX-2, could rapidly degrade hexazinone with a half-life of 3.08 days and 2.95 days in mineral salt medium (MSM), while their mixed bacterial culture was found to degrade hexazinone, at an initial concentration of 50 microg/ml, by enhancing 2.3-fold over that when the isolates were used alone. Two microbial metabolites (A and D) were obtained by preparative TLC and identified on the basis of the spectral data of IR, 1H NMR and HPLC-ESI-MS, but both of them were known products as they had been reported in soil and vegetation metabolites of hexazinone. However, metabolites B and C were new degradates, whose molecular weights (MW) were 157 and 156, respectively, being reported from microbial metabolism for the first time.