松嫩平原湿地生态环境退化机制探讨

随着人类活动对生态环境干扰的增强 ,生态环境的退化日益加剧。为避免人类活动的盲目性 ,有必要深入分析和研究生态环境的退化机制。本文界定了生态环境脆弱性的概念 ,探讨了松嫩平原湿地生态环境脆弱性的成因和湿地生态环境退化的机制 ,指出湿地退化的前提是湿地生态环境存在脆弱性 ,干扰因素是人类活动。研究结果可为人类活动提供指导 ,减少盲动性 ,以利于合理开发、利用湿地资源和保护湿地生态环境。     

青藏高原高寒草地的退化及其恢复

述评了青藏高原高寒草地的退化及其恢复治理。青藏高原高寒草地是世界著名的放牧生态系统之一,严重的草地退化正在危及着高原的生态环境,三分之一的高原草地已经退化。"黑土滩"退化草地,作为高原上严重退化草地的一种特殊形式,已经从上世纪80年代的396.57×104公顷增加到90年代的703.19×104公顷。然而,迄今为止青藏高原高寒草地的退化趋势仍然没有改变。研究表明高寒草地的退化是一种连续的过程,遵循如下的次序:未退化草地-轻度退化草地-中度退化草地-重度退化草地。高寒草地退化的原因包括人为和自然因素的影响。人为因素包括季节性过度放牧、盲目开垦草地、采矿、道路建设、开矿采金等等。自然因素包括气候变暖变干、鼠虫害影响、风和水的侵蚀、草皮层冻融等等。需要强调的是在许多高原地区过度放牧总是草地退化的主要原因。面临着这个严峻的形势,许多科学家和当地政府从20世纪80年代起充分重视退化草地恢复,以达到保护天然牧场和生态环境的目的。基于恢复生态学的原理,针对退化草地的恢复,一些有效的实践及综合治理的对策已经在青藏高原得到发展。退化草地恢复的实践包括围栏封育、松耙、补播、施肥、草皮移植、啮齿类动物及杂草的控制、选择和筛选优良牧草、建植人工半人工草地、优化家畜结构等等。基于这些实践,退化草地的综合恢复,人工草地建植及持续利用在青藏高原高寒草地分布区应进一步加强。     

不同加工处理对大豆蛋白质瘤胃降解及动态降解参数的影响

研究选用4头装有永久性瘤胃瘘管的肉牛,利用尼龙袋法比较研究大豆粕、膨化全脂大豆与焙烤大豆对瘤胃干物质、蛋白质降解率及瘤胃动态降解参数的影响。结果表明:与大豆粕相比,膨化全脂大豆及焙烤大豆的干物质及蛋白质的快速降解组分(a)比例显著下降(P<0.0001),慢速降解组分(b)比例显著提高(P<0.0001)。膨化能够显著降低大豆蛋白质的瘤胃降解率,进而提高蛋白质的过瘤胃比例。焙烤大豆的瘤胃干物质、蛋白质降解率显著低于大豆粕但高于膨化全脂大豆。     

奶牛常用蛋白质饲料和粗饲料的瘤胃降解特性研究

本研究旨在评定不同蛋白质饲料(豆粕、双低菜籽粕、膨化大豆、玉米蛋白粉、棉籽粕)和粗饲料(苜蓿干草、全株玉米青贮、燕麦草、苜蓿青贮、羊草)的营养价值,并研究其奶牛瘤胃降解特性.选择5头安装永久性瘤胃瘘管的健康荷斯坦牛,采用尼龙袋评定法评定饲料瘤胃有效降解率和动态降解率.结果表明:1)各蛋白质饲料干物质(DM)含量差异不显...     

Occurrence and mobility of the insecticide permethrin in rivers in the Southern Humber catchment,UK

The synthetic pyrethroid insecticides cis‐ and trans‐permethrin are widely used, particularly in sheep‐dips and for mothproofing within the textile industry. This study aims to establish the concentrations and mobility of permethrin within rivers in the Humber catchment, which contain some of the highest densities of wool‐scouring activity in the world. Our approach was to utilise three different surveys: (a) weekly and storm‐responsive sampling of ‘whole waters’ in the rivers Aire, Ouse, Don, Trent and Calder; (b) intensive sampling of ‘whole waters’ and suspended sediments in the rivers Aire (0.5 h) and Calder (1 h); (c) a bed‐sediment survey of the River Calder. Sediments were extracted by supercritical fluid extraction and all samples were analysed by gas chromatography with mass spectrometry. Results demonstrated the presence of permethrin in ‘whole waters’ and sediments, particularly in the rivers Aire and Calder, and at concentrations in the bed‐sediment likely to cause ecotoxicological effects to benthic macro‐invertebrates. Mass‐balance calculations indicated some loss of permethrin from the water column during transport, with the greatest losses at low river‐discharge. Isomer ratios (trans:cis) give retention times of permethrin in different components of the system as ‘whole water’ < suspended sediments < bed‐sediments, with estimates of 4–26 days for suspended sediments and a maximum of 103–125 days for surface bed‐sediments. © 2000 Society of Chemical Industry     

过氧化物预硫化天然胶乳制备的医用天然胶乳制品热氧降解及其动力学分析

使用热重分析法（TGA）研究了空气状态下过氧化物预硫化天然胶乳（PPVL）制备的医用胶乳胶管试样的热氧降解反应过程及其反应动力学。TG—DTG曲线显示,试样氧化降解过程为二步反应,DTG曲线相应出现明显主降解峰和次降解峰,它们失重1％时的温度（To）、降解峰温度（Tp）、终止温度（Tf）均随升温速率（β）的增加而向高温方向偏移,降解速率也随之增大。在第1步降解反应前,试样出现明显的氧化增重现象,增重峰的温度随β的增加而升高,而增重率随β的增大而减少：试样β为5℃／min的增重峰温度187．9℃,增重率1．33％。第1步反应的最大热氧降解率（Cp1）、最终热氧降解率（Cf1）,反应活化能（E）随着β的增加而增加;表观活化能Eo=107．5kJ／mol;不同β的降解反应级数（β）均是1．7,不受β的影响。第2步反应的Cp2和Cf基本上不受β的影响;n随β的大小而不同,但二者无相关关系;E随β的增加而增加,Eo=154．0kJ／mol。第1步反应和第2步反应的频率因子（A）均随β的增加而几乎呈几何级数增加。第1步反应最大相关系数r均在0．999以上,第2步反应的r均在0．982以上。各升温速率试样在600℃降解率为99．2％-99．5％不等。     

Aerobic soil metabolism of metsulfuron-methyl

A laboratory study was conducted to determine the degradation rates and identify major metabolites of the herbicide metsulfuron-methyl in sterile and non-sterile aerobic soils in the dark at 20°C. Both [phenyl-U-¹⁴C]- and [triazine-2-¹⁴C]metsulfuron-methyl were used. The soil was treated with [¹⁴C]metsulfuron-methyl (0.1 mg kg⁻¹) and incubated in flow-through systems for one year. The degradation rate constants, DT₅₀, and DT₉₀ were obtained based on the first-order and biphasic models. The DT₅₀ (time required for 50% of applied chemical to degrade) for metsulfuron-methyl, estimated using a biphasic model, was approximately 10 days (9–11 days, 95% confidence limits) in the non-sterile soil and 20 days (12–32 days, 95% confidence limits) in the sterile soil. One-year cumulative carbon dioxide accounted for approximately 48% and 23% of the applied radioactivity in the [phenyl-U-¹⁴C] and [triazine-2-¹⁴C]metsulfuron-methyl systems, respectively. Seven metabolites were identified by HPLC or LC/MS with synthetic standards. The degradation pathways included O-demethylation, cleavage of the sulfonylurea bridge, and triazine ring opening. The triazine ring-opened products were methyl 2-[[[[[[[(acetylamino)carbohyl]amino]carbonyl]amino] carbonyl]-amino]sulfonyl]benzoate in the sterile soil and methyl 2-[[[[[amino[(aminocarbonyl)imino]methyl] amino]carbonyl]amino]sulfonyl]benzoate in the non-sterile soil, indicating that different pathways were operable. © 1999 Society of Chemical Industry     

Degradation of oxadiazon in Kalyani alluvial soil

Residual fate and behaviour of the herbicide oxadiazon in Kalyani soil, paddy straw and grain were studied under subtropical conditions, in West Bengal following application @ 1 kg and 2 kg ha⁻¹. Dissipation of oxadiazon in soil followed first-order kinetics and DT₅₀ values ranged from 44 to 45 days. Residues at harvest in paddy grains and straw were also studied. Degradation of oxadiazon after 60 days of incubation at 28(± 1) °C in alluvial soil at water holding capacity yielded 10 metabolites of which four were characterised by spectroscopy. © 1999 Society of Chemical Industry     

Land degradation,rainfall variability and food production in the Sahelian zone of the Sudan

The recent agricultural policies in the Sudan have focused on mechanized large-scale, rainfed agricultural ventures achieving increased grain production through expansion of the cultivated area only, not through increased per unit yield. The total harvested area increased steadily from about 4·5 million ha in 1961 to about 14 million ha in 1996, with great year-to-year variations of harvested areas, and therefore total yields, revealing a fragile balance between production and need. Per unit yields of all crops are steadily decreasing, currently reaching rates far below their genetic potential. The work reported here was intended to look into the causes of the fluctuations in yield and to propose some strategic approaches that may offer a path to sustainability of such crop production. Several factors may be contributing to these poor yields. This study shows that loss of soil fertility and rainfall variability are among such factors. Crops yields were negatively correlated at a one per cent level of significance with the cropping season indicating significant decline in soil fertility. Soil fertility management and fertilizers use could therefore be of great importance in formulating proactive strategies to enhance productivity in the rainfed agriculture in the Sudan. Rainfall in different production subregions had different levels of correlation with yields of all crops. Comparison of long-term rainfall in the four subregions of the study area showed that rainfall decline had been in the magnitude of 30–40 per cent. The western parts of the study area (Kordofan and Darfur) experienced extreme rainfall anomalies than the eastern and central parts (Gedaref and Damazin), and had suffered greater periods of desiccation than the eastern and central parts. The decadal rainfall means showed below average rainfall for the last three decades in all subregions; the western parts again showing greatest desiccation. Copyright © 1999 John Wiley & Sons, Ltd.