寒旱区双层膜日光温室南侧不同保温结构土壤水热试验与模拟

针对北方寒旱地区冬季期间温室南侧边际区域土壤温度较低的问题,采用试验和模拟的方法,在温室中部设置无保温区、挤塑聚苯乙烯泡沫板保温区(保温材料埋深30和60 cm)和水泥砖保温区(保温材料埋深30 cm),对各试验区距地表5、15、25和55 cm土壤的温度和含水率变化进行研究。结果表明:1)距地表5 cm土壤温度主要受土壤含水率影响,并与含水率呈负相关;2)距地表15~55 cm土壤温度受保温结构作用影响较大,无保温组的土壤温度始终低于有保温组的土壤温度,最大土壤温度相差1.2 ℃;3)相同埋深下,挤塑聚苯乙烯泡沫板保温性优于水泥砖,2种保温结构的温室南侧边际区域最大土壤温度差值为0.3 ℃;4)对模拟运用瞬态法求解,模拟值与实测值在y=x函数线上最小拟合度为0.961,最大均方误差为0.037,表明所建模型模拟精度较高。     

The challenge of conserving grassland insects at the margins of their range in Europe

Insects have experienced higher rates of decline than other popular taxa in the calcareous grasslands of Europe. This paper reviews reasons why insects are so vulnerable to environmental change, particularly at the edges of their range. Case studies of the ant Myrmica sabuleti and the butterflies Polyommatus bellargus and Thymelicus acteon are used to illustrate the mechanisms responsible for this vulnerability and the need for different management regimes to maintain species’ niches in different parts of their range.     

Factors affecting plant species distribution in hedgerows of southern Quebec

Woody linear features of farmlands have received much attention as pools of diversity in European countries, but they have, in comparison, been little considered in eastern North American ecological studies. Here, we evaluate the relative contribution of environmental conditions, history of management practices within hedgerows, and adjacent land-use on herb and shrub species distribution in woody hedgerows of agricultural landscapes of southern Quebec, Canada. We pay particular attention to the distribution of forest herbs and weed species and identify the main factors that explain their presence. We also evaluate the amount of spatial structuring in the species data and explanatory variables.Our results show significant differences in species composition related to the unique influence of all sets of factors considered. Adjacent land-use (from intensive crop to fallow land) remains the best predictor of overall species distribution, followed by environmental conditions and history of management practices. The probability of finding forest herbs in hedgerows increases as intensity of adjacent agricultural practices (from intensive crop to fallow land) decreases. Potential weed species, on the other hand, are more likely to be found within narrow hedgerows adjacent to the more intensively managed fields. We discuss the results in terms of the interactions between the different determinants of plant diversity in hedgerows and demonstrate the necessity to distinguish between multiple structuring factors to devise proper conservation strategies. Such strategies will have to take into account the ecological as well as the agricultural exploitation context in which linear features are found to be effective.     

Future prospects for the rare, late-flowering Gentianella germanica and Gentianopsis ciliata in Dutch nutrient-poor calcareous grasslands

We discuss the population biology of two calcareous grassland gentians, Gentianella germanica and Gentianopsis ciliata, in relation to the habitat management currently practiced in The Netherlands. There, at the margin of their range, both species are rare. Gentianella germanica persists on six remaining locations, whereas Gentianopsis ciliata, with two populations, is nearly extinct. Gentianella germanica is a strict biennial, Gentianopsis ciliata an iteroparous perennial. Both species depend on insects for seed production and suffer from low insect visitation. Pollination experiments in one Dutch population demonstrated that Gentianopsis ciliata is self-compatible, but hardly sets any seed under natural conditions due to pollen limitation. The low reproductive success of both species is partly due to the low pollinator densities at their late flowering time, partly caused by the small population size of the gentians themselves, and partly a result of mowing too early. The latter has destroyed the seed crop of several subsequent years in one population of Gentianopsis ciliata and some of Gentianella germanica. In Gentianella germanica, the early mowing and low insect visitation seems to have resulted in selection of less herkogamous and consequently more autofertile individuals. The perspectives for Gentianopsis ciliata are currently extremely poor in The Netherlands. Under the present circumstances, extinction will most likely occur within 10-20 years. Population reinforcement (seeding, artificial cross-pollination with nearby populations) should be considered if we want to conserve this species. For both gentians, but also of other flagship species of nutrient-poor calcareous grasslands, the total grassland area needs to be enlarged and must constitute an interconnected network of reserves. The traditional management method, sheep grazing, is to be preferred over mowing, but only if the flock visits each grassland patch or reserve for only a short time of less than a day, and with intervals of more than 2 weeks between visits. If mowing is preferred for other reasons, it should be done rotationally, and not before October.     

水轮机汽蚀安全裕量问题探讨

水轮机运行完全避免汽蚀破坏是困难的。问题在于设法减轻汽蚀机件的破坏作用,同时应避免水轮机在汽蚀发展到使效率降低和机组强烈振动的情况下运行。汽蚀安全裕量便成为一个最为重要的可变参数,水轮机汽蚀安全裕量的选用,关乎水轮机装置允许吸出高度确定,直接影响水能资源的合理利用和工程建设的投资大小,而且也影响到机组运行寿命和维修管理费用等。因此,进一步对汽蚀安全裕量的取值问题进行探讨,不但是学术问题,而且具有一定的经济价值和实践意义。     

准噶尔盆地南缘无灌溉造林区土壤水分变化规律

对准噶尔盆地南缘——奇台县沙区典型样地土壤水分变化规律进行调查,结果显示:准噶尔盆地南缘无灌溉造林区土壤水分呈规律性的季节变化和垂直变化,春季冰雪融水是土壤水分的重要补给阶段,对土壤垂直分布影响较大,其他季节降雨少且雨量小,土壤水分的影响深度主要集中于地表30 cm的范围。另外,不同部位不同坡向的含水量及变化程度也不同,背风坡明显好于迎风坡,因此,可根据植物种的生物学特性和生态适应性,因地制宜地进行无灌溉植被恢复,现有的调查研究工作也证明植被可自然恢复,但需要一定的时间。     

基于GIS的贺兰山两侧沙漠边缘带近20a来土地景观格局变化

毛乌素沙地与腾格里沙漠位于贺兰山东西两侧,是中国北方重要的沙漠之一。20世纪80年代至21世纪初,受北方气候变化与沙漠边缘地带人类活动强度加大的影响。两大沙漠边缘地带所属的陕西、甘肃、以及宁夏各县土地利用/土地覆盖发生了显著的变化。同时,由于受到自然地带差异以及其它因素的影响,两大沙漠边缘带土地利用/土地覆盖变化表现出不同的特征。试用景观生态学中景观格局分析方法对这种差异进行描述,通过对两大沙漠边缘带土地利用/土地覆盖格局变化对比研究,力图揭示我国北方干旱区与半干旱区沙漠边缘生态脆弱带生态环境对气候与人类活动变化表现出的不同响应方式。     

The relationship of environmental factors to spatial and temporal variation of fish assemblages in a floodplain river in Texas, USA

Abstract –  Spatial and temporal variation of species–environment relationships were evaluated for shallow-margin and deep-water fish assemblages in the Brazos River, a large floodplain river in Texas, USA. Total variation among the deep-water assemblages (11 species, 86% turnover across gill net samples) was greater than for shallow-margins (38 species, 64% turnover across seine samples). For both shallow-margin and deep-water assemblages, variation was greater among sites than between winter and summer seasons. Shallow-margin assemblage structure was related to depth, velocity and substrate, whereas for deep-water assemblages river discharge, temperature and velocity were important. Season itself accounted for little of the variation among either shallow (6.7%) or deep-water (2.3%) assemblages. Overall temporal patterns of shallow-margin samples appeared to show responses to juvenile recruitment, spates and migration of coastal fishes, whereas for deep-water samples, patterns related to use of reproductive habitats, juvenile recruitment and seasonal activity levels. Brazos River assemblages were less variable overall in comparison with studies along similar length of reach in headwater streams and wadeable rivers. The residual variation in species distribution (54% for shallow-margin and 67% for deepwater) that was not explained by instream variables and season suggests a greater influence of biotic interactions in rivers, particularly those across the spatially dynamic interface of main channel habitats and shallow river margins.     

公路边坡稳定性分析及防治措施

内蒙古集呼高速公路K450段地处丘陵地区，以路堑形式通过，施工中发现坡体岩土结构较复杂，雨季后期，该段突然发生滑动破坏，本文对边坡稳定问题进行了研究，分析了产生边坡稳定的主要原因，对边坡稳定提出了相应的整治措施，收到了良好的效果。     

卸油管路校核计算理论的补充分析和修正

铁路轻油罐车的卸油管路系统，在夏天作业时常发生气阻气蚀现象，根据这一事实，调查了我国诸多油库，从大量的生产数据中发现，理论计算结果与实际生产状况存在着较大的差距，进而分析了恶劣工况下促使气阻的气蚀提前形成的各种原因，如烃类汽化特征、溶解气和夹带气泡、气泡窝存、罐内液体温度不均匀、管路漏失等加以考虑，并对过去的计算理论作了补充。为了增加管路系统的剩余压力，确保卸油安全，还提出了向罐车内输入压缩空气，