Surface wetness duration under controlled environmental conditions

Surface wetness is an important variable for forecasting plant disease. It is commonly measured with sensors, but these provide an indirect measurement and there is variability between different makes of sensors. Consequently, there is no standard for surface wetness measurement. The objective of this study was to derive and validate a physically based theoretical definition of surface wetness for both drops and films drying under controlled conditions. The validation compared observations of surface wetness with theoretical simulations for a range of factors: atmospheric variables including temperature, humidity, net radiation and wind speed; plant physical properties including surface wettability, leaf width and thickness; and initial water distribution including drop volume and film thickness. The drying of drops and films was studied in a wind tunnel and a laboratory setting. Surface wetness duration was most sensitive to initial drop volume or film depth, relative humidity and surface wettability in the case of water distributed as drops. Surface wetness duration was relatively insensitive to other atmospheric variables. Water distribution whether drop or film, made a four-fold difference in evaporation rate compared to leaf width, which was unimportant for leaves larger than 3 cm. The observations were compared to the theoretical estimations using a surface energy balance model. The surface energy balance model is based on a combination equation and a generic transfer coefficient. The transfer coefficient is dependent upon whether the water is present as drop or film and is assumed to be independent of leaf width or drop dimension. Considerations of drop geometry are ignored, although the initial wet area must be known. The theoretical understanding of drop and film drying under controlled conditions could potentially be useful in a field scale model of surface wetness. Since all the factors that influence surface wetness can be explicitly defined, such a field scale model has potential to be used as a theoretical standard for surface wetness estimation. Additional research is required to test this model under controlled conditions of condensation.     

黑河流域中下游地区土地沙漠化现状及其原因分析

利用最新的土地沙漠化遥感监测数据(2000年),研究分析了黑河流域中下游地区的土地沙漠化现状及土地沙漠化发展的原因,并提出了其土地沙漠化防治的具体对策和措施。结果表明,2000年黑河流域中下游地区共有沙漠化土地13508.4km2,土地沙漠化类型包括耕地、草场、砾质沙漠化以及沙丘活化4种,总面积占监测土地面积(114446km2)的11.8%,其中轻度沙漠化土地27.4km2,占沙漠化土地总面积的0.2%,中度沙漠化土地1321.4km2,占9.8%,重度沙漠化土地2274.3km2,占16.8%,严重沙漠化土地9885.3km2,占73.2%,区内土地沙漠化形势严峻,以严重沙漠化土地类型占优势,特别是在黑河流域下游地区。黑河流域中下游地区土地沙漠化的发生和发展是自然和人为因素共同作用的结果,其中人类对流域内水资源的不合理利用是其主要驱动力。     

科尔沁沙地不同风沙土的风蚀特征

通过风洞实验，研究了科尔沁沙地两种典型风沙土的风蚀特征。流动沙丘土样和农田土样的风蚀率随风速的增加均呈幂函数关系增长。风干的农田土样在风速3．7m／s时开始出现风蚀现象，但流沙土样的临界起沙风速是4．3m／s。在低风速段．农田土样的风蚀率大于流沙土样，但当风速增加到大约5．7m／s以上时，流沙土样的风蚀率开始大于农田土样，并且差值随风速的增加而加大。两种土样的风蚀率随土样含水率的增加呈负幂函数关系迅速减小。但流沙土样风蚀率的减小要比农田土样更迅速。流沙土样的临界起沙风速随含水量的增加呈线性关系增长，而农田土样的临界起沙风速随含水量的增加呈二次幂函数关系增长。两种风沙土在风蚀特征方面的差异，主要是由质地不同引起的。增加土壤含水量，是本地区风季减小风蚀的有效方法。     

50MeV/u碳离子辐照休眠和萌发春麦种子的M_1代比较

50MeV u碳离子辐照春麦 86 336和 1 46 1 5的休眠和萌发种子。通过M1代生物学性状和苗期POD、SOD和CAT酶活性、蛋白质含量以及MDA含量等研究表明 :1 )同对照相比 ,许多生物学性状的变化表现出萌发种子大于休眠种子 ;除蛋白质含量外 ,SOD酶活性、POD酶活性、CAT酶活性和MDA含量等在休眠种子和萌发种子间差异显著 ;2 )两个春麦材料的表现 ,在有些性状的变化上也有所区别。     

黄土丘陵区农村节能吊炕的环境经济效益分析

节能吊炕在改善室内热舒适性的同时,降低农户的经济支出和生态环境的破坏。通过在甘肃庄浪县2个村的6户农家建造新式节能吊炕,与4户使用传统炕的农户一起进行燃料使用与温度观测记录;并结合农户用能现状问卷调查,获取数据,建立经济计量模型,对吊炕产生的环境经济效益进行分析与评价;最后对其推广前景进行展望。结果表明,高崖韩村吊炕户平均每户每年产生的总环境经济效益为836.99元,下湾村吊炕户平均每户每年产生的总环境经济效益为919.41元。若对庄浪县所有农户都推广使用节能吊炕,全县每年将会产生7381.58~8108.46万元/a的环境经济总效益。节能吊炕具有显著的环境经济效益和良好的推广前景,是现阶段提高农户冬季取暖用能水平、降低经济支出的有效途径,对农村用能技术的改进、生态环境的改善、温室气体的减排、具有重要的理论和现实意义。     

准格尔旗土地利用变化与影响因素分析

准格尔旗位于我国农牧业交错区，生态环境脆弱．水土流失和土地退化严重。根据多年统计资料分析了该区土地利用变化情况，包括土地利用数量变化，空间变化，利用程度及效益变化，质量变化。最后，初步分析了影响该区土地利用的影响因素。结果表明．准格尔旗1987—2000年间土地治理取得明显成效，林地、草地显著增加，未利用地显著减少，但也存在土地生产力降低等问题。土地利用变化受包括调整土地结构、人口变化、粮食产量变化、工业经济发展、国家资金支持、法律法规等因素影响。     

西部地区退耕还林还草尺度问题的探讨

中国西部地区正在施行的退耕还林还草工程无疑是西部植被恢复、生态环境改善的一项重大举措,但就西部地区生态环境的本底条件来看,我们认为有必要确认西部地区退耕还林还草的尺度范围,对西部生态环境的改善程度有一个共识,以确保国家以有限的投资获取西部地区最大的生态与经济效益。     

风沙土开垦中的风蚀研究

针对以往对土壤风蚀与土地开垦的关系缺乏定量研究，本文以野外实地采集的风沙土样为实验材料，对土地开垦过程中影响风蚀的两个主要因素－地表破坏与植被破坏分别进行风洞实验，结果表明，土壤风蚀率随地表破坏率的增大呈二次幂函数增加；随植被盖度的减少呈指数增加。综合地表破坏及植被盖度对土壤风蚀的影响，最后得出，土壤风蚀率随土地开垦率的增大呈指数增大。在此基础上提出了风沙土开垦中，有效地防止土壤风蚀需要掌握的临界     

不同孔隙度尼龙网对风沙流减弱作用的风洞模拟

通过对不同孔隙度尼龙网对风沙流减弱作用的风洞模拟实验,旨在探求输沙量与孔隙度和风速二者之间的关系,从而为防沙新材料的开发、野外工程防沙的优化设计及其应用提供理论依据。如果没有风蚀过程发展导致风沙流的出现,就不可能有因沙粒输送和堆积过程中引起的各种沙害。因此,防治沙害、改善沙区生态环境的根本措施还是选择合适的材料抑制或削弱风沙流的强度。而防沙材料本身又对携沙气流产生影响,如何协调二者之间的互馈关系,使得防沙材料发挥最大的防沙效益便是本文研究的目的。在前人研究的基础上,作者以平均净阻沙率、网后平均输沙率和风沙流动态变化趋势为参考指标,初步确定尼龙网防沙效益的最佳孔隙度β应该在40%左右。     

逐渐干旱胁迫下两种生物土壤结皮藓类的渗透调节作用响应

Biological soil crusts (biocrusts) widely occur in semiarid and arid regions throughout the world and play important roles in many desert ecosystems: protecting soil from wind erosion and detaining nutrient-rich dust and organic carbon. An experiment was conducted in the Shapotou revegetated area of the Tengger Desert, Ningxia Hui Autonomous Region of China to investigate the physiological responses of the dominant biocrust mosses, Bryum argenteum and Didymodon vinealis, to desiccant stress using different osmotic adjustments. B. argenteum and D. vinealis accumulated K⁺, total soluble sugar, sucrose, trehalose, proline, and glycine betaine during desiccation. The proline content of B. argenteum was about two times higher than that of D. vinealis. The K⁺ and glycine betaine contents in B. argenteum were slightly higher than those in D. vinealis. In contrast, the total soluble sugar, sucrose, and trehalose contents in D. vinealis were about 3 to 5 times higher than those in B. argenteum. With gradual desiccation stress, the Na⁺ content of B. argenteum was low and did not significantly change. On the contrary, the Na⁺ content of D. vinealis sharply increased and reached a very high level of about 10 to 18 times higher than that of B. argenteum, indicating that B. argenteum and D. vinealis gradually adapted to desiccation stress by osmotic substances accumulation to different degrees.