Influence of water level fluctuation on the spatial dynamic of the water chemistry at Lake Fertõ/Neusiedler See     

Mria Dinka  Edit goston-Szab  rpd Berczik  Gyula Kutrucz 《Limnologica》2004,34(1-2):48

Lake Fertõ/Neusiedler See is a steppe lake situated on the Hungarian-Austrian border with a surface area of 309 km². It is an extremely shallow lake with regulated outflow. 54% of the whole lake and 85% of the Hungarian part (75 km²) is covered by reed. There are numerous reedless areas (inner ponds) of variable size within the reed belt, which is enmeshed with canals connecting the inner ponds with the open water areas. Fundamental differences were recorded in the water chemistry of the three water type areas, open water, canals and inner ponds. The degree of these differences is basically determined by the distance from the open water areas and the water level of the actual years. An extremely high, an average and an extremely low water level year was examined, in order to present the spatial and temporal differences in the water chemistry of the investigated water bodies. Differences due to the water level fluctuation between years in the three different water types are discussed on the basis of electrical conductivity, cation, and anion concentration changes of the water. Our results support the concept of high instability of Lake Fertõ and describe habitats with remarkable temporal and spatial variability. The high influence of water level on habitat conditions at different sites of the lake recommend a carefull water level regulation strategy.  相似文献   

Evidence for freeze–thaw events and their implications for rock weathering in northern Canada     

Kevin Hall 《地球表面变化过程与地形》2004,29(1):43-57

Discussions regarding weathering in cold environments generally centre on mechanical processes and on the freeze–thaw mechanism in particular. Despite the almost ubiquitous assumption of freeze–thaw weathering, unequivocal proof of interstitial rock water actually freezing and thawing is singularly lacking. Equally, many studies have used the crossing of 0 °C, or values close to that, as the basis for determining the number of ‘freeze–thaw events’. In order to assess the weathering regime at a site in northern Canada, temperatures were collected at the surface, 1 cm and 3 cm depth for sets of paving bricks, with exposures both vertical and at 45°, orientated to the four cardinal directions. Temperature data were collected at 1 min intervals for 1 year. These data provide unequivocal proof for the occurrence of the freezing and thawing of water on and within the rock (freeze–thaw events). The freeze event is evidenced by the exotherm associated with the release of latent heat as the water actually freezes. This is thought to be the ?rst record of such events from a ?eld situation. More signi?cantly, it was found that the temperature at which freezing occurred varied signi?cantly through the year and that on occasion the 1 cm depth froze prior to the rock surface. The change in freeze temperature is thought to be due to the chemical weathering of the material (coupled with on‐going salt inputs via the melting of snowfall), which, it is shown, could occur throughout the winter despite air temperatures down to ?30 °C. This ?nding regarding chemical weathering is also considered to be highly signi?cant. A number of thermal stress events were also recorded, suggesting that rock weathering in cold regions is a synergistic combination of various chemical and mechanical weathering mechanisms. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

重庆城区浓雾的基本特征   总被引：13，自引：5，他引：13  

江玉华王强  李子华马力 《气象科技》2004,32(6):450-455

统计分析沙坪坝1951～2002年间发生的浓雾事件，结合2001年12月重庆市雾的外场试验资料，探索重庆市主城区浓雾的基本特征。重庆主城区浓雾随年代演变有减缓趋势；主城区浓雾是自然雾与烟尘等的混合物，河谷及城市效应使雾更浓；城市中出现浓雾的大气边界层特征是在近地面层有逆温及增湿降温现象；高浓度气溶胶的净辐射效应阻碍白天混合层发展，使大气边界层趋于稳定，它是重庆连续几天有雾的原因之一；浓雾具有一定的湿沉降作用，能有限地清洁空气；有浓雾的天气条件下，建议降低污染物的排放总量，以避免严重大气污染事件发生。  相似文献   

近30年夏季亚欧大陆中高纬度阻塞高压的统计特征   总被引：10，自引：0，他引：10  

李峰  丁一汇 《气象学报》2004,62(3):347-354

文中利用1970～2001年NCEP再分析500 hPa逐日高度场资料,根据阻塞高压的天气学定义,采用客观统计方法检索出近32 a亚欧中高纬度392个阻塞高压个例,对其进行了气候学分析.结果表明,亚欧中高纬地区夏季阻塞高压活动频繁,10 d以下的过程占绝对多数,地理分布主要集中在45～70°N之间,纬向上可划分5个高发区,其中乌拉尔山和贝加尔湖东部阻高活动频次最高,同时,每个区域中又存在着相应的阻高活跃区.亚欧中高纬地区夏季阻高活动具有明显的季节内变化特征.6月份,阻塞活动多发生在乌拉尔山地区和鄂霍次克海地区,以双阻为主要形势;7月份,欧洲区和贝加尔湖地区的阻塞活动有所增多,尤其贝加尔湖东部地区增多明显,而乌拉尔山地区的阻塞形势明显减少,鄂霍次克海地区的阻塞活动位置向北移动,多发生在60°N以北,双阻形势逐渐减弱,贝加尔湖地区的中阻形势有所增强.8月份,阻塞形势主要存在于贝加尔湖东西两区,中阻形势占据主导地位.亚欧中高纬地区夏季阻塞高压活动年际变化特征也很突出,且这种年际振荡有明显的地理差异.另外,研究表明亚洲北部的阻高活动多以稳定型为主,移动型阻高个例仅占6.6%.移动型阻高以起源于乌拉尔山地区最多,移距最长,生命期最长.偶极子类阻高多集中在贝加尔湖东部与乌拉尔山地区,约占该地区总阻高频次的62.0%和49.7%,平均生命期分别达到7 d/次和9 d/次以上.  相似文献   

秦岭造山带岩浆岩地球物理场特征     

张守林  傅水兴  李恭 《物探与化探》2004,28(6):482-484

根据不同类型岩浆岩的岩石密度、磁性的不同,通过重磁异常分离、延拓、求导、异常的彩色编码及重、磁特征信息的复合处理等,按重磁反映的岩浆岩带所处的构造单元部位、岩浆系列特征以及与矿带的时空关系,将秦岭造山带划分为2带和7个群段.  相似文献   

准噶尔盆地表层结构基本类型及特征   总被引：1，自引：0，他引：1  

赵峰  陈志刚  郑鸿明  杨晓海  王泉 《新疆地质》2004,22(2):191-195

地震勘探区内表层及近地表结构的地球物理特征，往往取决于相应的地质体结构的变化．研究不同表层及近地表地质体的地质特征和地球物理特征，对地震勘探中静校正方法的确定以及静校正量的求取至关重要．准噶尔盆地就其表层地质结构可分为山前冲积扇、戈壁、农田、沙漠等类型，不同类型的地质结构体具有各自独特的地球物理特征。  相似文献   

化学腐蚀下砂岩三轴细观损伤机理及损伤变量分析   总被引：10，自引：4，他引：10  

陈四利  冯夏庭  周辉 《岩土力学》2004,25(9):1363-1367

利用CT识别技术对化学腐蚀下的砂岩进行了三轴加载全过程的即时扫描试验，得到了在不同级荷载作用下砂岩的压密、微裂纹萌生、扩展和破裂的CT图像和CT数，分析了砂岩损伤演化的细观机理。同时，建立了一个基于化学腐蚀影响和CT数的损伤变量模型。  相似文献   

长江中游洪水沉积特征与标志初步研究   总被引：4，自引：0，他引：4       下载免费PDF全文

李长安  张玉芬 《水科学进展》2004,15(4):485-488

洪水记录是研究洪水规律的重要依据。通过对1998、1999、2002年长江中游洪水沉积物的系统观察、对比和研究,结果表明,长江中游洪泛沉积在沉积体形状、沉积结构和沉积物成分等方面,具有与正常河道沉积明显不同的特点,可为古洪水事件确定提供可能和依据。根据沉积环境的不同,长江中游洪泛沉积大致可分为3种类型:溃口洪水事件的沉积、滨岸带的洪水沉积和洪水漫滩沉积。进而对各种类型的沉积学特征进行了分析、归纳和总结,初步建立了其识别标志。  相似文献   

第二松花江流域水电厂综合中长期水文预报的分析研究     

范垂仁谢武贤  关志成冷雪 范思毅 《水文》2004,24(2):31-34,54

基于对第二松花江流域上游小山、松山、两江水电站中长期水文预报研究成果，论述了综合中长期水文预报的研究思路和定性预报、定量预报的分析研究方法。该研究通过2002年实践检验，具有较高的预报精度。  相似文献   

磷对金刚石增强型硬质合金复合齿性能的影响     

刘晓阳  史晓亮  段隆臣  汤凤林 《煤田地质与勘探》2004,32(4):62-64

在金刚石增强型硬质合金复合齿基体中添加不同量红磷，可降低复合齿烧结温度，实现低温活化烧结。研究表明：添加0．3％(ωB)P的复合齿基体性能最好，采用化学镀Ni-P合金添加P和球磨添加0．1％P的方式，复合齿超硬部分的磨耗比和复合齿的抗冲击功优于单纯通过球磨添加0．3％P的超硬复合齿。为了实现金刚石增强型硬质合金复合齿的低温活化烧结，磷元素最优的添加方式是化学镀结合球磨的添加方式。  相似文献