Re‐establishment of soil water repellency after destruction by intense burning in a Mediterranean heathland (SW Spain)     

Antonio Jordán  Félix A. González  Lorena M. Zavala 《水文研究》2010,24(6):736-748

Soil water repellency has been conventionally considered as a fire‐induced effect, but an increasing number of studies have suggested that natural background repellency occurs in many soil types, and many of them have suggested that water repellency can be re‐established over time after being destroyed. An experimental fire was conducted to study changes of the soil surface during the first 18 months following intense burning. The main objectives of this paper are as follows: (1) to investigate in situ water repellency changes at three soil depths (0, 2 and 4 cm) immediately after burning; (2) to evaluate the medium‐term evolution of water repellency under field conditions; and (3) to outline the main hydrological consequences of these changes. Also, different water repellency tests (water drop penetration time, ethanol percentage test (EPT) and contact angle (CA) between water drops and the soil surface) were carried out for comparison purposes. Field experiments showed that soil water repellency was partly destroyed after intense burning. Changes were relatively strong at the soil surface, but diminished progressively with depth. Levels of water repellency were practically re‐established 18 months after burning. This suggests that water repellency in the studied area is not necessarily a consequence of fire, but can instead be a natural attribute. Finally, although limited in time, destruction of soil water repellency has important consequences for runoff flow generation and soil loss rates, and, indirectly, for water quality. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Limpets as prey: Lipophrys pholis choice for size     

Ana C. Silva  Ana C. Amador  Sónia Brazão  Claúdia Faria  Diana Boaventura 《Marine Ecology》2010,31(4):525-532

Patellid limpets are key species on rocky shores, structuring intertidal assemblages through their grazing. Their role as prey for fish is, however, often overlooked in studies of intertidal ecosystem functioning. The shanny Lipophrys pholis is a common predator of limpets on rocky shores in Northern Europe and, in this study, we examined the characteristics of its predation on limpets based on prey size. The limpet size range that adult L. pholis (10–12.5 cm) can eat was examined in the laboratory using Patella depressa in 0.2 cm classes, varying between 0.5 cm and 3.0 cm in maximum shell length. There was a limpet size refuge above 1.8 cm, while all smaller sizes were readily consumed by the shanny. The predator attacking behaviour was also examined and found to vary with prey size. Limpets up to 0.8 cm were crushed by the jaw‐constricting force and eaten whole, whereas larger prey were prised from the substratum and the body subsequently separated from the shell. To examine whether there was a L. pholis preference for P. depressa size, a two‐stage laboratory experiment was done using two size classes defined as small (0.7–0.8 cm maximum shell length) and large (1.5–1.6 cm maximum shell length). In the first stage, the predator was given each limpet size class separately. In the second stage, the fish was given a choice between the two classes. Lipophrys pholis was shown to have a preference for the large size class (1.5–1.6 cm). The average number of limpets consumed by the shanny was examined for the duration of one high‐tide typical of the central region of Portugal (≈ 4 h). On average, approximately five limpets (up to an eight limpet maximum) were consumed. The present study shows that L. pholis has a feeding preference based on limpet size, which suggests that the limpet population structure and intra‐ and inter‐specific interactions may be influenced by the shanny predation.  相似文献   

Fracture mechanics analysis of multiple cracks in anisotropic media     

Chia‐Huei Tu  C.‐S. Chen  T.‐T. Yu 《国际地质力学数值与分析法杂志》2011,35(11):1226-1242

This paper presents a single‐domain boundary element method (BEM) for linear elastic fracture mechanics analysis in the two‐dimensional anisotropic material. In this formulation, the displacement integral equation is collocated on the un‐cracked boundary only, and the traction integral equation is collocated on one side of the crack surface only. A special crack‐tip element was introduced to capture exactly the crack‐tip behavior. A computer program with the FORTRAN language has been developed to effectively calculate the stress intensity factors of an anisotropic material. This BEM program has been verified having a good accuracy with the previous researches. Furthermore, by analyzing the different anisotropic degree cracks in a finite plate, we found that the stress intensity factors of crack tips had apparent influence by the geometry forms of cracks and media with different anisotropic degrees. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

不同强度热带气旋对中国降水变化的影响     

杨慧  任福民  杨明仁 《地球科学进展》2019,(7):747-756

基于1960—2017年2 000多个气象台站逐日降水数据和中国气象局热带气旋(TC)最佳路径资料集,采用客观天气图分析法(OSAT)识别得到TC降水。研究表明,中国TC降水总体呈显著下降趋势,较12年前的研究结果下降趋势变缓;TC盛期(7~9月)降水占到TC总降水的78.5%,TC盛期降水和TC非盛期降水均呈显著下降趋势。TC降水气候趋势在空间分布上以减少为主要特征,并表现出明显的地域差异,自南向北呈"减少—增多—减少"的分布型,减少趋势中心位于广东和海南。按TC影响期最大强度分级(弱TC、中等强度TC和强TC)研究不同强度TC降水的变化,结果显示,强TC降水表现出显著减少趋势,主要决定着TC总降水的影响范围和趋势等主要特征。进一步分析发现,影响TC频数在1960—2017年呈显著减少趋势,并在1995年发生突变;对1995年前后2个时期的对比研究显示,与前一时期(1960—1994年)相比,后一时期(1995—2017年)影响TC活动频次在20°N以南的海域呈现出显著的减少趋势,减少大值中心位于南海北部,而且这一特征也主要由影响TC中的强TC所决定;强TC的这一变化趋势导致了华南地区尤其是广东和海南TC降水日数的减少,进而使得TC降水减少。  相似文献   

鄂尔多斯盆地都思兔河流域白垩系含水层特征及供水前景分析     

姜军  徐永  马媛 《地球科学与环境学报》2012,(1):47-54

在鄂尔多斯盆地都思兔河流域供水水文地质详查的基础上,通过水文地质钻探、抽水试验、样品分析等手段,查明了流域含水层的结构、埋深以及含水层和隔水层在水平和垂直方向上的变化规律,探讨了各含水层之间的水力联系,并求取了含水层的水文地质参数;对比圈定了包乐浩晓、巴彦布拉格、好勒包勒吉3处富水区;采用地下水流数值模拟方法对上述3处富水区地下水开采量进行计算,提出了27种地下水开采方案,并经过对比得到地下水开采推荐方案。结果表明:包乐浩晓、巴彦布拉格、好勒包勒吉3处富水区主要补给为侧向径流及大气降水入渗补给,排泄方式以潜水面蒸发及向河流排泄为主;在地下水浅埋区,结合含水层单井涌水量的大小,确定采用管井开采方式、中段悬挂式非完整井结构,平均布井,井深300m,单一开采白垩系环河组的地下水,最大限度夺取潜水蒸发排泄量;根据推荐方案,上述3个富水区总开采量达到123 500m3/d,可为该地区地下水资源开发与利用提供技术保障。  相似文献   

几种鱼礁模型对真鲷诱集效果的研究   总被引：1，自引：0，他引：1  

田方  唐衍力  唐曼  张萍萍 《海洋科学》2012,36(11):85-89

观察了真鲷(Pagrosomus major)对4种不同结构模型礁的行为反应,并对不同结构模型礁的诱集效果进行了比较,进而选择诱集效果最好的1种模型礁,研究该模型礁在不同光强下诱集效果的差异.实验结果表明:未投放礁时,真鲷在水槽中的分布无选择性,呈随机分布;而投礁后各种模型礁均能对真鲷产生诱集效果,真鲷在鱼礁标志区的分布率从6%提高到17.89%~21.50%,其中以表面积大且无孔的 D型模型礁的诱集效果最好;双模型礁投放后对真鲷的聚集率均在20%以上,其中表面积大且有孔的2个模型礁聚集率最大;随光强增强,真鲷的聚集率不断下降,研究发现这可能与真鲷的领域行为有很大关系.  相似文献   

近60年西北太平洋台风年代际变化特征及成因的初步分析   总被引：1，自引：0，他引：1  

余帆  李培  李向军  张涛 《海洋预报》2012,29(1):1-5

利用60年台风资料,对西北太平洋台风的频数、路径和强度变化做统计分析。结果表明:西北太平洋的台风活动在20世纪60年代是高峰期,70年代则是低谷期,从20世纪90年代后期开始,台风活动总体处于低谷期;台风路径主要以转向为主,在20世纪60、70年代平均路径比较偏南,而进入21世纪后平均路径比较偏北;强度在20世纪50、60年代总体较强,后25年总体较弱;西北太平洋台风异常偏多时,西北太平洋副高弱且位置偏东,太平洋海温分布呈"拉尼娜"特征;台风异常偏少时,副高强且位置偏西,太平洋海温分布呈"厄尔尼诺"特征。  相似文献   

重力式海洋平台沉箱的断裂分析     

刘楠  王银邦  王欣 《中国海洋大学学报(自然科学版)》2012,(Z2):156-159,165

研究重力式海洋平台沉箱的表面裂纹最大深度,通过考虑沉箱有一个内表面裂纹,将问题简化为无裂纹重力式平台问题和带裂纹矩形板问题的叠加,应用有限元方法对重力式海洋平台无裂纹情形进行了静力分析,得到了与裂纹位置对应处的环向拉应力。计算裂纹矩形板的应力强度因子,得到海洋环境荷载下沉箱内表面裂纹的最大深度为0.066 8m,计算结果可供海洋平台的设计参考。  相似文献   

大连海域近海面湍流结构及谱特征   总被引：1，自引：0，他引：1  

张翔  李云波  张永刚  梁新友  姚琪  曲涛 《海洋通报》2012,31(1):9-14

利用黄海北部大连海域2009年10月—11月的近海面大气湍流观测资料,对湍流强度、方差相似关系、风速与温度分量谱及湍流通量协谱等进行了分析。结果表明:该海域在海风环境下湍流强度随着风速的增大逐渐减小,且强度均小于0.5;湍流方差相似关系基本上满足1/3定律,近中性环境下无量纲化三维风速方差主要受海滨地形的影响;各速度分量谱在惯性副区符合理论上的-2/3次幂规律,不稳定条件下由于湿度因素的影响,温度谱谱线在高频部分收缩较差,略有上翘;动量谱在惯性副区更接近-2/3幂率,感热谱在惯性区基本符合-4/3的分布,但是谱线分布与稳定度没有明显的规律性。  相似文献   

海洋表层温度对台风"蔷薇"路径和强度预测精度的影响     

赵彪  乔方利  王关锁 《海洋学报(英文版)》2012,31(4):41-52

基于中尺度大气模式WRF(Weather Research and Forecasting Model),首先对2007年3次船舶辐射通量观测进行模拟,以检验WRF对长波和短波辐射通量的模拟能力,结果表明使用中国近海海洋环境数值预报系统环流模式POM(Princeton Ocean Model)模拟的高时空分辨率的海洋表层温度能够显著改进短波辐射通量的模拟,而对长波辐射通量模拟的改进不明显。然后,将业务化运行的中国近海海洋环境数值预报系统后报的逐时海洋表面温度(SST)作为WRF底边界条件,对2008年15号强台风"蔷薇"(Jangmi)过程进行了数值后报试验。结果表明,与使用NCEP/NCAR的SST试验后报的台风中心位置偏差相比,使用高时空分辨率的SST能够较为显著地改善"蔷薇"的路径模拟,台风中心位置模拟偏差减少11%,尤其在台风减弱阶段,台风中心位置模拟偏差减少37%。台风强度在台风发展的不同阶段对下垫面SST的变化敏感性不同。台风路径附近的海表面温度下降会导致海洋向大气输送的热量减少从而减弱台风强度。  相似文献