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991.
The physicochemical and biological characteristics of coastal waters form a gradient extending from land to ocean. In the Mediterranean this gradient is particularly large, due to the sea’s weak tides. Within coastal waters, those waters in contact with land are called coastal inshore waters (CIW), defined herein as between 0 and 200 m from the shoreline. Here we present the first physicochemical and biological characterization of CIW of the NW Mediterranean Sea. This case study is based on 19 years of data collected from coastal inshore (CIW; 0–200 m), nearshore (CNW; 200–1500 m), and offshore (COW; >1500 m) waters of the Catalan coast. Analyses of these data showed that the physicochemical and biological characteristics of CIW differ significantly from those of CNW and COW due to: (1) significantly higher concentrations of dissolved inorganic nutrients (nitrate = 11.07 μM, nitrite = 0.52 μM, ammonium = 6.43 μM, phosphate = 0.92 μM, silicates = 5.99 μM) and chlorophyll-a (=2.42 μg/L) in CIW than in either CNW or COW (in some cases up to one order of magnitude); (2) a greater variability of dissolved inorganic nutrients and chlorophyll-a in CIW than in CNW and COW, and (3) the presence of a mostly urban population and the effects of river inflows as a primary source of CIW variability but with minimal impact on CNW or COW. In addition, the risk of eutrophication was found to be highest in CIW, placing human and environmental interests at greater risk than in the outermost coastal waters. The results highlight the importance of considering the distinctive physicochemical and biological properties of CIW in future coastal waters studies. This is of major importance in assessments of eutrophication and coastal water quality, not only to identify the pressure–impact relationships but also to allow the timely detection of local environmental problems and thus avoid endangering the unique communities of CIW and ensuring the sustainability of human activities. In conclusion, CIW characterization is essential to integrate coastal zone management. 相似文献
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994.
大地电磁全信息资料三维共轭梯度反演研究(英文) 总被引:7,自引:2,他引:5
在对张量阻抗数据、倾子数据和共轭梯度算法深入分析的基础上,我们实现了大地电磁全信息资料三维共轭梯度反演算法。基于全信息资料的三维共轭梯度反演研究,探讨了同时利用五个电磁场分量整理得到的大地电磁资料进行三维反演定量解释的方法以及全信息数据在三维反演中的作用。理论模型合成数据的反演结果表明,在三维反演中使用张量阻抗和倾子数据结合的全信息数据的反演结果优于只使用张量阻抗数据(或只使用倾子数据)的反演结果,提高了反演结果的分辨率和可信度。合成数据的反演算例也验证了所实现的大地电磁全信息资料三维共轭梯度反演算法的正确性和稳定性。 相似文献
995.
本文利用一种改进的广义S变换对地震波进行时频分解,求取地震波低频段时频谱的吸收衰减梯度,并与利用传统的广义S变换得到的高频段及低频段的吸收衰减梯度进行对比,以期更好地指示油气.理论推导、数值模拟及实际应用结果表明:基于改进的广义S变换的低频吸收衰减梯度可与传统的广义S变换得到的高频吸收衰减梯度相互佐证,更好指示油气. 相似文献
996.
In August 2005 severe flood events occurred in the Alps. A sediment routing model for steep torrent channel networks called SETRAC has been applied to six well‐documented case study streams with substantial sediment transport in Austria and Switzerland. For these streams information on the sediment budget along the main channel is available. Flood hydrographs were reconstructed based on precipitation data and stream gauges in neighbouring catchments. Different scenarios are modelled and discussed regarding sediment availability and the effect of armouring and macro‐roughness on sediment transport calculations. The simulation results show the importance of considering increased flow resistance for small relative flow depth when modelling bedload transport during high‐intensity flood events in torrents and mountain rivers. Without any correction of increased flow resistance using a reduced energy slope, the predicted bedload volumes are about a factor of 10 higher on average than the observed values. Simulation results were also used for a back‐calculation of macro‐roughness effects from bedload transport data, and compared with an independent estimate of flow resistance partitioning based on flow resistance data. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
997.
998.
Invasive plant species are a growing concern in many regions of the world, yet little information is available on the effects of habitat type and distance to urban settlements on the ability of alien plants to become established. We studied plant communities from the arid steppes to the Andean forest within two national parks and surroundings, in northwestern Patagonia, Argentina. Alien and native vascular plant species were sampled using 90 × 100 m2 plots and analyzed in relation to both climatic and environmental variables and distance to urban centres. We also compared life-forms of alien and native species. Precipitation and distance to an urban centre were important determinants of alien species community richness and composition, and shrubland sites had significantly more alien species than forest or steppe sites. Alien flora (15% of the species) was composed of a higher proportion of annuals and biennials than native flora. Our results suggest that precipitation, distance to source population, and anthropogenic disturbance influence the invasion process in this region, together with the availability of open niches. This work stresses the importance of monitoring invasive species in natural reserves, and of considering habitat types as well as idiosyncratic characteristics of the non-natives for developing management strategies. 相似文献
999.
地热田温度场分析, 不仅为地热田类型划分和热源机理研究提供科学根据, 而且可以为确定地热田有利开采区域和深度提供直接依据。本文报道了咸阳地热田13口钻孔的系统(准)稳态测温数据, 对研究区温度的垂向分布特征做了初步分析, 并据此划分了地热田水动力系统。结果表明, 咸阳地热田属于以传导为主的沉积盆地型地热田, 地温梯度为26.2~40.1 ℃/km, 平均为32.4 ℃/km。然而, 与典型的传导型地热田相比, 咸阳地热田的地温场特征又存在特殊性, 表现为钻孔温度-深度曲线分段性明显: 浅部受地表水流动对温度场的影响, 地温曲线呈现出锯齿形波动; 钻孔中上部受地表水和深部水热活动影响较小, 温度曲线为传导性地热特征; 井孔中下部测温曲线明显"下凹", 揭示了地下水沿渭河断裂侧向补给的同时使地层温度降低; 井孔下部温度随深度异常增大, 表明存在异常压力流体封存箱。测温资料揭示了咸阳地热田水动力系统在垂向上存在多层结构: 浅部为垂向重力驱动型, 中上部为正常压实型, 中下部为侧向重力驱动型, 下部为封闭型。基于咸阳地热田水动力系统的多层结构, 建议将各系统赋存的地热资源分别进行规划和开发。 相似文献
1000.
一种基于点云数据的DEM生成方法 总被引:1,自引:0,他引:1
利用机载激光雷达点云滤波已成为获取高精度数字高程模型的重要手段之一。本文充分考虑规则格网和虚拟格网的优势,利用规则格网进行建筑物区域与非建筑物区域的初步分离;然后,利用虚拟格网进行非地面点的去除,最后,用获得的地面点生成DEM,取得了较好的实验效果,具有一定的实用价值。 相似文献