2012年秋季白脊管藤壶在江苏如东互花米草盐沼向附着及分布

互花米草Spartina alterniflora自1979年引入至今,已在我国海岸带大范围扩张并对盐沼湿地生态系统产生了很大影响.本研究以附着生物藤壶为例,研究了互花米草扩张对附着生物的影响.通过对5个断面共28个样方的米草植株、附着藤壶以及藤壶在互花米草上的最大附着高度调查,获得结果如下:藤壶在互花米草滩上的附着范围位于潮沟两侧,且呈宽度约为5 m的带状分布;潮沟规模越大,其向陆方向的延伸范围越宽;每个站位藤壶附着的相对最大高度都位于同一水平.附着藤壶均为白脊管藤壶Fistulobalanus albicostatus,平均干重237±69g·m-2,大部分藤壶直径在2～10mm之间.互花米草的平均干重为981±81g·m-2,潮沟附近互花米草高壮但密度较小,远离潮沟互花米草矮小但密度较大.分析表明,互花米草为藤壶提供了附着基质,并影响藤壶在潮间带的平面分布格局(尽管藤壶的生态位保持不变).影响白脊管藤壶分布特征的原因主要是海水浸没时间的差异;负地形的浸没时间更有利于藤壶的附着和生存;另外潮沟较高的潮水流速除了利于白脊管藤壶幼体的附着外,还可以通过水流的涨、落为其带来充足的食物.     

Selection of Less Biased Threshold Angles for SAM Classification Using the Real Value–Area Fractal Technique

The accuracy of classification of the Spectral Angle Mapping (SAM) is warranted by choosing the appropriate threshold angles, which are normally defined by the user. Trial‐and‐error and statistical methods are commonly applied to determine threshold angles. In this paper, we discuss a real value–area (RV–A) technique based on the established concentration–area (C–A) fractal model to determine less biased threshold angles for SAM classification of multispectral images. Short wave infrared (SWIR) bands of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images were used over and around the Sar Cheshmeh porphyry Cu deposit and Seridune porphyry Cu prospect. Reference spectra from the known hydrothermal alteration zones in each study area were chosen for producing respective rule images. Segmentation of each rule image resulted in a RV–A curve. Hydrothermal alteration mapping based on threshold values of each RV–A curve showed that the first break in each curve is practical for selection of optimum threshold angles. The hydrothermal alteration maps of the study areas were evaluated by field and laboratory studies including X–ray diffraction analysis, spectral analysis, and thin section study of rock samples. The accuracy of the SAM classification was evaluated by using an error matrix. Overall accuracies of 80.62% and 75.45% were acquired in the Sar Cheshmeh and Seridune areas, respectively. We also used different threshold angles obtained by some statistical techniques to evaluate the efficiency of the proposed RV–A technique. Threshold angles provided by statistical techniques could not enhance the hydrothermal alteration zones around the known deposits, as good as threshold angles obtained by the RV–A technique. Since no arbitrary parameter is defined by the user in the application of the RV‐A technique, its application prevents introduction of human bias to the selection of optimum threshold angle for SAM classification.     

基于遥感影像的黄河内蒙古段冰-水分类研究

及时获取凌汛期河冰和水体的空间分布特征,对于预测冰凌灾害、提高防凌信息化管理水平有重要意义。遥感技术是当前获取河冰和水体空间分布的最主要手段之一。但是,黄河水体有大量悬浮泥沙,这给基于遥感技术的高精度冰-水分类带来了挑战。以黄河内蒙古段为例,基于Landsat 8 OLI遥感影像数据,在利用归一化积雪指数（NDSI）及河道矢量数据排除无关地物的基础上,对比了近红外波段反射率值、归一化差异水体指数（NDWI）、归一化积雪指数（NDSI）、改进的归一化积雪指数（MNDSI）以及归一化差异未封冻水体指数（NDUWI）在黄河内蒙古段典型河道河冰、水体分类中的表现,计算各指标总体分类精度及Kappa系数并进行阈值稳定性分析。结果表明：在利用NDSI和高清历史影像排除河道外无关地物后,NDUWI在各子段影像中的总体分类精度和Kappa系数均达到90.00%及0.90以上,其河冰、水体最优区分阈值大体分布于阈值中值附近。研究结果可为凌汛期黄河冰凌监测方法的选取以及冰上爆破位置的拟定提供依据。     

多时相遥感影像的变化监测方法研究

多时相遥感影像图变化监测已经在国民经济及国防建设领域得到了广泛应用。通过分析同一地域不同时相的遥感图像变化监测提供地物发生变化的信息,对资源环境数据进行更新及利用。论文围绕变化监测中的一些关键理论方法进行了研究。     

A near‐annual palaeohydrological study based on testate amoebae from a sub‐alpine mire: surface wetness and the role of climate during the instrumental period

We present the first testate amoeba‐based palaeohydrological reconstruction from the Swiss Alps, and the first depth to the water table (DWT) calibration dataset for this region. Compared to existing models, our new calibration dataset performs well (RMSEP = 4.88), despite the length of the water table gradient covered (53 cm). The present‐day topography and vegetation of the study mire Mauntschas suggest that it is partly ombrotrophic (large Sphagnum fuscum hummocks, one of which was the coring site) but mostly under the minerotrophic influence of springs in the mire and runoff from the surrounding area. Ombrotrophic Sphagnum fuscum hummocks developed at the sampling site only during the last 50 years, when testate amoebae indicate a shift towards dry and/or acid conditions. Prior to AD 1950 the water table was much higher, suggesting that the influence of the mineral‐rich water prevented the development of ombrotrophic hummocks. The reconstructed DWT correlated with Pinus cembra pollen accumulation rates, suggesting that testate amoebae living on the mire and P. cembra growing outside of it partly respond to the same factor(s). Finally, temperature trends from the nearby meteorological station paralleled trends in reconstructed DWT. However, contrary to other studies made on raised bogs of northwestern Europe, the highest correlation was observed for winter temperature, despite the fact that testate amoebae would more logically respond to moisture conditions during the growing season. The observed correlation with winter temperature might reflect a control of winter severity on surface moisture during at least the first part of the growing season, through snow melt and soil frost phenomena influencing run‐off. More ecohydrological work on sub‐alpine mires is needed to understand the relationships between climate, testate amoebae and peatland development. Copyright © 2009 John Wiley & Sons, Ltd.     

Groundwater geochemistry of the Chihuahua City region in the Rio Conchos Basin (northern Mexico) and implications for water resources management

The Chihuahua City region, located in the semiarid-arid northern highlands of Mexico, has experienced intensive groundwater abstraction during the last 40 years to meet water demands in the region. A geochemical survey was carried out to investigate the evolution from baseline to modern conditions of a 130-km flow path including the El Sauz–Chihuahua–Aldama–San Diego de Alcalá regions. The research approach included the use of major chemical elements, chlorofluorocarbons and environmental isotope (¹⁸O, ²H, ¹³C and ¹⁴C) tracers. Stable isotopes indicate that groundwater evolves from the evaporation of local rainfall and surface water. Groundwater located at the lower end of the flow section is up to 6000 years old and older groundwater in the order of 9000 years BP was found in a deep well located in the upper part of the flow system, implying contribution from a neighbour basin. The background groundwater chemistry upstream of Chihuahua City results from feldspar weathering. Beyond Chihuahua City the chemical conditions are strongly modified owing to disposal of sewage from public and industrial water supplies into the Rio Chuviscar, subsequent allocation of this water to agricultural irrigation areas and direct infiltration under the river bed. As a consequence, anions like chloride and sulphate are mainly related to surface sources. Nitrate is controlled in part by sewage from public supply and industry and in part by agricultural practices. Arsenic and fluoride are related to weathering of rock formations of local mineralized ranges and subsequent enrichment of the basin-fill by magmatic processes. The results of this study have implications for groundwater management in an arid region that depends entirely on groundwater for domestic, industrial and agricultural water consumption. Copyright © 2008 John Wiley & Sons, Ltd.     

Improvement of distributed snowmelt energy balance modeling with MODIS‐based NDSI‐derived fractional snow‐covered area data

Describing the spatial variability of heterogeneous snowpacks at a watershed or mountain‐front scale is important for improvements in large‐scale snowmelt modelling. Snowmelt depletion curves, which relate fractional decreases in snow‐covered area (SCA) against normalized decreases in snow water equivalent (SWE), are a common approach to scale‐up snowmelt models. Unfortunately, the kinds of ground‐based observations that are used to develop depletion curves are expensive to gather and impractical for large areas. We describe an approach incorporating remotely sensed fractional SCA (FSCA) data with coinciding daily snowmelt SWE outputs during ablation to quantify the shape of a depletion curve. We joined melt estimates from the Utah Energy Balance Snow Accumulation and Melt Model (UEB) with FSCA data calculated from a normalized difference snow index snow algorithm using NASA's moderate resolution imaging spectroradiometer (MODIS) visible (0·545–0·565 µm) and shortwave infrared (1·628–1·652 µm) reflectance data. We tested the approach at three 500 m² study sites, one in central Idaho and the other two on the North Slope in the Alaskan arctic. The UEB‐MODIS‐derived depletion curves were evaluated against depletion curves derived from ground‐based snow surveys. Comparisons showed strong agreement between the independent estimates. Copyright © 2010 John Wiley & Sons, Ltd.     

The role of lithology,catchment size and the alluvial zone on the hydrogeochemistry of two intermittent Mediterranean streams

Hydrology and solute concentrations of two intermittent Mediterranean streams draining two nested catchments were compared. The two catchments were mainly underlain by granitic rocks and different types of sericitic schists. Only the lowland catchment had an alluvial zone and a well‐developed riparian forest. The rainfall–runoff relationship and the correlation between daily flow concentrations showed that hydrological behaviour was similar at both sites during most of the year. However, reverse fluxes were detected during the wetting and drying up periods only in the stream with an alluvial zone. The intermittence in stream flow also had effects on absolute solute concentrations, temporal solute dynamics and streamwater stoichiometry. Streamwater chemistry was not affected by drainage area, except for cations produced mainly by bedrock dissolution (i.e. calcium and magnesium) that increased with increasing catchment size. Differences in the relationship among cations and anions were detected between the two streams, which could be attributed to biogeochemical processes occurring in the alluvial zone. The multivariate model used in this study showed that stoichiometry was more useful than absolute concentrations when analyzing the influence of different lithologies on streamwater chemistry. Such differences were amplified in autumn, likely due to a low hydrological connectivity between the two nested catchments. Copyright © 2007 John Wiley & Sons, Ltd.     

Floodplain hydrology of the Mekong Delta,Vietnam

The Mekong Delta is one of the largest and most intensively used estuaries in the world. Each year it witnesses widespread flooding which is both the basis of the livelihood for more than 17 million people but also the major hazard. Therefore, a thorough understanding of the hydrologic and hydraulic features is urgently required for various planning purposes. While the general causes and characteristics of the annual floods are understood, the inundation dynamics in the floodplains in Vietnam which are highly controlled by dikes and other control structures have not been investigated in depth. Especially, quantitative analyses are lacking, mainly due to scarce data about the inundation processes in the floodplains. Therefore, a comprehensive monitoring scheme for channel and floodplain inundation was established in a study area in the Plain of Reeds in the northeastern part of the Vietnamese Delta. This in situ data collection was complemented by a series of high‐resolution inundation maps derived from the TerraSAR‐X satellite for the flood seasons 2008 and 2009. Hence, the inundation dynamics in the channels and floodplains, and the interaction between channels and floodplains, could be quantified for the first time. The study identifies the strong human interference which is governed by flood protection levels, cropping patterns and communal water management. In addition, we examine the tidal influence on the inundation in various parts of the Delta, since it is expected that climate change‐induced sea level rise will increase the tidal contribution to floodplain inundation. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of meteorological and hydrogeological factors on gross recharge percentage at unconfined sandy aquifers with an equatorial climate

A thorough understanding of rainfall recharge processes and their controlling factors is essential for management of groundwater systems. This study investigates the effects of various meteorological and hydrogeological factors on the gross recharge percentages, the rainfall–recharge relationships and the recharge threshold values for unconfined sandy aquifers under an equatorial climate. Among the meteorological factors investigated, rainfall intensity was found to have the most significant impact on the gross recharge rate. The effects of potential evaporation rate, relative humidity and air temperature on the gross recharge percentage were significant when the vadose zone thickness is larger than 2·5 m. The recharge threshold values were found to depend strongly on the vadose zone thickness. The rainfall–recharge relationships could generally be well defined by a normal–log relationship. The rainfall–recharge relationships derived here are applicable to yield estimates of gross recharge percentages for unconfined sandy aquifers under an equatorial climate, using rainfall intensity and vadose zone thickness as input variables. In this study, a theory was developed and validated to provide physical explanations for the observations, based on the residence time of the percolated rainwater within the vadose zone. Among the soil hydraulic parameters tested, porosity and saturated hydraulic conductivity were found to have the most pronounced effects on the gross recharge percentage. Utilizing the sensitivity results and the theory derived, an approach was developed for extending the application of the derived rainfall–recharge relationships to other sand textures. The approach was found to be capable of producing rough and fast estimations of gross recharge percentage for other sand textures. Copyright © 2007 John Wiley & Sons, Ltd.