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191.
This paper quantitatively explores farmers' vulnerability to flood in the Poyang Lake Region (PLR) with the supports of GIS spatial functions. The analysis consists of three major steps,which is based on the spatial unit of township. Firstly,the spatial extent and charac-teristics of flood risk areas were determined using a digital elevation model (DEM) derived from the 1:50,000 topographic map. Secondly,for each of the township,six indices indicating the economic activities of local farmers were calculated. These indices are: rural population proportion,cultivated land proportion,GDP per unit area,employment proportion of primary industry,net rural income per capita and agricultural income proportion. These six indices were then normalized and used for later vulnerability assessment. Thirdly,the normalized indices (as GIS data layers) were overlaid with the flood risk areas to produce the risk coeffi-cient for each township and to calculate the overall vulnerability for each township. The analysis results show that in the PLR there are high flood risk areas where the farmers' livings are seriously influenced or threatened. About 55.56% of the total 180 townships in the flood risk areas have a high degree of flood vulnerability. The townships under flood risk are mainly distributed in the areas around the Poyang Lake and the areas along the "five rivers".  相似文献   
192.
太湖富营养化遥感评价研究   总被引:2,自引:0,他引:2  
讨论利用Landsat/TM数据进行太湖富营养化评价的可行性,提出一种与常规湖泊富营养化评价方法(综合营养状态指数法)接轨的遥感评价新方法,建立了太湖富营养化遥感评价模型(中国湖泊营养状态指数模型TSIc),利用Landsat/TM数据定量反演出的太湖Chl - a浓度作为TSIc模型的输入变量,计算出太湖营养状态TSIc值,最后按照湖泊富营养化评价分级标准将太湖营养状态分为贫营养(TSIc<30)、中营养(30≤TSIc≤50)、轻度富营养(50<TSIc≤60)、中度富营养(60<TSIc≤70)和重度富营养(>70)5级.  相似文献   
193.
段雪梅  胡守云  杨涛 《第四纪研究》2007,27(6):1105-1112
对武汉汤逊湖湖泊沉积物T06-1样芯进行了磁性测量、重金属分析和粒度分析,探讨了利用磁参数追踪、指示城市湖泊重金属污染的可行性.结果表明,低矫顽力的亚铁磁矿物主导了沉积物的磁性特征.磁参数χ,SIRM和ARM与重金属Cr,Zn,Cu和Pb呈现较为一致的垂向变化特征:55cm之下,磁参数值和重金属的含量均较低且稳定;在50~10 cm之间,两者基本呈现随深度的减小而增加的趋势,其中在20~10 cm区间,出现小范围内波动;而10cm至表层,元素含量和磁参数值随深度减小而急剧增加.选取粘土(<4μm)对沉积物中Cr,Zn,Cu和Pb进行粒度校正的结果显示:校正后元素的变化趋向于平稳,但在表层的10cm处Cr,Pb,Zn和Cu的含量仍然较高,表明了表层沉积物中金属元素的含量主要受人类活动的影响.相关分析也表明了磁参数χ,SIRM和ARM与重金属Cr,Pb,Zn和Cu之间均呈显著相关关系(0.62≤R≤0.86),表明磁参数可以用于追踪和指示汤逊湖湖泊沉积物重金属污染.  相似文献   
194.
Abstract

Abstract MODerate-resolution Imaging Spectroradiometer (MODIS) is a new generation remote sensing (RS) sensor and its applications in hydrology and water resources have attracted much attention. To overcome the problems of slow response in flood disaster monitoring based on traditional RS techniques in China, the Flood Disaster Monitoring and Assessing System (FDMAS), based on MODIS and a Geographic Information System (GIS), was designed and applied to Dongting Lake, Hunan Province, China. The storage curve of Dongting Lake for 1995 was obtained using 1:10 000 topographic map data and then a relationship between water level at the Chenglingji hydrological station and lake area was derived. A new relationship between water level and lake area was obtained by processing MODIS images of Dongting Lake from April 2002 to April 2003 and the influence of lake area variation on water level was analysed with the 1996 flood data. It was found that the water level reduction reached 0.64 m for the 1996 flood if the original lake area curve was replaced with the area curve of 2002. This illustrates that the flood water level has been considerably reduced as a result of the increased area of Dongting Lake since the Chinese Central Government’s ?return land to lake? policy took effect in 1998.  相似文献   
195.
Y. Chebud  A. Melesse 《水文研究》2013,27(10):1475-1483
Lake Tana is the largest fresh water body situated in the north‐western highlands of Ethiopia. In addition to its ecological services, it serves for local transport, electric power generation, fishing, recreational purposes, and source of dry season irrigation water supply. Evidence shows that the lake has dried at least once at about 15,000–17,000 before present owing to a combination of high evaporation and low precipitation events. Past attempts to understand and simulate historical fluctuation of Lake Tana based on simplistic water balance approach of inflow, outflow, and storage have failed to capture well‐known events of drawdown and rise of the lake that have happened in the last 44 years. This study tested different stochastic methods of lake level and volume simulation for supporting Lake Tana operational planning decision support. Three stochastic methods (perturbations approach, Monte Carlo methods, and wavelet analysis) were employed for lake level and volume simulation, and the results were compared with the stage level measurements. Forty‐four years of daily, monthly, and mean annual lake level data have shown a Gaussian variation with goodness of fit at 0.01 significant levels of the Kolmogorov–Smirnov test. The stochastic simulations predicted the lake stage level of the 1972, 1984, and 2002/2003 historical droughts 99% of the time. The information content (frequency) of fluctuation of Lake Tana for various periods was resolved using Wigner's Time‐Frequency Decomposition method. The wavelet analysis agreed with the perturbations and Monte Carlo simulations resolving the time (1970s, 1980s, and 2000s) in which low frequency and high spectral power fluctuation has occurred. The Monte Carlo method has shown its superiority for risk analysis over perturbation and deterministic method whereas wavelet analysis reconstructed historical record of lake stage level at daily and monthly time scales. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
196.
Two cores were recovered in the southeastern part of Lake Shkodra (Montenegro and Albania) and sampled for identification of tephra layers. The first core (SK13, 7.8 m long) was recovered from a water depth of 7 m, while the second core (SK19, 5.8 m long) was recovered close to the present‐day shoreline (water depth of 2 m). Magnetic susceptibility investigations show generally low values with some peaks that in some cases are related to tephra layers. Naked‐eye inspection of the cores allowed the identification of four tephra layers in core SK13 and five tephra layers in core SK19. Major element analyses on glass shards and mineral phases allowed correlation of the tephra layers between the two cores, and their attribution to six different Holocene explosive eruptions of southern Italy volcanoes. Two tephra layers have under‐saturated composition of glass shards (foiditic and phonolitic) and were correlated to the AD 472 and the Avellino (ca. 3.9 cal. ka BP) eruptions of Somma‐Vesuvius. One tephra layer has benmoreitic composition and was correlated to the FL eruption of Mount Etna (ca. 3.4 cal. ka BP). The other three tephra layers have trachytic composition and were correlated to Astroni (ca. 4.2 cal. ka BP), Agnano Monte Spina (ca. 4.5 cal. ka BP) and Agnano Pomici Principali (ca. 12.3 cal. ka BP) eruptions of Campi Flegrei. The ages of tephra layers are in broad agreement with eight 14C accelerator mass spectrometric measurements carried out on plant remains and charcoal from the lake sediments at different depths along the two cores. The recognition of distal tephra layers from Italian volcanoes allowed the physical link of the Holocene archive of Lake Shkodra to other archives located in the central Mediterranean area and the Balkans (i.e. Lake Ohrid). Five of the recognised tephra layers were recognised for the first time in the Balkans area, and this has relevance for volcanic hazard assessment and for ash dispersal forecasting in case of renewed explosive activity from some of the southern Italy volcanoes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
197.
《水文科学杂志》2013,58(4):808-824
Abstract

We report results of three field campaigns conducted at 39 stations. At each station, we measured reflectance spectra in situ and collected water samples for measuring chlorophyll a (CHL) and suspended solids (SS) concentrations in the laboratory. To identify the indicative bands and develop suitable estimation models for CHL (C CHL) and SS (C SS) concentrations in Taihu Lake, a spectral-feature method and a derivative method were applied. The following conclusions were drawn: (a) the critical C CHL and C SS probably causing their spectral variation are, respectively: 0, 10, 50 and 75 μg L?1, and 0, 10, 50 and 100 mg L?1; (b) the derivative method is better than the spectral-feature method for estimating C CHL and C SS; (c) the optimal variable for CHL is a reflectance second-order derivative at 501 nm or a reflectance first-order derivative at 698 nm; the optimal variable for SS can change when its concentration is low and the range is narrow; otherwise, the optimal variable is a reflectance first-order derivative at 878 nm; and (d) the CHL and SS have an effect on one another's retrieval. The C CHL estimation accuracy would benefit from narrowing the C SS range. With C CHL increasing and its range broadening, the corresponding C SS estimation accuracy decreases gradually.  相似文献   
198.
Abstract

Abstract The geographical context and hydroclimatology of the English Lake District means that the region is an important monitor of changes to nationally significant environmental assets. Using monthly rainfall series for sites in and around the central Lake District, a continuous ~200-year precipitation index was constructed for a representative station close to Grasmere. The bridged series shows a significant decline in summer rainfall since the 1960s, offset by increases in winter and spring that are strongly linked to North Atlantic forcing. Over longer time periods, the index exhibits several notable dry (1850s, 1880s, 1890s, 1930s, 1970s) and wet (1820s, 1870s, 1920s, 1940s, 1990s) decades. These patterns are strongly reflected by reservoir inflow series and by indicators of the biological status of the region’s freshwater lakes. It is argued that long-term climate indices will become increasingly important as managers seek to evaluate recent and project environmental changes within the context of long-term natural variability.  相似文献   
199.
青海湖沉积物中的粘土矿物   总被引:5,自引:0,他引:5       下载免费PDF全文
徐昶  林乐枝 《地质科学》1989,5(4):348-354
本文对青海湖沉积物中的粘土矿物和沉积环境进行了初步研究。沉积物的粒度成分一般以粉砂级为主,湖周沉积物较粗,湖内沉积物较细。湖中粘土矿物以伊利石-绿泥石为主,含少量蒙脱石和高岭石等。沉积物表层未见蒙脱石,粘土中Al2O3、K2O和MgO的相对百分含量的特征与海粘土的化学成分特征相似。  相似文献   
200.
The diatom biostratigraphy of the topmost sediment meter of Rotsee, Central Switzerland, is characterized by a major change fromCyclotella comensis-dominated toStephanodiscus hantzschii/S. parvus-dominated assemblages. A comparison between old phytoplankton samples, taken between 1910–1930, and subfossil diatom assemblages is used for dating the upper 35 cm of the core. There is evidence that the change in dominant diatoms occurred in 1919/20, thus before the opening of an artificial inlet in 1922, and is due to increasing eutrophication. Furthermore, the sedimentary carbonate content can be used as a good indicator for past phytoplankton productivity in Rotsee.  相似文献   
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