At present, researches on climate change of the Heihe River basin mainly focus on the relationship between basin climate change
and regional water resources, regional desertification and dynamic climatic seasons of sandstorm, but less on climate change
of oasis region, where there are more intense and frequent human activities. Based on data of precipitation, temperature,
strong wind and dust events frequencies obtained from the six meteorological stations of Zhangye region in Heihe River basin,
the features of climate change during 1968–2005 were carefully studied. Results show that the regional temperature rise rate
exceeded the average level of China. The annual precipitation changed a little, but the precipitation had a slowly increasing
trend in spring and winter. Frequencies of strong wind and sandstorm days show obviously descending trends, which had a close
correlation with the regional temperature rise and the precipitation increase in spring and winter. Meanwhile, further human
economic activities and exploitations to the oasis in the inland valley of arid regions also affected the climate change of
this region, which has a sensitive and fragile eco-environment.
__________
Translated from Journal of Desert Research, 2007, 27(6): 1048–1054 [译自: 中国沙漠] 相似文献
Selenium (Se) is an essential micronutrient to biota, but can become a potent toxicant at elevated concentrations. The natural sources and chemical properties of Se species make the boundary between deficiency and toxicity narrow for some biota, with both phenomena common around the globe. Large areas of farmland in the Colorado River Basin (CRB) generate salinized drainage water with Se concentrations much higher than 5 μg/L, the U.S. Environmental Protection Agency chronic water-quality criterion for the protection of aquatic life. We have carried out detailed field and laboratory studies to investigate Se geochemistry and remediation in two of these areas: the Middle Green River Basin, Utah and the Salton Sea Basin, California, located respectively in the Upper and Lower CRB. Results from these and other studies show that approximately 90% of the dissolved Se in the Colorado River and its tributaries originally is derived from the Upper Cretaceous Mancos Shale and equivalent pyritic marine units that outcrop in the Upper CRB. Selenium is mobilized commonly by biogeochemical oxidation of this pyritic shale and is concentrated mainly as selenate (SeO4^2-) in soils and agricultural drainage water of dry climates by evaporation. Minor (0%-5%) amounts of Se are present as the selenite species (HSeO3^-) and (SEO3^2-), but these species and the more reduced species, elemental Se (SeO) and selenide (Se^2-), have much lower solubility and/or have high sorptive affinity towards organic matter, clay minerals and iron oxyhydroxides. The concentration of dissolved Se (-2.5 μg/L) and salinity in the Lower Colorado River water are among the highest of the world major rivers. Because of low precipitation (7 cm/a) and extreme evapotranspiration (-1.8 m/a) rates in the Salton Sea Basin, California, Se values in irrigation water imported from the Colorado River increase to 〉300 μg/L in drainage wastewater. Removal of Se from contaminated wastewater by nanofiltration membranes was demonstrated in laboratory and pilot-scale field experiments. 相似文献
The Second Songhua River was subjected to a large amount of untreated effluent from petrochemical industries in Jilin City in the 1960s to the 1970s. The objectives of this study were to investigate the mercury and other heavy metal contamination in the sediment of the river. The river bottom sediment was sampled from the river segment between Jilin City to Haerbin City in 2005. Total concentrations of Hg, Cd, Cu, Cr, Pb, Zn, Ni, As, Sc, and major cations (A1, Fe, Mg, Ca, K, Na) in the sediment were measured by atomic fluorescence spectrometer, ICP-MS, and ICP-OES, respectively, following digestion with various acids. We found the concentrations of most elements in the uncontaminated sediment were significantly correlated to those of Sc. 相似文献
The Dead Sea fault system and its branching faults represent one of the most tectonically active regions in the Middle East. The aim of this study is to highlight the degree of hazards related to the earthquake activities associated with the Dead Sea rift, in terms of speculating the possible future earthquakes. The present investigation mainly is based on available data and vertical crustal modeling of Jordan and the Dead Sea model for the Dead Sea basin with particular emphasis of the recent earthquake activities, which occurred on December 31st, 2003 (Mc = 3.7), February 11th, 2004 (strongest Mc = 4.9 R), and March 15th, 2004 (Mc = 4). The present research examines the location of the strong events and correlates them with the various tectonic elements in the area. The source mechanism of the main shock and the aftershock events is also examined. The analyses were based on the available short period seismogram data, which was recorded at the Natural Resources Authority of Jordan, Seismological Observatory. The seismic energy appears to have migrated from the south to the north during the period from December 31st up to March 12th, where the released seismic energy showed a migration character to the southern block of the eastern side of the Dead Sea, which led the seismic event to occur on March 15th. 相似文献
One of the most significant water resources in the Republic of Croatia is the catchment area of the Kupa River, located in
the region bordering the Republic of Slovenia. About 88% of the total amount of water in this catchment originates in Croatia
and just 12% from Slovenia; therefore, the largest part of the catchment area (about 1000 km2) is on the Croatian side of the border. It is a typical karst area of the Dinarides with aquifers characterized by a relatively
rapid water exchange, high groundwater flow velocities and aquifers open to human impact from the surface. Consequently, the
aquifers are highly vulnerable and at risk. Due to the availability of large quantities of high-quality spring water (about
6 m3/s), the entire area has a strategic importance within the context of any future development strategy pertaining to the western
part of Croatia. The catchment area on the Croatian side was investigated using a wide range of research methods that included
a classical hydrogeological approach, the detailed hydrologic calculation of water balance to the hydrogeochemical analyses
and modelling. The objective was to determine protection zones and protection measures for the whole area. The difficulties
are increased due to the fact that the karst catchment area is crossed by major traffic corridors, oil pipelines and a railway
and that many settlements and a highly developed wood industry are present. The combination of protecting water resources
with adequate prevention measures and necessary remedial activities that should satisfy the very strict requirements necessary
for the protection of the karst aquifers while still allowing for present and future human activities is difficult – but not
impossible – to achieve. One good example is the present highway with a closed dewatering system and waste water treatment
before the water passes into the karst underground system. 相似文献
Whereas certain linkages between stream channel morphology and stream ecology are fairly well-understood, how geomorphology influences trophic interactions remains largely unknown. As a first step, a simple, heuristic model is developed that couples reach-scale geomorphic morphology with trophic dynamics between vegetation, detritus, herbivores, and predators. Predation is assumed to increase with depth beyond a threshold depth, and herbivory is assumed to decrease with velocity beyond a threshold velocity. Results show that the modeled food chain is sensitive to channel geometry, particularly around the threshold conditions for predators and herbivores. Importantly, geomorphic influences are not isolated to a particular trophic level, but rather are transferred through the food chain via top-down and bottom-up effects. The modeled system is particularly sensitive to changes in the end-members of the food chain: vegetation and predators. Results illustrate that geomorphic disturbances, known to affect a single trophic level (e.g., fish), likely impact multiple trophic levels in the stream ecosystem via trophic interactions. Such impacts at the multiple trophic level are poorly understood. While limited by the lack of empirical long-term data for testing and calibration, this simple model provides a structure for generating hypotheses, collecting targeted data, and assessing the potential impacts of stream disturbance or restoration on entire stream ecosystems. Further, the model illustrates the potential for future coupled stream models to explore spatial and temporal linkages. 相似文献
The Late Cretaceous–Cenozoic evolution of the eastern North Sea region is investigated by 3D thermo-mechanical modelling. The model quantifies the integrated effects on basin evolution of large-scale lithospheric processes, rheology, strength heterogeneities, tectonics, eustasy, sedimentation and erosion.
The evolution of the area is influenced by a number of factors: (1) thermal subsidence centred in the central North Sea providing accommodation space for thick sediment deposits; (2) 250-m eustatic fall from the Late Cretaceous to present, which causes exhumation of the North Sea Basin margins; (3) varying sediment supply; (4) isostatic adjustments following erosion and sedimentation; (5) Late Cretaceous–early Cenozoic Alpine compressional phases causing tectonic inversion of the Sorgenfrei–Tornquist Zone (STZ) and other weak zones.
The stress field and the lateral variations in lithospheric strength control lithospheric deformation under compression. The lithosphere is relatively weak in areas where Moho is deep and the upper mantle warm and weak. In these areas the lithosphere is thickened during compression producing surface uplift and erosion (e.g., at the Ringkøbing–Fyn High and in the southern part of Sweden). Observed late Cretaceous–early Cenozoic shallow water depths at the Ringkøbing–Fyn High as well as Cenozoic surface uplift in southern Sweden (the South Swedish Dome (SSD)) are explained by this mechanism.
The STZ is a prominent crustal structural weakness zone. Under compression, this zone is inverted and its surface uplifted and eroded. Contemporaneously, marginal depositional troughs develop. Post-compressional relaxation causes a regional uplift of this zone.
The model predicts sediment distributions and paleo-water depths in accordance with observations. Sediment truncation and exhumation at the North Sea Basin margins are explained by fall in global sea level, isostatic adjustments to exhumation, and uplift of the inverted STZ. This underlines the importance of the mechanisms dealt with in this paper for the evolution of intra-cratonic sedimentary basins. 相似文献