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41.
Sediment properties, such as water content and density, have been used to estimate the dry and wet weights, as well as the volume of sediment recovered and discharged, during benthic impact experiments conducted in the Pacific and Indian Oceans. The estimates show that the weights of dry (355-1332 t) and wet sediment (1651-4888 t) recovered during the experiments, are not only a function of the total duration and distance covered during the experiment, but also depend on water content and density of the sediment. Estimation of dry sediment and its volumetric ratio in the discharge, are key parameters for calculating the discharged volume. The estimated volume of wet sediment recovered (1427-4049 m 3 ) as well as discharged (2693-6951 m 3 ) during the experiments, provide important inputs to evaluate the sediment resettlement and migration. Using these estimates, the average depth of excavation on the seafloor, can also been calculated. However, the stages of sediment recovery and discharge are expressed differently in some of the experiments. In order to standardize these, different stages have been identified, and definitions of certain terms have been suggested, for use in the future. The methods of calculating different properties, as well as weight and volume of discharged sediment are described in the paper for use in other applications concerning deep-sea discharges. 相似文献
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The spatial and seasonal taxonomic composition patterns of macrofauna and nematodes in a eutrophic subtropical harbour, previously suffered from sewage pollution, were studied in relation to a number of sediment parameters. In the polluted, inner-harbour area, levels of organic contents and heavy metals were high, whereas species number, abundance and diversity of nematodes and macrofauna were the lowest in comparison to the cleaner, outer-harbour area. Different taxonomic composition patterns of nematodes and macrofaunal assemblages were found between inner-harbour and outer-harbour area, which was highly correlated with sediment nutrient levels. Different responses of macrofaunal and nematode communities to sewage pollution suggested that macrofauna might be more tolerant than nematodes to eutrophic conditions due to their ability to modify the sediment. The present findings indicated the usefulness of studying both nematode and macrofaunal communities, in order to reveal different aspects of the benthic ecosystems in response to organic enrichment. 相似文献
44.
Recovery scenarios for deep over-exploited aquifers with limited recharge: methodology and application to an aquifer in Belgium 总被引：2，自引：0，他引：2
Recharge of deep-seated aquifers must be provided through leakage from overlying geological formations and can be very limited.
Although hydraulic characteristics of these aquifers may be favorable for extensive exploitation, the renewability of the
groundwater resource may be very restricted and only significant on long time scales. Over-exploitation of such aquifers leads
to steadily declining piezometric levels and water balancing and steady state conditions are not to be expected on the short
term. Recovery of such systems is very difficult, also because of the socio-economic dependencies of the water resource and
the long time it requires to replenish the system. Management plans for restoration should be based on the transient hydrodynamical
behaviour. A recovery plan should be developed based on results of a groundwater flow model. In a first step must be simulated
how long it will take for the aquifer system to fully recover by natural recharge. As this will most often be a very long
time it can be cancelled out as a realistic scenario. An alternative objective is to be formulated which could be achieved
in the near future on a time scale of years or decades. Using model simulations, reduction schemes of exploitation rates shall
be quantified that will allow to reach these defined goals, such as raising piezometric levels above the top of the aquifer
itself or above the top of the overlying geological unit. The methodology is illustrated with an example of a deep hard rock
aquifer in Belgium where piezometric levels have dropped below the top. The objective here was to raise the levels again above
the top within the next 50 years. However, this is not accomplished by balancing aquifer recharge and discharge, but is reached
by a lateral redistribution of the water over the aquifer extent. A full recovery of this aquifer would require at least a
century with only a very limited amount of exploitation. 相似文献
45.
One-dimensional numerical simulation of non-uniform sediment transport under unsteady flows 总被引：16，自引：9，他引：7
One-dimensional numerical models are popularly used in sediment transport research because they can be easily programmed and cost less time compared with two- and three-dimensional numerical models. In particular, they possess greater capacity to be applied in large river basins with many tributaries. This paper presents a one-dimensional numerical model capable of calculating total-load sediment transport. The cross-section-averaged sediment transport capacity and recovery coefficient are addressed in the suspended load model. This one-dimensional model, therefore, can be applied to fine suspended loads and to hyperconcentrated flows in the Yellow River. Moreover, a new discretization scheme for the equation of unsteady non-uniform suspended sediment transport is proposed. The model is calibrated using data measured from the Yantan Reservoir on the Hongshui River and the Sanmenxia Reservoir on the Yellow River. A comparison of the calculated water level and river bed deformation with field measurements Shows that the improved numerical model is capable of predicting flow, sediment transport, bed changes, and bed-material sorting in various situations, with reasonable accuracy and reliability. 相似文献
46.
Artificially enhancing recharge rate into groundwater aquifer at specially designed facilities is an attractive option for increasing the storage capacity of potable water in arid and semi‐arid region such as Damascus basin (Syria). Two dug wells (I and II) for water injection and 24 wells for water extraction are available in Mazraha station for artificial recharge experiment. Chemical and stable isotopes (δ2H and δ18O) were used to evaluate artificial recharge efficiency. 400 to 500*103 m3 of spring water were injected annually into the ambient shallow groundwater in Mazraha station, which is used later for drinking purpose. Ambient groundwater and injected spring water are calcium bicarbonate type with EC about 880 ± 60 μS/cm and 300 ± 50 μS/cm, respectively. The injected water is under saturated versus calcite and the ambient groundwater is over saturated, while the recovered water is near equilibrium. It was observed that the injection process formed a chemical dilution plume that improves the groundwater quality. Results demonstrate that the hydraulic conductivity of the aquifer is estimated around 6.8*10?4 m/s. The effective diameter of artificial recharge is limited to about 250 m from the injection wells. Mixing rate of 30% is required in order to reduce nitrate concentration below 50 mg/l which is considered the maximum concentration limit for potable water. Deuterium and oxygen‐18 relationship demonstrates that mixing line between injected water and ambient groundwater has a slope of 6.1. Oxygen‐18 and Cl? plot indicates that groundwater salinity origin is from mixing process, and no dissolution and evaporation were observed. These results demonstrate the efficiency of the artificial recharge experiments to restore groundwater storage capacity and to improve the water quality. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
47.
48.
土地资源是国家重要的自然资源,土地资源的合理开发利用有力地支持了国民经济的发展。但在闭坑的露天煤矿中,对矿山地形地貌、土地资源、生态植被等影响较大,为促进生态可持续发展,应积极采取自然恢复、辅助再生、生态重建等措施,及时对损毁区域进行生态修复,改善生态环境。实现煤炭开采扰动区域的地质环境达到稳定、损毁土地得到治理利用、生态系统功能得到恢复和提升、废弃资源得到综合利用等目标。本文以黔北某露天煤矿为例,通过采取生态重建技术该露天煤矿进行修复,恢复耕地33682 4 hm2,林地14262 6 hm2,农村道路1389 7 hm2,公路用地0271 8 hm2。通过地貌重塑、土壤重构、植被重建等生态重建技术对矿山损毁区进行修复,以期为同类型矿山生态修复提供借鉴。 相似文献
49.
S. Redondo-Gómez L. Andrades-MorenoR. Parra E. Mateos-NaranjoA.M. Sánchez-Lafuente 《Journal of Arid Environments》2011,75(3):309-312
Cyperus capitatus Vandelli (Cyperaceae) is distributed in coastal sandy habitats and mobile dunes of south Europe. Its seed germination ecology is not known, despite its potential to be used in re-vegetation projects. Laboratory experiments were conduced to assess the effects of salinity, light regime, cold stratification and burial on seed germination of this species. Overall, increasing salinity delayed germination, increased seed dormancy and mean time to germination (MTG), and reduced final germination percentage, inhibiting it completely above 1% of salinity; although it did not affect seed viability. C. capitatus seeds exhibited their greatest germination at levels between 0 and 1% in non-stratified seeds, and between 0 and 0.5% for stratified seeds. Thus, the effect of salt was greater for stratified seeds at 5 °C. Germination in light/darkness conditions was similar to that in full darkness. Finally, burial in sand of C. capitatus seeds appeared to have a significant effect on cumulative percentage of germination. Seeds buried at depths greater than 2 and 3 cm showed a lower germination success than those on sand surface or buried at shallower depths. Burial also affected the beginning and speed of seed germination. 相似文献
50.
同位素技术是研究区域地下水循环规律的主要手段之一。本文对平原区地下水进行了取样分析,运用同位素技术并结合水文地质条件,研究了北京市平原区地下水循环演化规律。运用^3H和^14C的测年技术确定了地下水年龄;利用D和18^O关系曲线探讨了地下水的起源;按照是否积极参加了现代水循环的原则将第四系地下水划分为浅层水和深层水;对浅层水和深层水的更新状况进行了研究。研究表明,浅层水广泛分布于北京平原区,径流条件好,更新快;深层水主要分布于永定河、潮白河冲洪积扇下部及冲洪积平原的深部地区,补给条件相对差,与现代大气降水联系弱,径流条件差,更新慢。 相似文献