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311.
Adrian Williams 《中国科学D辑(英文版)》2002,45(1):109-114
The paper describes Western Australian examples and causes of land degradation. It outlines shortcomings in the methodologies used to rehabilitate these areas. From this a protocol is suggested for an ‘holistic’ approach to land rehabilitation. 相似文献
312.
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315.
Mt. Qomolangma lies in the collision zone between the fringe of Eurasia plate and Indian plate. The crustal movement there
is still very active so far. In the past three decades China carried out five geodetic campaigns in Mt. Qomolangma and its
north vicinal area, independently or cooperatively with other countries, including triangulation, leveling, GPS positioning,
atmospheric, astronomical and gravity measurements. On the basis of the observation results achieved in the campaigns the
crustal movements in the area were studied and explored. A non-stationary phenomenon both in time and space of the crustal
vertical movement in the area is found. There seems to be some relevance between the phenomenon of non-stationary in time
and seismic episode in China. The phenomenon of non-stationary in space is possibly relevant to the no-homo- geneity of crustal
medium and non-uniform absorption of terrestrial stress. The horizontal crustal movement in the area is in the direction of
NEE at a speed of 6–7 cm per year, and the trend of strike slip movement is manifested evidently in the collision fringe of
Indian plate and Qinghai-Xizang block. 相似文献
316.
Quantitative reconstruction of the lake water paleotemperature of Daihai Lake, Inner Mongolia, China and its significance in paleoclimate 总被引:5,自引:2,他引:5
By measuring Sr/Ca ratios of the ostracod shells (Limnocthere cf. inopinata) in sediments of the Daihai Lake, and combined with Sr2+/Ca2+ ratios of the lake water, this paper obtained paleosalinity of the lake water. Vaporizing experiment of the lake water in
laboratory showed that there was a quantitative relationship between salinity and oxygen isotope. Using this relationship,
oxygen isotope values of the paleo-lake water were calculated. By measuring the oxygen isotope of the authigenic carbonate
in the lake’s sediments, and in combination with the oxygen isotope values of the paleo-lake water, the paleotemperature of
the lake water was calculated. Finally, based on these proxies, the paleoclimate in the lake basin was explored. 相似文献
317.
The groundwater table has been declining at a rate of 0.65 m/yr in Luancheng County since large scale groundwater extraction
carried out in the 1960s. The drop of precipitation, substantial increase in agricultural output, variations of crop planting
structure and construction of water conservancy projects in the headwater area all tie up with the decline of the groundwater
table. On the basis of analyzing the hydrogeological conditions and the water resources utilization of Luancheng County, a
three-dimensional groundwater flow model was developed to simulate the county’s groundwater flow through finite-difference
method using Visual Modflow software. We divide the research field into four parts after analyzing the hydrogeological condition.
Based on parameter calibration and adjustment using measured data, the hydraulic conductivity and specific yield were simulated.
Using the calibrated model, we analyze the agricultural water saving potentiality and its influence on the groundwater. The
results are as follows: (1) if we decrease the amount of water extracted by 0.14xl08 m3, the average groundwater table of the five observation wells in December will rise by 0.33 m; (2) if we decrease the water
by 0.29x 108m3, the average groundwater table of the five observation wells in December will rise by 0.64 m; and (3) if we increase the
water by 0.29 x 108m3, the average groundwater table of the five observation wells in December will decline by 0.45 m. So we can draw a conclusion
that controlling the agricultural water use is an important way to prevent the decline of groundwater table. 相似文献
318.
Soil sediment samples of 10 layers with a spacing of 10 cm each were collected in different floodplain zones adjacent to Huolin
River in the Xianghai Nature Reserve, and contents of total N, total P and organic matters were analyzed. The results showed
that contents of total N, total P and organic matters were generally decreasing with the increase of distance from sample
locations to the river channel, and contents of the three items were generally higher in the upper soil layer than that in
the lower soil layer. The content variations displayed how flooding functions influenced nutrient matter content variations
in floodplain soils since the flood inundation frequencies of the sample locations varied. The correlation analysis displayed
that there were remarkable relativities between total N, total P and organic matters within definite spatial distance from
the Huolin River channel. 相似文献
319.
中国东部地区耕地土壤肥力变化趋势研究 总被引:57,自引:5,他引:57
随着人口、资源和环境之间的矛盾日趋尖锐,中国耕地土壤肥力及其变化日益为世人所关注。本文利用最近20年东北地区的吉林和黑龙江省,华北地区的北京市和河北省以及长江下游地区的江苏和浙江省的15个县市180个样本点的土壤数据资料,分析了20世纪80年代以来东部地区农业土壤肥力的演变趋势。结果表明,从总体上看,东部地区除土壤速效钾下降和酸碱性有所退化外,农业土壤的有机质、全氮和速效磷平均含量都增加了。在空间分布上,土壤肥力的变化趋势存在明显差异。长江下游和华北地区的平均肥力提高,东北地区下降。另外,除华北地区的土壤酸碱性有改善外,长江下游和东北地区土壤都存在酸化倾向。 相似文献
320.