黄河源区地下水位下降对生态环境的影响

The Effect of Groundwater Table Lowering on Ecological Environmentin the Headwaters of the Yellow River

黄河源区1:250000区域环境地质调查资料与以往资料的对比表明,黄河源区区域地下水位近几十年来呈现明显的下降趋势,主要表现在:地下水露头泉口下移,河谷区民井地下水位下降及山前冲洪积扇前缘泄出带下移.多年冻土的退化直接导致了冷生隔水层的下移,从而引起区域地下水位的下降.区域地下水位的下降导致生态水位下降,包气带土壤层的含水量减少,使该区出现植被草场退化、生物多样性减少、沼泽湿地萎缩、鼠害猖獗、荒漠化加剧及黄河断流等生态环境问题.

Owing to climate change and human activities, regional groundwater table and ecological water table are generally decreasing, resulting in a series of environmental geological problems, such as degradation of swampy meadow and vegetation, and desertification. On the base of field survey, the cause of the groundwater table decreasing is analyzed, and the relationship between the ecological environmental effect and groundwater table lowering is discussed. It is found that groundwater table has greatly changed. The groundwater outcrop in mountain areas are moving downwards with decreasing runoff. The groundwater table of civil well in river valleys has fallen 0.52 to 1.18 m. Meanwhile, lake shrinking causes groundwater table lowering around the basin and the outcome in alluvial and diluvium deposits also moves downwards. The groundwater table lowering is caused by permafrost degradation, geological structure action, lake shrinking and human activities. The survey results show that permafrost is in degradation in the headwaters of the Yellow River, discontinuous permafrost degrades into thawed area, the lower boundary of permafrost is rising, and permafrost table is decreasing. The permafrost degradation results in cryogenic waterproof layer moving downward and groundwater table obviously lowering. With groundwater table lowering, a series of ecological environmental problems appear. Swampy meadow and vegetation is in degradation and biological diversity is on the decrease owing to the ecological water table lowering and the depth of seasonal thaw layer increasing. Desertification is enlarging.