鄂尔多斯高原植被盖度变化对地下水补给的影响

With the implementation of the ecological restoration project in arid zones, the ecological environment improves continually. However, the increase of vegetation coverage may reduce groundwater recharge and consequently the conflict between groundwater supply and demand will be more severe. Therefore, the impact of vegetation coverage on groundwater recharge should be quantified. Firstly, the difference is compared in terms of soil water and groundwater recharge in the vegetated and non-vegetated lysimeters and the impact is revealed. The relation between groundwater and vegetation is further studies using the variable saturated simulations. Then the Hailiutu River Catchment in the Ordos Plateau is selected as the study area, and the vegetation coverage is determined using the combination of remote sensing and the in-situ measurement. The time series analysis and depth-varied specific yield are introduced to modify the water-table fluctuation method and the impact of water-table depth on recharge is removed using the soli water numerical modeling. Based on the above studies, the relation between vegetation coverage and groundwater recharge is developed quantitatively using the precipitation infiltration coefficient as the comparison index.With the implementation of the ecological restoration project in arid zones, the ecological environment improves continually. However, the increase of vegetation coverage may reduce groundwater recharge and consequently the conflict between groundwater supply and demand will be more severe. Therefore, the impact of vegetation coverage on groundwater recharge should be quantified. Firstly, the difference is compared in terms of soil water and groundwater recharge in the vegetated and non-vegetated lysimeters and the impact is revealed. The relation between groundwater and vegetation is further studies using the variable saturated simulations. Then the Hailiutu River Catchment in the Ordos Plateau is selected as the study area, and the vegetation coverage is determined using the combination of remote sensing and the in-situ measurement. The time series analysis and depth-varied specific yield are introduced to modify the water-table fluctuation method and the impact of water-table depth on recharge is removed using the soli water numerical modeling. Based on the above studies, the statistic relation between vegetation coverage and groundwater recharge is developed quantitatively using the precipitation infiltration coefficient as the comparison index. This study will reveal the pattern of groundwater recharge and vegetation coverage variation and explore the mechanism of the response of groundwater recharge to vegetation coverage and provides the scientific bases for the harmonic development of groundwater and ecology and for the full understanding of the feedback between them in arid regions.

随着旱区生态恢复工程的实施，生态环境不断改善，但植被盖度增加可能会导致地下水补给减少，进一步加剧水资源的供需矛盾，因此迫切需要研究植被盖度对地下水补给的影响。本研究首先利用地中蒸渗仪对比试验，对比植被覆盖区和裸土区土壤水、地下水补给的差异，揭示植被盖度增加对地下水补给的影响，利用变饱和仿真数值模拟研究不同条件下植被与地下水的关系；然后以鄂尔多斯高原海流兔河流域为研究区，采用遥感测量与地面校验相结合的方法确定植被盖度；引入时间序列分析法和随埋深变化的给水度计算方法，改进基于地下水动态的补给量计算方法，利用土壤水数值模拟技术消除埋深对地下水补给的影响；在此基础上，以降雨入渗补给系数为对比指标，建立植被盖度与地下水补给的统计模型。本研究将定量揭示旱区地下水补给与植被盖度变化的规律，探索地下水补给对植被盖度变化的响应机理，为旱区地下水与植被生态的和谐发展和全面认识两者的互馈机制提供科学依据。

随着西北干旱半干旱地区生态恢复工程的实施，许多地区的植被盖度不断增加，但其对地下水补给的影响尚需加强研究。本项目以鄂尔多斯高原为研究区，综合采用野外试验和数值模拟方法，定量分析了植被盖度变化对地下水补给的影响，确定了造成地下水补给变化的原因。利用遥感技术分析了2000年以来植被盖度的变化，总体上讲，70%以上的地区植被盖度增加，造成植被盖度增加的原因主要是生态恢复造成的，而与气候变化关系不大。通过对比分析裸土和有植被的地中蒸渗仪的监测数据，发现有植被的蒸渗仪的土壤水势在生长期下降剧烈，比裸土区蒸渗仪的土壤水势要低很多，这表明植被大大消耗了土壤水，加剧了土壤水的亏空程度，使得降雨入渗转化成地下水的比例降低。在考虑随埋深变化的给水度的基础上，利用地下水动态法计算了降水入渗补给量，建立了地下水补给与埋深的关系。利用数值模拟分析了植被盖度增加后地下水补给的变化，模拟结果表明，植被盖度增加后，地下水的补给急剧降低，在很多月份，降雨很难入渗补给地下水。项目成果揭示了植被盖度变化对地下水补给影响机制，即在干旱半干旱地区，植物叶片的降雨截留、植物非降雨期的蒸腾导致的土壤水亏空以及植物直接消耗地下水用于蒸腾导致了植被盖度增加后，地下水资源量减小。研究成果表明，植被（特别是乔木）直接消耗地下水，因此植物的增加会导致整个地区的地下水资源减小，但同时乔木又需要地下水才能度过干旱季节，因此在旱区实施生态修复，必须要依据水资源的承载力来开展，实现水与生态的和谐发展。