黄土高原白草塬土地利用变化对地下水补给的影响

为研究黄土高原土地利用变化对地下水补给的影响，在甘肃会宁县白草塬采集农地、杏林地、杏林‖柠条地和杏林‖苜蓿地4种土地利用方式0~10 m剖面土样，通过制定表征土壤水分亏缺的指标和氯离子质量平衡法，从土壤水分含量、储水量、干燥化和深层渗漏量等角度分析了土地利用变化对地下水补给的可能影响。结果表明：不同土地利用方式对土壤水分作用强度和深度不同。0~10 m剖面的平均土壤含水量表现为农地＞杏林地＞杏林‖柠条地＞杏林‖苜蓿地。0~5 m包含杏树的两种间作地平均土壤含水量已达到或接近萎蔫湿度，土壤达到中度甚至重度干燥化；5~10 m各利用方式干燥化程度有所减轻。4种样地土壤水分深层渗漏量为8.8~13.6 mm·a^-1，占多年平均降雨量的4.0%。由于土地利用类型转换时间不到10年，尽管土地利用变化对土壤水分有较大影响，但对地下水补给的影响尚不显著。

Impacts of changes in land use on groundwater recharge on Baicao loess tableland

To evaluate the impacts of changes in land use on groundwater recharge,we sampled 10 m soil profiles under four types of land uses (farmlands, apricot orchards, apricot-caragana intercropping lands, and apricot-alfalfa intercropping lands) on Baicao loess tableland. After determining the soil water contents and chloride contents in soil water, we quantified the land use change impacts on groundwater based on some indices including soil water content, water storage, desiccation, and deep drainage. Different types of land uses have impacts on soil water with varying magnitudes and depths. The averaged soil water contents across the 10 m profiles were in the order of farmlands > apricot orchards> apricot-caragana intercropping lands >apricot-alfalfa intercropping lands. The two intercropping lands with apricot had soil water contents that were very close to the wilting point in the 0~5 m soil profiles, which subsequently resulted in moderate or even severe desiccation. But, the desiccation was alleviated with the depth, especially in the soil of 5~10 m deep. The deep drainages of soil water under the four land uses ranged from 8.8 to 13.6 mm·a^-1, accounting for 4.0% of average annual precipitation. Since the changes from farmlands to other types occurred within last 10 years, the impacts of the land use changes on the groundwater recharge were not significant though their effects on soil water contents were large.