石羊河流域下游天然绿洲地下水生态功能强弱周期性与机制

西北内陆的石羊河流域下游区降水稀少、蒸发强烈，天然植被对潜水埋深具有强烈依赖性，对地下水这种生态功能的强弱变化特征与机制尚缺乏深入认识。本文采用原位监测、高分辨遥感探测与解译和多元相关分析方法，研究地下水生态功能强弱变化与潜水埋深、气温、降水和出山地表径流水量之间的关系。结果表明：(1)地下水生态功能越强，天然植被覆盖度越高或归一化植被指数值越大；(2)地下水生态功能具有时效性和年际及日际变化周期性，每年4月至7月上旬是地下水生态功能作用逐渐增强时段，每日7∶30—19∶00是地下水生态功能主要作用时段，主要受控于气温、日照、蒸发、上游区降水与出山地表径流水量和潜水埋深的一年四季周期性变化影响；(3)每年潜水埋深大于极限生态水位时段，地下水生态功能处于失效状态，且气候越干旱，每年的失效时段起始越早和结束越晚。因此，西北内陆的石羊河流域下游天然绿洲区地下水生态功能强弱具有年际、年内变化周期性。

Periodicity and mechanism of groundwater ecological function in natural oasis in the lower reaches of Shiyang River Basin

In the lower reaches of Shiyang River Basin in the northwest China, precipitation is scarce and evaporation is strong.The natural vegetation is strongly dependent on the phreatic water depth.There is still a lack of in-depth understanding of the characteristics and mechanisms of this ecological function of groundwater.In this paper, in-situ monitoring, high-resolution remote sensing detection and interpretation, and multivariate correlation analysis are used to study the relationship between groundwater ecological function and phreatic water depth, temperature, precipitation, and surface runoff.The results show that:(1) the stronger the groundwater ecological function, the higher the natural vegetation coverage or the greater the normalized vegetation index;(2) The groundwater ecological function has timeliness and interannual and diurnal variation periodicity.The period from April to the first ten days of July each year is the period when the groundwater ecological function gradually increases.7:30-19:00 every day is the main action period of groundwater ecological function, which is mainly controlled by the periodic changes of temperature, sunshine, evaporation, precipitation in the upstream area, surface runoff and phreatic water depth throughout the year;(3) When the phreatic water depth is greater than the limit ecological water level every year, the groundwater ecological function is in a failure state, and the more arid the climate is, the earlier the failure period starts and ends.Therefore, the ecological function of groundwater in the natural oasis in the lower reaches of Shiyang River Basin in the northwest inland has the periodicity of interannual and intra annual changes.