包气带岩性结构对地下水生态功能影响特征

Influences of lithology and structure of the vadose zone on groundwater ecological function

西北内陆流域下游区天然植被对地下水生态功能具有强烈依赖性,而包气带岩性结构对地下水生态功能具有明显影响,但是在目前的研究中,缺乏定量分析评判。以甘肃石羊河流域下游天然绿洲区为研究区,基于包气带岩性结构野外调查、室内土柱试验和Hydrus1-D数值模拟,研究包气带岩性结构与地下水耦合作用的生态效应,分析不同岩性结构包气带获取地下水供给水分和持水能力差异,定量对比不同包气带岩性结构对地下水生态功能影响特征,得到以下认识:(1)在地下水水位埋深增大和减小的情况下,不同包气带岩性结构对地下水生态功能影响不同;(2)当地下水水位埋深逐渐减小时,在相同植被条件下,包气带岩性颗粒越细,其支持毛细水上升高度和速度越大,土壤获得地下水的补给水分越快越多,对地表植被的生长越有利;(3)当地下水水位埋深大幅增大后,旱区包气带的有效持水量具有继续维持陆表植被存活的生态效应,中等岩性颗粒的有效持水量最大,对维持植被的生态效应最明显。与单一岩性相比,多种岩性的组合结构有效持水量较大,生态效应更强。研究结果加深了对包气带在地下水生态功能中调节作用的认识,可以为旱区水资源的精细化管理及生态保护提供科学依据。

The natural vegetation in the lower reaches in the inland basins of northwest China is strongly dependent on the groundwater ecological function,and the lithology and structure of the vadose zone has a significant impact on the groundwater ecological function.However,there is a lack of systematic and specific research on how to quantitatively analyze and evaluate the degree of influence.The natural oasis area in the lower reaches of the Shiyang River Basin in Gansu Province is taken as the research area,and field investigation,soil column test and numerical simulation with Hydrus1-D are carried out to study the ecological effect of the coupling effect between the vadose zone and groundwater.The difference of water supply ability and water holding ability of the vadose zone with different lithologic structure is analyzed,and the influences of lithology and structure of the vadose zone on the groundwater ecological function is quantitatively compared.The results show that(1)the lithological structure of different vadose zones has different effects on the groundwater ecological function when the groundwater depth increases or decreases.(2)When the groundwater depth decreases gradually,under the same vegetation condition,the finer the lithologic particles in the vadose zone,the higher the height and speed of the supporting capillary water rises,and the faster the soil obtains groundwater recharge,and the more beneficial it is to the growth of the surface vegetation.(3)The effective water holding capacity of the vadose zone in the arid area has ecological effect of maintaining the survival of land surface vegetation after the local groundwater depth increases greatly.The effective water holding capacity of the medium lithologic particles is the largest,which has the most obvious ecological effect on maintaining vegetation.Compared with a single lithology,the combination of multiple lithologies is more conducive to hold larger effective water capacity and stronger ecological effect.The results will be helpful to strengthen the understanding of the regulation of the vadose zone in groundwater ecological function,and can provide a scientific basis for the fine management of water resources and ecological protection in arid regions.