Influence of Multi-Layered Structure of Vadose Zone on Ecological Effect of Groundwater in Arid Area: A Case Study of Shiyang River Basin, Northwest China

Haohao Cui,Jinzhe Wang,Xujuan Lang,Guanghui Zhang,Qian Wang

doi:10.3390/w14010059

Abstract

The natural vegetation in arid areas of northwest China is strongly dependent on the availability of groundwater. Significantly, capillary water plays an essential role in regulating the ecological groundwater level in the multilayered structure of the vadose zone. The soil-column test and field survey in the lower reaches of the Shiyang River Basin were conducted to investigate the influence of the multi-layered structure of the vadose zone on maintaining the ecological effect of groundwater. Based on the field survey, the results show that the depth of groundwater is 3.0 m, and the rising height of capillary water is 140 cm. In the soil-column test, the height of the wetting front of the column was 125 cm. During the water releasing test, the water held by the vadose zone was 182.54 mm, which would have maintained Haloxylon’s survival in a growing season. Therefore, the multi-layered structure of the vadose zone extends the ecological groundwater depth and consequently enhances the ecological function of groundwater. Importantly, with a lower groundwater level, the clay soil layer within the rising height range of the original capillary water would hold more water and maintain a higher water content for a certain period to supply surface vegetation.

Highlights

Inland basins of northwest China have a typical continental climate, which is characterized by low precipitation and high evaporation, as well as scarce water resources.the natural vegetation of inland basins is highly dependent on groundwater [1,2].Groundwater depth controls water availability to vegetation and is essential for conserving groundwater-dependent ecosystems (GDEs)
Once the depth of groundwater table is lower than ecological groundwater level for a long time, the natural vegetation ecosystem will lose the water supplied by groundwater through the supporting capillary zone [3]
This paper aims to study the influence of the multi-layered structure of the vadose zone on the ecological effect of groundwater: (1) to explore the lithological structure of the vadose zone in the typical natural vegetation area; (2) based on the exploration results, to survey pit profile, including the field test of groundwater capillary rise height; (3) to discuss the availability of water-holding capacity in the vadose zone on vegetation root water uptake by a soil-column test

Summary

Introduction

Inland basins of northwest China have a typical continental climate, which is characterized by low precipitation and high evaporation, as well as scarce water resources.the natural vegetation of inland basins is highly dependent on groundwater [1,2].Groundwater depth controls water availability to vegetation and is essential for conserving groundwater-dependent ecosystems (GDEs). Inland basins of northwest China have a typical continental climate, which is characterized by low precipitation and high evaporation, as well as scarce water resources. The natural vegetation of inland basins is highly dependent on groundwater [1,2]. Groundwater depth controls water availability to vegetation and is essential for conserving groundwater-dependent ecosystems (GDEs). Once the depth of groundwater table is lower than ecological groundwater level for a long time, the natural vegetation ecosystem will lose the water supplied by groundwater through the supporting capillary zone [3]. It will lead to natural vegetation degradation or even death and desertification [4]. Since the 1950s, because of the rapid development of the economy and society, groundwater has been over-exploited, which led to the continuous decrease of groundwater depth, exceeding the ecological groundwater level of natural vegetation in most inland basins

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