Capacity and Distribution of Water Stored in the Vadose Zone of the Chinese Loess Plateau

Abstract

Vadose zone water is up to 3.1 × 1012 m3 in the Chinese Loess Plateau. The deep vadose zone (below 5 m) stores 92.4% of the total vadose zone water. Vadose zone water distribution is uneven, depending on loess thickness and precipitation. Vadose zone water accounts for 42.1% of water resources in the Chinese Loess Plateau. Water stored in the vadose (unsaturated) zone provides the majority of water required by plants and buffers water resources; thus, it is central to understanding ecological and hydrological processes in the Chinese Loess Plateau (CLP) with its thick loess deposits. We used multisource data on soil water content (SWC) and vadose zone thickness, combined with a spatial interpolation method, to quantify the vadose zone water and further deduce the water resource composition in the CLP. Vadose zone water is approximately 3.1 × 1012 m3 (±27.5%) in the CLP, 92.4% of which is stored in the deep vadose zone (>5 m and above the groundwater table). The water resources composition of the CLP comprises precipitation, river water, vadose zone water, and the saturated zone water (shallow groundwater), accounting for 2.1, 0.1, 42.1, and 55.7%, respectively. Although a large amount of water exists in the vadose zone, the SWCs in the upper (<5 m) and deep vadose zones are 47.4 and 65.3%, respectively, of the mean field capacity, both being at a low level. Our findings bridge the knowledge gaps on the deep vadose zone water and water resources composition in the CLP, providing the basis for decision‐making on balancing revegetation and water resources conservation.

Long-term vegetation restoration increases deep soil carbon storage in the Northern Loess Plateau

“…Besides, our results showed that SWS was positively related to SIC storage in different layers for different vegetation, contrary to Zhao et al 30 . In this case, the SIC storage below 1 m has a prolonged rate of carbon exchange and has not been influenced by groundwater 40 and the parent material of this soil is loess, including more inorganic C 38 , revegetation relatively consumes lower soil water content from deeper soil layer. In summary, SOC accumulates through the consumption of soil water by plants and concurrently can increase soil water retention.…”

Towards improved global estimates and model representations of water storage in the unsaturated zone

“…Very few studies have characterised moisture and storage in the deep unsaturated zone (taken here to be beneath the zero-flux plane, the depth below which water movement is downward) (Ireson et al 2006;Zhu et al 2019). Studies of the deeper unsaturated zone are principally carried out with the aim of quantifying recharge to the saturated zone (Wang et al 2009;Mattern and Vanclooster 2010;Min et al 2015;Xiang et al 2019).…”

“…The magnitude of water storage in the unsaturated zone has been highlighted to be large and of regional importance. For example, Zhu et al (2019) estimate a volume of water up to 3.1 x 10 12 m 3 stored in the unsaturated zone of the Chinese Loess Plateau, which accounts for 42.1% of the water resources in this region. However, understanding the magnitude of water storage in the unsaturated zone at the global scale is currently very limited.…”

Achieving Sustainable Earth Futures in the Anthropocene by Including Local Communities in Critical Zone Science

“…‐ >90% of soil water stored >5 m depth; inherently fast hydraulic conductivity leads to transfer of N into the deep soil profile at Loess Plateau CZO (Y. J. Zhu et al., 2019a, 2019b)…”