Soil Water Dynamics Under Different Land Uses in Loess Hilly Region in China by Stable Isotopic Tracing

Abstract

Exploring soil water dynamics under different land use types is important for water resource management and vegetation restoration in the Loess Plateau. In this study, we investigated the hydrogen and oxygen isotopic compositions of soil water from four different land use types to explore the mechanism of soil water movement and transformation and analyse the influence of land use. The results show that the range of stable isotopes (δD and δ18O) in soil water was smaller than that in precipitation. Values for δD and δ18O in soil water showed relatively similar temporal variation, heavy isotopes were enriched in the soil water in July and depleted in October. Stable isotope values in shallow (<100 cm depth) soil water and deep (>200 cm depth) soil water were low. The δD and δ18O values in woodlands decreased gradually with increasing depth. Across the four land use types, the maximum variation in δD and δ18O was in the shallow depth of the soil profile. Groundwater was recharged mainly from precipitation and then from soil water. The ratio of groundwater recharge by soil water under different land use types followed this rank order: woodland (35.70%) > grassland (31.14%) > shrubland (29.47%) > cropland (29.18%). Matrix flow and preferential flow coexisted during infiltration, and the occurrence of preferential flow was related to the land use type. The main reason for the variation in isotopic composition in soil water is the difference in soil evaporation, which is influenced by different vegetation cover. Owing to the difference in soil evaporation and fractionation, precipitation on cropland, shrubland, and grassland can recharge more soil water than on woodland.

Characteristics of hydrogen and oxygen isotopes and their differences of different water bodies in the subalpine shrubland of the eastern Qilian Mountains in China

“…This was more consistent with the findings of many scholars. For example, the studies, by Du et al (2021) in the Loess Plateau and Pu et al (2020) in the Hani terraces, had shown that isotope variation of soil water was significant in shallow soil layers on the semi-sunny aspect and more stable in deeper soil layers (Yong et al 2020). It has also been shown that shallow soil water of 0-30 cm was the main water source of subalpine shrubs and exhibits greater variability affected by precipitation, evaporation and transpiration (Szutu and Papuga 2019;.…”

“…Since surface soil water is significantly affected by precipitation, evaporation and plant transpiration, isotope values of soil water gradually decrease with increasing of soil depth. With the increase of soil depth, the mixing of surface soil water and deep soil water caused the isotope values of soil water increasing and gradually stabilizing Du et al 2021;Zhao et al 2018).…”

Characteristics of hydrogen and oxygen isotopes and their differences of different water bodies in the subalpine shrubland of the eastern Qilian Mountains in China

“…This was more consistent with the ndings of many scholars. For example, the studies, by Du et al (2021) in the Loess Plateau and Pu et al (2020) in the Hani terraces, had shown that isotope variation of soil water was signi cant in shallow soil layers on the semi-sunny aspect and more stable in deeper soil layers (Yong et al 2020). It has also been shown that shallow soil water of 0-30 cm was the main water source of subalpine shrubs and exhibits greater variability affected by precipitation, evaporation and transpiration (Szutu and Papuga 2019; .…”

“…Since surface soil water is signi cantly affected by precipitation, evaporation and plant transpiration, isotope values of soil water gradually decrease with increasing of soil depth. With the increase of soil depth, the mixing of surface soil water and deep soil water caused the isotope values of soil water increasing and gradually stabilizing Du et al 2021;Zhao et al 2018). There were differences in the uctuation of δ 18 O values of soil water of different aspects at different soil depths.…”

Soil water consumption characteristics in rain-fed apple orchards and wheat fields

“…Studies have suggested that soil water storage capacity in vegetated land is substantially higher than in bare or fallow land [19][20][21]. In addition, the spatiotemporal distribution and migration of soil water under different land cover types have been extensively studied [22][23][24][25][26][27][28]. Yang et al [29] reported that different intensities of desiccation occurred below 3-m soil depths in various forestlands, excluding young apple orchards and shrub stands (Hippophae rhamnoides and Caragana korshinskii); soil desiccation intensity increased with an increase in the age of forest trees.…”