Abstract
The stable isotopes (δD and δ18O) in soil water allow tracing of the flow and transportation of water in the soil. However, there are few studies on the use of soil water stable isotopes to explore the soil water in the floodplain, especially in determining the soil water source and infiltration mechanism. The Bayesian mixing model (MixSIAR) was integrated with the line conditioned excess (lc-excess) of stable isotopes (δD and δ18O) in precipitation, soil water (0–150 cm), river water, and groundwater to determinate the source and recharge mechanisms of two different soil profile types in the floodplain of the upper Yellow River in Lanzhou, China. The results showed that soil water below 80 cm was affected by river water recharge, affecting soil water content and stable isotopic composition at S1 sampling points (profile parallel to river water); this effect was not observed at S2 (profile is higher than the river water) sampling points. The isotopic compositions of the soil water sources at the two sampling points (S1: δD = −77.41‰, δ18O = −11.01‰; S2: δD = −74.02‰, δ18O = −10.56‰) were depleted more than those in the long-term amount-weighted precipitation isotopes (δD = −56.30‰, δ18O = −8.17‰). The isotope signatures of soil water sources are similar to the isotope characteristics of some high-intensity precipitation events (≥30 mm/day), indicating that soil water originates from a fraction of the total precipitation. The piston flow (60%) and the preferential flow (40%) coexist, but soil moisture and rainfall intensity will affect the sequence of the two infiltration methods. This study provides insights for understanding the hydrological process of the upper Yellow River and evaluating groundwater quality and protecting the floodplain environment.
Highlights
As an important part of the water cycle system, soil water connects different hydrological components such as precipitation, surface water, and groundwater [1,2]
Traditional methods mainly studied the characteristics of water conservancy parameters during infiltration and establish soil water movement models using these parameters
The objectives of this study were to: (1) analyze the characteristics and laws soil water changes on the floodplain of the Lanzhou section of the Yellow River based on soil water content and stable isotopes of soil water hydrogen and oxygen, and (2) based on hydrogen and oxygen isotopic data of various water bodies, lc-excess and the Bayesian framework were used to describe the infiltration mechanism of precipitation in soil
Summary
As an important part of the water cycle system, soil water connects different hydrological components such as precipitation, surface water, and groundwater [1,2]. Soil water determines the water availability for agriculture, but it is an important factor in soil fertility. It is important for better understanding the soil water transport process, for characterizing the movement of salt, carbon, nitrogen, and other substances, and for increasing the sustainable utilization of water resources [3,4]. Traditional methods mainly studied the characteristics of water conservancy parameters during infiltration and establish soil water movement models using these parameters.
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