Using Soil Water Stable Isotopes to Investigate Soil Water Movement in a Water Conservation Forest in Hani Terrace

Huimei Pu,Weifeng Song,Jinkui Wu

doi:10.3390/w12123520

Abstract

Water conservation forests significantly contribute to the stability of mountain agricultural ecosystems in Hani Terrace. In this study, we analyzed the relationship between the stable isotopic composition of soil water and precipitation to determine the mechanisms of soil water movement in the small watershed of Quanfuzhuang. We observed significant seasonal variations in soil water sources: antecedent precipitation was the dominant supply during the dry season, and current precipitation dominated during the rainy season. The recharge ratio of precipitation to soil water in the grassland was significantly higher than that in the arbor land and shrubland. The influence of water infiltration, old and new soil water mixing, and soil evaporation on the soil water stable isotopes gradually decreased from the surface (0–20 cm) to the deep (60–80 cm) soil. We observed significant seasonal variability in average soil water δ18O in the upper 0–60 cm and lower variability at 60–100 cm. The average soil water δ18O was generally higher in the dry season than in the rainy season. The mixing of old and new water is a continuous and cumulative process that is impacted by soil structure, soil texture, and precipitation events. We therefore identified a significant time delay in soil water supply with increasing soil depth. Moreover, the piston flow of soil water co-occurred with preferential flow, and the latter was the dominant supply during the rainy season.

Highlights

Water resource shortages are a worldwide concern
The annual average soil moisture content of the three woodland types occurred in the order of arbor land > grassland > shrubland
Quanfuzhuang watershed and concluded the following: Soil moisture showed significant seasonal variability in Hani Terrace, and soil water content and its stability increased from the surface to the deep soil

Summary

Introduction

Water resource shortages are a worldwide concern. Soil water is a dominant water resource and is intrinsically linked to atmospheric precipitation, surface water, groundwater, biogeochemical cycles, and the water cycle [1]. The study of soil water movement is important for assessing soil water supplies, water redistribution mechanisms, soil nutrient and pollution transport processes, and areal water resource potential [2,3,4,5]. Hydrogen and oxygen stable isotopes, as elements of H2 O, can accurately reflect water movement in soil. Isotopic measurements can identify the soil water source, infiltration, evaporation, and other water movement processes to infer the dynamic changes, movement features, and supply mechanisms of soil water. Many studies have assessed soil water movement processes using stable isotope techniques. Using the stable isotope tracer method, Brinkmann et al [10] found that the retention time of rainfall in soil ranged from days to months and increased with soil depth

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Discussion

Conclusion