Variability of δ2H and δ18O in Soil Water and Its Linkage to Precipitation in an East Asian Monsoon Subtropical Forest Plantation

Sidan Lyu

doi:10.3390/w13202930

Abstract

The linkage between δ2H and δ18O of soil water and precipitation provides a way of understanding precipitation infiltration, residence time, and soil water source. Soil water at 0–5, 15–20, and 40–45 cm depths and event-based precipitation were collected in a subtropical forest plantation. Correlations between the δ18O of soil water and precipitation on the same day were used to determine the critical threshold of precipitation infiltration. Residence time of precipitation in soil was determined with correlations between the δ18O of soil water and cumulative precipitation before sampling. Soil water source was determined by the intersection points of Soil Water Evaporation Lines (SEL) and local meteoric water lines. The results showed that precipitation >5–6 mm could pass through canopy and litter, and infiltrate into soil. Residence times varied from a few days to several months, and increased with soil depth. The model-based approach for SEL estimation were more robust than the regression-based approach due to the inverse variability in the δ2H and δ18O of soil water source and soil evaporative fractionation. Soil water at a 0–5 cm depth originated mainly from precipitation in the current season, while those at 15–20 and 40–45 cm depths originated mainly from precipitation in the previous season.

Highlights

Zoltán KernSoil water, as a key link in the hydrological cycle, partitions precipitation into evaporation, transpiration, and runoff [1]
The linkage of soil water with precipitation is increasingly relevant due to the changes in rain patterns caused by climate change [3]. δ2 H and δ18 O in water have been widely used as ideal tracers of water movement and mixing among different water pools [4]. δ2 H and δ18 O in soil water can largely retain the isotopic signal of precipitation due to the infiltration of precipitation larger than a certain amount, and by the lack of fractionation during root water uptake, except that by some halophytes or woody xerophytes [5,6]
Seasonal Variability of δ2 H and δ18 O in Soil Water and Precipitation δ18 O is solely used for identifying the seasonal variability of δ2 H and δ18 O in soil water and precipitation in Sections 3.1–3.3, due to the very high consistency of the temporal variability of δ2 H and δ18 O

Summary

Introduction

Zoltán KernSoil water, as a key link in the hydrological cycle, partitions precipitation into evaporation, transpiration, and runoff [1]. Precipitation is the main source of soil water replenishment, and it controls the mixing and redistribution of soil water [2]. The linkage between δ2 H and δ18 O in soil water and precipitation is useful for the understanding of precipitation infiltration, residence time, and soil water source [8]. The determination of the critical threshold for the precipitation recharge of soil water is central to the accurate estimation of soil water replenishment and water balance [2,9]. Some authors have estimated this threshold with throughfall measurements using rain-gauges and determined that it corresponded to throughfall when precipitation was 0 based on linear regression between the two [10]. Others used the relationship between the variability in soil water content and precipitation amount to estimate this threshold [11].

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Discussion

Conclusion