Spatiotemporal patterns of soil water replenishment and their seasonal origins in a subtropical red soil critical zone

Abstract

Assessing the integration of precipitation and its isotopic signals in soil water is crucial for understanding the sensitivity of soil available water to precipitation variability. Here the investigations of water stable isotopes and in-situ soil water content were conducted for determining the spatiotemporal patterns of soil water replenishment and their seasonal origins in a subtropical red soil critical zone. Variations in soil water content provide valuable information regarding the quantity and depth of soil water replenishment in response to precipitation events. Soil water replenishment often penetrated to a depth of 100 cm or more from winter to early summer (from December to the next June), but the corresponding replenishment amounts were relatively low. However, most soil water replenishment events were generally limited to the upper 40 cm soil layers between midsummer and autumn (from July to November), with relatively large amounts in summer. The temporal and vertical variations in the seasonal origin index of soil water indicated that summer precipitation constituted the largest fractions (∼66 %) of soil water storage in the entire explored soil profile (thickness = 130 cm) during the study period. Winter precipitation was overrepresented in soil water only at the depth of 0–20 cm in spring, but it may vary slightly from year to year due to changes in winter precipitation patterns (amount and frequency). The findings of the current study broadly highlight how precipitation contributes to soil water storage over space and time, which has significant implications for plant water sources.