Temporal variation of stable isotopes in a precipitation–groundwater system: implications for determining the mechanism of groundwater recharge in high mountain–hills of the Loess Plateau, China

Abstract

The groundwater in shallow loess aquifers in high mountain–hills in the western Loess Plateau in China is almost the sole water resource for local residents. However, the question about how the loess groundwater naturally circulates in these high mountain–hills, characterized by low precipitation and high potential evaporation, remains unclear. The objectives of this study are to evaluate the application of hydrogen and oxygen isotopes to (1) examine temporal variations of the isotopic composition of precipitation and shallow groundwater and (2) uncover the mechanism of groundwater recharge in high mountain–hills. Results from 2 years of monitoring data show a difference in the stable isotopes for groundwater and local precipitation between the winter and summer periods. Similar to precipitation, stable isotopes in groundwater are observed to be depleted in winter and enriched in summer, particularly in oxygen isotope. A prominent characteristic is that H and O isotopes of groundwater show a very clear response to strong precipitation in the rainy season in 2013. The results highlight that local precipitation is the likely recharge source for groundwater in shallow loess aquifers. Annual recharge from local precipitation maintains the groundwater resource in the shallower loess aquifer. The mechanisms governing shallow loess groundwater recharge in high mountain–hills were evaluated. In addition to possible vertical slow percolation of soil water through the unsaturated zone, rapid groundwater recharge mechanisms have been identified as temporal preferential infiltration through sinkholes, slip surface or landslide surface and through the interface of loess layer and palaeo‐soils. Most groundwater can be recharged after a heavy rainy season. Copyright © 2015 John Wiley & Sons, Ltd.

Determination of groundwater recharge mechanism in the deep loessial unsaturated zone by environmental tracers

“…Gates et al (2011) concluded that drainage through the unsaturated zone contributed little to spring discharge in the Zhifangou Catchment due to the distinct isotopic signatures between spring water and soil pore water. Furthermore, Tan et al (2016) observed that the groundwater isotopic compositions had a clear response to precipitation in rainy season in Gansu Province, which is very close to our study area.…”

“…precipitation or deep confined water. According to the hydrogeological characteristics, it is highly unlikely that deep confined groundwater flows upward through the thick red clay (22−78 m in thickness, Fig.2) with low permeability to recharge shallow groundwater, rather than discharging directly to lower gullies (Tan et al, 2016). This conclusion is confirmed by the groundwater tritium contents in our study since groundwater from the confined aquifer is tritium free while the shallow groundwater has detectable tritium content.…”

“…The groundwater from pre-bomb events should be tritium free; however, the results from this study as well as those distributed widely across CLP contradicted with this assumption. Specifically, the tritium contents greater than 10 TU have been detected in the other regions (Huang et al, 2014;Lin and Wei, 2006;Liu et al, 2009;Ma et al, 2006;Su et al, 2009;Tan et al, 2016). In this study, the tritium contents of groundwater are very low though preferential flow dominates groundwater recharge.…”

Reconstructed Precipitation Tritium Leads to Overestimated Groundwater Recharge

“…The first hypothesis does not seem likely in the study region. Although the study region could have dual modes (piston and preferential flow) of groundwater recharge, the preferential flow only occurs in some topographical lows with vertical fissures, macropore or sinkholes (Gates et al, ; Li, Chen, et al, ; Li, Lin, et al, ; Lin & Wei, ; Tan et al, ). However, the soil water, the chloride, and nitrate concentrations in soil water below the active layers are under steady state (T. Huang et al, ; Y. Huang et al, ; Li, Chen, et al, ; Wang et al, ).…”

Water Stable Isotopes in an Alpine Setting of the Northeastern Tibetan Plateau

“…As componets of the water molecule, the stable isotopes 18 O and 2 H (D) are useful tracers to describe regional water cycle because they reveal information about hydrological processes including precipitation, infiltration, evaporation, and transpiration [1]. In spite of their low abundance in nature, these heavy isotopes are sensitive to changes in climate and hydrology.…”