Spatio-temporal variations of δ2H and δ18O in precipitation and shallow groundwater in the Hilly Loess Region of the Loess Plateau, China

Abstract

Groundwater is of utmost significance to socioeconomic development and ecological recovery for the Loess Plateau. However, studies regarding the mechanism governing groundwater recharge over this area appear to be inadequate. This study is to examine the spatio-temporal variations of d 2 H and d 18 O in precipitation and shallow groundwater. On the basis of this, the mechanisms governing shallow groundwater recharge were explored. Precipitation and groundwater were sampled monthly from May to October during the period 2004-2006 at 13 sites in the Chabagou Catchment (187 km 2 ). In the Caopingxigou Experimental Watershed (0.1 km 2 ), meteorological variables were observed and rainfall larger than 5 mm was sampled immediately after each rain event. Across the area, 90% of the precipitation occurred from May to September primarily in the form of heavy rains or rainstorms with great spatial variability. There were about 30 localized rains in each year. It was indicated that there existed notable seasonality and pronounced spatial variability in precipitation isotopic compositions. Contributing factors and indications of isotopic compositions, as well as their climatic indications such as monsoon intensities and mixing processes of water vapor, were investigated. The d 2 Hd 18 O relation of groundwater was found to be d 2 H = 3.22 9 d 18 O -38.1, deviating from the local meteoric water line d 2 H = 7.57 9 d 18 O ? 3.9. The range of d values in groundwater is shrunken to be 15-21% of that in individual precipitations, and groundwater in the middle reaches shows a wider range of d values. Isotopic results showed that groundwater originates from precipitation with hydrogen and oxygen isotopic compositions being -69 and -9.7%, respectively, and most groundwater experiences serious evaporation and adequate mixing with old water during infiltration or percolation in the aerated zone. It was also founded that obvious fluctuations of isotopic compositions in groundwater mainly appear in the middle reaches especially at sites that are close to valleys, suggesting varying sources of groundwater from precipitation, precipitation runoff, isotopically enriched surface water and/or lateral recharge of adjacent groundwater.Electronic supplementary material The online version of this article (

Soil profile evolution following land‐use change: implications for groundwater quantity and quality

“…It is difficult to find the traditional ‘isotopic altitude and latitude effect’ for precipitation (Yang et al ., ) and in groundwater. According to the only basin‐scale study in the LPC, an ‘altitude effect’ for precipitation does not occur during the summer monsoon (Liu et al ., ). This suggests that in the semiarid LPC, groundwater is recharged by seasonal large rainfall with rapid infiltration and not much evaporation.…”

“…Stable isotopic compositions for shallow groundwaters from the study area (elevation = 1800–1900 m, a.s.l. ), the Ansai terrace (1100–1200 m; Gates et al ., ), the Chibagou hilly region (898–1302 m); (Liu et al ., ) and typical loess plains, e.g. Changwu (~1200 m; Wang, ), Xifeng (~1420 m), Luochuan (~1150 m; Huang, ) and Xi'an (400–1200 m; Qin and Tao, ) are all close to the GMWL and are depleted in heavy isotopes (Figure ), compared with the weighted average of −6.6‰ for precipitation from Yinchuan (1112 m) in the northern LPC, −7.1‰ from Xi'an (400 m) in the south (IAEA and WMO, ) and −7.8‰ in the Ordos Basin (Yang et al ., ).…”

“…() for Ansai, Liu et al . () for Chibagou, Wang () for Changwu, Huang () for Xifeng and Luochuan, Qin and Tao () for Xi'an and IAEA and WMO () for precipitation from Xi'an]. The size of the blue circle stands for the relative amount of precipitation.…”

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

“…Liu et al . () concluded that the spatio‐temporal variations of precipitation isotopic compositions in the Loess Plateau are dominated by the difference in water vapour origin, monsoon intensity and hydrological processes. As indicated from the diagrams of monthly variation of δ 2 H and δ 18 O (Figure a and c), the isotopes of precipitation in high mountain–hills of the Loess Plateau also show regular seasonal variations.…”

“…A number of studies documenting tracer movement in the soil column have pointed to the existence of preferential fluid flow through vertical fissures, macropores, cracks, decayed plant roots and earthworm burrows to rapidly recharge groundwater (Roy and David, ; Yan and Wang, ; Van Ommen et al ., ; Komor and Emerson, ; Ritsema et al ., ; Gehrels et al ., ; Ritsema and Dekker, ; Vincent et al ., ; Gates et al ., ; Yasuda et al ., ). Rainfall infiltration has also been assumed to be more like a piston infiltration mode to slowly percolate downward and recharge groundwater (Yan, ; Qu, ; Zhang et al ., ; Lin and Wei, ; Huang et al ., ) or two modes of piston and preferential flow may simultaneously exist to recharge groundwater (Gazis and Feng, ; Xu et al ., ; Liu et al ., , ). Some studies conclude that the depleted isotopic signature of loess groundwater may be also consistent with isotopic compositions of palaeo‐waters in northern China, where the groundwater may have been recharged during glacial–interglacial transitional periods (Chen et al ., ; Currell et al ., ; Gates et al ., ; Liu et al ., ).…”