Combination of CFCs and stable isotopes to characterize the mechanism of groundwater–surface water interactions in a headwater basin of the North China Plain

Abstract

Mountainous areas are characterized by steep slopes and rocky landforms, with hydrological conditions varying rapidly from upstream to downstream, creating variable interactions between groundwater and surface water. In this study, mechanisms of groundwater-surface water interactions within a headwater catchment of the North China Plain were assessed along the stream length and during different seasons, using hydrochemical and stable isotope data, and groundwater residence times estimated using chlorofluorocarbons. These tracers indicate that the river is gaining, due to groundwater discharge in the headwater catchment both in the dry and rainy seasons. Residence time estimation of groundwater using chlorofluorocarbons data reveals that groundwater flow in the shallow sedimentary aquifer is dominated by the binary mixing of water approximating a piston flow model along 2 flow paths: old water, carried by a regional flow system along the direction of river flow, along with young water, which enters the river through local flow systems from hilly areas adjacent to the river valley (particularly during the rainy season). The larger mixing ratio of young water from lateral groundwater recharge and return flow of irrigation during the rainy season result in higher ion concentrations in groundwater than in the dry season. The binary mixing model showed that the ratio of young water versus total groundwater ranged from 0.88 to 0.22 and 1.0 to 0.74 in the upper and lower reaches, respectively. In the middle reach, meandering stream morphology allows some loss of river water back into the aquifer, leading to increasing estimates of the ratio of young water (from 0.22 to 1). This is also explained by declining groundwater levels near the river, due to groundwater extraction for agricultural irrigation. The switch from a greater predominance of regional flow in the dry season, to more localized groundwater flow paths in the wet season is an important groundwater-surface water interactions mechanism, with important catchment management implications.

Assessment of streamflow components and hydrologic transit times using stable isotopes of oxygen and hydrogen in waters of a subtropical watershed in eastern China

“…For example, some studies reported that topographic characteristics were the main factor influencing F yw , including topographic gradient, elevation and drainage density (Jasechko et al, 2016(Jasechko et al, , 2017Clow et al, 2018). Other studies suggested precipitation, rainfall intensity and groundwater levels were important factors (von Freyberg et al, 2017;Wilusz et al, 2017;Wang et al, 2018). In contrast, a study across 22 contrasting catchments in Germany found no significant correlations between F yw and catchment characteristics (Lutz et al, 2018).…”

The Role of Topography in Controlling Evapotranspiration Age

“…Results of the third-year spin-up from the PF-CLM model were repeatedly used to spin-up the EcoSLIM model for a further 42 years at an hourly time step. We used the results of Wang et al (2018), who sampled groundwater from wells at depths between 2 and 90 m in the mountainous area in our modeling domain and got apparent groundwater ages of these samples from 24 to 42.5 years based on CFC-12 and 25.5-42 years based on CFC-113. Using this field information to guide our model analysis, we stopped the EcoSLIM spin-up at the end of the 42nd year.…”

Interaction of Surface Water and Groundwater Influenced by Groundwater Over-Extraction, Waste Water Discharge and Water Transfer in Xiong’an New Area, China

“…The majority of the precipitation (75%) falls from June to September (Figure 2). The mean annual air temperature is 13.8 • C and the mean absolute humidity is 61% based on data obtained from the Baoding meteorological station of the China meteorological data-sharing service [14,42]. Location of the study area in Lake Baiyangdian (BYD) watershed (a) and sampling sites in six sections from the Fu River to the Lake BYD watershed (b).…”