Spatiotemporal variation of surface water-groundwater interactions and key influencing factors during freeze-thaw cycles in a seasonal frozen region, Northeast China

Study area

The lower reach catchment of the Songhua River—a representative seasonally frozen soil region of Northeast China.

Study focus

The seasonal freeze-thaw process significantly impacts the hydrogeological environment and hydrodynamics, impacting surface water (SW)-groundwater (GW) interactions. However, the spatiotemporal variations of SW-GW interactions during the freeze-thaw cycle and the specific effects of freezing and thawing on this relationship remain unclear. Based on the long-term SW and GW levels and multi-period isotope sampling at different stages of the freeze-thaw process, we analyzed the interactions between SW and GW in the lower reach of the Songhua River—a representative river in the seasonally frozen soil region of Northeast China.

New hydrological insights for the region

The results indicate that GW flow patterns fluctuate throughout the freeze-thaw cycle. In the upstream region, GW discharge predominantly occurs through evapotranspiration and groundwater extraction during the non-freezing and thawing period (NFTP). Conversely, SW discharge emerges as the primary pathway for GW discharge during the freezing period (FP) and the thawing period (TP). In the downstream region, groundwater pumping has significantly modified natural SW-GW interactions, resulting in consistent and intense SW recharge of GW throughout the year. Topography, hydrogeological conditions, and human activities are critical factors for the spatial variability of SW-GW interactions. The freeze-thaw process and hydrological conditions controlling the temporal variability of SW-GW interactions, as well as abrupt changes in the direction of SW-GW interactions, can occur due to the freeze-thaw processes of the river. The findings emphasize that future studies and predictions of SW-GW interactions should fully account for the impact of the freeze-thaw process.