Hydrogeochemical identification of the subsurface sources of surface water in a river basin with arid climate

Abstract:

The interaction between groundwater and surface water plays a dominant role in the geo-environment in arid or semi-arid basins, especially in the discharge area around rivers. Tóth (1963) found that the lowest reaches of a large-scale basin could be the discharge area of local, intermediate and regional groundwater flow systems with different circulation depths. However, little research has been devoted to identify the dominant source of river water from a specific flow system in real river basins. In this study, the source of water in the Dosit River in the Ordos Cretaceous Basin is examined. The main aquifer of the watershed is the poorly consolidated Cretaceous sandstone with a thickness of 700–1000 m, which is overlain locally by Tertiary mudstones and extensively by thin unconsolidated Quaternary sediments. There are numerous wells with different depths which provides an excellent opportunity to sample groundwater from different flow systems. In addition, all of the artesian wells belongs to the intermediate and regional flow systems. Therefore, the analysis of hydrogeochemical and isotope techniques were used to investigate groundwater sources and their associated discharging processes to the river. Based on the Piper plot, several groups with distinct geochemical compositions could be found, which shows that the river water was mixed with groundwater from local and intermediate flow systems in the upstream, and dominated by groundwater from the intermediate flow system in the downstream. The relationship between δ D and δ¹⁸O supports this scenario. According to the Gibbs scheme, groundwater chemical evolution is mainly controlled by rock dominance and evaporation process, while, an evaporation trend could be found in river water. These results not only enhance the understanding of chemical evolution of groundwater in the study area, but also indicated the importance of artesian wells.

 

Tóth, J., 1963. A theoretical analysis of groundwater flow in small drainage basins. Journal of Geophysical Research, 68(16): 4795-4812.