Reactive transport modeling for the effect of pumping activities on the groundwater environment in muddy coasts

Abstract

Intensive pumping activities threaten the coast groundwater environment and have a negative impact on aquifer systems. A comprehensive understanding of these effects is important for the management of coastal groundwater resources. However, this is challenging, particularly for coastal saline groundwater systems due to complex water–rock interactions. In this study, a coupled variable–density flow and hydrochemical reaction model was used to examine the effects of pumping activities on the groundwater environment on the southern coast of Laizhou Bay, China, which is a typical muddy coast. The model successfully captured the hydrodynamic and hydrochemical changes, and the water–rock interactions, during three different exploitation stages: (1) evaporation and water–rock interactions were the primary controls on groundwater evolution during the weakly pumped stage (before 1995); (2) the groundwater level began to decrease and saltwater intrusion was aggravated during the small pumping stage (1995–2005); and (3) significant hydrodynamic and hydrochemical changes occurred at the saline/freshwater transition and pumping zones during a period of intensive pumping (after 2005). Our findings revealed that water–rock interactions are the primary drivers of hydrochemical evolution at the saline/freshwater transition and seaward saline groundwater zone, whereas hydrodynamic changes are the main drivers in the pumping and deep saline–brine water zones. Furthermore, we discussed the effects of hydrodynamic variations and water–rock interactions on the aquifer matrix and identified that irreversible changes occurred mainly in the pumping zone and saline/freshwater transition. In conclusion, our study highlights the importance of considering both hydrodynamic and hydrogeochemical factors when managing coastal groundwater resources. By developing a better understanding of these complex interactions, we can minimize the negative impacts of pumping activities and preserve the long-term sustainability of coastal groundwater resources.