Hydrochemical environment of a fractured karst aquifer influenced by petroleum hydrocarbons

A fractured karst aquifer polluted by petroleum hydrocarbons (PH) for several decades was selected to study the influences of PH on the hydrochemical environment. The research was implemented using the hydrochemical indicators (Ca²⁺, Mg²⁺, Na⁺+K⁺, HCO₃^-, NO₃^-, Cl^-, F^-, and SO₄^2-) and PH with the help of GIS and origin platforms, statistical analyses, and graphical methods. Results showed that PH had significant influences on the hydrochemical environment over the last several decades. The main principle elements influencing the evolution processes of hydrochemical environment were carbonates dissolution, leaking wastewater, and biodegradation processes from 1977 to 2019, and hydrochemistry types changed from HCO₃-Ca-Mg and HCO₃-Ca to HCO₃-Cl-Ca-Mg and HCO₃-Cl-Ca. The contribution rate of PH biodegradation to the representative ion increased at first, then decreased over time, which has a close relationship with the variation characteristics of PH. The dynamic evolution processes of hydrochemical environment have significances for indentifying the influencing mechanisms of hydrogeochemical reactions, which could provide valuable scientific suggestions for the local administrators to take effective efforts to optimize and protect the karst groundwater environment.