Assessment of karst groundwater quality and its ecological environmental effects in Beijing

This paper presents the results of hydrogeological survey engineering.

Objective As an important water supply source in Beijing, karst groundwater plays an irreplaceable role in the security of the urban water supply and the improvement of the ecological environment.

Methods Based on the analysis of 278 karst groundwater samples systematically collected in Beijing in June 2021, both single-factor quality evaluation and comprehensive quality evaluation of karst water were carried out in different karst water systems. Additionally, the organic indicators were statistically counted and analyzed for the first time.

Results (1) The average values of pH, TDS, and TH of karst water in Beijing are 7.69, 334.77 mg/L, and 262.01 mg/L, respectively. These results indicate that the groundwater is weakly alkaline, with low salinity and low hardness, suggesting generally good water quality. (2) The detection rates for unconventional indicators, in descending order, were benzoapyrene (4.32%), tribromomethane (3.60%), and total xylene (2.52%). These contaminants warrant significant attention. (3) The results of groundwater quality evaluation show that the overall proportion of karst water quality falling within Classes I−III is 82.01%, while Classes IV and V constitute 17.99%. The exceedance points are primarily located at the interface between mountainous and plain areas, with the primary exceedance indicators being Fe, TH, NH₃-N, Mn, SO₄²⁻, F⁻, and NO₃-N.

Conclusions As the important water source supply area and ecological protection zone in Beijing's ecological conservation area, karst groundwater in the study area plays a very important role for ensuring the safety of the capital's water supply and protecting the ecological environment. In the future, to practically protect karst groundwater, measures such as increasing vegetation cover to enhance water conservation and recharge capacity, strictly controlling point source and non-point source pollution to reduce pollutant inputs, continuously optimizing the monitoring network for early warning, and broadly promoting public awareness and education on ecological protection should be implemented systematically.