Groundwater Discharge as a Critical Driver of Freshwater Lake Acidification in Central China

Abstract

Abstract Lake acidification has emerged as a widespread environmental challenge globally, yet the role of lacustrine groundwater discharge (LGD) in this process remains poorly understood. Here, through seasonal monitoring of lake pH and LGD‐derived total alkalinity (TA) and dissolved inorganic carbon (DIC) fluxes in a hydrologically representative freshwater lake within the central Yangtze River plain, we provided robust evidence that LGD profoundly exacerbated lake acidification. The groundwater (pH: 6.53–7.85) had a higher acidity than the lake water (pH: 7.26–8.83), and the negative correlation between 222Rn activity and pH in the lake water suggested potential role of groundwater discharge in lowering lake pH. Seasonal hydrological changes induced notable fluctuations in LGD rates, which were consistent with changes in lake TA, DIC concentrations, and lake pH. During the dry season, LGD rate peaked at 80.03 mm/d, which caused the lake's average TA:DIC ratio to decline to its annual minimum (1.28 ± 0.07), and the pH to drop to 7.86 ± 0.18. Although the inflow of Yangtze River water temporarily raised lake pH to 8.72 ± 0.06, continued LGD input remained the dominant driver of acidification after the wet season. Unlike ocean acidification, LGD‐driven acidification exhibits strong seasonality and more uniform spatial distribution. The influence of LGD on lake acidification is more directly controlled by the original hydrochemical characteristics of groundwater. Our study reveals for the first time the dynamic impact of LGD on acidification in a typical inland freshwater lake, central China, and provides new insights into the acidification of specific freshwater lakes.

Keywords

• groundwater discharge
• alkalinity
• dissolved inorganic carbon
• lake acidification
• seasonal variations