Effects of metabolism on carbonate systems and localized alkalization in plant-dominated lakes

Material cycling and chemical equilibrium in ecosystems, including the carbonate system, are regulated by the system acidity and alkalinity, which are, in turn, affected by biological, physical, and chemical interactions. In this study, we collected daily and seasonal measurements from three different habitats in Baiyangdian Lake (BYDL), two with submerged plants and one without plants. The pH fluctuated widely at the diel scale because of photosynthesis and respiration metabolic processes, with variations of up to 2.1 units (from pH 7.9 to pH 10.0) in the pH in the areas dominated by submerged plants. Metabolism strongly influenced the spatial and temporal patterns in the pH, the dissolved organic carbon balance, and the carbonate chemistry. The dissolved organic carbon balance was also linked to the CaCO₃ precipitation. We examined how the buffering capacity changed in scenarios with different levels of submerged plant biomass and found that, although the carbonate buffering contributions to the pH increased (from 7 % to 37 %) as the plant biomass increased, the buffering capacity was not sufficient to offset the alkalinization, resulting in persistent high-pH conditions. These findings highlight how metabolism and buffering affect the pH level, and provide a scientific basis for lake restoration and freshwater management.