Significant lake acidification recorded in northeast China during the warm and humid mid-Holocene

Acidification is a major ecological problem in a large number of lakes around the world. In recent decades, research has primarily focused on the effects of human-induced acid deposition on lake ecosystems. However, there has been relatively little research on how changes in the natural environment influence the acid-base balance of lakes. In this study, we tracked the changes of lake acidity in the past ∼10,000 years by using the records of sedimentary diatoms in Buteha Lake, a volcanic lake in northeast China. We also compare the historical changes in lake acidity with variations in vegetation and aeolian activity recorded in the same core and regional data to evaluate the relationships among lake acidity, vegetation changes, and dust deposition. The diatom results show that during the mid-Holocene (8200-4500 cal yr BP), acid-tolerant diatoms (Eunotia species) were very abundant. This pattern was followed by a gradual decline during the late Holocene, with a slight increase observed in recent decades. Proliferation of acid-tolerant diatoms indicate that severe lake acidification occurred during the mid-Holocene. The trend of lake acidification closely resembles the regional vegetation changes, contrasting with the intensity of aeolian activity. Our results suggest that lake acidification in the mid-Holocene was not directly linked to change in temperature and/or precipitation, but rather was driven by the balance between acidic and alkaline substance inputs. Specifically, climate warming and stronger monsoons enhanced terrestrial vegetation, increasing acidic humic substance inputs to the lake, while decreased alkaline dust deposition synergistically exacerbated acidification. This study provides a scientific basis for predicting the future development of lake environment in northeast China, and offers valuable insights for environmental research on natural lakes acidification globally. We predict that if global warming continues and precipitation increases in the future, more lakes, especially those that depend on dust inputs to maintain their acid neutralizing capacity, may experience acidification due to the decrease of alkaline dust deposition and the increase of acidic humic substances input caused by vegetation expansion.