Climate-fire-human interactions and their impact on the limnology conditions of the Dongyuan Lake, Southern Taiwan during the last 1800 cal years BP

In recent years, the severe impact of wildfires has sharply increased due to rising temperatures and drought-like conditions. Therefore, in addition to continuous wildfire monitoring, a long-term understanding of the climate-wildfire relationship is warranted. This study has explored the climate-wildfire relationship in the southern Taiwan region over the past two millennia, focusing on the influence of climate and human activities on wildfire occurrences and their subsequent impact on lake. To achieve this, carbon, nitrogen, carbon isotopic composition of organic matter, charcoal, and diatom assemblages were analysed in the Dongyuan Lake core sediments. Wildfires occurring between 1850 and 1050 cal years BP were largely caused by drier climate conditions. However, wildfires occurring during 750-500 cal years BP and from 350 cal years BP to the present, intervals characterized by wet climate conditions, coincided with a significant number of archaeological sites near Dongyuan Lake, suggesting human-induced burning in the region. The observed wet interval during 1050-750 cal years BP in southern Taiwan attributed to the Medieval Warm Period (MWP), and dry interval during 500-350 cal years BP linked to Little Ice Age (LIA). The low carbon content in Dongyuan Lake sediments coincided with peaks of charcoal accumulation, indicating the loss of carbon due to wildfires and the dilution of sediments. The principal component analysis (PCA) of diatom data showed that PC1 and PC2 represented the lake's acidic conditions, suggesting an increase in pH from 750 to 150 cal years BP. This variation in pH appeared to be linked with wildfire intensity and frequency. PC1 and PC2 also showed strong acidic conditions during the last 150 years, plausibly due to the increase in acid rain conditions in the last century.