Disentangling the impact of anthropogenic and natural processes on the environment in a subtropical subalpine lake catchment in northeastern Taiwan over the past 150 years

Human activities impose significant changes on sedimentation processes and vegetation cover within lake catchments. However, the needed time for an anthropogenically disturbed natural state to be reversed back to its natural state by environmental protection programs is still ambiguous. Here we employ a multi-proxy approach to delineate major en-vironmental disturbances such as logging and forest fires on the catchment in Cueifong Lake, a subtropical subalpine lake in northeastern Taiwan. X-ray Fluorescence (XRF) core scanning, bulk total organic carbon (TOC), bulk total ni-trogen (TN), stable carbon isotope (813Corg) analysis, and macro-charcoal counting were utilized to reconstruct changes in the catchment environment based on a sediment core from Cueifong Lake. The results show that the ele-ment content changed distinctly around 1975 CE, which coincided with the onset of profound deforestation in the lake vicinity recorded in historical documents and aerial photos. After the cessation of the logging event, the detrital input increased, accompanied by decreasing C/N ratios and increasing 813Corg values. This suggests that increased ter-restrial nutrient input promoted algae growth. After the deforestation phase, our results imply a gradual recovery of elemental composition in the catchment environment. By extrapolating the XRF element records, we suggest that it might take >50 years for the sedimentary regime to reach its pre-logging baseline. In contrast to the depositional sys-tem, the C/N and 813Corg shifted significantly -potentially irreversibly -towards an algae-dominant environment in-stead of recovering to the pre-logging condition. This could be due to both 1) the changes in the different vegetation species used for reforestation and/or 2) anthropogenically introduced fishes in the 1980s. This study proposes the first assessment of the needed recovery time for subtropical Asian subalpine forests after large-scale log-ging activity and thus provides an apparent reference for policy decisions on natural resource development and envi-ronmental protection.

Automated summary

Human activities have caused significant changes in sedimentation processes and vegetation cover in lake catchments. However, the time needed for anthropogenically disturbed areas to return to their natural state through environmental protection programs is still uncertain. This study focuses on the Cueifong Lake catchment in Taiwan and uses a multi-proxy approach to investigate major environmental disturbances such as logging and forest fires. The results suggest that it may take more than 50 years for the sedimentary regime to fully recover from logging activities, while the vegetation composition may shift irreversibly towards an algae-dominant environment.