Potassium Isotopes in Huguangyan Maar Lake Sediments: Catchment Erosion versus Anthropogenic Activity since 1900 C.E

Potassium (K), an essential element for life, is released in large quantities through anthropogenic activities, altering the geochemical K cycle. K isotopes, therefore, have the potential to trace anthropogenic processes. Huguangyan Maar Lake (HML), a hydrologically enclosed lake, provides an ideal setting to preserve the historical records of anthropogenic activities. This study investigated the K contents and isotopic compositions (δ⁴¹K) in recent HML sediments to trace catchment K cycling and human impacts over the past 120 years in southern China. Results show that leachate K (K_leachate) is influenced by coal combustion, while residue K (K_residue) is mainly derived from bedrock erosion. Prior to 1950 C.E., the HML catchment experienced minimal human disturbance, as indicated by stable K contents and δ⁴¹K values. Between 1950 and 2000 C.E., increasing K_residue contents suggest intensified catchment erosion due to human activities following the founding of the People's Republic of China, though direct anthropogenic inputs remained limited. After 2000 C.E., fluctuations and decreasing δ⁴¹K_leachate values reflect varying air pollution from anthropogenic activities such as coal combustion and vehicle emissions associated with industrialization and subsequent environmental policies. This study highlights the possibility of K isotopes as a novel tracer of anthropogenic influence on the K geochemical cycle.