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_residuecontents 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_leachatevalues 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.