A 200-year record of polycyclic aromatic hydrocarbon (PAH) deposition in Lake Balkhash, arid Central Asia: PAH sources and inferred human history

Stratigraphic distributions of polycyclic aromatic hydrocarbons (PAHs) in lake sediments can be used to infer past human activities in watersheds. We explored the PAH history and human stressors on Lake Balkhash, Kazakhstan, arid Central Asia, using a 200-year-long sediment record from the lake. Concentrations of Σ₁₆PAH in the sediments ranged from 18.6 to 292.6 ng g⁻¹ dw, with 3–4-ring PAHs dominating. Before 1910, Σ₁₆PAH concentrations showed a slowly increasing trend, except for several high values. After 1910, Σ₁₆PAH concentrations increased sharply. Using stratigraphically constrained cluster analyses, PAH delivery to the Lake Balkhash sediment was divided into four stages. We tracked the PAH sources using diagnostic ratio combinations, i.e., Ant/(Ant + Phe) vs Flt/(Flt + Pyr) and Bap/Bghip vs IP/(IP + Bghip). Stage I (1800–1840 CE) and Stage II (1840–1910 CE) PAHs were derived primarily from incomplete combustion of biomass and fossil fuel combustion during military conflicts, and Stage III (1910–2000 CE) PAHs came mainly from a mixture of coal, fossil fuel and biomass combustion. In Stage IV (2000–2017 CE), except for mixed sources, input of vehicle emissions and oil-spill sources increased. Using shifts in the PAH composition and sources, four periods of human activity in the watershed, ranging from low to high impact, were identified: I) early agriculture, II) social unrest, III) rapid industrial growth and agricultural expansion, and IV) elevated industrial use of oil. Moreover, we identified substantial human-disturbance events that occurred in the lake basin ca. 1810, 1850, 1910 and 1965, illustrating that PAHs in lake-sediment cores can provide insights into past human activities in watersheds.