The influence of anthropogenic perturbations on the accumulation of polycyclic aromatic hydrocarbons in a lake system of Central Himalayas

Delineating the impact of various natural and anthropogenic drivers on the environment is a
paramount challenge in paleoenvironmental reconstruction. In the present study, we used faecal
biomarker (coprostanol) and polycyclic aromatic hydrocarbons (PAHs) in the lake sediments
alongside population census and meteorological parameters from Central Himalayas to delineate
the anthropogenic and natural signals of environmental changes for the past ~70 years (1950-
2018 AD). The resulting stress from the human activities is evident by an abrupt increase in the
coprostanol (0.1-5.5 mg/g) and pyrolytic PAHs concentration (1422-32077 ng/g) in the
sediments. Further, with the metric of population rise, economic and infrastructural development,
the composition of PAHs in the sediments has changed: the proportion of heavy molecular
weight PAHs increased from 57% to 86%, whereas low molecular weight PAHs decreased from
43% to 14% indicating an increase in the proportion of fossil fuels combustion and a decrease in
biomass burning sources. Based on reanalysis datasets, the computed temporal variation of
annual precipitation and annual temperature over the region clearly indicated that natural drivers
have no direct influence on the PAHs concentration and other biogeochemical parameters. In
addition, the hysplit back trajectory analysis provided evidences of the atmospheric deposition of
black carbon from the countryside biomass burning and petrogenic pollution from the nearby
megacities.