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

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