Molecular signatures of natural organic matter and anthropogenic contaminants from high altitude fresh water lake (Rewalsar) in NW Indian Himalaya

The n-alkane (n-C₁₀ to n-C₃₅) distributions and anthropogenic markers (sterol and PAH) from the surface sediments of Rewalsar Lake, Himachal Pradesh (India) were investigated to disentangle natural and anthropogenic organic matter sources. The presence of odd numbered n-alkanes (n-C₂₇, n-C₂₉ and n-C₃₁) along with TAR, CPI and ACL values provide dominance of allochthonous over autochthonous organic matter sources. Detailed examination of allochthonous sources further reflect the accumulation of pollutants (PAHs and sterols) that mark the intensified toxicity and high degradation rates of lake system. The results obtained from diagnostic PAH indices highlight that the lake is immensely influenced by miscellaneous sources i.e, pyrogenic and petrogenic. Further, the occurrence of sewage contaminants particularly coprostanol and epicoprostanol suggest high anthropogenic loading due to sewage discharges. The overall accumulation of contaminants in the lake can be attributed to anthropogenic activities involving chemical and sewage overflow, agricultural and industrial discharges, land use changes, developmental activities. The uncontrollable pollution status of the Rewalsar lake is supported by low pristane/phytane (Pr/Ph) ratio that denotes anoxia. Moreover, dominance of coarse particles (silt and sand) over clay-sized particles further confirms high human intervention in the catchment area. Therefore, the study provides comprehensive understanding on organic matter source apportionment as well as role of anthropogenic stressors in the wake of rapid urbanization around Rewalsar lake.