Biogeochemical records of paleoenvironmental changes in Nainital Lake, Kumaun Himalayas, India

• Rapid urbanization and increased tourism around Nainital Lake in the Kumaun Himalayan region in north India has raised concerns about sediment and water pollution. Lead-210 dated sediment cores from the lake represent similar to 95 years of accumulation and yield a mean sedimentation rate of similar to 4.7 mm year(-1). Total organic carbon (TOC), percent N and S and their atomic C/N and C/S ratios, stable isotopes (delta C-13, delta N-15, and delta S-34), and specific biomarkers (n-alkanes and pigments) were measured in the core. Organic matter is primarily derived from in-lake algal production and TOC flux varies from 1.0 to 3.5 g m(-2) year(-1). Sediments are anoxic (Eh -328 to -187 mV) and have low (0.10-0.30 g m(-2) year(-1)) N, but high (0.37-1.0 g m(-2) year(-1)) S flux. Shifts in delta C-13, delta N-15, and delta S-34 suggest in-lake microbial processes dominated by denitrification and sulfate reduction. The sediments are dominated by short-chain hydrocarbons with low Carbon Preference Index values. The pigments indicate a gradual shift to cyanobacterial domination of the phytoplankton community in recent years. Despite an increase in external input of nutrients, the trophic state of the lake has remained largely unchanged, and the perceived human-induced impacts are limited.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Lake sediments

Paleoproductivity

Organic matter

Stable isotopes

Hydrocarbons

Pigments

Earth sciences

Geovetenskap

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