Lake desiccation drives carbon and nitrogen biogeochemistry of a sub-tropical hypersaline lake

Saline lakes across the globe have experienced severe reduction in their surface area as a result of climate change and human-induced perturbations like water diversion and extraction. The changing lake volume is predicted to have large-scale implication on the in-lake biogeochemistry. This study explores the carbon (C) and nitrogen (N) cycling in a desiccating hypersaline lake (Sambhar Lake, India) along with adjacently located brine reservoir and salt pans by measuring concentrations and stable isotopic ratios of different C and N pools during winter and monsoon. Incubation experiments to estimate the net nitrification and mineralization rates in lake sediments were also performed. The Lake witnessed a large decrease in surface area and showed a clear signature of desiccation on lake biogeochemistry. Both particulate and dissolved fractions of C and N in the lake increased as the lake desiccated from monsoon to winter. Low N isotopic composition (delta N-15) of particulate organic matter during winter suggested the presence of N-2 fixers in this nutrient-rich saline environment. Taken together, significant difference in C and N concentrations and isotopic compositions were observed across the lake, brine reservoir, and salt pans, suggesting considerable modulation of in-lake processes due to human interventions.