Hydro- and biogeo-chemistry of the largest hypersaline lake of India

Abstract:

Biogeochemistry of inland saline lakes have received little attention across the globe, including India. During the present study, we focused on understanding seasonal variations in carbon and nitrogen dynamics in the Sambhar lake, an inland hypersaline lake, located in the semi-arid region of western India. To further assess the effect of land-use, the area in and around Sambhar was divided into three distinct sampling classes: the natural lake, the brine reservoir, and innumerable salt pans spread across the edges of the lake. Water samples collected from these land-use categories were measured for major ions, nutrients concentration, dissolved inorganic carbon (DIC), oxygen isotopic composition, dissolved gases, particulate organic matter (POM) and its carbon and nitrogen isotopes. Majority of measured parameters showed distinctive signature in each land-use category. Significantly low NH₄⁺: NO₃^- in the salt pans compared to natural lake and brine waters indicated excessive groundwater use in salt pans. Significantly high δ¹³C_DIC and δ¹³C_POM during winter suggested a bicarbonate dominated system with high productivity and high rates of C remineralization. During winter, low δ¹⁵N_POM along with high NH₄⁺ pool, suggested the presence of N fixers or the uptake of isotopically light, re-mineralized dissolved inorganic nitrogen, brought up by water column mixing. Dissolved CH₄ and N₂O concentrations were high and varied seasonally depending on water column stratification and the sensitivity of microbes to the changing pH of the system. Experiments performed to measure the net rates of N-transformation in the salt flats during periods of desiccation suggested potential role of saline water bodies as hot spots for nutrients recycling.