EGU24-4590, updated on 08 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Triple sulfur isotope constraints on the sulfur cycling in Lake Sevan, Armenia

Alexey Kamyshny1, Khoren Avetisyan1,2, Natella Mirzoyan3, and Rayford Payne4
Alexey Kamyshny et al.
  • 1Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel
  • 2Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, Canada
  • 3Acopian Center for the Environment, American University of Armenia, Yerevan, Republic of Armenia
  • 4Department of Marine Biotechnology, University of Maryland, Baltimore, USA

Lake Sevan is a meso-eutrophic water body, which was severely impacted by anthropogenic level decrease, pollution and eutrophication during the last century. Starting in the 1970s, a decrease in the water level and an increase in dissolved inorganic nitrogen concentrations resulted in oxygen depletion in the hypolimnion of the lake during summer–autumn thermal stratification of the water column. Our work shows that in October 2019, the redox conditions in the hypolimnion progressed not only to full depletion of oxygen and nitrate, but to the formation of a hydrogen sulfide-rich deep-water layer, which covers 66% of lake’s bottom and accounts for 19% of its water volume. Concentrations of hydrogen sulfide in the hypolimnion of Major and Minor Sevan in October were as high as 9 and 39 μM, respectively.

Triple sulfur isotope composition of sulfate and hydrogen sulfide in the water column of the lake provides further constraints on the biogeochemical processes which result in the formation of hydrogen-sulfide hypolimnion. Values of δ34S for hypolimnetic sulfide are lower by only 7–12 ‰ compared to epilimnetic sulfate, while δ33S values of sulfide are similar to the δ33S values of sulfate. These isotopic fingerprints are not consistent either with microbial sulfate reduction in the water column or with its combination with re-oxidative sulfur cycle as the sources of hydrogen sulfide in the hypolimnion. We attribute the formation of a sulfidic deep-water layer to a combination of microbial sulfate reduction in the water column and diffusion of hydrogen sulfide from the sediments.

How to cite: Kamyshny, A., Avetisyan, K., Mirzoyan, N., and Payne, R.: Triple sulfur isotope constraints on the sulfur cycling in Lake Sevan, Armenia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4590,, 2024.