Preliminary assessment of methane emissions from small Armenian lakes

Introduction. Estimation of methane emission from the lake surface for Caucasus region had been done for the first time. The aim of the study - evaluation of methane (CH4) diffusive flux dynamic from the surface of poorly studied alpine Armenian lakes. Four lakes situated on the Lesser Caucasus had been studied in July-October 2023. Methane flux from lakes was measured by SPD203 gas analyzer of Sanpometer Company with boundary layer method. Portative instruments were used for lake hydro - chemical parameters measurements. Daily and seasonal dynamics of CH4 emission was estimated. Results and discussion. Tropic state and hydro - chemical features of lakes were determined. Lakes Shushanalich, Parzliman and Margalich have low salinity, neutral pH value, meso - and eutrophic conditions. Alpine Aknalich Lake is oligo - tropic and has light alkalinity pH. Dissolved oxygen is low in all lakes; reduction conditions could be on the bottom in summer. All lakes are dimictic with water layer overturn in spring and autumn that increases methane emission. Average CH4 flux from the lakes was 6.5 gCH4 m-2 d-1, maximal - 16.25 gCH4 m-2 d-1. Daily dynamic has a sinusoidal function, with smaller amplitude in autumn. Strong relation of CH4 flux and air (water) temperature is observed. Temporal variability of methane flux to atmosphere has exponential function and declines with exposure time. CH4 flux is higher during middle of the day comparedto morning or evening hours; methane flux during the autumn can be 2-3 times lower than in the summer. Evaluated diffusive methane fluxes from lakes of the region have greater values than previously estimated. Conclusion. For the first - time carried out estimations of methane flux from lakes reflect significant natural source of greenhouse gases emission for Lesser Caucasus. Obtained results are the starting point for the regional assessment of gas emission from all water bodies with different eutrophic status and hydrodynamic. Resume. An assessment of methane emissions from the surface of small mountain lakes in Armenia has been carried out for the first time. Patterns of changes in methane fluxes during the day in the summer and autumn season have been revealed. The dependence of the methane emission on the air temperature is constructed. The obtained values of the methane flux indicate values 2-3 times higher than the previously obtained estimates. In the future, it is necessary to measure methane in the winter - spring season and assess the CH4 flux from lacustrine sediments. Suggestions for practical applications and directions for future research. The obtained values of the methane flux from the surface of small alpine lakes in Armenia can be further used to model greenhouse gas emissions from aqua landscapes and to assess climate change in the entire Caucasus region.