Methane and Nitrous Oxide Emissions From an Anthropogenically Transformed Lake (Lake Licheńskie, Poland)

Abstract

For over 50 years Lake Licheńskie (LLi), central Poland, has been involved in the cooling system of two power plants (PP). Owing to the discharge of cooling waters the lake was prone to considerable environmental changes which involved its thermal structure, mixing regime and water parameters. In this study we investigated how the man-made transformations affected greenhouse gas emissions (GHG; CH₄ and N₂O) from the lake. The GHG emissions in Lake Licheńskie were monitored at the deepest site from December 2014 to November 2015 and between March 2022 and February 2023. The values obtained were compared to reference lakes encompassing 10 natural and undisturbed inland and coastal lakes in Poland. Our results revealed that LLi was a net source of CH₄ and N2O to the atmosphere but the fluxes were low. The mean annual diffusive fluxes were 0.21–0.38 mmol·m⁻² d⁻¹ for CH₄ and 4.90–7.40 μmol·m⁻² d⁻¹ for N₂O. The CH₄ emissions were significantly lower than in most of reference lakes, while the N2O emissions were comparable. Therefore, the human intervention resulted in reduction of CH₄ release from LLi but it had minor effect on the N₂O. The most likely reason for the low direct fluxes of GHGs from the surface waters was the high flushing rate of the lake and export of dissolved gases to adjacent lakes and canals. Hence, the overall emission from the connected lake and canal system was not mitigated by the man-made changes to the lake system.