Summer greenhouse gas fluxes in different types of hemiboreal lakes
Date
2022Embargo Lift Date
15.06.2024Author
Rõõm, Eva-Ingrid
Lauringson, Velda
Laas, Alo
Kangro, Kersti
Viik, Malle
Meinson, Pille
Cremona, Fabien
Nõges, Peeter
Nõges, Tiina
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Lakes are considered important regulators of atmospheric greenhouse gases (GHG). We estimated late summer open
water GHG fluxes in nine hemiboreal lakes in Estonia classified under different lake types according to the
European Water Framework Directive (WFD). We also used the WFD typology to provide an improved estimate of
the total GHG emission from all Estonian lakes with a gross surface area of 2204 km2 representing 45,227 km2 of
hemiboreal landscapes (the territory of Estonia). The results demonstrate largely variable CO2 fluxes among the lake
types with most active emissions from Alkalitrophic (Alk), Stratified Alkalitrophic (StratAlk), Dark Soft and with predominant binding in Coastal, Very Large, and Light Soft lakes. The CO2 fluxes correlated strongly with dissolved CO2
saturation (DCO2) values at the surface. Highest CH4 emissions were measured from the Coastal lake type, followed by
Light Soft, StratAlk, and Alk types; Coastal, Light Soft, and StratAlk were emitting CH4 partly as bubbles. The only emitter of N2O was the Alk type. We measured weak binding of N2O in Dark Soft and Coastal lakes, while in all other studied lake types, the N2O fluxes were too small to be quantified. Diversely from the common viewpoint of lakes as net
sources of both CO2 and CH4, it turns out from our results that at least in late summer, Estonian lakes are net sinks
of both CO2 alone and the sum of CO2 and CH4. This is mainly caused by the predominant CO2 sink function of
Lake Peipsi forming ¾ of the total lake area and showing negative net emissions even after considering the Global
Warming Potential (GWP) of other GHGs. Still, by converting CH4 data into CO2 equivalents, the combined emission
of all Estonian lakes (8 T C day−1
) is turned strongly positive: 2720 T CO2 equivalents per day. This research was inspired by GLEON (Global Lake Ecological Observatory Network) and was funded by Estonian Research Council (PSG32, PUT1598, PSG10, PRG709, PRG1167 and ETF8486), the European Union H2020 WIDESPREAD (TREICLAKE 951963) and the Swiss Program “Enhancing public environmental monitoring capacities”.