Greenhouse gas emissions from Baltic coastal lakes

Coastal lakes (CL) act as limnetic-beta-oligohaline systems located on non-tidal coastlines in fresh and salt water mixing zone. Owing to considerable terrestrial nutrient input and a high autochthonous productivity CLs release greenhouse gases (GHG) to the ambient atmosphere, however, neither emission from the system was assessed nor controls on the emission were recognized so far. In this study we attempted to quantify diffusive emissions of CH4, CO2 and N2O from CLs based on data collected from seven lakes located on a south coast of the Baltic Sea in Poland. Lake water samples were collected with quarterly resolution along salinity, water depth and wind fetch gradients. From our data it emerged that the concentrations of GHGs were determined by temperature. CH4 showed dependence on salinity, lake water depth and wind fetch. N2O was controlled by dissolved O-2 and NO3- and CO2 was largely related to wind fetch. It also appeared that concentrations of N2O and CO2 were influenced by terrestrial nutrient input. The mean fluxes of CH4, CO2 and N2O for the whole system were 21.7 mg.m(-2).d(-1), 12.7 g.m(-2).d(-1) and 0.74 mg.m(-2).d(-1), respectively which was equivalent to 7.9 g CH4.m(-2).y(-1), 4.6 kg CO2.m(-2).y(-1) and 269 mg N2O.m(-2).y(-1). CH4 and N2O were released throughout the year and CO2 was predominantly emitted during winter. We showed that diffusive emissions of the GHGs showed relationships to the surface area of the lakes as well as the ratio of catchment area to lake area (CA/LA). The study would benefit from further extension with higher resolution analyses of the lakes over longer timescales and quantification of ebullitive GHG emission (CH4 in particular). (c) 2020 The Authors. Published by Elsevier B.V.