Sediment respiration and lake trophic state are important predictors of large CO₂ evasion from small boreal lakes

Abstract

We show that sediment respiration is one of the key factors contributing to the high CO 2 supersaturation in and evasion from Finnish lakes, and evidently also over large areas in the boreal landscape, where the majority of the lakes are small and shallow. A subpopulation of 177 randomly selected lakes (o100 km 2 ) and 32 lakes with the highest total phosphorus (P tot ) concentrations in the Nordic Lake Survey (NLS) data base were sampled during four seasons and at four depths. Patterns of CO 2 concentrations plotted against depth and time demonstrate strong CO 2 accumulation in hypolimnetic waters during the stratification periods. The relationship between O 2 departure from the saturation and CO 2 departure from the saturation was strong in the entire data set (r 2 5 0.79, n 5 2 740, Po0.0001). CO 2 concentrations were positively associated with lake trophic state and the proportion of agricultural land in the catchment. In contrast, CO 2 concentrations negatively correlated with the peatland percentage indicating that either input of easily degraded organic matter and/or nutrient load from agricultural land enhance degradation. The average lake-area-weighted annual CO 2 evasion based on our 177 randomly selected lakes and all Finnish lakes 4100 km 2 (Rantakari & Kortelainen, 2005) was 42 g C m À2 LA (lake area), approximately 20% of the average annual C accumulation in Finnish forest soils and tree biomass (covering 51% of the total area of Finland) in the 1990s. Extrapolating our estimate from Finland to all lakes of the boreal region suggests a total annual CO 2 evasion of about 50 TgC, a value upto 40% of current estimates for lakes of the entire globe, emphasizing the role of small boreal lakes as conduits for transferring terrestrially fixed C into the atmosphere.

Periphyton support for littoral secondary production in a highly humic boreal lake

“…Decomposition of terrestrial C is the primary source of CO 2 in Finnish lakes during winter before ice melt (Kortelainen et al 2006). Vesterinen et al (2016) reported very high littoral primary production and biomass development by the periphyton in Mekkojärvi throughout the summer of 2012.…”

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

“…Numerous processes were found to proceed faster in small aquatic systems than in larger ones. Sequestration rates of organic carbon (Downing, 2010;Downing et al, 2008), the concentrations of CH 4 , CO 2 , and dissolved organic carbon (DOC) in the water column (Bastviken et al, 2004;Juutinen et al, 2009;Kelly et al, 2001;Kortelainen et al, 2006;Xenopoulos et al, 2003), and CH 4 and CO 2 emissions from the water to the atmosphere increase with decreasing lake size (Juutinen et al, 2009;Kortelainen et al, 2006;Michmerhuizen et al, 1996;Repo et al, 2007).…”

Within‐lake and watershed determinants of carbon dioxide in surface water: A comparative analysis of a variety of lakes in the Japanese Islands

“…If this is the case, thermal stratification determining vertical mixing plays a crucial role in regulating flux of CO 2 at the water-air interface in summer. A study examining Scandinavian lakes also suggests the importance of sediment respiration as a source of CO 2 supersaturation at the surface water (Kortelainen et al 2006). Relatively high pCO 2 values in shallow isothermal lakes support an empirical model proposed by den Heyer and Kalff (1998), who suggest that contribution of sediment respiration to the total CO 2 production is high for shallow lakes because the lake bottom is as warm as the surface and likely receives organic matter with a high proportion of labile component, both of which increase heterotrophic activities at the sediment.…”

“…For example, even when within-lake CO 2 production is high because of large inputs of terrigenous organic matter, pCO 2 may remain low as a result of the high consumption of CO 2 by increased primary producers due to large input of nutrients (Schindler et al 1997;del Giorgio et al 1999;Hanson et al 2003). Several studies have also implicated that the majority of consumption and decomposition of organic carbon may take place at the lake bottom (den Heyer and Kalff 1998;Jonsson et al 2003;Kortelainen et al 2006). If this is the case, pCO 2 at the surface water is likely higher for shallow well-mixed lakes than deep stratified lakes where the produced CO 2 would be confined below the thermocline during the stagnant seasons.…”