Dynamic carbon budget of a large shallow lake assessed by a mass balance approach
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To study the role of large and shallow hemiboreal lakes in carbon processing, we calculated a 3-year carbon mass balance for Lake Võrtsjärv (Estonia) based on in situ measurements. This balance took into account hydrological and biogeochemical processes affecting dissolved inorganic (DIC), dissolved organic (DOC) and particulate organic (POC) carbon species. Accumulation varied greatly on a seasonal and yearly basis. The lake exported carbon during most of the year except during spring floods and in late autumn. In-lake processes were responsible for exporting POC and storing DOC while DIC switched between storage and export. The carbon cycle was alternatively dominated in 2009 by biogeochemical processes and in 2011 by riverine fluxes, whereas in 2010 the two process types were of the same magnitude. These results suggest that the role of large shallow lakes like Võrtsjärv in the global C cycle is equally driven by hydrological factors, in particular seasonal water level changes, and by biogeochemical in-lake reactions.
KeywordsMass balance Carbon budget Accumulation Shallow lake DIC CO2 Methane Macrophytes
The study was supported by the Estonian Ministry of Education (project SF0170011s08), by the Estonian Science Foundation through grants, ETF9102, JD109 ETF8486 and ETF8729 and by 7th EU Framework Programme, Theme 6 (Environment including Climate Change) project REFRESH (Adaptive strategies to Mitigate the Impacts of Climate Change on European Freshwater Ecosystems, Contract No. 244121). The Estonian Ministry of Environment supported data collection in the state monitoring programme. We gratefully acknowledge the water level data contributed by the Estonian Institute of Hydrology and Meteorology. We are thankful to two anonymous reviewers for valuable comments and suggestions.
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