Carbon Dioxide and Methane Dynamics in a Small Boreal Lake During Winter and Spring Melt Events. Issue 8 (25th August 2018)

• Record Type: Journal Article
• Authors: Denfeld, B. A.; Klaus, M.; Laudon, H.; Sponseller, R. A.; Karlsson, J.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 8(2018)
• Page Start: 2527
• Page End: 2540
• Publication Date: 2018-08-25
• Subjects: winter limnology -- carbon cycle -- carbon dioxide -- methane -- emissions -- ice‐covered lake; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2018JG004622
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: In seasonally ice‐covered lakes, carbon dioxide (CO2 ) and methane (CH4 ) emission at ice‐off can account for a significant fraction of the annual budget. Yet knowledge of the mechanisms controlling below lake‐ice carbon (C) dynamics and subsequent CO2 and CH4 emissions at ice‐off is limited. To understand the control of below ice C dynamics, and C emissions in spring, we measured spatial variation in CO2, CH4, and dissolved inorganic and organic carbon from ice‐on to ice‐off, in a small boreal lake during a winter with sporadic melting events. Winter melt events were associated with decreased surface water DOC in the forest‐dominated basin and increased surface water CH4 in the mire‐dominated basin. At the whole‐lake scale, CH4 accumulated below ice throughout the winter, whereas CO2 accumulation was greatest in early winter. Mass‐balance estimates suggest that, in addition to the CO2 and CH4 accumulated during winter, external inputs of CO2 and CH4 and internal processing during ice‐melt could represent significant sources of C gas emissions during ice‐off. Moreover, internal processing of CO2 and CH4 worked in opposition, with production of CO2 and oxidation of CH4 dominating at ice‐off. These findings have important implications for how small boreal lakes will respond to warmer winters in the future; increased winter melt events will likely increase external inputs below ice and thus alter the extent and timing of CO2 and CH4 emissions to the atmosphere at ice‐off. Plain Language Summary: Many lakes are ice‐covered for a portion of the year, where ice serves as a barrier to the atmosphere, trapping greenhouse gases, like carbon dioxide and methane. At ice‐off, these greenhouse gases are released into the atmosphere. Yet due to difficulties associated with sampling ice‐covered lakes, there is limited information about the factors that contribute to carbon dioxide and methane release at ice‐off. Moreover, projected warmer winters, with increased precipitation as rain and reduced duration of ice cover, suggest that the contributing factors may change in the future. To gain insight into greenhouse gas dynamics in ice‐covered lakes, we measured carbon dioxide and methane from ice‐on to ice‐off in a small boreal lake during a winter with sporadic melting events. We show that winter melt events alter carbon inputs below ice with implications for the timing and type of greenhouse gases released at ice‐off. Our study brings new insight to greenhouse gas dynamics in ice‐covered lakes and highlights challenges in understanding the implications of changing ice‐cover patterns as the climate warms. Key Points: Winter melt events were linked to decreased dissolved organic carbon in the forest lake basin and increased methane in the mire lake basin Wintertime accumulation, as well as external inputs and internal processes during snowmelt, contributed to ice‐off carbon gas emissions Increased winter melt events will alter land‐water connections, with implications for the timing and type of carbon sourced to lakes