Abstract The processing of organic carbon in surface waters represents a critical component of the carbon (C) cycle in boreal landscapes and is closely linked to greenhouse gas (GHG) emissions, primarily carbon dioxide (CO2) and methane (CH4). Utilizing a unique data set with dense monitoring of dissolved organic carbon (DOC), dissolved CO2, and CH4 at the inlets and outlet of the boreal humic headwater lake Langtjern (Norway), we constructed an organic and inorganic C budget for the wet year 2023. Catchment inputs of DOC (14. 7 g C m−2 yr−1) exceeded lake export (12. 4 g C m−2 yr−1), whereas CO2 (in: 0. 9, out: 1. 2 g C m−2 yr−1) and CH4 (in: 0. 001, out: 0. 008 g C m−2 yr−1) exhibited the opposite pattern. The atmospheric evasion of CO2 and CH4 were 1. 50 and 0. 012 g C m−2catchment yr−1, respectively, demonstrating that the lake was a hotspot of GHGs. Estimated mineralization rates derived from inorganic (1. 80 ± 0. 83 g C m−2catchment yr−1) and organic C (1. 30 ± 0. 43 g C m−2catchment yr−1) mass balances were in reasonable agreement, and their main uncertainties came from catchment inputs and lake evasion. Lake dissolved organic matter mineralization and CH4 production rates were positively correlated with water temperature. Catchment C inputs were strongly dependent on precipitation while DOC removal was limited by water residence time. We expect that a wetter climate will exert a stronger future control on boreal lake GHG production than warming by reducing aquatic processing time.
Lu et al. (Fri,) studied this question.