Carbon dioxide evasion from headwater systems strongly contributes to the total export of carbon from a small boreal lake catchment

摘要

Inland waters are hotspots for carbon (C) cycling and therefore important for landscape C budgets. Small streams and lakes are particularly important; however, quantifying C fluxes is difficult and has rarely been done for the entire aquatic continuum, composed of connected streams and lakes within the same catchment. We investigated carbon dioxide (CO_2) evasion and fluvial fluxes of dissolved inorganic carbon and dissolved organic carbon (DIC and DOC) in stream and lake systems within the 2.3km~2 catchment of a small boreal lake. Our results show pronounced spatial and temporal variability in C fluxes even at a small spatial scale. C loss from the catchment through CO_2 evasion from headwaters for the total open water-sampling period was 9.7 g C m~(-2) catchment, dominating the total catchment C loss (including CO_2 evasion, DIC, and DOC export from the lake, which were 2.7, 0.2, and 5.2 g C m~(-2) catchment, respectively). Aquatic CO_2 evasion was dominated by headwater streams that occupy ~0.1% of the catchment but contributed 65% to the total aquatic CO_2 evasion from the catchment. The importance of streams was mainly an effect of the higher gas transfer velocities than compared to lakes (median, 67 and 2.2 cm h~(-1), respectively). Accurately estimating the contribution of C fluxes from headwater streams, particularly the temporal and spatial dynamics in their gas transfer velocity, is key to landscape-scale C budgets. This study demonstrates that CO_2 evasion from headwaters can be the major pathway of C loss from boreal catchments, even at a small spatial scale.