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Forskningsartikel - Refereegranskat, 2011

Spatiotemporal variability of the gas transfer coefficient (K-CO2) in boreal streams: Implications for large scale estimates of CO2 evasion

Wallin, Marcus B.; Oquist, Mats G.; Buffam, Ishi; Billett, Michael F.; Nisell, Jakob; Bishop, Kevin H.


Boreal streams represent potentially important conduits for the exchange of carbon dioxide (CO2) between terrestrial ecosystems and the atmosphere. The gas transfer coefficient of CO2 (K-CO2) is a key variable in estimating this source strength, but the scarcity of measured values in lotic systems creates a risk of incorrect flux estimates even when stream gas concentrations are well known. This study used 114 independent measurements of K-CO2 from 14 stream reaches in a boreal headwater system to determine and predict spatiotemporal variability in K-CO2. The K-CO2 values ranged from 0.001 to 0.207 min(-1) across the 14 sites. Median K-CO2 for a specific site was positively correlated with the slope of the stream reach, with higher gas transfer coefficients occurring in steeper stream sections. Combining slope with a width/depth index of the stream reach explained 83% of the spatial variability in K-CO2. Temporal variability was more difficult to predict and was strongly site specific. Variation in K-CO2, rather than pCO(2), was the main determinant of stream CO2 evasion. Applying published generalized gas transfer velocities produced an error of up to 100% in median instantaneous evasion rates compared to the use of actual measured K-CO2 values from our field study. Using the significant relationship to local slope, the median K-CO2 was predicted for 300,000 km of watercourses (ranging in stream order 1-4) in the forested landscape of boreal/nemoral Sweden. The range in modeled stream order specific median K-CO2 was 0.017-0.028 min(-1) and there was a clear gradient of increasing K-CO2 with lower stream order. We conclude that accurate regional scale estimates of CO2 evasion fluxes from running waters are possible, but require a good understanding of gas exchange at the water surface.

Publicerad i

Global Biogeochemical Cycles
2011, Volym: 25, nummer: 3, artikelnummer: GB3025