Measurements of CO and CH evasion from UK peatland headwater streams.

Peatland headwater streams are consistently supersaturated with respect to gaseous C and are known to degas CO and CH directly to the atmosphere. Using a combination of injection of a purposeful gas tracer (propane) and a soluble tracer (NaCl) we carried out 49 measurements of the gas transfer coefficient on 12 representative stream reaches to quantify the gas transfer rates of CO and CH in headwater (1st-3rd order) streams draining six UK peatlands. These were compared to measured stream reach physical variables, such as discharge and water travel time. Whilst we found that evasion rates were highly variable in space and time, $$ {\text{K}}_{{{\text{CO}}_{2} }} $$ (gas transfer coefficient of CO) was positively related to discharge. Individual study sites showed a high degree of variability in gas transfer rates; at all 49 sites median/mean values for $$ {\text{K}}_{{{\text{CO}}_{2} }} $$ were 0.087/0.157 and $$ {\text{K}}_{{{\text{CH}}_{4} }} $$ 0.092/0.176 min. Median/mean instantaneous CO and CH evasion rates were 133/367 and 0.22/1.45 μg C m s, respectively. Methane evasion rates were therefore more than two orders of magnitude lower than CO, with CH invasion (rather than evasion) measured on 37 % of occasions. Our gas flux measurements from peatland headwater streams are higher than values previously used to estimate landscape scale fluxes and emphasise the importance of the evasion flux term in the overall carbon balance. [ABSTRACT FROM AUTHOR]