Variability in CO2 concentrations and sources in a peatland stream during storm-flow events

Peatland streams are known to be supersaturated in CO2 with respect to the atmosphere [Billett and Moore, 2007; Dawson et al., 1995; Hope et al., 2001], and as such potentially represent an important conduit for the release of soil derived carbon to the atmosphere. However, relatively little is known about short-term temporal variability in CO2 concentrations in response to the extreme hydrological events which make up a large proportion of the annual flow regime. Here we use submerged, non-dispersive infra-red (NDIR) sensors to make continuous measurements of CO2 concentrations during 18 storm events in a Scottish peatland stream. Individual storms exhibited 3 distinct types of hysteresis loop. We suggest that differences in loop form may be due to differences in the relative contributions of soil water or differences in contributing catchment source area. We found a negative concentration-discharge relationship over the full study period, suggesting that CO2 rich deep peat/ground water was the major source of aquatic CO2 under low flow conditions. By removing the effect of dilution and estimating additions and losses of CO2, we also show the importance of both surface peat CO2 inputs into the stream and evasion loss during stormflow. Downstream CO2 export during the study period was dominated by stormflow events (71%), highlighting the importance of accurately accounting for high flow CO2 sources.