A model of potential carbon dioxide efflux from surface water across England and Wales using headwater stream survey data and landscape predictors

[摘要] Measurements of CO₂ partial pressures (pCO₂) in small headwaterstreams are useful for predicting potential CO₂ efflux because theyprovide a single concentration representing a mixture from differenthydrological pathways and sources in the catchment. We developed a model topredict pCO₂ in headwater streams from measurements undertaken onsnapshot samples collected from more than 3000 channels across the landscapeof England and Wales. We used a subset of streams with upstream catchmentareas (CA) of less than 8 km² because below this scale thresholdpCO₂ was independent of CA. A series of catchment characteristics werefound to be statistically significant predictors of pCO₂, includingthree geomorphic variables (mean altitude, mean catchment slope and relief)and four groups of dominant catchment land cover classes (arable, improvedgrassland, suburban and all other classes). We accounted for year-round,temporal variation in our model of headwater pCO₂ by including weeklyor monthly analyses of samples from three headwater catchments with differentland use and geomorphic features. Our model accounted for 24% of thespatial and temporal variation in pCO₂.

We combined predictions from the pCO₂ model (on a 1 km grid) andmonthly runoff volumes (litres) on 0.5° resolution grid acrossEngland and Wales to compute potential C fluxes to the atmosphere. Our modelpredicts an annual average potential C flux of 65.4 kt C across England andWales (based on free C concentrations), with lower and upper 95% confidencevalues of 56.1 and 77.2 kt C, respectively.

[学科分类] 地球化学与岩石