Temperature and precipitation drive temporal variability in aquatic carbon and GHG concentrations and fluxes in a peatland catchment

The aquatic pathway is increasingly being recognised as an important component of catchment carbon and greenhouse gas (GHG) budgets, particularly in peatland systems due to their large carbon store and strong hydrological connectivity. In this study we present a complete 5-year dataset of all aquatic carbon and GHG species (POC, DOC, DIC, CO2, CH4, N2O) from an ombrotrophic Scottish peatland. We show that short term variability in concentrations exists across all species and this is strongly linked to discharge. Seasonal cyclicity was only evident in DOC, CO2 and CH4 concentration; however temperature correlated with monthly means in all species except DIC. Whilst the temperature correlation with monthly DOC and POC concentrations appeared to be related to biological productivity in the terrestrial system, we suggest the temperature correlation with CO2 and CH4 was primarily due to in-stream temperature-dependent solubility. Interannual variability in total aquatic carbon concentration was strongly correlated with catchment GPP indicating a strong potential terrestrial aquatic linkage. DOC represented the largest aquatic carbon flux term (19.3 ± 4.59 g C m−2 yr−1), followed by CO2 evasion (10.0 g C m−2 yr −1). Despite an estimated contribution to the total aquatic carbon flux of between 8 - 48%, evasion estimates have the greatest uncertainty. Interannual variability in total aquatic carbon export was low in comparison with variability in terrestrial biosphere-atmosphere exchange, and could be explained primarily by temperature and precipitation. Our results therefore suggest that climatic change is likely to have a significant impact on annual carbon losses through the aquatic pathway, and as such aquatic exports are fundamental to the understanding of whole catchment responses to climate change.