Complex hydroclimatic drivers of peatland stream CO2 and CH4 emissions revealed from a multi-catchment temporal study

Peatlands represent a dominant global soil carbon pool, but their role here is vulnerable to climate change and land use pressures. Peatland streams are known conduits of terrestrial carbon loss, rapidly transferring CO2 and CH4 from peat soils to the atmosphere. Despite their recognised contribution to global river greenhouse gas emissions, the hydroclimatic drivers here remain obscured across spatiotemporal gradients.To address these research needs, we applied a novel isotopic framework (radiocarbon, δ13C, δD, δ18O), to constrain age and sources of peatland stream CO2 and CH4, alongside constraints on hydrological flow paths and CH4 oxidation mechanisms. Over four seasonal visits, we sampled eight catchments on the Isle of Lewis, Scotland, spanning gradients of catchment areas, geomorphology, and land use. The Lewis Peatlands represent one of Europe’s largest continuous blanket bogs, and our catchments capture 30% of their surface area. All sites were subject to the same climate and underlying geology, enabling us to isolate spatiotemporal drivers across catchments.Chamber-based emissions (flux) measurements reveal high variability of both CO2 (–4.17 ± 2.35 to 106.73 ± 11.26 mmol m-2 d-1) and CH4 (0 to 2.44 ± 0.34 mmol m-2 d-1), with inconsistent coupling in the magnitude of CO2 and CH4 emissions, suggesting independent supply controls. We explore these catchment-specific patterns considering their geomorphological attributes. We find that both CO2 and CH4 fluxes decrease exponentially with catchment area. Surface moisture indices derived using remote sensing show stronger CH4 emissions in wetter catchments, while the magnitude of CO2 emissions was more strongly linked to temperature. Preliminary radiocarbon data hint that CO2 tends to become younger in drier catchments associated with summer sampling, validating the observed seasonal controls of CO2 dynamics. While stronger CO2 and CH4 fluxes generally aligned with younger carbon turnover, these pathways also act as a significant export mechanism for older carbon, with some of the highest fluxes formed of older carbon.Preliminary stable isotope data indicate greater inter-catchment variability in stream CH4 sources than CO2. Pending isotopic data will enable us to track these patterns over one year of sampling. Globally, only six published datasets report coupled river 14C-CO2 and 14C-CH4, making this one of the first studies to track these paired data over time. Combined with geochemical context and geospatial analyses, this framework will enable us to better constrain what are clearly highly dynamic and variable processes and avoid missing hotspots and key drivers of these peatland carbon loss mechanisms.