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.