Comparing light and dark chamber measurements of CH₄ fluxes in drained and rewetted raised bogs of Ireland

The important factors regulating methane (CH₄) fluxes in rewetted peatlands such as the vegetation types, water table depths (WTDs) and in situ conditions (pH, redox, soil temperature and moisture) are widely reported, but the impact of light and dark conditions on CH₄ fluxes from multiple vegetation types are understudied. This field study investigated if the CH₄ fluxes from multiple vegetation communities (Sphagnum communities, Eriophorum angustifolium, Molinia caerulea, Typha latifolia, Phragmites australis, Juncus effusus, Calluna vulgaris, Carex rostrata and open water) responded differently to light and dark conditions. Triplicate light and dark measurements of carbon dioxide (CO₂) and CH₄ fluxes were measured in succession on the same day using the closed chamber method from the above-mentioned vegetation communities from five peatland sites located in the Irish midlands. The field measurements showed that the CH₄ fluxes were higher in light conditions compared to dark conditions for C. rostrata (49.0 ± 18.2 in light, 18.9 ± 7.8 g CH₄ m⁻² h⁻¹ in dark) and E. angustifolium (25.8 ± 9.1 in light, 11.2 ± 4.4 mg CH₄ m⁻² h⁻¹ in dark) compared to other vegetation communities. The mixed-effect model results indicated that differences between light and dark measurements were strongly related to CO₂ fluxes. When the vegetation was sequestering CO₂, CH₄ fluxes increased, conversely, during the respiration only, CH₄ fluxes decreased. Future work should examine the impact of vegetation specific phenological mechanisms that influence CH₄ fluxes in light and dark conditions using multiple years of field data.