Comparing Light and Dark Chamber Measurements of CH4 Fluxes in Drained and Rewetted Raised Bogs of Ireland

The important factors regulating methane (CH ₄ ) 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 CH ₄ fluxes from multiple vegetation types are not widely reported. This field study investigated if the CH ₄ 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 simultaneous light and dark measurements of carbon dioxide (CO ₂ ) and CH ₄ fluxes were measured on the same day using the chamber method from the above-mentioned vegetation communities from five peatland sites located in the Irish midlands. The field measurements showed that the CH ₄ fluxes were higher in light conditions compared to dark conditions for Carex rostrata (0.05 ±0.02 in light, 0.02 ±0.01 g CH₄ m⁻² hr⁻¹ in dark) and Eriophorum angustifolium (0.02 ±0.01 in light, 0.01 ±0.00 g CH₄ m⁻² hr⁻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 CO ₂ fluxes. When the vegetation was sequestering CO ₂ , CH ₄ fluxes increased, alternatively, during the respiration, CH ₄ fluxes decreased. Future work should examine the impact of vegetation specific phenological mechanisms that influence CH ₄ fluxes in light and dark conditions using multiple years of field data.