Spatial scale-dependent land–atmospheric methane exchanges in the northern high latitudes from 1993 to 2004

[摘要] Effects of various spatial scales of water table dynamics onland–atmospheric methane (CH₄) exchanges have not yet been assessed forlarge regions. Here we used a coupled hydrology–biogeochemistry model toquantify daily CH₄ exchanges over the pan-Arctic from 1993 to 2004 attwo spatial scales of 100 km and 5 km. The effects of sub-grid spatialvariability of the water table depth (WTD) on CH₄ emissions wereexamined with a TOPMODEL-based parameterization scheme for the northern highlatitudes. We found that both WTD and CH₄ emissions are better simulatedat a 5 km spatial resolution. By considering the spatial heterogeneity ofWTD, net regional CH₄ emissions at a 5 km resolution are38.1–55.4 Tg CH₄ yr⁻¹ from 1993 to 2004, which are on average42% larger than those simulated at a 100 km resolution using agrid-cell-mean WTD scheme. The difference in annual CH₄ emissions isattributed to the increased emitting area and enhanced flux density withfiner resolution for WTD. Further, the inclusion of sub-grid WTD spatialheterogeneity also influences the inter-annual variability of CH₄emissions. Soil temperature plays an important role in the 100 km estimates,while the 5 km estimates are mainly influenced by WTD. This study suggeststhat previous macro-scale biogeochemical models using a grid-cell-mean WTDscheme might have underestimated the regional CH₄ emissions. The spatialscale-dependent effects of WTD should be considered in future quantificationof regional CH₄ emissions.

[学科分类] 地球化学与岩石