High-resolution peat volume change in a northern peatland: Spatial variability, main drivers, and impact on ecohydrology

The depth of the groundwater table below the surface and its spatiotemporal variability are major controls on all major biogeophysical processes in northern peatlands, including ecohydrology, carbon balance, and greenhouse gas exchange. In these ecosystems, water table fluctuations are buffered by compression and expansion of peat. Controls on peat volume change and its spatial variability, however, remain elusive, hampering accurate assessment of climate change impact on functioning of peatlands. We therefore (1) analysed patterning of seasonal surface elevation change at high spatial resolution (0.5 m); (2) assessed its relationship with vegetation, geohydrology, and position within the peatland; and (3) quantified the consequences for peatland surface topography and ecohydrology. Changes in surface elevation were monitored using digital close-range photogrammetry along a transect in a northern peatland from after snowmelt up to midgrowing season (May–July). Surface elevation change was substantial and varied spatially from −0.062 to +0.012 m over the measurement period. Spatial patterns of peat volume change were correlated up to 40.8 m. Spatial variation of peat volume change was mainly controlled by changes in water table, and to a lesser extent to vegetation, with peat volume change magnitude increasing from lawn < hollow < flark. Our observations suggest that patchiness and vertical variability of peatland surface topography are a function of the groundwater table. In dry conditions, the variability of surface elevation increases and more localized groundwater flows may develop. Consequently, spatially variable peat volume change may enhance peatland water retention and thereby sustain carbon uptake during drought.