The impact of peatland restoration practice on hydrological functions in tropical environments

Tropical peatlands are understudied systems serving as global carbon stores with high biodiversity. Many tropical peatlands have been drained for agriculture leading to their degradation. Restoration of these peatlands often involves blocking drainage ditches, yet little is known about the effectiveness of those initiatives in the recovery of peatland hydrological functions. This study aims to assess the spatial and temporal water-table dynamics in forested, drained, and ditch-dammed tropical peatlands in Sebangau, Kalimantan, Indonesia, investigating variables that contribute to hydrodynamic variability, and modelling possible solutions to improve water-table restoration strategies. Dry-season water tables at all sites were deeper than 40 cm from the surface and ditches had no standing water. In the wet season, the percentage of time during which water tables at wells were deeper than 40 cm from surface was between 16% and 87% at the forested site, from 0% to 38% at the drained site, but 0% at the blocked site. When compared to the forested system, water-table responses to storms were very different at the blocked site, suggesting that it did not function as a natural system. Nevertheless, ditch dams accelerated the water-table rise during the transition from the dry to wet seasons and minimised the hydraulic gradients in the peatland during the wet season. Hydrodynamic modelling of a typical drained peat plot in the study area showed that in the El Niño year, bunds reduce the number of days with water table deeper than 40 cm from the surface by 50% to 73%. A combination of ditch dams and shallow surface reservoirs formed via bunding in restoration plots might help store extra water, reducing the impacts of losses due to evapotranspiration and seepage during the dry season.