Dynamic of groundwater table, peat subsidence and carbon emission impacted from deforestation in tropical peatland, Riau, Indonesia

Abstract

Drainage canals have triggered peat subsidence and lowered groundwater table, enabling wildfires and peat degradation in Riau, Indonesia. This study examines the changes on groundwater table, peat subsidence rate, and carbon emission in response to deforestation and land cover changes. We established 31 study sites in some land cover types (i.e., oil palm plantation, acacia regrowth and shrub), with 124 monitoring shallow wells and 31 subsidence poles that were setup and have been monitored for 18 months. Groundwater table of all plots averaged -55 cm in Dosan Village, higher than that in Dayun Village (-66 cm). In accordance, peat had subsided in faster rate (8.4 cm year-1) in Dayun Village than that in Dosan (3.3 cm year-1). This average annual groundwater table has resulted in carbon emissions from peat decomposition up to 66 t CO2eq ha-1 year-1. On the other hand, canal discharge of these sites ranged from 2 to 73 dm3 s-1, averaging 26 dm3 s-1. These results evidence that land uses converted from peat forest, and the dimension of canal control the decrease in groundwater table, the pace of peat subsidence, and rate of carbon emissions in tropical peatlands.