Exploration of the importance of physical properties of Indonesian peatlands to assess critical groundwater table depths, associated drought and fire hazard

M Taufik,A.A Veldhuizen,J.H.M Wösten,H.A.J Van Lanen

doi:10.1016/j.geoderma.2019.04.001

M Taufik, A.A Veldhuizen + Show 2 more

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https://doi.org/10.1016/j.geoderma.2019.04.001

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Abstract

Widespread degradation of Indonesian peatlands by deforestation and excessive drainage results into more frequent fires, particularly in El Niño years, which causes: (i) release of enormous amounts of peat soil carbon to the atmosphere, impacting climate, (ii) severe air pollution, affecting human health and air traffic, and (iii) decreased ecosystem services through loss of biodiversity. Groundwater table decline is the main driver of these negative processes and, therefore restoration of peatland hydrology is essential. Although groundwater table depth is critical to counteract peatland degradation, optimal depths are not generic for all peatlands, but depend on peat physical properties (i.e. water retention, unsaturated conductivity), which are related to the degree of peat humification (Fibric, Hemic, Sapric). Unfortunately only few of these peat physical properties are available while they are essential input data in hydrological models required to extend the usually short observed groundwater hydrographs. An experiment with the Soil-Water-Atmosphere-Plant model (SWAP) for two locations in Indonesian peatlands illustrates the impact of the degree of peat humification on physical properties and thereby on calculated groundwater table depth, hydrological drought and associated fires hazards. The Variable Threshold Method is applied to convert groundwater table depths into hydrological drought, and next the modified Keetch-Byram Drought Index (mKBDI) is used to assess wildfire hazard. Peat physical properties that reflect higher peat humification (Hemic and Sapric) result into lower water tables during dry periods, in particular during El Niño years, more severe hydrological drought, and an earlier and longer fire season. Using the limited available peat physical properties the importance is demonstrated of initiating a comprehensive programme to build a database of peat physical properties covering different environmental conditions in which tropical peatlands occur. Availability of such a database connected to a long-term monitoring programme, will support the ongoing rewetting, revegetation and revitalisation programme for Indonesian peatlands, which eventually will contribute to sustainable livelihoods for local people and reduce impact on the regional climate.

Highlights

Indonesia has about 20–21 Mha of peatland (Wahyunto et al, 2003, 2004, 2006; Page and Rieley, 2016) of which some 13 Mha is located in Sumatra and Kalimantan
The objective of this study is to explore for Indonesian peatlands the importance of scarcely available peat physical properties for three calculated, highly relevant land and water management aspects namely groundwater table depth, hydrological drought and associated wildfire hazard
Time series of daily groundwater table depths over the period 1980–2015 are simulated for a location in Kalimantan and in Sumatra (Fig. 4)

Summary

Introduction

Indonesia has about 20–21 Mha of peatland (Wahyunto et al, 2003, 2004, 2006; Page and Rieley, 2016) of which some 13 Mha is located in Sumatra and Kalimantan. Indonesian peatlands are relatively young, about 5000–10,000 years before present (Neuzil, 1997; Dommain et al, 2011), some inland peatlands, such as at Danau Sentarum NP in West Kalimantan are over 30,000 years old (Anshari et al, 2001). These areas were covered with peat swamp forest, logging, drainage, conversion to industrial plantations, and recurrent fires changed its land use drastically (Dohong et al, 2017). Of the remaining peatland in Geoderma 347 (2019) 160–169

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