Articles | Volume 9, issue 3
Biogeosciences, 9, 1053–1071, 2012

Special issue: Understanding the impacts of hydrological changes on terrestrial...

Biogeosciences, 9, 1053–1071, 2012

Research article 20 Mar 2012

Research article | 20 Mar 2012

Subsidence and carbon loss in drained tropical peatlands

A. Hooijer1, S. Page2, J. Jauhiainen3, W. A. Lee4, X. X. Lu5, A. Idris6, and G. Anshari7 A. Hooijer et al.
  • 1Deltares, P.O. Box 177, Delft 2600 MH, The Netherlands
  • 2Department of Geography, University of Leicester, UK
  • 3Department of Forest Sciences, University of Helsinki, Finland
  • 4Singapore Delft Water Alliance, National University of Singapore, Singapore
  • 5Department of Geography, National University of Singapore, Singapore
  • 6University of Jambi, Jambi, Indonesia
  • 7Center for Wetlands People and Biodiversity, Tanjungpura University, Pontianak, Indonesia

Abstract. Conversion of tropical peatlands to agriculture leads to a release of carbon from previously stable, long-term storage, resulting in land subsidence that can be a surrogate measure of CO2 emissions to the atmosphere. We present an analysis of recent large-scale subsidence monitoring studies in Acacia and oil palm plantations on peatland in SE Asia, and compare the findings with previous studies. Subsidence in the first 5 yr after drainage was found to be 142 cm, of which 75 cm occurred in the first year. After 5 yr, the subsidence rate in both plantation types, at average water table depths of 0.7 m, remained constant at around 5 cm yr−1. The results confirm that primary consolidation contributed substantially to total subsidence only in the first year after drainage, that secondary consolidation was negligible, and that the amount of compaction was also much reduced within 5 yr. Over 5 yr after drainage, 75 % of cumulative subsidence was caused by peat oxidation, and after 18 yr this was 92 %. The average rate of carbon loss over the first 5 yr was 178 t CO2eq ha−1 yr−1, which reduced to 73 t CO2eq ha−1 yr−1 over subsequent years, potentially resulting in an average loss of 100 t CO2eq ha−1 yr−1 over 25 yr. Part of the observed range in subsidence and carbon loss values is explained by differences in water table depth, but vegetation cover and other factors such as addition of fertilizers also influence peat oxidation. A relationship with groundwater table depth shows that subsidence and carbon loss are still considerable even at the highest water levels theoretically possible in plantations. This implies that improved plantation water management will reduce these impacts by 20 % at most, relative to current conditions, and that high rates of carbon loss and land subsidence are inevitable consequences of conversion of forested tropical peatlands to other land uses.

Final-revised paper