Preprints
https://doi.org/10.5194/bg-2022-218
https://doi.org/10.5194/bg-2022-218
 
17 Nov 2022
17 Nov 2022
Status: this preprint is currently under review for the journal BG.

A process-based model for quantifying the effects of canal blocking on water table and CO2 emissions in restored tropical peatlands

Iñaki Urzainki1,2, Marjo Palviainen3, Hannu Hökkä4, Sebastian Persch5, Jeffrey Chatellier5, Ophelia Wang5, Prasetya Mahardhitama5, Rizaldy Yudhista5, and Annamari Laurén2,3 Iñaki Urzainki et al.
  • 1Natural Resources Institute Finland (Luke), Latokartanonkaari 9, FI-00790 Helsinki, Finland
  • 2School of Forest Sciences, Faculty of Science and Forestry, University of Eastern Finland, Joensuu Campus, P.O. Box 111, (Yliopistokatu 7), FI-80101 Joensuu, Finland
  • 3University of Helsinki, Department of Forest Ecology, P.O. Box 27, FI-00014 Helsinki, Finland
  • 4Natural Resources Institute Finland, Oulu, Paavo Havaksen tie 3, FI-90570 Oulu, Finland
  • 5Forest Carbon PTE LTD, Singapore

Abstract. Drainage in tropical peatlands increases CO2 emissions, the rate of subsidence, and the risk of forest fires, among other negative environmental impacts. These effects can be mitigated by raising the water table depth (WTD) using canal or ditch blocks. The performance of canal blocks in raising WTD is, however, poorly understood, because the WTD monitoring data is limited and spatially concentrated around canals and canal blocks. This raises the following question: how effective are canal blocks in raising the WTD over large areas? In this work we composed a process-based hydrological model to assess the rewetting performance of 168 canal blocks in a 22000 ha peatland area in Sumatra, Indonesia. We simulated daily WTD over one year using an existing canal block setup and compared it to the situation without blocks. The study was performed across two El-Niño Southern Oscillation (ENSO) scenarios, and four different peat hydraulic properties. Our simulations revealed that while canal blocks had a net positive impact on WTD rise, they lowered WTD in some areas, and the extent of their effect over one year was limited to a distance of about 600 m around the canals. We also show that canal blocks are most effective during dry periods and in peatlands with high hydraulic conductivity. Averaging over all modelled scenarios, blocks raised the annual mean WTD by only 0.9 cm. This value was 2.78 times larger in the dry year than in the wet year (1.39cm versus 0.50 cm), and there was a 2.76 fold difference between the scenarios with the maximum and minimum hydraulic conductivity (1.50 cm versus 0.54 cm). Using a linear relationship between WTD and CO2 emissions, we estimated that, averaging over peat hydraulic properties, canal blocks prevented the emission of 1.03 Mg ha-1 CO2 in the dry year and 0.37 Mg ha-1 CO2 in the wet year.

Iñaki Urzainki et al.

Status: open (until 29 Dec 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-218', Santosa Sandy Putra, 07 Dec 2022 reply
  • CC1: 'Publisher's comment on preprint exchange', Copernicus Publications, 08 Dec 2022 reply

Iñaki Urzainki et al.

Video supplement

WTD difference in dry and wet years for all parameters Iñaki Urzainki https://zenodo.org/record/7299526

Iñaki Urzainki et al.

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Short summary
Drained peatlands (peat areas where ditches have been excavated to enhance crop productivity) are one of the main sources of carbon dioxide emissions globally. Blocking the ditches by building dams is a common strategy to raise the water table and to mitigate carbon dioxide emissions. But how effective is ditch-blocking in raising the overall water table? Our work tackles this question by making use of the available data and physics-based hydrological modeling.
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