Impacts of peatlands rewetting on greenhouse gas emissions in Riau Province

impact peatlands

Picture:

1. Riau Province is home of around 3 Mha of peatlands and mostly converted

2. The blocking of drainage canal to raise groundwater level continuously monitored using Divers (inzet)

3. Sampling sites representing three different land-uses: reforested peatland, oil pal, and rubber pladtations

4. GHG sampling using closed chamber method for gas chromatography analysis

Background and Program Description

Land-use, land-use change and forestry activities is the largest contributor of national greenhouse gas (GHG) emissions. Among the activities are generally conducted in high carbon reservoirs, peatland ecosystems.

In order to take urgent action to combat climate change and its impacts, the Department of Geophysics and Meteorology, IPB University was approached by the Government of Indonesia to generate new knowledge on climate change mitigation actions. We consider understanding the impacts of peatland restoration through rewetting as strategic mitigation option by quantifying high tier country-specific emission factors. In various land-uses.

In collaboration with Peat Restoration Agency, an ad hoc government agency tasked to restore 2 million hectares of degraded peatlands in 5 years (2016-2020), we quantified emission factors of three main GHGs, CO2, CH4, and N2O in reforested peatlands, oil palm, and rubber plantations. Other parameters, such as peat depth and groundwater level (GWL) were also monitored.

Implementation

Field measurement campaigns were carried from January 2018 through December 2019 in 3-4 months intervals for GHG fluxes, while GWL was   logged throughout the period. These involved three students as part of their PhD and Master projects.

Direct measurements of CO2 emissions were carried out using portable infrared gas analyzer, while for CH4 and N2O fluxes the gases were sampled using closed chamber technique and analyzed using gas chromatography from the samples collected. Ranges of emission factors will be generated from these measurements

Soil temperature and GWL was continuously monitored using diver to show the impacts of rewetting on GHG emissions, the drainage canal was blocked in December 2018 to raise the water table.

Riau is one of the provinces in Indonesia undergoing extensive land use change. The choice of land-use plots for the campaign was based on the common practices when tropical peat swamp forests are deforested and converted. This way we can simulate the future trend at larger scale.

Results and Impacts

The response of GHG fluxes to rewetting differ between land-use types. It was probably caused by a combination of canopy cover (soil temperature) and root system. More specifically:

  • The average total CO2 emissions before canal blocking in reforested areas, oil palm and rubber plantations were 10.93, 16.66, and 23.70 Mg CO2 ha-1yr-1. After the canals were blocked, the average total CO2 emissions were 3.57, 10.47, and 15.27 Mg CO2 ha-1yr-1 in the respective land-uses.  
  • Methane (CH4) flux before blocking were -0.10, 0.34, and 0.50 mg m-2 hr-1 in reforested area, oil palm and rubber plantation respectively, while the fluxes after blocking were 8.02, 5.36, and 0.64 mg m-2 hr-1. 
  • On the other hand, N2O decreased from 0.40, 0.40, and 0.40 mg m-2 hr-1 in forested area, oil palm and rubber plantations to -0.20, -0.45, and 2.15 mg m-2 hr-1 respectively.

Decreasing trends in GHG emissions of due to rewetting, especially for CO2 (up to 67%) suggest that from climate change mitigation perspectives, the action need to be scaled up.

Challenges and Lessons Learned

It is realized that the sample size over two years period is rather limited despite large spatial and temporal variability of GHG fluxes. However, providing ranges of emissions (upper and lower limits) would suffice to further generate less uncertain emission factors. 

 The emission factors, which is crucial for national GHG inventory may be adopted provided the uncertainty analysis is carried out. The factors may be extrapolated to express spatially explicit emissions from at landscape level. 

Replicability

The techniques of gas sampling and analysis are pretty standard and widely applied. Separating heterotrophic and autotrophic respiration from total CO2 emission should be implemented elsewhere. This is particularly important as peat characteristics differ from site to site depending on the organic material inputs and biogeochemical processes taking place.

 In short, one should attempt to have more samples with stratified sampling procedures to capture such variability. To this end, measurement campaign would be cost effective.

Tahun Kegiatan: 2019
Lokasi Kegiatan: Riau Province

Penanggung Jawab Kegiatan: Prof Daniel Murdiyarso