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Assessing net uptake of greenhouse gases (GHG) in natural wetlands

GHG source. GHG sink. Topic C4. Slide 2 of 20. Assessing net uptake of greenhouse gases (GHG) in natural wetlands Assessing net emissions of greenhouse gases in degraded wetland forests and converted wetlands. Objectives. Topic C4. Slide 3 of 20. Greenhouse gases: Which ones?.

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Assessing net uptake of greenhouse gases (GHG) in natural wetlands

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  1. GHG source GHG sink Topic C4. Slide 2 of 20 • Assessing net uptake of greenhouse gases (GHG) in natural wetlands • Assessing net emissions of greenhouse gases in degraded wetland forests and converted wetlands Objectives

  2. Topic C4. Slide 3 of 20 Greenhouse gases: Which ones? • Carbon dioxide (CO2) Simultaneously taken up and emitted through photosynthesis, respiration and decomposition processes

  3. Topic C4. Slide 4 of 20 N fertilizer consumption (million tons N) Atmospheric N2O (ppb) www.ferilizer.org/ifa/statistics Greenhouse gases: Which ones? • Methane (CH4) • Produced and consumed by soil microorganisms • Wetland vegetation (e.g. rice plants) can act as a conduit from the soil to the atmosphere • Nitrous oxide (N2O) • Produced and consumed by soil microorganisms • High emissions can be expected in nitrogen fertilized land uses • Global warming potential • Capacity of each GHG in heating the atmosphere (Forster et al. 2007)

  4. Topic C4. Slide 5 of 20 How to calculate the net exchange of carbon in a terrestrial ecosystem? Change over time in the carbon (C) stock Changeover time in the carbon (C) fluxes Time 1, Stock 1 Time 1, CInto1-COut1 Time 2, Stock 2 Time 2, CInto2-COut2 CInto1 COut1 COut2 CInto2

  5. Topic C4. Slide 6 of 20 Combination of the two methods Stock change Flux change • Ecosystem GHG Meteorological techniques: • C stocks in vegetation: Straightforward And relatively inexpensive Expensive and sophisticated Heterotrophic soil respiration Litter fall • C transfer into and out of peat: Feasible • Peat • Peat C stocks: • High spatial variability, sampling to mineral soil: • Rarely suitable Root mortality Dissolved organic C

  6. Topic C4. Slide 7 of 20 Example 1: C fluxes in a peat forest Heterotrophic soil respiration 6.9 Litterfall7.4 Total outputs 7.5 Total inputs 8.9 Dissolved organic carbon 0.6 Root mortality 1.5 Assumption vegetation in equilibrium: No carbon accumulation Forest C accumulation rate: -1.4 Mg C ha-1 y-1 = -5.3 Mg CO2 ha-1 y-1 Peat C accumulation rate = Inputs – Outputs = -1.4 Mg C ha-1 y-1 Hergoualc’h and Verchot (2014)

  7. Topic C4. Slide 8 of 20 Example 2: C fluxes in an oil palm plantation on peat Heterotrophic soil respiration 12.3 Total outputs 13.2 Litterfall1.5 Total inputs 5 Dissolved organic carbon 0.9 Root mortality 3.6 Time-averaged vegetation C stock accumulation -1 Mg C ha-1 y-1 OP C loss rate: 7.2 Mg C ha-1 y-1 = 26.4 Mg CO2 ha-1 y-1 Hergoualc’h & Verchot (2011, 2014) Peat C loss rate = Inputs – Outputs = 8.2 Mg C ha-1 y-1

  8. Topic C4. Slide 9 of 20 Net exchange of GHGfluxes • Net CO2 fluxes Peat CO2 = (Sh + DOC) – (L + R) Vegetation C stock change Heterotrophic soil respiration (Sh) Litterfall (L) • CH4from the soil and the vegetation • N2O from the soil Root mortality (R) • Additional emissions from vegetation and soil burning (wildfires or land-clearing fires) Dissolved organic C (DOC) • GHG CO2-eq. = (Net CO2 + CH4 + N2O)

  9. Topic C4. Slide 10 of 20 Net GHG exchange: Example • Peat swamp forest Net CO2 = -5.3 Mg CO2 ha-1 y-1 CH4 soil = 2.7 Mg CO2eq. ha-1 y-1 N2O soil = 1.2 Mg CO2eq. ha-1 y-1 Net GHG uptake = -1.3 Mg CO2eq. ha-1 y-1 Hergoualc’h and Verchot (2014)

  10. Topic C4. Slide 11 of 20 The use of proxies for assessing peat GHG emissions • Peat N mineral content: A promising proxy (Hergoualc’h & Verchot, 2014) Careful Peat C loss  Soil respiration Heterotrophic soil respiration = Total soil respi. – root respi. Peat C loss  Heterotrophic soil respiration

  11. Topic C4. Slide 12 of 20 The use of proxies for assessing peat GHG emissions • Groundwater table • Relationship • Peat CO2 emissions (Mg CO2 ha-1 y-1) = • 91  drainage depth (m) • Does not assess peat net CO2 losses but soil respiration • Omits a considerable number of studies • Is not significant in drained ecosystems with drainage depth > 0.3 m Current proxies may provide the order of magnitude of the fluxes but not reliable estimates of them

  12. Topic C4. Slide 13 of 20 Soil GHG measurement using chambers High temporal variability of the fluxes • Minimum sampling intensity Monthly over a year • Diurnal & nocturnal variation of the fluxes to be evaluated • Intensive sampling required when high emissions are suspected to happen Example: Nitrogen fertilization in an oil palm plantation on peat

  13. Topic C4. Slide 14 of 20 Soil GHG measurement using chambers • Example 1: Hummock/hollow stratification in peat swamp forests High spatial variability of the fluxes  Stratified sampling approach when different spatial positions are suspected to consistently produce different emission rates • Example 2: Close to/far from palm in an oil palm plantation on peat  Minimum of 5 replicate chambers per strata

  14. Topic C4. Slide 15 of 20 Soil GHG flux upscale in time and space • Annual budget • Calculated by integration with linear interpolation between measurement dates; especially if intensive sampling is undertaken FZ • Spatial upscaling • Example: • Fertilized oil palm plantation on peat • 2 spatial positions: • Fertilized area (FZ), non-fertilized area (NFZ) • Fluxes at the plot scale: • N2Oplot = 10% N2OFZ + 90% N2ONFZ NFZ 1.5 m

  15. Topic C4. Slide 16 of 20 Gas sampling and GHG concentration analysis • Chamber fanned manually previous to each sampling • Soil CO2 efflux Portable infra-red gas analyzer (IRGA) • Soil N2O, CH4 4 samples/chamber (t0’, t10’, t20’, t30’) Transportation to the laboratory Analysis by gas chromatography Flux calculated from concentration change over time

  16. Topic C4. Slide 17 of 20 Other C fluxes • Partitioning of soil respiration • Incubation of root-free soil cores, respiration-root mass regression, root trenching, isotopic discrimination • Aboveground litter • Litter fall collected in traps, ‘in situ’ litter decomposition experiment • Root dynamics • Mini-rhizotrons, sequential coring, ingrowth nets, ‘in situ’ root decomposition experiment

  17. Topic C4. Slide 18 of 20 Monitoring of environmental factors affecting GHG emissions and C fluxes • Weather (rainfall, air temperature) Hourly or daily (weather station) • Groundwater table, soil temperature, soil moisture, water-filled pore space Concomitant with GHG sampling • Soil nitrogen mineralization and nitrification At least twice a year (wet and dry seasons)

  18. Topic C4. Slide 19 of 20 References • Comeau L-P, Hergoualc'h K, Smith J and Verchot LV. 2013. Conversion of intact peat swamp forest to oil palm plantation: Effects on soil CO2 fluxes in Jambi, Sumatra. Working Paper 110. Bogor, Indonesia: CIFOR. • Drösler M, Verchot LV, Freibauer A, et al. 2014. Chapter 2: Drained inland organic soils. In Hiraishi T, Krug T, Tanabe K, et al. (eds)2013 Supplement to the 2006 IPCC guidelines for national greenhouse gas inventories: Wetlands. Switzerland: IPCC • Forster P, Ramaswamy V, Artaxo P, et al. 2007. Changes in atmospheric constituents and in radiative forcing. In Solomon S, Qin D, Manning M, et al. (eds) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK: Cambridge University Press. • Hergoualc’h K and Verchot LV. 2014. Greenhouse gas emission factors for land use and land-use change in Southeast Asian peatlands. Mitig Adapt Strateg Glob Change 19:789–807. • Hergoualc’h K and Verchot LV. 2011. Stocks and fluxes of carbon associated with land-use change in Southeast Asian tropical peatlands: A review. Global Biochemical Cycles 25. doi:10.1029/2009GB003718 • Ryan MG and Law BE. 2005. Interpreting, measuring, and modeling soil respiration. Biogeochemistry 73:3–27.

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