Greenhouse Gas Emissions from Tropical Peatlands: Biogeochemical Processes and

Mitigation Strategies

An ESI Seed Grant Project2015-2017

Carbon Cycling inTropical Peatlands

Alison Hoyt, Alex Cobb, Laure Gandois, Xiaolei Liu, Shane O Reilly, Guangchao Zhuang, Roger Summons, David VanInsberghe, Martin Polz, Shuhei Ono, Benjamin Kocar,

Sunitha Pangala, Estelle Chaussard, Charles Harvey

(Hooijer et al, 2010)

Huge C fluxes – large uncertainties!

Range of annual emissions from tropical peat :

637 – 2255 Mt/y CO2

2-7% of 2011 global emissions

Overview:

Background:• What is peat? Why does it accumulate?• Current trends – deforestation & drainage• Local impacts: fire, flooding• Global impacts: GHG emissions

CO2 Fluxes:• Why do drained peatlands release CO2 to the atmosphere?

Methane (CH4) Cycle:• Do tropical peatlands produce more CH4 than we realize?• If so, how is it transported? Where is it oxidized?

(Posa et al, 2011)

Borneo

Peatlands of Southeast Asia

Peat areas shown in black

Deforestation in Borneo

(Hugo Ahlenius, UNEP/GRID-Arendal)

View into the canopy of a tropical peat swamp forest

Cross-section of peat below the surface, cut for road construction

Why do drained peatlands

release CO2 to the atmosphere?

Why does peat accumulate?Saturated soils -> Anaerobic conditions ->

Slow decomposition -> Organic matter accumulation

Carbon accumulates over thousands of years

Draining peatlands releases sequestered carbon as peat decomposes

Natural peat dome hydrologyThe water table is close to the surface everywhereDecomposition is slow, peat accumulates

This lowers the water table -> Creates aerobic conditions -> Faster decomposition -> Peat oxidation ->Result: Subsidence + CO2 emissions

Peatlands are drained by adding canals

Peat subsidence in Johor, Malaysia

(Deltares)

Drainage and peat oxidation lead to subsidence

NASA Image by Jeff Schmaltz,2006

Peat fires burn long-term carbon stocks

Do tropical peatlands produce more CH4 than we realize?If so, how is it transported? Where is it oxidized?

CH4 Fluxes

Methanogenesis

Diffusion

Measured CH4 emissions from tropical peat swamp forests are unexpectedly low

These measurements focus on measuring the surface flux, which only captures diffusion and ebullition

Ebullition

Methanogenesis

Tree Transport

Aerobic Oxidation

Diffusion

Anaerobic Oxidation

Lateral Transport

Do tropical peatlands produce more CH4 than we realize?

Other pathways are playing a much more important role!Much of the CH4 produced is transported laterally, and then oxidized in rivers

Alex CobbSunitha PangalaLaure Gandois

René DommainHa NguyenLucy Hutyra

Khalish IderisAmy Chua

Kai Fuu MingXiaomei Xu

Vincent GauciEd HornibrookCharles Harvey

Xiaolei LiuLiz Corbett

Jeff ChantonEstelle Chaussard

Sandra SeppalainenHajah Jamilah

Joffre bin AhmadKamariah Abu Salim

Mahmud YusoffJoffre bin AhmadJangarun ak Eri

Pudek ak ZulkifleeNur Salihah Haji Su’ut

Acknowledgements