The document discusses the degradation of palm swamp peatlands in the Peruvian Amazon, highlighting its impact on greenhouse gas emissions. Through a three-year study, it examines the variation of nitrous oxide (N2O) and methane (CH4) fluxes under different degradation conditions, revealing that high degradation markedly increases greenhouse gas emissions, specifically carbon dioxide (CO2). It concludes that forest degradation significantly impacts CO2 and greenhouse gas budgets, complicating monitoring efforts and indicating the potential future influence of climate change on emissions.

1. Kristell Hergoualc’h, J van Lent, R Bhomia, N Dezzeo, J Grandez, M Lopez
LV Verchot
Degradation of palm swamp peatlands in
the Peruvian Amazon severely raises
emissions of greenhouse gases
11th INTECOL, 14th October 2021

2. Peruvian peatlands
 Key contributor tropical peatlands
Gumbricht et al (201
 Amazonian peatlands mainly Mauritia
flexuosa-dominated forests (Draper et al. 2014)
 C-dense ecosystems (850 Mg C ha-1) (Draper et al. 2014)
 Recurrent degradation over 30 years: M. flexuosa
palms cut for fruit collection (Horn et al. 2018)
 73% M. flexuosa-dominated stands degraded in
pilot area (Hergoualc’h et al. 2017)

3. Objectives
 How do peat N2O and CH4 fluxes and
the components of the peat CO2
budget vary spatially at the
microscale and macroscale and
temporally under undegraded and
degraded conditions?
 How do environmental variables
control the spatial and temporal
variation of the fluxes?
 How are the peat CO2 and peat GHG
budgets affected by degradation?
Caballero Rodriguez

4. Experiment
Highly
deg.
Medium
deg.
Intact
 Iquitos, Northern Peruvian
Amazon
 Degradation gradient
I: Intact
mD: medium degradation
hD: high degradation
 3 years (including El Niño/La Niña episodes) monthly monitoring of:
→ Soil fluxes of CH4, N2O, CO2 (total & heterotrophic respiration), and
peat C inputs (litterfall, root mortality)
→Environmental variables (rainfall, temperature, moisture, soil
mineral N content and dynamic)

5. Experiment
 Disaggregation by microtopography (hummock vs. hollow), and palm
status (live vs. cut)
 Degradation impacts on forest structure & soil microtopography
considered for site-scale assessments
0
50
100
150
200
250
Intact mDeg hDeg
M.
flexuosa
(#
ha
-1
)
Cut
Live
Live M. flexuosa Cut M. flexuosa
Hummock
size reduced
by 30%

6. Soil N2O fluxes
 Microscale
b, 2
a
0
2
4
6
8
10 Intact
b, 1
a
b
a
0
2
4
6
8
10 Medium Degradation
Live hummock Live hollow
Cut hummock Cut hollow
b, 2
a a
a
0
2
4
6
8
10 High Degradation
N2O hummock > N2O hollow (except for cut palms at hDeg)
N2O mDeg < N2O Intact, N2O hDeg for hummock live palm
 Macroscale
Site-scale emissions relatively steady over years
N2O mDeg (0.5) < N2O Intact (1.3), N2O hDeg (1.1) (kg N ha-1 y-1)
=> Heterogeneous soil WFPS fluctuations along the forest complex

7. Controls of soil N2O fluxes
 Water-filled pore space (WFPS)
 Water table level (WT)
 WT and Net
nitrification

8. Soil CH4 fluxes
a, 1
b, 2
0
250
500
750
1000
1250
Intact
b, 2
a, 1
b
a
Medium Degradation
Live hummock Live hollow
Cut hummock Cut hollow b, 2
a, 1
b
a
High Degradation
 Microscale
CH4 hummock < CH4 hollow at the Intact, opposite at degraded sites
CH4 Intact < CH4 degraded for hummock, opposite for hollow
 Macroscale
Site-scale emissions increased with
precipitation
No diff. in CH4 annual emissions among
sites (161-226 kg C ha-1 y-1)

9. Controls of soil CH4 fluxes
 Water table level (WT)
 Air temperature
 Soil net nitrification rate

10. Soil heterotrophic respiration
No difference between microtopographies
Sh hDeg > Sh Intact, mDeg
 Macroscale
Sh hDeg (9.0) > Sh Intact (5.9), Sh mDeg (6.2) (Mg C ha-1 y-1)
Sh: St ratio hDeg, mDeg (0.95) > Sh: St Intact (0.60)
2
2
2
0
20
40
High Degradation
1
0
20
40
Intact
1
1 1
0
20
40
Medium Degradation
Live hummock Live hollow
Cut hummock Cut hollow
 Microscale

11. Controls of soil heterotrophic respiration
 Water-filled pore space (WFPS)
Sh = -0.2 x WFPS + 37.8
R² = 0.46
15
20
25
30
35
40
45
50
5 55 105
Sh
(kg
C
ha
-1
d
-1
)
WFPS (%)

12. Soil C inputs (Mg C ha-1 y-1)
 Litterfall
Dominated by tree leave fall (80%)
Litterfall hDeg (2.3) < Litterfall Intact (5.2), LitterfallmDeg (6.0)
 Root mortality
Root hDeg (1.5) ≈ RootmDeg (2.0)
≈ Root Intact (3.4)
0
0.2
0.4
0.6
0.8
-40 10
Mortality
(Mg
C
ha
-1
y
-1
)
WT from previous month (cm)
Y= -0.01 × WT+ 0.12
R²= 0.27
High tolerance of tree species to
high water saturation

13. Peat C budget
Computed in year 2 when all components were monitored
Dissolved organic C: Default value from Southeast Asia
 Peat C budget = (Sh + DOC) – (Litterfall + Root mortality) (IPCC)
 Soil C functioning
-2 ± 1 0 ± 1 6 ± 1
-10.0
-6.0
-2.0
2.0
6.0
10.0
Intact mDeg hDeg
Mg
C
ha
-1
y
-1
Root Mort Litterfall Sh DOC
Intact: Sink of C
mDeg: Neither a sink nor a source of C
hDeg: Large source of C

14. Peat GHG budget
→ CH4 contributes importantly to the peat GHG budget
→ In its natural state, the soil in palm swamp peatlands act as a net
source of GHG
→ High degradation more than doubles the peat GHG budget due to
CO2 emissions
 In CO2 equivalent (GWP of 86
& 268 for CH4 & N2O)
-5
0
5
10
15
20
25
30
Intact mDeg hDeg
Mg
CO2eq.
ha
-1
y
-1
CO2 budget CH4 N2O
18 ± 8 42 ± 4
20 ± 8

15. Concluding remarks
 Impacts forest degradation on GHG emissions in tropical peatlands
→ Complex to monitor: Micro- to macro-scale & specific to degradation
type
→ Not significant on site-scale N2O and CH4 emissions
→ Suppression of the C sink in mDeg, turned the sink into a large
source in hDeg
→ Ecosystem-level losses (Vegetation + soil) remain to be addressed
 Climate change impacts?
Projected greatest precipitation in the study area may foster CH4
emissions which is not considered in current modeling efforts (Wang et
al 2018)

16. Thank you! Questions?