Presented by Kristell Hergoualc'h at Annual Meeting of the Society of Wetland Scientists 2021: Adaptation drives innovation, on 8 Jun 2021

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?