1. Seasonal wetlands are characteristic of
large tropical deltas. Our findings provide a
means to assess the effects of changing
moisture regimes, which are being altered by
upstream dam installation and local land use
change, on greenhouse gas emissions in
these dynamic environments.
Abstract
Objectives
• Soil, gas, and water samples were collected
from a seasonal wetland in the Mekong
River Delta to analyze N2O, CO2, and CH4
gas fluxes, porewater chemistry, and soil
moisture content.
• Samples were analyzed for:
1. Non-purgeable Organic Carbon
2. CO2, CH4, N2O (via GC)
3. C, N (via elemental analyzer)
• Soil cores were collected to observe gas
fluctuations under controlled flood
simulations.
Methods
Results: Lab Manipulations
Conclusions
• Soil moisture is a prime controller of gas
efflux.
• Upon soil draining, CH4 and CO2 efflux
increase.
• CH4 has a short-lived pulse
upon draining
• CO2 increases for an extended
duration
• Greenhouse gas emissions from
soils/sediments in the Mekong Delta are
controlled by soil moisture.
Acknowledgments
Thanks to Doug Turner, and Guangchao Li
for their analytical help. This research was
funded by SURGE (Summer Undergraduate
Research in Geoscience and Engineering)
Program of Stanford’s Earth School.
• To understand the effects of soil flooding
on greenhouse gases.
• To project changes in gas fluctuations
across the Mekong Delta and other tropical
sedimentary basins.
[1] University of California, Riverside [2] Stanford University [3] Boise State University
Amy K. Salvador[1,2] Michael V. Schaefer[2] Katherine A. Roberts[2] Marco Keiluweit[2]
Samantha C. Ying[1] Shawn Benner[3] Scott Fendorf[2]
Greenhouse Gas Emissions Following Seasonal Flooding of Tropical River
Deltas
Left. Licor CO2 flux chamber. Right. Controlled
flooding at test site.
Further Studies
• Linking hydrologically-dependent carbon
fate to groundwater arsenic
concentrations.
• Projecting soil greenhouse gas fluxes in
tropical river deltas
Non-purgeable Organic Carbon
0
20
40
60
80
100
120
140
160
20
25
30
35
40
45
50
55
60
65
NPOC(mg/L)
SoilMoisture(%)
7 cm Wet Fence
0
10
20
30
40
50
60
20
25
30
35
40
45
50
55
NPOC(mg/L)
SoilMoisture(%)
21 cm Wet Fence
NPOC
concentrations
are higher and
more variable in
porewater near
the soil surface.
High amounts of
dissolved
organic carbon
(DOC) result with
increased soil
moisture.
Hypothesis
Carbon dioxide and N2O undergo pulsed
efflux upon initial wetland drainage.
Methane efflux is at maximum during lowest
ponded water levels.
Soil cores were subject to flooding and
draining to simulate field variation.
SoilMoisture[%]SoilMoisture[%]
NPOC[mg/L]NPOC[mg/L]
Date (5/10-5/24/2015)
Variability in CO2 efflux with soil core moisture
content.
-Endemic microbial populations maintain
similar conditions to soil ecosystems.
-Induced floodwaters simulated soil
moisture conditions.
-CO2 efflux measured with Licor gas
analyzer.
Field Results
1.2
1.0
0.8
0.6
0.4
0.2
0.0
CH4-CFlux[µmolm
-2
s
-1
]
0.55
0.50
0.45
0.40
0.35
0.30
0.25
Soil Moisture [g g
-1
]
6
5
4
3
2
1
0
CO2-CFlux[µmolm
-2
s
-1
]
0.55
0.50
0.45
0.40
0.35
0.30
0.25
Soil Moisture [g g
-1
]
CO2 efflux
resulting from
field
manipulated
flooding-
draining.
CO2 and CH4
efflux with soil
drying (time
period of red-
box above),
illustrating initial
CH4 pulse and
steady CO2
increase.
Variability of CO2
and CH4 fluxes in
response to
changes in soil
core moisture.
http://ttspmediastudents.pbworks.com/
CO2 and CH4
efflux pulses
upon soil drying