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Net ecosystem CO2 exchanges between a dwarf A.marina mangrove
and the atmosphere-
Application of the eddy-covariance flux tower to « Le C♥ur de Voh »
mangrove (New Caledonia)
Leopold, A., Marchand, C., Renchon, A., Deborde, J., Quiniou, T., Allenbach, M.2016. Agricultural Forest Meteorology 223, 217‐232
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Mangroves: Net sink or source for CO2?Daytime Nighttime
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Vertical flux (F)As a result of covariance between gaz
concentration (CO2, ρC) and vertical wind component (w)
F(CO2) = w.ρC
Eddy-covariance,A powerful tool,
to measure atmosphere-ecosystem exchanges
From Burba, 2005
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USA,Florida
ChinaIndia
Mangroves and Eddy-Covariance…A rare love story…
Northern hemisphereHumid tropical and sub‐tropical climates
Modified from Giri et al. 2011
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The story of the New Caledonian flux tower
Sourthern hemisphereSub‐tropical but semi‐arid climate
Measurements: Net Ecosystem CO2 Exchange (NEE)
Determination: Net Ecosystem Productivity (NEP), ‐NEEEcosystem Respiration (Reco)Gross Ecosystem Productivity (GEP)
© A.LEOPOLDModified from Giri et al. 2011
GEP = −NEE + Reco
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BACKGROUNDBACKGROUND
35 000 ha
88%
New Caledonian Mangroves
Total Area
East Coast
West Coast
Modified from Virly, 2006
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A famous mangrove grows on the New Caledonia’s West Coast« Le Cœur de Voh »
©1990, Y. Arthus‐Bertrand ©2012, CNES/ASTRIUM
Avicennia marina var. australasica- Dwarf- Hmax < 2m- Hmean= 57.2±30.3cm- 3.3±0.2 trees m-2
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‐IRGA‐ closed path, LI‐7200 ‐Sonic anemometer‐Windmaster
‐Data logger CR1000 + meteorological sensors‐ air temperature and humidity‐ PAR / solar radiation‐ soil heat flux plates‐ sediment temperature‐ rain gauge
‐Tide gauges custom built
H= 3.10m
© A.LEOPOLD
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‐500
0
500
1000
1500
2000
2500
‐12
‐10
‐8
‐6
‐4
‐2
0
2
4
6
8NEE (µ
mol m
‐2s‐1)
PAR (µmol photons m
‐2s ‐1)Photosynthesis (day) vs. Respiration (day & night)
Data from Leopold et al. 2016
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Mangroves,
As a unique forested ecosystem…
Seasonal variations of NEE
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Seasonal variations of NEE
‐6.0
‐5.0
‐4.0
‐3.0
‐2.0
‐1.0
0.0Mar‐14
Apr‐14
May‐14
Jun‐14
Jul‐1
4
Aug‐14
Sep‐14
Oct‐14
Nov
‐14
Dec‐14
Jan‐15
Feb‐15
Mar‐15
0.00.51.01.52.02.53.03.54.04.5
1 2 3 4 5 6 7 8 9 10 11 12 13
µmolCO
2m
‐2s‐1
Daytime NEE
µmolCO
2m
‐2s‐1
Nighttime NEE
90% values :‐5 to +2 µmol m‐2 s‐1
Min: ‐10.7 µmol m‐2 s‐1
90% values :0.38 to +3 µmol m‐2 s‐1
Max: 8.80 µmol m‐2 s‐1
Florida mangrove*Min: ‐10 to ‐25 µmol m‐2 s‐1
Florida mangrove*Max: up to 10 µmol m‐2 s‐1
*Data from Barr et al. 2010
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Seasonal variations of NEE
‐10
‐8
‐6
‐4
‐2
0
2
4
6
NEE
(µmol m
‐2 s
‐1)
End of dry and cold season (October)
End of wet and warm season (April)
Wet and warm season (February)
Seasonal variation of both daytime and nighttime NEE minima and maxima
Modified from Leopold et al. 2016
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Seasonal variations of NEE,subsequent to seasonal variation of driving factors
VPDopt = 2.25 kPa Topt = 26.8 °C
Minimal NEE, i.e. maximal CO2 fixation rate at the ecosystem scale
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Mangroves,
As a unique forested ecosystem…
The impact of tidal cycle on NEE
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Mangroves, As a unique forested ecosystem…
The impact of tidal cycleDecrease of NEE during flooding waters
(a) As a consequence of lower CO2 released by respiration
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‐12
‐10
‐8
‐6
‐4
‐2
0
2
4
6
8NEE (µ
mol m
‐2s‐1)
Decrease of NEE during flooding waters
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0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30 35 40
Nighttim
e NEE
(µmol m
‐2s‐1)
Low Tide
High Tide
Tair (°C)
(a) As a consequence of lower CO2 released by respiration
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Mangroves, As a unique forested ecosystem…
The impact of tidal cycleDecrease of NEE during flooding waters
(a) As a consequence of lower CO2 released by respiration
(b) As a consequence of higher CO2 absorbed byphotosynthesis because of water availability
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Decrease of NEE during flooding waters(b) As a consequence of higher CO2 absorbed byphotosynthesis because of water availability
Any flooding waters
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Decrease of NEE during flooding waters(b) As a consequence of higher CO2 absorbed byphotosynthesis because of water availability
At saturing PAR, NEE minimum decreases with flooding waters.
Trees seem stressed by missing water
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Mangroves,
As a unique forested ecosystem…
The impact of a semi‐arid climateon NEP
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The impact of semi arid climate on mangrove productivity
NC West Coast:Annual rainfall < 1,000 mm, with a high seasonality
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NEP of a dwarf A.marina mangrove growing under semi arid climate
‐20
‐15
‐10
‐5
0
5
10
15
20
Mar.14‐Mar.15
Relative low annual NEP= 72.9 gC m‐2Mon
thly NEP
(gC m
‐2)
Minima during the dry season:‐ Low water inputs & high porewater salinity‐ Reduced stomatal conductance & leaf photosynthesis?
Sink
Source
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Low water inputs = High porewater salinity
Decrease of gas exchanges by stomatal closure?See Carine Bourgeois ‘s poster (N° 78)(PhD candidate, AUT Auckland, IRD New CaledoniaSupervisors: Dr. A. Alfaro and Dr. C. Marchand)
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NEP of a dwarf A.marina mangrove growing under semi arid climate
‐20
‐15
‐10
‐5
0
5
10
15
20
Mar.14‐Mar.15
Relative low annual NEP= 72.9 gC m‐2Mon
thly NEP
(gC m
‐2)
Minima during the rainy season‐ high freshwater inputs‐ high photosynthesis ‐ high respiration: resumption growth?
Sink
Source
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NEP decreases with rainfall,When seawater is not a limiting factor
‐20
‐15
‐10
‐5
0
5
10
0 50 100 150 200 250 300
Mon
trhly NEP
(Tno
rm.)
(gCO
2m
‐2)
Monthly cumulative rainfall (mm)
Do frehswater inputs promote the growth resumption and subsequent respiratory metabolism??
(see Robert et al., 2014 and Santini et al., 2015)
< 80% of time> 80% of time
Air‐exposed sediments
R²a = 0.995p<0.001
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Perspectives
(a) Inter‐annual variation of NEP?
(b) May the NEP be lower?Carbon exports: DOC, DIC, POC?
(e.g., 25% to 70% of NEP (Barr et al. 2010))
(c) NEE Partitioning: what is the contribution of carboncycling components on the NEE measured?
‐ Soil‐ Vegetation (root, leaves, pneumatophores, trunks)‐ Water column
Mar.14‐Mar.15
Relative low annual NEP= 72.9 gC m‐2
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Vietnam
NCNZ
Latitudinal, climatic and biodiversity gradients: ‐ New Zealand (36°S), temperate climate, 1 mangrove species‐ New Caledonia (21°S), semi‐aride climate, 25 mangrove species‐ Vietnam (10°N), tropicale climate, 60 mangrove species
Eddy‐covariance network in the Indo‐Pacific area
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© KARI, ESA image
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In situ installation of flux tower:
- Wind rose and available distances
- Daytime: Trade winds (« Alizees »): SE- Nighttime: Land breeze: NE
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Data acquisition and processingSampling rate 10Hz
Quality control:‐ Qc =2 according to Goulden et al. 1996‐ U* threshold‐ Footprint
Relationships with environmental data (30‐min interval)(solar radiation, PAR, Air temperature, VPD)
« Gap‐filling »(Online tool from Max Planck Institut)
30‐min mean CO2 fluxes (Eddy‐pro software©) : NEE
Daytime / nighttime datasetsLow tide/ high tide datasets
Partitionning: GEP and RecoAnnual Budgeting: NEP
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Low water inputs = high porewater salinity
05
101520253035404550
40 60 80 100
Dep
th (cm)
Porewater salinity
Range from 40 to 100i.e., 1.4 à 2.8 fold the seawater salinity
Wet and warm seasonDry and cold season
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High salnity of porewater along the year=
Dwarf trees
0
20
40
60
80
100
120
140
160
180
200
0 20 40 60 80 100
N = 899Léopold, unpublished data
Heigh
t (cm
)
Basal perimeter (cm)‐
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Rainfall seasonality controls mangrove immersion rate by seawater at high intertidal locations
The impact of semi arid climate on mangrove productivity
Rainy season:‐ high rainfall & immersion rates
Dry season:‐ low rainfall & immersion rates
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Dry season:‐ Low rainfall and immersion rate‐ Very high porewater salinity (>100)
=Low photosynthesis
Mon
trhlyGEP
(gCO
2m
‐2 m‐1)
0
20
40
60
80
100
120
March14
March15
Wet and warm seasonDry and cold season
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Rainfall seems to have benefit effects on mangrove photosynthesis…
But also on ecosystem respiration…
0
20
40
60
80
100
120
0
50
100
150
200
250
300
Mon
thly Rainfall (mm)
Mon
thly Reco (gC m
‐2)
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Global climate changes…As a consequence of anthropogenic GHG increase.
Years before 2005
CO2(ppm
)375 ppm
250
300
10000 5000 0
280 ppm
modified from IPCC, 2005
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0
200
400
600
800
1000
1200
0 500 1000 1500 2000
Rainfall rate,as a driver of subtropical mangrove NEP
Annual cumulative rainfall (mm)
Annu
al NEP
(gCO
2m
‐2.an‐
1 )
Voh, NC
Chine
Everglades, USA