Macrophyte Dynamics at the Amazon Floodplain

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Are the humid tropics a source or sink for
atmospheric carbon?    Global estimates of
atmospheric CO2 exchange indicate the tropics are
near equilibrium or are a source.   Ground-based
measurements indicate that the carbon uptake by
mature, upland rainforests is similar to or
greater than the carbon being released by
tropical deforestation.
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Tropical forests, deforestation and regrowth

• Ecology of tropical forests
• Human endeavors in tropical forests
• Deforestation in the Amazon
• Forest conditions in temperate regions
• Global overview of changes in NPP and forest cover

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Tropical forest canopy
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Tropical forest understory
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Accessing forest canopy
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In the canopy
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Slash and burn agriculture in Amazon
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Slash and burn agriculture in Amazon
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Agroforestry
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Selective logging
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Mining
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Annual fluxes of carbon from deforestation and
regrowth in the Brazilian Amazon From 1989 to
1998 source to atmosphere of 0.2 Pg C per
year Logging may add another 5 to 10 Fires
following droughts may double rate Changes in
soil carbon not included Annual source from
land-use change and fire approximately offsets
sink calculated for natural forests in
region Interannual variability plus or minus
0.2 Pg C per year
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Bookkeeping model used Changes in carbon
include (1) Immediate loss to atmosphere from
plant material burned at time of
clearing Requires estimates of deforestation,
biomass (greatest uncertainty) and proportion
burned (2) Slower release from decay of plant
material Wood products and dead wood at site
0.1 per y Elemental C 0.001 per y (3)
Accumulation during forest regrowth
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Impoverishment of Amazonian forests by logging
and fire Logging severely damages 10,000 to
15,000 km2 per y Surface fires burn additional
large areas Hence, current estimates of
deforestation may include less than half of
forest area impoverished each year
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Carbon Sink Estimates for USA Carbon
accumulation in north temperate forests
attributed to historical changes in land use
(dominant factor) and to enhanced tree growth by
carbon dioxide fertilization, N deposition and
climate change (minor). For period from 1980 to
1989 carbon sink for coterminous USA of between
0.30 and 0.58 Pg C per y (net carbon flux after
subtracting export by rivers and commerce)
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Other Carbon Balances European forests in
Austria, Finland, Germany, Sweden and Switzerland
are increasing. In severely polluted areas, such
as parts of northwestern Russia, forest are
impoverished. Chinese forests Source from 1949
to 1980, but in recent years afforestation
efforts have sequestered carbon. Boreal and
Arctic tundra seem to be net sources to the
atmosphere as a result of increased soil
decomposition, but warming may also increase
growing season for plants.
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 What are fluxes of carbon associated with rivers
and wetlands?
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Floodplains are pulsing systems   with a large
aquatic-terrestrial transition zone
(Junk 1997)
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Key aspects of floodplain systems   Amplitude
, frequency, predictability and sources of
flooding   Vegetative cover and extent of open
water
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Flooded forest, woodland and shrubs
Upper and lower left high water Lower right low
water
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Aquatic macrophytes
Upper and lower left high water Lower center and
right low water
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Amazon basin Mainstem floodplain Central quadrat
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Lake Calado
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Inputs and outputs of organic carbon
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Lake Calado Carbon Inputs C() Runoff,
seepage rainfall 4 Amazon River
4 Flooded forest litterfall 8 NPP by
macrophytes 64 NPP by algae 20
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Lake Calado Carbon Losses C() Outflow
18 Burial 5 Methane
evasion 2 Carbon dioxide evasion 75
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Lake Calado Water balance () Runoff,
net seepage rainfall 72 Amazon River
inflow 22 Lateral inputs 6 Outflow
to Amazon River 93 Evaporation 7
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Evasion of CO2 from rivers and floodplains in
central Amazon basin   Remotely-sensed and
geomorphically-derived estimates of
inundation   Measurements of dissolved
CO2   Calculation of CO2 evasion to the atmosphere
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Rivers and Floodplains
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Streams and riparian (lt 100 m in width)
Ji-Parana
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Inundation in Amazon Rivers
2
5
2
0
1
5
Flooded Area (x 104 km2)
1
0
5
0
J
F
M
A
M
J
J
A
S
O
N
D
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River channels and floodplains of tributaries (gt
100 m wide) 79,000 to 290,000 km2   Streams
and small rivers (lt 100 m wide) 21,000 to
51,000 km2   Amazon river and floodplain waters
are highly supersaturated in dissolved CO2
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Dissolved CO2 in Amazon Rivers
Manacapurú
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4
pCO2 (x 103 ?atm)
0
J
F
M
A
M
J
J
A
S
O
N
D
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CO2?habitat K (Csurface Catm equil)
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What are fluxes of carbon dioxide associated with
rivers and wetlands in the Amazon?   Basin-wide,
evasion of CO2 from rivers and wetlands to the
atmosphere is about 0.5 Gt C y-1.   Amazon River
export to the ocean is 0.036 Gt C y-1 of organic
carbon and 0.035 Gt C y-1 of dissolved inorganic
carbon.
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Evasion of methane from Amazon wetlands   Remotely
-sensed estimates of seasonally of inundation and
wetland vegetation Measurements of methane
emission from wetland habitats (open water,
flooded forests and floating macrophytes)
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Remote sensing of temporal variation in extent of
inundation and aquatic vegetation
Monthly inundated areas Mixture model of 37 GHz
polarization difference observed by Scanning
Multichannel Microwave Radiometer (1979-1987)
Inundation and aquatic vegetation at high (1996)
and low (1995) river levels Segmentation and
classification of L-band synthetic aperture radar
data obtained by Japanese Earth Resources
Satellite
Validation of inundation and aquatic vegetation
Examination of airborne digital videography
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Time series (monthly) of inundation derived from
passive microwave emissions obtained as 37 GHz
polarization difference observed by Scanning
Multichannel Microwave Radiometer
Within Amazon Basin Central Amazon
Llanos de Moxos Roraima Bananal
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Synthetic aperture radar (SAR)
SARs are active microwave sensors. Because they
provide their own illumination, they operate
independently of solar illumination.
SARs have nearly all-weather imaging capability.
With SAR remote sensing, we can gain information
not only from the amplitude of the returned
pulse, but also from the polarization and phase.
Slide courtesy of L. Dutra
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SAR double-bounce scattering from flooded forest
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Cabaliana Floodplain (from JERS)
High Water
Low Water
0 30 km
Water Bare/herbaceous, non-flooded Herbaceous,
flooded Shrub, non-flooded
Shrub, flooded Woodland, flooded Forest,
non-flooded Forest, flooded
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Digital videography for validation
Hess et al. 2002. Int. J. Remote Sens. 23
1527-1556
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Methane emission measurements
Selected habitat-specific measurements (aquatic
macrophytes, flooded forest and open water) from
Devol et al. (1990, JGR 95 16417-16426)
composited from 8 lake seasonal survey and
regional sampling using different emission rates
from aquatic macrophytes for high and low water
levels. River channel emission from Richey et
al. (1988, LO 33 551-561)
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Amazon basin Mainstem floodplain Central quadrat
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Solimoes Amazon River Floodplain
Methane Emission, Tg C y-1 Aquatic
macrophytes 0.63 0.1   Flooded forest 0.61
0.2   Open water 0.087 0.02   River
channel 0.008 0.001   Total 1.3 0.3
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Uncertainty Analysis
Uncertainties in the regional emission rates were
determined by Monte Carlo error analyses that
combined error estimates for the measurements of
emission and for calculations of inundation and
habitat areas.
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Methane emission from Solimoes-Amazon floodplain
Mean Area uncertainty
Minimum, mean and maximum inundation (Sippel et
al. 1998) with one standard error in methane
emission from Devol et al. (1990)
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Central Amazon Basin (1.77 million km2)
Methane Emission CO2 Evasion Tg C y-1
Tg C y-1 6.8 1.3
210 60
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Amazon Basin below 500m wetlands 17, uplands
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Upper Negro savannas
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Upper Negro (RNL)
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Tropical South American Savannas
Mean Flooded Methane Emission
Area, km2 Tg C y-1 Mojos 29,500
2.1   Roraima 3,500
0.3   Bananal 13,100
0.9   Orinoco 34,700
2.5   Pantanal 34,900 2.5
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Balbina - decaying trees
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Uatuma River below Balbina
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Lowland Amazon Basin (lt500 m asl) (5.19 million
km2)
Methane Emission 22 Tg C y-1   Greenhouse
gas potential 0.2 Pg C y-1 as CO2
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Lowland Amazon Basin (lt500 m asl) (5.19 million
km2)
Methane uptake in soils 1.1 0.2 Tg C
y-1 Net emission from pastures 0.1 Tg C y-1
plus cattle, termites and burning Upland forest
canopy release 4 - 38 Tg C y-1
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Carbon budget for Amazon basin, summed over
terrestrial and aquatic environments, appears
closer to being in balance than inferred from
upland data alone.