TOWARDS A BETTER QUANTIFICATION OF CROPLANDS EXTENT AND MANAGEMENT CONTRIBUTION TO CARBON CYCLING
Description: The
development of agriculture responding to increasing demand for food raises the
question of the role of cultivated land in relation to carbon sources and
sinks, their spatial patterns and temporal variability.
Author's Names: P.C. Smith, N. Viovy, Y. Meurdesoif, S. Gervois, et al
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Added on: 04-Aug-2005 Downloads: 20
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PROBLEM OF ESTIMATING WILDFIRES IMPACT ON CARBON CONTENT IN ATMOSPHERE
Description: During photosynthesis,
atmospheric carbon sequestration goes on at the expense of formation and
accumulation of organic substance, and an inverse process (carbon emission in
the atmosphere) takes place during decomposition and oxidation of this organic
substance. On land, in non-swamp ecosystems, these processes are balanced as a
whole both under climax forms and interchange of: 1) periods of active
oxidation of organic substance under influence of disturbing factors (more
often, fires), and 2) periods of active formation of organic substance in the
process of regeneration successions.
Author's Names: A.V. Volokitina, T.M.Sofronova, and M.A.Sofronov
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AIRCRAFT TO INVENTORES: A MULTISCALED INVESTIGATION OF CARBON FLUXES IN A MONTANE LANDSCAPE
Description: As a result of landuse, 50%
or more of forests in the Northern Hemisphere mid-latitudes are in hilly to
mountainous terrain, accounting for half or more of the mid-latitude Gross
Primary Productivity. The mid-latitude sink observed in the atmosphere may
reflect carbon dynamics occurring in complex terrain. This is challenging: these regions are
inherently highly heterogeneous and currently reflect complex land use
histories, and atmospheric techniques for estimating spatially integrated
carbon fluxes don’t work well in sloping terrain. Consequently, the impacts of
climate, harvesting regimes, disturbances and fire/pest management on carbon
exchange are poorly constrained in mountains. While mountains are
heterogeneous, the orientation of slopes to incident radiation and
gravitational flows of air and water result in organization of the variability
that can be exploited. Analysis using model-data fusion techniques of long-term
eddy covariance data showed 1) mid-aged Rocky Mountain forests are sinks, 2)
most of the net uptake occurs in the spring when melting snow provides moisture
for photosynthesis but low soil temperatures inhibit respiration and 3)
interannual variability is mainly due to GEE and is largely driven by spring
temperature and precipitation, which both determine spring fluxes and set the
stage for mid-summer soil moisture conditions.
Author's Names: David Schimel, Britton Stephens, Russell Monson, et al
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MODELING DAILY AND SEASONAL DYNAMICS OF CO2 STABLE CARBON ISOTOPIC EXCHANGE BETWEEN BOREAL ...
Description:
In
this study, we developed an integrated modeling system to simulate dynamics of a
stable carbon isotope of CO2, moisture, energy, and momentum between
boreal ecosystems and the atmosphere as well as their diffusion processes
through the whole convective boundary layer (CBL), using remotely sensed
surface parameters to characterize the surface heterogeneity, and the marine
boundary layer matrix data to represent the CBL top condition. Model validation
and primary results in boreal ecosystems were presented in this paper.
Author's Names: B. Chen, J. M. Chen, L. Huang, and P. Tans
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DIRECT COMPARISON OF EDDY COVARIANCE AND BOWEN RATIO ENERGY BALANCE MEASUREMENTS OF CO2 FLUXES ...
Description: The objectives of this study were to (1) compare
annual mass and energy fluxes of sensible carbon dioxide (CO2), heat
flux density (H), and latent heat flux density (LE) from Campbell Scientific,
Inc. (CSI) manufactured eddy
covariance (EC) and Bowen Ratio/energy balance (BREB) instrumentation in a
tallgrass prairie site and (2) make similar short term (5-14 d) comparison in
other grazing ecosystems throughout the western United States. The long-term
tallgrass prairie site was located in central Oklahoma
with measurements being made from August 2001- October 2004, while the
short-term sites were located in Oregon, Colorado, Idaho, North Dakota, and Arizona
during the summers of 2003 and 2005. Results from the long-term (< 36-month)
co-located EC and BREB units indicated that both systems demonstrated similar
seasonal patterns, yet the EC consistently failed to close the energy balance
by 25-35% when compared to the BREB.
Author's Names: G.L. Doyle, W.A. Dugas, and H. Mayeux
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DIAGNOSING CONTROLS OVER GPP AND ECOSYSTEM RESPIRATION USING FLUX DATA AND ASSIMILATION MODELING
Description: We used data assimilation to estimate the
contributions of GPP, heterotrophic (Rh) and autotrophic (Ra) respiration to
Net Ecosystem Exchange at the Niwot Ridge long-term eddy covariance site using
5 years of data. The assimilation problem is solved by optimizing state and
parameter values in a version of the PnET ecosystem model by minimizing the
misfit between modeled and observed NEE, subject to Bayesian prior estimates of
the model parameters and initial state. Seventeen free parameters, about half
of the total, are estimated, with the remaining parameters defined from other
studies. The model computes GPP, Rh and Ra fluxes for each day and night, and
thus produces an estimate of the separation of NEE into its components. We
checked the model’s partitioning of the NEE into GPP and total respiration by
comparing the modeled and observed diurnal NEE cycle, and evaluated the Rh-Ra
partitioning by comparing modeled and observed Net Primary Productivity, which
constrains this partitioning since GPP- Ra=NPP. While some discrepancies exist,
overall the assimilation model had considerable skill on diurnal to interannual
timescales.
Author's Names: W. Sacks, D. Schimel, R. Monson, G. Churkina
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C4 VEGETATION COVERAGE AND PHOTOSYNTHESIS IN SOUTH AMERICA: SEASONAL AND INTERANNUAL VARIATIONS
Description: We build upon a previous
approach to predict C3 and C4 fractions on the land
surface using new higher resolution satellite datasets on vegetation growth
form and crop type coverage. The approach relies upon the near-universal
restriction of C4 photosynthesis to the herbaceous growth form and
the differing performance of C3 and C4 plants in various
temperature and radiation regimes. MODIS-derived data provide detailed
information on growth form composition (%herbaceous, %woody, and %bare for each
grid cell). Precipitation and temperature variations are derived from station
data climatologies. Combining these data with MODIS-derived NPP fields from
2001, we predict latitudinal variations in C3 and C4 photosynthesis
for South America. These variations will be discussed in the context of the
global carbon cycle and the difficulty they pose for interannual inversion
studies using global CO2 and d13C atmospheric data.
Author's Names: C.J. Still1,2, and R. Powell
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SIMULATING EFFECTS OF LAND USE CHANGE ON CARBON FLUXES WITH A PROCESS MODEL IN SUBTROPICAL ...
Description:
A process model was used to simulate changes in the carbon fluxes and
stocks at a site that was transformed a grassland to a plantation at Qian
Yanzhou. The total carbon storage of the zonal vegetation (evergreen broadleaf
forest) was simulated and taken as the saturated carbon storage value of that site. The simulated vegetation density and soil organic
carbon (SOC) were compared with the observed. The simulates indicate
that after 20 years planting of the needle leaf forests (Pinus Massoniana, Cunninghamia lanceolata and Pinus elliottii ect) on ex-grassland, the net carbon storage increase in the plantation
was 8.03 kg
C/m2,in which the
vegetation carbon storage increased 8.5334
kg C/m2 and the soil carbon storage decreased 0.518 kg C/m2. The total
carbon storage of 20 years plantation is 58.6%
of the saturated value. The study also shows that between 0 and 7 years of land
use change the soil carbon was decreased and between 7 and 20 years it was
predicted to increase slowly.
Author's Names: M. Huang, J. Ji, M. Cao, and K. Li
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THE IMPACT OF CLOUDS ON ECOSYSTEM CO18O ISOFLUXES IN THE GREAT PLAINS
Description:
Mechanistic
explanations for the downward excursion in d18O of atmospheric CO2
observed during the mid-1990s and the generally large interannnual variability
characteristic of this isotopologue are lacking. We hypothesize that the
excursion and related variations in d18O of atmospheric
CO2 may be linked to global-scale variations in cloud cover.
However, very little is known about the influence of clouds on
biosphere-atmosphere CO18O exchanges. Recent work has demonstrated
the influence of boundary layer clouds on canopy photosynthesis through
increases in the diffuse radiation fraction and relative humidity, combined
with decreases in leaf temperature. In concert, these alterations tend to
increase canopy photosynthesis and conductance, which should also increase CO18O
isofluxes. However, photosynthetic CO18O isofluxes also depend
critically on the d18O of leafwater,
and enhanced cloudiness typically decreases the d18O of leafwater by
enhancing relative humidity and water vapor exchange across stomata. Thus, the net impact of differing cloud regimes on
biosphere-atmosphere CO18O exchanges is difficult to predict.
Preliminary simulations suggest a large impact of diffuse radiation on canopy
photosynthesis by increasing the flux from shade leaves. The impact of this
effect on biosphere-atmosphere CO18O exchanges is diluted somewhat by the lower enrichment in
leafwater d18O on cloudy days
with high diffuse radiation fractions. Our results suggest that these effects
are very dependent on LAI and photosynthetic pathway (C3 or C4).
Author's Names: C.J. Still, W.J. Riley, S.C. Biraud, D. Noone, et al
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INTEGRATION OF EXISTING DATA TO ESTIMATE THE INFLUENCE OF SOIL AND WATER MANAGEMENT ON CARBON ...
Description: Human
activities have altered rates of carbon erosion from soils and carbon
deposition in sediments. We are
developing methods to quantify the present-day and historical effects of these
changes on the carbon mass balance of the conterminous U.S. land surface. Because our analysis uses a combination of
diverse existing datasets, we devote particular attention to methods for the
estimation of uncertainties that are consistent with the statistical character
of the source data.
Author's Names: Eric T. Sundquist, Katherine Visser Ackerman, et al
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