排序方式： 共有9条查询结果，搜索用时 15 毫秒
1
1.
2.
Jason Timmons Young Min Cho Timothy Townsend Nicole Berge Debra Reinhart 《Geotechnical and Geological Engineering》2012,30(1):95-105
Commercially available hydraulic total overburden pressure cells were installed in the sand drainage layer of a municipal
solid waste landfill and monitored for a period of 3,110 days. Both overburden pressure and temperature were measured in the
landfill as it was filled with compacted waste. Topographic surveys of the landfill were periodically conducted to measure
the height of waste above the pressure cells and to determine the landfill volume for indirect unit weight estimation. The
average ratio of measured to theoretically-predicted overburden pressure was 0.6, indicating that on average the pressure
cells underestimated the load. The overburden pressure measured near the toe of the landfill was greater than that predicted
by the unit weight of landfilled material, while most of the overburden pressure measurements further inside the landfill
were less than predicted. Several possible causes for this phenomenon are discussed, including the uneven distribution of
forces resulting from the heterogeneous nature of the waste and cover soil. The earth pressure cells were capable of detecting
the placement of individual waste lifts. 相似文献
3.
Juan F. García-Quijano Gaby Deckmyn Reinhart Ceulemans Jos van Orshoven Bart Muys 《Climatic change》2008,86(3-4):397-424
There is a gap between the increased scientific understanding of carbon pools and fluxes at individual trees/stand and that
of forested landscape with complex structures (i.e. variety of species, age classes, site characteristic and management practices).
The question about how results generated from a simulated physiologically distinct individual(s)/stands grown at a particular
location (scale) can be extrapolated (scaling) across a diverse population in time and space with diverse environments, has
been troubling scientists for many years. Scale and scaling present three problems in common: (a) spatial heterogeneity, (b)
non-linearity in response and (c) disturbance regimes. Scale, in particular, presents other three problems: (d) threshold
scale for processes, (e) dominant processes with scales and (f) emerging properties of the system. Scaling presents problems
with (g) feedbacks between plants and environment and (h) plant interactions. The present study proposes a modeling framework
linking a process-based model SECRETS – to overcome some of the scale and scaling problems (a, b, c, d and g) – to a C accounting
model GORCAM – to integrate the effects of C stock in wood products and from fossil fuel substitution. The capabilities of
the modeling framework are tested against three theoretical complex forested landscapes that combine some of the five following
scenarios: existing multifunctional forest under (1) actual and (2) changing environmental conditions, and afforestation of
an agricultural area with (3) a new multifunctional forest or with (4) a short rotation coppice (poplar) or with (5) an agricultural
crop (miscanthus) for bioenergy production. Forest reserves calculations are included for completeness of the landscape C
balance and as reference. Results, on the one hand, suggest that the framework is able to simulate C sequestration and stock
in ecosystem pools, wood products and fossil fuel substitution of the scenarios under actual environmental conditions. However,
comparison of results under changing environmental conditions, against specific plant literature suggest SECRETS formulation
must be improved with recent development in photosynthesis, stomatal conductance and N balances. On the other hand, results
also suggest that under actual environmental conditions, the optimum landscape scenario to sequester C and avoid fossil emissions
to the atmosphere is composed by existing multifunctional forest, reserves and afforestation with short rotation coppice for
bioenergy production. 相似文献
4.
L. Meiresonne D. A. Sampson A. S. Kowalski I. A. Janssens N. Nadezhdina J. Cermk J. Van Slycken R. Ceulemans 《Journal of Hydrology》2003,270(3-4):230-252
Four distinct approaches, that vary markedly in the spatial and temporal resolution of their measurement and process-level outputs, are used to investigate the daily and seasonal water vapour exchange in a 70-year-old Belgian Scots pine forest. Transpiration, canopy interception, soil evaporation and evapotranspiration are simulated, using a stand-level process model (SECRETS) and a soil water balance model (WAVE). Simulated transpiration was compared with up-scaled sap flow measurements and simulated evapotranspiration to eddy covariance measurements.
Reasonable agreement in the temporal trends and in the annual water balance between the two models was observed, however daily and weekly predictions often diverged. Most notably, WAVE estimated very low, to no transpiration during late autumn, winter and early spring when incident radiation fell below 50 W m−2 while SECRETS simulated low (0.1–0.4 mm day−1) fluxes during the same period. Both models exhibited similar daily trends in simulated transpiration when compared with sap flow estimates, although simulations from SECRETS were more closely aligned. In contrast, WAVE over-estimated transpiration during periods of no rainfall and under-estimated transpiration during rainfall. Yearly, total evapotranspiration simulated by the models were similar, i.e. 658 mm (1997) and 632 mm (1998) for WAVE and 567 mm (1997) and 619 mm (1998) for SECRETS.
Maximum weekly-average evapotranspiration for WAVE exceeded 5 mm day−1, while SECRETS never exceeded 4 mm day−1. Both models, in general, simulated higher evapotranspiration than that measured with the eddy covariance technique. An impact of the soil water content in the direct relationship between the models and the eddy covariance measurements was found.
The results suggest that: (1) different model formulations can reproduce similar results depending on the scale at which outputs are resolved, (2) SECRETS estimates of transpiration were well correlated with the empirical measurements, and (3) neither model fitted favourably to the eddy covariance technique. 相似文献
5.
Juan F. García-Quijano Jan Peters Liesbet Cockx Gerrit van Wyk Andrei Rosanov Gaby Deckmyn Reinhart Ceulemans Shane M. Ward Nicholas M. Holden Jos Van Orshoven Bart Muys 《Climatic change》2007,83(3):323-355
A three-step methodology to assess the carbon sequestration and the environmental impact of afforestation projects in the
framework of the Flexible Mechanisms of the Kyoto Protocol (Joint Implementation and Clean Development Mechanism) was developed
and tested using a dataset collected from the Jonkershoek forest plantation, Western Cape, South Africa, which was established
with Pinus radiata in former native fynbos vegetation and indigenous forest. The impact of a change in land use was evaluated for a multifunctional,
a production and a non-conversion scenario. First, the carbon balance was modelled with GORCAM and was expressed as (1) C
sequestration in tC ha−1 year−1 in soil, litter, and living biomass according to the rules of the first commitment period of the Kyoto Protocol, and (2)
CO2 emission reductions in tC ha−1 year−1, which includes carbon sequestered in the above-mentioned pools and additionally in wood products, as well as emission reductions
due to fossil fuel substitution. To estimate forest growth, three data sources were used: (1) inventory data, (2) growth simulation
with a process-based model, and (3) yield tables. Second, the effects of land use change were assessed for different project
scenarios using a method related to Life Cycle Assessment (LCA). The method uses 17 quantitative indicators to describe the
impact of project activities on water, soil, vegetation cover and biodiversity. Indicator scores were calculated by comparing
indicator values with reference values, estimated for the climax vegetation. The climax vegetation is the site-specific ecosystem
phase with the highest exergy content and the highest exergy flow dissipation capacity. Third, the land use impact per functional
unit of 1 tC sequestered was calculated by combining the results of step 1 and step 2. The average baselines to obtain carbon
additionality are 476 tC ha−1 for indigenous forest and 32 tC ha−1 for fynbos. Results show that the influence of the growth assessment method on the magnitude of C sequestration and hence
on the environmental impact per functional unit is large. When growth rate is assessed with the mechanistic model and with
the yield table, it is overestimated in the early years and underestimated in the long term. The main conclusion of the scenario
analysis is that the production forest scenario causes higher impacts per functional unit than the multifunctional scenario,
but with the latter being less efficient in avoiding CO2 emissions. The proposed method to assess impacts on diverse components of the ecosystem is able to estimate the general tendency
of the adverse and positive effects of each scenario. However, some indicators, more specifically about biodiversity and water
balance, could be improved or reinterpreted in light of specific local data about threat to biodiversity and water status. 相似文献
6.
7.
8.
Quality analysis applied on eddy covariance measurements at complex forest sites using footprint modelling 总被引：7，自引：0，他引：7
C. Rebmann M. Göckede T. Foken M. Aubinet M. Aurela P. Berbigier C. Bernhofer N. Buchmann A. Carrara A. Cescatti R. Ceulemans R. Clement J. A. Elbers A. Granier T. Grünwald D. Guyon K. Havránková B. Heinesch A. Knohl T. Laurila B. Longdoz B. Marcolla T. Markkanen F. Miglietta J. Moncrieff L. Montagnani E. Moors M. Nardino J.-M. Ourcival S. Rambal Ü. Rannik E. Rotenberg P. Sedlak G. Unterhuber T. Vesala D. Yakir 《Theoretical and Applied Climatology》2005,80(2-4):121-141
Summary Measuring turbulent fluxes with the eddy covariance method has become a widely accepted and powerful tool for the determination of long term data sets for the exchange of momentum, sensible and latent heat, and trace gases such as CO2 between the atmosphere and the underlying surface. Several flux networks developed continuous measurements above complex terrain, e.g. AmeriFlux and EUROFLUX, with a strong focus on the net exchange of CO2 between the atmosphere and the underlying surface. Under many conditions basic assumptions for the eddy covariance method in its simplified form, such as stationarity of the flow, homogeneity of the surface and fully developed turbulence of the flow field, are not fulfilled. To deal with non-ideal conditions which are common at many FLUXNET sites, quality tests have been developed to check if these basic theoretical assumptions are valid.In the framework of the CARBOEUROFLUX project, we combined quality tests described by Foken and Wichura (1996) with the analytical footprint model of Schmid (1997). The aim was to identify suitable wind sectors and meteorological conditions for flux measurements. These tools were used on data of 18 participating sites. Quality tests were applied on the fluxes of momentum, sensible and latent heat, and on the CO2-flux, respectively. The influence of the topography on the vertical wind component was also checked. At many sites the land use around the flux towers is not homogeneous or the fetch may not be large enough. So the relative contribution of the land use type intended to be measured was also investigated. Thus the developed tool allows comparative investigations of the measured turbulent fluxes at different sites if using the same technique and algorithms for the determination of the fluxes as well as analyses of potential problems caused by influences of the surrounding land use patterns. 相似文献
9.
Reinhart Bartsch 《Solar physics》1973,30(1):93-102
It is shown that the east-west asymmetry is quite different for spot-groups of different classes of evolution and that there exists a conspicuous difference between the ascending and descending branches with regard to the east-west asymmetry and the asymmetry between corresponding lunes. Some results point to the existence of systematic errors in the classification of the spot-groups. 相似文献
1