Multiscale analysis of vegetation surface fluxes: from seconds to years   总被引：2，自引：0，他引：2  

Gabriel Katul  Chun-Ta Lai  Karina Schfer  Brani Vidakovic  John Albertson  David Ellsworth  Ram Oren 《Advances in water resources》2001,24(9-10)

The variability in land surface heat (H), water vapor (LE), and CO₂ (or net ecosystem exchange, NEE) fluxes was investigated at scales ranging from fractions of seconds to years using eddy-covariance flux measurements above a pine forest. Because these fluxes significantly vary at all these time scales and because large gaps in the record are unavoidable in such experiments, standard Fourier expansion methods for computing the spectral and cospectral statistical properties were not possible. Instead, orthonormal wavelet transformations are proposed and used. The are ideal at resolving process variability with respect to both scale and time and are able to isolate and remove the effects of missing data (or gaps) from spectral and cospectral calculations. Using the spectra, we demonstrated unique aspects in three appropriate ranges of time scales: turbulent time scales (fractions of seconds to minutes), meteorological time scales (hour to weeks), and seasonal to interannual time scales corresponding to climate and vegetation dynamics. We have shown that: (1) existing turbulence theories describe the short time scales well, (2) coupled physiological and transport models (e.g. CANVEG) reproduce the wavelet spectral characteristics of all three land surface fluxes for meteorological time scales, and (3) seasonal dynamics in vegetation physiology and structure inject strong correlations between land surface fluxes and forcing variables at monthly to seasonal time scales. The broad implications of this study center on the possibility of developing low-dimensional models of land surface water, energy, and carbon exchange. If the bulk of the flux variability is dominated by a narrow band or bands of modes, and these modes “resonate” with key state and forcing variables, then low-dimensional models may relate these forcing and state variables to NEE and LE.  相似文献   

Organochlorines in mussel and shrimp from the Saronikos Gulf (Greece)     

John Satsmadjis  Gabriel P. Gabrielides 《Marine pollution bulletin》1983,14(9):356-358

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Intermittent Surface Renewals and Methane Hotspots in Natural Peatlands     

Zorzetto  Enrico  Peltola  Olli  Grönholm  Tiia  Katul  Gabriel G. 《Boundary-Layer Meteorology》2021,180(3):407-433

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Chemical characterization of porewaters in an intertidal mudflat of the Seine estuary: relationship to erosion-deposition cycles     

Bally G  Mesnage V  Deloffre J  Clarisse O  Lafite R  Dupont JP 《Marine pollution bulletin》2004,49(3):163-173

A seasonal field study was carried out in the Seine estuary to determine the chemistry of sediment porewaters using the 'peeper' technique and changes in the elevation of the mudflats using the 'Altus' technique. This approach allowed us to evaluate the release of nutrients and to link these releases to the sediment hydrodynamics. Our results show that nutrient and organic matter cycling in a Seine estuary mudflat exhibits a seasonal behaviour, which is mainly influenced by variations in hydrodynamics. Sediments, rich organic matter, were input during floods and they were mineralized during summer and autumn, releasing nutrients and dissolved organic carbon into the sediment porewaters. The nutrient release, including ammonium, is mainly linked to the mineralization of organic matter, while the release of phosphate is delayed. The delay could be the result of phosphate association with organic matter and/or its co-precipitation with calcium and iron.  相似文献   

Radiocarbon Data on Lateglacial and Holocene Landslides in the Northern Apennines     

Giovanni Bertolini  Nicola Casagli  Leonardo Ermini  Claudio Malaguti 《Natural Hazards》2004,31(3):645-662

The Emilia Romagna slope of the Northern Apennines is strewnwith over 32,000 landslides, 5,000 of which are larger than 1 million cubic metres. They representthe remains of geomorphic agents that shaped the Apennines during the Holocene. Dating themby means of radiocarbon methods adds a contribution to the knowledge about the last periodof the geological geomorphological history of the Apennines. They can also be used to examinethe influence of Quaternary climatic changes on the instability of slopes and, for practicalor planning functions, to assess the periodicity of activity phases of the landslides. Thedating has been carried out on wood remnants buried under the landslide bodies. In some cases theentire tree trunk was found.In this paper we present radiocarbon dating of 20 casestudies in the Northern Apennines. Results range approximately from 13790–13670 cal y BP to950–790 cal`y BP. The oldest case is that of the Morsiano earth-flow, while the younger datedevent is represented by the Marano case that represents an example of how radiometric analysescan further enhance the available historical data. In the Cavola case, wood remnants of different ageswere found at different depths (from 9 to 45 m), allowing the dating of the first and followingperiods of activity of the landslide. The results are discussed and some considerations on the correlationbetween landslide occurrence and Holocene climate changes are proposed.  相似文献   

Carbon and water cycling in a Bornean tropical rainforest under current and future climate scenarios     

Tomo&#x;omi Kumagai  Gabriel G. Katul  Amilcare Porporato  Taku M. Saitoh  Mizue Ohashi  Tomoaki Ichie  Masakazu Suzuki 《Advances in water resources》2004,27(12):1844

We examined how the projected increase in atmospheric CO₂ and concomitant shifts in air temperature and precipitation affect water and carbon fluxes in an Asian tropical rainforest, using a combination of field measurements, simplified hydrological and carbon models, and Global Climate Model (GCM) projections. The model links the canopy photosynthetic flux with transpiration via a bulk canopy conductance and semi-empirical models of intercellular CO₂ concentration, with the transpiration rate determined from a hydrologic balance model. The primary forcing to the hydrologic model are current and projected rainfall statistics. A main novelty in this analysis is that the effect of increased air temperature on vapor pressure deficit (D) and the effects of shifts in precipitation statistics on net radiation are explicitly considered. The model is validated against field measurements conducted in a tropical rainforest in Sarawak, Malaysia under current climate conditions. On the basis of this model and projected shifts in climatic statistics by GCM, we compute the probability distribution of soil moisture and other hydrologic fluxes. Regardless of projected and computed shifts in soil moisture, radiation and mean air temperature, transpiration was not appreciably altered. Despite increases in atmospheric CO₂ concentration (C_a) and unchanged transpiration, canopy photosynthesis does not significantly increase if C_i/C_a is assumed constant independent of D (where C_i is the bulk canopy intercellular CO₂ concentration). However, photosynthesis increased by a factor of 1.5 if C_i/C_a decreased linearly with D as derived from Leuning stomatal conductance formulation [R. Leuning. Plant Cell Environ 1995;18:339–55]. How elevated atmospheric CO₂ alters the relationship between C_i/C_a and D needs to be further investigated under elevated atmospheric CO₂ given its consequence on photosynthesis (and concomitant carbon sink) projections.  相似文献   

Estimation of the mass density contrasts and the 3D geometrical shape of the source bodies in the Yilgarn area, Eastern Goldfields, Western Australia   总被引：1，自引：0，他引：1  

Gabriel Strykowski  Fabio Boschetti  Gbor Papp 《Journal of Geodynamics》2005,39(5):444-460

We invert 2D surface gravity data constrained both by geological and seismic information. We use a number of pre-processing tools in order to reduce the general multi-body inversion into several single-body inversions, whereby we can reduce the overall complexity of the inversion task. This is done with as few assumptions as possible. Furthermore, for a single-body inversion we uncouple the determination of the shape of the causative sources from the determination of their mass density contrast to the surroundings. The inversion for the geometrical shape of the source body is done in steps. Firstly, a rough 3D shape of the source is modelled—a model consisting of the vertical mass columns of equal height. The horizontal extension is implied by the surface gravity signal. Subsequently, the shape of each source body is modified to obtain a better fit to the surface gravity data. In each modification step, the overall change of the shape of the source body is followed by an update of the mass density contrast to the surroundings. The technique was applied to a set of gravity data from the Eastern Goldfield area in Western Australia. The area has been widely studied in the past. In 1999, two seismic profiles that cross-sect the area were measured. Furthermore, an extensive geological modelling for the area has been conducted. The practical goal of this work was to verify the geological interpretation using the potential field data (mainly the gravity data although magnetic data were also available) and only weakly constrained by the seismic information. The result was the reconstruction of the ‘rough’ 3D geometry of the source bodies and the estimation of a constant mass density contrast to the surroundings. A possible extension of this technique for detailed studies of the geological model is briefly discussed.  相似文献   

Landslides in Emilia-Romagna region (Italy): strategies for hazard assessment and risk management   总被引：1，自引：2，他引：1  

Giovanni Bertolini  Monica Guida  Marco Pizziolo 《Landslides》2005,2(4):302-312

In Emilia-Romagna, over 32,000 landslide bodies cover one-fifth of the hilly and mountainous territory. The majority of them originated as earth-flows after the last glacial maximum and grew during the rainiest periods of the Holocene through the superimposition of new earth-flows. Reactivation of these large landslides is the main problem the geologists of Emilia-Romagna are facing now. Intense and/or prolonged precipitation play a major role as triggering factors in reactivating landslide bodies, but also the importance of snowmelt is suggested by the monthly distribution of landslide events. Almost all the present-day landslide activity is due to the reactivation of pre-existing landslide bodies. Consequently, territorial planning and geo-thematic cartography are fundamental tools for the reduction of risk. The Emilia-Romagna geo-thematic cartography (1:10,000) is legally binding and regulates land use in regional, municipal and basin plans.  相似文献   

An Investigation of Higher-Order Closure Models for a Forested Canopy   总被引：11，自引：10，他引：1  

Gabriel Katul 《Boundary-Layer Meteorology》1998,89(1):47-74

Simultaneous triaxial sonic anemometer velocity measurements vertically arrayed at six levels within and above a uniform pine forest were used to examine two parameterization schemes for the triple-velocity correlation tensor employed in higher-order closure models. These parameterizations are the gradient-diffusion approximation typically used in second-order closure models, and the full budget for the triple-velocity correlation tensor typically employed in third-order closure models. Both second- and third-order closure models failed to reproduce the measured profiles of the triple-velocity correlation within and above the canopy. However, the Reynolds stress tensor profiles (including velocity variances) deviated greatly from the measurements only within the lower levels of the canopy. It is shown that the Reynolds stresses are most sensitive to the parameterization of the triple-velocity correlation in these lower canopy regions where local turbulent production is negligible and turbulence is mainly sustained by the flux transport term. The failure of the third-order closure model to reproduce the measured third moments in the upper layers of the canopy-top contradicts conclusions from a previous study over shorter vegetation but agrees with another study for a deciduous forest. Whether the third-order closure model failure is due to the zero-fourth-cumulant closure approximation is therefore considered. Comparisons between measured and predicted quadruple velocity correlations suggest that the zero-fourth-cumulant approximation is valid close to the canopy-atmosphere in agreement with recent experiments.  相似文献   

The local effect of intermittency on the inertial subrange energy spectrum of the atmospheric surface layer   总被引：1，自引：0，他引：1  

Jozsef Szilagyi  Gabriel G. Katul  Marc B. Parlange  John D. Albertson  Anthony T. Cahill 《Boundary-Layer Meteorology》1996,79(1-2):35-50

Orthonormal wavelet expansions are applied to atmospheric surface layer velocity measurements. The effect of intermittent events on the energy spectrum of the inertial subrange is investigated through analysis of wavelet coefficients. The local nature of the orthonormal wavelet transform in physical space makes it possible to identify a relationship between the inertial subrange slope of the local wavelet spectrum and a simple indicator (i.e. the local variance of the signal) of local intermittency buildup. The slope of the local wavelet energy spectrum in the inertial subrange is shown to be sensitive to the presence of intermittent events. During well developed intermittent events (coherent structures), the slope of the energy spectrum is somewhat steeper than -5/3, while in less active regions the slope is found to be flatter than -5/3. When the slopes of local wavelet spectra are ensemble averaged, a slope of -5/3 is recovered for the inertial subrange.  相似文献