bluuebunny/crossref_metadata_2025 huggingface dataset:
Compressional‐wave Q estimation from full‐waveform sonic data
Authors: Dasios A. , Astin T.R. , McCann C.
Published: March 2003

There is significant evidence that the anelastic loss of seismic energy is linked to petrophysical properties such as porosity, permeability and clay content. Thus, reliable estimation of anelastic attenuation from seismic data can lead to improved methods for the prediction of petrophysical properties. This paper is concerned with methods for the estimation of attenuation at sonic frequencies (5–30 KHz) from in situ data. Two independent methods have been developed and tested for estimating compressional‐wave attenuation from full‐waveform sonic data. A well‐established technique, the logarithm spectral ratio (LSR) method, is compared with a new technique, the instantaneous frequency (IF) method. The LSR method uses the whole spectrum of the seismic pulse whilst the IF method uses a carefully estimated value of instantaneous frequency which is representative of the centre frequency of the pulse. In the former case, attenuation estimation is based on the relative variation of amplitudes at different frequencies, whilst in the latter case it is based on the shift of the centre frequency of the pulse to lower values during anelastic wave propagation. The IF method does not assume frequency independence of Q which is a necessary assumption for the LSR method, and it provides a stable frequency log, the peak instantaneous frequency (PIF) log, which may be used as an indicator for attenuation under certain limitations. The development and implementation of the two methods is aimed at minimizing the effect of secondary arrivals, such as leaky modes, and involved a series of parameter tests. Testing of the two methods using full‐waveform sonic data of variable quality, obtained from a gas‐bearing sandstone reservoir, showed that the IF method is in general more stable and suitable for full‐waveform sonic data compared with the LSR method. This was evident especially in data sets with high background noise levels and wave‐interference effects. For good quality data, the two methods gave results that showed good agreement, whilst comparison with other log types further increased confidence in the results obtained. A significant decrease (approximately 5 KHz) in the PIF values was observed in the transition from an evaporite/shale sequence to the gas‐bearing sandstone. Average Q values of 54 and 51 were obtained using good quality data from a test region within the gas‐saturated sandstone reservoir, using the LSR and IF methods, respectively.
Finding the shape of a local heterogeneity by means of a structural inversion with constraints
Authors: Ditmar Pavel
Published: March 2003

Various aspects of structural inversion are considered. The aim of the inversion is limited to finding the shape of an isolated 2D homogeneous body, although the technique may be generalized to the case of interfaces with steep fragments, faults or overhangs. The unknown parameters are shifts of border points. The shift directions can be normal to the initial heterogeneity configuration or to another contour. Medium properties (seismic velocities, densities, etc.) within the heterogeneity are assumed to be known. The optimal shape is determined iteratively, a quadratic objective function being minimized at each iteration with the conjugate‐gradient method. Special attention is paid to preventing self‐intersections, for which purpose each unknown parameter is forced to lie within a certain predetermined interval. In order to achieve this, the classical conjugate‐gradient method has been modified accordingly. Three numerical examples are considered. These illustrate how the developed technique can be applied to different practical problems. The first example is devoted to monitoring an oil/steam interface by gravity gradiometry measurements. In the second example, a cross‐hole seismic experiment is simulated. It is shown that a structural inversion can restore the configuration of a local body much more accurately than traditional seismic tomography. In the third example, the shape of a salt dome is reconstructed by joint inversion of refracted traveltimes and gravity measurements. This example demonstrates how different kinds of data, used simultaneously in a structural inversion, can complement each other.
Successful application of ground‐penetrating radar in the exploration of gem tourmaline pegmatites of southern California
Authors: Patterson Jeffrey E. , Cook Frederick A.
Published: March 2003

Application of ground‐penetrating radar has been successful in delineating gem‐bearing zones in the Himalaya pegmatite mine of the Mesa Grande district of southern California. The high frequency of the electromagnetic signal allows features as small as a few centimetres to be resolved within 1–2 m of the surface of a mine wall. Careful initial set‐up consisted of: (i) selection of antennae with sufficiently high central frequencies; (ii) recording with a short time of scan to reduce end‐of‐scan noise levels; (iii) choosing appropriate colour schemes to highlight extreme amplitude variations. Operation during data collection consisted of pre‐painting marking points on the mine face and air launching the signal to reduce false anomalies caused by rocking of the antenna on the rough surfaces. Data processing using the Hilbert transform provided images of the cavity geometry that were then used by the blasting captain for accurate placement of explosives. The instantaneous frequency plot was found to be effective in distinguishing air‐filled from clay‐filled pockets, and the instantaneous phase plot was helpful in selecting potential targets where the amplitude was less than the maximum range. When carefully used in conjunction with good knowledge of the geological conditions, the method promises to provide an important tool for mapping internal structures of pegmatites, thus assisting future mining activities.
Modelling the seismic attributes of overpressured siliciclastic rocks, with a genetic annealing (GAN) algorithm
Authors: Domnesteanu Patricia , Domnesteanu Robert , McCann Clive
Published: March 2003

ABSTRACT A genetic annealing (GAN) algorithm is used to derive an empirical model which predicts compressional‐wave velocity values for overpressured siliciclastic rocks. The algorithm involves non‐linear random searching and mutation techniques and its annealing component imposes a very strict control over the rate of convergence of the search. This technique provides an alternative to the standard calculations involving the effective stress coefficient (n). The pore pressure is introduced into the model as an explicit variable and as part of an overpressure coefficient, (Pp/Pc) − the ratio of pore to confining pressure. Empirical model‐derived data and known laboratory data are compared and their differences are shown to be within statistically acceptable error limits. The empirical equation fits all under‐ and overpressured data simultaneously, irrespective of pore fluid pressure level, with the same parameters. It is used to predict seismic velocities very accurately for extreme levels of overpressure, starting from normally pressured experimental data. The model highlights the effect of pore pressure on the compressional‐wave velocity of fully saturated samples with different clay contents. It can be used when the experimental data available are sparse and particularly when a prediction of material behaviour is necessary at specific pore fluid pressure and depth conditions.
Acquisition and processing of high‐resolution reflection seismic data from a survey within the complex terrain of the Bavarian Folded Molasse
Authors: Thomas R. , Bram K. , Fertig J. , Schwerd K.
Published: March 2003

A high‐resolution reflection seismic survey was carried out in the southern part of the Bavarian Molasse Basin in 1998 and 1999. The survey aimed to investigate the near‐surface structure of the complicated transition from the unfolded Foreland Molasse to the Folded Molasse, and the Folded Molasse to the internally complicated thrust systems of the Helveticum, the Ultrahelveticum and the Rhenodanubian Flysch. The study is linked to the TRANSALP seismic project, and the results help to fill the gap between the surface and the upper 300–500 ms two‐way traveltime (TWT), typical of deep‐reflection seismic experiments. The environmental conditions encountered in the study area required that particular attention be paid to the acquisition parameters for the three seismic lines (each about 4 km long). The energy source was a small vibrator; the geophone spread, spacing and frequency range were adjusted to image reflectors, which were expected to dip steeply southwards.

In general, the unprocessed field records did not show signals that could be attributed to specific reflectors. Individual trace processing considerably improved the data quality, taking into account the influence of the Quaternary cover and also the strong lateral velocity variations of the shallow subsurface. The effects of the various processing steps, such as muting, refraction statics, residual statics and velocity analysis, are discussed. To assess the NMO velocities, the qualitative analysis of the seismic energy in a common‐shotpoint gather offered advantages over an analysis in a common‐midpoint gather or in a stacked section, and proved to be very effective. As demonstrated along the Miesbach 9801 line, low‐velocity zones extend locally down to about 400 ms, adjacent to zones of extremely high velocities close to the surface, reflecting steeply dipping strata.

Besides the Quaternary cover on top, the Miesbach 9801 and Miesbach 9802 lines exhibit many horizontal reflections, in places down as far as 1400 ms TWT, indicating the sedimentary sequences of the unfolded Foreland Molasse. The southern part of both lines is dominated by southward‐dipping reflection bands, indicating units of the Folded Molasse. The reflection pattern shown by the Miesbach 9901 line suggests that there is almost no Quaternary cover. Southward‐dipping elements reflect the internal structure of the Folded Molasse, whereas a rather diffuse reflection signature may be attributed to Rhenodanubian Flysch units.
Modelling and inversion of electromagnetic data using an approximate plate model
Authors: Pirttijärvi Markku , Pietilä Risto , Hattula Aimo , Hjelt Sven‐Erik
Published: March 2003

This paper presents a computational method for the interpretation of electromagnetic (EM) profile data in the frequency domain using a thin plate model within a two‐layer earth. The modelling method is based on an integral equation formulation, where the conductor is represented by a lattice structure composed of two‐dimensional surface elements. Several approximations are used to simplify the theoretical basis and to decrease the computation time. The simple parametric model allows efficient use of optimization methods. We employ a linearized inversion scheme based on singular value decomposition and adaptive damping. The new forward computation method and the parameter optimization are combined in the computer program, emplates. The modelling examples demonstrate that the approximate method is capable of describing the characteristic behaviour of the EM response of a thin plate‐like conductor in conductive surroundings. The efficacy of the inversion is demonstrated using both synthetic and field data. An optional depth compensation method is used to improve the interpreted values of the depth of burial. The results show that the method is cost effective and suitable for interactive interpretation of EM data.
Experimental validation of the wavefield transform of electromagnetic fields
Authors: Das Kaushik , Becker Alex , Lee Ki Ha
Published: March 2003

The wavefield transform is a mathematical technique for transforming low‐frequency electromagnetic (EM) signals to a non‐diffusive wave domain. The ray approximation is valid in the transform space and this makes traveltime tomography for 3D mapping of the electrical conductivity distribution in the subsurface possible. The transform, however, imposes stringent frequency bandwidth and signal‐to‐noise ratio requirements on the data. Here we discuss a laboratory scale experiment designed to collect transform quality EM data, and to demonstrate the practical feasibility of transforming these data to the wavefield domain.

We have used the scalable nature of EM fields to design a time‐domain experiment using graphite blocks to simulate realistic field conditions while leaving the time scale undisturbed. The spatial dimensions have been scaled down by a factor of a thousand by scaling conductivity up by a factor of a million. The graphite blocks have two holes drilled into them to carry out cross‐well and borehole‐to‐surface experiments. Steel sheets have been inserted between the blocks to simulate a conductive layer.

Our experiments show that accurate EM data can be recorded on a laboratory scale model even when the scaling of some features, such as drill‐hole diameters, is not maintained. More importantly, the time‐domain EM data recorded in cross‐well and surface‐to‐borehole modes can be usefully and accurately transformed to the wavefield domain. The observed wavefield propagation delay is proportional to the direct distance between the transmitter and receiver in a homogeneous medium. In a layered medium, data accuracy is reduced and, hence, our results are not so conclusive. On the basis of the experimental results we conclude that the wavefield transform could constitute a valid approach to the interpretation of accurate, undistorted time‐domain data if further improvement in the transform can be realized.
Wavefield extrapolation and prestack depth migration in anelastic inhomogeneous media
Authors: Zhang Jianfeng , Wapenaar Kees
Published: March 2003

Wavefield depth extrapolation and prestack depth migration in complex anelastic media are studied. Kjartansson's frequency‐independent Q law is used to describe the absorption of seismic energy. The macromodel used is analogous to the macromodel used for current migration schemes except that an additional frequency‐independent Q macromodel needs to be provided. Absorption in the forward one‐way propagator is introduced by assuming a complex phase velocity, and the inverse one‐way propagator is obtained using the reciprocity theorem for one‐way wavefields in dissipative media. The stability of the inverse propagator is achieved by limiting the angle of propagation of wavefields. A table‐driven explicit operator scheme for imaging complex 2D anelastic media is presented. High‐accuracy, short convolution operators are designed by the weighted least‐squares method, and two kinds of imaging conditions are proposed. Numerical examples of depth extrapolation in laterally varying media, the migration of a spatial impulse with dispersion as well as shot record depth migration demonstrate the potential of the proposed explicit forward operator, the explicit inverse operator and the prestack depth migration scheme, respectively.
Multiple attenuation: coping with the spatial truncation effect in the Radon transform domain
Authors: Wang Yanghua
Published: March 2003

The limited size of the spatial aperture of a seismic gather causes multiple‐ and primary‐reflection energy to spread out and cross‐hatch the image of the parabolic Radon transform. This spatial truncation effect devastatingly impairs the separation of primary and multiple reflections in a Radon demultiple process. It is difficult to suppress the spatial truncation effect completely, but it is at least possible to model or to identify implicitly such an effect and then to design automatically a mute function, i.e. a 2D mask filter in the Radon transform domain. This is referred to as the adaptive surgical mute scheme. By using this scheme, it is possible to extract the multiple‐reflection energy cleanly from the Radon transform image, so that the multiple reflections can be more effectively attenuated. It is also possible to preserve the diffused primary‐reflection energy after the surgical mute, so that the final multiple‐attenuated seismic profile is amplitude‐preserved.
Model estimates of methane emission from irrigated rice cultivation of China
Authors: HUANG YAO. , SASS RONALD L. , FISHER FRANK M.
Published: March 2003

A model developed by the authors (Huang et al. 1998) was further validated against field measurements from various regions of the world and calibrated to estimate methane emission from irrigated rice cultivation of China. On the basis of available information on rice cultivated area, growth duration, grain yield, soil texture and temperature, methane emission from Chinese rice paddies was estimated for 28 rice cultivated provinces in mainland. The calculated daily methane emission rates, on a provincial scale, ranged from 0.15 to 0.86 g m–2 with an average of 0.32 g m–2. Five of the top six locations with higher daily methane emissions are located at a latitude between 28° and 31° N. A total amount of 9.66 Tg (1 Tg = 1012 g) CH4 per year, ranging from 7.19 to 13.62, was estimated to be released from Chinese rice paddy soils. Of the total, 45% is emitted from the single‐rice growing season, and 19% and 36% are from the early‐rice and the late‐rice growing seasons, respectively. Approximately 70% of the total is emitted in the region located at latitude between 25° and 32° N. The emissions from rice fields in Sichuan and Hunan Province were calculated to be 2.85 Tg y–1, accounting for ≈ 30% of the total. Comparisons of the estimated and the observed emission rates show that the estimates were, in general, close to the measurements at most locations.
Growth, loss, and vertical distribution of Pinus radiata fine roots growing at ambient and elevated CO2 concentration
Authors: Thomas Stephen M. , Whitehead David , Reid JefF. B. , Cook Freeman J. , Adams JohN. A. , Leckie AlaN. C.
Published: March 2003

Increased below‐ground carbon allocation in forest ecosystems is a likely consequence of rising atmospheric CO2 concentration. If this results in changes to fine root growth, turnover and distribution long‐term soil carbon cycling and storage could be altered.

Bi‐weekly measurements were made to determine the dynamics and distribution of fine roots (< 1 mm diameter) for Pinus radiata trees growing at ambient (350 μmol mol–1) and elevated (650 μmol mol–1) CO2 concentration in large open‐top chambers. Measurements were made using minirhizotrons installed horizontally at depths of 0.1, 0.3, 0.5 and 0.9 m.

During the first year, at a depth of 0.3 m, the increase in relative growth rate of roots occurred 6 weeks earlier in the elevated CO2 treatment and the maximum rate was reached 10 weeks earlier than for trees in the ambient treatment. After 2 years, cumulative fine root growth (Pt) was 36% greater for trees growing at elevated CO2 than at ambient CO2 concentration, although this difference was not significant. A model of root growth driven by daily soil temperature accounted for between 43 and 99% of root growth variability.

Total root loss (Lt) was 9% in the ambient and 14% in the elevated CO2 treatment, although this difference was not significant. Root loss was greatest at 0.3 m. In the first year, 62% of fine roots grown between mid‐summer and late‐autumn disappeared within a year in the elevated CO2 treatment, but only 18% in the ambient CO2 treatment (P < 0.01). An exponential model relating Lt to time accounted for between 74 and 99% of the variability. Root cohort half‐lives were 951 d for the ambient and 333 d for the elevated treatment.

Root length density decreased exponentially with depth in both treatments, but relatively more fine roots grown in the elevated CO2 treatment tended to occur deeper in the soil profile.
The impact of ultraviolet‐B radiation on the motility of the freshwater epipelic diatom Nitzschia lineariz
Authors: Moroz Adrienne L. , Ehrman James M. , Clair Thomas A. , Gordon Robert J. , Kaczmarska Irena
Published: March 2003

Depletion of the stratospheric ozone layer has been of increased concern due to correlated increases in ambient ultraviolet radiation. Our research investigated the diel response of the motile behaviour of Nitzschia lineariz in both natural (freshwater stream) and experimental conditions. We classified the behaviour of individual diatom cells as gliding, immobile and oscillating. The experimental conditions were of simultaneous exposure either to net ambient solar radiation (control) or to ambient plus enhanced UV‐B levels (treatment). UV‐B for the control condition was filtered out using polyester filters; cells exposed to UV‐B were irradiated through cellulose diacetate filters. UVB‐313 levels were augmented to 33% (290 mW m–2) and 66% (365 mW m–2) above the local average ambient levels (220 mW m–2) for 10 h. The mobile behaviour of cells was examined and quantified every 2 consecutive hours from dawn to dusk in subsampled populations. The number of gliding cells in subsample populations declined on overcast days at both the 33 and 66% UV‐B enhancement levels, whereas the number of immobile and oscillating cells increased with increased UV‐B exposure. On sunny days, mobile behaviour was not affected at either enhancement level, which suggests that cellular repair mechanisms may be activated during sunny conditions.
Scaling net ecosystem CO2 exchange from the community to landscape‐level at a subarctic fen
Authors: Griffis Timothy J. , Rouse Wayne R. , Waddington J. M.
Published: March 2003

Landscape‐ and community‐level CO2 measurements were made at a subarctic sedge fen near Churchill Manitoba during the 1997 growing season. Climatic conditions were warmer and drier than the 30‐y normal. Landscape‐scale micrometeorological measurements indicated that the wetland gained 49 g CO2 m−2 during the growing season. Chamber‐scale measurements from the main vegetation community types showed that small hummocks (Carex spp. sites) dominated the CO2 exchange, yielding an effective scaling factor of 70%. Scaled parameters of two algorithms describing photosynthesis and respiration for each community type show strong similarity to those derived at the landscape level. Scaling photosynthesis, respiration, and net ecosystem CO2 exchange from the community to landscape‐level over the season is within the maximum probable error of each methodological approach and helps substantiate the 1997 CO2 budget. We explore the equilibrium response of net ecosystem CO2 exchange of this fen to climatic change by examining the feedback of water table position on vegetation distribution and nitrogen availability. Based on the effective scaling factors computed for each community type, we hypothesize that a small decrease in mean water table position could nearly triple the net uptake of CO2 at this wetland.
CO2 stabilization, climate change and the terrestrial carbon sink
Authors: White Andrew , Cannell Melvin G. R. , Friend Andrew D.
Published: March 2003

A nonequilibrium, dynamic, global vegetation model, Hybrid v4.1, with a subdaily timestep, was driven by increasing CO2 and transient climate output from the UK Hadley Centre GCM (HadCM2) with simulated daily and interannual variability. Three IPCC emission scenarios were used: (i) IS92a, giving 790 ppm CO2 by 2100, (ii) CO2 stabilization at 750 ppm by 2225, and (iii) CO2 stabilization at 550 ppm by 2150. Land use and future N deposition were not included. In the IS92a scenario, boreal and tropical lands warmed 4.5 °C by 2100 with rainfall decreased in parts of the tropics, where temperatures increased over 6 °C in some years and vapour pressure deficits (VPD) doubled. Stabilization at 750 ppm CO2 delayed these changes by about 100 years while stabilization at 550 ppm limited the rise in global land surface temperature to 2.5 °C and lessened the appearance of relatively hot, dry areas in the tropics.

Present‐day global predictions were 645 PgC in vegetation, 1190 PgC in soils, a mean carbon residence time of 40 years, NPP 47 PgC y−1 and NEP (the terrestrial sink) about 1 PgC y−1, distributed at both high and tropical latitudes. With IS92a emissions, the high latitude sink increased to the year 2100, as forest NPP accelerated and forest vegetation carbon stocks increased. The tropics became a source of CO2 as forest dieback occurred in relatively hot, dry areas in 2060–2080. High VPDs and temperatures reduced NPP in tropical forests, primarily by reducing stomatal conductance and increasing maintenance respiration. Global NEP peaked at 3–4 PgC y−1 in 2020–2050 and then decreased abruptly to near zero by 2100 as the tropical source offset the high‐latitude sink. The pattern of change in NEP was similar with CO2 stabilization at 750 ppm, but was delayed by about 100 years and with a less abrupt collapse in global NEP. CO2 stabilization at 550 ppm prevented sustained tropical forest dieback and enabled recovery to occur in favourable years, while maintaining a similar time course of global NEP as occurred with 750 ppm stabilization. By lessening dieback, stabilization increased the fraction of carbon emissions taken up by the land. Comparable studies and other evidence are discussed: climate‐induced tropical forest dieback is considered a plausible risk of following an unmitigated emissions scenario.
Water use of two Mojave Desert shrubs under elevated CO2
Authors: Pataki D. E. , Huxman T. E. , Jordan D. N. , Zitzer S. F. , Coleman J. S. , Smith S. D. , Nowak R. S. , Seemann J. R.
Published: March 2003

Plant responses to elevated atmospheric CO2 have been characterized generally by stomatal closure and enhanced growth rates. These responses are being increasingly incorporated into global climate models that quantify interactions between the biosphere and atmosphere, altering climate predictions from simpler physically based models. However, current information on CO2 responses has been gathered primarily from studies of crop and temperate forest species. In order to apply responses of vegetation to global predictions, CO2 responses in other commonly occurring biomes must be studied. A Free Air CO2 Enrichment (FACE) study is currently underway to examine plant responses to high CO2 in a natural, undisturbed Mojave Desert ecosystem in Nevada, USA. Here we present findings from this study, and its companion glasshouse experiment, demonstrating that field‐grown Ephedra nevadensis and glasshouse‐grown Larrea tridentata responded to high CO2 with reductions in the ratio of transpirational surface area to sapwood area (LSR) of 33% and 60%, respectively. Thus, leaf‐specific hydraulic conductivity increased and stomatal conductance remained constant or was increased under elevated CO2. Field‐grown Larrea did not show a reduced LSR under high CO2, and stomatal conductance was reduced in the high CO2 treatment, although the effect was apparent only under conditions of unusually high soil moisture. Both findings suggest that the common paradigm of 20–50% reductions in stomatal conductance under high CO2 may not be applicable to arid ecosystems under most conditions.
Leaf mineral concentrations of Erica arborea, Juniperus communis and Myrtus communis growing in the proximity of a natural CO2 spring
Authors: Peñuelas Josep , Filella Iolanda , Tognetti Roberto
Published: March 2003

Leaf mineral concentrations of co‐occurring Erica arborea, Juniperus communis and Myrtus communis were measured at bimonthly intervals throughout a year in a natural CO2 spring and in a nearby control site with similar soil chemistry in a Mediterranean environment. There were different responses to the elevated [CO2] (c. 700 μL L−1) of the spring site plants depending on the element and the species. In the CO2 spring site K, Ca, Mg, Mn, Al, Fe, and Ti leaf concentrations and the ratio C/N showed significant greater values in at least one or two of the three species. Leaf S concentration were greater in all three species. Leaf concentrations of N, Sr, Co, and B were lower in at least one or two species, and those of C and Ba were lower in all the three studied species near the CO2 spring. P, Na, Zn, Si, Cu, Ni, Cr, Pb, Mo, V and Cd leaf concentrations and the specific leaf area (SLA, measured in Myrtus communis) did not show any consistent or significant pattern in response to the elevated [CO2] of the spring site. There was a slight trend towards maximum concentrations of most of these elements during autumn–winter and minimum values during the spring season, especially in Myrtus communis. Multivariate principal component analyses based on the leaf elemental concentrations clearly differentiated the two sites and the three species. Lower concentrations at the spring site were not the result of a dilution effect by increased structural or nonstructural carbon. In contrast to most experimental studies of CO2 enrichment, mainly conducted for short periods, several of these elements had greater concentrations in the CO2 spring site. Nutrient acclimation and possible causes including decreased nutrient export, increased nutrient uptake capacity, photosynthetic down‐regulation, Mediterranean water stress, and higher H2S concentration in the spring site are discussed.
Plant carbon balance, evolutionary innovation and extinction in land plants
Authors: Cowling Sharon A.
Published: March 2003

The plant fossil record was reviewed to highlight how consideration of plant carbon balance strengthens our understanding of various evolutionary innovation and extinction events. Following a brief physiological primer to carbon acquisition and allocation in C3‐plants, specific evolutionary events are discussed in connection with postulated carbon‐based mechanisms. Primary topics include: (i) the evolution of plants with the C4‐photosynthetic pathway; (ii) the surprising lack of plant extinctions during the Pleistocene (1.6 million years ago, Ma); (iii) the trend toward declining plant diversity and increasing rates of herbivory across the Palaeocene/Eocene transition (57–52 Ma); and (iv) megaherbivore extinctions at the end of the Pleistocene (10 thousand years ago, Ka). A framework is presented for testing hypotheses on the cause–effect relationships between global carbon cycling, plant carbon dynamics and the evolution of terrestrial ecosystems.
Potassium limits potential growth of bog vegetation under elevated atmospheric CO2and N deposition
Authors: HOOSBEEK MARCEL R. , VAN BREEMEN NICO , VASANDER HARRI , BUTTLER ALEXANDRE , BERENDSE FRANK
Published: March 2003

The free air carbon dioxide enrichment (FACE) and N deposition experiments on four ombrotrophic bogs in Finland, Sweden, the Netherlands and Switzerland, revealed that after three years of treatment: (1) elevated atmospheric CO2concentration had no significant effect on the biomass growth ofSphagnumand vascular species; and (2) increased N deposition reduced Sphagnum growth, because it increased the cover of vascular plants and the tall mossPolytrichum strictum, while vascular plant biomass growth was not affected. This paper focuses on water chemistry, plant nutrient content, and litter decomposition rates. Potassium limitation, or low supply of K and P, may have prevented a significant increase ofSphagnumgrowth under elevated CO2and N deposition. Vascular plant growth under elevated CO2and N deposition was also limited by K, or by K in combination with P or N (N in CO2experiment). Elevated CO2and N deposition had no effect on decomposition rates ofSphagnumand vascular plant litter. Aside from a possible effect of N deposition on light competition between species, we expect that elevated atmospheric CO2and N deposition concentrations will not affectSphagnumand vascular plant growth in bogs of north‐west Europe due to K‐, or K in combination with N‐ or P‐, limited growth. For the same reason we expect no effect of elevated CO2and N deposition on litter decomposition. Net primary production of raised ombrotrophic bogs that are at or close to steady state, is regulated by input of nutrients through atmospheric deposition. Therefore, we hypothesize that the expected increase of plant growth under elevated CO2and N deposition is diminished by current levels of K (and to some extent P and N) in atmospheric deposition.
Effects of aggregated classifications of forest composition on estimates of evapotranspiration in a northern Wisconsin forest
Authors: MACKAY D. S. , AHL D. E. , EWERS B. E. , GOWER S. T. , BURROWS S. N. , SAMANTA S. , DAVIS K. J.
Published: March 2003

Forest management presents challenges to accurate prediction of water and carbon exchange between the land surface and atmosphere, due to its alteration of forest structure and composition. We examined how forest species types in northern Wisconsin affect landscape scale water fluxes predicted from models driven by remotely sensed forest classification. A site‐specific classification was developed for the study site. Using this information and a digital soils database produced for the site we identified four key forest stand types: red pine, northern hardwoods, aspen, and forested wetland. Within these stand types, 64 trees representing 7 species were continuously monitored with sap flux sensors. Scaled stand‐level transpiration from sap flux was combined with a two‐source soil evaporation model and then applied over a 2.5 km × 3.0 km area around the WLEF AmeriFlux tower (Park Falls, Wisconsin) to estimate evapotranspiration. Water flux data at the tower was used as a check against these estimates. Then, experiments were conducted to determine the effects of aggregating vegetation types to International Geosphere– Biosphere Program (IGBP) level on water flux predictions. Taxonomic aggregation resulting in loss of species level information significantly altered landscape water flux predictions. However, daily water fluxes were not significantly affected by spatial aggregation when forested wetland evaporation was included. The results demonstrate the importance of aspen, which has a higher transpiration rate per unit leaf area than other forest species. However, more significant uncertainty results from not including forested wetland with its high rates of evaporation during wet summers.
Modelling carbon balances of coastal arctic tundra under changing climate
Authors: Grant Robert F. , Oechel Walter C. , Ping Chien‐Lu
Published: March 2003

Rising air temperatures are believed to be hastening heterotrophic respiration (Rh) in arctic tundra ecosystems, which could lead to substantial losses of soil carbon (C). In order to improve confidence in predicting the likelihood of such loss, the comprehensive ecosystem model ecosys was first tested with carbon dioxide (CO2) fluxes measured over a tundra soil in a growth chamber under various temperatures and soil‐water contents (θ). The model was then tested with CO2 and energy fluxes measured over a coastal arctic tundra near Barrow, Alaska, under a range of weather conditions during 1998–1999. A rise in growth chamber temperature from 7 to 15 °C caused large, but commensurate, rises in respiration and CO2 fixation, and so no significant effect on net CO2 exchange was modelled or measured. An increase in growth chamber θ from field capacity to saturation caused substantial reductions in respiration but not in CO2 fixation, and so an increase in net CO2 exchange was modelled and measured. Long daylengths over the coastal tundra at Barrow caused an almost continuous C sink to be modelled and measured during most of July (2–4 g C m−2 d−1), but shortening daylengths and declining air temperatures caused a C source to be modelled and measured by early September (∼1 g C m−2 d−1). At an annual time scale, the coastal tundra was modelled to be a small C sink (4 g C m−2 y−1) during 1998 when average air temperatures were 4 °C above normal, and a larger C sink (16 g C m−2 y−1) during 1999 when air temperatures were close to long‐term normals. During 100 years under rising atmospheric CO2 concentration (Ca), air temperature and precipitation driven by the IS92a emissions scenario, modelled Rh rose commensurately with net primary productivity (NPP) under both current and elevated rates of atmospheric nitrogen (N) deposition, so that changes in soil C remained small. However, methane (CH4) emissions were predicted to rise substantially in coastal tundra with IS92a‐driven climate change (from ∼20 to ∼40 g C m−2 y−1), causing a substantial increase in the emission of CO2 equivalents. If the rate of temperature increase hypothesized in the IS92a emissions scenario had been raised by 50%, substantial losses of soil C (∼1 kg C m−2) would have been modelled after 100 years, including additional emissions of CH4.
Options for mitigating methane emission from a permanently flooded rice field
Authors: Cai Zucong , Tsuruta Haruo , Gao Ming , Xu Hua , Wei Chaofu
Published: March 2003

Permanently flooded rice fields, widely distributed in south and south‐west China, emit more CH4 than those drained in the winter crop season. For understanding CH4 emissions from permanently flooded rice fields and developing mitigation options, CH4 emission was measured year‐round for 6 years from 1995 to 2000, in a permanently flooded rice field in Chongqing, China, where two cultivations with four treatments were prepared as follows: plain‐cultivation, summer rice crop and winter fallow with floodwater layer annually (convention, Ch‐FF), and winter upland crop under drained conditions (Ch‐Wheat); ridge‐cultivation without tillage, summer rice and winter fallow with floodwater layer annually (Ch‐FFR), and winter upland crop under drained conditions (Ch‐RW), respectively. On a 6‐year average, compared to the treatments with floodwater in the winter crop season, the CH4 flux during rice‐growing period from the treatments draining floodwater and planting winter crop was reduced by 42% in plain‐cultivation and by 13% in ridge‐cultivation (P < 0.05), respectively. The reduction of annual CH4 emission reached 68 and 48%, respectively. Compared to plain‐cultivation (Ch‐FF), ridge‐cultivation (Ch‐FFR) reduced annual CH4 emission by 33%, and which was mainly occurred in the winter crop season. These results indicate that draining floodwater layer for winter upland crop growth was not only able to prevent CH4 emission from permanently flooded paddy soils directly in the winter crop season, but also to reduce CH4 emission substantially during the following rice‐growing period. As an alternative to the completely drainage of floodwater layer in the winter crop season, ridge‐cultivation could also significantly mitigate CH4 emissions from permanently flooded rice fields.
Seasonal patterns of soil CO2 efflux and soil air CO2 concentration in a Scots pine forest: comparison of two chamber techniques
Authors: PUMPANEN JUKKA , ILVESNIEMI HANNU , PERÄMÄKi MARTTI , HARI PERTTI
Published: March 2003

A non‐vented non‐steady state flow‐through chamber and a non‐vented non‐steady state non‐flow‐through chamber technique were used to measure CO2 efflux of a young Scots pine forest on a fertile till soil in southern Finland. Soil temperature, soil moisture and soil CO2 concentration were measured concurrently with CO2 efflux for two and a half successive years. The CO2 efflux showed a seasonal pattern, effluxes ranging from low 0.0–0.1 g CO2 m−2 h−1 in winter to peak values of 2.3 g CO2 m−2 h−1 occurring in late June and in July. The daily average effluxes in July measured by flow through chambers were 1.23 and 0.98 g CO2 m−2 h−1 in 1998 and 1999, respectively. The annual accumulated CO2 efflux was 3117 and 3326 g CO2 m−2 in 1998 and 1999, respectively. The spatial variation in CO2 efflux was high (CV 0.18–0.45) and increased with increasing efflux. Soil air CO2 concentration showed similar seasonal pattern the peak concentrations occurring in July–August. The CO2 concentrations ranged from 580 to 780 µmol mol−1 in the humus layer to 13 620–14 470 µmol mol−1 in the C‐horizon. In winter the soil air CO2 concentrations were lower, especially in deeper soil layers. Drought decreased CO2 efflux and soil air CO2 concentration. The in situ comparison on forest soil between the chamber methods showed the non‐flow‐through chamber to give ∼∼50% lower efflux values than that of the flow‐through chamber. When calibrated against known CO2 efflux ranging from 0.4 to 0.8 g CO2 m−2 h−1 generated with a diffusion box method developed by Widén and Lindroth [Acta Universitatis Agriculturae Suecia Silvestria, 2001], the flow‐through chamber gave equal effluxes at the lower end of the calibration range, but overestimated high effluxes by 20%. Non‐flow‐through chamber underestimated the CO2 efflux by 30%.
Land use induced changes of organic carbon storage in soils of China
Authors: WU HAIBIN , GUO ZHENGTANG , PENG CHANGHUI
Published: March 2003

Using the data compiled from China's second national soil survey and an improved method of soil carbon bulk density, we have estimated the changes of soil organic carbon due to land use, and compared the spatial distribution and storage of soil organic carbon (SOC) in cultivated soils and noncultivated soils in China. The results reveal that ∼ 57% of the cultivated soil subgroups (∼ 31% of the total soil surface) have experienced a significant carbon loss, ranging from 40% to 10% relative to their noncultivated counterparts. The most significant carbon loss is observed for the non‐irrigated soils (dry farmland) within a semiarid/semihumid belt from northeastern to southwestern China, with the maximum loss occurring in northeast China. On the contrary, SOC has increased in the paddy and irrigated soils in northwest China. No significant change is observed for forest soils in southern China, grassland and desert soils in northwest China, as well as irrigated soils in eastern China. The SOC storage and density under noncultivated conditions in China are estimated to ∼ 77.4 Pg (1015 g) and ∼ 8.8 kg C m−2, respectively, compared to a SOC storage of ∼ 70.3 Pg and an average SOC density of ∼ 8.0 kg C m−2 under the present‐day conditions. This suggests a loss of ∼ 7.1 Pg SOC and a decrease of ∼ 0.8 kg C m−2 SOC density due to increasing human activities, in which the loss in organic horizons has contributed to ∼ 77%. This total loss of SOC in China induced by land use represents ∼ 9.5% of the world's SOC decrease. This amount is equivalent to ∼ 3.5 ppmv of the atmospheric CO2 increase. Since ∼ 78% of the currently cultivated soils in China have been degraded to a low/medium productivities and are responsible for most of the SOC loss, an improved land management, such as the development of irrigated and paddy land uses, would have a considerable potential in restoring the SOC storage. Assuming a restoration of ∼ 50% of the lost SOC during the next 20–50 years, the soils in China would absorb ∼ 3.5 Pg of carbon from the atmosphere.
The effect of the spatial distribution of plant species within the sward on the searching success of sheep when grazing
Authors: Dumont  , Maillard  , Petit
Published: March 2003

The ability of grazing sheep to exploit preferred patches of grass species according to their spatial distribution was studied. The choices made by groups of four ewes in three cocksfoot (Dactylis glomerata) plots (80 × 80 m), in which 136 patches (30 × 30 cm) of perennial ryegrass (Lolium perenne) were either randomly distributed (plot Rand) or grouped (plots Ag.1 and Ag.2) to create preferred feeding sites (four rich sites of twenty‐five patches and four poorer sites of nine patches) were compared. On measurement days, each group was allocated to one of the three plots, and grazed it in at least four successive 30‐min tests. At the end of the experiment the ewes were allowed to graze the plots continuously for 3 months to assess the medium‐term effect of grazing sheep on the depletion rate of patches. Behavioural observations showed that, once the ewes had discovered a preferred feeding site in plots Ag.1 or Ag.2, they frequently returned to it within a test and between tests, whereas they failed to learn the precise location of many isolated patches in plot Rand. Thus in 2 h of grazing, the ewes spent 0·40 more time feeding on perennial ryegrass when the patches were grouped than when they were randomly distributed, and perennial ryegrass depletion was greater in plots Ag.1 and Ag.2 than in plot Rand (0·193 vs. 0·105 of initial height). The richer sites were also more depleted than the poorer ones (0·209 vs. 0·152 of initial height). When the plots were continuously grazed, perennial ryegrass depletion remained greater in plots Ag.1 and Ag.2 than in plot Rand for at least 3 weeks. Hence the spatial distribution of patches can affect diet selection by sheep, and so probably their impact on grasslands.
The effect of some acid‐based additives applied to wet grass crops under various ensiling conditions
Authors: Randby Å. T.
Published: March 2003

Some acid‐based silage additives, which are less corrosive and easier to handle than Formic acid 85% (FA), were evaluated in a laboratory‐scale silage experiment. These were Foraform (645 g kg–1 formic acid, 60 g kg–1 NH3), Ensimax [213 g kg–1 formic acid, 200 g kg–1 acetic acid, 190 g kg–1 of dry matter from wood pulp liquor with a high concentration of lignosulphonates (WPL)], and a modified version of Ensimax with a higher proportion of formic acid and a lower proportion of acetic acid. Each single ingredient, and all combinations of ingredients in the original Ensimax, were studied when applied in the quantities they make up in the additive. Untreated silage was used as a negative control and FA as a positive control. The additives were assessed using three different crops and by sealing the silos immediately after filling or after a 24 h delay. Both the full and half of the recommended application rates of the additives and of the single ingredients of Ensimax were studied.

No significant differences were found between FA and Foraform when applied at 3 and 4 l t–1, respectively, which provided the crop with the same dose of pure formic acid. Inclusion of WPL in Ensimax did not influence silage fermentation, i.e. the effect of Ensimax could be ascribed to the effect of formic plus acetic acid alone. Compared with Ensimax, the modified version, in which 148 g kg–1 of formic acid was substituted for 150 g kg–1 of acetic acid, clearly improved fermentation in terms of increased concentration of true protein, reduced fermentation of acetic and propionic acid, and reduced ammonia value and pH. When the silos were sealed immediately, sugar concentrations in the silage correlated positively with the application rate of acids, whereas no such relationship was found when the sealing was delayed for 24 h. No consistent relationship was found between the application rate of acids and ethanol concentrations in the silage.

Easy‐to‐handle acidic additives like Foraform and Ensimax may replace FA when applied according to their molar concentration of acids. This means that 4·0 l t–1 of Foraform and 7·3 l t–1 of Ensimax are equivalent to 3 l t–1 of FA.
A variant of the dry‐weight rank method for botanical analysis of grassland with dominance‐based multipliers
Authors: Nijland G. O.
Published: March 2003

A new variant of the dry‐weight rank method for botanical investigation of grassland is described and its usefulness evaluated. Multipliers proportional to the dominance percentages of the three species with the highest dominance percentages are used instead of fixed multipliers. The method is theoretically more valid and applicable to a broader range of grasslands than the variants with fixed multipliers. It does not involve more costs and gives as good or better predictions of the dry‐weight percentages than the variants with fixed multipliers.