http://www.sciencedirect.com/science/article/pii/S1674987111000405   总被引：1，自引：0，他引：1  

Jean de la Paix Mupenzi  Lanhai Li  Jiwen Ge  Achal Varenyam  Gabriel Habiyaremye  Nzayisenga Theoneste  Kamanzi Emmanuel 《地学前缘(英文版)》2011,2(4):599-607

This study has focused on the processes of soil degradation and chemical element concentration in tea-growing regions of Rwanda, Africa. Soil degradation accelerated by erosion is caused not only by topography but also by human activities. This soil degradation involves both the physical loss and reduction in the amount of topsoil associated with nutrient decline. Soil samples were collected from eleven tropical zones in Rwanda and from variable depth within each collecting site. Of these, Samples from three locations in each zone were analyzed in the laboratory, with the result that the pH of all soil samples is shown to be less than 5 (pH < 5) with a general average of 4.4. The elements such as iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn) are present in high concentration levels. In contrast calcium (Ca) and sodium (Na) are present at low-level concentrations and carbon (C) was found in minimal concentrations. In addition, elements derived from fertilizers, such as nitrogen (N), phosphorous (P), and potassium (K) which is also from minerals such as feldspar, are also present in low-level concentrations. The results indicate that the soil in certain Rwandan tea plantations is acidic and that this level of pH may help explain, in addition to natural factors, the deficiency of some elements such as Ca, Mg, P and N. The use of chemical fertilizers, land use system and the location of fields relative to household plots are also considered to help explain why tea plantation soils are typically degraded.  相似文献   

Provenance analysis of the Paleozoic sequences of the northern Gondwana margin in NW Iberia: Passive margin to Variscan collision and orocline development     

Daniel Pastor-Galán  Gabriel Gutiérrez-Alonso  J. Brendan Murphy  Javier Fernández-Suárez  Mandy Hofmann  Ulf Linnemann 《Gondwana Research》2013,23(3):1089-1103

The Cantabrian Zone of NW Iberia preserves a voluminous, almost continuous, sedimentary sequence that ranges from Neoproterozoic to Early Permian in age. Its tectonic setting is controversial and recent hypotheses include (i) passive margin deposition along the northern margin of Gondwana or (ii) an active continental margin or (iii) a drifting ribbon continent. In this paper we present detrital zircon U–Pb laser ablation age data from 13 samples taken in detrital rocks from the Cantabrian Zone sequence ranging from Early Silurian to Early Permian in depositional age. The obtained results, together with previously published detrital zircon ages from Ediacaran–Ordovician strata, allow a comprehensive analysis of changing provenance through time. Collectively, these data indicate that this portion of Iberia was part of the passive margin of Gondwana at least from Ordovician to Late Devonian times. Zircon populations in all samples show strong similarities with the Sahara Craton and with zircons found in Libya, suggesting that NW Iberia occupied a paleoposition close to those regions of present-day northern Africa during this time interval. Changes in provenance in the Late Devonian are attributed to the onset of the collision between Gondwana and Laurussia.Additionally, the Middle Carboniferous to Permian samples record populations consistent with the recycling of older sedimentary sequences and exhumation of the igneous rocks formed before and during the Variscan orogeny. Late-Devonian to Permian samples yield zircon populations that reflect topographic changes produced during the Variscan orogeny and development of the lithospheric scale oroclinal buckling.  相似文献   

The relationship between reference canopy conductance and simplified hydraulic architecture     

Kimberly Novick  Ram Oren  Paul Stoy  Jehn-Yih Juang  Mario Siqueira  Gabriel Katul 《Advances in water resources》2009

Terrestrial ecosystems are dominated by vascular plants that form a mosaic of hydraulic conduits to water movement from the soil to the atmosphere. Together with canopy leaf area, canopy stomatal conductance regulates plant water use and thereby photosynthesis and growth. Although stomatal conductance is coordinated with plant hydraulic conductance, governing relationships across species has not yet been formulated at a practical level that can be employed in large-scale models. Here, combinations of published conductance measurements obtained with several methodologies across boreal to tropical climates were used to explore relationships between canopy conductance rates and hydraulic constraints. A parsimonious hydraulic model requiring sapwood-to-leaf area ratio and canopy height generated acceptable agreement with measurements across a range of biomes (r²=0.75)$(r^2=0.75)$. The results suggest that, at long time scales, the functional convergence among ecosystems in the relationship between water-use and hydraulic architecture eclipses inter-specific variation in physiology and anatomy of the transport system. Prognostic applicability of this model requires independent knowledge of sapwood-to-leaf area. In this study, we did not find a strong relationship between sapwood-to-leaf area and physical or climatic variables that are readily determinable at coarse scales, though the results suggest that climate may have a mediating influence on the relationship between sapwood-to-leaf area and height. Within temperate forests, canopy height alone explained a large amount of the variance in reference canopy conductance (r²=0.68)$(r^2=0.68)$ and this relationship may be more immediately applicable in the terrestrial ecosystem models.  相似文献   

Post-Last Glacial Maximum evolution of a “fjord-type” lake based on high-resolution seismic data: the Lago Roca/Acigami (southern Tierra del Fuego,Argentina/Chile)     

Donaldo Mauricio Bran  Jorge Gabriel Lozano  Dario Civile  Emanuele Lodolo  María E. Cerredo  Alejandro Tassone  Luca Baradello  Maurizio Grossi  Juan Vilas 《第四纪科学杂志》2020,35(3):396-409

Lago Roca/Acigami is a “fjord-type” lake located in the southernmost part of South America, in the proximity of the Beagle Channel. A high-resolution seismic survey was carried out to analyse the seismic stratigraphy of the lake and to shed some light on the post-Last Glacial Maximum history of the area. Six seismic units were recognised, and their nature and depositional context were interpreted using seismic stratigraphy and acoustic facies analysis. A buried large ridge was identified within the glacial unit (SU1), interpreted as a frontal moraine that indicates a stabilisation phase. After retreat of the glacier from the basin, the trough was flooded by meltwater and a lake developed (SU2). The seismic facies, from bottom to top, depict a transition from ice-contact (SU2; SU3) to ice-distal proglacial conditions (SU4). A thick draping unit (SU5) marks a marine transgressive event and the instauration of a fjord environment in the basin. The marine transgression was a rapid event preceded by a fall in the lake level that caused an erosional unconformity. During the fjord phase the sedimentation remained controlled by meltwater discharge. Sea level fall, and subsequent disconnection from the Beagle Channel was accompanied by a progradation of the glaciofluvial deltaic sediments and the occurrence of several mass-wasting deposits (SU6). © 2019 John Wiley & Sons, Ltd.  相似文献   

Strategic elements in the Fort Cooper Coal Measures: potential rare earth elements and other multi-product targets     

J. H. Hodgkinson  M. Grigorescu 《Australian Journal of Earth Sciences》2020,67(3):305-319

Abstract

Mineral matter in coals has been found to host valuable elements including germanium, lithium and rare-earth elements (REE), but such content of Australian coals remains under-explored. The aim of this paper is to provide a proof-of-concept study that determines elemental concentrations in the mineral matter of the high-ash, Fort Cooper Coal Measures (FCCM), Bowen Basin, Queensland. Coal in the FCCM has good coking properties but has not been extensively explored owing to its high ash content. This study performs a preliminary assessment of the elements from the coal portion that would typically become waste after washing or combustion. Given that the needs for industrial extraction methods will change over time, cataloguing and documenting the elemental composition of coal may assist future development of multiple products for the benefit of both the coal and mineral industries. This preliminary study has revealed similar elevations of REE and higher-than-average crustal concentrations of lithium, bismuth and scandium in some of the samples. Further analyses will be required on a larger dataset to better understand elemental associations and explore spatial patterns of elemental content that may indicate localised enrichments. Understanding the potential of valuable elements in the FCCM may stimulate interest in multiple-product-coal (or elemental-coal) mining in this under-exploited resource and further encourage the reduction of waste from other Australian coals at the wash-plant stage.  相似文献   

Ejective and Sweeping Motions Above a Peatland and Their Role in Relaxed-Eddy-Accumulation Measurements and Turbulent Transport Modelling     

Gabriel Katul  Olli Peltola  Tiia Grönholm  Samuli Launiainen  Ivan Mammarella  Timo Vesala 《Boundary-Layer Meteorology》2018,169(2):163-184

The three turbulent velocity components, water vapour (\(\text {H}_2\text {O}\)), carbon dioxide (\(\text {CO}_{2}\)), and methane (\(\text {CH}_{4}\)) concentration fluctuations are measured above a boreal peatland and analyzed using conditional sampling and quadrant analysis. The overarching question to be addressed is to what degree lower-order cumulant expansion methods describe transport efficiency and the relative importance of ejections and sweeps to momentum, \(\text {CH}_{4}\), \(\text {CO}_{2}\) and \(\text {H}_2\text {O}\) fluxes across a range of atmospheric flow regimes. The patchy peatland surface creates distinctly different source and sink distributions for the three scalars in space and time thereby adding to the uniqueness of the set-up. The measured and modelled fractional contributions to the momentum flux show that sweep events dominate over ejections in agreement with prior studies conducted in the roughness sublayer. For scalar fluxes, ejections dominate the turbulent fluxes over sweeps. While ejective motions persist longer for momentum transport, sweeping events persist longer for all three scalars. Third-order cumulant expansions describe many of the results detailed above, and the results are surprising given the highly non-Gaussian distribution of \(\text {CH}_{4}\) turbulent fluctuations. Connections between the asymmetric contributions of sweeps and ejections and the flux-transport term arising in scalar turbulent-flux-budget closure are derived and shown to agree reasonably well with measurements. The proposed model derived here is much simpler than prior structural models used to describe laboratory experiments. Implications of such asymmetric contributions on, (i) the usage of the now proliferating relaxed-eddy-accumulation method in turbulent flux measurements, (ii) the constant-flux assumption, and (iii) gradient-diffusion closure models are presented.  相似文献   

Resuspension of urban soils as a persistent source of lead poisoning in children: A review and new directions   总被引：1，自引：0，他引：1  

Mark A.S. Laidlaw  Gabriel M. Filippelli   《Applied Geochemistry》2008,23(8):2021-2039

Urban soils act as the repository for a number of environmental burdens, including Pb. Significant attention has been devoted to reducing Pb burdens to children with outstanding success, but the fact that blood Pb levels above 10  μg/dL are disproportionately found in children living in many USA cities (15–20% in some cities compared to a national average of less than 2%) indicates that not all of the sources have been eliminated. Although the health risk of fine particulates has begun to raise concerns in cities, little attention has been paid to Pb associated with these particulates and the potential role of this pathway for continued Pb burdens of urban youth. This review summarizes recent work on particulate resuspension and the role of resuspension of Pb-enriched urban soils as a continued source of bio-available Pb both outside and inside homes, then presents recent efforts to model Pb burdens to children based on the atmospheric parameters that drive particulate resuspension. A strong seasonal relationship is found between atmospheric particulate loading and blood Pb levels in children, and new particulate loading models are presented for a range of US cities involved in the Interagency Monitoring of Protected Visual Environments (IMPROVE) program. These seasonal particulate loading models have implications for a number of respiratory health impacts, but can also be used to calculate seasonal patterns in bio-available Pb redistribution onto contact surfaces (the primary pathway for ingestion-related uptake in toddlers) and assist clinicians in interpreting time-specific blood Pb tests.  相似文献   

S1: A small but perplexing component of the tide     

Gabriel Godin 《Ocean Dynamics》1990,43(2):73-83

  相似文献   

Estimation of surface heat and momentum fluxes using the flux-variance method above uniform and non-uniform terrain   总被引：4，自引：0，他引：4  

Gabriel Katul  Stewart M. Goltz  Cheng-I Hsieh  Yung Cheng  Fred Mowry  John Sigmon 《Boundary-Layer Meteorology》1995,74(3):237-260

Eddy-correlation measurements above an uneven-aged forest, a uniform-irrigated bare soil field, and within a grass-covered forest clearing were used to investigate the usefulness of the fluxvariance method above uniform and non-uniform terrain. For this purpose, the Monin and Obukhov (1954) variance similarity functions were compared with direct measurements. Such comparisons were in close agreement for momentum and heat but not for water vapor. Deviations between measured and predicted similarity functions for water vapor were attributed to three factors: 1) the active role of temperature in surface-layer turbulence, 2) dissimilarity between sources and sinks of heat and water vapor at the ground surface, and 3) the non-uniformity in water vapor sources and sinks. It was demonstrated that the latter non-uniformity contributed to horizontal gradients that do not scale with the vertical flux. These three factors resulted in a turbulence regime that appeared more efficient in transporting heat than water vapor for the dynamic convective sublayer but not for the dynamic sublayer. The agreement between eddy-correlation measured and flux-variance predicted sensible heat flux was better than that for latent heat flux at all three sites. The flux-variance method systematically overestimated the latent heat flux when compared to eddy-correlation measurements. It was demonstrated that the non-uniformity in water vapor sources reduced the surface flux when compared to an equivalent uniform terrain subjected to identical shear stress, sensible heat flux, and atmospheric water vapor variance. Finally, the correlation between the temperature and water vapor fluctuations was related to the relative efficiency of surface-layer turbulence in removing heat and water vapor. These relations were used to assess critical assumptions in the derivation of the flux-variance formulation.  相似文献   

Latent and sensible heat flux predictions from a uniform pine forest using surface renewal and flux variance methods   总被引：1，自引：0，他引：1  

Gabriel Katul  Cheng-I Hsieh  Ram Oren  David Ellsworth  Nathan Phillips 《Boundary-Layer Meteorology》1996,80(3):249-282

A surface renewal model that links organized eddy motion to the latent and sensible heat fluxes is tested with eddy correlation measurements carried out in a 13m tall uniform Loblolly pine plantation in Duke Forest, Durham, North Carolina. The surface renewal model is based on the occurance of ramp-like patterns in the scalar concentration measurements. To extract such ramp-like patterns from Eulerian scalar concentration measurements, a newly proposed time-frequency filtering scheme is developed and tested. The time-domain filtering is carried out using compactly-supported orthonormal wavelets in conjunction with the Universal Wavelet Thresholding approach of Donoho and Johnstone, while the frequency filtering is carried out by a band-pass sine filter centered around the ramp-occurrence frequency as proposed by other studies. The method was separately tested for heat and water vapour with good agreement between eddy correlation flux measurements and model predictions. The usefulness of the flux-variance method to predict sensible and latent heat fluxes is also considered. Our measurements suggest that the simple flux-variance method reproduces the measured heat and momentum fluxes despite the fact that the variances were measured within the roughness sublayer and not in the surface layer. Central to the predictions of water vapour fluxes using the flux-variance approach is the similarity between heat and water vapour transport by the turbulent air flow. This assumption is also investigated for this uniform forest terrain.  相似文献