Particle fluxes dynamics in Blanes submarine canyon (Northwestern Mediterranean)     

Diana Zúñiga  M. Mar Flexas  Anna Sanchez-Vidal  Johan Coenjaerts  Antoni Calafat  Gabriel Jordà  Jordi García-Orellana  Joan Puigdefàbregas  Miquel Canals  Manuel Espino  Francesc Sardà  Joan B. Company 《Progress in Oceanography》2009,82(4):239-251

Within the framework of the multidisciplinary RECS project and with the aim of describing the particle flux transfer from the continental shelf to the deep basin, an array of five mooring lines equipped with a total of five pairs of PPS3/3 sequential-sampling sediment traps and RCM-7/8 current meters were deployed 30 m above the bottom from March 2003 to March 2004 inside and outside the Blanes Canyon. One mooring line was located in the upper canyon at 600 m depth, one in the canyon axis at 1700 m depth and other two close to the canyon walls at 900 m depth. A fifth mooring line was deployed in the continental open slope at 1500 m water depth.The highest near-bottom downward particle flux (14.50 g m⁻² d⁻¹) was recorded at the trap located in the upper canyon (M1), where continental inputs associated with the presence of the Tordera River are most relevant. On the other hand, the downward fluxes (4.35 g m⁻² d⁻¹) in the canyon axis (M2) were of the same order as those found in the western flank (M3) of the canyon. Both values were clearly higher than the value (1.95 g m⁻² d⁻¹) recorded at the eastern canyon wall (M4). The open slope (M5) mass flux (5.42 mg m⁻² d⁻¹) recorded by the sediment trap located outside the canyon system was three orders of magnitude lower than the other values registered by the inner canyon stations. The relevance of our data is that it explains how the transport pathway in the canyon occurs through its western flank, where a more active and persistent current toward the open ocean was recorded over the entire year of the experiment.Off-shelf sediment transport along the canyon axis showed clear differences during the period of the study, with some important events leading to strong intensifications of the current coupled with large transport of particle fluxes to the deepest parts of the canyon. Such events are primarily related to increases in river discharge and the occurrence of strong storms and cascading events during the winter.In summary, in this study it is shown that the dynamics of the water masses and the currents in the study area convert the sharp western flank of the Blanes Canyon in a more active region that favors erosion processes than the eastern flank, which has a smoother topography and where the absence of erosional conditions yields to steadier sedimentary processes.  相似文献   

Model calibration using hydropedological insights to improve the simulation of internal hydrological processes using SWAT+     

Edward Smit  George van Zijl  Edward Riddell  Johan van Tol 《水文研究》2024,38(5):e15158

Soils affect the distribution of hydrological processes by partitioning precipitation into different components of the water balance. Therefore, understanding soil-water dynamics at a catchment scale remains imperative to future water resource management. In this study, the value of hydropedological insights was examined to calibrate a processes-based model. Soil morphology was used as soft data to assist in the calibration of the Soil Water Assessment Tool (SWAT+) model at five different catchment scales (48, 56, 174, 674, and 2421 km²) in the Sabie River catchment, South Africa. The aim of this study was to calibrate the SWAT+ model to accurately simulate long-term monthly streamflow predictions as well as to reflect internal soil hydrological processes using a procedure focusing on hydropedology as a calibration tool in a multigauge system. Results indicated that calibration improved streamflow predictions where R² improved by 2%–8%. Nash-Sutcliffe Efficiency (NSE) improved from negative correlations to values exceeding 0.5 at four of the five catchment scales compared to the uncalibrated model. Results confirm that soil mapping units can be calibrated individually within SWAT+ to improve the representation of hydrological processes. Particularly, the spatial linkage between hydropedology and hydrological processes, which is captured within the soil map of the catchment, can be adequately reflected within the model simulations after calibration. This research will lead to an improved understanding of hydropedology as soft data to improve hydrological modelling accuracy.  相似文献   

Toward accountable land use mapping: Using geocomputation to improve classification accuracy and reveal uncertainty     

Johan Beekhuizen  Keith C. Clarke 《International Journal of Applied Earth Observation and Geoinformation》2010

The classification of satellite imagery into land use/cover maps is a major challenge in the field of remote sensing. This research aimed at improving the classification accuracy while also revealing uncertain areas by employing a geocomputational approach. We computed numerous land use maps by considering both image texture and band ratio information in the classification procedure. For each land use class, those classifications with the highest class-accuracy were selected and combined into class-probability maps. By selecting the land use class with highest probability for each pixel, we created a hard classification. We stored the corresponding class probabilities in a separate map, indicating the spatial uncertainty in the hard classification. By combining the uncertainty map and the hard classification we created a probability-based land use map, containing spatial estimates of the uncertainty. The technique was tested for both ASTER and Landsat 5 satellite imagery of Gorizia, Italy, and resulted in a 34% and 31% increase, respectively, in the kappa coefficient of classification accuracy. We believe that geocomputational classification methods can be used generally to improve land use and land cover classification from imagery, and to help incorporate classification uncertainty into the resultant map themes.  相似文献   

Morphology and stratigraphy from several deglaciations in the Transtrand Mountains,western Sweden     

Johan Kleman  Ingmar BorgstrM  Ann-Marie Robertsson  Marianne Lillieskld 《第四纪科学杂志》1992,7(1):1-17

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Measuring coastal cliff retreat in the Kongsfjorden area, Svalbard, using terrestrial photogrammetry     

Bjørn Wangensteen  Trond Eiken  Rune S. Ødegård  & Johan Ludvig Sollid 《Polar research》2007,26(1):14-21

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Accessory minerals of the Cínovec (Zinnwald) granite cupola, Czech Republic: indicators of petrogenetic evolution     

Z. Johan  V. Johan 《Mineralogy and Petrology》2005,83(1-2):113-150

Summary A fully cored drillhole was drilled to 1596m by the Czech Geological Survey in 1961–1963 in the central part of the Cínovec (Zinnwald) granite cupola. Two types of granite were intersected: zinnwaldite granite (ZG), observed down to a depth of 730m, and protolithionite granite (PG), occurring to the end of the hole. The core was used to study the distribution and chemistry of: zircon, thorite, xenotime, monazite, bastnäsite, synchysite, REE oxyfluorides and hydroxyfluorides. Zircon occurs throughout the drillcore; it is strongly hydrated and fluorinated with about 18.5wt.% H₂O content in the apical part of the cupola. Its F-content reaches 2.41wt.%. Within the PG, the F concentration in zircon is low. Zircon is poor in Th and U and its HfO₂ contents vary from 1.01 to 5.24wt.%. Thorite is common in the PG, becoming rare in the ZG. It is strongly hydrated (up to 14wt.% H₂O) and fluorinated (up to 2.04wt.% F). Extensive solid solution between ThSiO₄ and YPO₄ was observed. Xenotime is strongly hydrated (up to 16wt.% H₂O), but its F content is low (<0.31wt.%). Two types of monazite were identified: Th-rich (up to 9.3wt.% ThO₂) in the ZG, and Th-poor (<2.5wt.% ThO₂) in the PG. Monazite remained stable during the hydration and fluorination process. Its REE chondrite-normalized distribution patterns show negative anomalies for La and Nd and a pronounced negative anomaly for Eu. Chemical compositions of several REE oxyfluorides and hydroxyfluorides were studied. REE fluorocarbonates are represented by bastnäsite and synchysite. Bastnäsite is abundant in the ZG. Its chondrite-normalized REE patterns are characterized by an important negative Eu anomaly and downward kinks at La and Nd. Synchysite-(Ce) and synchysite-(Y) are particularly well developed in the deeper parts of the cupola, and exhibit REE distribution patterns characterized by a weak negative Eu anomaly (synchysite-(Ce)), or a weak positive Eu anomaly (synchysite-(Y)).The distribution of accessory minerals reveals five major evolution stages: (1) Early magmatic crystallization of albite and orthoclase. (2) A late magmatic stage comprising protolithionite, quartz, accessory zircon, thorite, xenotime and monazite. (3) Interaction of this magmatic association with a fluid phase rich in F, CO₂ and H₂O, leading to the transformation protolithionite zinnwaldite and to the remobilisation of Nb, Ta, Ti, W, Sn. Accessory minerals formed during stage (2) were hydrated and fluorinated, except monazite. (4) The transfer of volatiles into the apical part of the cupola followed by the opening of the magmatic system generated microgranites and hydrolysis-type reactions leading to the appearance of REE oxyfluorides and hydroxyfluorides. (5) A late CO₂- and F-rich fluid phase was responsible for the deposition of REE fluorocarbonates. Monazite and xenotime became unstable in the apical part of the cupola. An influx of fluids with high Ca-activity occurred late during stage (5) and led to the formation of synchysite, and finally to the extensive precipitation of fluorite.  相似文献   

Colloidal rare earth elements in a boreal river: Changing sources and distributions during the spring flood     

Karen Andersson  David Turner  Björn Stolpe  Johan Ingri 《Geochimica et cosmochimica acta》2006,70(13):3261-3274

Variations in the physico-chemical speciation of the rare earth elements (REE) have been investigated in a subarctic boreal river during an intense spring flood event using prefiltered (<100 μm) samples, cross-flow (ultra)filtration (CFF), flow field-flow fractionation (FlFFF), and diffusive gradients in thin films (DGT). This combination of techniques has provided new information regarding the release and transport of the REE in river water. The colloidal material can be described in terms of two fractions dominated by carbon and iron, respectively. These two fractions, termed colloidal carrier phases, showed significant temporal changes in concentration and size distribution. Before the spring flood, colloidal carbon concentrations were low, the colloids being dominated by relatively large iron colloids. Colloidal concentrations increased sharply during the spring flood, with smaller carbon colloids dominating. Following the spring flood, colloidal concentrations decreased again, smaller carbon colloids still dominating. The REE are transported mainly in the particulate and colloidal phases. Before the spring flood, the REE composition of all measured fractions was similar to local till. During the spring flood, the REE concentrations in the colloidal and particulate fractions increased. The increase was most marked for the lighter REE, which therefore showed a strong enrichment when normalized to local till. Following the spring flood, the REE concentrations decreased again and reverted to a distribution similar to local till. These changes in the concentration and distributions of carbon iron and REE are interpreted in terms of changing hydrological flow paths in soil and bedrock which occur during the spring flood.  相似文献   

Local mobility and the spatial dynamics of measles in a rural area of Kenya     

Alan Ferguson  Johan Leeuwenburg 《GeoJournal》1981,5(4):315-322

Population mobility at different scales is important in the analysis of contagious diseases. The role of local mobility among young children is related to spatial and temporal patterns of measles in part of rural Kenya. The dynamics of measles are examined over a period of 3 1/2 years, during which there were two epidemics; the path of the second of these epidemics is studied, using a spatial averaging technique (the centroid). Limited local mobility of children under the age of five, related to low levels of susceptibility provides a probable explanation of the slow diffusion of measles epidemics.This paper is reprinted from Rural Africana, Spring 1981, with the kind permission of the Editors.  相似文献   

Short gravity waves on steady non-uniform currents obtained through up-/downwelling     

Johan N. Hartnack 《Ocean Engineering》2000,27(4):831

Small amplitude water waves propagating in a medium with a steady non-uniform current are investigated. The non-uniform current is obtained by up- or downwelling through the horizontal bed. A new locally valid velocity potential correct to the second order is derived describing the combined wave–current motion. From this solution expressions for the local evolution of the wave amplitude and the wave number are extracted. These expressions are compared with the results found using the principle of wave action conservation and the linear dispersion relation, and good agreement is found at small distances compared to the wavelength. Unlike earlier works there is no restriction to deep water. The results valid for deep water are found as a special case of the general solution and agree with the solution found by Longuet-Higgins, M.S. and Stewart, R.W. (1961) The changes in amplitude of short gravity waves on steady non-uniform currents. Journal of Fluid Mechanics, 10(4), 529–549. Furthermore, it is shown that the principle of wave action conservation in fact holds for waves propagating in a medium with a steady non-uniform current maintained by up-/downwelling also on finite depth.  相似文献   

Time-series analysis of multi-resolution optical imagery for quantifying forest cover loss in Sumatra and Kalimantan,Indonesia     

Mark Broich  Matthew C. Hansen  Peter Potapov  Bernard Adusei  Erik Lindquist  Stephen V. Stehman 《International Journal of Applied Earth Observation and Geoinformation》2011

Monitoring loss of humid tropical forests via remotely sensed imagery is critical for a number of environmental monitoring objectives, including carbon accounting, biodiversity, and climate modeling science applications. Landsat imagery, provided free of charge by the U.S. Geological Survey Center for Earth Resources Observation and Science (USGS/EROS), enables consistent and timely forest cover loss updates from regional to biome scales. The Indonesian islands of Sumatra and Kalimantan are a center of significant forest cover change within the humid tropics with implications for carbon dynamics, biodiversity maintenance and local livelihoods. Sumatra and Kalimantan feature poor observational coverage compared to other centers of humid tropical forest change, such as Mato Grosso, Brazil, due to the lack of ongoing acquisitions from nearby ground stations and the persistence of cloud cover obscuring the land surface. At the same time, forest change in Indonesia is transient and does not always result in deforestation, as cleared forests are rapidly replaced by timber plantations and oil palm estates. Epochal composites, where single best observations are selected over a given time interval and used to quantify change, are one option for monitoring forest change in cloudy regions. However, the frequency of forest cover change in Indonesia confounds the ability of image composite pairs to quantify all change. Transient change occurring between composite periods is often missed and the length of time required for creating a cloud-free composite often obscures change occurring within the composite period itself. In this paper, we analyzed all Landsat 7 imagery with <50% cloud cover and data and products from the Moderate Resolution Imaging Spectroradiometer (MODIS) to quantify forest cover loss for Sumatra and Kalimantan from 2000 to 2005. We demonstrated that time-series approaches examining all good land observations are more accurate in mapping forest cover change in Indonesia than change maps based on image composites. Unlike other time-series analyses employing observations with a consistent periodicity, our study area was characterized by highly unequal observation counts and frequencies due to persistent cloud cover, scan line corrector off (SLC-off) gaps, and the absence of a complete archive. Our method accounts for this variation by generating a generic variable space. We evaluated our results against an independent probability sample-based estimate of gross forest cover loss and expert mapped gross forest cover loss at 64 sample sites. The mapped gross forest cover loss for Sumatra and Kalimantan was 2.86% of the land area, or 2.86 Mha from 2000 to 2005, with the highest concentration having occurred in Riau and Kalimantan Tengah provinces.  相似文献