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  • 1
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    Ground motions induced by a producing hydrocarbon reservoir that is overlain by a viscoelastic rocksalt layer: a numerical model (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-19
    Description: Hydrocarbon reservoir pressure depletion leads to stress changes inside the reservoir and ground deformation which is registered at the surface as subsidence. As reservoirs are often overlain by layers of rocksalt (or other evaporites), which are materials that flow so as to relax stresses inside them, there is the potential for time-varying surface subsidence. This work focuses on understanding the macroscopic mechanisms that lead to rocksalt flow-induced ground displacements. A Finite Element Model is used for this purpose in which the rocksalt layer is represented by a viscoelastic Maxwell material. Two distinct mechanisms that lead to displacement are observed. These are active during different stages of the deformation and have different timescales associated with them. An important observation is that the timescale for deformation that is measured at the ground surface is not equal to the timescale for deformation of a viscoelastic material element, but can be many times larger than that. The sensitivity of the response to the thickness and location of the rocksalt layer is also presented. Conclusions are drawn which allow for the relative importance of the presence of the rocksalt layer to be assessed and for a framework for understanding time-dependent subsidence above producing hydrocarbon reservoirs to be developed. Finally the changes in stress distribution around a producing reservoir are also briefly discussed.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 2
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    Comparing landscape evolution models to quantitative field data at the millennial time scale in the Belgian loess belt (2011)
    Wiley
    Details
    Publication Date: 2011-02-22
    Description: In this paper we compare three landscape evolution models with respect to their ability to correctly simulate measured 2500 year landscape evolution in two small catchments in the Belgian Loess Belt. WATEM LT and LAPSUS both model tillage and water erosion and deposition and have detachment-limited descriptions for water erosion and deposition. Equations in LAPSUS are more mechanistic than those in WATEM LT. WATEM LTT resembles WATEM LT, but is a transport-limited model. All three models are DEM-based. Calibration and validation simulations were performed forward in time on (1D) transects for four spatial resolutions, and backward in time for (2D) catchments at 20 m resolution. For transects, model outputs were compared to discretized observations of transect shape. For catchments, outputs were compared to point observations of palaeo-altitude, averaged over landscape element classes. For transects, the three models performed well, resulting in Model Efficiency Factors of 0.92 to 0.99 for calibration and 0.62 to 0.96 for validation. However, for catchments, simulations showed that the transport-limited WATEM LTT model could not realistically simulate long-term landscape evolution. Performance of WATEM LT and LAPSUS at catchment scale was similar to that on transects, although LAPSUS has problems with backward calculation. Our tests demonstrate that a transport-limited approach cannot be used to model long-term landscape evolution in the Belgian loess Belt, which is in agreement with our theoretical and empirical understanding of soil erosion processes in this environment. The difference in performance between transport-limited and detachment-limited models is only clear when the models are evaluated in a 2D catchment. The lack of such distinction when models were applied in a 1D transect highlights the importance of evaluating landscape evolution models in a 2D setting so that effects of flow convergence/divergence can be accounted for. Copyright © 2011 John Wiley & Sons, Ltd.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
    Published by Wiley
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  • 3
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    The impact of agricultural soil erosion on the global carbon cycle (2007)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2007-10-27
    Description: Agricultural soil erosion is thought to perturb the global carbon cycle, but estimates of its effect range from a source of 1 petagram per year(-1) to a sink of the same magnitude. By using caesium-137 and carbon inventory measurements from a large-scale survey, we found consistent evidence for an erosion-induced sink of atmospheric carbon equivalent to approximately 26% of the carbon transported by erosion. Based on this relationship, we estimated a global carbon sink of 0.12 (range 0.06 to 0.27) petagrams of carbon per year(-1) resulting from erosion in the world's agricultural landscapes. Our analysis directly challenges the view that agricultural erosion represents an important source or sink for atmospheric CO2.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Van Oost, K -- Quine, T A -- Govers, G -- De Gryze, S -- Six, J -- Harden, J W -- Ritchie, J C -- McCarty, G W -- Heckrath, G -- Kosmas, C -- Giraldez, J V -- da Silva, J R Marques -- Merckx, R -- New York, N.Y. -- Science. 2007 Oct 26;318(5850):626-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Physical and Regional Geography Research Group, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium. kristof.vanoost@uclouvain.be〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17962559" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Comment on "Managing soil carbon" (I) (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-09-14
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Van Oost, K -- Govers, G -- Quine, T A -- Heckrath, G -- New York, N.Y. -- Science. 2004 Sep 10;305(5690):1567; author reply 1567.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Physical and Regional Geography Research Group, K. U. Leuven, Redingenstraat 16b, 3000 Leuven, Belgium. k.vanoost@exeter.ac.ukand〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15361608" target="_blank"〉PubMed〈/a〉
    Keywords: Agriculture/*methods ; Carbon/*analysis ; *Soil/analysis ; Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Long-term organic carbon sequestration in tidal marsh sediments is dominated by old-aged allochthonous inputs in a macro-tidal estuary (2018)
    Wiley
    Details
    Publication Date: 2018-02-14
    Description: Tidal marshes are vegetated coastal ecosystems that are often considered as hotspots of atmospheric CO 2 sequestration. Although large amounts of organic carbon (OC) are indeed being deposited on tidal marshes, there is no direct link between high OC deposition rates and high OC sequestration rates due to two main reasons. First, the deposited OC may become rapidly decomposed once it is buried and, second, a significant part of preserved OC may be allochthonous OC that has been sequestered elsewhere. In this study we aimed to identify the mechanisms controlling long-term OC sequestration in tidal marsh sediments along an estuarine salinity gradient (Scheldt estuary, Belgium and The Netherlands). Analyses of deposited sediments have shown that OC deposited during tidal inundations is up to millennia old. This allochthonous OC is the main component of OC that is effectively preserved in these sediments, as indicated by the low radiocarbon content of buried OC. Furthermore, OC fractionation showed that autochthonous OC is decomposed on a decadal timescale in saltmarsh sediments, while in freshwater marsh sediments locally-produced biomass is more efficiently preserved after burial. Our results show that long-term OC sequestration is decoupled from local biomass production in the studied tidal marsh sediments. This implies that OC sequestration rates are greatly overestimated when they are calculated based on short-term OC deposition rates, which are controlled by labile autochthonous OC inputs. Moreover, as allochthonous OC is not sequestered in-situ, it does not contribute to active atmospheric CO 2 sequestration in these ecosystems. A correct assessment of the contribution of allochthonous OC to the total sedimentary OC stock in tidal marsh sediments as well as a correct understanding of the long-term fate of locally-produced OC are both necessary to avoid overestimations of the rate of in-situ atmospheric CO 2 sequestration in tidal marsh sediments. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 6
    Electronic Resource
    Electronic Resource
    Impact of land use changes on the hydrological properties of volcanic ash soils in South Ecuador (2002)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 18 (2002), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. The effect of land use on the water retention capacity of Umbric Andosols in south Ecuador was studied. The objective was to acquire a better insight into the hydrological processes of the ecosystem and the role of the soil, in order to assess the impact of changing soil properties due to land use change on the hydrology of the high Andes region. Field data on the water retention capacity at wilting point of Umbric Andosols were collected for both cultivated field conditions and original bush vegetation. The pH in water and in NaF, texture, organic matter content and dry bulk density were measured to show which physicochemical soil characteristics are responsible for the water retention of the Umbric Andosols and for the irreversible loss in water retention due to air drying. Organic matter content appears to be very important and certainly more important than allophane clay content. Water retention of the organic litter layer was calculated to be 16 mm, this would be lost when vegetation was cleared and the land cultivated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.2002.tb00226.x
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  • 7
    Electronic Resource
    Electronic Resource
    Effectiveness of stone bunds in controlling soil erosion on cropland in the Tigray Highlands, northern Ethiopia (2005)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 21 (2005), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Use of stone bunds to enhance soil and water conservation was first introduced to Tigray, northern Ethiopia in 1981. This study was designed to examine the factors that control the effectiveness of bunds installed on cropland. Qualitative and quantitative assessments of soil loss and sediment accumulation were conducted on 202 plots at 12 representative sites in Dogu'a Tembien district. Mean annual soil loss from the foot of the bunds due to tillage erosion was estimated at 39kgm−1yr−1 or 20tha−1yr−1, a rate which decreased with increasing age of bund. The assessed mean annual soil loss rate by sheet and rill erosion in the absence of stone bunds is 57tha−1yr−1. The mean measured annual rate of sediment accumulation behind the stone bunds is 119kgm−1yr−1/sp or 59tha−1yr−1. The measurements show that the introduction of stone bunds to the region has led to a 68% reduction in annual soil loss due to water erosion. This reduction is due to the accumulation of sediment behind the stone bunds, which occurs faster in the early years after construction and decreases as the depression behind the bunds becomes filled with sediment. New stone bunds are particularly effective in trapping sediment in transport, but regular maintenance and increase in height of the bunds is necessary to maintain their effectiveness. The average USLE P factor for stone bunds in the study area is estimated to be 0.32.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.2005.tb00401.x
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  • 8
    Electronic Resource
    Electronic Resource
    The effectiveness of loose rock check dams for gully control in Tigray, northern Ethiopia (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 20 (2004), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Over the last two decades, large gully control programmes have been established in Ethiopia. Based on detailed observations and measurements of 400 check dams in the highlands near Hagere Selam (Tigray, northern Ethiopian Highlands), the effectiveness of the check dam technique was assessed. In this study, catchment area, slope gradient, technical characteristics and the presence of smectite clays are the main factors controlling dam stability. Simple and logistic regression techniques were used to analyse the data. The frequent collapse of dams (39% after two years) is strongly associated with drainage area (A) and slope gradient of the soil surface near the gully (S), the product of these factors (S×A) being a proxy for runoff energy. Good functioning dams have a spillway, apron, concave plan form (when looking downslope) and are built at vertical intervals and with heights that result in a negative slope gradient of the line connecting the spillway and the foot of the upstream dam. Therefore, a reverse slope of this line is recommended. Furthermore, if large cracks are present in smectite-rich soils, the construction of check dams can lead to piping and concentrated flow bypassing the dam. Given that the collapse of some check dams seems inevitable where catchment areas are large or there are steep slopes, it is necessary to repair dams as soon as partial collapse starts and to complement this gully control technique with biological control measures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.2004.tb00337.x
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  • 9
    Electronic Resource
    Electronic Resource
    Evaluating an integrated approach to catchment management to reduce soil loss and sediment pollution through modelling (2002)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 18 (2002), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Soil erosion and sediment delivery cause many environmental problems posing a substantial financial burden upon society. Policy makers therefore look for a strategy to minimize their impact. The spatial nature of soil erosion and sediment delivery, as well as the variety of possible soil conservation and sediment control measures, requires an integrated approach to catchment management. To evaluate such management, a spatially distributed soil erosion and sediment delivery model is necessary. Such a model (WaTEM/SEDEM) was applied to three agricultural catchments in Flanders (Belgium). The model was first used to identify where the measures to control soil loss should be taken. Secondly, a scenario analysis was used to select the most effective set of techniques. The findings showed that soil conservation measures taken in fields are not only effective in reducing on-site soil loss, but also in drastically reducing sediment yield. Off-site sediment control measures appear to be much less effective in reducing sediment yield than previously thought. The results also suggest that data from field experiments cannot be extrapolated to a catchment scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.2002.tb00257.x
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  • 10
    Electronic Resource
    Electronic Resource
    Simulation of the redistribution of soil by tillage on complex topographies (2003)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 54 (2003), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Tillage redistributes soil and contributes significantly to the within-field soil variation, especially on topographically complex terrain. Although the basic principles of the redistribution are well understood, models for simulating the redistribution are poor predictors. This paper presents a modelling structure that allows a simulation of the redistribution of soil constituents on complex topographies for various tillage implements. The model simulates the redistribution of soil constituents by convoluting the probability distribution of the tillage displacement with the spatial distribution of the soil constituents. The probability distributions in two dimensions are derived from a series of tillage experiments conducted with a mouldboard plough at various positions in the landscape. Furthermore, the effects of topography and tillage direction on the probability distributions were characterized and implemented in the model. A first application showed that the direction of tillage significantly affects the long-term redistribution of soil constituents. The inclusion of other implements in the model was explored, and we found that data in the literature could be used for simulating the long-term effects of tillage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2003.00470.x
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