Spatio-temporal analysis of tree height in a young cork oak plantation     

L. Sedda  P.M. Atkinson  M.R. Filigheddu  G. Cotzia  S. Dettori 《International journal of geographical information science》2013,27(7):1083-1096

Cork oak is one of the most valuable natural forest genera in the Mediterranean basin. Modelling cork oak growth has been a challenge for foresters in recent years because of strong site and genetic influences, below-ground competition, management regimes and age effects. Because cork productivity is related to forest height, which is, in turn, related directly with site characteristics, an increase in the accuracy of height prediction implies improved productivity estimation. A Bayesian maximum entropy (BME) geostatistical model was applied to characterize the space–time pattern of height of young cork oak in a forest stand from central Sardinia in the years 2000, 2002, 2003, 2006 and 2008. Cork oak height maps were produced for each of the 5 years. The main goals were to analyse and interpret through time (i) the changes in spatial correlation and (ii) the changes in spatial distribution of cork oak height. The plantation was characterized by an increasing spatial dependence through time, whereas the temporal range was 2 years. Cork oak height was significantly correlated with wind speed (reduced by a neighbouring forest) in all the years implying a single trend. The correlations were larger for 2006 and 2008 than for previous years. Three other environmental variables (shade, elevation and slope) were less significant and their influence restricted to 2 years only. This research has several implications for the management of cork oak in the young phase.  相似文献   

The marine controlled source electromagnetic response of a steel borehole casing: applications for the NEPTUNE Canada gas hydrate observatory   总被引：1，自引：0，他引：1  

Andrei Swidinsky  R. Nigel Edwards  Marion Jegen 《Geophysical Prospecting》2013,61(4):842-856

Gas hydrates are a potential energy resource, a possible factor in climate change and an exploration geohazard. The University of Toronto has deployed a permanent seafloor time‐domain controlled source electromagnetic (CSEM) system offshore Vancouver Island, within the framework of the NEPTUNE Canada underwater cabled observatory. Hydrates are known to be present in the area and due to their electrically resistive nature can be monitored by 5 permanent electric field receivers. However, two cased boreholes may be drilled near the CSEM site in the near future. To understand any potential distortions of the electric fields due to the metal, we model the marine electromagnetic response of a conductive steel borehole casing. First, we consider the commonly used canonical model consisting of a 100 Ωm, 100 m thick resistive hydrocarbon layer embedded at a depth of 1000 m in a 1 Ωm conductive host medium, with the addition of a typical steel production casing extending from the seafloor to the resistive zone. Results show that in both the frequency and time domains the distortion produced by the casing occurs at smaller transmitter‐receiver offsets than the offsets required to detect the resistive layer. Second, we consider the experimentally determined model of the offshore Vancouver Island hydrate zone, consisting of a 5.5 Ωm, 36 m thick hydrate layer overlying a 0.7 Ωm sedimentary half‐space, with the addition of two borehole casings extending 300 m into the seafloor. In this case, results show that the distortion produced by casings located within a 100 m safety zone of the CSEM system will be measured at 4 of the 5 receivers. We conclude that the boreholes must be positioned at least 200 m away from the CSEM array so as to minimize the effects of the casings.  相似文献   

Novel observations of benthic enrichment in contrasting flow regimes with implications for marine farm monitoring and management     

Nigel B. Keeley  Barrie M. Forrest  Catriona K. Macleod 《Marine pollution bulletin》2013,66(1-2):105-116

We examine macrofaunal and physico-chemical responses to organic enrichment beneath salmon farms in contrasting flow environments, and reveal pronounced flow-related differences in the magnitude and spatial extent of effects. Total macrofaunal abundances at high flow sites were nearly an order of magnitude greater than at comparable low flow sites, representing a significant benthic biomass. These very high abundances occurred in conjunction with moderate-to-high species richness, and were evident in the absence of appreciable organic matter accumulation. Biological responses to increasing sulfide were variable; however a significant biological threshold was evident at 1500 μM. Macrofaunal responses at high flow sites differed substantially from the Pearson–Rosenberg model. The atypical ecological conditions were attributed to (i) limited accumulation of fine sediments, (ii) maintenance of aerobic conditions in near-surface sediments, and (iii) an abundant food supply. Thus, enhanced resilience to organic waste at well-flushed sites appears related to both biological and physical processes.  相似文献   

Erosive water level regime and climatic variability forcing of beach–dune systems on south‐western Vancouver Island,British Columbia,Canada     

Derek K. Heathfield  Ian J. Walker  David E. Atkinson 《地球表面变化过程与地形》2013,38(7):751-762

Increases in the frequency and magnitude of extreme water levels and storm surges are correlated with known indices of climatic variability (CV), including the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), along some areas of the British Columbia coast. Since a shift to a positive PDO regime in 1977, the effects of ENSO events have been more frequent, persistent, and intense. Teleconnected impacts include more frequent storms, higher surges, and enhanced coastal erosion. The response of oceanographic forcing mechanisms (i.e. tide, surge, wave height, wave period) to CV events and their role in coastal erosion remain unclear, particularly in western Canada. As a first step in exploring the interactions between ocean–atmosphere forcing and beach–dune responses, this paper assembles the historic erosive total water level (TWL) regime and explores relations with observed high magnitude storms that have occurred in the Tofino‐Ucluelet region (Wickaninnish Bay) on the west coast of Vancouver Island, British Columbia, Canada. Extreme events where TWL exceeded an erosional threshold (i.e. elevation of the beach–foredune junction) of 5·5 m aCD are examined to identify dominant forcing mechanisms and to classify a regime that describes erosive events driven principally by wave conditions (61·5%), followed by surge (21·8%), and tidal (16·7%) effects. Furthermore, teleconnections between regional CV phenomena, extreme storm events and, by association, coastal erosion, are explored. Despite regional sea level rise (eustatic and steric), rapid crustal uplift rates have resulted in a falling relative sea level and, in some sedimentary systems, shoreline progradation at rates approaching +1·5 m a^–1 over recent decades. Foredune erosion occurs locally with a recurrence interval of approximately 1·53 years followed by rapid rebuilding due to high onshore sand supply and often in the presence of large woody debris and rapidly colonizing vegetation in the backshore. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A tribute to Ei Horikoshi (1932–2009)     

Masaaki Shimizu  Shigeru Otoh  Nigel J. Cook 《Resource Geology》2012,62(4):327-328

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Evaluating a thermal image sharpening model over a mixed agricultural landscape in India     

C. Jeganathan  N.A.S. Hamm  S. Mukherjee  P.M. Atkinson  P.L.N. Raju  V.K. Dadhwal 《International Journal of Applied Earth Observation and Geoinformation》2011

Fine spatial resolution (e.g., <300 m) thermal data are needed regularly to characterise the temporal pattern of surface moisture status, water stress, and to forecast agriculture drought and famine. However, current optical sensors do not provide frequent thermal data at a fine spatial resolution. The TsHARP model provides a possibility to generate fine spatial resolution thermal data from coarse spatial resolution (≥1 km) data on the basis of an anticipated inverse linear relationship between the normalised difference vegetation index (NDVI) at fine spatial resolution and land surface temperature at coarse spatial resolution. The current study utilised the TsHARP model over a mixed agricultural landscape in the northern part of India. Five variants of the model were analysed, including the original model, for their efficiency. Those five variants were the global model (original); the resolution-adjusted global model; the piecewise regression model; the stratified model; and the local model. The models were first evaluated using Advanced Space-borne Thermal Emission Reflection Radiometer (ASTER) thermal data (90 m) aggregated to the following spatial resolutions: 180 m, 270 m, 450 m, 630 m, 810 m and 990 m. Although sharpening was undertaken for spatial resolutions from 990 m to 90 m, root mean square error (RMSE) of <2 K could, on average, be achieved only for 990–270 m in the ASTER data. The RMSE of the sharpened images at 270 m, using ASTER data, from the global, resolution-adjusted global, piecewise regression, stratification and local models were 1.91, 1.89, 1.96, 1.91, 1.70 K, respectively. The global model, resolution-adjusted global model and local model yielded higher accuracy, and were applied to sharpen MODIS thermal data (1 km) to the target spatial resolutions. Aggregated ASTER thermal data were considered as a reference at the respective target spatial resolutions to assess the prediction results from MODIS data. The RMSE of the predicted sharpened image from MODIS using the global, resolution-adjusted global and local models at 250 m were 3.08, 2.92 and 1.98 K, respectively. The local model consistently led to more accurate sharpened predictions by comparison to other variants.  相似文献   

Modelling of elastic damping in nonlinear time-history analyses of cantilever RC walls     

Eleni Smyrou  M. J. Nigel Priestley  Athol J. Carr 《Bulletin of Earthquake Engineering》2011,9(5):1559-1578

Damping constitutes a major source of uncertainty in dynamic analysis and an open issue to experimental and analytical research. After a thorough review of the current views and approaches existing in literature on damping and its appropriate modelling, this paper focuses on the implications of the available modelling options on analysis. As result of a series of considerations, a damping modelling solution for nonlinear dynamic analyses of cantilever RC walls is suggested within the frame of Direct Displacement-Based Design, supported by comparative analyses on wall structures.  相似文献   

A Tracer Methodology for Identifying Ambient Flows in Boreholes     

L. Maurice  J.A. Barker  T.C. Atkinson  A.T. Williams  P.L. Smart 《Ground water》2011,49(2):227-238

Identifying flows into, out of, and across boreholes is important for characterizing aquifers, determining the depth at which water enters boreholes, and determining the locations and rates of outflow. This study demonstrates how Single Borehole Dilution Tests (SBDTs) carried out under natural head conditions provide a simple and cheap method of identifying vertical flow within boreholes and determining the location of in‐flowing, out‐flowing, and cross‐flowing fractures. Computer simulations were used to investigate the patterns in tracer profiles that arise from different combinations of flows. Field tracer tests were carried out using emplacements of a saline tracer throughout the saturated length of boreholes and also point emplacements at specific horizons. Results demonstrated that SBDTs can be used to identify flowing fractures at the top and bottom of sections of vertical flow, where there is a change in vertical flow rate within a borehole, and also where there are consistent decreases in tracer concentration at a particular depth. The technique enables identification of fractures that might be undetected by temperature and electrical conductance logging, and is a simple field test that can be carried out without pumping the borehole.  相似文献   

Petrography and provenance of the Early Permian Fluvial Warchha Sandstone,Salt Range,Pakistan     

Shahid Ghazi  Nigel P. Mountney 《Sedimentary Geology》2011,233(1-4):88-110

The Warchha Sandstone of the Salt Range of Pakistan is a continental succession that accumulated as part of a meandering, fluvial system during Early Permian times. Several fining-upward depositional cycles are developed, each of which is composed of conglomerate, cross-bedded sandstone and, in their upper parts, bioturbated siltstone and claystone units with distinctive desiccation cracks and carbonate concretions. Clast lithologies are mainly of plutonic and low-grade metamorphic origin, with an additional minor sedimentary component. Textural properties of the sandstone are fine- to coarse-grained, poorly to moderately sorted, sub-angular to sub-rounded, and with generally loose packing. Based on modal analyses, the sandstone is dominantly a feldspathoquartzose (arkose to sub-arkose). Detrital constituents are mainly composed of monocrystalline quartz, feldspars (more K-feldspar than plagioclase) and various types of lithic clasts. XRD and SEM studies indicate that kaolinite is the dominant clay mineral and that it occurs as both allogenic and authigenic forms. However, illite, illite-smectite mixed layer, smectite and chlorite are also recognised in both pores and fractures. Much of the kaolinite was likely derived by the severe chemical weathering of previously deposited basement rocks under the influence of a hot and humid climate. Transported residual clays deposited as part of the matrix of the Warchha Sandstone show coherent links with the sandstone petrofacies, thereby indicating the same likely origin. Illite, smectite and chlorite mainly occur as detrital minerals and as alteration products of weathered acidic igneous and metamorphic rocks. Based primarily on fabric relationship, the sequence of cement formation in the Warchha Sandstone is clay (generally kaolinite), iron oxide, calcareous and siliceous material, before iron-rich illite and occasional mixed layer smectite–illite and rare chlorite. Both petrographic analysis and field characteristics of the sandstone indicate that the source areas were characterised by uplift of a moderate to high relief continental block that was weathered under the influence of hot and humid climatic conditions. The rocks weathered from the source areas included primary granites and gneisses, together with metamorphic basement rocks and minor amounts of sedimentary rocks. Regional palaeogeographic reconstructions indicate that much of the Warchha Sandstone detritus was derived from the Aravalli and Malani ranges and surrounding areas of the Indian Craton to the south and southeast, before being transported to and deposited within the Salt Range region under the influence of a semi-arid to arid climatic regime.  相似文献   

Rapid Eocene erosion,sedimentation and burial in the eastern Himalayan syntaxis and its geodynamic significance     

Wang-Chun Xu  Hong-Fei Zhang  Nigel Harris  Liang Guo  Fa-Bing Pan 《Gondwana Research》2013,23(2):715-725

The lower Bomi Group of the eastern Himalayan syntaxis comprises a lithological package of sedimentary and igneous rocks that have been metamorphosed to upper amphibolite-facies conditions. The lower Bomi Group is bounded to the south by the Indus–Yarlung Suture and to the north by unmetamorphosed Paleozoic sediments of the Lhasa terrane. We report U–Pb zircon dating, geochemistry and petrography of gneiss, migmatite, mica schist and marble from the lower Bomi Group and explore their geological implications for the tectonic evolution of the eastern Himalaya. Zircons from the lower Bomi Group are composite. The inherited magmatic zircon cores display ²⁰⁶Pb/²³⁸U ages from ~ 74 Ma to ~ 41.5 Ma, indicating a probable source from the Gangdese magmatic arc. The metamorphic overgrowth zircons yielded ²⁰⁶Pb/²³⁸U ages ranging from ~ 38 Ma to ~ 23 Ma, that overlap the anatexis time (~ 37 Ma) recorded in the leucosome of the migmatites. Our data indicate that the lower Bomi Group do not represent Precambrian basement of the Lhasa terrane. Instead, the lower Bomi Group may represent sedimentary and igneous rocks of the residual forearc basin, similar to the Tsojiangding Group in the Xigaze area, derived from denudation of the hanging wall rocks during the India–Asia continental collision. We propose that following the Indian–Asian collision, the forearc basin was subducted, together with Himalayan lithologies from the Indian continental slab. The minimum age of detrital magmatic zircons from the supracrustal rocks is ~ 41.5 Ma and their metamorphism had happened at ~ 37 Ma. The short time interval (< 5 Ma) suggests that the tectonic processes associated with the eastern Himalayan syntaxis, encompassing uplift and erosion of the Gangdese terrane, followed by deposition, imbrication and subduction of the forearc basin, were extremely rapid during the Late Eocene.  相似文献