Mapping benthic habitat in regions of gradational substrata: An automated approach utilising geophysical,geological, and biological relationships     

Craig J. Brown  Jenny S. Collier 《Estuarine, Coastal and Shelf Science》2008

The relationship between acoustic backscatter, sediment characteristics and benthic habitat is examined using high-resolution sidescan sonar data collected at the Loch Linnhe artificial reef site on the west coast of Scotland. The site is typical for the continental shelf of NW Europe, with a mix of seabed environments from muddy to coarse, stony substrata on a 10–100 m length scale. A sidescan sonar mosaic was produced and classified according to derived backscatter parameters (mean, median and standard deviation of the backscatter values) using an unsupervised classification procedure. The accuracy of the final classified map was assessed by comparison with a ground-truthing survey in which the biological habitat was derived from underwater video footage. The sidescan correctly predicted seabed surface characteristics of observed biological habitat with 78% accuracy. A second, and more challenging test of the acoustic data to correctly predict biological habitat was made by comparing it with data from 21 grab sampling stations. These stations were divided into three groups using multivariate statistical techniques based on their backscatter properties. Benthic assemblage structure was found to be significantly distinct between the high and low, and the medium and low backscatter stations. There was a low to moderate but significant correlation between the multivariate patterns of acoustic backscatter, benthic assemblage structure, and particle size distribution. The work shows that even in areas with subtle and gradational changes in substratum, the sidescan was able to predict biological community with an acceptable accuracy.  相似文献   

Introduction: Interaction between environment and fisheries—The role of stakeholder participation     

Riku Varjopuro  Tim Gray  Jenny Hatchard  Felix Rauschmayer  Heidi Wittmer 《Marine Policy》2008

This paper is an introduction to the special issue on a role of participation in dealing with the interactions between environment and fisheries. In this introduction, we explore the recent discussion on the ecosystem-based approach to fisheries management (EBAFM) and extract important points for implementation of EBAFM from the social science literature on participation and participatory processes in environmental management. The introduction finishes by describing the analytical framework for studying participatory processes.  相似文献   

Subglacial drainage system structure and morphology of Brewster Glacier,New Zealand     

Ian Willis  Wendy Lawson  Ian Owens  Bob Jacobel  Jenny Autridge 《水文研究》2009,23(3):384-396

A global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of Brewster Glacier. These are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure (P_w): (i) P_w = ice overburden; (ii) P_w = half ice overburden; (iii) P_w = atmospheric. Additionally, 16 dye‐tracing experiments at 12 locations were performed through a summer melt season. Dye return curve shape, together with calculations of transit velocity, dispersivity and storage, are used to infer the likely morphology of the subglacial drainage system. Taken together, the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden. By mid‐summer, water pressures are closer to half‐ice overburden and the channelised drainage system is more hydraulically efficient. Surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout. Streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Correction     

Jeffrey S. Smith  Charles O. Collins  Jenny Pettit 《Geographical review》2014,104(1):121-121

  相似文献   

Particle aggregation in microgravity: Informal experiments on the International Space Station     

Stanley G. Love  Donald R. Pettit  Scott R. Messenger 《Meteoritics & planetary science》2014,49(5):732-739

We conducted experiments in space to investigate the aggregation of millimeter‐ and submillimeter‐sized particles in microgravity, an important early step in planet formation. Particulate materials included salt (NaCl), sugar (sucrose), coffee, mica, ice, Bjurböle chondrules, ordinary and carbonaceous chondrite meteorite fragments, and acrylic and glass beads, all triply confined in clear plastic containers. Angular submillimeter particles rapidly and spontaneously formed clusters strong enough to survive turbulence in a protoplanetary nebula. Smaller particles generally aggregated more strongly and quickly than larger ones. We observed only a weak dependence of aggregation time on particle number density. We observed no strong dependence on composition. Round, smooth particles aggregated weakly or not at all. In a mixture of particle types, some phases aggregated more readily than others, creating selection effects that controlled the composition of the growing clumps. The physical process of aggregation appears to be electrostatic in nature.  相似文献   

North polar frontal clouds and dust storms on Mars during spring and summer     

Huiqun Wang  Jenny A. Fisher 《Icarus》2009,204(1):103-113

The complete archive of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) Mars Daily Global Maps (MDGM) are used to study north polar clouds and dust storms that exhibit frontal structures during the spring and summer (L_s 0-180°). Results show that frontal events generally follow the edge of the polar cap during spring and mid/late summer with a gap in the distribution in early summer. The exact duration and timing of the gap vary from year to year. Ten to twenty percent of spring and summer time frontal events exhibit complex morphologies. Distinct temperature signatures are associated with features observed in images in many but not all cases. The general travel paths of the frontal events are eastward around the polar cap. Westward paths exist only at the edge of the polar cap in late spring/early summer. Occasionally, the paths curve toward or away from the polar cap in certain longitude sectors.  相似文献   

Finding common ground? Spaces of dialogue and the negotiation of Indigenous interests in environmental campaigns in Australia   总被引：5，自引：0，他引：5  

Jenny Pickerill 《Geoforum》2009,40(1):66-79

Critiquing the usefulness of cosmopolitanism this paper argues that we need a more nuanced and subtle understanding of how commonalities are found, created and maintained across difference. This paper uses two juxtapositions of perspective (around place and environment) to explore how such boundaries of difference can be negotiated. It uses an examination of the ways in which environmental groups in Australia have sought to negotiate Indigenous interests through creating spaces of dialogue and changing working practices. It is based on 30 interviews with both Indigenous and non-Indigenous activists across two case regions; Cape York (Queensland) and Barmah-Millewa (Victoria/New South Wales). Four issues were identified that have proved particularly contentious in negotiations to build collaborative campaigns: language; power and ownership; scale and timeframes; and economics. There are examples of both successes and ongoing problematic practices across these tensions. However there is also a growing mutual ownership of the issues. Moving beyond a colonial paternal sense of responsibility, to a dynamic and engaged mutuality of concern for both processes and outcomes has resulted in gradual, small, and progressive steps forward in Indigenous/non-Indigenous collaborative environmental campaigning.  相似文献   

An extended finite volume method and fixed-stress approach for modeling fluid injection–induced tensile opening in fractured reservoirs     

Rajdeep Deb  Patrick Jenny 《国际地质力学数值与分析法杂志》2020,44(8):1128-1144

Fluid injection–induced tensile opening is modeled using an extended finite volume method (XFVM). An embedded fracture strategy is used for the flow problem, that is, the fractures are discretized using finite volume segments without resolving the grid around them. Further, the discontinuities across fractures are modeled using special basis functions. The fracture openings due to enhanced fluid pressure and the associated shear slip due to traction free boundary condition on the fracture segments are both modeled using these special discontinuity basis functions. Mass transfer between fractures and matrix is modeled using the pressure difference. The enhancement of fracture storativity due to tensile opening leads to stronger coupling between flow and mechanics. An iterative scheme relying on the fixed-stress approach for fractures, which conserves the stress dependent terms over each iteration of the flow problem, has been introduced. Tensile opening has been simulated for single fractures embedded in two- and three-dimensional matrices. The convergence criterion for sequentially implicit fixed-stress scheme for fractures embedded in elastic media is established and has been validated numerically. Further, for 2D simulations, the effect of the matrix permeability for fracture propagation due to tensile opening has been studied.  相似文献   

Evaluating Groundwater Interbasin Flow Using Multiple Models and Multiple Types of Data          下载免费PDF全文

Ming Ye  Liying Wang  Karl. F. Pohlmann  Jenny B. Chapman 《Ground water》2016,54(6):805-817

The groundwater interbasin flow, Q_y, from the north of Yucca Flat into Yucca Flat simulated using the Death Valley Regional Flow System (DVRFS) model greatly exceeds assessments obtained using other approaches. This study aimed to understand the reasons for the overestimation and to examine whether the Q_y estimate can be reduced. The two problems were tackled from the angle of model uncertainty by considering six models revised from the DVRFS model with different recharge components and hydrogeological frameworks. The two problems were also tackled from the angle of parametric uncertainty for each model by first conducting Morris sensitivity analysis to identify important parameters and then conducting Monte Carlo simulations for the important parameters. The uncertainty analysis is general and suitable for tackling similar problems; the Morris sensitivity analysis has been utilized to date in only a limited number of regional groundwater modeling. The simulated Q_y values were evaluated by using three kinds of calibration data (i.e., hydraulic head observations, discharge estimates, and constant‐head boundary flow estimates). The evaluation results indicate that, within the current DVRFS modeling framework, the Q_y estimate can only be reduced to about half of the original estimate without severely deteriorating the goodness‐of‐fit to the calibration data. The evaluation results also indicate that it is necessary to develop a new hydrogeological framework to produce new flow patterns in the DVRFS model. The issues of hydrogeology and boundary flow are being addressed in a new version of the DVRFS model planned for release by the U.S. Geological Survey.  相似文献   

The fate of antimony in a major lowland river system,the Waikato River,New Zealand     

Nathaniel Wilson  Jenny Webster-Brown 《Applied Geochemistry》2009

Antimony is an element that is becoming of increasing concern as an environmental contaminant. Geothermal systems are a source of Sb into some fresh waters of New Zealand’s North Island. The purpose of this research was to determine the factors controlling the behaviour of geothermally-derived Sb in the large lowland Waikato River system. The Waikato River is New Zealand’s longest and most utilised river. Antimony in the system exhibited mainly conservative behaviour, and seasonally variable dilution was found to be the most important control on Sb concentrations. The most significant potential removal process was identified as adsorption of Sb onto suspended particulate material (SPM). The adsorption of Sb onto the SPM is enhanced at low (<5) pH conditions, and in the anoxic base of stratified lakes. There was evidence that the adsorption of Sb is mainly onto Fe oxides in SPM, and changes with changing Fe concentrations. Therefore, Sb adsorption was higher in winter (when Fe concentrations in SPM were higher) than in summer. In Lake Ohakuri, which was stratified during the late summer/early autumn of 2007, there was also potential for removal of Sb as Sb₂S₃ in the presence of sulfide formed in the anoxic layer. The behaviour of Sb was conservative through the estuary at the mouth of the river.  相似文献