Co‐evolution of riparian vegetation and channel dynamics in an aggrading braided river system,Mount Pinatubo,Philippines          下载免费PDF全文

Karen B. Gran  Michal Tal  Emily D. Wartman 《地球表面变化过程与地形》2015,40(8):1101-1115

Increased bank stability by riparian vegetation can have profound impacts on channel morphology and dynamics in low‐energy systems, but the effects are less clear in high‐energy environments. Here we investigate the role of vegetation in active, aggrading braided systems at Mount Pinatubo, Philippines, and compare results with numerical modeling results. Gradual reductions in post‐eruption sediment loads have reduced bed reworking rates, allowing vegetation to finally persist year‐round on the Pasig‐Potrero and Sacobia Rivers. From 2009–2011 we collected data detailing vegetation extent, type, density, and root strength. Incorporating these data into the RipRoot model and BSTEM (Bank Stability and Toe Erosion Model) shows cohesion due to roots increases from zero in unvegetated conditions to > 10·2 kPa in densely‐growing grasses. Field‐based parameters were incorporated into a cellular model comparing vegetation strength and sediment mobility effects on braided channel dynamics. The model shows both low sediment mobility and high vegetation strength lead to less active systems, reflecting trends observed in the field. The competing influence of vegetation strength versus channel dynamics is a concept encapsulated in a dimensionless ratio between timescales for vegetation growth and channel reworking known as T*. An estimated T* between 1·5 and 2·3 for the Pasig‐Potrero River suggests channels are still very mobile and likely to remain braided until aggradation rates decline further. Vegetation does have an important effect on channel dynamics, however, by focusing flow and thus aggradation into the unvegetated fraction of braidplain, leading to an aggradational imbalance and transition to a more avulsive state. The future trajectory of channel–vegetation interactions as sedimentation rates decline is complicated by strong seasonal variability in precipitation and sediment loads, driving incision and armoring in the dry season. By 2011, incision during the dry season was substantial enough to lower the water‐table, weaken existing vegetation, and allow for vegetation removal in future avulsions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Location‐based social media behavior and perception: Views of university students          下载免费PDF全文

Matthew Haffner  Adam J. Mathews  Emily Fekete  G. Allen Finchum 《Geographical review》2018,108(2):203-224

Location‐based social media (LBSM), a specific type of volunteered geographic information (VGI), is increasingly being used as a spatial data source for researchers in geography and related disciplines. Many questions, though, have been raised about VGI data in terms of its quality and its contributors. While a number of studies have explored users’ demographics and motivations for contribution to explicitly geographic forms of VGI, such as OpenStreetMap and Wikimapia, few have focused on these aspects with implicitly geographic forms of VGI, such as LBSM (for example, Twitter and Instagram). This study, through use of an online survey, specifically assesses the LBSM behavior and perceptions of 253 university students, noting differences found in gender, race, and academic standing. We find that the greatest differences are those between males and females, rather than through race or academic standing, and LBSM appears less biased than other forms of VGI.  相似文献   

Hillslope soil water flowpaths and the dynamics of roadside soil cation pools influenced by road deicers          下载免费PDF全文

Robert J. Rossi  Daniel J. Bain  Emily M. Elliott  Marion Divers  Bridget O'Neill 《水文研究》2017,31(1):177-190

Over the past 60 years, road deicers (i.e. road salt) have been applied to roadways in high latitudes to improve road conditions in winter weather. However, the dissolution of road deicers in highway runoff creates waters with high concentrations of sodium, which can mobilize soil metals via soil cation‐exchange reactions. While several studies have detailed the interactions of road salt‐rich solutions and surface and ground waters, less attention has been given to how local hydrologic flowpaths can impact the delivery of these solutions to near‐road soils. Between 2013 and 2014, soil water samples were collected from a roadside transect of lysimeter nests in Pittsburgh, Pennsylvania (USA). Soil water samples were analysed for metal concentrations and resulting data used to examine cation dynamics. While patterns in soil water calcium and magnesium concentrations follow patterns in soil water sodium concentrations, additional processes influence patterns in soil water potassium concentrations. Specifically, we observe the highest calcium and magnesium concentrations in the deepest lysimeters, suggesting divalent cations are mobilized to, and potentially accumulate in, deeper soil horizons. In contrast, soil water potassium concentrations do not follow this pattern. Additionally, in all examined elements (Ca, Mg, K, Na, and Cl), the timing of concentration peaks appears be influenced by a combination of both distance from the roadside and sampling depth. These relationships not only suggest that multiple soil water flowpaths interact with our study transect but also confirm that road salt plumes persist and migrate following the road salting season. Characterizing the interactions of sodium‐rich solutions and roadside soil cation pools clarifies our understanding of metal dynamics in the roadside environment. A deeper understanding of these processes is necessary to effectively restore and manage watersheds as high total dissolved solid solutions (e.g. road deicing melt, unconventional natural gas brines, and marginal irrigation water) continue to influence hydrological systems. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Effects of water loss on primary production: A landscape-scale model   总被引：4，自引：0，他引：4  

Emily?H.?StanleyEmail author  Stuart?G.?Fisher  Jeremy?B.?Jones  Jr. 《Aquatic Sciences - Research Across Boundaries》2004,66(1):130-138

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Community volunteer assessment of recreational water quality in the Hutt River,Wellington     

Amanda E. Valois  Juliet R. Milne  Mark W. Heath  Rob J. Davies-Colley  Emily Martin  Rebecca Stott 《新西兰海洋与淡水研究杂志》2020,54(2):200-217

ABSTRACT

Water is an important component of many recreational opportunities and New Zealand invests significant resources in recreational water quality (RWQ) monitoring to assess risks to public health. However, monitoring primarily focuses on microbiological hazards and RWQ is considerably broader than this. The goal of this study was to take a comprehensive approach to evaluating RWQ while exploring the potential for greater public involvement in monitoring. A popular river swimming site was co-monitored weekly by volunteers and a council field officer. The attributes monitored–water temperature, visual clarity, benthic cyanobacteria and filamentous periphyton cover, E. coli and rubbish–were identified from a volunteer workshop. There was good concordance between volunteer and council data suggesting that volunteer measurements can be considered reliable. This highlights the potential for volunteers, with professional support, including training and quality assurance, to extend council RWQ surveillance to additional monitoring sites while improving public engagement on water management.  相似文献   

Introduction to Focus Section: Feminist Research and Knowledge Production in Geography   总被引：1，自引：0，他引：1  

Nancy Hiemstra  Emily Billo 《The Professional geographer》2017,69(2):284-290

Over the past two decades, feminist geographers have contributed in critical ways to thinking on the conduct, complications, and consequences of feminist research. The robust existing body of work is testament to the foundational import of these contributions, but the articles in this Focus Section suggest that there are still important things to argue, talk about, and reflect on with regard to the epistemological aspects of doing feminist geography. These six articles bring together real-life examples of complex issues that feminist researchers in geography face today, with the overarching aim of sparking discussions about the relationship between feminist research and knowledge production. Specifically, the articles expand key concepts facilitating reflexive processes and offer new tools for feminist researchers. This Introduction reviews the existing literature pertaining to both of these goals, and summarizes and situates the articles that follow.  相似文献   

Spatial assimilation and its discontents: Asian ethnic neighborhood change in California     

Emily Walton 《Urban geography》2017,38(7):993-1018

This study investigates the geographic and compositional dynamics of ethnic neighborhoods over time among the fastest growing racial group in California, Asian Americans. I conduct spatial analysis of Census data from 2000 and 2010 to represent changes in ethnic neighborhood boundaries and their associated structural and demographic characteristics. First, I document changing ethnic neighborhood patterns among four Asian national origin groups—Chinese, Filipino, Korean, and Vietnamese Americans. Second, I synthesize this information, assessing the theoretical implications of these changes by describing indications of spatial assimilation, ethnic stratification, and resurgent ethnicity among ethnic neighborhoods and the potential repercussions for the successful incorporation of both immigrant and native-born Asian Americans. Overall, this paper demonstrates that Asian ethnic neighborhood dynamics are far from monolithic and that different spatial incorporation processes manifest both within and between groups.  相似文献   

Rapid crystallization of the Animikie Red Ace Pegmatite,Florence county,northeastern Wisconsin: inclusion microthermometry and conductive-cooling modeling   总被引：1，自引：0，他引：1  

Mona-Liza C. Sirbescu  Emily E. Hartwick  James J. Student 《Contributions to Mineralogy and Petrology》2008,156(3):289-305

We evaluated the crystallization regime of a zoned pegmatite dike and the degree of magma undercooling at the onset of crystallization by analyzing coeval fluid and melt inclusion assemblages. The liquidus temperature of the pegmatite magma was ~720°C, based on re-melting of crystallized-melt inclusions in heating experiments. The magma crystallized sequentially starting with a thin border zone, which formed in less than one day at an average temperature of ~480°C based on primary fluid inclusions, meaning 240°C undercooling. The primary inclusions from the outer zones were postdated by secondary inclusions trapped between 580 and 720°C, representing fluid exsolved from hotter, still crystallizing inner pegmatite units. The huge temperature contrast between the pegmatite’s inner and outer zones was simulated by conductive-heat numerical modeling. A 2.5 m wide dike emplaced in 220°C rocks cools entirely to <400°C in less than 50 days. Unidirectional and skeletal textures also indicate rapid, disequilibrium crystallization.  相似文献   

A Historical Atlas of Tibet          下载免费PDF全文

Emily T. Yeh 《Geographical review》2018,108(1):171-173

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The Global Earthquake Vulnerability Estimation System (GEVES): an approach for earthquake risk assessment for insurance applications   总被引：4，自引：0，他引：4  

Robin Spence  Emily So  Sarah Jenny  Hervé Castella  Michael Ewald  Edmund Booth 《Bulletin of Earthquake Engineering》2008,6(3):463-483

For the insurance and reinsurance industries, earthquake loss estimation is crucial not only to adequately price its product but also to manage the accumulation risk in the face of the ever-increasing exposure in highly seismic regions. Changes in the built environment and a continuously evolving earthquake science make it a necessity for the industry to constantly refine earthquake loss estimation models. In particular, it has been recognized for a long time that the vulnerability of buildings to ground shaking is a key parameter in any earthquake risk model. Current methods tend either to rely on the limited historical damage and loss data or on the numerical simulation of the response of individual buildings to the ground-shaking produced by earthquakes. Although both methods have their advantages and pitfalls, we are proposing here a simple solution, using transparent input data, that can be realistically used for the needs of the insurance and reinsurance industry, whether detailed information about the insured structures is available or not. The resulting product is known as GEVES (Global Earthquake Vulnerability Estimation System). It is primarily intended for evaluating the mean damage ratio (MDR) suffered by a portfolio of buildings classified by use, under the action of a given earthquake scenario (i.e. an earthquake of given size at a given distance from the portfolio of buildings). A key assumption was that macroseismic intensity rather than spectral displacement would be the basis of loss estimation. The paper describes the model with emphasis on its structure and the justification for the assumptions made. In addition to a new set of earthquake vulnerability functions, the paper also provides recommendations on some aspects of the earthquake hazard, in particular about how to define macroseismic intensity at the site of interest, for a given earthquake scenario. This paper also discusses validation of the GEVES model against calculated vulnerability approaches, and the treatment of uncertainty within the model.  相似文献