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   

Spatial variation in organic matter utilization by benthic communities from Yura River–Estuary to offshore of Tango Sea,Japan     

Emily S. Antonio  Akihide Kasai  Masahiro Ueno  Nam-il Won  Yuka Ishihi  Hisashi Yokoyama  Yoh Yamashita 《Estuarine, Coastal and Shelf Science》2010

We investigated the distribution of δ¹³C and δ¹⁵N of organic matter among benthic communities from the upper estuary of Yura River to offshore of Tango Sea, Japan, to determine spatial variation in utilization of organic matter by benthic communities. The δ¹³C values of benthic animals ranged from −27 to −15‰ in the upper estuary, −21 to −15‰ in the lower estuary, −20 to −16‰ in the shallow coast (5–10 m depths), −18 to −16‰ in the deep coast (30–60 m depths) and −19 to −15‰ in offshore (100–150 m depths) stations. Adapting the dual isotope values to mixing models, we estimated the relative contributions of potential food sources to the benthos diet. Phytoplankton and macroalgae that intruded the estuary in summer were utilized as alternative food aside from the terrestrial-origin organic matter assimilated by the estuarine benthic consumers. Resuspended benthic microalgae were important source of energy in the shallow coastal stations, while abundant supply of phytodetritus fueled the deep coastal and offshore benthic food webs. Spatial difference in the diet of benthic communities depends largely on the shifts in the primary carbon source. Thus, benthic communities are important link of autochthonous/allochthonous production and secondary production in the continuous river–estuary–marine system.  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   

Energy changes of cosmic rays in the interplanetary region     

L. J. Gleeson  G. M. Webb 《Astrophysics and Space Science》1978,58(1):21-39

A clarification and discussion of the energy changes experienced by cosmic rays in the interplanetary region is presented. It is shown that the mean time rate of change of momentum of cosmic rays reckoned for a fixed volume in a reference frame fixed in the solar system is 〈p〉 =p V·G/3 (p=momentum,V is the solar wind velocity andG=cosmic-ray density gradient). This result is obtained in three ways:

1. by a rearrangement and reinterpretation of the cosmic-ray continuity equation;
2. by using a scattering analysis based on that of Gleeson and Axford (1967);
3. by using a special scattering model in which cosmic-rays are trapped in ‘magnetic boxes’ moving with the solar wind.

The third method also gives the rate of change of momentum of particles within a moving ‘magnetic box’ as 〈p〉_ad = ?p ?·V/3, which is the adiabatic deceleration rate of Parker (1965). We conclude that ‘turnaround’ energy change effects previously considered separately are already included in the equation of transport for cosmic rays.  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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A study of the force-field equation for the propagation of galactic cosmic rays     

L. J. Gleeson  I. H. Urch 《Astrophysics and Space Science》1973,25(2):387-404

A new development is given of the solution of the equation of the force-field approximation for the propagation of galactic cosmic rays in the interplanetary region. It leads to simpler methods for determining the force-field parameters. A method is given for determining the separable diffusion coefficient from observations of galactic electron spectrum and near-Earth electron spectra; it is shown that this diffusion coefficient is not unique but may have a periodic-like dependence upon rigidity; and the method is used to obtain diffusion coefficients for 1965 and 1968. Approximate formulae relating small changes in intensity and diffusion coefficient are developed and some applications of these noted; in one it is shown that the form of, and changes in, diffusion coefficient deduced previously for a neutron monitor event during June–September 1969 are unnecessarily constrained and therefore probably not correct.  相似文献   

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