Effective dispersion in a chemically heterogeneous medium under temporally fluctuating flow conditions     

Vanessa Zavala-Sanchez  Marco Dentz  Xavier Sanchez-Vila 《Advances in water resources》2007

We investigate effective solute transport in a chemically heterogeneous medium subject to temporal fluctuations of the flow conditions. Focusing on spatial variations in the equilibrium adsorption properties, the corresponding fluctuating retardation factor is modeled as a stationary random space function. The temporal variability of the flow is represented by a stationary temporal random process. Solute spreading is quantified by effective dispersion coefficients, which are derived from the ensemble average of the second centered moments of the normalized solute distribution in a single disorder realization. Using first-order expansions in the variances of the respective random fields, we derive explicit compact expressions for the time behavior of the disorder induced contributions to the effective dispersion coefficients. Focusing on the contributions due to chemical heterogeneity and temporal fluctuations, we find enhanced transverse spreading characterized by a transverse effective dispersion coefficient that, in contrast to transport in steady flow fields, evolves to a disorder-induced macroscopic value (i.e., independent of local dispersion). At the same time, the asymptotic longitudinal dispersion coefficient can decrease. Under certain conditions the contribution to the longitudinal effective dispersion coefficient shows superdiffusive behavior, similar to that observed for transport in s stratified porous medium, before it decreases to its asymptotic value. The presented compact and easy to use expressions for the longitudinal and transverse effective dispersion coefficients can be used for the quantification of effective spreading and mixing in the context of the groundwater remediation based on hydraulic manipulation and for the effective modeling of reactive transport in heterogeneous media in general.  相似文献   

Reply to Molina-Garza et al. (2019) “Discussion of: Ortega-Flores et al. (2018) provenance analysis of Oligocene sandstone from the Cerro Pelón area,southern Gulf of Mexico”     

Berlaine Ortega-Flores  Michelangelo Martini  Luigi Solari  Vanessa Colás  Sandra Guerrero-Moreno  Elena Centeno-Garcia 《International Geology Review》2020,62(4):421-427

ABSTRACT

The origin of the Oligocene turbidites from the Cerro Pelón area in south Gulf Mexico proposed by Ortega-Flores et al. (2018) is in disagree with the interpretations made by Molina-Garza et al. (2019), which main criticism is based on U-Pb ages of detrital zircons from the matrix of a conglomerate unit, which they refer to as ‘Nanchital Conglomerate’, as well as on the presence of limestone, gabbros, and mafic protolith-derived clasts. Molina-Garza et al. (2019) basically interpret the Nanchital Conglomerate as Miocene in age, which was sourced mainly from metamorphic complexes including their sedimentary covers located to the west and south of the Cerro Pelón area. For some reason, Molina-Garza et al. (2019) suppose that the Nanchital Conglomerate should have the same provenance sources that the Oligocene turbidites from Cerro Pelón area, reported by Ortega-Flores et al. (2018). Based on the foregoing, we strongly disagree with Molina-Garza et al. (2019) considering that, from the beginning, they intend to compare two units of different age. Additionally, the scarce data reported from both the matrix and the clasts of the Nanchital Conglomerate are not determinant for interpreting the provenance of this conglomeratic unit and subsequently, to consider the same rock sources from the Oligocene through Miocene time.  相似文献   

Disruption of Routine Behaviors Following the Deepwater Horizon Oil Spill     

Vanessa Parks  Leah Drakeford  Michael R. Cope  Tim Slack 《社会与自然资源》2018,31(3):277-290

This paper frames the unfolding impacts of the Deepwater Horizon oil spill as a process of lifeway disruption, analyzing the degree to which residents of spill affected communities were prevented from undertaking routine behaviors during the disaster. Special attention is paid to the influence of time, natural resource employment, and community sentiment. Drawing on data from the Louisiana Community Oil Spill Survey, the results show that people in the spill impacted region were prevented from engaging in routine behaviors, though this disruption has steadily decreased over time, suggesting a general trend toward recovery. Consistent with the renewable resource community concept, the results also show that those with ties to the fishing industry were more likely to be prevented from undertaking routine behaviors than were nonfishers. Finally, community sentiment is shown to ameliorate routine behavior disruption, thus, promoting resilience. Overall, these results challenge notions of monolithic paths to disaster recovery.  相似文献   

Using Multiple Methods to Understand the Nature of Relationships in Social Networks     

Vanessa M. Adams  Katie Moon  Jorge G. Álvarez-Romero  Örjan Bodin  Michaela Spencer  Deborah Blackman 《社会与自然资源》2018,31(7):755-772

Effective natural resource management (NRM) often depends on collaboration through formal and informal relationships. Social network analysis (SNA) provides a framework for studying social relationships; however, a deeper understanding of the nature of these relationships is often missing. By integrating multiple analytical methods (including SNA, evidence ratings, and perception matrices), we were able to investigate the nature of relationships in NRM social networks across five service types (e.g., technical advice, on-ground support) in our case study region, Daly catchment Australia. Only one service type was rated as highly associated with free choice in establishing relationships: technical advice/knowledge. Beneficial characteristics of NRM organizations, such as collaborative and transparent, were associated with the presence of freely chosen relationships between organizations. Our results suggest a need to improve our understanding of organizational roles and characteristics, in particular for use in applied NRM contexts, such as network weaving or disseminating information.  相似文献   

Habitat use of inter‐tidal chitons – role of colour polymorphism          下载免费PDF全文

Vanessa Mendonça  Catarina Vinagre  Henrique Cabral  Ana C. F. Silva 《Marine Ecology》2015,36(4):1098-1106

This study presents a new approach to examining European chiton habitat use according to morphological characteristics. Time‐search transects were conducted on four Portuguese rocky shores at two shore levels. The chiton species, abundance and individual morphometric features were recorded and related to the substratum dominant epiphytes and surface roughness. The chiton Lepidochitona cinerea (Linnaeus 1767) was the dominant species (77%), followed by Leptochiton algesirensis (Capellini 1859) (15%) and Acanthochitona crinita (Pennant 1777) (8%). Species abundance did not vary significantly with shore level or amongst shores. Six colour morphs were considered for Lepidochitona cinerea, four for A. crinita and one for Lepidochiton algesirensis. Substratum characteristics significantly explained the variation in species and colour morph distribution. There was a high correlation between the presence/absence and type of epiphytic algae and the substratum surface roughness level. We hypothesize that three mechanisms operating either independently or in interaction may explain the non‐random distribution of colour polymorphisms according to their habitat characteristics: (i) presence of algae that are part of their diet; (ii) use of rock as shelter – for instance, crevices and cover resulting from algae fronds and; (iii) morph–rock colour matching as a camouflage mechanism to reduce predation pressure.  相似文献   

A participatory systems approach to understanding climate adaptation needs     

Helen Ross  Sylvie Shaw  David Rissik  Neil Cliffe  Susie Chapman  Vanessa Hounsell  James Udy  Nghia Trong Trinh  Jess Schoeman 《Climatic change》2015,129(1-2):27-42

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PAH transport by sinking particles in the open Mediterranean Sea: a 1 year sediment trap study   总被引：1，自引：0，他引：1  

Bouloubassi I  Méjanelle L  Pete R  Fillaux J  Lorre A  Point V 《Marine pollution bulletin》2006,52(5):560-571

One year time series of sinking particles were collected at two depths in the open Mediterranean Sea and analysed for polycyclic aromatic hydrocarbons (PAH). Average total PAH concentrations were 593+/-284 ng g(-1) at 250 m and 551 +/- 198 ng g(-1) at 2850 m. Total PAH fluxes averaged 73 +/- 58 ng m(-2) d(-1) at 250 m and 53 +/- 39 ng m(-2) d(-1) at 2850 m. Contamination levels and, thus, exposure of marine organisms to PAH are comparable in surface and deep waters. Deep waters appear as a significant, yet overlooked, PAH sink. PAH temporal patterns show noticeable seasonality. This is partly due to varying levels of specific components such as the winter increase of pyrolytic PAH. Downward transport processes and the nature of sinking particles also impact on PAH fluxes, as inferred during periods of increasing productivity. Different phase-associations and interactions with particulate organic carbon for low-MW fossil PAH and high-MW pyrolytic PAH influence their downward transport efficiency.  相似文献   

Late Miocene paleoenvironment of the Lambert Graben embayment, East Antarctica, evident from: Mollusc paleontology, sedimentology and geochemistry     

Jason M. Whitehead  Werner Ehrmann  David M. Harwood  Claus-Dieter Hillenbrand  Patrick G. Quilty  Charles Hart  Marco Taviani  Vanessa Thorn  Andrew McMinn 《Global and Planetary Change》2006,50(3-4):127-147

The Upper Miocene (10.7–9.0 Ma) Battye Glacier Formation was deposited 250 km inland from the modern Amery Ice Shelf edge in Prydz Bay, East Antarctica. The composition of clay minerals distinguishes a Lower Member, which reflects regional erosion of Precambrian metamorphic basement, from an Upper Member, which records increased erosion of local Permian–Triassic Amery Group strata. The Upper Member was deposited in an ice-proximal environment akin to the modern fjords of East Greenland, with substantial diamict deposition resulting from melting iceberg discharge. The Lower Member was deposited in an ice-distal environment and included the accumulation of the fossil-bearing McLeod Beds. The McLeod Beds contain much siliceous biogenic sediment (≤ 15% opal), which is rare to absent in the predominantly hemipelagic mud of modern East Greenland fjords. The McLeod Beds also contain largely monospecific in situ Hiatella sp. mollusc assemblages suggestive of environmental stress, potentially caused by low salinity melt-water and a high input of terrigenous sediment, which excluded most other benthic taxa. Geochemical results from primary aragonite in Hiatella shells imply large freshwater input into the marine environment during mollusc growth, causing low δ¹⁸O, Na, Mg and high Fe values. The present study indicates that iceberg melt-water influence entering the marine environment was greater during the Late Miocene than today around Antarctica, and documents the paleoenvironment associated with a discrete period of ice margin retreat and marine incursion into the Lambert embayment.  相似文献   

Relationship between geoacoustic properties and chemical content of submarine polymetallic crusts from offshore Brazil     

Arthur Ayres Neto  Vanessa Alves da Costa  Clara Pinto Ferreira Maia Porto  Thais Cristina Vargas Garrido  Jean-Pierre Hermand 《Marine Georesources & Geotechnology》2020,38(4):437-449

Abstract

Marine mining is the ocean’s new exploration frontier, and polymetallic crusts (PMCs) and ferromanganese nodules are considered a strategic resource for the future. Acoustic geophysical methods are a valuable tool for oceanic research and have been employed for several decades in the exploration of marine resources and environmental evaluations. The main objective of this work was to investigate the correlation between the chemical composition of PMCs from three different areas along the Brazilian continental margin and their physico-acoustic attributes (P-wave velocity, density and acoustic impedance). The results show that the geoacoustic properties of PMCs are correlated to their chemical composition. Measurements showed positive and negative trends between acoustic impedance and studied elements (Fe, Mn, Co, Cu, Zn, W and Ni) according to the direction of measurement, indicting high anisotropy levels. Our study sheds initial light on the correlation between acoustic properties and metal content of PMCs. The study facilitates assessments of the acoustic responses of PMCs allowing more efficient prospection and exploitation compared to ship-board geophysical techniques that are too qualitative to identify PMCs. The results can contribute to determining the best procedures and techniques for more efficient future exploration of this resource.  相似文献   

“Convoluted Journeys”: Integrating Nonprofit Organizations and University Science     

Vanessa Crossgrove Fry  Jen Schneider  Sally Sargeant-Hu  Carl Anderson  Erik Olson 《社会与自然资源》2019,32(3):239-254

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