Particle suspensions and their regions of effect in the Neuse River Estuary: Implications for water quality monitoring     

J. Stephen Fries  Rachel T. Noble  Hans W. Paerl  Gregory W. Characklis 《Estuaries and Coasts》2007,30(2):359-364

Monitoring of estuarine condition depends on water quality parameters that have significant and interpretable ecological effects and can be assessed either in situ or via rapid laboratory techniques. Two commonly measured parameters are water column turbidity (NTU) and total suspended solids (TSS). Under certain conditions, either of these measures could represent a proxy for runoff and provide rapid, in situ measures to improve protection of the public by decreasing the time required to detect and monitor associated effects (e.g., reduced water clarity and eutrophication). The Neuse River Estuary (NRE) has experienced a decline in water quality due to anthropogenic inputs, including stormwater containing nutrient and particle loads. Water samples were collected from the NRE during both dry weather and storm events over 16 mo across the entire estuarine gradient. Particle size distributions, ratio of particulate organic carbon to nitrogen, chlorophylla (chla), TSS, and NTU were measured in each of these samples, with the data separated into regions based on salinity and depth of sample collection. Particle analyses were directed at identifying suspensions dominated by phytoplankton, runoff particles, or resuspended sediments. Particle size distributions for suspensions in Region I (all samples with salinity less than 2) varied little during sampling, resulting in a robust NTU-TSS relationship. This relationship confirmed the usefulness of turbidity as a measure of runoff and resuspension of recently deposited runoff in the upper NRE. Phytoplankton cells represented a majority of the particles in Region II (surface samples with salinity greater than 2), based on the close relationship between chla and total particle volume in these samples. Suspensions of large, nearly uniform diameter particles, which are likely aggregates and resuspended sediment, were observed in Region III (bottom samples with salinity greater than 2). Using these techniques as part of routine monitoring, particle suspension measures in different hydrographic regions of an estuary provide evidence useful for identifying the source and water quality consequences of particle suspensions (e.g., microbial contamination and algal blooms).  相似文献   

Evaluating approximations for halo merging histories     

Rachel S. Somerville  Gerard Lemson  Tsafrir S. Kolatt  Avishai Dekel 《Monthly notices of the Royal Astronomical Society》2000,316(3):479-490

We study the merging history of dark matter haloes in N -body simulations and semi-analytical 'merger trees' based on the extended Press–Schechter (EPS) formalism. The main focus of our study is the joint distribution of progenitor number and mass as a function of redshift and parent halo mass. We begin by investigating the mean quantities predicted directly by the Press–Schechter (PS) and EPS formalism, such as the halo mass and conditional mass functions, and compare these predictions with the results of the simulations. The higher moments of this distribution are not predicted by the EPS formalism alone and must be obtained from the merger trees. We find that the Press–Schechter model deviates from the simulations at the level of 30–50 per cent on certain mass scales, and that the sense of the discrepancy changes as a function of redshift. We show that this discrepancy is reflected in the higher moments of the distribution of progenitor mass and number. We investigate some related statistics such as the accretion rate and the mass ratio of the largest two progenitors. For galaxy sized haloes ( M ∼10¹² M_⊙), we find that the merging history of haloes, as represented by these statistics, is well reproduced in the merger trees compared with the simulations. The agreement deteriorates for larger mass haloes. We conclude that merger trees based on the extended Press–Schechter formalism provide a reasonably reliable framework for semi-analytical models of galaxy formation.  相似文献   

Gravitational lensing by elliptical galaxies     

Daniel J. Mortlock  Rachel L. Webster 《Monthly notices of the Royal Astronomical Society》2000,319(3):860-871

The fraction of high-redshift sources which are multiply imaged by intervening galaxies is strongly dependent on the cosmological constant, and so can be a useful probe of the cosmological model. However its power is limited by various systematic (and random) uncertainties in the calculation of lensing probabilities, one of the most important of which is the dynamical normalization of elliptical galaxies. Assuming ellipticals' mass distributions can be modelled as isothermal spheres, the mass normalization depends on the velocity anisotropy, the luminosity density, the core radius and the area over which the velocity dispersion is measured. The differences in the lensing probability and optical depth produced by using the correct normalization can be comparable to the differences between even the most extreme cosmological models. The existing data are not sufficient to determine the correct normalization with enough certainty to allow lensing statistics to be used to their full potential. However, as the correct lensing probability is almost certainly higher than is usually assumed, upper bounds on the cosmological constant are not weakened by these possibilities.  相似文献   

Quantifying the impact of climate change on drought regimes using the Standardised Precipitation Index     

Katie Jenkins  Rachel Warren 《Theoretical and Applied Climatology》2015,120(1-2):41-54

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Sensitivity of modern climate to the presence,strength and salinity of Mediterranean-Atlantic exchange in a global general circulation model     

Ruza F. Ivanovic  Paul J. Valdes  Lauren Gregoire  Rachel Flecker  Marcus Gutjahr 《Climate Dynamics》2014,42(3-4):859-877

Mediterranean Outflow Water (MOW) is thought to be a key contributor to the strength and stability of Atlantic Meridional Overturning Circulation (AMOC), but the future of Mediterranean-Atlantic water exchange is uncertain. It is chiefly dependent on the difference between Mediterranean and Atlantic temperature and salinity characteristics, and as a semi-enclosed basin, the Mediterranean is particularly vulnerable to future changes in climate and water usage. Certainly, there is strong geologic evidence that the Mediterranean underwent dramatic salinity and sea-level fluctuations in the past. Here, we use a fully coupled atmosphere–ocean General Circulation Model to examine the impact of changes in Mediterranean-Atlantic exchange on global ocean circulation and climate. Our results suggest that MOW strengthens and possibly stabilises the AMOC not through any contribution towards NADW formation, but by delivering relatively warm, saline water to southbound Atlantic currents below 800 m. However, we find almost no climate signal associated with changes in Mediterranean-Atlantic flow strength. Mediterranean salinity, on the other hand, controls MOW buoyancy in the Atlantic and therefore affects its interaction with the shallow-intermediate circulation patterns that govern surface climate. Changing Mediterranean salinity by a factor of two reorganises shallow North Atlantic circulation, resulting in regional climate anomalies in the North Atlantic, Labrador and Greenland-Iceland-Norwegian Seas of ±4 °C or more. Although such major variations in salinity are believed to have occurred in the past, they are unlikely to occur in the near future. However, our work does suggest that changes in the Mediterranean’s hydrological balance can impact global-scale climate.  相似文献   

Lights, camera … action? Altered attitudes and behaviour in response to the climate change film The Age of Stupid     

Rachel A. Howell   《Global Environmental Change》2011,21(1):177-187

The film The Age of Stupid depicts the world in 2055 devastated by climate change, combining this with documentary footage which illustrates many facets of the problems of climate change and fossil-fuel dependency. This study investigates the effects of the film on UK viewers’ attitudes and behaviour through a three-stage survey. Analysis of changes in attitudes focussed particularly on respondents’ concern about climate change, motivation to act, fear about the potential for catastrophe, beliefs about responsibility for action, and sense of agency. The film increased concern about climate change, motivation to act, and viewers’ sense of agency, although these effects had not persisted 10-14 weeks after seeing it. It was also successful in promoting some mitigation actions and behavioural change, although respondents reported barriers to further action, such as limited options for improving home energy efficiency among those in rented accommodation. However, filmgoers were atypical of the general public in that they exhibited very high levels of concern about climate change, knowledge about how to reduce their carbon emissions, and contact with organisations campaigning about climate change, before they saw the film. The paper considers how these factors may have enabled viewers to respond to the film as they did, as well as policy implications for those seeking to develop effective climate change communications.  相似文献   

Anaerobic precipitation of manganese and co-existing metals in mine impacted water treated with crab shell-associated minerals   总被引：1，自引：0，他引：1  

Mary Ann Robinson-Lora  Rachel A. Brennan   《Applied Geochemistry》2011,26(5):853-862

The chemical and physical treatment mechanisms by which crab shell removes metals from mine impacted water (MIW) were evaluated under anaerobic and biologically limited conditions in closed systems and kinetic tests. Raw (R-SC20) and deproteinized (DP-SC20) crab shell were tested and compared to limestone to quantify the contribution of chitin-associated minerals and proteins to alkalinity generation and metal precipitation. Single-metal closed systems (initial Mn and Fe = 0.18 mM and Al = 0.34 mM) containing 5 g/L of either R- or DP-SC20, yielded an increase in pH from 3 to 9.2-10.2, generation of 0.83-1.87 mM of alkalinity, and resulted in ?95% removal of metals within 72 h. In contrast, 5-125 g limestone/L only raised the pH to 7.8-8.3, produced lower alkalinity (0.56-0.63 mM), and resulted in less metal removal (?85%). In kinetic tests with 5 g-DP-SC20/L, removal of ?95% of the initial metal load was achieved after 0.5, 6, and 48 h for Al, Fe, and Mn, respectively. Geochemical calculations (PHREEQC) indicate that limestone-treated systems were close to equilibrium with calcite (CaCO₃), whereas octacalcium phosphate (Ca₄H(PO₄)₃) appears to be a controlling phase in systems treated with R- and DP-SC20. The probable mechanisms for Mn removal are the precipitation of rhodochrosite (MnCO₃) and/or sorption. In the case of Al and Fe, geochemical calculations point to the precipitation of hydroxides; however, visual observations in Fe systems suggest the formation of green rust, a precursor of other, more stable phases like goethite or lepidocrocite. Several factors may account for the faster changes observed with R- and DP-SC20 compared to limestone: increased dissolution and degree of supersaturation, the presence of phosphates, the release of organic compounds, and a significantly larger surface area. These results are the first to verify and quantify the capacity of crab shell-associated minerals to treat MIW under biologically limited conditions.  相似文献   

Long-term regional hurricane hazard analysis for wind and storm surge   总被引：2，自引：0，他引：2  

Pruttipong Apivatanagul  Rachel Davidson  Brian Blanton  Linda Nozick 《Coastal Engineering》2011

This paper introduces a new method to estimate the long-term regional hurricane wind and storm surge hazard. The output is a relatively small set of hurricane scenarios that together represent the regional hazard. For each scenario, the method produces a hazard-consistent annual occurrence probability, and wind speeds and surge levels throughout the study area. These scenarios can be used for subsequent evacuation or loss estimation modeling. This optimization-based probabilistic scenario (OPS) method involves first simulating tens of thousands of candidate hurricane scenarios with wind speeds and approximate surge depths. A mixed-integer linear optimization is then used to select a subset of scenarios and assign hazard-consistent annual occurrence probabilities to each. Finally, a surge model is used to estimate accurate surge depths for the reduced set of events. The method considers the correlation between winds and surge depths and the spatial correlations of each; it is computationally efficient; and it makes explicit the tradeoff between the number of scenarios selected and the errors introduced by using a reduced set of events. A case study for Eastern North Carolina is presented in which a final set of 97 hurricanes provides unbiased results with errors small enough for many practical uses.  相似文献   

Future projections of temperature-related climate change impacts on the railway network of Great Britain   总被引：1，自引：0，他引：1  

Erika J. Palin  Hazel E. Thornton  Camilla T. Mathison  Rachel E. McCarthy  Robin T. Clark  John Dora 《Climatic change》2013,120(1-2):71-93

Great Britain’s main line railway network is known to experience various temperature-related impacts, e.g. track buckling and overhead power line sag at high ambient temperatures. Climate change could alter the frequency of occurrence of these impacts. We have therefore investigated the climate change impact on various temperature-related issues, identified during workshops with rail industry specialists, using a perturbed physics ensemble (PPE) of the Met Office’s regional climate model (RCM), HadRM3. We have developed novel approaches to combine RCM data with railway industry knowledge, typically by identifying key meteorological thresholds of interest and analysing exceedance of these out to the 2040s. We performed a statistical analysis of the projected changes for each issue, via bootstrapping of the unperturbed PPE member. Although neither the PPE nor the bootstrapping analysis samples the full range of uncertainty in the projections, they nonetheless provide complementary perspectives on the suitability of the projections for use in decision-making. Our main findings include projected increases in the summertime occurrence of temperature conditions associated with (i) track buckling, (ii) overhead power line sag, (iii) exposure of outdoor workers to heat stress, and (iv) heat-related delays to track maintenance; and (v) projected decreases in the wintertime occurrence of temperatures conditions associated with freight train failure owing to brake problems. For (i), the statistical significance varied with track condition and location; for (ii) and (iii), with location; and for (iv) and (v), projected changes were significant across Great Britain. As well as assessing the changes in climate-related hazard, information about the vulnerability of the network to past temperature-related incidents has been summarised. Combining the hazard and vulnerability elements will eventually support a climate risk assessment for the industry.  相似文献   

Systematic errors in weak lensing: application to SDSS galaxy–galaxy weak lensing     

Rachel Mandelbaum  Christopher M. Hirata  Uro&#; Seljak  Jacek Guzik  Nikhil Padmanabhan  Cullen Blake  Michael R. Blanton  Robert Lupton  Jonathan Brinkmann 《Monthly notices of the Royal Astronomical Society》2005,361(4):1287-1322

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