The relative importance of chlorophyll and colored dissolved organic matter (CDOM) to the prediction of the diffuse attenuation coefficient in shallow estuaries     

Alison B. Branco  James N. Kremer 《Estuaries and Coasts》2006,29(3):530-530

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Nitrogen dynamics in nontidal littoral sediments: Role of microphytobenthos and denitrification     

Kristina Sundbäck  Alison Miles  Frank Linares 《Estuaries and Coasts》2006,29(6):1196-1211

Previous measurements from cool microtidal temperate areas suggest that microphytobenthic incorporation of nitrogen (N) exceeds N removal by denitrification in illuminated shallow-water sediments. The present study investigates if this is true also for fully nontidal sediments in the Baltic Sea., Sediment-water fluxes of inorganic (DIN) and, organic nitrogen (DON) and oxygen, as well as denitrification, were measured in early autumn and spring, in light and dark, at four sites representing different sediment types. All sediments were autotrophic during the daytime both in the autumn and spring. On a 24-h time scale, they were autotrophic in the spring and heterotrophic in early autumn. Sediments funcitoned as sources of DIN and DON during the autumn and sinks during the spring, with DON fluxes dominating or being as important as DIN fluxes. Microphytobenthos (MPB) activity controlled fluxes of both DIN and DON. Significant differences between sites were found, although sediment type (sand or silt) had no consistent effect on the magnitude of MPB production or nutrient fluxes. The clearest effect related to sediment type was found for denitrification, although only in the autumn, with higher rates in silty sediments. Estimated N assimilation by MPB, based on both net primary production (0.7–6.5 mmol N m⁻² d⁻¹) and on 80% of gross primary production (1.9–9.4 mmol N m⁻² d⁻¹) far exceeded measured rates of denitrification (0.01–0.16 mmol N m⁻² d⁻¹). A theoretical calculation showed that MPB may incorporate between 40% and 100% of the remineralized N, while denitrification removes, <5%. MPB assimilation of N appears to be a far more important N consuming process than denitrification in these nontidal, shallow-water sediments.  相似文献   

Uncertainty analysis for estimating flood frequencies for ungauged catchments using rainfall-runoff models     

David A. Jones  Alison L. Kay 《Advances in water resources》2007

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Spatial variability in selenium and mercury interactions in a key recreational fish species: Implications for human health and environmental monitoring     

H.J. Jones  E.C.V. Butler  C.K. Macleod 《Marine pollution bulletin》2013

Selenium’s (Se) protective effects against mercury (Hg) toxicity have been demonstrated; however, this is seldom considered in health assessments, where dietary exposure is still evaluated by Hg concentration alone. Se:Hg ratios and selenium health benefit values (Se HBVs) offer a more comprehensive seafood safety model. Here we describe total mercury (THg), methylmercury (MeHg) and Se concentrations in fish from a Hg-polluted estuary. Spatial variation in THg, MeHg and Se was evident, though all regions maintained Se:Hg ratio values >1. Se HBV varied between regions and in one region mean negative values (−5.17) were evident. This study provides the first evidence that quoting a single all-encompassing Se HBV is not appropriate when species demonstrate strong site fidelity. It highlights the need for research into Se–Hg relationships in environments with established Hg pollution and reinforces the assertion that Se concentration be considered in assessments of human health risk to Hg exposure.  相似文献   

Bronfenbrenner’s bioecological theory for modelling community resilience to natural disasters   总被引：1，自引：1，他引：0  

Helen J. Boon  Alison Cottrell  David King  Robert B. Stevenson  Joanne Millar 《Natural Hazards》2012,60(2):381-408

This paper advocates the use of Bronfenbrenner’s bioecological theory as a framework to analyse resilience at diverse scales. Bronfenbrenner’s bioecological theory can be employed to (a) benchmark social resilience, (b) target the priority interventions required and (c) measure progress arising from these interventions to enhance resilience to natural disasters. First, the paper explores resilience to natural disasters in the context of climatic change as building resilience is seen as a way to mitigate impacts of natural disasters. Second, concepts of resilience are systematically examined and documented, outlining resilience as a trait and resilience as a process. Third, issues arising in relation to the measurement of resilience are discussed. Fourth, Bronfenbrenner’s bioecological systems theory is described and proffered to model and assess resilience at different scales. Fifth, studies are described which have supported the use of the bioecological systems theory for the study of resilience. Sixth, an example of the use of Bronfenbrenner’s theory is offered and the paper concludes with suggestions for future research using Bronfenbrenner’s theory.  相似文献   

Latest Pleistocene and Holocene dune construction at the north-eastern edge of the Rub Al Khali, United Arab Emirates   总被引：4，自引：0，他引：4  

Andrew S. Goudie  Alison Colls  Stephen Stokes  Adrian Parker  Kevin White  & Asma Al-Farraj 《Sedimentology》2000,47(5):1011-1021

Optical dating of two dune profiles developed in linear dunes in Ras Al Khaimah, United Arab Emirates, has been used to establish the timing and rate of dune accretion. One section at Awafi was over 17 m high, while that at Idhn was over 40 m high. The Awafi dune appears to have accumulated very rapidly ≈10 000 years ago, with a vertical accumulation rate of about 3·3 m ka⁻¹. The Idhn dune appears to have accumulated over the past 1000 years, with 20 m of sediment accumulating in a time period of about 270 years. The Awafi dune may have accumulated in response to the transgression of the Persian Gulf by rising sea levels in late Pleistocene and Holocene times. The Idhn dune may have accumulated rapidly because of intensified human activity, a short-lived climatic event, or because it may periodically be reactivated after erosion by fluvial action at its base.  相似文献   

A 6000 year water level history of Europe Lake, Wisconsin, USA     

Barry B. Miller  Allan F. Schneider  Alison J. Smith  Donald F. Palmer 《Journal of Paleolimnology》2000,23(2):175-183

Europe Lake occupies a small, closed, basin that would have been an embayment in Lake Michigan during the high water level events in the larger lake. Cores recovered from the lake reveal late Holocene water level fluctuations in the basin that are inferred from changes in taxa and abundance of molluscs, ostracodes, magnetic susceptibility, organic carbon, and oxygen isotopes.Non-glacial, Holocene lacustrine/paludal sedimentation in this portion of the Europe Lake basin started after 6600 RCYBP and was probably initiated by a rise in the water table of the deep bedrock aquifer, during the Nipissing transgression in Lake Michigan. Isotopically light ground water from this source was probably a major contributor during this phase to the negative ¹⁸O spikes in Valvata tricarinata and Amnicola limosa.The start of stable lacustrine conditions is marked by maximum diversity of ostracode and mollusc taxa and a shift toward much more positive ¹⁸O values. The Europe Lake basin at this time became an embayment of Lake Michigan. This event was probably coeval with the peak of the Nipissing transgression, when the water plane reached an altitude of about 183 m.The isolation of Europe Lake from Lake Michigan started at about 2390 RCYBP and is probably due to a drop in water level in Lake Michigan and/or to isostatic uplift of the Door Peninsula. Since isolation from Lake Michigan, water levels in Europe lake have been controlled primarily by fluctuations in local precipitation, evaporation and ground water discharge.  相似文献   

Past,present and future nutrient loads of the North Sea: Causes and consequences     

Jan E. Vermaat  Abigail McQuatters-Gollop  Marieke A. Eleveld  Alison J. Gilbert 《Estuarine, Coastal and Shelf Science》2008

Comprehensive, aggregate nutrient budgets were established for two compartments of the North Sea, the shallow coastal and deeper open regions, and for three different periods, representing pre-eutrophication (∼1950), eutrophication (∼1990) and contemporary (∼2000) phases. The aim was to quantify the major budget components, to identify their sources of variability, to specify the anthropogenic components, and to draw implications for past and future policy. For all three periods, open North Sea budgets were dominated (75%) by fluxes from and to the North-East Atlantic; sediment exchange was of secondary importance (18%). For the coastal North Sea, fluxes during the eutrophication period were dominated by sediment exchange (49% of all inputs), followed by exchange with the open sea (21%), and anthropogenic inputs (19%). Between 1950 and 1990, N-loading of coastal waters increased by a factor of 1.62 and P-loading by 1.45. These loads declined after 1990. Interannual variability in Atlantic inflow was found to correspond to a variability of 11% in nutrient load to the open North Sea. Area-specific external loads of both the open and coastal North Sea were below Vollenweider-type critical loads when expressed relative to depth and flushing. External area-specific load of the coastal North Sea has declined since 1990 from 1.8 to about 1.4 g P m⁻² y⁻¹ in 2000, which is close to the estimate of 1.3 for 1950. N-load declined less, leading to an increase in N/P ratio.  相似文献   

Variable Tl,Pb, and Cd concentrations and isotope compositions of enstatite and ordinary chondrites—Evidence for volatile element mobilization and decay of extinct 205Pb          下载免费PDF全文

Emeliana Palk  Rasmus Andreasen  Mark Rehkämper  Alison Stunt  Katharina Kreissig  Barry Coles  Maria Schönbächler  Caroline Smith 《Meteoritics & planetary science》2018,53(2):167-186

New Tl, Pb, and Cd concentration and Tl, Pb isotope data are presented for enstatite as well as L- and LL-type ordinary chondrites, with additional Cd stable isotope results for the former. All three chondrite suites have Tl and Cd contents that vary by more than 1–2 orders of magnitude but Pb concentrations are more uniform, as a result of terrestrial Pb contamination. Model calculations based on Pb isotope compositions indicate that for more than half of the samples, more than 50% of the measured Pb contents are due to addition of modern terrestrial Pb. In part, this is responsible for the relatively young and imprecise Pb-Pb ages determined for EH, L, and LL chondrites, which are hence only of limited chronological utility. In contrast, four particularly pristine EL chondrites define a precise Pb-Pb cooling age of 4559 ± 6 Ma. The enstatite chondrites (ECs) have highly variable ε^114/110Cd of between about +3 and +70 due to stable isotope fractionation from thermal and shock metamorphism. Furthermore, nearly all enstatite meteorites display ε²⁰⁵Tl values from −3.3 to +0.8, while a single anomalous sample is highly fractionated in both Tl and Cd isotopes. The majority of the ECs thereby define a correlation of ε²⁰⁵Tl with ε^114/110Cd, which suggests that at least some of the Tl isotope variability reflects stable isotope fractionation rather than radiogenic ingrowth of ²⁰⁵Tl from ²⁰⁵Pb decay. Considering L chondrites, most ε²⁰⁵Tl values range between −4 and +1, while two outliers with ε²⁰⁵Tl ≤ −10 are indicative of stable isotope fractionation. Considering only those L chondrites which are least likely to feature Pb contamination or stable Tl isotope effects, the results are in accord with the former presence of live ²⁰⁵Pb on the parent body, with an initial ²⁰⁵Pb/²⁰⁴Pb = (1.5 ± 1.4) × 10⁻⁴, which suggests late equilibration of the Pb-Tl system 26–113 Ma after carbonaceous chondrites (CCs). The LL chondrites display highly variable ε²⁰⁵Tl values from −12.5 to +14.9, also indicative of stable isotope effects. However, the data for three pristine LL3/LL4 chondrites display an excellent correlation between ε²⁰⁵Tl and ²⁰⁴Pb/²⁰³Tl. This defines an initial ²⁰⁵Pb/²⁰⁴Pb of (1.4 ± 0.3) × 10⁻⁴, equivalent to a ²⁰⁵Pb-²⁰⁵Tl cooling age of 55 + 12/−24 Ma (31–67 Ma) after CCs.  相似文献   

Diversity and burglary: Do community differences matter?     

Usman L. Gulma  Andy Evans  Alison Heppenstall  Nick Malleson 《Transactions in GIS》2019,23(2):181-202

Diversity within a population has been linked to levels of both social cohesion and crime. Neighborhood crimes are the result of a complex set of factors, one of which is weak community cohesion. This article seeks to explore the impacts of diversity on burglary crime in a range of neighborhoods, using Leeds, UK as a case study. We propose a new approach to quantifying the correlates of burglary in urban areas through the use of diversity metrics. This approach is useful in unveiling the relationship between burglary and diversity in urban communities. Specifically, we employ stepwise multiple regression models to quantify the relationships between a number of neighborhood diversity variables and burglary crime rates. The results of the analyses show that the variables that represent diversity were more significant when regressed against burglary crime rates than standard socio‐demographic data traditionally used in crime studies, which do not generally use diversity variables. The findings of this study highlight the importance of neighborhood cohesion in the crime system, and the key place for diversity statistics in quantifying the relationships between neighborhood diversities and burglary. The study highlights the importance of policy planning aimed at encouraging community building in promoting neighborhood safety.  相似文献