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71.
Daily, cloud-free data interpolating empirical orthogonal function (DINEOF) reconstructions of sea-surface temperature (SST) and chlorophyll (Chl-a) satellite imagery are compiled into monthly mean images for a six-year period (2003–2008) and used to identify their spatial and temporal variability on the South Atlantic Bight. Monthly-mean SST has the highest variability on the inner-shelf, decreasing seaward approaching the more stable temperatures of the Gulf Stream (GS). Monthly-mean Chl-a concentrations are similarly highest on the inner shelf throughout the year and decrease cross-shelf toward the nutrient depleted open ocean. Empirical orthogonal function (EOF) analyses on SST and Chl-a show a clear seasonal cycle in their 1st mode of variability, with SST lagging behind Chl-a by approximately one month. The 1st EOF modes account for 95.8% and 46.4% variance of SST and Chl-a, respectively. Chl-a EOF mode 1 in particular shows a highly regionalized spatial pattern with values on the central SAB clearly out of phase with the southern and northern SAB. This regional difference is likely a result of shelf geometry and stratification, which modulate GS influence on the shelf. SST EOF mode 2 exhibits a seasonal cycle as well, which previous studies have shown to be a function of local wind. Chl-a EOF mode 2 is well correlated with the cumulative river transport onto the SAB, but accounts for a relatively small 10.8% of Chl-a variability. 相似文献
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A two-dimensional multicomponent reactive transport modeling approach was used to simulate contaminant transport and the evolution of redox processes at a large-scale kerosene-contaminated site near Berlin, Germany. In contrast to previous site-scale modeling studies that focused either on one or two contaminants or on steady-state redox conditions, multiple contaminants and electron acceptors, including mineral phase Iron (III), were considered with an evolving redox zonation. Inhibition terms were used to switch between the different electron acceptor processes in the reaction scheme. The transient evolution of redox zones and contaminant plumes was simulated for two separate transects of the site, which have different geology and ground water recharge distributions and where quite different downstream contaminant and terminal electron–accepting process (TEAP) distributions are observed. The same reaction system, calibrated to measured concentrations along one of the transects, was used in both cases, achieving a reasonable match with observed concentrations. The differences between the two transects could thus to some extent be attributed to the different hydrological and hydrogeological conditions, in particular ground water recharge distributions. Long-term simulations showed that the distribution of TEAPs evolves as Fe(III) becomes depleted, with conditions becoming increasingly methanogenic, leading to changes in contaminant plume lengths. The models were applied to assess the potential effects of planned changes in land use at the site that may affect the ground water recharge distribution. The simulated redox zonation responded strongly to changes in recharge, which in turn led to changes in the contaminant plume lengths. 相似文献
75.
Numerical hydrodynamic models of the northeastern Queensland shelf, forced by regional winds and modelled boundary currents in the northern Coral Sea, are used to provide improved estimates of general flow trajectories and water residence times within the Great Barrier Reef (GBR) shelf system. Model performance was checked against a limited set of current metre records obtained at Lark Reef (16°S) and the Ribbon Reefs (15.5°S). Estimates of water parcel trajectories are derived from a series of numerical tracer experiments, with daily releases of neutrally buoyant, un-reactive particles at 320 sites along the coast between Cape York (10.7°S) and Hervey Bay (25°S). Flow trajectories and residence times for tracer particles introduced to the GBR lagoon in the southern—ca. 22°S, central—19°S, and northern reef—14°S are emphasised. For purposes of the analysis, the year was divided into two seasons based on mean alongshore current direction. Most coastal sourced tracers entering the central GBR lagoon between 16° and 20°S during the northward-current season (January–August) primarily encounter the outer-shelf reef matrix after exiting the lagoon at its northern “head” (nominally 16°S), after 50–150 days. Up to 70% of tracer particles entering in the southward-current season (August–December) eventually crossed the lagoon to the outer-shelf reef matrix, with median crossing times between 20 and 330 days. During favourable wind conditions, tracers introduced at the coast may move rapidly across the lagoon into the reef matrix. The tracer experiments indicate that most coastal-sourced tracers entering the GBR lagoon remain near the coast for extended periods of time, moving north and south in a coastal band. Residence times for conservative tracer particles (and implied residence times for water-borne materials) within the GBR shelf system ranged from ca. 1 month to 1 year—time frames that are very long relative to development times of planktonic larvae and cycling times for nutrient materials in the water column, implying they are transformed long before reaching the outer reef matrix. 相似文献
76.
Melanie Shaw Miles J. Furnas Katharina Fabricius David Haynes Steve Carter Jochen F. Mueller 《Marine pollution bulletin》2010,60(1):113-122
Pesticide runoff from agriculture poses a threat to water quality in the world heritage listed Great Barrier Reef (GBR) and sensitive monitoring tools are needed to detect these pollutants. This study investigated the utility of passive samplers in this role through deployment during a wet and dry season at river mouths, two near-shore regions and an offshore region. The nearshore marine environment was shown to be contaminated with pesticides in both the dry and wet seasons (average water concentrations of 1.3-3.8 ng L−1 and 2.2-6.4 ng L−1, respectively), while no pesticides were detected further offshore. Continuous monitoring of two rivers over 13 months showed waters flowing to the GBR were contaminated with herbicides (diuron, atrazine, hexazinone) year round, with highest average concentrations present during summer (350 ng L−1). The use of passive samplers has enabled identification of insecticides in GBR waters which have not been reported in the literature previously. 相似文献
77.
Rigorous landslide hazard zonation using Newmark's method and stochastic ground motion simulation 总被引:2,自引:0,他引:2
Researchers and practitioners in earthquake engineering have recognized geographic information systems (GIS) to be a significant tool in modeling spatial phenomenon related to hazard and risk. GIS, as an engineering tool, has been primarily used for its spatial data storing and presentation features. Models are often simplified to be more compatible with the light computational capabilities of many GIS. If not simplified, heavy computations are generally performed external to the GIS. A prototype vector-based GIS was developed that employs a rigorous approach to Newmark's displacement method for assessing earthquake triggered landslide hazards. The rigorous Newmark's analysis provides desirable flexibility by allowing input of actual ground motions. The prototype hazard GIS incorporates a popular shot filtered noise technique for generating artificial ground motions. The rigorous approach was compared to a popular simplified approach for computing Newmark displacements. Distribution of regional displacements was found to be similar with the simplified approach giving more and larger extreme displacements. The rigorous approach is suitable for large scales to model various seismic scenarios and their effect on seismically induced landslide potential. 相似文献
78.
Miranda Miles 《GeoJournal》1996,39(1):81-88
This article examines the coping strategies of domestic workers in the city of Manzini. The Swaziland government has made many efforts to improve the social and economic conditions of the Swazi people after independence in 1968. Yet a failure to recognise domestic work as paid employment has minimised the effect of government policy in improving the lives of women who dominate this sector. The anomalies that it raises as paid housework has meant that conditions in the domestic service sector have changed little since the colonial era. Domestic workers are in practical terms, not protected by legal systems of labour relations. Coupled with other barriers that prohibit their access to land and shelter and dismally low wages, they have adopted many coping strategies in the city to maintain their families and their dignity. 相似文献
79.
A massive oil spill affected approximately 215 km of coastline as a result of the grounding and subsequent explosion of the supertanker Urquiola at the entrance to the harbour at La Coruña, Spain, on 12 May 1976. A total of 99–100 000 tons of Persian Gulf crude oil was lost, most of which burned, but an estimated 25–30 000 tons washed ashore. Over 2000 tons of dispersants were applied to the oil at sea. Land-based clean-up and control methods were largely inadequate to combat the spread of oil, and were ineffective at preventing large scale environmental damage. 相似文献
80.