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781.
Sources and remediation for mercury contamination in aquatic systems--a literature review 总被引:5,自引:0,他引:5
Wang Q Kim D Dionysiou DD Sorial GA Timberlake D 《Environmental pollution (Barking, Essex : 1987)》2004,131(2):323-336
Sources of mercury contamination in aquatic systems were studied in a comprehensive literature review. The results show that the most important anthropogenic sources of mercury pollution in aquatic systems are: (1) atmospheric deposition, (2) erosion, (3) urban discharges, (4) agricultural materials, (5) mining, and (6) combustion and industrial discharges. Capping and dredging are two possible remedial approaches to mercury contamination in aquatic systems, and natural attenuation is a passive decontamination alternative. Capping seems to be an economical and effective remedial approach to mercury-contaminated aquatic systems. Dredging is an expensive remedial approach. However, for heavily polluted systems, dredging may be more effective. Natural attenuation, involving little or no cost, is a possible and very economical choice for less contaminated sites. Proper risk assessment is necessary to evaluate the effectiveness of remedial and passive decontamination methods as well as their potential adverse environmental effects. Modeling tools have a bright future in the remediation and passive decontamination of mercury contamination in aquatic systems. Existing mercury transport and transformation models were reviewed and compared. 相似文献
782.
An investigation of biodegradation of chlorinated phenol in an anaerobic/aerobic bioprocess environment was made. The reactor configuration used consisted of linked anaerobic and aerobic reactors, which served as a model for a proposed bioremediation strategy. The proposed strategy was studied in two reactors before linkage. In the anaerobic compartment, the transformation of the model contaminant, 2,4,6-trichlorophenol (2,4,6-TCP), to lesser-chlorinated metabolites was shown to occur during reductive dechlorination under sulfate-reducing conditions. The consortium was also shown to desorb and mobilize 2,4,6-TCP in soils. This was followed, in the aerobic compartment, by biodegradation of the pollutant and metabolites, 2,4-dichlorophenol, 4-chlorophenol, and phenol, by immobilized white-rot fungi. The integrated process achieved elimination of the compound by more than 99% through fungal degradation of metabolites produced in the dechlorination stage. pH correction to the anaerobic reactor was found to be necessary because acidic effluent from the fungal reactor inhibited sulfate reduction and dechlorination. 相似文献
783.
This study focuses on sediment exchange dynamics in Mwache Creek, a shallow tidal mangrove wetland in Kenya. The surface area of the creek is 17 km2 at high water spring. The creek experiences semidiurnal tides with tidal ranges of 3.2 m and 1.4 m during spring and neap tides, respectively. The creek is ebb dominant in the frontwater zone main channel and is flood dominant in the backwater zone main channel. During rainy season, the creek receives freshwater and terrigenous sediments from the seasonal Mwache River. Heavy supply of terrigenous sediments during the El Ni?o of 1997-1998 led to the huge deposition of sediments (10(60 tonnes) in the wetland that caused massive destruction of the mangrove forest in the upper region. In this study, sea level, tidal discharges, tidal current velocities, salinity, total suspended sediment concentrations (TSSC) and particulate organic sediment concentrations (POSC) measured in stations established within the main channel and also within the mangrove forests, were used to determine the dynamics of sediment exchange between the frontwater and backwater zones of the main channel including also the exchange with mangrove forests. The results showed that during wet seasons, the high suspended sediment concentration associated with river discharge and tidal resuspension of fine channel-bed sediment accounts for the inflow of highly turbid water into the degraded mangrove forest. Despite the degradation of the mangrove forest, sediment outflow from the mangrove forest was considerably less than the inflow. This caused a net trapping of sediment in the wetland. The net import of the sediment dominated in spring tide during both wet and dry season and during neap tide in the wet season. However, as compared to heavily vegetated mangrove wetlands, the generally degraded Mwache Creek mangrove wetland sediment trapping efficiency is low as the average is about 30% for the highly degraded backwater zone mangrove forest and 65% in the moderately degraded frontwater zone mangrove forest. 相似文献
784.
We present results from experiments on the migration of 137Cs through columns containing quartz sand. Times for 137Cs movement through these columns and the quantity of 137Cs adsorbed by the sand decreased as the ionic strength of the pore water increased from 0.002 to 0.1 m. The breakthrough curves were characterized by a slow approach towards steady-state concentrations as well as by long tails, indicating that 137Cs adsorption to the sand grains was, at least in part, controlled by rate-limited reactions. Various formulations for solute mass transfer were tested for their ability to fit the experimental breakthrough curves. Based on a statistical analysis, a nonlinear, two-site model was identified as the most appropriate for describing the suite of experimental data. Variation in the model parameter that describes the rate of 137Cs adsorption to the sand showed no consistent pattern with changes in ionic strength. In contrast, model parameters describing the sorption capacity of the sand grains and the fraction of kinetic sorption sites on the sand decreased with increasing ionic strength. The parameter describing the rate of 137Cs desorption varied directly with changes in ionic strength. 相似文献
785.
Trade-offs in foraging success and predation risk with spatial position in colonial spiders 总被引:1,自引:1,他引:1
Summary Colonial web-building spiders respond to trade-offs between selective forces relative to spatial position within colonies and thus provide support for the selfish herd theory. The size distribution of spiders within colonies of Metepeira incrassata, a colonial orb-weaver (Araneae: Araneidae) from tropical Mexico is nonrandom; larger (mature) spiders and females guarding eggsacs are more prevalent in the center, whereas more small (immature) spiders are found on the periphery. Experimental field studies with spiders of selected size classes show that larger spiders actively and aggressively seek protected positions in the center of the colony webbing, even though prey availability and capture rates are significantly higher on the periphery. Attacks by predatory wasps, other spiders, and hummingbirds are more frequent on the periphery than in the core of the colony. Reproductive females on the periphery are at greater risk because they are captured more often than smaller spiders, and if their egg sacs consequently remain unguarded, chances of cocoon parasitism are increased. As a result, spiders in the core of the colony have greater reproductive success, producing more egg sacs with greater hatching frequency. Colonial spiders thus appear to be making a trade-off between foraging and protection from predation and show a spatial organization predicted by the selfish herd theory. The influence of such trade-offs on individual fitness and the structure of colonies is discussed.
Offprint requests to: G.W. Uetz 相似文献
786.
Conservation Corridors and Contagious Disease: A Cautionary Note 总被引:10,自引:0,他引:10
George R. Hess 《Conservation biology》1994,8(1):256-262
Recent conservation proposals frequently include the establishment of corridors to connect isolated patches of wildlife habitat. Much attention has been focused on the potential benefits of corridors with little note given to potentially adverse consequences. A simulation model is developed here to study the effect of corridors on the survival of a metapopulation in the presence of a fatal disease that is spread by direct contact between susceptible and infected individuals. For the disease modeled here, a landscape of patches connected by corridors generally suffers fewer metapopulation extinctions than a landscape of isolated patches. However, under a narrow range of conditions, results suggest that corridors may dramatically increase the probability of metapopulation extinction. This occurs when disease-induced mortality is low enough to allow infected individuals to spread the disease, but high enough to reduce population levels to the point that random demographic and environmental events cause frequent metapopulation extinctions. This has important implications for the design and management of conservation reserve networks. Although discussion focuses primarily on conservation corridors, the model results apply to any management techniques that increase the movement of individuals among populations. 相似文献
787.
Elias Mavromatidis Theodoros I. Lekas George Kallos 《Environmental Fluid Mechanics》2007,7(6):537-568
A three-dimensional numerical model (Regional Atmospheric Modeling System—-RAMS) was used to study the formation and evolution
of water forms in a two-layer cloud structure observed during a field campaign over Brest (France). The model performance
in regular operations, using conventional meteorological data as initial and lateral boundary conditions, was also examined.
Remote sensing observations of the cloud system and in-situ aircraft data, selected during the campaign, were used to validate
the model outputs. The model simulations showed that the lower cloud formation was characterized by high number concentration
of pristine ice and snow, while the concentration of aggregates, graupel and hail were considerably lower. Hydrometeors in
liquid phase appeared demonstrating high number concentration and water content on the top of this layer. The upper cloud
layer consisted only of frozen water substances in lower amounts. The qualitative and quantitative comparison of the model-calculated
meteorological and microphysical fields to the available observational data revealed that the model reflected fairly well
the cloud structure (e.g., the spatio-temporal variability of the cloud parameters, the geometry of the cloud system). However,
there were deviations as far as the model underestimating the ice water content (IWC) and number concentration (Nt) fields is concerned, especially at the atmospheric layer between 2.5 and 4 km of altitude. These deviations of the model
simulated quantities from the measured ones may be attributed either to the performance of the model’s microphysics scheme,
to instrument inaccuracies and to the local disturbance caused by the aircraft. 相似文献
788.
789.
A quantitative methodology for indexing environmental sensitivity and pollution potential 总被引:1,自引:0,他引:1
A methodology for rating the suitability of sites forthe location of industrial facilities is formulated and appliedto the case of a coal-fired power plant location. The methodologycomprises two major interlinked components: the environmentalplant location indexing component, which involves theidentification, scaling and weighting of environmentalsensitivity factors; and the impact analysis component, whichinvolves the superimposition of the pollution generation impactsof an industrial facility on spatially gridded zones of variousenvironmental sensitivities. For each rectangular areal unitdefined by a square grid, the Unit Pollution Potential Index isdetermined by the severity and distribution of key environmentalsensitivity factors and the coverage of superimposed pollutanteffects as determined by contaminant fate and transport models.For any alternative site of a planned facility, the summation ofthe unit indices over the area of influence of the facilityprovides the quantitative Pollution Index, which can be used as abasis for comparison of alternative sites for planned facilities.For this paper, this methodology is applied to the hypotheticalcase of the siting of a coal-fired power plant in thenortheastern region of the United States, in which threealternative sites are considered. The three sites: A, B and Cyielded indices of 47.83, 47.91 and 47.6, respectively, indicatingthat site C is the most suitable for siting the power plant. 相似文献
790.
Van Dolah RF Chestnut DE Jones JD Jutte PC Riekerk G Levisen M McDermott W 《Environmental monitoring and assessment》2003,81(1-3):85-95
The South Carolina Estuarine and Coastal Assessment Program (SCECAP) was initiated in 1999 to assess the condition of the state's coastal habitats using multiple measures of water quality, sediment quality, and biological condition. Sampling was subsequently expanded to include components required for the National Coastal Assessment (Coastal 2000) Program. Habitats are classified as either tidal creeks (<#60; 100 meters in width) or larger open water bodies. Approximately 30 sites are sampled within each habitat during the summer months using a probability-based random sampling design. Results obtained from the first two years of sampling documented significant differences in several water quality parameters (DO, salinity, pH, turbidity, fecal coliform bacteria, total nitrogen, TKN, total phosphorus) and biological measures (chlorophyll-a, finfish and crustacean abundance and biomass and a number of benthic species) between the tidal creek and open water habitats. These differences highlight the value of partitioning shallow water habitats separately from the larger open water bodies traditionally sampled in estuarine monitoring programs, especially since tidal creeks serve as critical nursery areas for many species. Based on the differences observed, there is a clear need to identify different physical and biological thresholds for evaluating the condition of each habitat type. 相似文献