A reduction in dissolved oxygen concentration is one of the most important direct effects of nutrient over-enrichment of coastal waters on fishes. Because hypoxia can cause mortality, reduced growth rates, and altered distributions and behaviors of fishes, as well as changes in the relative importance of organisms and pathways of carbon flow within food webs, hypoxia and anoxia can lead to large reductions in the abundance, diversity, and harvest of fishes within affected waters. Nutrient enrichment, however, typically increases prey abundance in more highly oxygenated surface waters and beyond the boundaries of the hypoxic zone. Because of this mosaic of high and low oxygen areas within a system, not only the actual oxygen concentration of bottom waters, but the spatial arrangement, predictability, and persistence of highly oxygenated, high productivity habitats, and the ability of fishes to locate and use those favorable habitats, will determine the ultimate effect of low oxygen on fish populations. Negative effects of hypoxia on fish, habitat, and food webs potentially make both fish populations and entire systems more susceptible to additional anthropogenic and natural stressors. 相似文献
Bottom-up and top-down models are used to support climate policies, to identify the options required to meet GHG abatement targets and to evaluate their economic impact. Some studies have shown that the GHG mitigation options provided by economic top-down and technological bottom-up models tend to vary. One reason for this is that these models tend to use different baseline scenarios. The bottom-up TIMES_PT and the top-down computable general equilibrium GEM-E3_PT models are examined using a common baseline scenario to calibrate them, and the extend of their different mitigation options and its relevant to domestic policy making are assessed. Three low-carbon scenarios for Portugal until 2050 are generated, each with different GHG reduction targets. Both models suggest close mitigation options and locate the largest mitigation potential to energy supply. However, the models suggest different mitigation options for the end-use sectors: GEM-E3_PT focuses more on energy efficiency, while TIMES_PT relies on decrease carbon intensity due to a shift to electricity. Although a common baseline scenario cannot be ignored, the models’ inherent characteristics are the main factor for the different outcomes, thereby highlighting different mitigation options. Policy relevance The relevance of modelling tools used to support the design of domestic climate policies is assessed by evaluating the mitigation options suggested by a bottom-up and a top-down model. The different outcomes of each model are significant for climate policy design since each suggest different mitigation options like end-use energy efficiency and the promotion of low-carbon technologies. Policy makers should carefully select the modelling tool used to support their policies. The specific modelling structures of each model make them more appropriate to address certain policy questions than others. Using both modelling approaches for policy support can therefore bring added value and result in more robust climate policy design. Although the results are specific for Portugal, the insights provided by the analysis of both models can be extended to, and used in the climate policy decisions of, other countries. 相似文献
Using a combination of geophysical and geotechnical data from Storfjorden Trough Mouth Fan off southern Svalbard, we investigate the hydrogeology of the continental margin and how this is affected by Quaternary glacial advances and retreats over the continental shelf. The geotechnical results show that plumites, deposited during the deglaciation, have high porosities, permeabilities and compressibilities with respect to glacigenic debris flows and tills. These results together with margin stratigraphic models obtained from seismic reflection data were used as input for numerical finite element models to understand focusing of interstitial fluids on glaciated continental margins. The modelled evolution of the Storfjorden TMF shows that tills formed on the shelf following the onset of glacial sedimentation (ca. 1.5 Ma) acted as aquitards and therefore played a significant role in decreasing the vertical fluid flow towards the sea floor and diverting it towards the slope. The model shows that high overpressure ratios (up to λ ca. 0.6) developed below the shelf edge and on the middle slope. A more detailed model for the last 220 kyrs accounting for ice loading during glacial maxima shows that the formation of these aquitards on the shelf focused fluid flow towards the most permeable plumite sediments on the slope. The less permeable glacigenic debris flows that were deposited during glacial maxima on the slope hinder fluid evacuation from plumites allowing high overpressure ratios (up to λ ca. 0.7) to develop in the shallowest plumite layers. These high overpressures likely persist to the Present and are a critical precondition for submarine slope failure. 相似文献
Chile has a rich, but poorly known history of placer gold mining. At present, this sector is almost nonexistent and there are some restrictions for its revival: disperse and partial information on existing resources and limited technical expertise to assess the potential of placer gold mine sites. This paper presents the background, methodology and results of the prioritization process of known prospects of this kind in Chile. This research was part of a publicly funded project aimed to incentivize the development of this industry. The ranking was carried out using the analytic hierarchy process, which allowed to include different quantitative and qualitative variables related to the economic potential, technical aspects, contextual viability and socioeconomic factors in the analysis. The results show that, despite the increasing relevance of environmental and community issues in mining development, the business potential and the economic/technical aspects are the main factors in the early selection of a site to advance in exploration and development activities. Both variables represented around 40% and 37% of weights in the final selection, respectively. In contrast, contextual viability and local socioeconomic impacts only accounted for the remaining 23%. This study also shows that the inclusion of experts with different backgrounds in the process enriches the analysis and does not significantly distort the final outcome of the prioritization. Finally, the relevance of using MCDM tools when assessing the attractiveness of mine sites for their development is highlighted, particularly when public funds for subsequent exploration activities are committed.
The Earth surface slide movement at Soledad is a mountain-slide type of movement. Estimations of the thickness of the layer which is moving range between 10 and 100 m. There is no proof that the movement is water induced, but it could be influenced by the water household. The slope of the slide area is H: D = 1: 2.
The height difference in the moving area studied, according to this paper, is 1 km. The actual rate of movement is about 12 cm/yr. 相似文献
Observation under the electron microscope of diatom frustules from Bolivian Altiplano saline lakes shows that many of these are coated with particles occurring as tiny sheets. The frustules can be found to be almost completely replaced by these sheets. Isolated sheet aggregates seem to have resulted from completely transformed frustules. Section observations of altered frustules bear out that the sheets have grown from biogenic silica through replacement. Selected area diffraction, dark field observation, microdiffraction, and elemental microanalysis show that the particles on the diatom frustules consist of a poorly crystallized MG-smectite.The unambiguous localisation of this authigenesis allows us to reconstruct its hydrochemical and sedimentological environment. Observation of the most recent lake sediments has pointed out that at least two main conditions are required for this authigenesis at 5°C: saturation with respect to amorphous silica, and a pH above 8.2. Variations in the Mg concentration have no significant effect. 相似文献
In this study, we describe remarkable intraspecific variation in sensitivity to the broadly distributed pollutants, polychlorinated biphenyls (PCBs), among wild populations of the nonmigratory estuarine Atlantic killifish (Fundulus heteroclitus). Variation among killifish populations was characterized in 28-day laboratory challenges using embryonic and larval life stages and the highly toxic, dioxin-like PCB congener, 3,3′4,4′,5-hexachlorobiphenyl (PCB126). In summarizing results for 24 populations, we show that killifish populations vary over four orders of magnitude in their sensitivity to PCB126 and that this variation is adaptive to the magnitude of contamination at their residence site. The four least-sensitive killifish populations reside in US Atlantic coast urban harbors >100 km apart from one another: New Bedford, MA, Bridgeport, CT, Newark, NJ, and Norfolk, VA, USA. Prior studies examining all but the CT population have shown that these killifish are relatively insensitive to local contaminants, with mixed evidence concerning the heritability of this trait. We show here that tolerance to PCB126 is extreme, with some mechanistic similarities among these four killifish populations. However, these populations do not respond identically to each other, and in at least one population, tolerance appears to degrade over the F1 and F2 generations tested. Complementary ongoing studies using molecular approaches provide opportunity to identify unique and shared mechanisms of tolerance in these independently evolving populations and explore the adaptive benefits and costs of contemporary evolutionary responses in the wild. 相似文献