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151.
Island populations of endemic birds are known to be particularly susceptible to extinction. This paper focuses on factors behind past and present declines of the highly endangered Takahe ( Porphyrio mantelli ), a flightless rail endemic to New Zealand. Subfossil evidence indicates that Takahe were once found throughout this island nation, being most abundant along forest margins and streams in lowland regions. Their numbers have declined dramatically since human colonization about 800–1000 years ago, probably due to a combination of habitat destruction and hunting by early Polynesian settlers. Today, the wild Takahe population consists of about 100 adult birds in an isolated alpine habitat and approximately 30 individuals recently released on several small offshore islands. Despite protection and intensive management, including removal of an introduced competitor (red deer, Cervus elaphus ), the alpine population has continued to decline. In contrast, the Takahe's nearest relative, the Pukeko ( Porphyrio porphyrio ) has expanded its range across New Zealand despite heavy hunting pressure since its colonization from Australia less than 1000 years ago. We suggest that, unlike Pukeko, Takahe lack appropriate behavioral responses to cope with mammalian predators such as stoats ( Mustela erminea ), which have been introduced relatively recently by European colonists. A study comparing predator defense behavior between these two closely related species is currently underway.  相似文献   
152.
Simulation models are used to examine the possible effects of discrete fuel distributions and of several fire-spread mechanisms on fire shapes. Two postulated fire spread mechanisms —heat accumulation and flame contact—are shown to yield near-ellipses in continuous fuels, but a wide range of shapes in discrete and very patchy fuels. The alternative shapes include ovoids, “tear-drop” (with the ignition point at varying positions on the major axis), and straight lines. Simulated fires in discrete, patchy fuels are less regular in shape than in uniform and continuous fuels and show little or no backburning. The results may explain certain observed differences between wildfire shapes that occur in different environments and at different burning intensities.  相似文献   
153.
The methodology for estimating radiocaesium distribution between solid and liquid phases in lakes is applied for three prealpine lakes: Lake Constance (Germany), Lake Lugano (Switzerland) and Lake Vorsee (Germany). It is based on use of the exchangeable distribution coefficient and application of the exchangeable radiocaesium interception potential (RIPex). The methodology was tested against experimental data. Good agreement was found between estimated and measured 137Cs concentrations in Lake Constance and Lake Lugano, whereas for Lake Vorsee a discrepancy was found. Bottom sediments in Lake Vorsee are composed mainly of organic material and probably cannot be described in terms of the specific sorption characteristics attributed to illitic clay minerals.  相似文献   
154.
155.
Land availability is a key consideration for evaluating the potential of biomass energy. This depends not only on how much land is physically suitable for growing the biomass crop, but also on the environmental implications of an energy farm and the extent to which land can be freed from competing uses. Energy planning should include inventories to realistically assess the amount of land potentially available for biomass production and the trade-offs involved in using such land for biomass farms.  相似文献   
156.
A general model TOHM was developed to predict the terrestrial fate of zinc, cadmium, chromium, lead and mercury emitted by the operation of a coal-fired electric generating facility. The general model consisted of interfacing submodels describing atmospheric dispersion, precipitation, soil chemistry, and soil erosion. The models were developed from input data from a semi-arid region of the southwest United States, and except for the climatic and topographic constraints, are not site specific. TOHM was found to predict no substantial increase in indigenous levels of zinc, chromium and lead in the impact (deposition) area. However, both mercury and cadmium were predicted to be emitted and eroded to the environmental sink (receiving lake) in concentrations exceeding that naturally present in the system. TOHM is currently unvalidated, though comparison of soil erosion predictions with erosion quantities measured in the impact area gives good agreement.  相似文献   
157.
A simple method is presented to evaluate microbial activity in aquatic sediments. The method is based on resazurin reduction by microbial electron transport chains and reduced chemical compounds present in the sample. The addition of m-cresol, which inhibits enzyme activity, allows one to measure microbial metabolism by difference. Small aliquots of sediment (about 1 g FW) are incubated at 20°C with resazurin solution, with and without m-cresol. The sample is then filtered and the unreduced resazurin is measured at 600 nm.

Testing the method with a bacterial suspension gave a resazurin reduction of 89 μg/h/109 cells. In a few marine coastal sediment samples, the resazurin reduction in aerobic conditions was in the range of 0.31 to 219.3 μg/h/g DW, which is equivalent to an oxygen consumption of 0.02 to 15.32 μg/h/g DW.  相似文献   
158.
The estuarine processes which can influence the release of nutrients of the River Tiber into the Tyrrhenian Sea have been studied. A conservative behaviour has been found for silicate in different hydrographic conditions.

For nitrogen, positive increments in respect of the dilution values were found in summer, due to regeneration processes; on the contrary a conservative behaviour was observed when seawater did not intrude into the river.

Dissolved phosphorus showed, in all the hydrographic conditions, a positive deviation in respect of the theoretical dilution values. This deviation has been attributed to regeneration processes which take place during the summer period. The chemical release of phosphate from particulate matter is predominant when the saline wedge is absent.  相似文献   
159.
By means of environ analysis the four-compartment model of matter cycle through the ecosystem of a mesotrophic bog is investigated. The aggregated compartments are: plants, animals, fungi combined with bacteria, and litter. The model is based on data obtained by observations and estimations made on the experimental area of “Tajozhny Log” ocated in the southern taiga sub-zone. Environ analysis enables one to set up, in the quantitative form, certain conclusions on the relative importance of individual system components and diverse processes in the matter cycle, as well as to obtain a number of quantitative characteristics of the turnover. Environ analysis is discussed as a preliminary stage in developing more complex, dynamic models of the matter cycle.  相似文献   
160.
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