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91.
Increasing anthropogenic pollution of the environment can have adverse consequences for organisms which are more subtle than direct toxicity. Detectable levels of persistent pollutants remain even if the substance is no longer used. An example is atrazine, a herbicide in common use throughout the world but one which has been banned in Germany since 1992. As a lipophilic substance, atrazine is bioconcentrated which may lead to chronic intoxication or physiological stress. In order to withstand chemical stressors, many organisms possess detoxication enzymes, for example certain P-450 monoxygenases and glutathione S-transferases. But detoxication demands cellular energy, and in developing organisms, such as fish embryos which have particularly high energy needs for sustaining growth and organogenesis, the additional energy needs of detoxication may present additional stress. In this study, uptake of atrazine, cytochrome P-450 binding spectra, effects on microsomal and soluble glutathione S-transferase activities, and the initial detoxication steps of atrazine via microsomal and soluble glutathione S-transferases were studied using early life stages of zebrafish.  相似文献   
92.
The problem of stellar structure investigations with regard to rotational motions and magnetic fields is drafted. In addition, some already known special solutions are discussed.  相似文献   
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This study investigates spatial patterns and temporal dynamics of aquifer–river exchange flow at a reach of the River Leith, UK. Observations of sub‐channel vertical hydraulic gradients at the field site indicate the dominance of groundwater up‐welling into the river and the absence of groundwater recharge from surface water. However, observed hydraulic heads do not provide information on potential surface water infiltration into the top 0–15 cm of the streambed as these depths are not covered by the existing experimental infrastructure. In order to evaluate whether surface water infiltration is likely to occur outside the ‘window of detection’, i.e. the shallow streambed, a numerical groundwater model is used to simulate hydrological exchanges between the aquifer and the river. Transient simulations of the successfully validated model (Nash and Sutcliff efficiency of 0·91) suggest that surface water infiltration is marginal and that the possibility of significant volumes of surface water infiltrating into non‐monitored shallow streambed sediments can be excluded for the simulation period. Furthermore, the simulation results show that with increasing head differences between river and aquifer towards the end of the simulation period, the impact of streambed topography and hydraulic conductivity on spatial patterns of exchange flow rates decreases. A set of peak flow scenarios with altered groundwater‐surface water head gradients is simulated in order to quantify the potential for surface water infiltration during characteristic winter flow conditions following the observation period. The results indicate that, particularly at the beginning of peak flow conditions, head gradients are likely to cause substantial increase in surface water infiltration into the streambed. The study highlights the potential for the improvement of process understanding of hyporheic exchange flow patterns at the stream reach scale by simulating aquifer‐river exchange fluxes with a standard numerical groundwater model and a simple but robust model structure and parameterization. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
97.
Dead stranded sea turtles were recovered and examined to determine the impact of anthropogenic debris and fishery activities on sea turtles on the coast of Rio Grande do Sul State, Brazil. Esophagus/stomach contents of 38 juvenile green Chelonia mydas, 10 adults and sub-adults loggerhead Caretta caretta, and two leatherback Dermochelys coriacea turtles (adult or sub-adult) included plastic bags as the main debris ingested, predominated by white and colorless pieces. The ingestion of anthropogenic debris accounted for the death of 13.2% of the green turtles examined. Signs of damage over the body and carapace indicated that fishing activities caused the death of 13.6% (3/22) of loggerheads and 1.5% (1/56) of green turtles. Therefore, it appears that direct and indirect effects of fishing activities may pose a threat to these species in Brazilian waters. Other sources of plastic debris should be investigated as well as the direct impact of fisheries, especially bottom trawl and gill nets, in order to establish effective conservation action.  相似文献   
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In this paper, the application of a fully distributed hydrological model J2000 with limited hydrological data was investigated in an alpine small and glacierized catchment, the Qugaqie (55 km2 with 7.3% glacier area), in the central Tibetan Plateau (TP). The J2000 was examined to investigate the influence on model performance, as well as on data, parameters and sensitivities. The model was calibrated with time series of discharge at the basin outlet for the summers of 2006 and 2007 and validated for the summer of 2008 by examining multiple objective functions. The model coefficients of determination were 0.62 and 0.91 for the calibration periods in 2006 and 2007, respectively, and 0.56 for the validation period in 2008. Simulated discharge was generally less than the observed values for the calibration and validation periods. The sensitivity to alteration in meteorological parameter has revealed that a change in air temperature would cause a dramatic increase of discharge in the Qugaqie catchment. Hypothetical climate scenario experiments showed that the increase of air temperature by 1°C resulted in 14% increase in runoff, whereas 20% increase in precipitation caused 9% increase in runoff but 12% reduction in glacier melt.  相似文献   
99.
岩浆侵入体对有机质生烃(成熟)作用的影响及数值模拟   总被引:3,自引:1,他引:2  
火山作用带来的热源对有机质的成烃进程和成烃量产生了重要影响,这种热效应一方面可以加速烃源岩的成熟和成烃作用,另一方面可以破坏先期形成的油藏。目前国内外对火山作用的生烃热效应方面的研究主要在热成熟度参数变化描述及岩浆侵入体引起的围岩热蚀变程度的讨论。火山作用对成烃/成藏的利弊,影响的时/空范围、程度的定量研究尚未报道。本次在前人研究基础上,建立了描述岩浆侵入体散热的热传导模型,进一步结合EasyRo%模型和前人报道的实测Ro数据进行了模型检验。通过调整模型的参数和岩浆侵入体厚度、位置及个数等进行了火山作用对有机质成熟作用及生烃影响的研究。模拟结果表明:岩浆侵入体的热作用范围是有限的,但是不同地质情况,影响的范围广度也不相同,对于相同厚度的侵入体,初始温度越高,作用范围越广,但是一般X/D3(X/D代表离接触面的距离与侵入体厚度的比值)。对于不同厚度侵入体而言,在侵入体热作用影响的范围内,侵入体越厚,热作用的范围越广。同时数值模拟结果也表明岩浆侵入体的存在可以改变烃源岩生烃期。  相似文献   
100.
The methods proposed in a foregoing paper are used for the derivation of the eddy viscosity of a two-dimensional homogeneous isotropic turbulence. In contrast to three-dimensional isotropic turbulence is shown that for the two-dimensional case the eddy viscosity (i) has no definite sign, (ii) tends to zero if the molecular viscosity tends to zero, (iii) is negative for special cases. However, the modes with large wave numbers decay in any case as is shown by investigating a dispersion relation.  相似文献   
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