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排序方式: 共有244条查询结果,搜索用时 15 毫秒
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Thomas Petzoldt Lars Rudolf Karsten Rinke Jürgen Benndorf 《Ecological modelling》2009,220(9-10):1358-1368
A mechanistic model was applied to study the influence of diurnal vertical migration (DVM) of planktonic crustaceans on the succession and composition of the phytoplankton community. While zooplankton was restricted to only one functional group, the phytoplankton community was divided into two functional groups which are distinguished by their maximum growth rates and vulnerability to zooplankton grazing. DVM causes a pulsed grazing regime and may also entail a corresponding reduction of the cumulative daily rates of ingestion and losses of zooplankton. To study the relative importance of these two mechanisms of DVM to phytoplankton we performed a scenario analysis consisting of 5 different scenarios. The results show that DVM has a strong influence on the phytoplankton community. Well edible algae benefit during the first 3–4 weeks of summer stratification by reduced daily grazing. The typical shift from small, well edible algae to larger, poorly or non-edible phytoplankton is distinctly delayed. Under the assumption of unchanged daily grazing, however, a pulsed grazing regime has nearly no influence on the resulting phytoplankton composition. As similar effects are also found for completely non-edible phytoplankton, indirect effects via phosphorus availability must be assumed. Thus, the scenario analysis reveals that the observed effects of DVM on phytoplankton can be explained by a combination of two mechanisms: (1) reduction of the daily zooplankton grazing, and (2) changed assimilation and remineralisation of phosphorus. Surprisingly and in contradiction to earlier reports there is almost no DVM effect on phytoplankton due to the sole action of a pulsed grazing regime. 相似文献
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Przemyslaw Zydak Rudolf Klemens 《Journal of Loss Prevention in the Process Industries》2007,20(4-6):417-426
Dust dispersion from a layer is a complicated problem, which has not been completely solved yet, especially if an Eulerian–Eulerian approach has to be used to model the two-phase dusty flow. In previous investigation, a phenomenological model of the dust dispersion process from a layer was developed, but the evaluation of the model revealed some weaknesses. In the current paper, the model of the dust dispersion process was presented and three improvements of the model were studied: Saffman force, Magnus force and particles collisions. The implementation of Magnus and Saffman forces into the code did not improve the numerical results and it was shown that it had very little influence on the dust lifting process, in case the phenomenological model of the layer is used. Some explanations were proposed in the paper. Besides, an empirical model of particles collisions was also added to the code and its influence on the results was studied. It was shown that the particles collisions model improved the obtained results, but further modifications are to be studied in the future. 相似文献
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Carmen Rizzo Luigi Michaud Christoph Syldatk Rudolf Hausmann Emilio De Domenico Angelina Lo Giudice 《Environmental science and pollution research international》2014,21(4):2988-3004
Influence of different parameters on biosurfactant (BS) activity was carried out on strains that were isolated from the polychaetes Megalomma claparedei, Sabella spallanzanii and Branchiomma luctuosum and additional 30 strains that were previously identified as potential BS producers from crude oil enrichments of the same polychaete specimens. The selection of BS-producing strains from polychaete natural samples was carried out by using standard screening tests. The BS activity by each isolate was evaluated for the effect of salinity and temperature on emulsion production and surface tension reduction, during incubation in mineral medium supplemented with tetradecane or diesel oil. All isolates showed a similar time course of BS activity, and the latter was more influenced by salinity rather than temperature. Some of the BS producers belonged to genera that have not (i.e. Citricoccus, Cellulophaga, Tenacibaculum and Maribacter) or have poorly been (Psychrobacter, Vibrio, and Pseudoalteromonas) reported as able to produce BSs. This is remarkable as some of them have previously been detected in hydrocarbon-enriched samples. Results confirm that filter-feeding polychaetes are an efficient source for the isolation of BS producers. 相似文献
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Angélique San Miguel Peter Schröder Rudolf Harpaintner Thierry Gaude Patrick Ravanel Muriel Raveton 《Environmental science and pollution research international》2013,20(5):3464-3471
Mixed pollution is a characteristic of many industrial sites and constructed wetlands. Plants possessing an enzymatic detoxifying system that is able to handle xenobiotics seems to be a viable option for the removal of mixed persistent contaminants such organochlorines (OCs: monochlorobenzene (MCB), 1,4-dichlorobenzene (DCB), 1,2,4-trichlorobenzene (TCB), γ-hexachlorocyclohexane (HCH)). In this study, Phragmites australis plants were exposed to sub-lethal concentrations of OCs (7 days), in single-exposure (0.8 to 10 mg?l?1) and in mixture of OCs (0.2 mg?l?1 MCB?+?0.2 mg?l?1 DCB?+?2.5 mg?l?1 TCB?+?0.175 mg?l?1 HCH). Studies were conducted on the detoxification phase II enzymes; glutathione S-transferases (GST), and glucosyltransferases (UGT). Measurements of GST and UGT activities revealed that OCs may be buffered by glutathione and glucose conjugation. There appeared to be a correlation between the effects on phase II enzymes and the degree of chlorination of the benzene ring with, for example, the greatest effects being obtained for HCH exposure. In the case of mixed pollution, the induction of some GST isoenzymes (CDNB, 35 % non-significant) and UGT (118 %) in leaves and the inhibition of phase II enzymes in the other organs were measured. UGTs appear to be key enzymes in the detoxification of OCs. 相似文献
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A new polymer ligand exchanger (PLE) has been developed for the removal of phosphate in wastewater. This PLE, consisting of lanthanum(III) bound to chelex-100 resin, was prepared by passing LaCl3 solution through a column of chelex-100. Uptake of phosphate from water by this La-chelex resin was investigated in the column mode. The La-chelex resin was able to remove phosphate efficiently from water, and the uptake of phosphate was not affected by the presence of large amounts of anions (0.1M) such as chloride and sulfate. The La-chelex resin was also able to efficiently remove phosphate from seawater to <0.1mg-Pl(-1), and regenerated for reuse by removing the sorbed phosphate by eluting with 6M HCl. 相似文献