鄱阳湖生态经济区农民工回流决策与回流农民工职业选择的经济分析

基于货币成本收益和非货币成本收益,对鄱阳湖生态经济区农民工回流决策及回流农民工的职业选择进行了经济分析。结果显示,考虑机会成本因素后的转移纯收益小于0时,转移农民工就会主动回流,而回流纯收益与转移纯收益趋于平衡时,非货币因素也会成为影响农民工回流决策的重要因素。回流农民工职业纯收益大于0,农民工就会放弃原有职业选择新职业。     

青海湖流域生态环境保护与治理对策

通过论述青海湖区生态环境现状和生态环境恶化的原因,说明了青海湖区生态环境的重要地位和作用,生态环境保护、治理的意义,并提出了具体的治理措施。     

鄱阳湖水位特征与湿地生态保护

从分析江湖关系入手,研究鄱阳湖的水位及湿地生态特征,并提出人工控湖等加强湿地生态保护的对策建议。     

关于渝北区宝圣湖长效管理机制及城市湖库保护措施的探讨

通过对渝北区宝圣湖整治措施、整治效果及存在的问题进行分析,结合城市湖库污染成因,探讨了宝圣湖水环境保护长效管理机制及城市湖库环境保护措施,为城市湖库及其他地表水的保护提供依据。     

Variability of trace metal concentrations in Jeffrey pine (Pinus jeffreyi) tree rings from the Tahoe Basin, California, USA

Trace metal accumulation in tree rings of Jeffrey pines (Pinus jeffreyi) from the Lake Tahoe basin (Sierra Nevada, CA, USA) was determined using high resolution inductively coupled plasma mass spectrometry (HR-ICP–MS). The objectives of this study were (1) to establish baseline values for aluminium (Al), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), strontium (Sr), cadmium (Cd), barium (Ba), and lead (Pb); (2) to investigate the intra-tree and inter-tree variability of these trace metals, and (3) to assess differences in metal concentrations related to automobile traffic. Two field collection sites were selected with similar ecologic attributes, one proximal to a heavily traveled highway, and the other isolated from any local source of auto emissions. At each site two trees with similar features were selected, and two increment cores collected from each tree. Cores were cross-dated, cleaned of contamination, dissected into 5-year increments, ashed, and acid digested, before analysis by HR-ICP–MS. Time series spanning 191–326 years were developed for the 12 trace metals. Variability was high within and between trees, most likely because of physiologic mechanisms for element sequestration and allocation. The best intra-tree correlation was found for Ba, Sr, Mn, and Co; of these elements, Co showed an overall increase over time, whereas Sr and Ba displayed an opposite trend, and Mn fluctuated over time. Mean Co concentration at the near-highway site was higher, whereas mean Sr, Ba, and Mn concentrations were lower, than at the control site.     

Persistence of tebufenozide in aquatic ecosystems under laboratory and field conditions

The persistence and dissipation behaviour of tebufenozide, an ecdysone agonist, were investigated: (1) under laboratory conditions in aquatic models set up in glass aquaria, and (2) under field conditions in in-situ aquatic enclosures deployed in a mixed-wood boreal forest lake. Two models were set up in the laboratory study (Study I), which was conducted at constant conditions of temperature, water pH and photoperiod. In Model I, partitioning of tebufenozide from sediment, treated at a concentration of 1400 μg kg^-1, into untreated water was examined. The results showed that the chemical moved very little from the treated sediment into water. The concentration in sediment and water decreased gradually during the 90-day incubation period. Tebufenozide disappeared faster from the top layer of sediment than from the middle and bottom layers. The half-lives of disappearance were 64 days for the top layer but >90 days for the middle and bottom layers respectively. In Model II, partitioning from water, treated at a concentration of 350 μg litre^-1, into untreated sediment was investigated. The results showed that the chemical moved from treated water into sediment due to adsorption. Little vertical downward movement of the adsorbed residues from the top layer of sediment occurred into layers beneath. The adsorbed residues were also not released readily back into water. The concentration in water and sediment decreased gradually during the 90-day incubation period. The half-life of dissipation from water was 67 days. The field microcosm study (Study II), conducted under fluctuating conditions of temperature, water pH and photoperiod, involved application of tebufenozide onto aquatic enclosures at four concentrations of 0·05, 0·10, 0·26 and 0·5 mg litre^-1. This study also showed that the chemical moved downwards from the applied location and was adsorbed onto sediment. The chemical persisted longer in Study II than in Study I. Tebufenozide, being photo-labile, probably degraded faster after constant exposure to light in Study I than after exposure to fluctuating light in Study II. At 90 days after treatment in Study I, only about 55% of the applied material persisted in the sediment, and there was little accumulation. In Study II, the material not only persisted but also was accumulated in the sediment, since at 92 days post-treatment the residues were about 25 times higher than the applied concentration level. Residues in water also decreased more rapidly in Study I than in Study II, because the concentration at 90 days post-treatment was about 41% of the applied value. In Study II, however, about 65% of the applied chemical persisted in water at 92 days post-treatment. While the long persistence of tebufenozide in both the laboratory and field studies was attributable to its low vapour pressure, low water solubility, high octanol/water partition coefficient etc., the differences in the persistence characteristics observed in the two studies were due to the fluctuating environmental conditions and water pH encountered in the field study, compared with the constant environmental conditions and water pH utilized in the laboratory study. © 1997 SCI.     

Assessment of the Antimicrobial Activity of Algae Extracts on Bacteria Responsible of External Otitis

External otitis is a diffuse inflammation around the external auditory canal and auricle, which is often occurred by microbial infection. This disease is generally treated using antibiotics, but the frequent occurrence of antibiotic resistance requires the development of new antibiotic agents. In this context, unexplored bioactive natural candidates could be a chance for the production of targeted drugs provided with antimicrobial activity. In this paper, microbial pathogens were isolated from patients with external otitis using ear swabs for over one year, and the antimicrobial activity of the two methanol extracts from selected marine (Dunaliella salina) and freshwater (Pseudokirchneriella subcapitata) microalgae was tested on the isolated pathogens. Totally, 114 bacterial and 11 fungal strains were isolated, of which Staphylococcus spp. (28.8%) and Pseudomonas aeruginosa (P. aeruginosa) (24.8%) were the major pathogens. Only three Staphylococcus aureus (S. aureus) strains and 11 coagulase-negative Staphylococci showed resistance to methicillin. The two algal extracts showed interesting antimicrobial properties, which mostly inhibited the growth of isolated S. aureus, P. aeruginosa, Escherichia coli, and Klebsiella spp. with MICs range of 1.4 × 10⁹ to 2.2 × 10¹⁰ cells/mL. These results suggest that the two algae have potential as resources for the development of antimicrobial agents.