排序方式: 共有7条查询结果,搜索用时 15 毫秒
1
1.
ROUABHI Rachid DJEBAR-BERREBBAH H DJEBAR MR 《应用与环境生物学报》2006,12(4):514-517
Harmful bugs affect food production,directly by the qualitativeor quantitative reduction of the harvests,or indirectly while servinglike vectors of several illnesses of the plants and human[1].Many chemical products are used by human for a long time inthe… 相似文献
2.
Neuhauser EF Cukic ZV Malecki MR Loehr RC Durkin PR 《Environmental pollution (Barking, Essex : 1987)》1995,89(3):293-301
This study examines the steady state and non-steady state kinetics of five metals, cadmium, copper, lead, nickel, and zinc in earthworms. The steady state kinetics are based on field studies in which worms from contaminated and uncontaminated sites were collected and measurements were made of concentrations in the earthworms and soils. For each of the metals, evidence suggests that bioconcentration depends on the metal concentrations in the soil; bioconcentration is greater at lower soil concentrations. The studies of non-steady state kinetics involve uptake and elimination experiments in which worms are transferred from an uncontaminated soil to a contaminated soil (uptake studies) or from a contaminated soil to an uncontaminated soil (elimination studies). The voiding time is shown to be an important experimental variable in determining the measured levels of metal in earthworms because experimental measurements are usually made on a worm-soil complex (i.e. the soft tissue of the worm and the soil in the gut of the worm). Thus, for metals that are bioconcentrated in worm tissue, increasing the voiding period increases the concentration of the metal in the worm-soil complex. Conversely, for metals that are not bioconcentrated, increasing the voiding time leads to a decrease in concentrations in the worm-soil complex. 相似文献
3.
Recent growth in the distribution and abundance of cougars (Puma concolor) throughout western North America has created opportunities, challenges, and problems for wildlife managers and raises questions
about what factors affect cougar populations. We present an analysis of factors thought to affect cougar distribution and
abundance across the broad geographical scales on which most population management decisions are made. Our objectives were
to: (1) identify and evaluate landscape parameters that can be used to predict the capability of habitats to support cougars,
and (2) evaluate factors that may account for the recent expansion in cougar numbers. Habitat values based on terrain ruggedness
and forested cover explained 73% of the variation in a cougar abundance index. Indices of cougar abundance also were spatially
and temporally correlated with ungulate abundance. An increase in the number and total biomass of ungulate prey species is
hypothesized to account for recent increases in cougars. Cougar populations in Montana are coping with land development by
humans when other components of habitat and prey populations are sufficient. Our analysis provides a better understanding
of what may have influenced recent growth in cougar distribution and abundance in Montana and, when combined with insights
about stakeholder acceptance capacity, offers a basis for cougar management at broad scales. Long-term conservation of cougars
necessitates a better understanding of ecosystem functions that affect prey distribution and abundance, more accurate estimates
of cougar populations, and management abilities to integrate these components with human values. 相似文献
4.
The results of analyses for polychlorodibenzofuran (PCDF) content in two samples of polychlorobiphenyl (PCB) from used electrical transformers are presented and discussed. In neither sample was there evidence for enhanced PCDF concentrations even though one of them had been subjected to overheating while in service. 相似文献
5.
Results of analyses of eight samples of technical pentachlorophenol conducted by three different analytical methods are presented and discussed. 相似文献
6.
Wood samples treated with technical pentachlorophenol (PCP), technical sodium pentachlorophenoxide (NaPCP) and octachlorodibenzo-p-dioxin have been exposed outdoors for periods up to years. Analysis of extracts from the samples show that photolytic reductive dechlorination of highly chlorinated dibenzo-p-dioxins to less chlorinated isomers occurs. However there is no discernible increase in polychlorodibenzo-p-dioxin concentrations in the technical PCP treated wood presumably because further photolytic reactions and volatilisation compete effectively with the photolytic formation. There is no evidence for formation of octachlorodibenzo-p-dioxin (OCDD) in technical PCP treated wood in this study, probably because photolytic destruction and volatilisation compete effectively with formation reactions when the initial OCDD concentration is relatively high. 相似文献
7.
Nitrogen and phosphorus flux rates from sediment in the lower St. Johns River estuary 总被引:2,自引:0,他引:2
Internal cycling of nutrients from the sediment and water column can be an important contribution to the total nutrient load of an aquatic ecosystem. Our objective was to estimate the internal nutrient loading of the Lower St. Johns River (LSJR). Dissolved reactive phosphorus (DRP) and ammonium (NH(4)-N) flux from sediments were measured under aerobic and anaerobic water column conditions using intact cores, to estimate the overall contribution of the sediments to P and N loading to the LSJR. The DRP flux under aerobic water column conditions averaged 0.13 mg m(-2) d(-1), approximately 37 times lower than that under anaerobic conditions (4.77 mg m(-2) d(-1)). The average NH(4)-N released from the anaerobic cores (18.03 mg m(-2) d(-1)) was also significantly greater than in the aerobic cores for all sites and seasons, indicating the strong relationship between nutrient fluxes and oxygen availability in the water column. The mean annual internal DRP load was estimated to be 330 metric tons (Mg) yr(-1), 21% of the total P load to the river, while the mean annual internal load of NH(4)-N was determined to be 2066 Mg yr(-1), 28% of the total N load to the LSJR estuary. As water resource managers reduce external loading to the LSJR the frequency of anaerobic events should decline, thereby reducing nutrient fluxes from the sediment to the water column, reducing the internal loading of DRP and NH(4)-N. Results from this study demonstrate that the internal flux of nutrients from sediments may be a significant portion of the total load and should be accounted for in the total nutrient budget of the river for successful restoration. 相似文献
1