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Wim Salomons 《Journal of Soils and Sediments》2005,5(1):2-8
- Dedicated to Prof. Dr. Ulrich Förstner on his 65th birthdayBackground Sediments pose problems at their deposition sites when there is too little sediment (e.g. wetlands) or too much sediment (e.g. navigable waterways) and, additionally, when they are contaminated. These problems often have their origin upstream in the river catchment. Objective Global aspects of changes concerning sediment quantity and quality, as they affect downstream areas, are reviewed. A case study of estuarine sediments demonstrates how a holistic approach helps in understanding and predicting their present and future quality. Results and Conclusions Globally, large reservoirs intercept between 25 and 30% of the sediment and consequently supply the coast with impacts on wetlands and coastal morphology. In estuaries, the composition of sediments is determined by the mixing of marine sediments supplied from the coast and the supply by rivers. Natural tracers can be used to predict mixing ratios of marine to fluvial sediments in estuaries, and hence their contamination. Scenarios on implementation of pollution abatement, the implementation of regulations as well as climate change are needed to predict future sediment quality in downstream areas. The results show, even for a ‘green’ scenario, that sediment quality in the Rhine catchment will pose future problems due to the temporal storage of contaminants in soils and sediments.Recommendations and Outlook The current methods applied make use of existing models linking sediment transport with point and diffuse sources in the river catchments and scenarios on the development of strength of point and diffuse sources. However, more effort is needed to come to a uniform framework which includes land use changes and links with more advanced scenario methodology for long to medium-term management of sediment quality and quantity in river catchments. 相似文献
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A 21-d incubation experiment was conducted under controlled laboratory conditions to study the effects of elevated temperatures(10,25,and 40℃)on some microbiological and biochemical properties in flooded paddy soil amended or unamended with urea at 100μg N g^-1 soil and /or insecticide(triazophos) at field rate(FR).Enhancements in temperature led to increase the electron transport system(ETS)/dehydrogenase activity and phospholipid contents of the soil,while soil organic matter phenol and protein contents decreased with increasing tenperature with or wihtout the addition of inputs.An incerease of temperature from 10℃ to 25 or 40℃ enhanced the ETS activity 2 folds (on avergae for all soils),while the inclusion of N and insecticide increased and decreased it ,respectively,compared to the control.The soil phenol and protein contents were highly correlated with temperatures(for all soils,r=-0.936 and -0.971,respectively)and the additions of N and insecticide produced slight reductions and enhancemetns in them,respectively,At a particular tempeature,the soil protein contents remained unaffected among all the soil treatments.An overall slight increase in phospholipid contents with N and a small decline with insecticide addition were noticed against the untreated soil.the toxcity of fertilizer and insecticide decrased as the incubation temperature increased suggesting faster degradation of agrochemicals with raising temperature. 相似文献
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针对山地果园单向牵引式双轨运输机运行时存在钢丝绳松脱或断裂等问题,研制了一种摩擦制动装置,在描述载物滑车总体结构的基础上,重点分析了制动装置制动过程、关键结构的受力分析及台架制动测试试验.有限元分析表明,支撑柱的最大应力为6.3 MPa,最大位移为2.1×10-5 mm,且出现在支撑柱与摩擦片固定装置相连的螺栓截面上;轨道的最大应力为70.9 MPa,最大位移约为0.65 mm,且出现在直轨道与摩擦片接触面上,呈对称分布.台架试验结果表明,该制动装置的制动成功率为100%;高速摄影试验表明,随着装载质量的增大,制动时间及振幅均增加.该研究可为山地果园单向牵引式轨道运输机械的整机结构设计提供参考. 相似文献
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农用运输车由农机部门管理的几点思考 总被引:1,自引:0,他引:1
为保证农业的安全生产,笔者从理论要求、现实存在的问题、对策等几个方面对农用运输车的管理进行了初步探讨,得出农用运输车由农机部门管理的结论。 相似文献
219.
Estimate of sediment yield in a basin without sediment data 总被引:4,自引:0,他引:4
In this study, three mathematical models for the estimate of sediment yield, due to soil and stream erosion, at the outlet of a basin are presented. Each model consists of three submodels: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The rainfall-runoff and the stream sediment transport submodels are identical in the three mathematical models. The rainfall-runoff submodel that is used for the computation of the runoff in a sub-basin is a simplified water balance model for the soil root zone. For the estimate of soil erosion in a sub-basin, three different submodels are used alternatively, owing to the fact that erosion or sediment yield data are not available. The soil erosion submodels are (a) a modified form of the classical Universal Soil Loss Equation (USLE, [Foster, G.R., Meyer, L.D., Onstad, C.A., 1977. A runoff erosivity factor and variable slope length exponents for soil loss estimates. Transactions of the ASAE, 20 (4), 683–687]) taking into account both the rainfall erosion and the runoff erosion, (b) the relationships of Poesen [Poesen, J., 1985. An improved splash transport model. Zeitschrift für Geomorphologie, 29, 193–211] quantifying the splash detachment, as well as the upslope and downslope splash transport, (c) the relationships of Schmidt [Schmidt, J., 1992. Predicting the sediment yield from agricultural land using a new soil erosion model. Proceedings of the 5th International Symposium on River Sedimentation. Karlsruhe, Germany, pp. 1045–1051] including the momentum flux exerted by the droplets and the momentum flux exerted by the runoff. The sediment transport submodel for streams aims to estimate the sediment yield at the outlet of a sub-basin. This quantity results by comparing the available sediment amount in the main stream of a sub-basin with the sediment transport capacity by stream flow, which is computed by the relationships of Yang and Stall [Yang, C.T., Stall, J.B., 1976. Applicability of unit stream power equation. Journal of the Hydraulics Division, ASCE, 102, 559–568]. The mathematical models were applied to the basin of Kompsatos River, in northeastern Greece, with an area of about 565 km2. The whole basin was divided into 18 natural sub-basins for more precise calculations. Monthly rainfall data were available for 27 years (1966–1992); therefore, the calculations were performed on a monthly basis. The deviation between the three mean annual values of sediment yield at the basin outlet, for 27 years, resulting from the three mathematical models is relatively small. 相似文献
220.
Transmission of Mycoplasma dispar among calves collected and reared for beef production 总被引:1,自引:0,他引:1
R Tanskanen 《Acta veterinaria Scandinavica》1987,28(2):241-248
Fortytwo calves, 28 to 117 days old, were collected from 23 dairy farms and transported in a lorry, allowing direct contact between the calves, to 8 calf rearing farms. The average transport time per calf was 4.5 h, ranging from 0.3 to 12.8 h. The calves were sampled by nasal swabbing for mycoplasmas first before loading and then immediately after transport. Thirteen of the calves were transferred to farm I. They were placed in individual pens in a separate room to themselves, and were sampled at intervals for a period of 4 weeks.Ten of the 42 calves (23.8 %) originating from 5 of the source farms were found initially positive for M. dispar with titers > 4 log10 ecu; 3 of these 10 calves were delivered to farm I and 7 calves to 6 others of the 8 receiving farms. Three initially infected calved delivered to farms I continued to be positive throughout the follow-up period; among the 10 initially negative calves the frequency of detected infection, and the geometric mean titer (within parenthesis), developed so that on days 1, 7, 14, and 28 the figures were: 2 (2.5), 8 (4.3), 9 (4.7), and 10 (5.5), respectively.After transport 3 initially negative calves were found positive with low titers. Two of them were placed on farm I. In one of them positivity proved to be only transient; the case seems to represent a phenomenon of transfer of mycoplasmas without establishment of infection. In contrast, at least 4 (possibly 7) calves, negative both before and after transport–ascribed above to the group of 10 initially negative calves arriving on farm I–had in all likelihood caught the infection during the transport. Two of the 10 calves most likely caught the infection on the farm; for 3 calves the evidence was equivocal as to the 2 alternatives.Seven of the 42 calves (16.7 %) were found to be initially infected with M. bovir-hinis, 2 of the 42 with Acholeplasma laidlawii. Among the 13 calves transported to an reared on farm I, 8 were found to be positive at least once for M. bovirhinis during the study. Colonisation by this mycoplasma was partly detected only intermittently and the detectable prevalence among the 13 calves at its highest was only 38.5 %. 相似文献