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1.
ABSTRACT:   The effects caused by suspended particles in seawater and sediment cover of the substrate on the attachment to the substrate of zoospores, and on the subsequent growth and survival of gametophytes of the brown alga Eisenia bicyclis were examined in the laboratory. The attachment rate to the substrate of the zoospores was remarkably reduced by the sediment cover on the substrate, and it decreased to 3.8% of the no-sediment control by a slight sediment cover of 3.0 mg/cm2 (0.048 mm in thickness). The growth of gametophytes was not inhibited at 10 mg/cm2 or less of sediment cover, though it was stopped at 30 mg/cm2. The survival rate of gametophytes became 39.4% at 5 mg/cm2 on the substrate, and gametophytes were all blighted at 30 mg/cm2. The ratio of male to female of the surviving gametophytes became 81.5:18.5, when the sediment cover was 10 mg/cm2. The rate of total loss ( TL [%]) of zoospores and gametophytes of Eisenia bicyclis was obtained from the following equation: TL  = 100 (1 − exp[−0.0339  C ] exp[−1.24  Q ]), where, C (mg/L) and Q (mg/cm2) indicate the concentration of suspended particles in seawater and the sediment on the substrate, respectively.  相似文献   
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-  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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Identification of new parental lines is crucial for developing ecology‐specific hybrids with ideal agronomic performance. We screened a total of 570 different ecology‐specific Indian rice varieties for the presence of fertility restorer genes, Rf3 and Rf4 using tightly linked markers DRRM Rf3‐10 and RM6100, respectively. Among these varieties, 13% carried Rf3Rf3/Rf4Rf4, 31% carried rf3rf3/rf4rf4, 6% carried Rf3Rf3/rf4rf4 and remaining 50% carried Rf4Rf4/rf3rf3 allelic combinations. A mini set of 40 varieties with variable allelic combinations of fertility restorer genes were testcrossed with WA and Kalinga‐based CMS lines. All the 80 F1s were evaluated for spikelet fertility and fertility restoration ability. Rf3Rf3/rf4rf4 genotypes mostly behaved as partial maintainers or partial restorers. In contrast, rf3rf3/Rf4Rf4 genotypes were partial or effective restorers. However, double dominant genotypes showed better fertility restoration than the genotypes containing Rf3 or Rf4 individually. Some of the genotypes showed unexpected restoration pattern implying occurrence of other fertility restorer(s) apart from Rf3 and Rf4. The perfect restorers and maintainers identified in this study can be directly used in hybrid rice breeding.  相似文献   
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Irrigation schemes with sediment‐laden water are generally performing significantly below expectation and potential. Managing such irrigation schemes is challenging as in most cases the management aspects of sediment transport were not included in the design process and in some cases the proposed management plans are difficult to follow. The sediment transport process is affected by the flow conditions in the canal, and the latter are affected by the canal operation modes. Hence, system management is one of the important aspects that influence the sediment transport process. The mathematical model SETRIC has been used to analyse the existing management mode and its effect on the sediment transport process of the Sunsari Morang Irrigation Scheme in Nepal. Evaluation showed that the sub‐secondary canals of the Secondary Canal S9 have different sediment transport capacities. Some canals are facing more deposition problems than others. The problem is further increased by the existing water delivery mode. The modelling results show that it is possible to reduce sedimentation problems by improving existing water management practices. The proposed water management plan, based on the existing infrastructure, could be implemented to address the sediment transport problems in this scheme and other schemes with appropriate adaptation. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
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文章在分析牙克石市自然条件及水土流失特点的基础上,提出牙克石市水土保持生态修复的可行性及生态修复的措施,以及近年来牙克石市生态修复所取得的可喜成果。  相似文献   
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A backcrossing programme was carried out both to assess the stability of a cytoplasmic male‐sterility (CMS) source from Helianthus resinosus, designated RES1, and to incorporate it into inbred sunflower lines (HA89, RHA271, RHA801). All the progenies, grown in different environments, were completely male‐sterile. This suggests that the expression of this cytoplasm is stable. Female‐fertility of lines HA89, RHA271 and RHA801 carrying CMS RES1 were compared with those of the corresponding fertile inbred lines. There were no differences in the number of seeds per head. This indicates that female‐fertility is not affected by RES1 cytoplasm. Cytological studies showed that meiosis proceeds normally until the tetrad stage; consequently, the absence of pollen is caused by alterations that take place during postmeiotic stages. With the aim of identifying male‐fertility restorer genotypes, crosses were made between HA89 (CMS RES1) plants and different annual diploid and perennial hexaploid Helianthus species. All the diploid germplasm evaluated behaved as a CMS RES1 maintainer. However, the hexaploid species, H. resinosus, H. x laetiflorus, H. pauciflorus and H. tuberosus, restored pollen fertility in CMS RES1 plants.  相似文献   
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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.  相似文献   
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In September 2003 Hurricane Isabel swept through eastern North Carolina and Virginia, destroying most of what formerly ranked among the most extensive remaining stands of Atlantic White-cedar (Chamaecyparis thyoides L., cedar). As Atlantic White-cedar communities are dependent on irregular, large-scale disturbances, the hurricane event can be viewed as an opportunity for perpetuating cedar populations in the Great Dismal Swamp. The success of cedar regeneration in the Dismal Swamp has been influenced by the management strategies employed by Great Dismal Swamp National Wildlife Refuge (active management) and by the adjacent Dismal Swamp State Park (passive management). We investigated the regeneration success of Atlantic White-cedar 5 years following Hurricane Isabel by sampling five stands at the Dismal Swamp State Park withstanding varying impact from the storm and previous windthrow events. We compared our findings to regeneration surveys completed at the adjacent Great Dismal Swamp National Wildlife Refuge. Atlantic White-cedar seedling densities were up to 100 times higher in the actively managed Wildlife Refuge compared to the passively managed State Park. We also determined the seedbank of viable cedar seeds and we described the vegetation at the State Park. The stands at the State Park are now dominated by red maple (Acer rubrum) with a dense shrubby understory. Since viable cedar seeds were still present in the seedbank (>800,000 ha−1), future seedling establishment is possible at the State Park. However, active management is essential for achieving sufficient seedling densities and survival for regenerating a mature cedar stand.  相似文献   
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According to fixed-position data for 1985–2003 from nine runoff plots of Caijiachuan watershed which lies in Jixian County of Shanxi Province in Loess area, this paper studied the relationship between vegetation and runoff and sediment production in sloping lands in detail, which helps to provide scientific basis for vegetation re-construction and studies on environmental transformation of water and sediment in watersheds of Loess area. Although, many study results testify that forest vegetation has an important function in soil and water conservation and cutting runoff, the effect of vegetation on runoff and sediment transmission is complicated, and this needs to be studied in depth. The results of the paper showed the following. Firstly, the natural secondary forest performs better function of soil and water conservation than artificial Robinia pseudoacacia forest, and runoff and sediment produced in the former in individual rainfall were 65%–82% and 23%–92% of those produced in the latter. At the same time, better correlative relationship between runoff and sediment production and rainfall and rainfall intensity were testified by multiple regression, but the correlation decreased gradually with the increase of canopy density of forest. Secondly, the difference of runoff and sediment production in several land use types was very distinct, and the amount of runoff and sediment produced from Ostryopsis davidiana forest and natural secondary forest were the least, and runoff and sediment produced from in artificial Robinia pseudoacacia forest and Pinus tabulaeformis forest were 5-fold as much as those from O. davidiana forest. Besides, runoff and sediment produced in mixed planting of apple trees and crops were 16.14-fold and 2.96-fold than those of O. davidiana forest, respectively, but the amount decreased obviously after high-standard soil preparation in the case of the former. Thirdly, based on gray cognate analyses of factors affecting runoff and sediment production in sloping land, the factors of stand canopy density and herb and litter biomass were the most significant ones, whose gray incidence degree exceeded 0.6. Therefore, mixed forest with multi-layer stand structure and shrub forest should be developed in vegetation re-construction of Loess area, which will help to increase coverage and litter thickness in order to cut down the runoff and sediment dramatically in sloping land. __________ Translated from Chinese Journal of Applied Ecology, 2005, 16(9): 1,613–1,617 [译自: 应用生态学报, 2005, 16(9): 1,613–1,617]  相似文献   
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