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排序方式: 共有225条查询结果,搜索用时 15 毫秒
21.
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
22.
Biogeochemical processes describing nutrient cycling strongly affect the development of different soil horizons and soil acidification. However, in many soil acidification models these processes are not directly simulated, and spatially distributed soil properties are lumped into average values. This paper describes the extension of a one-layer soil acidification model (SMART) to a multi-layer model (SMARTEX) by including nutrient cycling, and the performance of both models regarding their ability for the assessment of the effects of acid deposition on forest soil. This was done by comparing simulation results of the two models with respect to changes in base cation amounts to historical data from sites in south Sweden. The results showed that the multi-layer model gives better results for the top soil, whereas the one-layer model gives better results for the rootzone and the total profile. Since the top soil is most important, the extended model is more suited to relate acid deposition to forest growth than the more general results of the one-layer model. However, the sensitivity of the multi-layer model to some parameters is large. A change in these parameters had strong effects on the separate layers, whereas the effects were cancelled out over the total profile. This sensitivity requires a careful parameterization of the model which might be troublesome to lack of data. 相似文献
23.
Superficial keratectomy and cryosurgery as therapy for limbal neoplasms in 13 horses 总被引:1,自引:1,他引:0
Objective To determine the usefulness and clinical outcome of a combined procedure of superficial keratectomy and cryosurgery as a treatment for limbal neoplasms in horses. Study design Retrospective study. Animals Thirteen horses with 14 limbal tumors. Methods Medical records of all patients with limbal tumors, referred to the Department of Equine Sciences of Utrecht University between 1995 and 2002, were retrieved. Patient data were analyzed with respect to signalment, tumor surface area and histologic diagnosis. Surgery, performed under general anesthesia, included surgical debulking of the tumor followed by cryosurgery. Long‐term follow‐up information was obtained by re‐evaluation in the clinic, by the referring veterinarian, and/or by telephone enquiry. Results Therapy was successful in 9 out of 14 eyes after the first attempt (64%); one eye needed retreatment (7%), and four eyes were eventually enucleated (29%). The mean follow‐up period was 4.8 years. The initial surface area of the tumor significantly influenced outcome (P < 0.01). Squamous cell carcinoma was the most predominant tumor type (79%). Haflinger horses accounted for 69% of the cases whereas their occurrence in the overall hospital population is approximately 5%. Conclusions and clinical relevance The described technique of superficial keratectomy and cryosurgery is a simple procedure for the treatment of limbal tumors in equine patients that does not require sophisticated equipment. Nor is it tampered by legal restriction, and appears to be effective in tumors with a small surface area (< 2 cm2). Haflinger horses seem to be predisposed for the development of ocular squamous cell carcinoma. 相似文献
24.
BACKGROUND: An important part of the production area of common bean (Phaseolus vulgaris L.) in Belgium is located on the sandy soils of the provinces of Antwerp and Limburg where Meloidogyne chitwoodi (Golden), M. fallax (Karssen) and M. hapla (Chitwood) are present. The host plant status of ten bean cultivars for root‐knot nematodes was determined by evaluating penetration, development and egg mass formation after inoculation with second‐stage juveniles. RESULTS: The tested cultivars were poor to good hosts for M. chitwoodi, non‐hosts or bad hosts for M. fallax and excellent hosts for M. hapla. Significantly fewer M. fallax were found in the roots, and their development was delayed. Penetration of M. hapla took place over a longer period than that of M. chitwoodi and M. fallax. The number of mature females of M. chitwoodi in cv. Polder 6 weeks after inoculation was no different from that in other cultivars, although fewer egg masses were found on this cultivar in the screening test. There was no influence of M. chitwoodi on vegetative growth of cv. Polder. CONCLUSION: The differences found in host plant status of bean cultivars stress the importance of a correct diagnosis of the Meloidogyne species in agricultural fields. Cultivar Polder showed potential as a trap crop for M. chitwoodi. Copyright © 2011 Society of Chemical Industry 相似文献
25.
Tuyttens FA Vanhonacker F Verhille B De Brabander D Verbeke W 《Research in veterinary science》2012,92(3):524-530
A group of 160 Flemish pig farmers (n=160) were surveyed about their attitude towards surgical castration with anaesthesia (SCA) and without (SCN), immunocastration (IC), sperm sexing (SS) and the production of entire males (EM). The farmers' general preference was recorded as SCN>SS>SCA=IC>EM. The farmers' self-reported knowledge of the strategies was associated with their preference for SCA (negatively) and SS (positively). Herd size was correlated with farmers' preference for SCA (negatively) and SS (positively). Farmers perceived surgical castration without anaesthesia as the most favourable strategy in terms of farm profitability, animal performance and effectiveness against boar taint, but they expected the lowest consumer acceptance for this strategy. Surgical castration with anaesthesia was ranked the least favourable in terms of labour conditions. Production of entire males was viewed as the least profitable and the least effective strategy. Sperm sexing was positively perceived, particularly in terms of labour conditions, animal welfare, effectiveness and expected consumer acceptance. The farmers' opinion was quite homogeneous, especially regarding surgical castration without anaesthesia and production of entire males. Increasing our understanding of the farmers' perceptions will hopefully facilitate communication about this intricate issue. 相似文献
26.
A good intake of fluids and essential nutrients in the first fourteen days is of vital importance to recuperating animals. Moreover, it is important to encourage cats and dogs to eat after illness or surgery, in order to promote optimal functioning of the gut and the immune system. Enteral nutrition is to be preferred to nasogastric feeding or parenteral nutrition. In the first stage of recovery, during the first 24 to 48 hours, it is important to feed the gut' with nutrients, and thereafter, in the second stage of recovery (after day 3), the calorie intake can be increased. Timely nutritional support with nutraceuticals, such as arginine, glutamine, taurine, long-chain polyunsaturated omega-3 fatty acids, and prebiotic fibres, can considerably shorten the recovery period of cats and dogs after illness or surgery 相似文献
27.
Jean Damascene Ndayambaje Wim J. M. Heijman Godefridus M. J. Mohren 《Agroforestry Systems》2013,87(4):797-814
The development of farm woodlots as an alternative source of livelihood for smallholder farmers in diverse biophysical and socio-economic conditions is a challenging issue in developing countries, such as Rwanda, where the majority of the population relies on subsistence farming. There is a need to understand why and when farmers decide to grow trees and woodlots on their farms. The objective of this study was to analyse the determinants and the purposes that enhance the propensity to grow woodlots in low, medium and high altitude regions of Rwanda. Necessary information for this study came from a survey of 480 households across these regions. The results showed regional variations in the determinants of woodlot farming, demonstrating the importance of not extrapolating the results between regions. Pooled data across regions indicated that age of the householder, number of salaried household members, farm size, travel distance to fuelwood sources and household location in medium forest cover region had positive significant effects on the propensity to grow farm woodlots. In contrast, household location in low forest cover region, ownership of livestock and monthly frequency of purchasing fuelwood were inversely related to the presence of farm woodlots. Many households planted eucalyptus woodlots for economic reasons, not for environmental purposes. Livestock and crop production were more attractive to rural households than woodlot farming. The findings of the study can be used by policymakers and extension services in order to promote sustainable land use practices by focusing on the challenges of competing land uses, farm size, unemployment, dependence on forests for fuelwood supply and subsistence farming. 相似文献
28.
Anna M. Piśkiewicz Henk Duyts Wim H. van der Putten 《Soil biology & biochemistry》2008,40(11):2729-2735
One of the major limitations to enhance sustainability of crop production systems is the inability to control root-feeding nematodes without using chemical biocides. In soils under wild vegetation, however, root-feeding nematodes affect plant performance and plant community composition varying from substantially to insignificantly. Previous studies in natural ecosystems have already shown that mutualistic symbionts, such as arbuscular mycorrhizal fungi and endophytes, may influence plant exposure to root-feeding nematodes. In order to learn more from natural systems, we examined nematode control in the root zone of a wild coastal foredune grass by microorganisms, other nematodes and microarthropods. We cultured all eight root-feeding nematode species that occur in the root zone of marram grass (Ammophila arenaria) in coastal foredunes of the Netherlands. Then, in an indoor growth experiment we exposed each nematode species to the potential natural antagonists collected from the same dune soil. Most of the eight dominant root-feeding nematode species could be controlled to some extent by more than one group of soil organisms added. The effectiveness of control varied among nematode species, which seemed to be controlled in a species-specific way. We conclude that in a natural soil the effectiveness of control by microorganisms, other nematodes or microarthropods varies among root-feeding nematode species. Most are controlled, at least to some extent, by soil microbes. However, some root-feeding nematode species are controlled only by microarthropods. Our results strongly suggest that sustainable agriculture will benefit from using a range of biological control mechanisms when controlling root-feeding nematodes, rather than relying on single control agents. Our suggestion also implies that conserving soil biodiversity is crucial in order to enhance the reliability of biological crop protection against soil-borne pests and diseases. 相似文献
29.
Mesquita João Rodrigo Istrate Claudia Santos-Ferreira Nânci L. Ferreira Ana S. Abreu-Silva Joana Veiga José van der Poel Wim H. M. Nascimento Maria S. J. 《Tropical animal health and production》2019,51(2):481-485
Tropical Animal Health and Production - As in most of the African continent, the status of hepatitis E virus (HEV) infection in domestic animals in São Tomé and Príncipe, an... 相似文献
30.
Predicting land cover changes and their impact on the sediment influx in the Lake Balaton catchment 总被引:2,自引:0,他引:2
The land cover pattern in the Lake Balaton catchment (Hungary) has been changing since decollectivization in the 1990s. These
land cover changes significantly impact the landscape connectivity, controlling the influx of sediments into the lake. A comparison
of high resolution land cover maps from 1981, 2000 and 2005 showed a significant extensification of the agriculture with land
cover conversions from arable land and vineyards to grassland and forest. For each land unit transition probabilities were
assessed using logistic regression techniques to evaluate to which extent land cover changes are controlled by physical or
socio-economic parameters. A stochastic land cover allocation algorithm was applied to generate future land cover patterns.
The landscape connectivity for each of the simulated land cover patterns was assessed by means of a distributed routing algorithm.
The simulations suggest that further land abandonment in the upslope parts of the catchment will cause a non-linear reduction
of average soil erosion rates. The changes, however, have a relatively low impact on the sediment volume entering the lake
because of the land unit’s poor connectivity with permanent river channels. The major contributors to the lakes sediment load
are the vineyards near the lakeshore. They are likely to be maintained because of their touristic value. A significant reduction
of the total sediment input in the lake can be expected only if soil conservation measures in the vineyards near the shorelines
are undertaken. 相似文献