共查询到20条相似文献,搜索用时 15 毫秒
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Rebecka T?rnqvist Jerker Jarsj? Josefin Thorslund P. Suresh C. Rao Nandita B. Basu Georgia Destouni 《PloS one》2015,10(3)
Irrigated agriculture can modify the cycling and transport of nitrogen (N), due to associated water diversions, water losses, and changes in transport flow-paths. We investigate dominant processes behind observed long-term changes in dissolved inorganic nitrogen (DIN) concentrations and loads of the extensive (465,000 km2) semi-arid Amu Darya River basin (ADRB) in Central Asia. We specifically considered a 40-year period (1960–2000) of large irrigation expansion, reduced river water flows, increased fertilizer application and net increase of N input into the soil-water system. Results showed that observed decreases in riverine DIN concentration near the Aral Sea outlet of ADRB primarily were due to increased recirculation of irrigation water, which extends the flow-path lengths and enhances N attenuation. The observed DIN concentrations matched a developed analytical relation between concentration attenuation and recirculation ratio, showing that a fourfold increase in basin-scale recirculation can increase DIN attenuation from 85 to 99%. Such effects have previously only been observed at small scales, in laboratory experiments and at individual agricultural plots. These results imply that increased recirculation can have contributed to observed increases in N attenuation in agriculturally dominated drainage basins in different parts of the world. Additionally, it can be important for basin scale attenuation of other pollutants, including phosphorous, metals and organic matter. A six-fold lower DIN export from ADRB during the period 1981–2000, compared to the period 1960–1980, was due to the combined result of drastic river flow reduction of almost 70%, and decreased DIN concentrations at the basin outlet. Several arid and semi-arid regions around the world are projected to undergo similar reductions in discharge as the ADRB due to climate change and agricultural intensification, and may therefore undergo comparable shifts in DIN export as shown here for the ADRB. For example, projected future increases of irrigation water withdrawals between 2005 and 2050 may decrease the DIN export from arid world regions by 40%. 相似文献
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Christian Siderius Hester Biemans Paul E. V. van Walsum Ekko C. van Ierland Pavel Kabat Petra J. G. J. Hellegers 《PloS one》2016,11(3)
One of the main manifestations of climate change will be increased rainfall variability. How to deal with this in agriculture will be a major societal challenge. In this paper we explore flexibility in land use, through deliberate seasonal adjustments in cropped area, as a specific strategy for coping with rainfall variability. Such adjustments are not incorporated in hydro-meteorological crop models commonly used for food security analyses. Our paper contributes to the literature by making a comprehensive model assessment of inter-annual variability in crop production, including both variations in crop yield and cropped area. The Ganges basin is used as a case study. First, we assessed the contribution of cropped area variability to overall variability in rice and wheat production by applying hierarchical partitioning on time-series of agricultural statistics. We then introduced cropped area as an endogenous decision variable in a hydro-economic optimization model (WaterWise), coupled to a hydrology-vegetation model (LPJmL), and analyzed to what extent its performance in the estimation of inter-annual variability in crop production improved. From the statistics, we found that in the period 1999–2009 seasonal adjustment in cropped area can explain almost 50% of variability in wheat production and 40% of variability in rice production in the Indian part of the Ganges basin. Our improved model was well capable of mimicking existing variability at different spatial aggregation levels, especially for wheat. The value of flexibility, i.e. the foregone costs of choosing not to crop in years when water is scarce, was quantified at 4% of gross margin of wheat in the Indian part of the Ganges basin and as high as 34% of gross margin of wheat in the drought-prone state of Rajasthan. We argue that flexibility in land use is an important coping strategy to rainfall variability in water stressed regions. 相似文献
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Aims
In Kenya, it is estimated that 60 to 80% of urban residents live in slum or slum-like conditions. This study investigates expenditures patterns of slum dwellers in Nairobi, their coping strategies and the determinants of those coping strategies.Method
We use a dataset from the Indicator Development for Surveillance of Urban Emergencies (IDSUE) research study conducted in four Nairobi slums from April 2012 to September 2012. The dataset includes information related to household livelihoods, earned incomes of household members, expenditures, shocks, and coping strategies.Results
Food spending is the single most important component, accounting for 52% of total households'' income and 42% of total expenditures. Households report a variety of coping strategies over the last four weeks preceding the interview. The most frequently used strategy is related to reduction in food consumption, followed by the use of credit, with 69% and 52% of households reporting using these strategies respectively. A substantial proportion of households also report removing children from school to manage spending shortfalls. Formal employment, owning a business, rent-free housing, belonging to the two top tiers of income brackets, and being a member of social safety net reduced the likelihood of using any coping strategy. Exposure to shocks and larger number of children under 15 years increased the probability of using a coping strategy.Policy Implications
Policies that contain food price inflation, improve decent-paying job opportunities for the urban poor are likely to reduce the use of negative coping strategies by providing urban slum dwellers with steady and reliable sources of income. In addition, enhancing access to free primary schooling in the slums would help limit the need to use detrimental strategies like “removing” children from school. 相似文献5.
Bilal Butt 《Human ecology: an interdisciplinary journal》2011,39(3):289-307
A large number of East African pastoralists reside around protected areas (PAs). Over the last few decades pastoralists have
been affected by the loss of grazing lands and increasing climatic variability. Many pastoralists who reside around PAs have
resorted to grazing inside PAs to counter environmental variability. However, there is little information on how PAs influence
the herding strategies of pastoralists. This case study from southern Kenya employs a spatially and temporally explicit mixed-methods
approach to understand and evaluate the herding strategies of pastoralists around a PA. The results find that pastoralists
access PAs on a regular basis, regardless of seasonality or herd size. Movement into PAs was partly driven by the loss of
grazing land to conservancies. PAs affected pastoral herding by presenting differential opportunity costs to disparate groups.
However, households with large herd sizes utilized the most flexible strategies to counter environmental variability and uncertainty. 相似文献
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Dora Black 《BMJ (Clinical research ed.)》1998,316(7135):931-933
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Colin Murray Parkes 《BMJ (Clinical research ed.)》1998,316(7143):1521-1524
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Marnia Lazreg 《Dialectical Anthropology》1975,1(1-4):295-305
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Coping Strategies in Livestock-dependent Households in East and Southern Africa: A Synthesis of Four Case Studies 总被引:2,自引:0,他引:2
Philip K. Thornton Randall B. Boone Kathleen A. Galvin Shauna B. BurnSilver Michael M. Waithaka Joan Kuyiah Stanley Karanja Ernesto González-Estrada Mario Herrero 《Human ecology: an interdisciplinary journal》2007,35(4):461-476
Integrated assessment seeks to combine models of the ecological as well as the social system to allow different scenarios
to be tested in terms of their likely impacts on ecological functioning and household well-being. We outline such work undertaken
in four case studies in East and southern Africa: pastoralist communities in northern Tanzania, agro-pastoralists in southern
Kenya, communal and commercial ranchers in South Africa, and mixed crop-livestock farmers in western Kenya. Results from these
case studies are synthesised to test the hypothesis that households’ capacity to adapt in the face of increasing external
stresses is governed by flexibility in livelihood options. The results support this hypothesis. There is considerable variation
in how households in these places cope with external stresses. Options include intensification, diversification, and increasing
off-farm economic activities, and these depend on household objectives and attitudes as well as on access to natural resources,
inputs and output markets. The results also indicate that generally it is the poorer households that can gain the most from
implementing such options for coping and managing risk. Quantifying likely household and ecosystem impacts of different options
is a crucial step in targeting appropriate technology, policy and adaptation interventions in the face of considerable system
changes. We conclude with some research needs to improve integrated assessment tools that may allow us to represent more realistically
the highly complex decision-making milieu of householders in sub-Saharan Africa who are dependent on ecosystem goods and services
for a large part of their livelihoods. 相似文献
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广东省生态农业建设及其发展对策 总被引:2,自引:0,他引:2
介绍了广东生态农业的产生和发展的背景及生态农业建设的基本情况,并着重对目前广东省生态农业建设的9种主要模式及其经济和生态效益以及存在问题进行了较详细的分析,在此基础上提出了广东生态农业发展的主要对策。 相似文献
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Dora Black 《BMJ (Clinical research ed.)》1998,316(7141):1376-1378
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A Yeadon 《BMJ (Clinical research ed.)》1974,2(5912):222-223
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Proteins damaged by stressors such as heat, oxidizing conditions or toxic agents are deleterious to cells and must be properly taken care of. Accordingly, misfolded proteins trigger a cellular stress response that aims to either repair defective polypeptides or eliminate faulty elements when salvage is not possible. This stress response provides time for additional stressor-specific pathways that adapt the cell to the changed environment if necessary. Recent studies have investigated how proteins that frustrate the folding machinery are recognized and cleared from the cell. Surprisingly, these clearance mechanisms are not restricted to the protein level. The stress response can also eliminate the mRNA of polypeptides that are refractory to folding. 相似文献