The aim of this thesis is to predict the future demand for water for irrigation of outdoor agricultural crops in England, and to assess the likely on-farm responses to potential water shortages and related legislative change. The past underlying growth in the demand for irrigation water was assessed, by regression analyses of the MAFF irrigation survey results, for each of eight crop categories and in total, using modelled irrigation need as a proxy for climate variation. The growth in total water demand was validated by comparison with the reported growth in total abstractions. These indicate an underlying growth in total irrigation water use between 1982 and 1995 of between 3% and 4% per annum, expressed as percentages of the 1995 values. The results show that irrigation has been increasingly concentrated on the more valuable crops, notably maincrop potatoes, small fruit and vegetables, and that those crops that are irrigated have been increasingly given more water. The future growth in the demand for irrigation water, for each of the eight crop categories and- in total, was modelled as the product of predicted future crop areas, proportions to be irrigated, depths of water to be applied and application efficiencies. On-farm economic modelling, macro-economic models, and expert opinion were used to predict future changes in each of these factors. A spreadsheet model was then used to calculate the future growth in irrigation water demand, for each crop category and in total, and for each Region and nationally. The same methodology has also been applied within a GIS to map the spatial variation in growth. In later work, the Foresight scenario approach has been used to consider alternative socio- economic futures. These results predict that in the short to medium term at least, the total demand for irrigation water will continue to grow rapidly, and its use will become even more concentrated on the high-value crops. Growth is greatest in those areas where water resources are already most scarce. Meanwhile, water availability for agriculture is expected to be constrained or even decline because of increased environmental protection, particularly in the drier parts of the country where irrigation is concentrated. Climate change has not been modelled in this work, but under current predictions, it is likely to have a double effect, simultaneously reducing water supply and increasing water demand, and hence increasing the scarcity and value of water and the benefits of water conservation. The farmers' likely responses to the almost inevitable water shortages have been assessed by estimating the net on-farm value of the water, and comparing this to the benefits and costs of the various options for either reducing demand or increasing on-farm supply, within likely technical, legal and other constraints. The aspects considered include irrigation methods, scheduling, agronomic practices, mulches, on-farm reservoirs, water harvesting and water re- use. This analysis shows that the on-farm benefits of irrigation are generally substantially higher than the direct costs of irrigation. The benefits of conserving water are highly variable, partly because inflexible licensing restricts opportunities to reallocate water between farms. The thesis shows that on those farms where water is valuable and scarce, this will lead to on-farm investment particularly in on-farm reservoirs, more advanced technology and better scheduling. Constraints to change are discussed. Meanwhile, on farms which already have adequate water resources, there is at present little financial incentive to adopt any irrigation water conservation measures at all. The thesis concludes that both farmers and water regulators must prepare for a less certain future in which water for irrigation is scarcer and more valuable, and demand is higher and more concentrated. The opportunities for action by various groups are discussed.

This was a study to determine if invertebrate vectors (i.e. flies and slugs) were able to acquire human pathogens from local ruminant faeces and potentially transfer them to vegetables or ready-to-eat food. A field survey revealed that slugs are able to acquire pathogenic strains of <i>E. coli</i> O.157 that were indistinguishable from those isolated from local sheep faeces. Laboratory experiments demonstrated that commensal <i>E. coli</i> had relatively long survival rates on and in slugs, where the slugs were able to transfer <i>E. coli</i> by direct contact or excretion. <i>Escherichia coli</i> had a slow decline rate in excreted slug faeces with a decimal reduction time of 13.9 days. The results suggest that slugs have the potential to transfer pathogenic <i>E. coli</i> to vegetables. The second part of this work aimed at identifying temporal or host related relationships in the <i>Campylobacter </i>population of cattle and sheep. The Multi-locus sequence typing (MLST) technique was used in addition to quantifying the prevalence and concentrations of <i>Campylobacter</i> excreted by cattle and sheep present on the same farm. Statistically significant temporal variations were identified in addition to differences between the two hosts. During the faecal sampling, flies were also collected. Flies were found to carry identical sequence types (STs) to those present in local ruminant faecal samples. However, despite the relatively low <i>Campylobacter</i> prevalence in flies, certain STs were over represented, suggesting some degree of host restriction. A low number of slugs were also sampled where the <i>Campylobacter</i> ST isolated, had not been identified on this farm or elsewhere. Flies and slugs are able to acquire <i>E. coli</i> <i>O157</i> and <i>Campylobacter</i> strains, thus posing a potential risk of transfer to vegetable crops.

No description available.

Chapter 1. Introduction General summary covering the toxicity and environmental distribution of arsenic, rice cultivation in Bangladesh including irrigations practices, previous knowledge of arsenic concentration and speciation in rice and the risk posed to the human food chain. Chapter 2. Variation in arsenic speciation and concentration in paddy rice related to dietary exposure Arsenic speciation was surveyed in different rice varieties from different parts of the globe to understand the contribution of rice to arsenic exposure. Pot experiments were utilised to ascertain whether growing rice on arsenic contaminated soil affected speciation and whether genetic variation accounted for uptake and speciation. ICP-MS was used to determine total arsenic concentration and a HPLC system with an anion-exchange chromatography column was employed to separate arsenic species. USA long grain rice had the highest mean arsenic concentration in the grain at 0.26 jag As g'1 (n = 7), and the highest grain arsenic value of the survey at 0.40 |ig As g'1. The main arsenic species detected in the rice extract were As(III), DMA(V) and As(5). In European, Bangladeshi and Indian rice 64 1 % (n=7), 80 3 % (n = 11) and 81 4 % (n = 15) of the recovered arsenic was found to be inorganic. In contrast DMA(V) was the predominant species in rice from the USA, with only 42 5 % (n = 12) of the arsenic being inorganic. Pot experiments show that the proportions of DMA(V) in the grain are significantly dependent on rice cultivar (p = 0.026) and that plant nutrient status is effected by arsenic exposure. Chapter 3. Increase in rice grain arsenic for regions of Bangladesh irrigating paddies with elevated arsenic in groundwaters. Three hundred and thirty of aman and boro rice, ninety-four vegetable and fifty pulse and spice samples were analysed for total organic and inorganic arsenic, using HPLC -ICP-MS. Conc. HNO3 was used for total digestion and 2M TFA for extraction. The districts with the highest mean arsenic rice grain concentrations were all from southwestern Bangladesh: Faridpur (boro) 0.51 > Satkhira (boro) 0.38 > Satkhira (aman) 0.36 > Chuadanga (boro) 0.32 > Meherpur (boro) 0.29 |ig As g"1. Predicted inorganic arsenic intake from rice is modelled with the equivalent intake from drinking water for a typical Bangladesh diet. Daily consumption of rice with a total arsenic level of 0.08 jag As g1 would be equivalent to a drinking water arsenic level of 10 |ig L'1. Chapter 4. Market basket survey shows elevated levels of As in South Central US processed rice compared to California: Consequences for human dietary exposure. One Hundred and thirty four samples of rice were collected from numerous large supermarkets in the towns and cities in the US. An (ORS)-ICP-MS was used to measure the elements Ti (m/z 49), Mn (m/z 55), Co (m/z 59), Cu (m/z 63), Zn (m/z 64, 66, 67, 68), As (m/z 75), Se (m/z 77, 78, 82) and In (m/z 115). Our findings show differences in transitional metal concentrations between polished and unpolished rice and geographical variation in As and selenium between rice processed in California and the South Central US. Modelling arsenic intake for the US population based on this survey shows that for certain groups (namely Hispanics, Asians, sufferers of Celiac disease and infants) dietary exposure to inorganic As from elevated concentrations in rice potentially exceeds the maximum intake of As from drinking water (based on consumption of 1 L of 0.01 mg L'1 In. As) and Californian state exposure limits. Chapter 5. Greatly enhanced arsenic shoot assimilation in rice leads to elevated grain levels compared to wheat barley. Paired grain, shoot and soil of one hundred and seventy three individual sample sets of commercially farmed temperate rice, wheat and barley were surveyed to investigate variation in the assimilation and translocation of As. Rice samples were obtained from the Carmargue (France), Donana (Spain), Cadiz (Spain), California (USA), and Arkansas (USA). Wheat and barley were collected from Cornwall and Devon (England) and the east coast of Scotland. An ICP-MS, was used to measure the elements Ti (m/z 49), As (m/z 75), Se (m/z 77, 78, 82) and In (m/z 115). Transfer of As from soil to grain was an order of magnitude greater in rice than for wheat and barley, despite lower rates of shoot to grain transfer. In rice, grain export of arsenic from the shoot appears to be under tight physiological control as grain/shoot ratio decreases by an order of magnitude (from ~0.3 to 0.003 mg/kg) as arsenic concentrations in shoot increase from 1 to 20 mg/kg.

No description available.

This is a study of the life and heritage of a plant and the people involved in the prod~ction of kangkong, Ipomoea aquatica Forskal within dynamic peri-urban spaces m mamland Southeast Asia. Kangkong has a distinction of being both a food in much ofAsia and a weed in other parts of the world. It has become an important vegetable in Cambodia, Thailand, and Viet Nam. The production of this vegetable largely occurs around cities. In Hanoi and Phnom Penh, the use of wastewater is an important aspect of its production while in Bangkok, though wastewater is not used, kangkong has become a commercial vegetable replacing rice production in 'some areas. Such disparate trajectories offer insights into the households involved in its production and the spaces upon which it thrives so that opportunities for understanding the desakota characteristics ofspatial change in mainland Southeast Asia can be made.In understanding desakota geographies, this study looks at the key factors that explain livelihood dependence through the use ofsurvey data and sequential regression. Then their geographical underpinnings are fleshed out The results showed that, in Bangkok, the occupational multiplicity of the wife explains dependence while it is the performance of kangkong production by both the husband and the wife in Hanoi. In Phnom Penh, it was shown that it is the occupational multiplicity of the husband that explains a household's dependence on kangkong production.

No description available.

No description available.

In Libya groundwater is the key source of freshwater, providing an essential supplement to surface water sources. Libya is mostly arid and semiarid and sparsely populated large North African country with annual average precipitation rates of 200 nun. More than 950/0 of the country receives less than 100 mm, and as consequence, recharge of groundwater is extremely limited. Groundwater availability and quality are also vulnerable both to climate change and over-abstraction, and in regions where the water table has lowered there has been a consequent impact on agricultural activities. This research examines the impact of water table change on land cover (particularly agricultural activities) in part of the Jeffara Plain NW Libya, during the period 1988 to 2000 using remotely sensed data. Landsat Thematic Mapper 5 images from 1988, 1992, 1996 and 2000 have been used in addition to various thematic maps of the study area and bore-hole data to assess the nature and extent of change. A supervised Maximum Likelihood approach (ML) was used to classify each image into land cover classes that were likely to have been directly affected by groundwater changes, with resulting accuracies between 670/0 and 76%, obtained. The change in the extent of land cover classes in all images was clearly visible and occurred as either an increase or a decrease between successive dates. From the questionnaire survey, and interviewing local farmers, it is clear that groundwater changes (quantity and quality) have had a significant impact upon the vegetation cover and agricultura activities of the area. To verify the changes and assess new tools for image classification, a second approach was tested with the application of Artificial Neural Networks (ANN) as alternative image classification method, and gave results with high accuracy (over 900/0), greater than those from the ML.

No description available.