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No description available.

Acid Sulphate Soils (ASS) often cause acidic pollution in canal water, which negatively impacts on water quality, biodiversity and the livelihood of farmers and fishermen, especially the landless poor. The problem is particularly acute in the coastal zones, where people already suffer from the consequences of salinity intrusion. Reducing acidic pollution is important for improving agricultural and aqua-cultural production and also the living conditions of people living in coastal zones with ASS. This study aims at developing an analytical tool that can simulate the propagation of acidic pollution and that would allow planers and managers to develop water management options and other resource management measures to reduce acidic pollution in the canal network of a coastal zone. / This study utilizes a systems approach, with a series of field, laboratory studies, in combination with statistical and GIS-based analyses and simulation modelling. Field and laboratory studies were carried out during 2001 - 2006 in Ca Mau peninsula, Mekong Delta, Vietnam, to fill in knowledge gaps on the source and amount of acidic loads from soil to the water surroundings, their interaction with saline water and their propagation in the canal network. Knowledge generated from this study was used in developing and validating a model to simulate the propagation of acidity in the tidal canal network with brackish water. / Measured data showed that the acidic pollution in the canal network varies seasonally. The pH of the canal water was lowest (3 – 4.5) at the beginning of the rainy season and highest (7 – 7.5) at the end of the rainy season and during the dry season. The reduced dredging activities in year 2005 and 2006 may explain why the acidic pollution decreased in 2005 – 2006 compared with 2001 –2004. The most serious acidic pollution occurs when the two following conditions are present simultaneously: (i) The existence of newly dredged canals (and hence the deposition of the excavated spoils on the canal embankment) in areas with ASS (especially with a severe ASS); and (ii) little or a lack of water exchange from tidal flows. Field experiments showed that ASS embankments within 2-3 years after dredging represent a high acidity hazard because they can release into the canal a total acidity, mainly from runoff and seepage water, of up to 2.7 mol H+day-1 per meter length of canal embankment. Functional relationships were established allowing quantification of the daily acid load transferred from fields and canal embankments to the canal network. / A laboratory titration experiment showed that saline water could buffer the effects of acidic pollution in the canal water. A new ACIDITY module was developed and was coupled to an existing hydraulics and salinity model (the Vietnam River Systems And Plains - VRSAP). The model was calibrated with measured data from 2003 and validated with data from 2005. The Model is the first of its kind able to simulate the temporal and spatial dynamics of changes of pH (as an indicator of acidity) at a regional scale, together with salinity and water flow characteristics in a tidal canal network with brackish water. The Model can be used to investigate the effects of different scenarios of water and other resource management options on the extent of acidic pollution in a coastal area. Analysis of simulation runs for various scenarios indicate that opening the two main sluices along the East Sea at high tide in one day every week in May and June for saline water intake, combined with widening the canals that connect these sluices to the West Sea can eliminate the acidity problem in the study area. Large scale dredging of canals of ASS in fresh water zone should be avoided as it can create severe acidic pollution of the canal water.

No description available.

No description available.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2007. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.Sc.)--University of Alberta, 2010. / A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Plant Biology, Department of Biological Sciences. Title from pdf file main screen (viewed on April 23, 2010). Includes bibliographical references.

Orientador: Jairo Osvaldo Cazetta / Banca: Luiz Evaldo de Moura Pádua / Banca: Leilson Costa Grangeiro / Banca: Arthur Bernardes Cecílio Filho / Banca: Fábio Henrique Tavares de Oliveira / Resumo: O fósforo é um dos nutrientes mais importantes para a cultura do meloeiro, que influencia significativamente a economia da região Nordeste. Assim, o objetivo deste trabalho foi avaliar o efeito da aplicação de doses de P na produção e qualidade de frutos de melão amarelo, cultivar Goldex F1. O experimento foi desenvolvido no Colégio Agrícola de Teresina/UFPI, entre maio e agosto de 2008. O delineamento experimental foi montado em 4 blocos casualizados em parcelas (tratamentos principais), com doses de P (0, 120, 240, 360 e 480 kg ha-1 de P2O5); as parcelas foram subdivididas no tempo (tratamentos secundários) aos 20, 27, 34, 41 e 48 dias após o transplante (DAT). Nas condições de cultivo do meloeiro em Teresina, a aplicação de doses de P2O5: 1 - A produção de frutos comerciais, massa e número de frutos comerciais por planta, diâmetro, comprimento e espessura da polpa de frutos comerciais aumentaram até a dose de 278 kg/ha P2O5; 2 - Doses acima de 278 kg/ha P2O5 prejudicaram o desenvolvimento inicial das plantas e a produção de frutos comerciais por planta; 3 - As doses de fósforo não influenciaram no teor de sólidos solúveis e acidez titulável dos frutos comerciais / Abstract: Phosphorus is a important nutrient for the melon, and this culture has significant importance for the economy in the Northeast of Brazil. Thus, the purpose of this study was to evaluate the effect of P levels on production and fruit quality of yellow melon variety Goldex F1. The experiment was conducted at the Agricultural College Teresina / UFPI between May and August 2008. The experiment was arranged in randomized blocks with five main treatments (P doses (0, 120, 240, 360 and 480 kg P2O5 ha-1) were subdivided in time (secondary treatment) at 20 , 27, 34, 41 and 48 days after transplanting (DAT). The results showed, under the conditions of this experiment, that: 1 - The productivity of comertial fruits, weight and number of comertial fruits per plant, as well as lengh and diameter of fruits and thickness of pulp increased with doses until 278 kg/ha P2O5; 2 - Doses above 278 kg/ha P2O5 tended to decrease initial planta development and production of fruit production; 3 - The phoshporus doses used do not affected significantly soluble solids and acidity of comercial fruits / Doutor