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Universidade Federal do Ceará (2015)

Reservoir eutrophication in the semiarid region : vulnerability and biomanipulation

Wiegand Mario Cesar

Titre : Reservoir eutrophication in the semiarid region : vulnerability and biomanipulation

EUTROFIZAÇÃO DE AÇUDES NO SEMIÁRIDO : VULNERABILIDADE E BIOMANIPULAÇÃO

Auteur : Wiegand Mario Cesar

Université de soutenance : Universidade Federal do Ceará

Grade : Doutorado 2015

Résumé partiel

With the increasing water demand and the concern that the supply can not meet that consumption, it is increasingly necessary conserving the available water, in quantity and (especially) quality. This conservation is especially important in semi-arid regions such as the Brazilian Northeast (NEB), where water is scarce. The main causes of pollution (water waste) in smal reservoirs (in the semiarid) are : the animal presence on the reservoir margins, where they defecate and urinate ; domestic wastewater (e.g. laundry water, water used in the household) ; removal of riparian vegetation, which protects reservoirs against silting and organic matter input ; presence of outdoor trash ; and use of agricultural inputs that contribute to the process of eutrophication. In turn, the main feature of eutrophication process is excess nutrients in water bodies, with considerable growth fluctuations and eventual death of algae and weeds. With the continuity of the process, there is the accumulation of dead matter in the deepest region of these environments, causing the increase in bacterial metabolism that causes the death of fish and other organisms by oxygen lack or reduction, plus the toxin production by blue-green algae, which are harmful to human health and to the biota at large. Therefore, studies that estimating the nutrient input become urgent. With such studies, strategies for the restoration of eutrophic reservoirs can be implemented. Among such strategies there is biomanipulation. Biomanipulation is a biological strategy based in the use of aquatic organisms (e.g. fish), to balance the aquatic ecosystem. Hypothesis : "Is it possible to treat an eutrophic reservoir using biomanipulation ?” If so, what are the particularities of biomanipulating a reservoir the semiarid region, especially considering its rich ictiological diversity, with predominantly omnivorous fish population and where fish reproduction occurs throughout the year ? Therefore, in order to answer these questions, this thesis was divided in two parts, the first comparing the state of eutrophication and its probable causes in two tropical reservoirs, one in wet climate (La Juventud, Cuba) and the other in semiarid climate (Marengo, Brazil). After estimating the trophic state of the two reservoirs in rainy and dry seasons, we evaluated the influence of hydrology and of land use on reservoir trophic level. It was found that the semi-arid tropical reservoir was eutrophic, while the reservoir on humid climate was mesotrophic. Considering that there is similar land use in the two basins and that, in the rainy season, the nutrient input in the wet basin is considerably higher than the nutrient input in the semiarid basin, the higher trophic state of the semi-arid basin is surprising. The variable that best explains this phenomenon is the water r

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