Estudo do conteúdo de calor e suas influências sobre variáveis limnológicas em reservatórios de abastecimento de água

Abstract

This work has recovered and produced historical series of physical, chemical and biological water quality parameters in six reservoirs built for public water supply in the state of Minas Gerais, Brazil. It pictures the evolution of some of these parameters, and calculates the heat contents, as well as the thermal behavior of these reservoirs informing the currentsituation of heat and quality of the dammed waters. The estudied reservoir were built between the decades of 1960 and 1990. Vargem dasFlores in the end of the 1960 decade, Serra Azul (in upper São Francisco river valley), and the Juramento (in the medium São Francisco river valley) in the beginning of the 1980 decade, and Rio Manso in the end of this. At the end of the 1990 decade the reservoirs of Ribeirão (in Medina) and Soberbo (in Pedra Azul) were built in the medium Jequitinhonha river valley, in the semi-arid region of Minas Gerais. Temperature measurements in the vertical profiles of the water bodies were carried outduring the routine sampling and eventually in 24-hour sampling (diel) and the heat contents in each reservoir were calculated in all the recovered data. A simplified operation conceptual model of the flux of several materials and of energy in the hypolimnion and in the epilimnionwas built. The model informs the flux of nutrients and substances as being regulated by patterns of temperature and heat. The evolution in time of thermal patterns and its possible influence over the studiedbiotopos physiology were discussed. Data related to water quality, in its most important physical and chemical aspects, and hydrobiological data, was recovered. The morphometric parameters of these structures were calculated and the data was used in the evaluation of current conditions and of influence of the engineering structures which compose the dam inthe water quality . Positive correlations between the heat content of the reservoirs and the evaluated limnological variables were obtained. It was observed that, in the reservoir where the use of the bottom discharge is efficient, there are changes in the heat content and, consequently, inthe phytoplanctonic populations. A reduction in the time of hydraulic residence in each reservoir is suggested, as well as the captation of the water down river from the dam, after its passage by the dispersing valves and not in the water body.