Dinâmica do nitrogênio e do fósforo e estado trófico nas águas do rio Turvo Sujo

• Autor(a) principal: Barros, Flávia Mariani
• Data de Publicação: 2008
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/643
• topic: Qualidade de água; Proliferação de algas; Modelagem; Water quality; Algae proliferation; Modelling; CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA::ENGENHARIA DE AGUA E SOLO

The accelerated eutrophication and the water contamination with chemical potentially toxic elements are among several problems proceeding from the pollution of the water resources. Nowadays, the eutrophication is recognized as one of the most important problems concerning to quality of the water. The water speed is one variable that should be considered in the evaluation of the trophic state index, as the environments with higher water speed rather tend to present a lower phytoplanktonic productivity. The pollutant incorporation capacity of the watercourses depends on their interactions with the physical, chemical and biological conditions, and the atmospheric reaeration is the main factor responsible for the introduction of oxygen into liquid medium, therefore turning possible the watercourse to reach the appropriate conditions of dissolved oxygen for the aerobic species survival. So, this study was conducted to evaluate the dynamics of the water quality variables within a section of the Turvo Sujo river at different yearly times, as aiming at prediction of the eutrophication and contamination with potentially toxic elements. The study was carried out in the Turvo Sujo river at a 5 km section approximately, that was located after the encounter of this river with the São Bartolomeu creek. The following variables were quantified: chlorophyll-a, total nitrogen, nitrate, ammonium, different phosphorus forms, hydrogenionic potential, turbidity, electric conductivity, dissolved oxygen, oxygen biochemistry demand, copper, manganese, iron, zinc, chromium, nickel, cadmium and lead. The quantification of the water quality and water speed were accomplished in five different points at different times over the year. The values of the deoxygenation coefficient (K1) were obtained, by applying the method for quantification of the sample oxygen consumption and subsequent data regression analysis. The values of the reaeration coefficient (K2) they were obtained, by using the Streeter-Phelps equation. The equations for estimating the K2 values as a function of hydraulic characteristics of the watercourse were also obtained. The regression analysis was used to analyze the data. The values of the turbidity and biochemical oxygen demand were higher over summer and autumn times, as corresponding to the highest flow rates in the Turvo Sujo river, whereas the values of the electric conductivity and hydrogenionic potential were higher at the times with higher occurrence of higher precipitations (spring and summer). The concentrations of the total nitrogen and ammonium were higher in autumn and winter times, whereas the nitrate concentrations were higher in both spring and summer times A wide variability occurred in the phosphorus concentrations, what might have happened due to resuspension of the river bottom sediment. The concentrations of copper and manganese were higher at summer time due to the highest surface runoff, whereas the most toxic elements such as chromium, cadmium and lead at higher concentrations were observed during spring, when the lowest surface runoff occurred. The variables providing better contribution to the adjustment of the a chlorophyll-a prediction equation were the total dissolved phosphorus, total nitrogen and the water speed. In practically all classifications concerning to the trophic state index for the Turvo Sujo river, the phosphorus concentration led to classify the environment into trophic class superior to that obtained when the chlorophyll-a was taken as reference; therefore, in rivers, the water speed is an extremely important factor that should be always linked to the chlorophyll-a data for either prediction of the eutrophization and the calculation of the trophic state index. At rainy seasons (spring and summer), the deoxygenation coefficient was higher than the drought time (autumn and winter). The flow rate of the river had stronger influence on K2 coefficient than the speed values, as the K2 values being higher in lower flow rates.