Análise dos fatores ambientais intervenientes na qualidade da água em trecho do Ribeirão Ponte de Pedra no município de Rondonópolis – MT

Abstract

The evaluation of water quality data involves a large number of variables, often making it expensive and difficult to manage effectively. This work aimed to analyze the influence of the environmental factors involved in the quality of the surface water in a stretch of a river basin in a biome conservation unit Cerrado, during the rains and droughts, for 10 years, in order to help the environmental agency in decision making regarding water quality monitoring. The Ribeirão Ponte de Pedra Basin is located in the southern region of the State of Mato Grosso, Brazil and is located in a transition area Plateau – interplanaltic depression / Pantanal. Physico-chemical variables were monitored: pH, water temperature, color, turbidity, electrical conductivity, total phosphorus, nitrogen series and suspended solids at 3 collection points (PC1, PC2 and PC3) in the period 2007 – 2017. Initially, the analysis of variance (ANOVA) was performed, where the level of significance of each variable was verified separated by the periods of rain and drought at the collection points, After the analysis, it was possible to transform the study into a single section. Regarding seasonality there were no significant differences between periods for most of the variables analyzed. Except for pH, ammoniacal nitrogen and suspension solids. The results of pH, period of drought, presented greater values reflecting in the decrease of the ammoniacal nitrogen and increase of the nitrate what is expected once it was observed propitious temperature for the conversion to happen, the opposite was verified in the rainy period with higher concentrations of ammoniacal nitrogen and lower concentrations of nitrate in the same period even with temperatures propitious for the conversion phenomenon to happen. In relation to the water temperature, the lowest results occurred in the drought period, which coincide with the lowest average air temperatures. Already in the rainy period it was observed the biggest temperatures of the water that should possibly be related to the presence of higher concentrations of solids in suspension in the same period, condition that elevates the heat content in the water, because these materials absorb underwater radiation. The total phosphorus variable although it did not present significant differences with respect to seasonality when it is evaluated in relation to Resolution CONAMA 357/2005 the mean values are compatible with class 3 rivers. The maximum value of total phosphorus found in the rainy period should possibly be related to the change of land cover from livestock to agriculture. Regarding the reduction of the number of variables to be monitored using the main component analysis technique (PCA) was observed a reduction of ten variables from the original database to four losing about 18% of the information, in the rainy period, and for three losing about 23.9% of the information in the drought period.