Análise do risco ecológico com base na qualidade de água na bacia do Rio Tenente Amaral, município de Jaciara/MT

Abstract

Due to the diversity of environmental impacts on aquatic ecosystems, environmental control of ecological risks should involve an integrated approach, by monitoring the physical, chemical and biological quality of the water. Studies of ecological risk has been an important analysis tool in order to evaluate the risk grade and the vulnerability that the ecosystems are submitted, once it covers the physical characteristics as well as the anthropic interferences in different ecosystems, being able to identify the situation of ecological components that ensure its integrity. The purpose of this study was to analyze the ecological risk caused by different uses, in aquatic systems (based on quality of water) in Tenente Amaral River watershed, located in the Municipality of Jaciara-MT, characterized by intense agricultural activity. The methodology was proposed by WWF, and it was adapted to the study watershed based on the following variables: sensitivity, frequency and severity. The analysis, first identified the influence of the stressors for an environmental integrity attribute, this being the severity based on water quality and the stressors frequency of occurrence and, moreover, it was assessed the sensitivity of the watershed to the selected stressors regarding to physical variables of topography, climate, drainage and slope. In order to validate the methodology based on the quality of water, it was carried out two samples collection to evaluate physicochemical parameters (pH, electrical conductivity, temperature, dissolved oxygen, nitrate, nitrite, phosphate, chloride, sulphate, fluoride and nitrogen ammonia); one in the dry season and the other in the rainy season, both lasting seven days, in the morning and afternoon at five monitoring points (subwatershed). Results indicated that for the analyzed anions, concentrations were relatively low, however, occurred high nitrate concentrations in the sub-watershed with natural vegetation. Among the parameters, only pH extrapolated, at some points, the maximum limits established by CONAMA Resolution 357 for rivers class II, during the analyzed periods. Regarding the Ecological Risk Index (ERI), the highest risks are associated with the sub-watershed with predominant use of pasture and watershed of contribution Tenente Amaral River. About the validation of the IRE based on the data of water quality, was observed that, for some physical and chemical parameters values relate to each other with the risk indices associated sub-basins analyzed, whether higher or lower.