Índice de qualidade da água em microbacias hidrográficas com diferentes coberturas vegetais, no sul do estado do Espírito Santo

Abstract

The aim of this work was to evaluate the relationship between land cover and water quality in the Horizonte Stream Watershed, located at Alegre County, Espírito Santo State, Brazil. Surface water and groundwater were collected at three watersheds bedside, each of them characterized by different vegetal cover: pasture, forest and coffee. Surface water samples were collected in the mouth of watersheds and groundwater in monitoring wells installed in the area. Collecting samples were made during periods of drought and rainfall. An index of water quality was developed using multivariate statistical technique called principal component analysis. The study of water quality included the following physicochemical characteristics: pH, electrical conductivity, dissolved solids, suspended solids, turbidity, biochemical oxygen demand, ammonia nitrogen, nitrate, nitrite, total phosphorus, calcium, magnesium, iron, sodium, potassium, zinc, copper and total coliforms. The principal component analysis provided the reduction of 13 features into two components that explained 91.2% of total variance. The first component, containing 61.95% of total variance, correspond to water mineralization processes, and the second one, with 29.25% of total variance, refers to organic contamination. Then, these characteristics were used to develop an index of water quality, which indicated better water conditions during the rainy season. Surface water and groundwater were suitable for human consumption after conventional treatment throughout the studied period, except the groundwater of watershed covered with pasture in the dry season.