Alterações físico-químicas no deflúvio de três sub-bacias hidrográficas decorrentes da atividade agrícola

Abstract

The main purpose of the present study was to investigate if the agricultural practices adopted in three watersheds located on the municipalities of Conselheiro Lafaiete and Itaverava, Minas Gerais state, Brazil, were altering the physical and chemical properties of streaming water. Samples of streaming water were collected from both the agricultural (cultivated area) and forested (upstream the cultivated area) sectors of each watershed during two expeditions, the first during the rainy season (01/13 to 02/03/1995), and the second during the dry season (06/16 to 07/20/1995), with eight samples collected per sampling point at three-day intervals. Water samples were analysed for 11 physical and chemical parameters of water quality: pH, electrical conductivity, total suspended solids, turbidity and concentrations of Cd, Ca, Mg, P, N02\ N03" and pesticide residues. Additionally, the agricultural production systems and the morphological and vegetational features of the watersheds were described, the daily rainfall was monitored,' soil samples were collected and analysed, and the water depth applied by irrigation during the dry season was mesured. Pronounced alterations on water quality parameters from the forested to the agricultural sectors were registered in all three watersheds, particularly for total suspended solids, turbidity, electrical conductivity, and total phosphorus. These effects were more significant on watersheds A and C, where proportional forest cover is lower and soil use is more intense. Residues of the insecticide aldicarb were detected in water samples collected from Watershed A during the dry season.