Produção e qualidade de água em microbacias e nascentes de região hidromineral de Minas Gerais

Abstract

The anthropic activities carried out in a river basin, especially those that promote changes in the soil surface, influence the quality of water resources. That way, the objective of this study was to evaluate the water quality using Water Quality Index (WQI) and Trophic State Index (TSI), as well as to compare the analyzed water quality parameters with the standards of Normative Deliberation COPAM/CERH n°01/2008, for class 2. This study comprised monitoring of four water springs and three watercourse located in the Jacutinga town, from which water samples were collected between October 2018 and July 2019 for analysis. The following water quality indicators were analyzed: pH, electrical conductivity, temperature, turbidity, total phosphorus, nitrate, chloride, dissolved oxygen (DO), biochemical oxygen demand (BOD), thermotolerant coliform (TC), total solids(TS), total suspended solids (TSS) and total dissolved solids (TDS).The WQIwas calculated following the methodology proposed by the IGAM (2018b), while the TSI followed the methodology proposed by Lamparelli (2004). To verify the seasonality effect, the WQI and TSI data were submitted to the Mann-Whitney test. Comparing with class 2 of normative deliberation, pH and DO values were lower than the standard the point 1. The mean values of total phosphorus were lower than the maximum allowed value in points 3 and 4. The TC concentration was higher than the standard in all water samples in points 1, 2, 6 and 7, and in two water samples in point 3. At the points 4 and 5, the TC concentration was within the allowed range. Regarding the mean WQI, the points 1, 2, 6 and 7 presented water of Moderate quality, while in points 3, 4 and 5 the water was classified as Good. The average values of STI indicated a Super-eutrophic state, in point 1, an eutrophic state for points 2 and 5, and an Ultra-oligotrophic state for points 3 and 4. In the point 6, the Super-eutrophic state was verified in the rainy period, and the Eutrophic state in the dry period, while at point 7 the Ultra-oligotrophic and Eutrophic states were observed for the respective periods. The STI did not present seasonal variation, whereas the WQI presented seasonal variation in point 2. Based on the results, it is concluded that the main causes of deterioration of water quality are related to the TC, nitrate and phosphorus, which may be directly related to the agriculture and animal farming activities practiced in the monitoring areas.