Diagnosis of the quality and trophic state of surface water in a stretch of the Machado River - Rondônia, Western Amazon

Abstract

This research aimed to diagnose the water quality in a stretch of the Machado River – Rondônia, using the water quality index (IQA) and the trophic state index (IET) as a tool. Collection was carried out at 9 sampling points, quarterly. Statistical analysis was bifactorial variance. The results of the variables pH, turbidity, total phosphorus, dissolved oxygen and Escherichia coli showed in some sampling points non-compliance with Conama Resolution No. 357/2005, for class II lotic environments, mainly in the flood and flood periods of the river. The IQA showed the worst average (49.89 ± 4.03) in the flood period, with the stretch classified as regular by the IQA_CETESB and bad by the IQA_IGAM. The low IQA values for the rainy season can attributed to the worsening of total solid parameters, total phosphorus, turbidity and Escherichia coli, which suffer great interference from the water supply by the surface runoff. The IET was more influenced by total phosphorus and allowed classifying the stretch under study at the oligotrophic level. In general, the water quality for the analyzed section is considered good due to the self-purification of the river and the point sources of pollution being located close to smaller streams.