Evaluation of the water quality monitoring program of mountain rivers located in a tropical protected Atlantic forest area (PARNASO, Brazil): are the impacts of the highway really assessed?

Road activities are recognized sources of pollution that affect the hydrochemistry of nearby water bodies. This study evaluated the Water Quality Monitoring Program in the Soberbo and Iconha rivers in the Guapi-Macacu watershed, which is affected by the BR-116 highway. The Rio-Teresópolis Concessionaire from 2009 to 2016 carried out quarterly sampling. The parameters analyzed were temperature, pH, turbidity, settleable solids, dissolved oxygen (DO), biochemical oxygen demand (BOD), nitrate (NO₃⁻), nitrite (NO₂⁻), ammonium (NH₄⁺), and total phosphorus (PO₄³⁻), total and thermotolerant coliforms, Fe, Ni, Cr, and Zn. Total phosphorus, pH, BOD, and thermotolerant coliforms sometimes exceed the freshwater limits set by the National Environment Council (CONAMA 357/05. [2005]. Classification of water bodies. https://www.siam.mg.gov.br/sla/download.pdf?idNorma=2747). However, these values did not change the classification of "good" according to the water quality index used by the Brazilian environmental authorities for river waters. Precipitation was an important factor in understanding the hydrochemistry. Monthly precipitation ranged from 779.8 mm in January 2013 to 2.8 mm in July 2010. Temporal analysis using nonparametric tests showed significant differences (p < .05) in almost all parameters, indicating a strong influence of precipitation patterns on water quality. On a spatial scale, only coliform was found to differ between rivers (p < .01), suggesting an anthropogenic influence. Principal component analysis showed that chemical weathering and mechanical erosion processes predominated in both rivers (PC1: Soberbo River, 20.3%; Iconha River, 26.7%). Rainfall was identified as a secondary factor associated with coliforms and NH₄⁺, especially in the Iconha River (PC2: Soberbo River, 10.8%; Iconha River, 11.9%), whose altitude indicated the atmospheric contribution of pollution from the metropolitan region of Rio de Janeiro. The reports of the Water Quality Monitoring Program were critically evaluated, resulting in recommendations aimed at optimizing their effectiveness and providing support for decision-making on the management of water resources in environmental protection areas.