Hydrochemistry of oxbow lakes of the Chandless River, southwest Amazon

This study investigated the hydrochemistry of three oxbow lakes and the Chandless River, within Chandless State Park (Acre, Brazil), during the dry season (June–July 2021). We tested whether oxbow lakes had lower nutrient concentrations than the river. Water samples were analyzed for cations and anions, alongside in situ measurements of pH, temperature, conductivity, and dissolved oxygen. Results showed higher pH, conductivity, and oxygen in the river, while lakes were more acidic with lower values. Contrary to the hypothesis, nutrient concentrations showed contrasting patterns among environments: Ca²⁺, Na⁺, and Mg²⁺ were higher in the river and Lake São João II, while SO₄²⁻ and NO₂⁻ dominated in Lakes Buião and São João I. The findings highlight distinct ionic profiles and the ecological uniqueness of each system—critical for managing the park's environmental diversity. Keywords: aquatic ecosystems, floodplains, hydrochemistry, limnology.