Linking Land Use, Seasonal Variation and Water Quality Through Dissolved Organic Matter Optical Properties in the Doce River Basin

ABSTRACT Human activities such as agriculture, mining and urbanization have profoundly altered tropical river systems, yet conventional water quality indicators often fail to fully capture these impacts, especially in turbid waters. In the Doce River Basin, Southeast Brazil, the characterization of dissolved organic matter (DOM) through its optical properties offers a promising alternative for monitoring ecological conditions. This study aimed to assess the relationships between water quality, land use and DOM optical properties and to evaluate their potential as complementary indicators in river basin management. Water samples were collected at 27 sites along the Doce River and its tributary, the Santo Antônio River, during both dry and wet seasons. DOM fluorescence and absorbance parameters were quantified and compared with physicochemical variables and surrounding land use. Results revealed marked seasonal differences in DOM composition, with protein‐like components predominating and humic‐like substances showing strong correlations with nutrient concentrations, particularly total nitrogen and nitrate. Optical indices were also significantly associated with the proportion of forested land, highlighting the role of landscape cover in regulating water quality. These findings indicate that DOM optical properties integrate information on chemical, biological and land use influences, providing a more comprehensive assessment than traditional single‐metric approaches. Incorporating optical metrics into water quality monitoring can improve the detection of human‐induced changes and strengthen conservation and management strategies in tropical river basins.