Depth-stratified oxygen stress index for quantifying vertical hypoxia and enabling precise management in stratified reservoirs

This study introduces the Depth-Stratified Oxygen Stress Index (DS_OSI), a depth-explicit metric designed to quantify vertical hypoxia in thermally stratified reservoirs. Hypoxia, which threatens drinking water quality, irrigation supplies, and aquatic ecosystems, is commonly assessed using fixed dissolved oxygen thresholds or complex process-based models that overlook depth-dependent interactions between temperature, ionic content, and stratification intensity. The DS_OSI, developed from vertical profiles of temperature, pH, conductivity, and dissolved oxygen collected at 3–5 meter intervals to a depth of 35 meters in the Sabalan Dam reservoir during peak summer stratification, achieves R² values greater than 0.92. The model offers an unprecedented framework for quantifying oxygen stress, enabling precise estimation of hypoxic volumes and onset depths. It contributes to the sustainable management of water resources by providing a reliable tool for mitigating hypoxia and supporting long-term reservoir health in stratified aquatic systems.