Purpose <p>Reservoir drawdown zones are dynamic water–land ecotones impacted by anthropogenic hydrological disturbances, yet mechanisms linking water-level fluctuations to the distribution of iron-bound organic carbon (Fe–OC) remain unclear. We investigated the distribution and regulatory mechanisms of Fe–OC along a water-level elevation (WEL) gradient.</p> Methods <p>Soil samples were collected from the upper, middle, and lower drawdown zones of the Xinfengjiang Reservoir, South China. Physicochemical properties, iron fractions, and Fe–OC contents were analyzed. Random forest modeling identified nonlinear relationships between Fe–OC and environmental variables, whereas structural equation modeling (SEM) quantified direct and indirect pathways regulating Fe–OC variation along the WEL gradient.</p> Results <p>The mean Fe–OC content (6.5&#xa0;g/kg) declined significantly with decreasing WEL. Conversely, Fe–OC in total soil organic carbon (SOC) (<i>f</i>_Fe‑OC) averaged 17.1%, indicating a substantial Fe–OC pool and carbon‑sequestration potential. The molar OC/Fe ratio (0.54–3.29) suggested that Fe–OC formation was dominated by adsorption and coprecipitation. Fe–OC correlated positively with SOC, free iron oxides (Fe_d), amorphous iron oxides (Fe_o), and electrical conductivity, whereas <i>f</i>_Fe‑OC was positively associated with Fe_d and Fe_o (<i>P</i> &lt; 0.05). Random forest analysis identified SOC, Fe_o, and Fe_d as primary predictors of Fe–OC. SEM showed that Fe–OC variation was mainly regulated by WEL, SOC, and iron forms through direct and indirect pathways.</p> Conclusion <p>Fe–OC dynamics in the Xinfengjiang Reservoir’s drawdown zones are jointly controlled by WEL, organic carbon, and iron speciation. These findings provide mechanistic insights into carbon stabilization under periodic inundation and support wetland conservation and ecological restoration.</p>