Seasonal climate and reservoir regulation drive coupled dynamics of dissolved organic matter and heavy metals

Cascade reservoirs serve as active biogeochemical reactors, yet their impacts on pollutant migration and transformation processes remain unclear. Here, we propose an attribution analysis framework to reveal the spatiotemporal patterns, coupled dynamics mechanisms, and key drivers of dissolved organic matter (DOM) and heavy metals in the upper Yellow River cascade reservoirs. The results indicate that synergistic photodegradation-microbial processes shift DOM composition from terrestrial humic-like to autochthonous protein-like components. This process reduces aqueous heavy metal concentrations but increases eutrophication risk, exhibiting strong seasonal variability. Reservoir discharge also risks secondary heavy metal release via sediment remobilization. Cascade reservoirs thus present dual “purification” and “pollution promotion” effects with cumulative downstream impacts. Quantitative models explain 75.1% of DOM and 69.8% of heavy metal variation, driven mainly by seasonal climate and reservoir operations. DOM transformation critically regulates heavy metal fate (33.8%). Clarifying these biogeochemical interactions is essential for watershed water security and targeted pollution control.

梯级水库作为活跃的生物地球化学反应器，但其对污染物迁移转化过程的影响仍未明晰。本研究构建了一套归因分析框架，以揭示黄河上游梯级水库中溶解有机物（Dissolved Organic Matter, DOM）与重金属的时空分布格局、耦合动力学机制及关键驱动因子。研究结果显示，光降解-微生物协同作用将DOM的组分从陆源类腐殖质转变为内源类蛋白质组分。该过程可降低水体中重金属浓度，却会加剧富营养化风险，且表现出显著的季节变异性。水库泄流还可能通过沉积物再活化引发重金属的二次释放风险。因此，梯级水库兼具"净化"与"促污染"双重效应，并会对下游产生累积性影响。定量模型可解释75.1%的DOM变异与69.8%的重金属变异，其主要驱动因子为季节气候与水库调度。DOM转化过程对重金属归趋具有关键调控作用（贡献率达33.8%）。阐明这类生物地球化学相互作用，对流域水安全与精准污染防控至关重要。