Mineralogical variability of suspended sediments induced by mega‐reservoir regulation (Yellow River, China)

Unravelling the mineralogical variability of fluvial sediments is crucial for tracing detrital signatures from mountain belts to ocean floors. Over the last century, dam construction has disrupted global fluvial sediment transport, yet the mineralogical consequences of such anthropogenic alterations remain poorly understood. This study investigates these impacts in the lower Yellow River, the sixth‐longest river on Earth and the most sediment‐laden. In this region, the mega Xiaolangdi Reservoir regulates hydrological conditions through the year (pre‐water regulation in May, water regulation in June, sediment regulation in July). A multi‐technique approach, including multiple‐window heavy‐mineral analyses of significant size classes by TESCAN Integrated Mineral Analyzer, bulk‐sediment X‐ray diffraction analyses and grain‐size analyses, was employed. The results reveal significant intersample (among samples) and intrasample (among size fractions within a sample) mineralogical variability. Suspension sorting, driven by size‐density‐shape relationships, produces distinct trends under different hydrological regimes. During the sediment regulation stage, a downstream fining trend coincides with a reduction in quartz and faster‐settling heavy minerals. In the pre‐water and water regulation stages, sediment is reworked from riverbanks due to the lack of sediment supplied from upstream and such a trend is blurred. Enhanced hydrodynamic conditions during the water regulation stage intensify selective‐entrainment processes, thus reducing heavy‐mineral concentration while increasing bulk‐sediment grain size. Across all stages, mica increases downstream due to its platy shape and consequently low settling velocity. Settling‐equivalence primarily governs intrasample variability, with size‐density correlation coefficients of 0.81 in May, 0.58 in June and 0.79 in July. This study provides new insights into fluvial sediment transport under reservoir regulation, highlighting the mineralogical effects of anthropogenic modification on natural sediment‐routing systems. As dam constructions continue to expand globally, addressing these issues becomes increasingly urgent for systematically evaluating the long‐term impact of dams on river systems.