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Outline
Objective To clarify the newly introduced pollution fingerprints during a single hydrological regulation cycle in the Three Gorges Reservoir Area， and accurately identify the sources and driving mechanisms of heavy metals under different hydrodynamic conditions. Methods In the typical riparian water-level fluctuation zones （Shibaozhai， Guojiaba， and Xiangxi River） in the middle and lower reaches of the Three Gorges Reservoir Area， intact net-deposited sediments across a complete hydrological cycle were collected using in-situ sediment columns. The potential ecological risk index （PERI）， canonical correspondence analysis （CCA）， and positive matrix factorization （PMF） were applied to systematically analyze the pollution characteristics， sources， and environmental driving mechanisms of heavy metals （As， Cd， Cr， Cu， Mn， Ni， Pb， Zn）. Results 1） Pollution characteristics： Cd was the primary pollution factor， with its average content significantly higher than the background value of the reservoir area. The ecological risk level in the reservoir center was significantly higher than that in the reservoir head， and the high-risk hotspots were concentrated in the deep flooding zone （145~155 m）. 2） Driving mechanisms： Flooding duration explained 54.5% of the variance in heavy metals， serving as the primary driving factor. The "hydraulic sorting effect" driven by long-term flooding facilitated the preferential adsorption and accumulation of fine particles and heavy metals in low-elevation areas. 3） Source apportionment： The PMF model identified three pollution sources， namely traffic/industrial sources （mainly contributing to Cd and Pb）， agricultural/mixed sources （mainly contributing to As， Cu， and Ni）， and natural sources （mainly contributing to Mn）. Among these， the contribution rate of industrial sources to Cd was nearly 100%. Conclusion It is confirmed that the net-deposited sediments can effectively retrace short-term pollution inputs in the reservoir area and confirm the interception effect of the midstream backwater fluctuation zone as a "sediment filter" and its vertical enrichment mechanism， thereby providing a scientific basis for the refined management and zoned prevention and control of heavy metal pollution in the water-level fluctuation zone of the Three Gorges Reservoir Area.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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