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Clarifying the new characteristics of Dongting Lake’s backwater effect on the lower Jingjiang River after the impoundment of the Three Gorges Reservoir is a critical issue at present. Focusing on the river section from Jianli to Chenglingji upstream of the confluence between the river and the lake， Copula functions were employed to investigate the characteristics of flow coincidences between the river and the lake in different periods. Based on the flow dynamics of alluvial rivers， a balanced-state flow pairing relationship was proposed， and an index for assessing the backwater intensity of the mainstream was developed. On this basis， the occurrence probability and timing of backwater events as well as the variation of backwater intensity during different periods within a year for the lower Jingjiang River before and after the impoundment of the Three Gorges Reservoir were quantitatively analyzed. The results indicate that， under the balanced state， the flow pairing between the river and the lake follows a nonlinear functional relationship. This relationship is close to the long-term mean fitted line of river-lake discharges and can be used to determine whether the mainstream is in a backwater or drawdown state. After the impoundment of the Three Gorges Reservoir， the duration of Jianli discharges at the medium-low flow level increased， resulting in a 44.6% rise in the coincidence probability of both the mainstream and lake inflows being at medium-low flow. The coincidence probability of the mainstream at medium flow and lake inflows at flood level （exceeding 30，000 m³/s） increased by 5.4%. As a result， the erosional base level at the river-lake confluence decreased， and on an annual scale， the mean backwater intensity of the lake on the mainstream weakened. However， the timing of the mainstream being in a backwater state shifted from above-bankfull flow levels to medium flow levels. The occurrence of extreme backwater intensity far exceeding the historical values during April-July has increased， warranting long-term attention.
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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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