近60年鄱阳湖东部湖湾水文连通变化及其对湿地植物与候鸟的影响

Variations of hydrological connectivity in the eastern bay of Lake Poyang in the last 60 years and its impacts on wetland plants and migratory birds

鄱阳湖碟形湖生物群落分布特征很大程度上受区域与主湖区水文连通性影响。由于水位波动,东部湖湾水文连通性受鄱阳湖主湖体水位影响较为敏感。本文以东部湖湾为例,分析主湖区水位变异程度及其影响,并从连通天数和发生时间等方面定量表征东部湖湾与主湖区的水文连通性,进而讨论水文连通性变化及其对湿地植物生境和候鸟栖息地的潜在影响。结果表明,当水位在13~16 m时,东部湖湾与主湖区存在着良好的水文连通关系,湿地植物适宜生境面积最大。2003年以后,鄱阳湖主湖区水位普遍降低,低枯水位持续时间延长,IHA/RVA法分析表明主湖区水位发生了中等程度改变,整体改变度为40.2%,东部湖湾与主湖区的连通关系发生明显改变,年连通天数减少了46.2 d,变化幅度为15.9%,而非连通期发生时间提前约1个月且年内时间跨度更长。水文连通性减弱造成310月东部湖湾平均水位下降了0.6 m,其中910月减少了约1 m,使薹草(Carex sp.)和苦草(Vallisneria natans)适宜水深对应的水面面积在多数月份呈增加趋势,特别是910月(幅度超过40%),但枯水提前导致沉水植物面积减少,湿生植物生物量增加。水文连通性减弱导致洲滩提前出露,薹草等湿生植物移向碟形湖湖心,苦草等沉水植物分布上限降低约1 m,候鸟觅食地点可能转移至湖心或其他浅滩。为有效保护鄱阳湖湿地生态系统,建议充分发挥长江三峡蓄洪补枯的调控作用等,以减缓水文连通性改变对洪泛区湿地植物生长和候鸟栖息所造成的影响。

The distribution characteristics of the biological communities in the flood plain areas of Lake Poyang are greatly influenced by the hydrological connectivity between a region and the main lake.Due to the water level fluctuations,the hydrological connectivity of the eastern bay of Lake Poyang is sensitive to the water level of the main lake.Taking the eastern bay of Lake Poyang as an example,this study analyzed the water level fluctuations in the main lake as well as its influences.The hydrological connectivity between the eastern bay and the main lake was quantitatively characterized from the aspects of connectivity days and occurrence time.Furthermore,the changes of hydrological connectivity and its potential impacts on the habitats of wetland plants and migratory birds were discussed.The results showed that when the water level was 13-16 m asl,there was a good hydrological connectivity between the eastern bay and the main lake,during which the suitable habitat area for the survival of wetland plants was the largest.The water level of the main lake has generally decreased since 2003,and the durations of low water levels have been prolonged.According to the results of IHA/RVA analysis,the water levels in the main lake had changed to a moderate extent,with an overall change degree of 40.2%.The hydrological connectivity between the eastern bay and the main lake has changed significantly,with annual connection days reduced by 46.2 days,and the variation is 15.9%.The occurrence time of non-connection period is about one month earlier,and the yearly time span is longer.The decreased hydrological connectivity caused the average water level of the eastern bay to drop by 0.6 m from March to October,with a decrease of about 1 m from September to October,while the water surface area corresponding to the suitable water depth for Carex sp.and Vallisneria natans increased in most months,especially from September to October(more than 40%),but the area of submerged macrophytes decreased and the biomass of hygrophytes increased.The weakening of hydrological connectivity led to the early emergence of the beaches,the transfer of hygrophytes such as Carex cinerascens to the center of the saucer-shaped lake,the decrease of the upper limit of submerged macrophytes such as Vallisneria natans by about 1 m,and the migration of migratory birds to the center of the lake or other shoals.In order to effectively protect the Lake Poyang wetland ecosystem,it is recommended that more attention should be payed to the regulating and control roles of the Three Gorges Dam on the Changjiang River in mitigating the impacts of changes in hydrological connectivity on wetland plants growth and migratory bird habitats in the flood areas of the lake.