鄱阳湖湿地界面水分传输及与植被演替/恢复过程的作用机理研究

Hydrological process is the driving force to wetland vegetation succession and recovery. Water transport is the key to reveal the interaction mechanism between wetland hydrology and vegetation. In the 21st century, extreme hydrology events occurred frequently in the river-connected lake wetlands in Yangtze River, which greatly threatened the stability of wetland ecosystem. However, researches on water transport in river-connected wetland are limited. How wetland vegetation succession and recovery in response to long-term hydrology changes is still unclear now. In this study, a typical delta wetland transect in Poyang Lake wetland will be selected as study area. Three different vegetation communities will be chosen to represent the mesophyte, hygrophyte and emergent plants ecosystem. The field observation，isotope technique and statistic methods will be comprehensively used to explore the interface water transformation through the ground/surface-water-soil-plant-atmosphere continuum in wetland and to analyze the vegetation water utilization mechanism. Besides, a coupled water transport and vegetation growth wetland eco-hydrology model will be developed to reveal the response mechanism of vegetation succession and recovery growth to the long-term lake water regime changes based on different hydrological process scenario. The stability and resilience of vegetation to hydrology changes will be further evaluated. The results of this study will enrich the understandings of the mechanisms of water movement and vegetation response to hydrological changes in river-connected wetlands, and provide guidelines for wetland water stage management and vegetation restoration program.

水文过程是湿地植被演替和恢复的驱动力，界面水分传输是揭示水文与植被相互作用机制的基础。进入21世纪以来，长江中下游通江湖泊极端水文事件频发，直接威胁到湿地生态系统的稳定。本研究针对目前通江湖泊湿地水分传输和植被演替恢复过程认识不足这一现状，以鄱阳湖典型洲滩湿地为研究区，选取中生、挺水和湿生3种不同生态型植被系统为研究对象，运用野外观测、同位素技术和统计方法，系统探求地下水/地表水-土壤-植被-大气系统界面水分通量的传输过程和转换关系，阐明不同生态型植被生长水源构成与水分利用规律。通过构建具有耦合机制的湿地水分运移与多种群植被生长竞争模型，基于不同的水文情景模拟，进而揭示长期水文过程变化对不同生态型湿地植被演替和恢复过程的作用机制，评估植被的抵抗力和恢复力。研究成果有助于加深对通江湖泊湿地水分传输机制和植被对水情变化响应机理的认识，为湿地水位调控和植被恢复决策提供科学参考依据。

水文过程是决定湿地植被分布和演替的关键因子，21世纪以来鄱阳湖水文情势发生明显改变，已直接影响到湖区湿地的水分补给和植被生态系统的稳定。本项目以鄱阳湖吴城国家自然保护区内典型洲滩湿地为研究区，选择高程梯度呈带状分布的中生、挺水和湿生3种不同生态型植被群落为研究对象，利用野外生态水文观测、稳定同位素技术，分析了降水、河湖水和湿地地下水等不同水体的补排过程，探明了湿地地下水和土壤水的补给来源及其季节变化，揭示了不同生态型植物的水分利用方式。结果发现，湿地地下水为历史长期降雨和湖水共同补给形成，且在丰水期主要受湖水补给，退水期地下水向河水排泄。植被群落土壤水在雨季主要受降水补给，夏季7-8月茵陈蒿群落深层土壤水受湖水侧向入渗和地下水的共同补给，并在蒸发作用下水分自深层土壤向浅层土壤传输；芦苇群落土壤水主要受地下水毛细上升水补给，毛细上升高度可达5 m；灰化薹草群落土壤水主要受降水和地下水补给。中生性植物茵陈蒿生长季生长初期主要利用0-40 cm浅层土壤水，夏季表层土壤干旱时转而吸收深层土壤水，贡献率可达74-95%；而芦苇在生长旺季主要利用地下水和深层土壤水，地下水的贡献率34%。此外，依托构建的茵陈蒿、芦苇植物群落根系吸水和水分垂向运移模型，模拟了淹水-出露状态下湿地系统水分运移，量化了GSPAC系统不同界面的水分通量。同时，设置了21世纪前后湖水位过程和连续4年低枯水位2种情景，模拟预测了长期水文条件变化对湿地系统水分补给和植被群落分布的影响，结果发现持续多年的湖泊干旱，可能导致中生性茵陈蒿群落分布向湖区扩展，湿生植物灰化薹草向高位滩地蔓延，芦苇群落面积萎缩。研究结果可为鄱阳湖湿地植被生态系统演变和科学保护提供理论参考。