水深梯度影响下浅水湖泊稳态转换特征因子及阈值变化研究

Water-depth gradient (WDG) and water level fluctuation (WLF) are typical hydrological characteristics in shallow lakes. Under the influence of WDG and water level fluctuations (WLF), a series of characters in shallow lakes, including the distribution and community structure of submersed macrophytes and the exchange of nitrogen and phosphors across the sediment-water interface (SWI) around the rhizosphere, would change significantly. These variations might lead to the alteration of regime shift between submersed macrophytes and algae dominant ecosystems in shallow lakes. However, the detailed mechanisms of the alteration still remains unclear. Therefore, this study focuses on the influence of (WDG) on the alterations of typical characteristics and the threshold values that trigger the regime shift in shallow lakes. Several classic areas with different water depth and the resultant discrepant submerged macrophyte communities would be selected as the study areas. The variations of biomass, structures, and other characteristics of the communities under different WDGs would be investigated. Simultaneously, the alterations of oxidation-deoxidation micro-environment and the exchanges of nitrogen and phosphorus across the SWI around the rhizosphere under the above variations would be studied. Base on the long-term, multi-factor field investigation, several statistical approaches would be carried out to identify the critical factors that lead to the catastrophe of the ecosystem under different WDGs. The results of the field investigation and the indoor simulation experiment would be analyzed synthetically to reveal the detail mechanisms of the variations of the threshold values of nitrogen and phosphorus during the regime shift under different WDGs. A new regime shift model would be built to deduce the regime shift under the influences of different WDGs and nutrient levels. The regime shift theory of shallow lakes would thereby be further improved. In addition, the new model might also be used for the prediction of the catastrophe of shallow lake ecosystems and provide theoretical foundations for the scientifically regulate of water level and submersed macrophytes in shallow lakes.

水深梯度与水位波动是浅水湖泊的典型水文特征，受其影响，沉水植物分布、群落结构特征及根际沉积物-水界面氮磷交换等将发生一系列转变，由此导致的浅水湖泊草-藻稳态转换过程改变及其机制尚不清晰。本研究关注水深梯度影响下触发浅水湖泊稳态转换的关键因子改变及其阈值波动特征。拟选择太湖典型水深变化并导致沉水植物群落分异水域作为调研对象，探明不同水深梯度下群落生物量、结构等特征响应规律，并获取在此响应下植物根际沉积物-水界面氧化还原微环境及界面氮磷交换的变化特征。基于长时间、多因子野外调研结果，使用统计分析方法归驱不同水深梯度下造成生态系统灾变的关键因子，并将野外调研结果与室内模拟实验结果相结合，揭示水深梯度影响下驱动生态系统灾变的营养盐阈值变化机制，建立水深梯度和营养盐耦合驱动下浅水湖泊稳态转换模型，以完善浅水湖泊稳态转换理论，预测预警浅水湖泊生态系统灾变，为湖泊水位科学调控及沉水植被恢复提供理论依据。

在富营养浅水湖泊生态恢复中，以沉水植被动态为标志的藻型浊水态与草型清水态之间互相转换成为研究热点，水深不仅可能作为一个重要因子影响沉水植物群落结构，同时可能与氮、磷营养盐以及沉积物等其他因子发生相互作用，从而使得驱动稳态转换过程发生的特征因子发生改变。因此，探寻不同水深梯度下驱动浅水湖泊草-藻稳态转换的主要因子如何改变，对完善浅水湖泊稳态转换理论及退化沉水植被恢复工作具有重要的理论及现实意义。.本项目选取我国长江中下游典型浅水湖泊太湖为对象，开展了不同水深梯度下一系列野外观测和室内模拟研究，探究了水深梯度下水体-沉积物营养盐赋存状况，研究了苦草等生长下水体-沉积物氮磷状况、对不同水深与不同沉积物营养状态的响应过程等，探明了水深梯度下太湖沉水植物分布特征及影响的关键环境因子，并判定其阈值，获得主要成果如下：.（1）沉水植物生境的水体理化特征、沉积物氮磷赋存状态、沉积物-水界面微环境以及微生物群落等受水深影响显著，并有明显的季节变化特征。该研究提供了基础数据，对判定不同水深梯度下湖泊稳态转换关键因子及其阈值提供了基础。.（2）较低水深（0.5 ~0.9 m）影响沉水植物生物量的环境因子为磷酸盐和悬浮颗粒物，磷酸盐的阈值为0.015 mg/L，悬浮颗粒物的阈值为32.63 mg/L；）；较高水深（1.2 ~1.75 m）影响沉水植物生物量主要因子为总氮和磷酸盐浓度，总氮的阈值为1.749 mg/L，磷酸盐阈值为0.012 mg/L。可见水越深，沉水植物生长对水质要求越高。.（3）沉水植物通过根系吸收沉积物中的生物有效磷，能够有效减少沉积物间隙水中的磷向上覆水的扩散量。.（4）水深和基质的独立和交互作用对苦草生长和生理性状均有显著影响。随水深增加，苦草会调整物质分配，使株长、叶宽和最大根长减少，沉积物则更多地表现出对苦草根系形态影响。130 cm水深的较高营养条件沉积物更适合苦草生长。探明了沉水植物生长的适宜水位与生长基质，对沉水植被恢复及良性生态系统管理具有重要意义。