鄱阳湖典型洲滩湿地植物水分利用对水情变化的响应机制研究

Under the influence of climate change and anthropological activities, the alterations of water regimes in Poyang Lake directly cause the great changes of wetland groundwater, soil moisture and ecological processes. It also takes effect on the plant’s root water absorption function, which is the hotspot issues in the wetland ecohydrological fields. The dominant vegetation community of lakeshore wetland will be studied in Poyang Lake. Based on the water isotope tracers and hydrologic monitoring, the characteristics of isotopic compositions from different water bodies will be analyzed that will reveal the hydraulic interactions among groundwater, soil water and lake water. The temporal variations of groundwater and lake water level will be studied and thus identify the responsive relationships between groundwater level and lake water regimes. The variations of soil properties, vegetation characteristics and soil moisture will be exhibited among diverse wetland vegetation zones, in order to better clarify the reason underlying the heterogeneity of soil moisture under the new water regimes. The depth and strength of plants water use sources will be quantified by the IsoSource model during the growing seasons. Finally, combined with the variations of plants ecophysiological parameters and water use source, we will highlight the plant’s water use strategies and their adaptive mechanisms under different water regimes, in order to specify the optimal water level for plant’s survival in lakeshore wetland, Poyang Lake. These findings will provide the scientific guidelines for the ecological water level regulation of the Poyang lake hydrological project.

在气候变化和人类活动的影响下，鄱阳湖水情的改变直接导致湿地地下水位、土壤水分和生态过程发生变化，影响着湿地植物根系吸水功能，这是目前湖泊湿地生态水文研究领域所关注的热点问题。本项目以鄱阳湖典型洲滩湿地优势植物群落为研究对象，基于稳定氢氧同位素示踪和水文监测，辨识湿地同位素变化特征，揭示湿地地下水-土壤水-湖水之间的水力联系，分析湿地地下水位和湖泊水位的季节变化，明确湿地地下水位变化与湖泊水情之间的响应关系，对比分析洲滩湿地土壤物理性质、植被特征和土壤水分的变化特征，揭示湿地土壤水分时空异质性形成的影响机理；基于多源混合模型定量识别生长季内湿地植物水分来源深度和强度，结合植物生理生态参数的特征分析，阐明在不同水情下湿地植物水分利用策略及其适应机制，提出适合洲滩湿地植物生长的最佳水位，将为鄱阳湖水利枢纽工程调控湖泊生态水位提供科学指导。

因水利工程水文调节和气候变化双重影响引起的长江中下游通江湖泊水位波动节律改变而致使洲滩湿地植物根系吸水深度和强度的变化，定量研究不同水情下湿地植物水分利用对湿地植被保护与恢复具有重要的实践意义。按照项目既定的研究目标和研究内容，完成了鄱阳湖典型洲滩湿地（新港、吴城、星子）土壤水分及其性质的调查、地下水位的原位监测、湖水和降水、洲滩湿地土壤和植物同位素样品采集，通过数据分析研究结果发现①鄱阳湖典型洲滩湿地土壤粒径主要以粉粒为主，主要是洲滩湿地在丰水期淤积有关，土壤TC、TN、TP沿高程梯度均呈典型的上凸型分布；②鄱阳湖北部水域湖水δ18O和δ2H值表征出明显的季节差异性，这主要受流域来水、长江水和湖泊水间关系的影响；③地下水位峰值与月降水量峰值不同步，地下水位峰值出现时间滞后降水峰值3-4个月；④洲滩湿地土壤水分均呈现自表层先增大后降低的趋势，通过多源混合模型模拟发现在新港、吴城和星子典型洲滩湿地植物（芦苇、虉草、藜蒿、南荻和苔草）根系吸水深度主要分布在30cm以上，平均利用比例占86.3%，而在新港离湖岸500m的样地芦苇根系吸水来源主要来自于30cm以下的深层土壤水（70%），这将为鄱阳湖湿地水位调控提供科学依据。