干湿交替作用下鄱阳湖湿地碳氮循环过程研究

Alternative wet and dry process periodically has a direct impact on the distribution of wetland plants and soil critical biogenic elements such as carbon, nitrogen cycle in the soil of Poyang Lake. This project is based on the clue of alternating dry and wet process of wetlands-soil carbon and nitrogen cycles-the response of vegetation to start the research. In the project, field survey, positioning observation, control experiments, model simulation and tracer research methods are comprehensively conducted to investigate the carbon and nitrogen cycle in the wetlands of the Poyang Lake. The key elements of hydrology, soil carbon and nitrogen and the vegetation are monitored to demonstrate the accumulation and variation of carbon and nitrogen under different hydrology and hydrodynamic conditions in the wetlands of Poyang Lake. The mechanism of accumulation and storage for carbon and nitrogen in the soil were explored under the condition of alternative wet and dry process. Carbon and nitrogen accumulation characteristics and occurrence of effects are studied among the soil-vegetation system within alternative wet and dry process. This research aims to reveal the key controlling factors on soil carbon and nitrogen cycling in the Poyang Lake wetlands. Furthermore, to develop a typical coupled lake wetland eco-hydrological model to reveal the process of soil carbon and nitrogen cycling under the alternative wet and dry conditions; to quantitatively evaluate water, carbon and nitrogen cycles based on the different hydrologic process and human activity scenario in the Poyang Lake wetlands. The findings in this project have an important theoretical significance and practical value in quantitative environmental evaluation of lake wetlands.

鄱阳湖湿地周期性干湿交替过程直接影响着湿地植物的分布和土壤碳、氮循环与转化过程。本项目以湿地周期性干湿交替变化-土壤碳氮循环-植被响应三者之间的耦合作用过程为主线，利用野外调查、定位观测、控制实验和模型模拟的方法，建立鄱阳湖湿地水文、土壤碳、氮与植被关键要素的定位监测断面，分析不同水文（流速、水位、淹水周期）条件和水动力条件对湿地土壤中碳、氮累积特征及变化过程的影响机制，阐明干湿交替条件下鄱阳湖典型湿地碳、氮元素的累积特征；揭示水文节律变化对鄱阳湖湿地土壤-植物系统中碳、氮迁移转化过程的影响机制，辨析干湿交替作用条件下鄱阳湖湿地土壤碳、氮循环过程与机理。设计水文情势变化多情景方案，运用构建的湿地生态水文耦合模型，模拟极端水文情势变化对鄱阳湖湿地碳、氮和水分循环过程的影响机理。研究结果在定量评价通江湖泊湿地水文过程的环境效应方面具有重要的意义。

湿地是陆地表层重要的生态系统，具有极高的生态服务功能，是区域碳、氮、水循环的重要场所。鄱阳湖湿地具有独特的水文特性和景观特征，研究鄱阳湖湿地碳、氮循环过程及其驱动机制对有效保护鄱阳湖湿地生态系统平衡具有重要科学意义。针对鄱阳湖湿地水文过程及其对碳、氮循环过程的影响机制不清的问题，本项目通过原位实验观测和过程模型模拟，得到如下结论：（1）鄱阳湖流域蒸散及组分具有明显的时空变化特征；站点尺度上的蒸散及组分随季节温度变化呈现先增大后减小的变化趋势，植被蒸腾占总蒸散的60%以上，蒸散总量和植被蒸腾主要贡献因子为净辐射；流域尺度上的植被蒸腾为流域蒸散主要贡献量，占50%以上，不同土地覆盖类型蒸散总体遵循“林地>草地>农田”的顺序递减；蒸散与平均温度、照射到植物的净辐射通量具有显著正相关性。（2）增温显著降低了鄱阳湖湖滨湿地CO2排放，却显著促进了N2O排放；氮添加以及增温和氮添加交互作用显著抑制了CH4排放，同时显著促进了N2O排放。鄱阳湖湖滨湿地温室气体年排放总量为3629.10 ± 355.01 g CO2 eq m-2，出露期和淹没期分别占82%和18%，CH4和N2O贡献了13%。（3）鄱阳湖典型洲滩植被对土壤养分积累与理化性状改良效果也不尽相同。此外各群落有机碳、总氮与总磷含量季节性差异不明显，这也表明土壤养分季节变化较小，也说明植被对土壤养分积累是一个长期的演变过程。（4）鄱阳湖湿地年内NPP呈双峰变化，季节增长率秋季>春季>冬季>夏季，年际NPP呈增加趋势；年均和季节NPP均由湖心向湖岸增加，年均NPP显著增加区域占湖区总面积31.56%；芦苇南荻和篱蒿的NPP呈下降趋势，其他植被类型均呈增加趋势；水情变化决定了鄱阳湖区NPP的变化与分布，气象因子的影响则相对较弱。通过项目实施，在国内外学术期刊发表论文9篇，其中SCI论文7篇。本项目研究成果有利于深入认识全球变化背景下的洪泛湖泊湿地碳、氮、水循环关键过程及机制，对鄱阳湖湿地生物地球化学循环提供了新的认识，对鄱阳湖湿地科学合理的保护具有重要的理论和实际意义。