鄱阳湖湿地植被固碳速率时空分异及其对水文情势的响应研究

The complex hydrological conditions of Poyang Lake wetland make its carbon sequestration processes of wetland vegetation be of high specialty and complexity. In recent years, the intensification of both climate change and human activities in this region has led to a significant change in its hydrological conditions, which has had a significant impact on its vegetation carbon sequestration. However, the current research is still relatively insufficient to understand the dynamic of vegetation carbon sequestration in Poyang Lake wetland and its response to hydrological conditions. Thus, this research focuses on the Poyang Lake wetland, investigating the spatiotemporal dynamics of vegetation carbon sequestration and its coupling with the hydrological conditions. Specifically, we will first use a combination of remotely sensed Vegetation Index (VI) time series and field vegetation data to retrieve the dynamic of biomass carbon stocks of this wetland, then it can be used to calculate the cumulative composite of biomass carbon stocks during a year, i.e. the annual vegetation carbon sequestration. Secondly, a distributed hydrological model and the Gaussian mixture model will be applied to describe and quantify the vegetation carbon sequestration-hydrological condition relationships in this wetland. Finally, a coupled eco-hydrological model will be developed in Poyang Lake wetland. Through its scenario simulations, the marginal response of vegetation carbon sequestration under multi-water regime evolution scenario will be simulated, and the response of vegetation carbon sequestration to hydrological conditions in this wetland will be revealed. The outcomes of this research will help reveal the reasons for the changes in vegetation carbon sequestration of Poyang Lake wetland in recent years, and provide a scientific basis for proposing a water resources management strategy to maintain the carbon sequestration function of vegetation in this wetland.

鄱阳湖复杂的水文情势使其湿地植被固碳过程表现出高水情变幅影响下的特殊性和复杂性。近年来，气候变化和人类活动的加剧导致其水情改变愈益明显，给湿地植被固碳造成了显著影响。然而，当前研究在湿地植被固碳速率及其对水文情势的响应方面仍相对薄弱。基于此，本项目以鄱阳湖湿地为研究区，以植被固碳速率-水文情势的耦合研究为核心，首先通过植被指数影像时间序列与同期样方调查数据重建湿地植被碳存量年内动态变化过程，在此基础上以累积存量法估算湿地植被年固碳速率并分析其时空分异及近年来的演变。然后，结合分布式水文模型与高斯混合模型，描述并量化湿地植被固碳速率对水情的响应行为。最后构建生态-水文耦合模型，基于情景模拟辨析多水情演化情景下的湿地植被固碳速率边际响应，阐明水情对湿地植被固碳速率的影响及机制。研究成果有助于揭示近年来鄱阳湖湿地植被固碳速率改变的原因，并为提出维持其植被固碳功能稳定的水资源管理策略提供科学依据。

气候变化与人类活动共同驱动了鄱阳湖水文情势近年来的急剧变化，并对其湿地植被固碳功能产生了显著影响。当前研究尚未系统量化鄱阳湖湿地植被固碳速率在水情骤变下的演变趋势与规律，因此也制约了对湿地植被固碳速率响应湖泊水情变化原因与机制的理解。本项目结合水文站实测数据、实地植被调查数据、遥感观测资料以及生态-水文过程模型等多源数据与方法，系统分析了2000~2020年间鄱阳湖湿地植被固碳速率以及湖泊各关键生态水文变量的时空演变，并建立了湿地植被固碳速率的水情变量响应曲线，构建了鄱阳湖湿地生态-水文耦合模型，对不同水情演变情景下的湿地植被固碳速率进行了模拟预测。结果表明，（1）鄱阳湖湿地2000-2020多年平均的植被固碳速率在81至844 g C m-2的范围内波动，区域均值约268 g C m-2，湿地植被固碳速率的空间异质性较大，标准差约163 g C m-2。（2）近20年间鄱阳湖湿地植被固碳速率总体呈增加趋势，变化速率介于-36.80至47.20 g C m-2 yr-1之间，区域整体呈增加趋势，变化速率约5.14 g C m-2 yr-1。湿地植被固碳速率变化趋势的空间差异巨大，湖心区显著增加而湿地边缘有所下降，湿地植被固碳速率的增长与减少区域分别约占全湖总面积的75%与25%。（3）近20年间的鄱阳湖湿地淹没开始时间在64%的湖区被推迟，推迟速率约为1.10天/年；仅在入江水道及碟形湖小幅提前，且提前趋势并不显著。淹没结束时间在72%的湖区显著提前，提前速率约为1.46天/年；仅在有闸控工程的碟形湖因延迟泄水而有所延迟。淹没历时在70%的湖区显著缩短，缩短速率约为2.19天/年，而在有闸控工程的碟形湖则有所延长。（4）鄱阳湖湿地植被固碳速率对淹没历时与末次淹水结束时间的响应曲线均呈倒U行，即在最适淹水历时（61天）与最适末次淹水结束时间（9月8日）之前均与淹水变量呈正相关，自此之后则与各淹水变量呈负相关。末次淹水结束时间对湿地植被固碳速率的影响最为显著，能解释植被固碳速率空间差异的94%。（5）末次淹水结束时间提前（延迟）情境下，湿地植被固碳速率在高位洲滩下降（增长）而在中低位洲滩增加（下降），具体变幅取决于末次淹水结束时间的提前（延迟）幅度。