基于水生植物生物物理参数反演的湿地生态功能退化研究

Due to the impacts of climate change and anthropogenic activities, wetland degradation has been a global issue. As one of the key elements of wetland research, the spatiotemporal variations of wetland vegetation is important for wetland monitoring and the mechanisms of wetland degradation. Currently, significant discrepancies of key ecological parameters of wetland still exist in the retrieval of terrestrial remote sensing, which directly affect the accuracy monitoring and the consistency of parameters. The main reason is the inappropriate consideration to radiative relationships between water background and the upper canopy of wetland vegetation. This proposal want to construct a radiative transfer based model that considering the water optic properties and water background contributions to the total canopy reflectance. Based on this, the key ecological parameters that reveal the vegetation structure, growing status, ability of photosynthesis and spatial distribution of wetland will be estimated through Artificial Neural Network (ANN) method. After that, this proposal will conduct the quantitative assessments over Honghe wetland of Sanjiang Plain, the key points are extracting the sparse wetland vegetation, identifying the vegetation types transitions and enhancing the spatiotemporal consistency of parameters. This proposal will make contributions to the mechanism research of wetland degradation and the project of wetland ecological functions restoring.

由于气候变化和人类活动影响，湿地退化已成为全球性问题。植被作为湿地的主要要素之一，其时空变化特征是湿地退化监测及退化机理研究的重要组成部分。目前湿地关键生态功能参数的遥感估算仍有较大误差，直接影响湿地植被退化监测的准确性和时空连续性，主要原因是遥感参数建模时未准确考虑湿地的水体背景对植被冠层反射信号的影响。本项目通过大量实测和广泛的模型模拟，分别基于植被和水体模型解决湿地植株和背景水体的反射率贡献，再将二者耦合起来构建针对湿地植被的生态功能参数估算模型。使用神经网络方法稳定经验关系估算湿地植被的生长结构、生长状态、光合作用能力以及空间分布等参数。本项目拟对三江平原洪河湿地开展多年多参数植被退化监测及定量评价，重点提高稀疏植被的识别能力、增强植被类型转换判别以及加强生态功能参数的时空连续性。本项目对湿地退化机理研究和湿地生态能修复工程实施具有重要参考意义。

湿地植被是全球碳收支监测和全球气候变化的重点研究对象。目前湿地关键生态功能参数的遥感估算仍有较大误差，一个重要原因就是反射率和地表反照率的估算不准确。本项目重点解决典型湿地植被地表反射率和反照率的准确估算问题，在此基础上判别湿地植被变化的生态效应。在本基金项目支持下，完成了三项研究任务：（1）构建优化了典型湿地植被反射率模拟模型，补充了早期模型对水体及水中植被考虑不足的缺陷，提升了模拟精度；（2）提出了适用于湿地植被的地表反照率估算方法，对提升湿地植被碳收支估算具有参考价值；（3）通过植被绿量和固碳量验证得到，三江平原地区固碳速率呈现“西多东少”的整体格局，湿地固碳能力并无显著增加，部分湿地区域固碳速率下降，本研究结论为下一步解析湿地植被固碳变化的原因提供了研究方向。