大坝下游河段对水文调节的河流景观生态响应研究--以长江中游下荆江段为例

Focused on the fluvial landscape patterns and processes, this study explores the ecological responses of ecologically-sensitive reaches to dam-induced hydrological flow regulation by using the methods of RS and GIS, field investigation and indoor experiments and by basing on the theoretical framework of fluvial landscape ecology. The lower Jingjiang reach, at the upstream of which several large-scale dams have been constructed, is chosen as the studied example. According to the factors of hydrogeomorphic features, land cover and land use, the method for fluvial landscapes classification will be proposed. The critical elements, patterns and processes in fluvial landscapes will be identified by using the landscape metrics analysis. The evolution of the structures, patterns and processes of fluvial landscapes in the past 15 years will be discussed and associated with the flow regulation. Thereby, the spatiotemporal responses of fluvial landscapes to flow regulation will be revealed. By emphasizing on the important landscape-ecological factors including landscape diversity, ecological functions, ecological sensitivity and hydrological connectivity, the landscape-ecological security mode will be proposed. Studies on these critical problems will expand the researches of fluvial landscape ecology in China and can provide the theoretical basis for preserving and restoring the river wetlands in the middle Yangtze River, which is intensively influenced by large-scale dams.

以河流景观生态格局与过程为切入点，选取其上游大坝工程设施密集、生态响应敏感的长江中游下荆江河段为实证对象，耦合RS与GIS、野外调查和室内实验分析，探究大坝下游河段对水文调节的生态响应。基于河流动力地貌、土地利用和土地覆被等因子，提出河流景观生态的分类方法和分类体系，识别河段尺度河流景观生态的关键景观要素、格局与过程，通过近15年来研究区河流景观结构、格局与过程的演进序列与水文情势的关联分析，揭示河流景观生态对水文调节的时空响应机制，综合考虑功能过程承载、生态响应的敏感性、生态过程控制和水文连接作用等景观生态特性，提出水文调节干扰下的河流景观生态安全模式。对水文调节作用下河流景观生态的时空响应机制和景观生态安全模式等关键问题开展研究，可以拓展我国河流景观生态学的研究内涵，为大型水利工程背景下长江中游河流湿地的保护与修复提供理论基础。

全球大多数河流受到大坝工程的影响，河流科学认识和生产实践迫切需要开展景观尺度河流研究，为河流生态保护、修复与管理提供科学支撑。本项目基于河流景观生态学，以长江中游下荆江为实证区，通过野外调查与实验数据及遥感数据，得到如下主要结论：（1）不同平面形态河段在景观结构与异质性格局上存在明显差异，微弯分汊的上荆江维持更大比例和面积的河床相水文地貌斑块；高弯曲的下荆江维持更大比例和面积的河漫滩相水文地貌斑块；下荆江横向水文连接度更高。（2）三峡大坝蓄水后，荆江河湾平面形态参量存在显著变异，上、下荆江及凸、凹岸变异程度不同且其时空过程具有非同步性；上、下荆江洲滩水文地貌单元的演变存在明显差异，上荆江累计冲刷6.46 km2，下荆江累计淤1.90 km2，下荆江凸、凹岸演变存在纵向互动关系。（3）基于实测产卵数据得到四大家鱼产卵生态水文需求特征；蓄水后产卵期推迟，产卵高峰期次数及其持续时间减少，使得鱼类在更高水温条件下产卵，产卵前及期间水位和流量的增长率与持续时间均显著减小。（4）不同土地利用方式下的芦苇地土壤，农业活动显著增加表层SOM、N、K含量，降低亚表层SOM、N、K含量，表层及亚表层P含量均减小；火烧秸秆明显增加土壤养分含量。（5）下荆江土地利用方式与水文地貌单元7种典型组合模式下土壤氮密度、氮储量不同，江心洲人工芦苇地最高，堤岸自然芦苇地和堤岸薏杨林地最低；同时其组分赋存形态不同。（6）下荆江典型洲滩湿地包括维管束植物45科125属148种，分布区系类型多样，特有种匮乏。（7）根据优势度、粒度、斑块形状复杂性、连接度和破碎性评价，得到下荆江关键景观要素：河流水面、河漫滩和牛轭湖，重要景观要素：江心洲和无护岸堤岸，不利景观要素为护岸堤岸，应采取相应的管理策略。（8）所建立的河段尺度河流景观分类方法——等级生态水文地貌斑块分类，包括分类等级、空间尺度、分类变量、特征变量等，下荆江河流景观生态分类系统包括6类、11亚类、22种。