三峡水库典型支流库湾藻类功能类群对水沙输移的响应

Since the impoundment of the Three Gorges Reservoir, the eutrophication became serious and algal bloom outbreak in the Three Gorges Reservoir, especially in the tributaries. Due to the special state of the tributaries in the Three Gorges Reservoir, the succession and extinction of phytoplankton community was affected not only by climatic factors such as temperature, light, but also by the hydrologic regime and sediments. In order to clarify the relationship between phytoplankton and water and sediments transport, we chose Xiangxi River a typical tributary of the Three Gorges Reservoir as the study area, and identified phytoplankton functional groups by ecological adaptive strategies. The recursive affect mechanism of the three main lines as water and sediments transport, change of habitat elements and phytoplankton functional groups succession was researched. Through data collection and in-situ observation, understanding of hydrological regime and sediment transport during different water period in the Xiangxi Bay, clear temporal pattern of physical and chemical factors, analyzed the effect of water and sediments on habitat elements by upstream runoff and mainstream intrusion, analyzing structural features and succession process of phytoplankton functional groups. Combined indoor simulation, we analyze the habitat requirements and ecological adaptability of typical phytoplankton functional groups, revealing the key regulatory factors for phytoplankton functional groups, to clarify the mechanism of algal community succession in response to water and sediments transport. This study is conducive to understand the regulation of water and sediments transport on algal community succession in large reservoir, and provide theoretical reference for eutrophication and algal blooms prevention.

三峡水库蓄水以来，主要入库支流均出现不同程度的富营养化和“水华”频发的现象。三峡水库藻类群落除了受水温、光照等因子影响外，还显著地受到水体流态和泥沙运动的影响。为了深入研究水沙输移与藻类演替间的内在耦合关系，本研究以三峡水库香溪河库湾为研究区域，以藻类功能类群为藻类种群生态属性分类依据，以“水沙输移—生境要素变化—藻类功能类群演替”三者的递推影响机制为研究主线，通过资料收集与原位观测，认识不同水文期，香溪河库湾的水文情势和泥沙输移特性，明晰理化因子的时空格局，分析上游来水来沙和干流水沙倒灌对库湾生境要素的影响，辨析藻类功能类群的结构特征与演替过程，结合室内模拟实验，分析典型藻类功能类群的生境需求与生态适应性，揭示藻类功能类群的关键调控因子，阐明藻类功能类群演替对水沙输移的响应机理。本研究有利于深入了解大型水库水沙输移对藻类演替的调控机制，为水体富营养化治理与藻类“水华”防控提供理论参考。

三峡水库建库后，香溪河库湾水体由建库前的河流型，转变为建库后的湖泊型，水体滞留时间变长，自净能力下降。库湾水动力特征主要受上游来流与干流倒灌的影响。上游来流流量较小，主要影响范围集中在回水区末端；干流水体则通过异重流倒灌、蓄水过程的表层倒灌等形式影响库湾。.香溪河库湾表层水体中值粒径中上游较低，下游和河口区域较高，而床沙中值粒径呈现从回水末端向河口逐渐减小的趋势。聚类分析表明，香溪河库湾中上游沉积物主要来自上游输入，而河口沉积物主要来自干流的倒灌沉积。.香溪河库湾水体理化指标存在明显的时空差异。在时间上，水温、浊度等在汛期显著高于枯期，而透明度等在汛期显著低于枯期；在空间上，各理化指标在汛期均存在沿程增大或减小的变化趋势，且变幅较大，而在枯期各指标则较为平均，沿程变化趋势不明显。水柱相对稳定性变化也呈现明显的季节性，且回水末端更容易出现分层现象，水体相对更稳定。.通过人工受控条件下不同流速和扰动对浮游植物群落的影响研究发现，低流速有利于浮游植物的生长并保持较高的Chla浓度和浮游植物多样性。随着流速的增强，浮游植物的生长受到抑制作用，Chla浓度和生物量下降，说明通过增强水动力条件控制藻类水华具有可行性。.而香溪河支流库湾中叶绿素a含量每年的3-9月份较高，其它月份较低，不同位点的叶绿素a浓度具有显著的差异性，藻类功能类群以LM，LO，Y，B，C，D和MP等类群为主。CCA分析表明以微囊藻为主的LM类群主要出现在水温较高，水体相对稳定的季节和区域；以隐藻为主的Y类群则能适应大多数环境；以暂时性浮游硅藻为主的MP类群则能够适应较低温度且浑浊的水体；以小环藻等浮游硅藻为主的B，C，D类群则对水体的混合相对不敏感，能够耐受一定的扰动。.由此可见，通过上下游水库的联合生态调度，增强库湾水体的扰动，破坏水体分层，对防控微囊藻等扰动敏感类型的藻类水华能够起到一定的作用，但对扰动不敏感的硅藻水华则作用有限。