过去100年三峡库区长江支流硅藻群落对气候变暖与水库调蓄水的响应及机制

The Three Gorges Reservoir aquatic ecosystem (TGRAE) may be impacted by the impounding of the Three Gorges Reservoir and the global warming at a long-term timescale (decades) due to the greatly changed hydrological situation and the combine effects by the aforementioned driving forces. However, the researches regarding the succession of the TGRAE and its associating driving forces at long-term scale are seriously inadequate, because of the scarcities of the background information of TGRAE before human disturbances, the comparison between pre- and post-reservoir impounding and the long-term response mechanisms of aquatic communities in TGRAR. As a result, the scarcities increase the difficulty of describing the consistency and dissimilarity of succession in TGRAE, the ecological trajectory of TGRAE and analyzing the corresponding driving forces. This application is planning to take the sediments of backwater in TGRAE as research objects, establish the depth-age model, fetch the variation information of aquatic ecosystem by analyzing diatoms in sediments, fetch the information of warming and water level fluctuation by analyzing the physicochemical parameters of sediments, establish the coupling relationships among the aforementioned information, eventually discuss the impacts of warming and water level fluctuation on the succession of diatom communities and probe the threshold value of aquatic ecosystem shift. This application based on the long-term succession of TGRAE is aiming to deepen our understanding on the succession process of TGRAE, provide beneficial suggestions on accurately assessing the effects of global warming and impounding in TGRAE, maintain health of TGRAE and improve water ecological security ultimately.

三峡水库的调蓄水极大地改变了三峡库区的水文情势，加上全球气候变暖的影响，或将对三峡库区水生生态系统（TGRAE）的演替产生长期的影响（十年以上时间尺度），但其演替机制尚不清楚，因为缺少TGRAE在人类干扰前的基态信息、水库建成前后的生态对比、水生生物群落的长期响应机制等资料，导致难以勾勒TGRAE演替的连贯性和差异性，难以描绘水生生态系统转变的轨迹并分析其诱因。本申请以三峡库区长江支流回水区的柱状沉积物为研究对象，通过沉积物记录的理化指标提取温度信息、水位波动信息，通过沉积物硅藻指代水生生态系统变化，探讨过去100年来硅藻群落对气候变暖、水库调蓄水的响应及其机制，探明引起水生生态系统发生转变的生态阈值。本申请旨在借助TGRAE的长期演替研究，加深理解水环境的演变过程，为正确评估气候变暖和水库调蓄水对TGRAE的影响提供有益的建议，为维护水生生态系统健康和提高水生态安全打下理论基础。

本项目的科学目标是重建三峡库区过去100多年的水文气候变化特征、水生生物群落特征及耦合的驱动因素。我们力图在以下四个方面做出有价值的贡献。第一，通过现代器测的降水资料定量分析三峡水库蓄水前后局地降水的变化特征及其驱动因素，评估三峡水库蓄水对局地降水的影响。相对于无水库情形，三峡水库蓄水导致西北部的年降水显著增加13.2%（P<0.05），腹地和南部年降水变化不显著（P>0.05）。第二，用更长远的眼光定量重建整个长江流域在过去过去500年的降水序列，采用小波分析方法审视降水序列的韵律、强度及其与气候驱动因子的周期耦合关系。长江流域降水与驱动因子（太阳活动、厄尔尼诺-南方涛动ENSO、太平洋年代际涛动PDO、北大西洋涛动NAO）的交叉小波表明太阳活动与流域西部降水具显著的8~11a共振周期，而东部降水在90~120a的长周期上滞后于太阳活动。PDO在15~25a和50~70a的周期上显著影响长江流域各区降水，对最东部降水的影响最显著。ENSO与降水2~16a的短周期共振显著且与Ⅰ区、Ⅲ区、Ⅳ区的降水多呈反相位关系而与Ⅴ区降水同相位变化。NAO与东部降水存在准64a周期的反相位关系。第三，用现代过程的水文气候指标和浮游动物群落结构变化定量评估前者对后者的影响。轮虫在四月和八月占优势，桡足类在一月最多。氮的变化(如硝酸盐和氨)显著影响浮游动物的物种群落结构。轮虫和原生动物与支肢类和桡足类相比，具有较高的温度适应性和高锰酸盐指数耐受性。浮游动物微型和中型的比例与温度、高锰酸盐指数呈较强的线性正相关，表明：在全球变暖和人类活动影响下，浮游水生生物倾向于缩小个体尺寸，重组食物网的生物量结构，对城市水生生态系统产生根本性的变化。第四，本项目通过表层沉积物和钻孔沉积物的地球化学指标和硅藻群落结构演替，解释并评估了人类活动和气候对水生生物群落的影响。附着或者底栖硅藻Achnanthes minutissima随着水位的增加大致呈下降的趋势，典型浮游硅藻Aulacoseira distans随着水深增加丰度增加。