【作者】 覃红燕；

【导师】 邹冬生；

【作者基本信息】 湖南农业大学 ， 生态学， 2013， 博士

【摘要】 洞庭湖为我国第二大淡水湖泊及国际重要湿地,具有物质生产、蓄水防洪、沟通航运及生物多样性保护等多种生态服务功能,是长江中下游地区社会经济可持续发展的重要生态屏障。水文情势是湿地生态学的重要内容,对水文情势研究有助于正确认识洞庭湖水沙变化规律,探明湿地演变趋势以及调蓄功能的水文成因,为洞庭湖湿地的保护及管理提供一定的理论依据。本文以典型水文站点50余年来的长时间序列资料为基础,运用多年平均值法、移动平均值法、Mann-Kendall趋势突变法(简称M-K法)、双累积曲线法、最佳模型拟合分析、遥感影像分析等方法对洞庭湖水文环境演变及其成因进行了详细研究,结果如下：(1)阐明了洞庭湖水沙平衡特征。洞庭湖年径流量、年输沙量、泥沙输出量及泥沙淤积量和淤积比近50余年来整体呈不断减少的趋势,其中2006—2009年间,洞庭湖淤积量和淤积比为负值,表现为冲刷状态。排沙比逐渐增加。进一步分析表明,径流量的减少主要是三口入湖径流量不断减少引起,而四水径流量年际变化不大。输沙量的减少是三口和四水输沙量均不断减少的结果。近50余年来,三口径流输入量和泥沙输入量占洞庭湖径流和泥沙输入总量的比例逐渐减少,而四水的不断增加。(2)揭示了湖南四水水沙演变规律及其成因。近50余年来,四水年径流量变化比较复杂,存在多个上升-下降过程,但总体上无明显上升或下降趋势。年输沙量总体上呈明显下降趋势,且突变时间存在差异,湘水是1996年,资水是1973—1974年,沅水是1997—1998年,澧水是1998年。年输沙量趋势性改变与该河流最大水库的建设密切相关。年径流量的减少、植被覆盖增加以及大中型水库的建设等综合作用是2001年后年输沙量较大幅度减少的主要原因。(3)探明了荆江三口水沙演变规律及其成因。三口年径流量和年输沙量在近50余年呈不断减少的趋势,以藕池口变化最为显著,突变时间最早。松滋口年径流量和年输沙量趋势性改变的时间分别为1980年和2003年,太平口趋势性改变的时间为1972年和1986年(年径流量)以及1998年和2003年(年输沙量),藕池口趋势性改变的时间为1967年,1972年和1989年(年径流量)以及1998年和2003年(年输沙量)。年径流量和年输沙量趋势性改变由上游径流量的不断减少及诸多人为工程共同作用的结果,其中裁弯和三峡工程的影响最为重要,但其对年输沙量的影响方式存在差异,裁弯主要是通过径流量的大幅减少而减少输沙量,而三峡工程主要是通过拦截泥沙于库、减少悬浮泥沙浓度而减少输沙量。(4)分析了洞庭湖水文情势变化规律并探讨了三峡工程对水文情势的影响。近50余年来,城陵矶年平均水位和最低水位呈上升趋势,月平均水位在1—3月份整体呈上升趋势,其他月份相对稳定。三峡水库运行后,1—4月水位略高于三峡运行前的平均水位,但5—12月份的明显偏低,以7、10和11月尤为显著。三峡出库流量对城陵矶水位具有决定性作用。三峡运行后洞庭湖水位的大幅下降主要是由于降雨减少、荆江河段冲刷作用改变水位-流量关系以及三峡蓄水导致出库流量减少等所引起,因为出库流量的减少大幅增加了湖内水位差,尤其在7—12月明显,加快了洞庭湖水泄入长江,起到了拉空效应。同时,荆江河段冲刷作用使荆江河道下切,三峡水库运行后相同的出库流量所对应的洞庭湖水位降低,需更高的三峡出库流量才能起到相同的对洞庭湖水位的顶托效应。(5)探明了近30余年来洞庭湖草洲变化规律并分析了机理。1982—2010年期间草洲面积持续扩张,累计增加497.76km2。1982—1995年期间草洲面积扩张较快,1995-2010年期间扩张速度放缓。在东洞庭湖,草洲主要扩张区域为长洲、新生洲、飘尾洲沿湖盆边缘部分、牛头洲大面积区域、武光洲—柴下洲区域、中洲—团洲部分；草洲面积减少仅发生在风车拐、北洲、物港子、六港子等少数区域。1995年前,草洲增加的区域与泥沙淤积区域基本一致,说明草洲扩张主要受泥沙淤积驱动；2005年后,草洲扩张主要是部分区域泥沙淤积和水位快速下降引起的。自1981年以来,22—24m高程的淹水时间持续下降。因此,泥沙淤积和水位下降引起的植物淹水时间减少可能是草洲扩张的主要原因。(6)揭示了洞庭湖蓄水能力演变过程并结合重大人类活动重点分析了面积和泥沙淤积对蓄水能力影响的数量关系。近50余年来,湖泊面积和湖泊蓄水能力可分为3个时期。1951—1958年和1960—1989年呈不断减少的趋势,而1995—2002年呈不断增加的趋势。湖泊容积和面积、面积及围垦面积间均存在明显的相关性,早期的围垦和大量的泥沙淤积对洞庭湖湖容的减少作用明显。三峡运行后,洞庭湖累积淤积量不断减小,其中三口输入的减少是湖泊累积淤积量减少的最主要原因,减少的泥沙淤积使洞庭湖年均增加了0.31×108m3的湖容。湖泊面积和累积泥沙淤积量与湖泊容积间存在极显著的相关性,拟合方程式为：湖泊容积=0.115×面积-0.987x累积淤积量-1.119E-5×面积2(R2=0.9984)。可见,随着泥沙淤积量的不断增加和湖泊面积的不断减少,洞庭湖蓄水能力呈不断下降的趋势。按照推算,1998年的退田还湖工程对增加湖容效果显著,但“4350”工程难以达到预期的大幅提高湖泊容积的效果。更多还原

【Abstract】 Dongting Lake, the second largest freshwater lake in China, is one of the most important wetlands in the world, with various ecological functions such as material production, water storage and regulation, as well as biodiversity conservation. Therefore, the Dongting Lake is an important ecological barrier of the Yangtze River for social and economic sustainable development. Hydrological regime is one of the most important contents in the study of wetland ecology. The research on the hydrological regime in the Dongting Lake is beneficial for us to understand the changing rhythms of runoff and sediment, to reveal the trend of wetland successions and the underlying hydrological mechanisms of water regulation function, and to provide theoretical basis for management and conservation of Dongting Lake wetlands. In this thesis, the characteristics of water and sediment balance in the Dongting Lake, the succession of hydrological regime of four rivers and three channels, the changes of hydrological regime and its responses to major projects (take Three Gorges Reservoir as a example), landscape changes and underlying reasons in the Dongting Lake, and the succession of the functions of water regulation and storage of Dongting Lake were studied based on more than50years of hydrological data with various statistical methods such as multi-year average values, moving average values, Mann-Kendall test, double mass analysis, and interpretation of remote sensing images. The results are as following:(1) The amount of annual runoff, annual sediment input and output, the amount of sedimentation and the ratio of total sedimentation to total sediment input decreased significantly along with the time in the recent50years. During1951-2009, the amount of sedimentation and the ratio of total sedimentation to total sediment input was negative, indicating the increase of the ratio of sediment output and the status of erosion. Further analysis indicated that the decrease of annual runoff was mainly caused by the decrease of the runoff from three channels. The inter-annual changes of runoff from four rivers had no significant changes. The decrease of sediment input was mainly caused by the decrease of the sediment input both from three channels and four rivers. The ratio of the runoff and sediment input from three channels to the total runoff and sediment input of Dongting Lake decreased significantly along with time, while that of from four rivers increased continuously.(2) The annual runoff of the four rivers had insignificant changes during1951-2009 years, even though there were several up-down processes. The volumes of annual sediment load from the Four Rivers showed a significantly decreasing trend generally. Moreover, the time of abrupt change was different among the four rivers, with Xiang River in1996, Zi River in1973-1974, Yuan River in1997-1998and Li River in1998. The trending changes of annual sediment input were related to the construction of the largest reservoir in the river. The comprehensive impacts of the reduction of annual runoff, increase of vegetation cover and construction of medium-and large-sized reservoirs were the main reasons accounting for the great reduction of annual sediment load after2001.(3) The annual runoff and the volumes of annual sediment load of the three channels decreased significantly during1956-2009. Among them, the change of the Ouchi Channel was most significant and time of abrupt change was the earliest. In Songzi Channel, the time of tendency change of annual runoff and sediment discharge was1980and2003respectively. In Taiping Channel, the time of tendency change was1972and1986for annual runoff, and1998and2003for annual sediment discharge. In Ouchi Channel, the time of tendency change was1967,1972and1989for annual runoff, and1998and2003for annual sediment discharge. The reduction of annual runoff and the volumes of annual sediment load were mainly caused by the decrement of runoff from upper mainstream and various hydrological project, especially the cutoff of Jingjiang River and the Three George Reservoir. However, the way that the two projects impacted the annual sediment input was different. The cutoffs deceased the sediment input was mainly through the reduction of runoff, while the Three Gorges Reservoir was mainly through the deposition of sediment in the reservoir and therefore decrease the concentration of suspended sediment.(4) During1955-2008, the annual mean water level and the annual lowest water level in Chenglingi increased apparently. The mean monthly water level increased during Jan.-Mar., while was relative stable in other months. After the operation of the Three Gorges Reservoir, the mean monthly water level was slightly higher during Jan.-April, and was lower during May-Dec, especially in July, Oct. and November. The runoff from Three Gorges Reservoir has decisive roles on water levels of Chenglingji. The significant decrease of water level of Dongting Lake was induced by the decrease of precipitation, the change of water level-runoff relationship due to the erosion of Jingjiang section, and the reduction of runoff from the reservoir due to the water storage of Three Gorges Reservoir. The large decease of runoff from the reservoir enlarged the water level difference inside and outside the lake, which has an "empty effect’. Therefore, the speed of water discharging from Dongting Lake into Yangtze River increased. Meanwhile, the erosion of Jingjiang section deepened the river channel. The same volume of runoff from reservoir maintained a lower water level of Dongting Lake, which means only a higher runoff from the Three Gorges Reservoir can has the same effect of "backup" to water level of Dongting Lake.(5) The grassland area increased continuously during1982-2010, which increased497.76km2totally. The speed of expansion was fast during1995-2010, and was relatively slow during1995-2010. The grassland area increased mainly in the following area, including the margins of the lake basin of Changzhou, Xinshengzhou and Piaoweizhou, large areas of Niutouzhou, Wuguang-Chaixiazhou and zhongzhou-tuanzhou. The grassland decreased only in the following area, Fengchengguai, Beizhou, Wugangzi and Liugangzi. The area of grassland that was increasing was consistent with the area where sedimentation occurred before1995and the expansion of grassland was driven by sedimentation. After2005, the expansion of grassland was caused by rapid decrease of water level and sedimentation in some regions. Since1981, the submergence time of areas between altitude of22-24m decreased continuously. Therefore, sand deposition and the decrease of submergence time caused by water level were the main reasons for expansion of grasslands.(6) For the51years, the changes of lake area and water storage capacity of Dongting Lake could be divided into three phases. Lake area and water storage capacity sharply decreased significantly from1951to1958and from1960-1989. However, lake area and water storage capacity increased sharply from1995to2002. Significant correlation between water storage capacity and lake area, lake area and impoldering area were found. After the operation of Three Gorges Reservoir, the accumulation of sand deposition decreased seriously, and which was mainly due to the decrement of sand deposition in three channels. The decreased sedimentation enlarged the lake volume by0.31×10m. Both lake area and accumulated volume of sand deposition are significantly correlated with lake volume. The formula was:lake volume=0.115×area-0.987×accumulated sedimentation-1.119E-5×area2. Therefore, water storage capacity decreased along with increasing sand deposition and with decreasing lake area.更多还原