【作者】 郭鸿博；

【导师】 于志刚； 陈洪涛；

【作者基本信息】 中国海洋大学 ， 环境科学， 2008， 硕士

【摘要】 大型水利工程(如大坝、水库等)的兴建,往往会对河流水文环境以及生态系统产生重要的影响,使得河流在径流分配和营养盐输送等方面均发生了很大变化。三峡工程是世界上最大的水利枢纽工程,随着其蓄水水位不断升高,水流进一步减缓、水力滞留时间延长、水库泥沙淤积量增大。这一系列水文水力学重大变化将导致长江干流水体中硅的浓度、结构、时空分布、输送通量等发生巨大变化。本论文在2006年4月、9月及2007年4月现场调查的基础上对长江干流及三峡水库各形态硅的时空分布与变化特征进行了研究,同时结合历史资料对水库中硅的收支和循环过程进行了探索,初步估算了“水库效应”对硅的滞留。长江干流的溶解态硅酸盐和悬浮颗粒物在涪陵至大坝之间浓度有明显的降低,中下游受“两湖”、汉江等的添加作用,浓度得到一定程度上升。而生物硅则表现为大坝以上江段含量较低,中下游江段浓度较高的特征。三峡水库干流平水期的研究中,悬浮颗粒物沿水流方向存在一个明显的降低过程,其中,木桐至万州江段悬浮颗粒物降幅明显,梯度变化较快,万州至大坝江段悬浮颗粒物相对稳定,变化幅度很小。这反映了三峡水库沉积的特征,即上游“过渡段”河流沉积明显,且沉积速率较快,大部分颗粒物在经过“过渡段”后得以沉降。而后,“湖泊段”悬浮颗粒物存在一个相对高值,可能表明此江段存在颗粒自生以及沉降现象。垂向分布上表现为表层浓度相对较低,底层浓度相对较高的特征。生物硅浓度在三峡水库中分布较均匀,而溶解态硅酸盐沿水流方向呈下降趋势,垂直分布上表底层均一。且与叶绿素无明显的相关性。表明水库干流浮游植物消耗并不是控制水库溶解硅分布的主要因素。相对于三峡水库而言,库区支流生物硅含量较高,尤其是香溪河库湾,生物硅含量明显高于干流以及其他库湾且与叶绿素a表现出一定的相关性,但在其他水域则未发现这种关系。这表明,生物硅的含量不仅与现存生物量有关,而且水体中的硅质生物碎屑及悬浮物的沉降均有关。香溪河库湾高的生物硅以及相对高的Chl a,反映了高的硅藻生物量。库湾有可能是DSi“滞留”和BSi产生的重要场所。对三峡水库中硅的收支与循环的估算结果表明,在2007年4月,通过径流输送的DSi和BSi在水库中的“表观滞留量”大约为3%和63%。对因硅藻类浮游植物初级生产所形成的BSi的量的估算表明水库中的生物作用对硅的捕获还是相当可观的。以水库中生物硅的净沉积通量与输入的DSi和BSi总量之比作为水库对硅的滞留效率,三峡水库中硅的滞留并不明显,大约为5.0%。更多还原

【Abstract】 Construction of irrigation works (dam, reservoir) always impact on hydrological conditions and ecosystems in the region, which can change the current and nutrients exchange in the river. Three Gorges Dam is the biggest irrigation works in the world. Within rising water level, stream is moving more slowly, resorting time of water is longer, and sinking sand is more. The various changes of hydrodynamics in Yangtze River main stream will impact silica seriously in consistence, structure and distribution. This paper is based on investigation at Yangtze River in April 2006, September 2006 and April 2007, researches on distribution and transformation character of silica in Yangtze River and Three Gorges Reservoir. Refer to historical data, this paper also researches on the budget and circle process, estimate on silica retention in Three Gorges Reservoir.Dissolved reactive silica (DSi) and suspended particulate matter (SPM) in Yangtze River main stream reduce rapidly between Fuling City and Three Gorges Dam. In middle and lower reaches of Yangtze River, the concentration of DSi and SPM rise because of supply from Dongting Lake, Poyang Lake and Hanjiang River. The distribution of biogenic silica (BSi) is lower in upriver area before Dam and higher in middle and lower reaches of Yangtze River.The research in dry season in run of river of TGR, the suspended particulate matter has obvious reduced along Yangtze River main stream. The content of suspended particulate matter falls rapidly between Mutong and Wanzhou, while stabilized between Wanzhou and Three Gorges Dam. This indications aggradation character of Three Gorges Reservoir, most of suspended particulate matter falls rapidly in the transitional zone in the reservoir and the suspended particulate matter in the lacustrine zone comparatively keeping a high level, may indicate the suspended particulate matter spontaneity and aggradations in the reach. Vertical distributing shows that concentration is comparatively low in surface layer and comparatively high in bottom layer.The concentration of BSi is uniformly in Three Gorges Reservoir. Dissolved silica concentration is falling along river.The stratification of DSi was not obviously, and no relation with chlorophyll a. This phenomenon indicates: in the Three Gorges Reservoir phytoplankton consume in main steam is not main factor of DSi distributing in Three Gorges Reservoir.Compared with Three Gorges Reservoir, the bays in tributary confluent contain more BSi .Xiangxi River is an example in evidence, BSi concentration is higher than main steam and other bays, and the concentration of BSi have relationship with chlorophyll a in a certain extent. But in other bay, we can’t find the same relationship. This phenomenon indicates that the biogenic silica have relationship with not only phytoplankton, but also the content of silica biogenic scraping and the accumulation of suspended particulate matter.With the production, deposition, sediment of biogenic silica and flux of dissolved silica at the sediment-water interface were studied, budget and circle in the Three Gorges Reservoir are described.The present retention of dissolved silica in the reservoir isabout 3%. Compared to total silica load, the retention of biogenic silica in the reservoir is only 5.0%.With its present storage capacity, the reservoir does not play an important role in silica sink.更多还原