【作者】 冉祥滨；

【导师】 于志刚；

【作者基本信息】 中国海洋大学 ， 海洋化学， 2009， 博士

【摘要】 随着社会经济的发展,流域内各种人类活动强烈地冲击着河流原有的生物地球化学过程,其中尤以水利工程的影响最为人们关注。长江三峡水利工程是当今世界最大的水利枢纽工程,其产生的“水库效应”不仅影响了三峡水库的物质循环,还可能对长江中下游、河口乃至近海生态系统产生深远的影响。本文以三峡水库为研究对象,系统研究了蓄水后三峡水库典型水域营养盐的分布特征、三峡水库干、支流水体混合过程等,并在此基础上,分析了蓄水前后三峡水库营养盐收支与滞留效率。主要结论如下:(1)135m蓄水后,三峡水库坝前水域营养盐浓度的季节变化明显,硝酸盐、亚硝酸盐、氨氮、磷酸盐浓度在平水期高、丰水期低;而溶解硅浓度在丰水期高、平水期低。坝前水域水化学参数分布均一,没有分层现象,控制其分布的主要机制为水动力学因素。(2)135m蓄水后,对悬浮颗粒物中磷的赋存形态分析表明,经过三峡水库后,水体悬浮颗粒物中磷的赋存形态及其含量发生了一定的变化,表现为弱吸附态磷、有机磷以及铁结合态磷等生物可利用的磷含量升高,而碎屑磷灰石磷以及非活性有机磷含量降低。悬浮颗粒物中磷的赋存形态组成的变化将改变颗粒态营养盐的输送规律。水库“淤粗排细”作用对悬浮颗粒物粒径产生显著影响,这可能是控制其变化的主要因素。(3)156m蓄水后,三峡水库营养盐垂向差异较小,没有分层现象;沿水流方向,溶解硅、颗粒态氮、颗粒态磷浓度有明显的降低趋势。平水期,硝酸盐是总氮主要组成部分,其次是溶解有机氮,颗粒氮所占份额较小;磷则以磷酸盐为主要组成部分,其次为溶解有机磷,颗粒态磷对总磷的贡献量不大。(4)三峡水库入库水体中亚硝酸盐、氨氮、溶解有机氮、磷酸盐浓度普遍高于出库水体,而硝酸盐、溶解有机磷浓度普遍低于出库水体;入库、出库硅酸盐浓度差异不大,且存在明显的季节变化规律。在2007年,输入到水库中的氮、磷及溶解硅总量分别为8.14×105t、1.34×104t和1.24×105t;自水库向下游输送的氮、磷及溶解硅总量分别为6.83×105t、1.01×104t和1.25×105t。受流量控制,入库、出库营养盐通量的60%左右是在丰水期输送的,通量季节变化明显。(5)对三峡水库进行了营养盐收支及滞留效应研究。结果表明,135m蓄水前总氮、总磷入库负荷与出库负荷相当;135m蓄水后,约18%的总氮、15%的总磷和10%溶解硅滞留于水库中,分别占长江入海总量的6%、4%、5%左右。156m蓄水后,三峡水库对亚硝酸盐、氨氮、溶解有机氮、溶解总氮、磷酸盐存在滞留现象,其表观滞留量分别为3.2×103t、6.39×103t、0.63×105t、0.21×105t、0.5×103t,对应滞留效率分别为62%、43%、31%、3%、30%。考虑水库内支流输入、点源排放等的贡献,对156m蓄水后滞留效率进行校正后,三峡水库对亚硝酸盐、氨氮、溶解有机氮、颗粒氮、总氮、磷酸盐和总磷实际滞留效率分别为67%、50%、37%、71%、16%、36%和7%。由于三峡水库的滞留效应导致的长江磷酸盐、溶解硅、总氮、总磷入海通量减少18%、2%、8%和4%。除磷酸盐外,三峡水库对长江入海营养盐通量影响有限。(6)对库区典型支流库湾的研究表明,常量离子在干、支流的混合过程中表现为保守,可以有效地指示库湾混合过程。干流水体的逆向“顶托”是控制支流库湾水体理化性质的主要物理机制。在库湾(香溪河库湾和大宁河库湾)混合过程中,生源要素表现出不保守的特征,其中硅酸盐、硝酸盐、磷酸盐表现为移出,而亚硝酸盐、氨氮表现为加入。支流库湾出现明显的富营养化现象。更多还原

【Abstract】 The Three Gorges Project (TGP) on the Yangtze River, the largest hydropower- complex project ever built in the world, completed its Phase-II construction and Phase-I water storage in 2003, finally elevating the pool level to about 135 m above mean sea level at the dam. The potential eco-environmental problems induced by the TGP are widely concerned in the world. Material transport research in particular is one of the most important concerns about the TGP. Reservoir effect will affect the biogeochemical processes of the Changjiang River. It is necessary and urgent to examine the reservoir effects of the TGR water storage on the Yangtze River material transport, which has important practical and theoretical significance.The main results in the thesis were drawn as follows:After the first stage of the TGR impoundment (135m), parameters of nutrient and water quality showed a uniform distribution, indicating that dynamics was the major fator to control nutrient and other parameters. However, sediment retention in the TGR had great influence on different phosphorus forms. Concentration of exchangeable P, iron-bound P, and organic P increased greatly in particles after across the TGR, while Detrital P decreased largely in particles. The retention effect of the large particles in TGR was the key factor controlling different phosphorus forms.In the TGR, nitrate was the main component of DIN, and DIN was the major parts of total nitrogen, while the contribution of DON and particle N is only of minor importance. Additional, phosphate was the major part of total phosphrous in the common period.During June to September in 2007, more than 60% fluxes of nutrient were transferred to downstream at Guizhou and Fuling station.Collected the history dates of nutrients in the past ten years in the Changjiang River of the Three-Gorge areas from the pubic documents and combined our studies in this region, a preliminary nutrient budget for the TGR was proposed to be used as first attempt to quantify the behavior of nutrients entering this reservoir after the second impoundment. As control, a budget was analyzed before the impoundment of the TGR. The nutrient budget showed that the Three-Gorge Reservoir was a net sink of total nitrogen and phosphorus after impoundment. The dam was responsible for removing around 18% of nitrogen and 15% of phosphorus entering the reservoir, which would be have significant downstream ecological and social implications. The deposition of particle nutrients and absorbed by phytoplankton would be responsible for this case of reducing nutrient as a result of a new dam.After the third filling of the TGR, more than 36% for phosphate, 4% for silica, 16% for total nitrogen and 7% for total phosphrous were retented by TGR, which would reduce nutrient fluxes of the Changjiang River to the East Sea (18% for phosphate, 2% for silica, 8% for total nitrogen and 4% for total phosphrous). So the TGR influenced phosphate thansport great than other nutrients.Inorganic ions and nutrients were measured in different layers of the Xiangxi and Daning Rivers to explore the mixing processes of representative bays in the TGR. Bicarbonate and calcium are the dominant ions. Carbonate weathering is the most important mechanism controlling the water chemistry. However, important differences exist between the main channel and its tributaries. Major ion levels in the TGR bays depend on hydrological mixing. Results show that the major ions of calcium, magnesium, sodium, potassium, strontium, sulfate, and chloride demonstrate chemically conservative behaviors during transit throughout the bays of the TGR. This means the ions can be used as tracers in the same way that salinity is used in estuaries to explore other non-conservative elements and to indicate specific source waters. These tracers could then be used to analyze nutrients in the mixing zone, where they are not conserved The reverse effect of the main channel on tributaries’backwater reach was the key factor controlling nutrient distribution in the Xiangxi and Daninghe Bays, with biological utilization acting as a secondary factor.更多还原