东江干流惠州段沉积物—水界面无机氮交换通量及影响因素研究

发布时间：2018-09-14 12:10

【摘要】：东江是广东省及香港特别行政区重要的饮用水源,其水质的好坏直接关系到广州、深圳、香港等城市的人民生活和经济发展。近年来,随着经济的快速发展和城市化进程的加快,大量富含氮的生活和工农业污水排放进入东江,已影响到东江干流的水质。氮的超标排放会造成水环境质量的下降,导致水体发生富营养化。同时,大量进入河流的氮蓄积在沉积物中,引发的内源性污染问题也日益突出,引起了国内外学者的广泛关注。因此了解流域内氮各形态的含量及分布状况,探讨沉积物中氮的释放特征及迁移转化规律,研究了沉积物-水界面氮的交换通量和影响因素,对控制东江干流的污染状况,合理保护东江优质水源具有重要意义。以东江干流(惠州段)为研究对象,在自然环境调查的基础上,于2013年6月~2014年3月在东江干流(惠州段)选取6个采样点进行采样,研究了东江干流(惠州段)水体氮的含量,进行水质评价,测定沉积物-水界面氮的交换通量,并进行了不同影响因素下的实验室模拟试验,分析了沉积物-水界面氮迁移转化的影响因素,主要得出以下结论:(1)东江干流(惠州段)水质大部分时间状况良好,其中TN水质较差,基本满足Ⅳ~Ⅴ类(湖、库,以N计),有些点位为劣Ⅴ类;氨氮浓度普遍不高,大部分时间采样点的值均小于0.5mg/L,水质基本满足Ⅱ类要求;硝氮浓度的变化范围为1.28~2.22 mg/L,水体中亚硝氮含量较低,浓度变化范围为0.001~0.071mg/L。采用内梅罗综合指数法对水体氮进行评价,结果表明:硝氮是水体的主要污染物,属于轻度污染;氨氮和亚硝氮属于清洁状态,其中亚硝氮清洁度较高。(2)东江干流(惠州段)沉积物-水界面氨氮全年交换通量均为正值,表明东江干流(惠州段)沉积物作为氨氮的源。硝氮、亚硝氮表现为各点位交换通量均较小。在交换通量模拟试验中,初始阶段沉积物中的氨氮迅速向上覆水释放。随着实验时间的延长,氨氮在沉积物与上覆水之间的交换减慢,氨氮的交换通量逐渐减小。硝氮在沉积物与水界面的交换通量与氨氮变化不同,硝氮的交换通量较小,且沉积物并不是一直作为硝氮的源或汇,而是多次出现汇源转换。(3)沉积物-水系统交换通量模拟试验表明:随着温度的升高,水体矿化产生的氨氮增多,同时消耗了溶解氧,阻止了硝化反应的进行。厌氧条件氨氮的释放速率高于有氧条件下的速率,有利于沉积物中氨氮的释放。硝化和反硝化作用作为沉积物-水系统氮素迁移和交换的主要过程,其发生同时受到溶解氧的限制。pH值越低,水体中氢离子的浓度越大,交换作用增强,沉积物中释放的氨氮就越多,加重上覆水中的氮素负荷,相反氨氮交换量减少;在碱性条件下,水体中氨氮减少,氨氮在沉积物和水体之间的浓度梯度增大,加速了氨氮从沉积物中的释放速率。综上结果表明,硝氮是上覆水主要的污染物,沉积物是氨氮重要的内在污染源。在沉积物中溶解氧不足条件下,硝氮被还原造成沉积物中氨氮浓度升高,沉积物成为氨氮的源。温度升高、溶解氧降低以及过酸、过碱条件均有利于沉积物中氨氮的释放。
[Abstract]:Dongjiang River is an important drinking water source in Guangdong Province and Hong Kong Special Administrative Region. Its quality of water is directly related to the people's lives and economic development of Guangzhou, Shenzhen and Hong Kong. In recent years, with the rapid economic development and the acceleration of urbanization, a large number of nitrogen-rich domestic and industrial and agricultural wastewater discharged into Dongjiang River has affected the East. Water quality in the main stream of the river. Excessive discharge of nitrogen will lead to the decline of water environmental quality and eutrophication. At the same time, the endogenous pollution caused by the accumulation of large amounts of nitrogen into the river sediments has become increasingly prominent, which has aroused widespread concern of scholars at home and abroad. The characteristics of nitrogen release, transport and transformation in sediments were discussed. The nitrogen exchange flux and influencing factors at the sediment-water interface were studied. It is of great significance to control the pollution of the main stream of the Dongjiang River and protect the high quality water sources of the Dongjiang River. In March 14, six sampling sites were selected to study the nitrogen content, water quality assessment, nitrogen exchange flux at the sediment-water interface, and laboratory simulation tests were carried out to analyze the influencing factors of nitrogen migration and transformation at the sediment-water interface. The main conclusions are as follows: (1) The water quality of the main stream of Dongjiang River (Huizhou Section) is in good condition for most of the time, and TN water quality is poor, which basically meets Class IV-V (lake, reservoir, N count), and some points are inferior Class V; the concentration of ammonia nitrogen is generally not high, the value of sampling points is less than 0.5mg/L in most of the time, and the water quality basically meets Class II requirements; The concentration range of nitrite nitrogen was 0.001-0.071 mg/L. The results showed that nitrate nitrogen was the main pollutant in the water body and belonged to light pollution. Ammonia nitrogen and nitrite nitrogen were clean state, and the nitrite nitrogen was clean. The annual ammonia-nitrogen exchange fluxes at the sediment-water interface in the prefecture section are all positive, indicating that the sediments in the main stream of the Dongjiang River (Huizhou section) are the source of ammonia-nitrogen. The exchange flux between sediment and overlying water slows down and ammonia-nitrogen exchange flux decreases gradually. The exchange flux of nitrate-nitrogen at the sediment-water interface is different from that of ammonia-nitrogen, and the exchange flux of nitrate-nitrogen is small. The sediment is not always used as the source or sink of nitrate-nitrogen, but often occurs sink-source conversion. (3) Simulation of exchange flux in sediment-water system. The results show that with the increase of temperature, the ammonia nitrogen produced by water mineralization increases, and the dissolved oxygen is consumed, which prevents nitrification. The release rate of ammonia nitrogen under anaerobic conditions is higher than that under aerobic conditions, which is beneficial to the release of ammonia nitrogen from sediments. The lower the pH value, the greater the concentration of hydrogen ion in the water, the stronger the exchange effect, the more ammonia nitrogen released from the sediment, which aggravates the nitrogen load in the overlying water and decreases the ammonia-nitrogen exchange capacity in the opposite direction. Under alkaline conditions, the ammonia-nitrogen in the water body decreases, and the ammonia-nitrogen concentration between the sediment and the water body increases. The results show that nitrate is the main pollutant in overlying water and sediment is an important internal source of ammonia nitrogen. Under the condition of insufficient dissolved oxygen in sediment, nitrate is reduced to increase the concentration of ammonia nitrogen in sediment and sediment becomes the source of ammonia nitrogen. The reduction of ammonia and the release of ammonia nitrogen from sediments are beneficial to the reduction of oxygen and the over acid conditions.
【学位授予单位】：吉首大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：X52

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