洱海氮来源及对上覆水的影响

发布时间：2019-03-25 16:08

【摘要】：洱海是云贵高原第二大淡水湖泊,近些年来水质处于下降阶段,存在富营养化风险,氮作为湖泊富营养化的主要影响因素之一,对于氮源的控制越发重要。本文以洱海入湖河流、干湿沉降、表层沉积物和上覆水为研究对象,利用碳氮元素分析和稳定同位素技术,对洱海氮来源以及对上覆水的影响和贡献进行研究,为控制洱海氮源进而抑制洱海富营养化进程提供了理论基础和科学建议。得到的主要结论如下:(1)洱海入湖河流TN和PN的变化总体上呈现从夏季到冬季依次下降,然后从冬季到春季有所增加的趋势,这种趋势与洱海不同月份入湖水量变化相关,主要变化原因在于水土流失;对入湖河流氮的来源研究结果显示土壤氮、化肥、废水和水生植物的贡献居多,其中化肥和废水的影响有季节性特点。干湿沉降TN随季节呈现波动式下降,与降雨量呈显著负相关;对干湿沉降来源研究结果显示,土壤氮、人畜粪便排放和燃料燃烧对干湿沉降贡献较大,并且没有季节性变化。表层沉积物TN和氨氮的扩散通量均表现为中部南部北部,表层沉积物中氮的释放主要以氨氮为主,并且季节性变化较大;对沉积物氮来源研究结果显示北部湖区以土壤流失氮、化肥和陆源有机质的贡献为主,中部以水源性有机质贡献居多,南部则属于陆源和水源混合型来源。(2)洱海上覆水氮的来源较为复杂,属于外源输入和内源释放的共同作用,洱海上覆水颗粒态有机物氮来源以浮游生物、水生植物和陆源C3植物为主。洱海夏季和秋季氮的主要输入途径中,河流和浮游生物的贡献较多,南部湖区河流贡献高于其余两个湖区,夏秋两个季节中都以河流贡献为最多,浮游生物次之。不同来源入湖氮中,以土壤氮、化肥和浮游生物贡献居多,洱海上覆水体中总体上外源和内源贡献相当,外源以河流输入为主,内源以浮游生物贡献为主。洱海三大湖区上覆水体中自表层至底层,表层以外源输入贡献为主,主要为河流的贡献,中层至底层内源的贡献逐渐增大,但同时外源影响依然存在。洱海上覆水氮的来源贡献与输入途径密不可分,这些不同来源入湖氮的贡献与不同途径的入湖负荷有必然联系,几种输入途径的入湖负荷体现出入湖河流内源释放其它途径干湿沉降的特点,这与不同途径入湖氮对上覆水的贡献研究结果是一致的,不同途径的入湖负荷与不同途径入湖氮对上覆水的贡献以及不同来源入湖氮对上覆水的贡献是呈正相关的。(3)根据研究结果从控制洱海上覆水氮的源头考虑,提出几点建议:(1)采取水土固持措施,减少洱海流域内的水土流失;(2)减少洱海流域内氮肥的施用量,大力推广新兴农业;(3)控制流域内生活污水和工业废水的排放,推广新兴工艺;(4)采取内源控制措施,减少内源氮的释放。
[Abstract]:Erhai Lake is the second largest freshwater lake in the Yunnan-Guizhou Plateau. In recent years, the water quality is in a declining stage and there is a risk of eutrophication. Nitrogen, as one of the main influencing factors of lake eutrophication, is becoming more and more important for the control of nitrogen sources. In this paper, the source of nitrogen and the influence and contribution to the overlying water of Erhai Lake are studied by using carbon and nitrogen element analysis and stable isotope technique, taking the rivers of Erhai Lake into lake, dry and wet sedimentation, surface sediments and overlying water as the object of study. It provides theoretical basis and scientific suggestion for controlling nitrogen source and inhibiting eutrophication process in Erhai Lake. The main conclusions are as follows: (1) the variation of TN and PN in Erhai Lake generally decreased from summer to winter, and then increased from winter to spring. This trend is related to the change of water quantity in Erhai Lake in different months. The main reason for the change is soil and water loss; The results showed that the contribution of soil nitrogen, chemical fertilizer, wastewater and aquatic plants was the most, and the effects of fertilizer and wastewater had seasonal characteristics. The TN of dry and wet deposition decreased with season, which was negatively correlated with precipitation, and the results showed that the contribution of soil nitrogen, human and animal excrement emission and fuel combustion to dry and wet deposition was significant, and there was no seasonal change. The diffusion fluxes of TN and NH _ 3-N in surface sediments are both in the south of central and northern parts of China. The release of nitrogen in surface sediments is dominated by ammonia-nitrogen, and the seasonal variation is great. The results of the study on the source of sediment nitrogen show that the contribution of soil loss nitrogen, fertilizer and land-derived organic matter is dominant in the northern lake area, and the contribution of water-derived organic matter is mostly in the middle of the lake. The southern part belongs to the mixed source of land source and water source. (2) the source of water nitrogen in Erhai Lake is complex, which belongs to the interaction of exogenous input and endogenous release, and the source of granular organic nitrogen in Erhai Lake is plankton. Aquatic plants and terrestrial C3 plants are dominant. In the summer and autumn of Erhai Lake, the contribution of rivers and plankton is more than that of the other two lakes. The contribution of rivers is the highest in summer and autumn, and the second is plankton in summer and autumn, while the contribution of rivers is higher in the southern lake than in the other two lakes in the summer and autumn of Erhai Lake. The contribution of soil nitrogen, chemical fertilizer and plankton was mostly from different sources of nitrogen in lake. The contribution of exogenous and endogenous in overlying water body of Erhai Lake was equal, the input of exogenous source was mainly river, and the contribution of endogenous plankton was dominant. In the overlying water body of Erhai Lake from surface to bottom, the external input is the main contribution, which is mainly the contribution of rivers. The endogenous contribution from middle to bottom gradually increases, but at the same time, the influence of exogenous sources still exists. The source contribution of water nitrogen in Erhai Lake is inextricably related to the input pathway, and the contribution of these different sources of nitrogen to the lake is bound to be related to the loading of different ways of entering the lake. The loading of several input channels reflects the characteristics of dry and wet deposition of endogenous release of other channels in and out of lake rivers, which is consistent with the research results of the contribution of different ways of entering lake nitrogen to the overlying water. There is a positive correlation between the input load of different channels and the contribution of nitrogen from different sources to the overlying water. (3) according to the results of the study, the source of controlling the nitrogen in the overlying water of Erhai Lake is considered, and the contribution of nitrogen from different sources to the overlying water is positively correlated with the contribution of nitrogen from different sources to the overlying water. Some suggestions are put forward as follows: (1) adopting soil and water fixation measures to reduce soil and water loss in Erhai Lake Basin; (2) reduce the amount of nitrogen fertilizer applied in Erhai Lake basin and popularize the emerging agriculture; (3) control the discharge of domestic sewage and industrial wastewater in the basin and popularize the new technology; (4) adopt endogenous control measures to reduce the release of endogenous nitrogen.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：X524

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