IMHE OpenIR  > 山地表生过程与生态调控重点实验室
三峡库区泥沙对磷迁移转化的影响
Alternative TitleInfluences of sediments on migration and transformation of phosphorus in the Three Gorges Reservoir
Language中文
王晓晓
Thesis Advisor吴艳宏
2017
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline自然地理
Keyword 磷形态 迁移转化 泥沙 消落带 三峡库区
Abstract三峡水库运行以后,其生态环境变化受到国内外关注。磷是水生态系统初级生产力的限制性营养元素,是水体富营养化的重要原因。泥沙作为磷的有效载体,对磷具有较强的吸附性,其输移过程中耦合了物理、化学和生物等作用。磷在水沙间的迁移转化受到自然条件变化(泥沙理化性质、水动力条件等)和人类活动(水库调蓄等)的影响,从而使库区水沙中的磷呈现出明显的时空变化。另外,河流交汇口是研究磷在水沙间迁移转化的重要场所。河流交汇后,在水环境出现明显变化的情况下,磷在水沙间的平衡被打破,磷会在水沙间进行迁移,并伴随磷形态的转化。因此,研究磷在库区水沙间的迁移和形态变化,有利于深入理解库区磷的地球化学过程,为库区的生态环境保护和环境治理提供帮助。为了探讨三峡水库蓄水后泥沙变化及其对磷迁移转化的影响,本研究选择整个三峡库区及其乌江口地区,分别在2014、2015和2016年采集表层水样、悬移质泥沙和沉积物样品,利用野外现场监测、室内水沙理化分析、泥沙磷形态提取、扫描电镜和X射线能谱分析等手段,对水沙理化性质、磷的赋存特征、磷在水沙间的迁移转化过程、影响因素及环境效应进行了研究,得到以下主要结果和结论:1)三峡库区水体和泥沙的理化性质表现出明显的空间变化。从变动回水区到常年回水区,水体中的悬移质泥沙、Fe2+和Al3+浓度呈现下降趋势,同时沉积物中的泥沙粒径逐渐变小,这表明泥沙进入库区后发生明显的分选、凝絮、沉积过程。在垂向上,沉积物理化指标(尤其是泥沙粒径)表现出明显的周期变化,表明不同水文期的泥沙来源具有明显差异。在乌江口地区,长江和乌江水体和泥沙的理化性质具有明显差异。两江交汇后,水沙理化性质出现明显变化,并且在不同季节呈现出不同的变化特征。2)库区沉积物中的磷呈现出明显的时空变化特征。空间上,沉积物中的总磷(TP)在整个库区没有明显变化,而生物有效磷(Bio-P)从库区变动回水区到常年回水区呈现出升高趋势。库区上游来沙中的Bio-P不容易沉积到变动回水区,而是进入到常年回水区中,并在常年回水区的沉积物中富集,从而使常年回水区中的Bio-P浓度偏高。在垂向上,表层30 cm沉积物中的Bio-P浓度高于30 cm以下沉积物中Bio-P的浓度。另外,计算了表层30 cm沉积物中磷的蓄积量,发现库区水下沉积物中磷的蓄积量在忠县至秭归段较高,而消落带沉积物中磷的蓄积量在涪陵至奉节段偏高。时间上,三峡水库正式运行以来,库区沉积物中的TP出现明显升高:2014年以前,忠县至坝前区域消落带沉积物中的TP升高幅度较大(平均升高415 mg/kg);而在2014年以后,消落带沉积物中TP的升高主要集中在重庆城区至万州段(升高幅度215 mg/kg)。库区变动回水区沉积物中的Bio-P在年内不同水文期会出现沉积分异,而常年回水区沉积物中Bio-P的沉积分异受水文期的影响较小。3)细颗粒的分布是影响泥沙中Bio-P浓度空间变化的主要因素。对不同粒径泥沙中的元素分布和磷形态分析发现,库区泥沙中的细颗粒物聚集区是磷元素分布的主要区域。具体而言,库区常年回水区沉积物中的Bio-P变化明显,沉积物中的Mnox、Alox和粉粒是Bio-P变化的主要影响因素;而库区变动回水区沉积物中以盐酸提取态磷(HCl-P)的变化为主,沉积物中的Feox、Ca、pH和砂粒为HCl-P变化的主要影响因素。在垂向上,沉积物中Bio-P的变化主要受到细颗粒泥沙分布的影响。另外,库区水位调节会引起消落带沉积物的干湿变化,消落带的淹没、落干过程会引起沉积物中细颗粒物及其吸附的Bio-P的流失,从而使Bio-P在水下沉积物中出现富集。4)在乌江口地区,TP在悬移质泥沙中的平均值(814 mg/kg)低于其在沉积物中的平均值(944 mg/kg),表明泥沙吸附了水体中的磷,并在乌江口下游出现沉积。长江和乌江交汇后,悬移质泥沙颗粒上的弱吸附态磷呈现出先迅速释放,然后快速吸附的过程。水中的溶解态磷倾向于向细颗粒泥沙(<8 μm)上分配,尤其是当水中溶解态磷的浓度偏高时,细颗粒泥沙表面吸附的磷较多。乌江口水体处于氧化环境,吸附到泥沙表面的磷会进一步向金属氧化物结合态磷转化。同时,CaMg(CO3)2沉淀会促进泥沙中的弱吸附态磷向Ca\Mg-P转化。乌江口泥沙中δ13C和C/N值的变化表明,泥沙中的有机质组成发生明显改变,从而使泥沙中有机磷(OP)发生变化。5)在室内模拟泥沙对磷吸附/释放实验的基础上发现,随着泥沙在乌江口地区的输移,泥沙对磷的吸附(P吸附)呈现出明显的波动性和周期性。泥沙对磷的吸附能力既受到水环境(SO42-、NO3-和pH值)变化的影响,同时也受到泥沙理化性质(Alox、Mn、Ca和Mg)的影响。研究期间(2015.11-2016.10),乌江口上游(长江和乌江)来沙量为0.559亿t,这些泥沙可以吸附水中4080 t磷。粒径>16 μm的泥沙会长时间滞留在库区中,这部分泥沙中Bio-P的释放应当引起关注。另外,随着库区上游来沙的进一步减少和泥沙中磷释放比例的增加,库区水体中磷浓度可能会出现升高趋势。
Other AbstractThe hydrodynamic conditions have been changed after the impoundment of the Three Gorges Reservoir (TGR), and the safety of the TGR ecosystem has been paid more attentions. Phosphorus (P) has been regarded as one of the limiting nutrients in freshwater ecosystems, and P bioavailability in the sediment is an important factor for eutrophication. Soluble P interacts strongly with sediment by the combined processes of sorption/desorption and mineral precipitation/dissolution. As a carrier of phosphorus, the sediment plays a key role in the migration and transformation of phosphorus, coupling physical, chemical and biologic processes in the river system. The retention and distribution of phosphorus in the sediment are influenced by natural conditions and human activities, for example, the operation of the TGR or the variations of fluvial environment, etc. Especially, in the confluence area of rivers, the aquatic environment changes quickly and the phosphorus equilibrium between the water and sediment will be broken up, resulting in the migration and transformation of phosphorus in rivers. Therefore, the confluence of the rivers is an ideal area to study the migration and transformation of phosphorus between water and sediment. To study the effects of sediment retention on the migration and transformation of phosphorus, the entire TGR and the confluence area of Yangtze River and Wujiang River were selected to collect water and sediment samples in the years of 2014, 2015 and 2016. Field monitoring and laboratory analysis were conducted to study the water and sediment physic-chemical properties, P fractions, and P distributions on the sediment particles. The main results and conclusions are as follows:1) The water and sediment physic-chemical properties presented spatial variations in the TGR area. The concentrations of suspended particles, Fe2+ and Al3+ decreased from upstream to downstream of the TGR, and the grain sizes of the sediment also showed a decrease trend. In the sediment profile, the grain size displayed vertical variations, indicating the sources of the sediment varied in different seasons. At the confluence of Yangtze River and Wujiang River, the water and sediment physic-chemical properties of the two rivers showed marked differences, resulting in the variation of water and sediment physic-chemical properties after the mixing of river waters. 2) The phosphorus in the sediments of the TGR exhibited notable spatial and temporal variations. Spatially, no marked variations of the total phosphorus (TP) were found in the sediments of the TGR. However, the bioavailable phosphorus (Bio-P) presented an increase trend from upstream to downstream of the TGR. The Bio-P in the sediment was not inclined to deposit in the fluctuating backwater zone (FBZ), therefore, the Bio-P could be transported to the permanent backwater zone (PBZ). The retention of Bio-P in the PBZ led to the increase of Bio-P concentrations in the PBZ sediment. The phosphorus pool in the sediment of the TGR was calculated according to the amount of the sediment reported by previous studies, and the reaches from Fuling to Zigui were the major distribution area for phosphorus. Temporally, the mean concentration of TP in the sediments (Zhongxian to the dam) increased by 415 mg/kg before 2014. However, during 2014-2016, the mean concentration of TP in the sediments mainly increased in the reaches from Chongqing to Wanzhou (increased by 215 mg/kg). The concentrations of Bio-P in the FBZ showed a seasonal variation in the sediment profiles, whereas no marked variations of Bio-P were found in sediment profiles of the PBZ. 3) The fine particle was a major factor that affected the distribution of Bio-P in sediments of the TGR. The SEM and P fractions analyses of the sediments indicated that the phosphorus mainly distributed on fine particles. Specifically, in the sediments of PBZ, the Bio-P, which was affected by Mnox, Alox and slit particles, controlled the variation of phosphorus in the sediments. However, the HCl-P dominated the variations of phosphorus in the sediments of FBZ, and the Feox, Ca, pH and sand particles were the main controlling factors. In addition, the operation of the TGR resulted in the water level fluctuations, and the sediments in the riparian zone experienced periodic episodes of desiccating and rewetting. The processes of desiccating and rewetting could lead to the loss of fine particles and the combined Bio-P, which concentrated in the underwater sediment.4) At the confluence of Yangtze River and Wujiang River, the mean concentration of TP in the suspended sediment particles (814 mg/kg) was lower than that in the underwater sediments (944 mg/kg), indicating the phosphorus deposited downstream the confluence. At the confluence area, the weakly absorbed phosphorus on the suspended sediment particles presented a rapid release process, and then adsorbed to the particles again. The dissolved phosphorus (DP) was inclined to be adsorbed on fine suspended particles (<8 μm), especially when the concentration of DP in the water became higher. The adsorbed phosphorus on the suspended sediment particles could be combined with metal hydroxides under the oxidizing conditions. The precipitation of CaMg(CO3)2 would enhance the combination of phosphorus with calcium and magnesium in the sediment particles. In addition, the values of δ13C and C/N indicated that the variation of organic phosphorus in the suspended sediment particles resulted from the changes of the organic matters sources. 5) The phosphorus adsorption and desorption characteristics of sediments in the TGR were described by the modified Langmuir isotherm equation. The phosphorus adsorption parameter (Padsorption) displayed periodic fluctuations during the transportation of suspended sediment at the confluence of the Yangtze River and Wujiang River. The water parameters (SO42-, NO3-, and pH) and sediment characteristics (Alox, Mn, Ca, and Mg) were main factors that affected the processes of phosphorus adsorption and desorption at the confluence. The environmental influences of phosphorus adsorption/desorption were evaluated in our study. The sediment discharge from the upstream TGR was 55.9 million tons from Nov. 2015 to Oct. 2016, which could adsorb 4.08 thousand tons of phosphorus from the water. In addition, the phosphorus adsorbed by the sediment particles larger than 16 μm (the particles larger than 16 μm would stay in the TGR for a long time) could release to the water easily, which should be paid more attentions. Considering the decrease of sediment from upstream TGR and the release of phosphorus from the sediments, the phosphorus concentration in the water of the TGR would increase in the future. 
Pages128
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/24595
Collection山地表生过程与生态调控重点实验室
Affiliation中国科学院成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
王晓晓. 三峡库区泥沙对磷迁移转化的影响[D]. 北京. 中国科学院大学,2017.
Files in This Item:
File Name/Size DocType Version Access License
三峡库区泥沙对磷迁移转化的影响.pdf(7070KB)学位论文 开放获取CC BY-NC-SAView Application Full Text
Related Services
Recommend this item
Bookmark
Usage statistics
Export to Endnote
Google Scholar
Similar articles in Google Scholar
[王晓晓]'s Articles
Baidu academic
Similar articles in Baidu academic
[王晓晓]'s Articles
Bing Scholar
Similar articles in Bing Scholar
[王晓晓]'s Articles
Terms of Use
No data!
Social Bookmark/Share
File name: 三峡库区泥沙对磷迁移转化的影响.pdf
Format: Adobe PDF
All comments (0)
No comment.
 

Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.