【作者】 童敏；

【导师】 黄民生；

【作者基本信息】 华东师范大学 ， 环境工程， 2014， 博士

【摘要】 温瑞塘河是温州市重要的滨海平原河网水系,由于近年来温州市经济快速发展,温瑞塘河生态环境受到了严重破坏,突出表现在其水质和底泥的极度污染。为此,温州市对河道底泥进行疏浚处理,并将疏浚后的底泥运至灵昆浅滩进行吹填造陆。本研究依托国家重大水专项课题《城市黑臭河道外源阻断、工程修复与原位多级生态净化关键技术研究与示范》(2009ZX07317-006),以温瑞塘河底泥为研究对象,开展底泥疏浚及近海吹填过程中重金属环境行为及其生态风险的研究,旨在为科学评价和合理规划河道底泥污染治理及资源化利用提供理论依据和技术支持。论文重点研究了如下内容：1)对温州市牛桥底河疏浚过程中上覆水及底泥中的理化因子和重金属含量进行跟踪监测,研究疏浚对河道上覆水水质和底泥重金属含量及形态的影响；2)对灵昆浅滩底泥吹填区土壤柱状样重金属含量、形态的时空变化特征及吹填区邻近土壤和植物中重金属分布进行研究,分析底泥吹填对邻近环境的影响；3)采用重金属生态风险评价模型和发光细菌、热带爪蟾胚胎毒性检测实验对疏浚过程及吹填区底泥进行生态风险分析；4)选取两种吹填区优势植物——南方碱蓬和芦苇,开展植物对重金属耐受性和修复效果的研究。本论文研究主要得到以下结论：(1)牛桥底河底泥疏浚显著降低了上覆水中的CODCr浓度,提高了DO含量和透明度。在疏浚不同阶段,上覆水中NH4+-N、TN、TP及重金属含量呈现“先升高,后降低”的变化趋势。表层底泥的TP、TOC和重金属含量呈现“先降低、后升高”的变化趋势,疏浚后1到3个月内底泥重金属含量最低。虽然疏浚工程可以暂时地显著削减河道中污染物的总量,但其对河道水质和底泥的改善效果仅能维持3-9个月。因此要实现河道水环境的彻底治理,须把外源污染控制、内源污染治理和水体原位修复三者结合起来实施。(2)牛桥底河疏浚前底泥中重金属的弱酸溶态所占的比例依次为Ni(34.8%)>Mn(33.7%)>Zn(30.6%)>Cd(16.7%)>Pb(13.4%)>Cu(9.8%)>Cr(4.4%), Ni.Zn和Mn对环境潜在危害性相对较大。疏浚结束后,表层底泥的氧化还原电位逐渐降低,有机质和硫化物含量下降,导致可还原态和可氧化态比例减少、弱酸溶态比例增大,重金属潜在生态风险增大。疏浚9个月后各重金属元素(除Pb)形态分布趋势与疏浚前基本一致。(3)灵昆岛底泥吹填区及外围区土壤受Cd和Hg污染严重,底泥吹填区土壤重金属Cd、Cr、Cu、Mn、Ni、Pb和Zn含量高于外围区土壤,其中Cd、Hg、 Cu、Zn和Ni含量超过土壤环境质量二级标准。在2012年7月到2013年4月期间,土壤重金属平均含量总体上呈现降低趋势,4号采样点重金属下降最显著,平均降幅依次为Hg(23.0%)>As(17.7%)>Cd(10.9%)>Zn(5.6%)>Mn(5.4%)>Cr(4.7%)>Cu(4.2%)>Pb(2.4%)>Ni(1.0%),重金属可能随雨水淋溶扩散至邻近土壤中,对邻近环境造成污染。邻近区土壤和植物中重金属含量随着离吹填区距离增大而逐渐降低,在距离吹填区25m范围内及余水排放渠附近含量较高。在2012年7月到2013年4月期间,灵昆岛底泥吹填区表层土壤重金属的生物有效态比例升高,生态风险增大。40-60cm处重金属可氧化态比例有所提高。(4)地累积指数(Igeo)评价表明,疏浚前牛桥底河底泥Cd、Zn和Pb为严重污染,潜在生态风险指数评价(RI)表明,疏浚前牛桥底河底泥存在极强的生态风险,Cd和Hg是主要的生态风险因子。Igeo和RI评价均表明疏浚工程的实施在一定程度上减轻了牛桥底河底泥的污染水平和生态风险。灵昆岛底泥吹填区土壤重金属污染严重,大部分样点具有极强生态风险,最主要的污染元素是Cd、Hg和Cu。灵昆岛底泥吹填区重金属元素的污染程度及潜在的生态风险高于外围区,同时邻近区的土壤受到吹填底泥的污染,其重金属污染及生态风险程度高于外围区。(5)发光细菌毒性检测结果表明,底泥疏浚前牛桥底河的上覆水具有中等毒性,其底泥具有较大毒性,发光细菌和热带爪蟾胚胎毒性检测实验均表明,疏浚工程实施后,牛桥底河的上覆水和底泥浸出液生物毒性先增强后减弱。总体而言,疏浚有助于减轻牛桥底河上覆水和底泥生物毒性。添加EDTA螯合重金属后,疏浚不同阶段底泥的相对发光强度较未加入EDTA时均有所提高,提高幅度为11.7%-18.9%,热带爪蟾胚胎存活率从处理前的14.8%-50.0%提高到27.4%-65.5%,底泥整体生物毒性降低。灵昆岛底泥吹填区土壤主要表现为中等毒性,邻近区土壤表现为轻微毒性,外围区土壤无毒性。暴露于底泥吹填区土壤浸出液中的热带爪蟾胚胎平均孵化率为86.5%,平均存活率为80.4%,平均畸形率为13.2%,平均体长为3.92mm,毒性高于外围区土壤。(6)盆栽实验结果表明,当栽培介质中底泥比例低于25%时,南方碱蓬在介质中生长更具有优势,但芦苇对高浓度重金属具有更强的耐受性。南方碱蓬和芦苇对重金属的修复效果随底泥比例的升高而逐渐降低。两种植物对介质中的Cd有较好的去除效果,对照组中南方碱蓬对介质中Cd的去除率为21.2%,芦苇对介质中Cd的去除率为25.2%。两种植物作用下介质中的Cu生物有效性提高。两种植物对重金属元素的吸收随着底泥比例的升高而逐渐升高,Cd主要分布南方碱蓬叶片和芦苇根中,最高积累量分别为70.96mg/kg和133.12mg/kg。两种植物对重金属的富集系数均在对照组达到最高,且对Cd和Cu的富集能力较强。南方碱蓬对Cd和Zn的转运系数均大于1,芦苇对Cr的转运系数大于1。更多还原

【Abstract】 Wenruitang River is the important coastal plain river network of Wenzhou City. With the fast economic development of Wenzhou City, the ecological environment of Wenruitang River has been seriously damaged, especially the water quality and sediment which was extremely polluted. In order to control the pollution, the sediment was dredged from the polluted river and transported to Linkun Shoal for land reclamation.With the support of the National Major Project (2009ZX07317-006), this dissertation took Wenruitang River as the research object and carried out research on the environmental behaviors of heavy metals in the whole process of sediment dredging and hydraulic reclamation, hopefully to provide a theoretical basis and technical support for the scientific assessment and reasonable planning of pollution control and resource disposal of polluted sediment. The main investigations of this research were as follows:1) monitoring physicochemical factors and heavy metal contents of surface water and sediment in the process of sediment dredging of Niuqiaodi River in Wenzhou City to determine the effect of dredging on water qulity and heavy metal removal of sediment;2) investigating temporal and spatial variation of heavy metal contents and speciations in core soil samples from sediment reclamation district in Linkun shoral and distribution of heavy metals in adjacent soils and plants to assess the effect of sediment reclamation on adjacent area;3)analysis of ecological risk of sediments in the process of dredging and hydraulic reclamation by the ecological risk assessment model of heavy metal and toxicity test of Luminescent bacteria and Xenopus tropicalis embryos;4) carring out research on the tolerance and phytoremediation of heavy metals by two dominant plants in reclamation district-Suaeda australis and Phragmites australis.The major results of this dissertation were listed as follows:(1) After the sediment dredging of Niuqiaodi River, the CODCr concentration in surface water was significantly reduced, while the DO content and transparency were enhanced. In different stages of dredging, the contents of NH4+-N, TN, TP and heavy metal in surface water were first increased, then decreased, while the contents of TP, TOC and heavy metal in sediment exhibited the opposite trend. The heavy metal contents in sediment reached the lowest level in one to three months after dredging, The contents of the pollutants in the river were significantly reduced after sediment dredging, but the improvement of water quality and sediment only lasts three to nine months. Therefore, the exogenous pollution control, endogenous pollution control and in situ remediation should be combined to achieve complete treatment of the river.(2) The acid-soluble fraction of heavy metals in sediments before dredging was Ni(34.8%)>Mn(33.7%)>Zn(30.6%)>Cd(16.7%)>Pb(13.4%)>Cu(9.8%)>Cr(4.4%), showing the potential hazards of Ni, Zn and Mn were relatively greater. After dredging, the oxidation reduction potential and the contents of organic matter and sulphide were decreasing, which resulted in the decrease of reducible fraction and oxidizable fraction and the increase of acid-soluble fraction, indicating greater potential ecological risk of heavy metals.The acid-soluble fraction of heavy metals was reduced again in9months after dredging.(3) The soils of sediment reclamation district and peripheral area were polluted by Cd and Hg. The contents of heavy metal Cd, Cr, Cu, Mn, Ni, Pb and Zn in soils of sediment reclamation were higher than that of peripheral area, with the contents of Cd, Hg, Cu, Zn and Ni higher than the second standard of soil environtmental quality. In general, the average contents of heavy metals in vertical direction decreased throughout the study from July2012to April2013, while the heavy metal contents in NO.4sample exhibited the most significant reduction, with the drop order of Hg(23.0%)>As(17.7%)>Cd(10.9%)>Zn(5.6%)>Mn(5.4%)>Cr(4.7%)>Cu(4.2%)>Pb(2.4%)>Ni(1.0%). The reduced heavy metals might spread to the adjacent soil with rainwater leaching solution and caused pollution to adjacent environment. The heavy metal contents in soils and plants of the adjacent area decreased with increasing distance from sediment reclamation district, while the heavy metals contents of the adjacent area were highest in25cm range of sediment reclamation district and near the drainage of remaining water. The bioavailable state of heavy metals in surface soils show a rise throughout the study from July2012to April2013, indicating greater ecological risk, while the oxidizable fraction of heavy metals in soils of40-60cm depth increased at the same time.(4) The evaluation results of the geoaccumulation index (Igeo) showed that heavy metal Cd, Zn and Pb in sediment of Niuqiaodi River before dredging belonged to serious pollution. The results of the potential ecological risk evaluation indicated the sediments of Niuqiaodi River were seriously polluted by heavy metals, mainly due to heavy metal Cd and Hg. The pollution index and ecological risk index both significantly decreased after the sediment dredging, with reduction of pollution levels of heavy metals in sediment. The soils of sediment reclamation district were seriously polluted, while most of sampling sites showed extremely strong ecological risk, mainly account for Cd, Hg and Cu. The geoaccumulation index and ecological risk index both illustrated that the pollution level and ecological risk of heavy metals in soils was sediment reclamation district> adjacent area> peripheral area, which was attributed to the pollution of sediment reclamation.(5) The toxicity test of Luminescent bacteria showed the surface water before sediment dredging belonged to medium toxicity, while the sediment belonged to great toxicity. Both the Luminescent bacteria and Xenopus tropicalis embryos tests indicated the toxicity of surface water and sediment firstly weakened, then enhanced in different stages of dredging. Generally speaking, sediment dredging were helpful for alleviating toxicity of surface water and sediment. The relative luminous intensity of sediment in different stages of dredging increased by11.7%-18.9%after the addition of EDTA for chelating heavy metals, while the survival rate of Xenopus tropicalis embryos increased from14.8%-50.0%to27.4%-65.5%, indicating the addition of EDTA reduced the toxicity of sediment. The soils of sediment reclamation district mainly belonged to medium toxicity. The soils of adjacent area belonged to slight toxicity, while the soils of peripheral area exhibited no toxicity. According to the toxicity test of Xenopus tropicalis embryos against soil leaching, the average hatching rate, survival rate, teratogenic rate and length was86.5%,80.4%,13.2%and3.92mm, respectively. The toxicity of sediment reclamation district was greater than peripheral area.(6) The results of pot experiment indicated Suaeda australis showed more vigorous growth than Phragmites australis under the treatment of low concentration of heavy metals. But Phragmites australis exhibited stronger tolerance to high concentration of heavy metals. The removal of heavy metals by Suaeda australis and Phragmites australis increased with the decreasing sediment ratio. Suaeda australis and Phragmites australis showed better removal of Cd, with removal rate of21.2%and25.2%respectively in the control group. The two plants had a positive effect on the bioavailability of Cu. The accumulation of heavy metals by two plants increased with the increasing sediment ratio, while Cd was mainly distributed in leaves of Suaeda australis and roots of Phragmites australis, with the maximum accumulation of70.96mg/kg and133.12mg/kg respectively. The bioaccumulation factors of two plants reached the highest value in the control group, while the two plants had stronger accumulation ability of Cd and Cu. The transportation factors (TF) of Suaeda australis for Cd and Zn and TF of Phragmites australis for Cr were higher than one.更多还原