【作者】 王辉；

【导师】 郑祥民；

【作者基本信息】 华东师范大学 ， 第四纪地质学， 2008， 博士

【摘要】 河流沉积物中蕴含丰富的环境信息。利用河流沉积物的磁性特征进行物源识别、沉积环境信息提取和环境污染评价是当前环境磁学的重要发展方向。沉积物中的重金属则常被用作判别河流水环境质量的重要指标。作为我国经济发展最快和城市化水平最高的地区之一,长江中下游干流地区的沉积物研究一直都是学术界的热点。以往的工作主要集中在长江口、三峡库区及干流的部分城市或区域江段,以流域整体为对象的系统研究相对薄弱。本文以长江中下游干流河道及长江口为研究对象,于2006年三峡水库156m蓄水前,在宜昌、荆州、城陵矶、鄂州、九江、湖口、安庆、铜陵、芜湖、南京、江阴、镇江、等城市江段以及长江口崇明环岛潮滩系统采集干流中泓沉积物、边滩沉积物、支流沉积物、表层水样及植物样品,综合运用环境化学、环境磁学、生态学、土壤学、水文学等学科知识及测试手段,从流域角度探讨了长江中下游河道沉积物的重金属地球化学及环境磁学特征。主要取得以下认识和成果:(1)磁铁矿主导了长江中下游河道沉积物的磁性特征,磁铁矿晶粒以假单畴(PSD)-多畴(MD)为主。纵断面上,从中游到下游,磁性矿物含量呈下降趋势,晶粒呈变细趋势;横断面上,从中泓到边滩,磁性矿物含量亦呈下降趋势,晶粒亦呈变细趋势。与干流相比,支流沉积物中不完整反铁磁性物质含量相对较多,亚铁磁性矿物晶粒较细。随着支流泥沙的入江,干流沉积物的磁性特征相应发生改变,支流物源贡献是干流沉积物的磁性特征空间变化的主要影响因子。(2)中泓沉积物的重金属总量及生物可利用态含量较低,与本流域土壤岩石元素背景值相近,符合土壤环境质量一级标准(GB15618-1995),不存在重金属污染。边滩与支流沉积物已遭受不同程度的重金属污染,与城市排污有关的Cu、Pb、As、Ni等元素含量较高。边滩与支流沉积物中生物可利用态重金属的含量较高,所占比重较大,容易通过食物链传递,危害性大,应予以关注。从中游到下游,中泓沉积物的重金属含量沿程分布差异较大。粒径与重金属沿程差异密切相关,经过粒径校正后的沿程差异明显减小。(3)长江中下游干流沉积物中汞的含量总体较低,基本能达到土壤环境质量一级标准。中泓沉积物基本保持自然地质背景状态。边滩沉积物中汞含量明显偏高,反映出人类活动对近岸水域影响较大。边滩沉积物汞的含量高值出现在九江-铜陵区域。(4)崇明环岛潮滩植物主要通过根系吸收沉积物中的重金属。吸收重金属时,各重金属元素共同进入植物根系,未发现选择性吸收现象。植物对重金属的吸收具有地域差异性,崇明北岸芦苇体内的重金属含量普遍高于南岸。互花米草对重金属的吸收与累积能力高于芦苇和蔗草。芦苇和互花米草体内重金属含量的分布规律为根系>茎>叶,地上部分的重金属含量一般大于50%,通过植物收割方式能有效转移重金属。被广泛用作造纸原材料的芦苇的收割在减轻长江口重金属污染上发挥着巨大生态效应。(5)中泓沉积物颗粒整体较粗,以砂粒为主,砂粒含量达63%,平均粒径112μm;边滩沉积物颗粒相对较细,以粉砂组分为主,粉砂组分含量达51%,平均粒径26μm;支流沉积物颗粒最细,以粘土和粉砂粒级组分为主,粘土和粉沙粒级组分含量分别为39%和52%,平均粒径9.2μm。(6)粒度是影响沉积物磁性特征的重要因素。由于长江中下游河道沉积物中晶粒以假单畴一多畴为主(粉砂)的磁铁矿,与较粗粒级的石英、长石(细砂)伴生,并富集于细砂沉积物中,因此长江中下游河道沉积物细砂组分的磁化率最大。但将沉积物筛分为三种不同的粒级组分后再测磁化率,出现磁化率与粒径成反比现象,即随着粒级的变细,磁化率愈高。粒度亦是影响重金属含量的重要因素,不同粒径颗粒吸附重金属能力不同。重金属元素Cu、Mn、Pb、As和Ni等性质较为相似,主要富集于细颗粒组分中;与此相反,Sr、Cr和Zr元素趋于富集在粗颗粒组分中。本论文的创新点:(1)综合运用环境磁学、环境地球化学、沉积学、生态学等手段,从流域角度探讨了长江中下游干流沉积物的磁学特征和地球化学特征,建立了沉积物元素数据库,为三峡完全封坝后的后续研究提供科学的比照参数。(2)系统探讨了长江中下游干流河道中泓、边滩、支流沉积物中重金属的总量与生物可利用态含量水平、污染状况、沿程分布及影响因素,为制定防治长江中下游重金属污染的对策措施提供依据。(3)研究了植物对沉积物中重金属吸收与累积的能力大小、地域差异、及其影响因素,探讨了重金属的植物生态效应。(4)探讨了粒度对长江中下游干流河道沉积物的磁性特征和重金属特征的影响。更多还原

【Abstract】 There is a variety of environmental information contained in the river sediments. Lots of methods have been introduced to research the information stored in the sediments. It’s an important developing direction in the Environmental Magnetism to use river sediments’ magnetic property to track material source, extract environmental information and assess environmental pollution. The content of heavy metals is an important index to evaluate the quality of the river. Since the middle and lower reaches of the Yangtze River belongs to one of the regions where the economy developed fast and the urbanization reached a high level, the health of water environment is a hot environmental topic. Because of sampling problems and other limited factors, past investigations of the river sediments in the mainstream of the Yangtze River mainly focused on the Yangtze River Estuary, Three Gorges Reservoir area as well as part cities or areas of the mainstream, and they are lack of the systemic study of the whole drainage area.In this work we investigate the sediments of the mainstream of the middle and lower reaches of the Yangtze River and the Yangtze River Estuary. Samples are from the central mainstream, the beach, the tributary, the surface water and the plant such as Spartina alterniflora, Phragmites australis and Scirpus mariqueter in Yichang, Jingzhou, Chenglingji, Ezhou, Jiujiang, Hukou, Anqing, Tongling, Wuhu, Nanjing, Jiangyin and Zhenjiang etc.. Sampling works have been done before the Three Gorges Reservoir stored water to the altitude of 156m in 2006. Through comprehensive use of Environmental Chemistry, Environmental Magnetism, Ecology, Pedology, Hydrology etc. as well as testing methods, heavy metals geochemistry and environmental magnetic property of sediments in the middle and lower reaches of the Yangtze River are discussed.Following results have been acquired:(1) The magnetic property of sediments in the middle and lower reaches of the Yangtze River is dominated by the ferromagnetic magnetite, with the particle size being pseudo single domain (PSD) - multi-domain (MD). From the middle reaches to the lower reaches, the content of magnetic minerals is decreasing, and their particles are fining. It’s the same from the central river to the beach. The content of imperfect anti-ferromagnetic materials in the tributary is higher than that in the mainstream, and their particles are finer. With sand from tributaries inflowing into the Yangtze River, the magnetic property in the mainstream changed accordingly. The material from tributaries is an important factor to the change of the magnetic property in the mainstream.(2) Contents of heavy metals and bio-available heavy metals are low in the central river. They are in the scope of background value of soil elements in this drainage area. So there is almost no pollution due to heavy metals. Sediments in the beach and tributaries have been polluted by heavy metals. The content of elements related with urban contamination draining such as Cu, Pb, As, Ni is high. The content of bio-available heavy metals is higher in the beach and tributaries. So heavy metals in the beach and tributaries are delivered more easily through food link and do greater harm, which should be paid more attention. The distribution of heavy metals is of great difference from the middle reaches to the lower reaches. The particle size is closely correlated with the distribution of heavy metals. The distribution of heavy metals fluctuates much steadier after the particle size correction.(3) The content of mercury is lower than the environment quality standard value for soil- category I in the central mainstream of the Yangtze River, mostly in the scope of the natural geological context. The content of mercury in the beach is obviously higher than it in the central mainstream of the Yangtze River, which shows that waters near the beach are influenced more frequently by human activities. The content of mercury in the beach shows such characteristics, that is, it is lower in both the upper reaches and the lower reaches and higher in the middle reaches, and the highest value appears in the area from Jiujian to Tongling, which is possibly related with the exploitation of mineral resources.(4)The plant absorbs heavy metals by the root mainly. When absorbing heavy metals, all heavy metals are absorbed into the plant root and selective absorption is not found. It shows regional differences when the plant absorbs and accumulates heavy metals. The content of heavy metals in Phragmites australis on the north shore is generally higher than that on the south shore. It’s possibly related with bank protection works of the south shore that damaged the natural ecosystem of the tidal flat. The content of heavy metals in Scirpus mariqueter of bao-town is higher than the others, most likely because of the pollution from the thermal power plant near around. The ability of Spartina alterniflora on absorption and accumulation of heavy metals is higher than that of Phragmites australis and Scirpus mariqueter. Distributions of heavy metals in Phragmites australis and Spartina alterniflora are both root>stem>leaf. The content of heavy metals in the part of plants aboveground (total of stem and leaf) is generally more than 50%. Phragmites australis as raw materials of the paper have enormous ecological effects on clearing heavy metals in the tidal flat.(5)The particle size is coarser overall in the central river, which is dominated by sand. The content of sand is 63%, and its average particle size is 112μm. The particle size is finer in the beach, which is dominated by silt. The content of silt is 63%, and its average particle size is 112μm. The particle size is the finest in tributaries, which are dominated by clay and silt. Contents of clay and silt are separately 39% and 52%, and their average particle size is 9.2μm.(6)The particle size is an important factor for the magnetic property. The susceptibility of fine-grained sediments is the highest in the middle and lower reaches of the Yangtze River, because in fine-grained sediments. The magnetite whose particle size is dominated by pseudo single domain and multi-domain (silt) accompany the cease quartz and feldspar (fine sand), and they are enrichment in fine sand. However, when the susceptibility is tested separately in three different particle sizes the susceptibility and the particle size change oppositely, that is, with finer particle the susceptibility is higher. The particle size is also an important factor for the content of heavy mental. Different particle sizes have different abilities to adsorb heavy metals. Heavy metals such as Cu, Mn, Pb, As, Ni and so on are mainly in the fine-grained sediments, and show similar properties. On the contrary, heavy metals like Sr, Cr and Zr are mainly in the coarse-grained sediments.The innovation of this dissertation: (1)Heavy metals geochemistry and environmental magnetic properties of sediments in the middle and lower reaches of the Yangtze River were discussed by comprehensive use of Environmental Chemistry, Environmental Magnetism, Sedimentology, and Ecology etc.. The database was established, which could provide scientific comparing parameters for following studies after the full closure of the Three Gorges Reservoir.(2)It was thoroughly investigated on the content of heavy metals and bio-available heavy metals, the pollution, distributions and affecting factors in the mainstream of the middle and lower reaches of the Yangtze River, which provides a basis for taking measures to prevent and treat heavy metals contamination.(3) The plant’s ability to absorb and accumulate heavy metals, regional differences and affecting factors were investigated. Also bio-availability of heavy metals was discussed(4)The particle size’s affection to the magnetic propertity and heavy metals’ characteristics was discussed in this dissertation.更多还原