【作者】 毕春娟；

【导师】 许世远； 陈振楼；

【作者基本信息】 华东师范大学 ， 自然地理学， 2004， 博士

【摘要】 本文以长江口滨岸潮滩为典型地区，选择几种重金属元素Cu、Pb、Fe、Mn、Zn、Cr等为研究对象，分析在受自然和高强度人类活动综合作用下的河口潮滩生态系统中，重金属元素在水体—沉积物—生物三相介质中的分布、累积、迁移和转化规律及其生态效应，探讨河口潮滩重金属的主要来源及其输入途径，估算潮滩重金属主要的源汇通量及其在滞留重金属方面所作的贡献大小，并以崇明东滩为典型断面试图建立潮滩重金属收支平衡模式，同时对整个长江口滨岸潮滩底质重金属进行了环境质量及生态风险评价。主要得到以下几条结论： (1) 长江口潮滩沉积物中的重金属含量处于我国中等偏下水平。评价结果显示，XP、SDK和LG的重金属污染水平最高，但仍属中度污染，其中Zn的污染贡献最大；从沉积物潜在生态危害程度来看，只有长江口南岸潮滩沉积物表现出中等的生态危害，其中Cu的毒性贡献最大。石洞口排污口及黄浦江等几条入海河流是重金属污染物输入的主要通道，水合铁锰氧化物是长江口地区重金属污染物输运、迁移的主要载体，受长江冲淡水及涨潮流双向水流的共同作用，重金属污染物大多滞留于长江口南岸边滩，并有相当一部分随涨潮流在上游潮滩中发生沉降与累积。极端天气条件比如风暴潮在短时间内虽能造成潮滩的严重侵蚀，但在较长的时间尺度下，不会影响潮滩重金属收支平衡。 (2) 在长江口潮滩沉积物中，Cu、Fe、Zn、Cr均以残渣态含量为主，Mn以碳酸盐结合态为主，其含量在48％以上，Pb的碳酸盐结合态、残渣态与铁锰氧化物结合态含量都很高。各重金属元素的非残渣态部分所占百分含量的排序为Mn＞Pb＞Zn＞Cu＞Cr＞Fe。在非残渣态中，碳酸盐结合态以Mn、Pb、Zn的含量最高，铁锰氧化物结合态以Pb的含量最高，有机结合态中Zr、Cu、Pb的含量达到9％以上。与总量相比，生物可利用态重金属所占百分含量依次为Cu 26％、Pb 36％、Fe 7％、Mn 49％、Zn 32％、Cr 14％和Al 1.6％，其大小顺序与前述非残渣态重金属所占百分含量排序一致，说明HA可提取态重金属可以用来解释沉积物中重金属的生物有效性问题。 (3) 重金属在潮滩沉积物中的迁移与转化受早期成岩作用、植被生长发育等多种因素的共同作用。在水动力作用较弱、没有植被生长的潮滩中，早期成岩作用对重金属在表层或次表层沉积物中的富集贡献较大。在有植物生长的高、中潮滩，夏、秋季根系的吸收富集使沉积物中的重金属含量降低，冬、春季死亡植物根系的归还使沉积物中的重金属含量相应上升。在污染较为严重、水动力作用相对较弱的潮滩沉积物中，Cu、Pb的地球化学行为主要受沉积物中有机质含量变化的控制，当有机质有充分时间进行降解时，Cu、Pb被溶解释放出来并发生扩散迁移，当沉积物淤积速度较快时，有机质来不及降解，在有机质含量高的沉积物层Cu、Pb含量也相对升高。华东帅范人学2004届博士学位论文摘要 (4)在水动力作用较强、受人为干扰较小的潮滩沉积物中，Fe、Mn、Cr、Zr等元素的峰值分布可以作为地球化学标记层来判断潮滩的冲淤变化。从春季到冬季，位于长江日北岸的寅阳近岸潮滩冲淤基本持平，但其季节冲淤变幅较大，达3一6cm。芦潮港近岸潮滩以侵蚀冲刷为主，潮滩冲淤变幅达7一scm。崇明东滩的季节性冲淤变幅较大，但总体上表现出淤积的趋势。沉积物中这种地球化学标记层的确定可以为研究潮滩冲淤变化提供一个颇有价值的替代「具。但在污染较为严重的地区，由于污染物掩盖了自然来源重金属的变化特征，沉积物中重金属的含量峰值不能作为地球化学标记层来判断潮滩的冲淤变化。 (5)在涨落潮过程中，颗粒态重金属一般在涨潮初期、高平潮前后及落潮末期出现较高含量。水体的盐度、Do及pH等环境因子对潮周期内颗粒态重金属的变化影响不大，悬浮颗粒中<IOom粒径的细颗粒及其有机质含量却表现出与颗粒态重金属一致的变化特征，说明这种变化土要与水动力条件有关。当水体流速增大时，底部再悬浮颗粒对水体中的颗粒态重金属起了很大的稀释效应，当水动力条件变弱时，粗颗粒大量沉降，单位质量的悬浮颗粒中细颗粒及其吸附与捕集的重金属含量相应上升。在秋季一次大潮过程中，颗粒态重金属在崇明东滩om线以上滩地中的滞留量分别为:Cu 2.lt、Pb 1.3t、Fe 2706t、Mn49.2t、zn7 It、Cr 2.2t和AI 4650t。 (6)芦苇与海三棱蕉草是长江口滨岸潮滩的优势种群，这两种植物对重金属的吸收具有较强的调节作用，不受沉积物中重金属含量的控制。Cu、Pb、Fe、Zn、C:在植物根系中的含量最高，Mn在海三棱蕉草茎叶中的含量接近或超过根系中的含量。海三棱蔗草枯叶能大量富集Cu、Pb、Fe、Zn、Cr，这种富集主要是由细颗粒沉积物的注入引起的，Mn在枯叶中未出现富集现象。海三棱蕉草与芦苇单位面积内对Fe的吸收量最大，其次依次是Mn、/n和Cu，对Pb、Cr的吸收量最小，比其它生物必需元素低一至几个数量级。单位面积内芦苇地上组织比海三棱蕉草能吸收更多的重金属。 (7)河蚁是长江口潮滩湿地特别是低潮滩分布最广的大型底栖动物，重金属主要在河蚁的软体组织中富集。河蚁对Cu有明显的选择性吸收作用，使河蛆体?更多还原

【Abstract】 The intertidal flat in coastal areas of the Yangtze estuary is a complex ecosystem influenced both by natural factors and strong human activities. The distribution, accumulation, transport and fate of heavy metals such as Cu, Pb, Fe, Mn, Zn, Cr and their ecological effects in water-sediment-organisms of such an ecosystem were analysed. Sources and transport channels of heavy metals in intertidal flat of the estuary were discussed. Based on which, the source fluxes and retention of heavy metals were quantitatively estimated. This is favourable for evaluating the intertidal flat contribution in accumulating heavy metals to the whole estuary. The intertidal flat in eastern shore of the Chongming Island was selected for a typical area to construct mass balance for heavy metals. Moreover, environment quality assessment and ecological risk assessment of the heavy metals in intertidal sediments were performed for the whole estuary. The main conclusions can be summed up as follows.(1) Concentrations of heavy metals in intertidal sediments of the Yangtze estuary lie between the mid to lower range for Chinese estuarine and coastal sediments indicating that the Yangtze Estuary receives low but appreciable heavy metal contaminant inputs. Assessment results show that the highest pollution of heavy metals lie in XP (Xu Pu), SDK (Shi Dong Kou) and LG (Lao Gang), but the pollution level of these areas belongs to mid pollution range, in which Zn contribute the most. Moreover, mid potential ecological risk of heavy metals in intertidal sediments is only found along the southern coast of the estuary, in which Cu is the most toxic element. Sewage outlet at SDK and main rivers flowing to the estuary such as Huangpu River are the main pollutant input channels and the hydro-oxides of iron and manganese are the main carriers when pollutants enter the water and are transported. Influenced by the fresh water and the tidal current, most of the heavy metals are deposited in the southern region and some even deposited in the upper areas of the estuary following the flood-tide current. Extreme weather conditions such as storm tide can cause heavily erosion of the intertidal sediments in short term, but may not largely influence the mass balance for heavy metals in intertidal sediments in a long time scale.(2) Cu, Fe, Zn and Cr in intertidal sediments of the Yangtze estuary are mainly in residual fraction, while the major chemical association of Mn is carbonates, with the content up to 48%. The carbonates, residuals and Fe-Mn oxides of Pb have similar contents in the sediments.Concentrations of non-residual heavy metals can be ordered as follows: Mn>Pb>Zn>Cu>Cr>Fe. In the non-residuals, the carbonates of Mn, Pb and Zn have high contents than the other elements and the Fe-Mn oxides have the highest content in Pb. Contents of the organic matter fraction were higher for Cr, Cu and Pb, with the contents up to 9%. The percentages of reducible Cu, Pb, Fe, Mn, Zn, Cr and Al in total concentrations are respectively 26%, 36%, 7%, 49%, 32%, 14% and 1.6%. This order is similar to that of the non-residuals, showing that the bioavailability of heavy metals can be represented by the concentrations of reducible heavy metals available to HA(hydroxylamine hydrochloride in 25% (v/v) acetic acid) to a large extent.(3) The transport and transformation of heavy metals in intertidal sediments are influenced by many factors such as the early diagenetic process, plant growing and so on. Concentrations of metals show surface or sub-surface elevation in mudflat sediments with weak hydrodynamic conditions, which are mainly caused by sediment early diagenetic process. However in salt marsh sediments, the concentrations of heavy metals at the depth of 5-15cm decrease gently due to the absorption of plant roots in summer and autumn and increase gradually to reach broad sub-surface maxima due to the metal release from the decomposition of plant roots at the same depth range in winter and spring. The biogeochemical activities of Cu and P更多还原