【作者】 沈军；

【导师】 陈振楼； 许世远；

【作者基本信息】 华东师范大学 ， 环境科学， 2009， 硕士

【摘要】 长江口滨岸带是一个特殊的开放系统。长江径流和河口区潮波系统在这里汇合,潮波流水动力作用强烈,泥沙输移和物质交换频繁,各物理要素(悬浮颗粒含量、流速等)和化学要素(盐度、溶氧、pH、Eh等)梯度变化剧烈,生物地球化学作用非常复杂,物理化学要素梯度变化大、生物种类丰富多样。然而长期以来,长江口滨岸带由于其特殊的地理位置,以及气候、水文、人类活动多要素的高强度耦合作用影响,汞污染形势严峻,生态环境较为脆弱。本文选取长江口陈行水库及其附近岸段作为典型区域,选取典型有毒重金属汞(Hg)为主要研究对象,分析在潮汐再悬浮及其与pH、盐度等环境条件耦合影响下,沉积物中汞的沉积物-水界面分布、累积、迁移和转化规律。在对大量第一手数据资料进行综合分析的基础上,本文主要得到以下几条结论:(1)长江口滨岸带已经遭受到较严重的汞污染,尤其是陈行水库地区,上覆水汞含量达到0.159μg/L,超过国家地表水Ⅲ类水标准50%以上,沉积物中汞累积量达到0.133μg/g,是长江口长江口沉积物底质标准0.027μg/g的4.93倍,对水源地取水造成了严重隐患。(2)潮汐扰动导致表层沉积物发生再悬浮,水体理化性质也发生周期性变化。一方面,水体氧化还原电位和盐度升高,有利于原本沉降的汞的溶出和释放;而另一方面,水体pH和悬浮颗粒物浓度升高,使水体环境总体向有利于汞的吸附沉降的方向演化。因此,再悬浮过程中汞的释放和沉降,是各种环境条件耦合作用的综合结果。(3)潮汐再悬浮过程中,潮汐动力扰动和颗粒物表面吸附-解析过程是控制汞再悬浮迁移转化的主导过程。在较强潮汐动力扰动下,沉积物发生再悬浮,原本沉降的汞将向上覆水发生再悬浮释放;同时在较强动力扰动下,颗粒物表面吸附的汞可以解析进入水体。这是造成水体可溶态汞含量升高的两个主要原因。而在在动力较弱时,通过对水体可溶态汞的捕集吸附及重力沉降,颗粒物表现为对水体可溶汞的去除,并最终回到表层沉积物。长江口沉积物总体上仍是汞的汇。(4)水动力强度、pH、盐度是影响颗粒物表面吸附-解析平衡的主要环境因素。较强水动力条件有利于颗粒物表面汞的解析;较高的pH(>8.5)、盐度(>1.5‰)环境有利于颗粒物絮凝沉降,从而表现为对上覆水可溶汞的去除。(5)再悬浮底泥扰动对水体的直接影响有一个范围,对上覆水影响上界大致在距沉积物-水界面100cm处,其上部近表层水体汞的交换是一个相对独立的体系;其沉积物影响的下界大约在4-5cm深度左右。更多还原

【Abstract】 The intertidal flat of coastal areas of the Yangtze estuary is a complex-open ecosystem influenced both by natural factors and strong human activities.The runoff and tide meet here,making acuity disturbing to transport and transfer of sand and suspensions.Parameters here,both Physical and Chemical change quite often.So its biochemistry process is very complexible,and biata is very sensitive and frailty. However,the environment of Yangtze estuary is suffering serious pollution of mercury because of its special geography position and gathering of climate, hydrography and human activities.So here,we choose Henhang wellspring as typical case of sampling profile,in order to study Transfer and Transform of Mercury during Resuspension under Dynamic Disturbing,concerning affection of pH,salinity,and dynamics.We conclude under firsthand datas as follow:1) The tideflat of Yangtze estuary has suffered serious mercury pollution especially at Chenhang wellspring.The mercury in water reaches 0.159μg/L,50% overtoil to National Standard ofⅢsurface water;and 0.133μg/g in sediment,4.93 times more than Standard of sediment of Yangtze river.The environment condition makes much risk to drinking water.2) The resuspension in surface sediment deal to tide disturbing drives periodical fluctuation of water characteristics.On the one hand,the rising of Eh and salinity intensify the release and disadsorption of mercury;on the other hand,the pH and TSS climb up,making it benefits the adsorption and deposition of mercury.So it’s the compositive result of release and deposition of mercury,by coupling action of all environmental factors.3) Tide disturbing and adsorbtion-disadsorbtion on TSS are two factors controlling transfer and transport of mercury.Under strong disturbing,the mercury would release from surface sediment for resuspension,and particle mercury would also dissolve into water.That will make high concentration of dissolved mercury. However,TSS would adsorb mercury while dynamics change weaker,and mercury would back to sediment through deposition of suspending particles.4) Dyamics,pH and salinity can affect adsorbtion-disadsorbtion balance upon suspending particles.Strong dynamics,high pH(＞8.5) and salinity(＞1.5) would advance deposition of particle,benefit for wipping off dissolved mercury.5) There are boundaries for resuspension,which arranging 100cm depth in water,and 4-5cm in sediment from sediment-water counterface.更多还原