重金属在河口区潮汐界面与盐度界面响应规律研究

Response Behaviors of Heavy Metals at Tidal Currents Interface and Salinity Interface in the Estuary Area

河口潮汐、盐度、悬浮颗粒物特征因影响化学物质在水体与其他介质之间分配行为,使得咸淡水生物利用度上产生差别,造成咸淡水水质基准标准的差异.重金属如铜,锌,铅,镉和铬等指标由于广泛分布在淡水及海水中,在较高的浓度下可具毒性效应,是现行《地表水环境质量标准》(GB 3838-2002)和《海水水质标准》(GB 3097-1997)常规监测项目.本研究以大辽河口为例,探索这些重金属指标在咸淡水河口区衔接情况和响应规律.首先,基于生物、化学和地质地理相似性确定潮汐界面(TCI)和河海边界(FSI)的位置,划分为潮汐淡水区及混合区.其次,分析了一个潮汐周期内重金属指标的变化特征,以及潮汐淡水区及混合区内盐度和悬浮颗粒物对分配系数Kd的影响,结果表明砷、镉和铬等指标更易受盐度的影响,而锌、铜、铅和镍等指标更易受悬浮颗粒物和潮汐状态的影响.最后,结合潮汐状态和分配系数研究结果,根据这些指标在TCI和FSI的变化趋势,归纳为两类响应规律:第一类如砷、镉和铬等指标,这类指标在FSI具有明显的突变点;第二类如锌、铜、铅和镍等指标,从TCI开始发生变化.两类指标在水相-沉积相-颗粒相介质的分配行为表明颗粒相和沉积相具有相似的变化趋势,尤其颗粒相中的重金属浓度,取决于悬浮颗粒物的浓度,指标响应差异主要存在于水相中.通过本研究识别出易受不同环境因子(如盐度和SS)控制的敏感指标,提出需关注河口本身特征造成的指标背景差异的必要性,将有助于我国现行水质标准制定、修订工作的实施和开展.

In China,trace metals（ such as dissolved Cu,Zn,Pb,Cd,and Cr） are the routine mandatory monitoring indicators in existing Freshwater Quality Standard（ FWQS,2002） and Seawater Quality Standard（ SWQS,1997）. Using Daliao River estuary as an example,we tried to research the general response patterns of these metals in estuarine system. Firstly,we determined the location of FSI（ freshwater-seawater interface） and TCI（ tidal currents interface）,which were based on biological,chemical and geographic similarities by descriptive and quantitative methods,respectively. Secondly,two hypotheses were proposed to explain the difference based on distribution coefficient Kdalong salinity and SS（ suspended solids） gradient,these results revealed that the indicators for As,Cd and Cr may be prone to be affected by salinity,and the ones in the second pattern may be more sensitive to SS. Finally,we classified the response behaviors into two patterns based on the changing trends along the distance and magnitudes affected by the FSI and TCI： 1the obvious boundary break point from FSI for As,Cd and Cr; 2 the boundary zones from TCI for Zn,Cu,Pb and Ni.The partitioning behaviors showed similar changing trends at particle and sediment phases,especially for particle phase,depending on the concentration of SS along the salinity. The difference between general behaviors for the two patterns mainly existed at water phase.In general,this paper highlighted the need to consider the background difference of trace metals and identified the sensitive indicators controlled by different environment factors（ such as salinity and SS） based on the native estuarine characteristics. Our work will assist the implementation of updating the current water quality standards in China.