河口近岸水体中颗粒态重金属的潮周期变化

对长江口崇明东滩近岸水体中颗粒态重金属的潮周期变化特征及其影响机制进行了研究.结果表明,受粒度影响,底层水体中颗粒态Cu、Pb、Fe、Mn、Zn、Cr、Al的总量分别高出表层沉积物的184%、99%、56%、62%、147%、50%和45%,其中Cu、Pb、Fe、Mn、Zn、Al可还原态部分在底层水体悬浮颗粒物中的含量也明显高出表层沉积物的2～3倍,但与重金属总量相比,上述元素的可还原态部分所占比例与表层沉积物相差不大.在5次潮汐循环过程中,颗粒态重金属均在涨潮初期、高平潮前后及落潮末期出现较高含量.这种变化主要与水动力条件有关,当水体流速增大时,从底部沉积物再悬浮起来的颗粒态重金属对水体中的永久性悬浮颗粒起了很大的稀释效应.水体中的盐度、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.

Variation of Particulate Heavy Metals in Coastal Water over the Course of Tidal Cycle in Estuary

Variation characteristics and its mechanism of particulate heavy metals in coastal water over the course of tidal cycle on the eastern coast of Chongming Island in Yangtze Estuary were studied.Concentrations of Cu,Pb,Fe,Mn,Zn,Cr and Al in suspended particles in bottom water were respectively 184%,99%,56%,62%,147%,50% and 45% higher than those in surface sediments influenced by particle size.The concentrations of the reducible Cu,Pb,Fe,Mn,Zn and Al in suspended particles of bottom water were also two to three times of those in surface sediments,but percentages of the reducible fraction of the abovementioned elements in total metal concentrations in suspended particles were similar to those in surface sediments.High concentrations of particulate heavy metals occurred at the beginning of the food-tide,around the slack water and latter of the ebb tide over the course of five tidal cycles,which was mainly caused by the hydrodynamic conditions.When current velocity increased,the particulate heavy metals resuspended from bottom sediments diluted the perpetual suspended particles in water to a large extent.Environmental factors such as salt,dissolved oxygen and pH in water have little influence on the variations of particulate heavy metals over the course of tidal cycle.