水力扰动对河口沉积物中重金属再释放的影响

Effect of Hydraulic Disturbance on Re-release of Heavy Metals in Estuarine Sediments

水力扰动伴生的沉积物再悬浮导致沉积物中重金属释放,会产生潜在的环境风险。为了探究水力扰动对沉积物中重金属释放的影响,模拟水体流动过程,分析了一次和二次悬浮对河口沉积物Cu、Cd和Cr释放的影响。基于泥沙启动规律,设定100、160和240 r·min^-13个扰动强度。研究发现扰动会使得粉砂、砂砾等大粒径颗粒物分解为小粒径颗粒物,从而使黏土占比增大。经过悬浮后,沉积物重金属会被再次释放到上覆水中,其中,在高强度(240 r·min^-1)扰动下,Cu释放浓度达到36μg·L^-1。Cd在低强度(100 r·min^-1)扰动下释放浓度最大,其峰值高于中、高强度扰动;Cu主要以弱酸溶解态和残渣态赋存于沉积物中,占比分别为49.3%和30.5%。Cd赋存形态主要为弱酸溶解态(占比为68.2%),且与其他重金属相比,其释放浓度峰值出现时间最短。Cr赋存形态主要为相对稳定的残渣态,占总量的82.7%,该赋存形态相对稳定,受环境因素变化影响较小,3种扰动强度对Cr的影响差异较接近。一次悬浮结束后,3种重金属均呈现持续释放趋势。二次悬浮的Cu浓度峰值高于一次悬浮,二次悬浮的Cd和Cr浓度峰值低于一次悬浮,表明Cu对于沉积物的二次悬浮更为敏感。重金属形态分析结果表明,重金属赋存形态对其释放行为影响较大,弱酸溶解态重金属对于扰动最为敏感,高强度扰动能够促进可氧化态重金属的氧化,增加重金属向上覆水的释放风险。

Sediment re-suspension caused by hydraulic disturbances may result in the release of heavy metals from the sediments,producing potential environmental risks.In order to investigate the effects of first and secondary suspension on releases of Cu,Cd,and Cr in estuarine sediments,a series of experiments were performed by simulated hydraulic disturbances.Based on the incipient motion of sediment transportation,three disturbance intensities with 100,160,and 240 r·min^-1 were conducted.The results indicate that disturbance could cause the large-size particles to be broken into small-size particles,increasing the clay proportion in sediment.After suspension,the heavy metals in sediment would be released again into the overlying water.The peak values of Cu in the overlying water reached 36μg·L^-1 under 240 r·min^-1.However,Cd release peaked at low disturbance(100 r·min^-1),which was higher than those under 160 and 240 r·min^-1.Cu in sediment was dominated by acid fraction(49.3%)and residue fraction(30.5%),while Cd was dominated by acid fraction(68.2%)with the shortest time to peak concentration in overlying water compared to other metals.For Cr,residual fraction was the dominant one(82.7%),which was relatively stable,so the release variations kept in a narrow range under three different disturbances intensities.After the first suspension,all heavy metals presented continuous release tendency.However,the peak concentration of Cu after secondary suspension was higher than that in first suspension,while contrary phenomena were observed for Cd and Cr,suggesting Cu release was sensitive to secondary suspension.The result of heavy metal fractions suggests that heavy metal release would be greatly influenced by their geochemical fractions.Overall,acid fraction presented high sensitivity to disturbances,and intensive disturbances enhanced the oxidation of the oxidation fraction heavy metals,increasing the potential risk of heavy metal release.