Effects Of Tubificid Bioturbation On Migration Of Cd²⁺ From Water To Sediment Using Planar Optode

Sediments are important constituent of rivers, lakes and other water ecological systems. However, owing to humans’ activities, heavy metal pollutions of sediments have been already aggravated. Biological disturbance effect can promote the physical mixing action between overlying water and sediment, change the structure of sediment pore and ultimately affect the micro environmental characteristics of the water/sediment system and then further affect the behavior of pollutants in the water. But the process of migration of heavy metals in sediment is not clear at present.This study is represented by tubificid as disturbance creatures, using planar optode to monitor disturbance of water/sediment simulation system of two-dimensional distribution of concentration of Cd²⁺ by different density of tubificid. From the processing pictures obtained by image acquisition system, the sensor can directly show the variability in the distribution and migration of Cd²⁺ vertical profile in water/sediment system. The process of Cd²⁺ from overlying water to sediment could be researched according to the distribution and migration of Cd²⁺ system of vertical section. This study shows that:（1） A Cd²⁺ plane sensing membrane has been developed in this study, and the membrane has advantages including a short response time（<20 s）, precise and good stability. What’s more, it can reflect the migration process of Cd²⁺ from overlying water to sediment;（2） In the absence of bioturbation, the concentration of Cd²⁺ distributed in the interface and the district within the depth of 2 cm from the interface of water/sediment was slightly increased. However, the concentration of Cd²⁺ distributed in the district deeper than 2 cm from the interface of water/sediment remained constantly. Under the bioturbation, the concentration of Cd²⁺ distributed in the district deeper than 5 cm from the interface of water/sediment was increased dramatically in varying degrees. And in size as follows: low density system < medium density system < high density system. But the concentration of Cd²⁺ distributed in the district deeper than 5 cm from the interface of water/sediment was remained constantly.（3） Bioturbation can change the equilibrium time of Cd²⁺ migration from overlying water to sediment. The equilibrium time of Cd²⁺ from water to sediment : no biological systems < low density system < medium density system < high density system.Compared with the absence of bioturbation, tubificid biological disturbance can significantly promote the migration of Cd²⁺ from water to sediment, Changing the horizontal and vertical distribution of heavy metals in sediment. Totally, the larger density of tubificid is and the longer duration is, the stronger effect of promoting is.