Effect Of Tubificids Bioturbation On Bioavailability Of Typical Heavy Metals In Sediments

There are a large number of benthic organisms in natural water body.These benthic organisms can affect the physicochemical properties of water-sediment interface by feeding,digging and other activities.These progresses may change the presence of heavy metal,and distribution in environment phases,ultimately affect absorption of heavy metal in aquatic organisms.Therefore,in this paper,the effects of earthworm on the biological effectiveness of heavy metals in sediments were evaluated by using aquatic plants under different density conditions through the establishment of water-deposit-aquatic plant-earthworm system.Heavy metal Cu is an essential nutrient for organisms.It can cause damage to organisms when Cu is excessive in the environment.,while Cd has higher biotoxicity itself.In addition,Cu mainly enters into plants in the form of coordination complex,and ion exchange is an important way for Cd.Therefore,Cu and Cd were selected as the heavy metals studied.The main research contents include: The effects of earthworm disturbance on the content of Cu and Cd in the water-sediment system.Including changes in the granular and dissolved States in overlying water,surface sediments(0-1cm),and the content of Cu and Cd in aquatic plants over time.The mechanism of Cu and Cd migration to plants in sediments was discussed by correlation analysis and the parameters of turbidity,pH and suspended particulate matter content in overlying water.The results showed that the disturbance effect of the earthworm on the system increased with the density of the earthworm,and the overburden turbidity and suspended particulate matter content in the high-density group were significantly higher than in the low-density group and the blank group.The disturbance intensity of the earthworm went through a process of first increasing and then decreasing.The turbidity and suspended particulate matter content in the high-density group reached the highest in about 7-10 days,and then gradually weakened and eventually became calm.The presence of earthworms has promoted the absorption of Cu by plants to varying degrees,especially for crown grass with more developed root systems.At the end of the experiment,the content of Cu in the plant is 150 % to 200 % of the blank group of the crown root line of the tremor group;About 20 % of water orchids,and about 50 % of black algae.Due to the low Cd background value in the sediments,the phenomenon of crown grass with more developed roots is more obvious,similar to the change of Cu content,and the Cd content of the crown root line of the earthworm group is about 50 % in the blank group.In addition,the content of Cu in the water overburden and the surface sediments increased with the increasing density of earthworm.However,Cd is more likely to be released in sediments and increases with the intensity of the tremor.The presence of earthworms promotes the migration of Cu and Cd to the upper environment in the system and increases the risk of Cu and Cd entering the plant.But at the same time,the process of plant absorption has some hysteresis and is affected by the light problem caused by the disturbance of the earthworm.In addition,the type and content of heavy metals in the environment will also affect the results and effects.