| During the rapid development of the city,a large amount of pollutants was discharged into the water body,and finally entered into the bottom sediment.The sediment,as sinks of various pollutions entering the water bodies,has accumulated much pollutants.With the microenvironment changes,such as strong disturbances and changes in the physical and chemical properties of the water environment,pollutants that originally fixed in sediment will be released into overlying water again.Due to the high complexity of water environment,the release of pollutants from sediments to aquatic phase can be affected by many factors.In natural aquatic environment,oligochaeta benthic tubificids,due to its widespread distribution,large numbers,and strong adaptability,plays an important role in the migration and transformation of pollutants.At the same time,it also has significant effects on the accumulation of pollutants in aquatic organisms.To investigate the effects of bioturbation on absorption and enrichment of pollutants from sediments by aquatic organisms,microcosm systems similar to natural aquatic environment were established,and the release of Cu and Zn from the sediment,and their accumulation in some typical aquatic organisms,including submerged plants,floating plants and fish,with the presence of tubificids of different densities were measured.The results showed that the presence of tubificids promoted the migration of the trace metals from sediment to overlying water,especially when there were more worms and especially for Cu which is not easily to be released from the sediment.During the experiment,Cu in overlying water was mainly in particulate fraction.While for Zn,it was mainly in dissolved form in the early stage of the experiment,and then the dominant fraction gradually changed to particulate fraction.The bioturbation of tubificids also promoted the accumulation of both Cu and Zn in the aquatic organisms.In one system,different types of aquatic organisms showed different features for the accumulation of Cu and Zn.Meanwhile,with the presence of different intensity of bioturbation,the concentration of Cu or Zn in the same kind of organism was different.After a 30-day experiment,trace metal concentration in the aquatic organisms generally decreased in the order of floating plants(lesser duckweed)>submerged plants(Amazon sword)>small fish(zebrafish),and the concentration of Zn in the organisms was usually significantly higher than that of Cu in the same organism,especially in duckweed and zebrafish.However,the presence of tubificids and the density of them had more considerable effects on the uptake of Cu by the organisms,than on the uptake of Zn.For example,after a 30-day experiment,in the system with high tubificid density(40000 ind./m~2),comparing with the background Cu concentration,Cu concentration in leaves of Amazon sword,roots of Amazon sword,lesser duckweed and zebrafish increased by 0.173,0.128,0.373 and 0.007 mg/g,respectively,which was 1.6,2.9,2.3and 2.4 times,respectively,greater than that in the control system without tubificids.At the same time,it was also found that high concentration of trace metals has obviously negative effects on aquatic organisms,especially on duckweed and zebrafish.In tubificid-containing systems,some duckweed dead.And in the system with high density of tubificids,zebrafish spinal curvature was observed.However,as the high tolerance of submerged plants to trace metals,no significant poisoning was observed.This research confirms that tubificids play an important role in the aquatic environment and have important environmental significance to the overlying water.By affecting the release of trace metals originally fixed in sediment,tubificids can effectively promote the bioaccumulation of metals by organisms. |
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