| Since exogenous pollution is being controlled effectively, endogenous pollution resulted from sediments will be the major pollution source of East Dongting lake. T. tubifex, an aquatic benthic oligochaete dominating the macrobiotic community of East Dongting lake, was used as study object in this research. By simulating the bioturbition activity of T. tubifex in laboratory, bioturbation effects on the release of typical pollutants of East Dongting lake such as organic matter, TN and TP were studied. The influences of temperature, pH and DO on pollutants releasing process during the sediments bioturbation of T. tubifex were investigated also. The major purpose of the present research is to recognize the characters of endogenous pollution from sediment of East Dongting lake and then provide basic parameters and scientific foundation for the bio-ecological sediment restoration of the lake.The principal findings of the present research are as follow:(1) The bioturbation of T. tubifex could promote the release of pollutants from sediment and the higher worm density, the stronger release intensity. Compared to control group, the introduction of worm with density of 1 ind./cm~2 and 2 ind./cm~2 induced 59% and 82% increase of COD release respectively. For TN the increase were 12% and 22%. The increase of TP release was observed also, and the increase magnitude were 153% and 166% respectively.(2) Proper increasing of temperature was helpful to enhance the promotive effect of worm bioturbation on pollution release from sediments. Such promotive effect was appreciably low while temperature increased from 5℃to 15℃but significant while increased from 15℃to 25℃. At 5℃, 15℃and 25℃, the mean release intensity were 13.52 mg/L, 20.44 mg/L and 23.21 mg/L for COD respectively, and 2.51 mg/L, 3.67 mg/L and 5.62 mg/L for TN and 0.19 mg/L, 0.45mg/L and 0.87 mg/L for TP.(3) For COD, T. tubifex but will resist the presence of COD in sediment release to overlying water; after adding optimal density of T. tubifex in sediment, pH = 5,7,9 and 11, respectively, their average increase - 7.36, -2.13, -2.66 and-8.41mg/L. For TN and TP, T. tubifex would be induced by acidic and alkali environment. Compared to neutral environment, the stress behavior under such conditions enhanced the bioturbation effect of T. tubifex. After the introduction of worm to sediments, The mean concentrations of TN and TP in overlying water wee5.91mg/L and 0.38 mg/L respectively for pH7, while 7.50mg/L and 0.49 mg/L for pH5 and 9.35mg/L and 1.06 mg/L for pH11.(4) The change of DO could influence the effect of T. tubifex bioturbation on sediment. Results showed that in both anaerobic and aerobic environment, the release of pollutants were promoted by T. tubifex bioturbation. For anaerobic, the mena release concentrations of COD, TN and TP were 20.56mg/L, 8.50mg/L and 1.93 mg/L respectively, compared to 8.38mg/L, 4.27mg/L and 0.35 mg/L in aerobic.The results showed that T. tubife bioturbation can promote the release process of COD, TN and TP through their migration, ingestion and egestion in sediments, by which the physical properties, chemical equilibrium are altered in sediments. Such environmental parameters as temperature, pH and DO can influence the worms life habit and have effect on results of bioturbation to release process of pollutants in sediments. The loading level of pollutants in sediment is hopeful to be cut down effectively by full utilization of the characters of T. tubifex bioturbation. Furthermore, pollutants loading level of the whole water body will be decreased provided proper technologies of pollutants treatment in situ are introduced also.
|
PDF Full Text Request