Experimental Study On The Inlfuence Of Tubiifcid Worms’ -bioturbation On Nitrogen Exchanging From The Sediment-water Interface Of Xiangjiang River

T. tubifex, an aquatic benthic oligochaete dominating the macrobioticcommunity of Xiangjiang River, was used as study object in this research. Bysimulating the bioturbition activity of T. tubifex in laboratory, bioturbation effects onthe release of Nitrogen pollutants of Xiangjiang River such as pH, NH₄⁺-N, NO₃^--N.The influences of temperature, DO and nitrogen concentration the overlying water onreleasing process during the sediments bioturbation of T. tubifex were investigatedalso. The major purpose of the present research is to recognize the characters ofendogenous pollution from sediment of Xiangjiang River and then provide basicparameters and scientific foundation for the bio-ecological sediment restoration of theRiver.The principal findings of the present research are as follows:（1） The bioturbation of T. tubifex could promote the release of pollutants fromsediment and the higher worm density, the stronger release intensity in a certainconcentration range. Compared to control group, the introduction of worm withdensity of 1 ind./cm2,2 ind./cm2and 3 ind./cm2induced 27% ,38% and 38% increaseof TN release respectively. For NH₄⁺-N the increase were 20.7%, 39.2% and 31.8%.Because of the bioturbition activity of T. tubifex, the release of NO₃^--N from sedimentdecreases gradually and stablise later except increasing slightly in the first 5 days.Overall, the bioturbation of T. tubifex could promote migration of the NO₃^--N couldpromote overlying water to sediment and strengthen the sediment as the role ofNO₃^--N sinks.（2） Adversity stress on T. tubifex would be induced by acidic and alkalienvironment. Compared to neutral environment, the stress behavior under suchconditions enhanced the bioturbation effect of T. tubifex. After the introduction ofworm to sediments, when the pH is 7,the mean concentrations of TN and NH₄⁺-N inoverlying water is 6.21mg/L,1.57mg/L , when the pH is 5, the mean concentrations ofTN and NH₄⁺-N in overlying water is 7.33mg/L,1.69 mg/L , when the pH is 11, themean concentrations of TN and NH₄⁺-N in overlying water is9.24mg/L,1.96mg/L .when the pH is 5,7,9and11,the mean concentrations of NO₃^--N inoverlying water is 0.74mg/L, 0.63mg/L, 0.72mg/L and 0.71mg/L. The acidic andalkali environment could strengthen the bioturbation of T. tubifex andpromote the nitrification and denitrification further.（3） The change of DO could influence the effect of T. tubifex bioturbation on sediment. Results showed that in both anaerobic and aerobic environment, the releaseof TN, NH₄⁺-N and NO₃^--N were promoted by T. tubifex bioturbation, and moreremarkable promotive effect was observed in anaerobic than in aerobic.（4） Different nitrogen concentration in the overlying water would also influencethe effect of T. tubifex bioturbation on sediment. The release rate of TN and NH₄⁺-Nis higher and reach to peak more quickly and stabilize in low TN and NH₄⁺-Nconcentration than high concentration. The nutrients nitrogen concentration （nutrientlevels） in the overlying water would not affect the law of the release of sedimentexcept the release rate and release amount.The results showed that T. tubifex bioturbation can promote the release processof nitrogen through their migration, ingestion and egestion in sediments, by which thepH ysical properties, chemical equilibrium are altered in sedimens. Suchenvironmental parameters as pH, DO and nitrogen concentration in the overlyingwater can influence the worms’life habit and effect on promotive results ofbioturbation to release process of pollutants in sediments. The loading level ofpollutants in sediment is hopeful to be cut down effectively by full utilization of thecharacters of T. tubifex bioturbation. Furthermore, pollutants loading level of thewhole water body will be decreased provided proper technologies of pollutantstreatment in situ are introduced also.