Effects Of Sinonovacula Constricta Bioturbation On Nitrogen In Sediment And Overlying Water

The bioturbation effects of on the transformation of different forms of nitrogen in sediments,and life activities such as bioturbation and excretion of benthic affect nutrient content and migration at the sediment-water interface were studied based on a laboratory experiment in this study.Two treatment groups and a control group were set up according to different biological densities,under the optimal survival condition.Results showed that:The content of total nitrogen?TN?in the sediment increased after the bioturbation of S.constricta..The content of non-transferable total nitrogen?NTN?increased by30.94%,and the content of transferable total nitrogen?TTN?decreased by 20.57%.The content of organic-sulphide form?OSF-N?was the highest among the four forms, accounting for 9.31%of TN,which was the main form of TTN.The content of carbonate form?CF-N?was the lowest and only 2.77%of TN.The ion exchange form?IEF-N?and the iron manganese oxide form?IMOF-N?accounted for 3.39%and 3.06%of TN,respectively.Above all,the bioturbation of S.constricta promoted the conversion of OSF-N to other forms,as well as the conversion of transferable total nitrogen to non-transferable total nitrogen.The results show that the bioturbation of S.constricta.promoted the content of NH₄⁺and NO₃^-+NO₂^-in the overlying water.With the increase of the density,the NH₄⁺content increases obviously,while the content of NO₃^-+NO₂^-increases first and then decreases.The NH₄⁺flux is-0.195?0.273?mol.L^-1.d^-1,that is,the ammonia nitrogen in the sediment is released into the overlying water.And the NO₃^-+NO₂^-flux is- 0.554?0.038?mol.L^-1.d^-1,indicating that the sediment absorbed nitrate nitrogen from the overlying water.Considering the effect of ammonia metabolism of S.constricta..the ammonia nitrogen content was checked by ammonia data.Although the NH₄⁺content decreased slightly,but the trend with time did not change.In addition,the NH₄⁺flux changed greatly in the initial stage of the experiment,and it changed from sediment to overlying water release to migrate from the overlying water to the sediment,and then stabilized with the not obviously changes.Above all,the bioturbation of S.constricta promoted the exchange of nitrogen nutrients between the sediment and the overlying water.The ammonia metabolism has a great influence on the flux in the early stage of the experiment,and the effect of ammonia metabolism gradually decreases over time.