[Variation of Nitrogen Forms in Sediments of Lihu Lake During Mineralization]

After 10 years of controlling point source sewage in Lihu Lake, the total nitrogen in water is still at a higher level. To explore the effects of sediment nitrogen release on overlying water, the method of submerged water cultivation was used to study changing characteristics of different nitrogen species in the process of sediment mineralization and the exchange between organic nitrogen and inorganic nitrogen of the mineralization process transformation process was discussed. The results showed that, the mean value of free nitrogen(FN) increased from 94.26 mg·kg^-1 to 230.71 mg·kg^-1 after nitrogen mineralization in the sediment, when ammonium and solved organic nitrogen (SON) were dominant; the mean value of exchangeable nitrogen (EN) increased from 82.50 mg·kg^-1 to 165.32 mg·kg^-1 with ammonium being the main species; the mean value of acid solution nitrogen (HN), which gave priority to amino acid nitrogen (AAN), decreased from 1044.70 mg·kg^-1 to 815.93 mg·kg^-1, and residual nitrogen (RN) basically remained unchanged. In the submerged cultivation process, acid solution state of total nitrogen fell from 67.18% to 52.50%, the reduction was mainly caused by mineralization and decomposition of AAN and ammonium nitrogen (AN), moreover, AAN was one of the most effective sources of inorganic nitrogen after sediment mineralization. Comparison of the results of estuaries and lakes showed that, the larger the amount of sediment was, the more the mineralized inorganic nitrogen was.