Characteristics Of Dissolved Organic Nitrogen In Lake Sediments

Eutrophication and algal bloom are global environmental problems. Distribution and structure characteristics of dissolved organic nitrogen (DON), major nutrition source of aquatic and main element of eutrophication, is important to make out eutrophication and algal bloom. It is necessary to analysis DON of lake sediment. In this study, composition, sources, seasonal variation, biological validity and structure characteristics of lake sediment DON in Yangtze valley were researched with3D fluorescence spectra and High performance liquid chromatography techniques.1、DON extracted with6different soil extractant. Based on aggregate analysis of DON concentration and fluorescence structure stability, CaCl1was the best soil extractant of the6extractant.2、Through the research on structure and content of DON of4lakes, we know that content of DON of lake sediment highest in Erhai Lake followed by Dongting Lake, Chaohu.Lake and Poyang Lake. Source of DON of lake sediment in Erhai Lake, Chaohu Lake and Poyang Lake is biogenetic derivation; Exogenous input is also important source for Dongting Lake.3、DON concentration of Dongting Lake(3sites) and Poyang Lake(3sites) were incubation under different temperature without light and vibration. Results shows that DON concentration changes over time show clear "w" type, bioavailability of DON among12%to85%. Incubation constituents were change in consistent, Kind of humic acid material increased and Kind of protein material decreased. This due to the tyrosine or tryptophan degradation or transformation.4、The seasonal variation of dissolved organic nitrogen (DON) and dissolved free amino acids (DFAA) were studied by the10sediment samples selected from the Erhai Lake. The results shown that,(1) the w(DON) of the sediments changed from10.41to59.58mg/kg. average of27.43mg/kg, account for the40%of total dissolved nitrogen (TDN) and the6%of total nitrogen. The rank order of the seasonal variation of the w(DON) was the spring> the winter> the summer> the autumn. and that of the regional variation was the south> the north> the middle of Erhai Lake.(2) The w(DFAA) of the sediments changed from4.11to9.89mg/kg, average of5.96mg/kg, account for22%of DON and9%of TDN. The highest value of DFAA was in the autumn and the lowest was in the summer. and that of the regional variation was the same as DON. The more serious polluted region the higher w(DFAA).(3) The seasonal variation of w(DON) and w(DFAA) was obviously, and which play an important role in nitrogen cycling of lakes ecosystem, especially for the place where aquatic plants flourish. So expect that the total nitrogen should be considered during the eutrophicatic control of Erhai Lake, and the effects of DON in the lake nitrogen cycling and in the eutrophication should also be paid more attention.5、Concentration of Levorotatory right amino acids for Erhai Lake(7sites), Dongting Lake (3sites), Poyang Lake(3sites) and Taihu Lake(2sites) were analyzed with HPLC. Results shows that main constituents of free amino acid for Dongting Lake, Poyang Lake and Taihu Lake including serine, isoleucine, histidine and lysine. Main constituents of Erhai Lake contain another two free amino acid, aspartic and alanine. Concentration of serine between1.2to12.89mg/kg, isoleucine among1.12to24.6mg/kg, histidine among0.42to7.22mg/kg, lysine among0.71to7.73mg/kg, aspartic among0.32and0.82mg/kg, alanine among1.2and2.55mg/kg. Erhai sediment DON free amino acids sequence is: isoleucine> serine> lysine> alanine> histidine> aspartic acid, aspartic acid content is relatively small.