The Characteristic Of Dissolved Organic Nitrogen(DON) In Lake Sediments And Their Responses To Drainage Basin

In the dissertation,the typical plateau lakes were selected to discuss the h istorical change of nitrogen form in the sediments and the accumulation and so urce characteristics of dissolved organic nitrogen?DON?and establish the respon se of accumulation and evolution characteristics of DON on the Lake Basin.T he content,composition and distribution characteristics of DON in surface sedi ment of Plateau Lakes with different nutrition level?Chenghai,Erhai,Dianchi,Lugu Lake?were studied to analysis the indication of DON to water quality a nd at last,the environmental influence factors of DON were studied by discuss ing the characteristics of DON in Erhai sediments.All the studies above were based on the accurate chronologies by radionuclide dating(²¹⁰Pb and ¹³⁷Cs),aim ing to provide theoretical foundation for the prediction of water environment a nd the management of lake eutrophication.The main results were showed in f ollowing:?a?The average sedimentation rate is 0.20cm/a and the primary particles is fine silt in Chenghai sediments.The spatial distribution of TOC,TN,C/N,T P in Chenghai sediments showed:South>Central>North,with the organic matter and nitrogen in southern sediments from the algae in external source an d authigenic source,and them in Northern and Central sediments from submer ged macrophytes and authigenic algae.Since 1770s,the nitrogen has the simila r trend with the average particle size in Chenghai sediments,as follows:before1770s,there were little changes,1770s to 1950s,there were fluctuated change and after 1950s,they increased significantly affected by human activities and lake environment.?b?The DON content of lake sediments in the Yunnan Plateau Lake area was 12¹20mg/kg,The DON structure of the sediment was stable andthe mole cular weight was large relatively,as a result,the pollution of sediments was se rious,with the pollution comes from biological source in the lake itself.There was a significant linear positive correlation between the fluorescence intensity o f the humus and the TLI of the nutrient index,and there was a significant lin ear negative correlation between the fluorescence intensity of the protein and th e TLI of the protein-like index,which indicated that the algae can be predicte d by the detection of the humus and protein-like substances Risk of outbreak.T here was a significant positive correlation between the fluorescence components C1,C2 and C3 in DON of Chenhai and Erhai sediments,which showed that t here was a good correlation between the characteristics of DON and the nutrie nt index of lake sediments in the middle trophic level during the eutrophicatio n evolution of the lake,which could better indicate the eutrophication level.?c?Before the 1980s,Luchang Lake Lugu Lake sediments DON SUV254,A₂₅₃/A₂₀₃,Sr were larger than Chenghai,indicating that the molecular humifi cation degree and benzene ring functional group than Cheng Haigao,has a mo re complex structure,less fat chain material Mainly macromolecules.In the lat e 1980s,the Chenghai Chenghai watershed took the lead in the development.The population growth rate was obviously faster than that of Lugu Lake.The humification degree of DON molecules in Chenghai sediment increased,and th e contents of carbonyl,carboxyl,hydroxyl and ester were increased.Increasing.The effective control of the plateau lakes in the late 2005s caused the lake s ediment DON to be affected periodically by the internal and external sources.?d?Under the condition without adding HgCl₂,DON content showed a fl uctuating rise trend with the extension of illumination time.NH₄⁺and DON co ntent were significantly negative correlated?R²=0.94,P<0.05?,suggesting a possible mutual conversion between NH₄⁺and DON.This reflected that illumi nation might promote the transformation of NH₄⁺to DON.The mean values of SUVA₂₅₄?1.78?1.85??A₂₅₃/A₂₀₃?0.346?0.344??E₂/E₃?5.848?5.772?and S _R?1.03?1.14?in the experimental group and control group were similar when adding HgCl₂.The values had certain difference without adding HgCl₂,which was characterized by the enhanced DON substituent aromatic ring structure co mplexity under light condition.And correspondingly,the carbonyl and carboxyl,hydroxyl and ester base types increased.PARAFAC isolated two types of com ponents,namely protein substance?peak T?and class fulvic acid substances?p eak A?.Potential transformation between humic substances and protein existed,during which microbes played important role.Both point?2?and?3?demonstra ted that light could enhance biological activity and further affect the transforma tion and degradation of DON.It may become an important factor affecting hu man health and substance transformation in lake ecosystem.