The Validation And Modification Of Amino Acid Degradation Index (Dauwe DI Index) In Dissolved Organic Nitrogen

Dissolved organic matter is an important research content of biogeochemistry and marine carbon cycle.Dissolved amino acid is an important component of dissolved organic matter,and an important reservoir of dissolved organic nitrogen.Because dissolved amino acids is the important aquatic biogenic material,its sources and removal processes are closely related to the activities of phytoplankton and decomposors.During the process of dissolved organic matter degradation,the molar percentage of amino acid changes in a specifc way.Although Dauwe DI index is a powerful parameter for particulate and sedimentary organic matter,it is unclear whether it is also valid for dissolved organic matter.Here,I try to validate and revise the Dauwe DI by the combication of laboratory and filed experiments as well as literature data.This work used high performance liquid chromatography(external standard method)to study the dissolved amino acids in the Slope of the South China Sea,western Pacific,Yangtze River,Wen Chang River.Meanwhile I analyzed the particulate amino acids in the Yangtze River and Wen Chang River.We combined with the dissolved organic carbon and the amino acid configuration(L and D)to study the distribution and composition of the organic matter.The study of the composition and distribution of amino acids is important to understanding the Dauwe DI index.In the South China Sea,at the section stations,dissolved amino acids at 400 m depth showed a high concentration,and organic matter is relatively fresh,likey reflecting a contribution by the mesopelagic fish.On the vertical distribution,the concentration of dissolved amino acids is high in surface water,and decreases with increasing depth.But Dauwe DI not show the same result.A correlation between dissolved amino acid concentration and dissolved oxygen content shows that the phytoplankton primary production contributes to the DOM.The correlation with the degree of degradation index coefficient show that the Dauwe DI index needs to be revised.The concentration and composition of dissolved amino aicd is different among different Rivers likely due to different geographical environments and the hydrological conditions.The molar percentage of glycine and D-arginine is significantly higher in the Yangtze River than other rivers.Glycine and alanine is relatived higher in dissolved organic mattet,while leucine,phenylalanine and valine is higher in the particulate organic mattert.The Dauwe DI value in this work is beyond the range of the original definition,again supporting a need to revise this index in DOM.In addition,in the Yangtze River,the Dauwe DI index and other degradation paratemers show good correlations.In the Arctic and Hainan,the correlation is weak or even nonexistent,which was attributed to the process of dissolved and particulate organic matter diagenesis.The relative enrichment of Gly,high content of glycine in the Yangtze River at the same time,and the effects of glycine on Dauwe DI index may overwhem statistical signals of other amino acids.During the process of organic matter diagenesis,the molar percentage of amino acid changes in a particular way.This work shows that Dauwe DI index has problems when applied to the dissolved organic matter in the South China Sea and rivers,which is consistent with previous results.Because this index is indicative of organic matter degradation,it is inevitably affected by the source of dissolved organic matter and particle state.The source and composition of amino acids can cause the change of the Dauwe DI.We used the data of the dissolved amino acids from the literatur and this study(the western Pacific and south China sea slope)to analyze the Dauwe DI index factor coefficient.The PCA analysis database contains "fresh" phytoplankton and degraded dissolved organic matter in deep water of the western Pacific Ocean.The results of this work show that the concentration of glycine,phenylalanine and serine is high in the degraded dissolved organic matter,while the other amino acids such as glutamic acid,leucine and isoleucine became depleted with increasing organic matter degradation degree.When compared with the Dauwe DI index,the modified DI index can be more effective in evaluating the degradation of DOM.