Studies On The Characterization Of Water POM/DOM And Relationships With Plankton Community In Poyang Lake

With the increasingly prominent role and status of lake carbon cycle in the global carbon cycle,the research on the migration and transformation of organic carbon in lakes has received more and more attention,and become a hot spot and frontier in global carbon cycle research.Particulate organic matter(POM)and dissolved organic matter(DOM),as the main forms of organic carbon in lake water,are the key to the study of lake carbon cycle.In the context of current climate change and hydrorhythm changes,it is important to elucidate the sources,distribution and influencing factors of POM/DOM in lakes to assess the evolution trend of the lake carbon cycle.Studies have shown that there is a strong relationship between microplankton communities and POM/DOM in lake water,but the specific relationship and mechanism between the two are not clear.Based on this,this study took Poyang lake,the largest freshwater lake in China,as the research object,and collected samples in different lake areas(South lake region;North lake region;Affiliated lake region;Estuary region)during the high and low water level periods in2021,and analyzed the composition,temporal and spatial distribution and source of POM/DOM in water by 3D fluorescence spectroscopy,combined with the analysis of microplankton,plant and bacterial communities,to explore the distribution characteristics of POM/DOM in Poyang Lake water and its relationship with plankton community.The main findings are as follows:(1)A total of 5 fluorescent components were determined in the POM-DOM of the water of Poyang Lake,and component 1(C1)was mainly microbial organic matter related to quinones,derived from bacteria,algae,and autogenous;Component 2(C2)can be classified as a hemiquinone(SQ2),whose origin is attributed to microbial activity under reducing conditions,with high molecular weight and high aromatics,mainly from terrestrial importation;The fluorescent signature of component 3(C3)has terrestrial plant-derived,humus;Component 4(C4)belongs to mainly terrestrial sources,protein-like,polyphenols,freshly produced tryptophan;Component 5(C5)is composed of a combination of humic acid and tryptophan samples,and terrestrial organic substances are imported.(2)The POM content of the water in the low water level period is greater than that in the high water level period,the POM content in the Affiliated lake region and the Estuary region during the high water level periods is greater than that in the South lake region and the North lake region,and the POM content in the North lake region and the Affiliated lake region in the low water level period is greater than that in the South lake region and the Estuary region.The POM of Poyang Lake water mainly comes from terrestrial sources,and the proportion in the high water level period is lower than in the low water level period.In terms of spatial distribution,the POM in the South lake region and the Affiliated lake region are more derived from autobiogenesis,that is,the degradation of bacteria and algae.The North lake region and Estuary region POM comes more from terrestrial sources,that is,the input of soil and plant debris.The strong correlation between water POM and sediment POM concentration showed that sediment POM had a significant effect on water POM.Except for the North lake region,the DOM content of the water in the low water level period was greater than that in the high water level period,the DOM content in the Affiliated lake region and the North lake region was greater than that in the South lake region and Estuary region during the high water level period,and the DOM content in the South lake region and the Affiliated lake region in the low water level period was greater than that in the North lake region and Estuary region.The relative content of different components of DOM in water was consistent in different hydrological seasons,and the proportion of terrestrial organic matter and autogenic organic matter was similar.(3)Microplankton communities had a significant impact on the composition and distribution of POM/DOM in Poyang lake.The Shannon index of phytoplankton was positively correlated with the content of humus components(C3)derived from land plants in POM/DOM.The Ace index and Chao1 index of plankton bacteria were significantly positively correlated with the content of high molecular weight and aromatic hemiquinone organic matter(C2)in POM/DOM,while the Shannon index was positively correlated with the content of humic acid and tryptophan components(C5).The main plankton microorganisms that significantly affect the distribution of POM in water include:Dicranophorus pronacis,Pediastrum and Microcoleaceae,and the main plankton microorganisms that significantly affect the distribution of DOM in water include:Simocephalus vetulus,Echinosphaerella and TX1A-33,etc.Many planktonic microorganisms also have a significant impact on the chemical composition of POM/DOM,including Nitocra lacustris,Monostyla bulla,Dinobryon,Ceratium,Calditrichota,WPS-2,etc.(4)Except for the plankton,temperature(T),redox potential(ORP),nitrate nitrogen(NO3~--N),total nitrogen(TN),turbidity(FNU)and alkaline phosphatase activity(APA)also significantly affect the distribution and chemical composition of POM/DOM in water,among which total nitrogen(TN)is the main environmental factor affecting the composition and distribution of POM/DOM.In summary,our study found that the POM of Poyang lake water mainly came from terrestrial sources,and the terrestrial and autogenic components of DOM in water were relatively uniform.The POM of the South lake region and the Affiliated lake region are more derived from autogenous sources,while the North lake region and the Estuary region of the lake are more derived from land-based sources.At the same time,the correlation between POM/DOM and plankton is different,plankton bacteria and phytoplankton have a greater impact on POM/DOM than zooplankton,and water temperature(T),oxidation-reduction potential(ORP),nitrate nitrogen(NO3~--N),total nitrogen(TN),turbidity(FNU)and alkaline phosphatase activity(APA)also have strong correlations on POM/DOM.This study not only gives us a comprehensive understanding of the composition,source and spatiotemporal distribution of POM/DOM in Poyang Lake,but also provides scientific data for analyzing the relationship between POM/DOM distribution and plankton communities.