Environmental Behavior Characteristics Of The Dissolved Organic Matter In The Xiaolangdi To Kaifeng Section Of Yellow River

Dissolved Organic Matter(DOM)is the largest pool of Organic carbon in the hydrosphere,it is involved in many biogeochemistry processes and has a significant impact on global climate change.As an important active component in water,DOM is also extremely sensitive to environmental changes.As the second largest river in China,the Yellow River plays a key role in the transport and transformation of carbon in the river basin.and its characteristics of high sediment and dense population distribution around the basin will undoubtedly significantly affect the environmental behavior of DOM in the river.Therefore,this paper takes the water body from Xiaolangdi to Kaifeng of the Yellow River as the research object,studies the structure composition,source and temporal and spatial variation characteristics of DOM of water body,and analyzes the influence of basic physical and chemical properties of water body,surrounding soil texture and socio-economic factors on DOM composition characteristics,so as to explore the environmental behavior characteristics of DOM of water body from Xiaolangdi to Kaifeng of the Yellow River.The main research results are as follows:(1)There was no significant spatial difference in DOM concentration and composition characteristics from Xiaolangdi to Kaifeng of the Yellow River.In terms of DOM concentration,dissolved organic carbon in water(DOC_W)and dissolved organic carbon in particulate matter(DOC_P)varied from 4.70～5.75 mg/L and 1.29～3.07 mg/L.The concentration of the biological availability of organic carbon in water(BDOC_W)range of 1.69～2.61 mg/L,accounts for36.38%～55.44%of water DOC_W,and the maximum concentration was 3.19 mg/L at sample5 in the lower reaches of the confluence of the Yellow River and its tributary Yiluo River,while the minimum concentration was 1.69 mg/L at sample 10 in the jurisdiction of Zhengzhou.In terms of DOM constituent characteristics,as the colored part of the DOM,colored dissolved organic matter(CDOM)is mainly composed of fulvic acid with high humification degree and high molecular weight in space.With the help of the parallel factor model,two humus-like components and two protein-like components were obtained in both CDOM_W and particulate matter CDOM_P.In CDOM_W,the UV humus fluorescence intensity of peak A was the highest,The fluorescence intensity of the L-tyrosine component at peak D of CDOM_P was the highest.Fluorescence parameters FI,BIX and HIX indicate that the CDOM source in each sampling site is a mixture of terrigenous and autogenous.(2)There are significant time differences in DOM concentration and composition characteristics from Xiaolangdi to Kaifeng of the Yellow River.In terms of DOM concentration,The concentration of DOC was low in April,and the DOC_P concentration at site 16 in Kaifeng City was the lowest(1.33 mg/L).The concentrations of DOC and BDOC reached the maximum in June,and the DOC_W and BDOC of site 15 were 5.24 mg/L and 1.65 mg/L.Meanwhile,the maximum concentration of CDOM also appeared in June.In terms of DOM constituent characteristics,In April,the humification degree of CDOM was low,and the autobiogenic ability was strong,The fluorescent components of CDOM_W were mostly protein-like components,which were mainly produced by endogenous sources.In june,the degree of humification of CDOM increased,the ultraviolet fulvic acid component of peak A became the main component of CDOM_W,and the probability of protein-like and humus-like components analyzed in CDOM_P was basically the same.In July,exogenous components with low humification degree,low autogenic ability and high molecular weight were the main components of CDOM.The source of CDOM at other sampling time points was the result of the interaction of terrigenous source and internal source.(3)Multiple quality indexes can better explain the changes of CDOM optical parameters.SS was positively correlated with C visible region humus,D terrigenous fulvic acid and A ultraviolet region humus obtained from fluorescence absorption peak,while was negatively correlated with M microbial source humus,N biological source DOM and T tryptophan,indicating that SS concentration was positively correlated with terrigenous organic matter concentration.At the sampling points with high soil clay content in soil topographic factors,CDOM in river water was mainly humus with high degree of humification,and its source was mainly exogenous input.In addition,among socioeconomic factors,population density has a higher interpretation significance on the optical parameters of CDOM in water.When population density is higher,the CDOM in water is mostly terrigenous organic matter components with higher humification degree and hydrophobicity content,while the autobiogenic component content is relatively low.