Composition,source And Distribution Of Dissolved Organic Matter In The Surface Water In Xi'an Section Of Weihe River

Dissolved Organic Matter(DOM),with its complex chemical structure and optical properties,has important impact on the migration and transformation of pollutants and the water ecosystem.In this paper,the optical properties,composition,source and spatial and temporal distribution of DOM in xi 'an section of weihe river were studied.And the influence parameters such as economic development,land use around the basin on DOM distribution is discussed.The main contents are as follows:(1)The abundance values of DOM and CDOM(Chromophoric Dissolved Organic Matter)in the water bodies were significantly different.The DOC concentrations in different months were 10.45(M arch),6.96(July),5.59(October)and 4.67 mg·L-1(December),respectively.And a(355)were 2.53(march),5.15(July),12.77(October)and 3.99 m-1(December).SUVA254 monthly mean concentration(humus degree)followed downstream(5.85)>upstream(5.33)middle>(4.6 L·(mg·m)-1),which was proportional to monthly average rainfall and runoff.The UV slope S is used to represent the DOM molecular weight level,The average concentration of four months was similar(0.016,0.018,0.015 and 0.016nm-1,respectively).and the DOM molecular weight in the mid-range region was relatively small in July.The spectral slope ratio SR indicated that the water DOM in March and December was a mixed source input dominated by endogenous sources.In July,the middle reaches were dominated by exogenous input;T he October paragraphs are dominated by exogenous inputs.(2)C1-C4 is defined as humus-like component and C5-C6 as protein-like component.The results of parallel factor analysis by fluorescence chromatography showed that C2/C3,C4/C2 and C5/C3 were detected in March.Cl-c4 and C6 were detected in July;In October,it was Cl,C2,C4 and C5.C1-c4 and C5 were detected in December..LC-OCD(liquid phase-organic carbon)analysis was carried out on water samples in July,October and December,and a total of 5 peaks were detected,humus accounted for the largest proportion,and low molecular organic acids were basically not detected.The preliminary analysis of molecular weight difference shows that the concentration of low molecular weight neutral substances and organic acids in the upstream cultivated land is relatively high,which mainly comes from the agricultural exogenous input,while the content of humus and degradation products in the downstream is the highest,which may come from the input of woodland grassland and carried by the middle water body.(3)By comparing the values of fluorescence parameters FI(Fluorescence intensity index),BIX(Biogenic index),HIX(Humus index)and principal component analysis,the DOM of each sampling point in July and December was analyzed in detail.In July,FI=1.64-2.15,BIX=0.65-1.12,HIX=0.55-0.77;in December,FI=1.66-2,BIX=0.77-1.04,and HIX=0.55-0.74.The sampling points of surface water in Xi 'an section of Weihe River are mostly mixed inputs dominated by endogenous sources,with large contribution from autogenous sources and close humification degree.In July,woodland and grassland in the downstream area accounted for a large proportion,and TP(total phosphorus)and Chla(chlorophyll-a)concentrations increased.In December,TP decreased and TN(total nitrogen)increased.In July and December,the cumulative variance contribution rate of principal component analysis was 85.8%and 89.7%,respectively,indicating that the upstream is mostly the internal source of DOM caused by industrial and agricultural wastewater,while the source and composition of DOM in the middle reaches are seriously affected by peripheral land sources and human activities.There are many forest wetlands in the lower reaches,which are affected by the middle reaches.DOM sources are relatively complex.(4)C5 was defined as the protein component containing tryptophan and white matter.Combined with environmental and economic factors in different regions of The Weihe Xi 'an section,DOM components of cultivated land types were analyzed and found to be distributed in each region,mainly C5.The fluorescence intensity of C1 and C4 components in forestland and grassland was higher than 1000Da.Urban land C3,C4 and C5 have high strength and are mostly neutral substances with molecular weight less than 350Da.DOM of construction land is mostly above 1000Da,with high fluorescence intensity of C2,C3,C4 and C5.Regression analysis was carried out for the monthly average rainfall,different molecular weight and different fluorescence intensity components.The increase in rainfall diluted the MOLECULAR weight and fluorescence intensity level of DOM,and the influence of human interference on the composition structure of DOM was more obvious.The linear correlation between economic factors and fluorescence components and DOM with different molecular weights was low.Population and GDP growth have a certain impact on DOM composition,structure and migration and transformation through indirect land type changes.