Analysis Of The Composition,distribution And Source Of Dissolved Organic Matter In Wetlands In Yinchuan City And Its Correlation With Heavy Metal Ions

Objective Analyze the composition characteristics of the dissolved organic matter（DOM）in the wetland of Yinchuan City,analyze its distribution and source,Evaluate the pollution level of heavy metals in wetland surface water and sediments,and explore the relationship between DOM and metal ions.Methods This research uses a combination of mathematical statistics and spatial geostatistics,in September-October 2019 and September-October 2020,15lakes and 1 river in Yinchuan City were collected for two years of surface water and sediment samples.Three-dimensional fluorescence and ultraviolet-visible methods are used to complete the analysis of dissolved organic matter（DOM）in the sample,and the measurement of metal ions in the sample is completed by ICP-MS.Analyze DOM by absorption spectroscopy,area integration method（FRI）,parallel factor method（PARAFAC）,and fluorescence index method,The Geo-accumulation index method,the potential risk index method,the Single factor pollution index method,and the Synthetic pollution index method were used to evaluate the pollution degree of various metal ions in the sediments and surface waters of the study area,and to explor e the relationship between DOM and metal ions.Results 1.The characteristic indices of absorption spectrum a355 and a254show:a355 sediment(1.13-20.56,4.20 m^-1)>water body(0.25-11.12,2.38m^-1),a254 sediment(0.09-20.01,3.47m^-1)>water body(0.02-8.13,1.84m^-1).The characteristic indexes of absorption spectrum E2/E3 and E3/E4 show:E2/E3 water body（0.14-3.79,1.47）>sediment（0.02-3.04,0.86）,E3/E4 water body（1.18-28,10.78）>sediment（3.09-11,6.18）,but the whole is greater than 3.5.FRI parses the wetland DOM into 5 areas,the area I is tyrosine-like protein,area II is tryptophan-like protein,area III is fulvic acid,area IV is soluble microbial metabolites,and area V is humus-like substances,the fluorescence percentage₄,n)value showed the largest area II,exceeding 25%,followed by areas I,IV,III,and V,which were 21.92%,21.72%,19.37%,and 11.96%,respectively.PARAFAC analyzed the wetland DOM in Yinchuan City into 4 components,the two tyrosine-like proteins（C2,C4）,and the two humus-like components（C1,C3）,C1is defined as traditional hum mus,and C2 is defined as microbial humus.The fluorescence abundance of each component is obviously different.Among them,the relative content of C2 component is the largest,e xceeding 35%（38.25%）,followed by C4（26.60%）,C1（19.60%）,and the smallest relative content is C3（15.56%）.2.The spatial distribution of each component of the DOM shows that the distribution ratio of each component at the sampling point is unbalanced,The protein-like component（C2+C4）is significantly larger than the humus-like component（C1+C30）,There are H23,H34（19-year water bodies）,H1,H8,H10,（20-year water bodies）,and H24 and H22（20-year sediments）have slightly higher humus levels.The difference between 2019 and 2020 water bodies is not obvious.The sediments C1 and C3（humus-like components）in 2020 are larger than those in 2020 water bodies.3.The spectral feature index Fn280 is significantly higher than Fn355;Fluorescence index FI:2.23±0.19 for water bodies in 2019,2.20±0.08 for water bodies in 2020,and 2.20±0.08 for sediments in 2020,all greater than 1.8,Biological index BIX:water body in 2019 1.01±0.07,water body in 20200.99±0.08,sediment in 2020 0.76±0.13,on the whole,the BIX value of the DOM in Yinchuan wetland is between 0.8-1.0.The humification index HIX:water body in 2019 is 1.21±0.55,water body in 2020 is 1.89±0.60,sediment in 2020 is2.78±0.92.The PCA results show that there are significant differences in diff erent characteristic areas,and there is no obvious difference in the water sample collection areas within the area.4.The several metal elements in the surface water and sediments of the wetland in Yinchuan are B,Mg,Al,Ti,Mn,Zn,Fe,As,Sr,Mo and B a.Among them,the results of Cu,Zn,Se,As,Cd,Cr,Pb in water,and Cd,As,Pb,Cr,Cu,Ni,and Zn in sediments are all exceeding the standard value.The geo-accumulative index_geo,the single-factor risk index⁴),and the potential ecological risk index RI show that none of the sediments Cd,Pb,Cr,Cu,Ni,and Zn are polluted.The potential ecological risk is low,but some sampling points of As have moderate pollution;The single-factor pollution index（Pi）and the synthetic pollution index P_syn show that the elements of Cu,Zn,Se,As,Cd,and Pb in the water body are all at a safe and clean level.5.The concentration of 26 heavy genus elements in wetland sediments in Yinchuan City was correlated with the abundance of 4 DOM components in the sediments and the fluorescence spectrum indicators.The results showed that there was a significant correlation between C1%and As,Cd,Ba,Tl,and Pb（P<0.05）;There is a significant correlation between C2%and Ti（P<0.05）;there is a significant correlation between C3%and As,Se,Cd,Sb,and Tl（P<0.05）;There is a significant correlation between C4%and As,Cd,Sb,Ba and Tl（P<0.05）.Overall,the concentration of heavy metals is positively correlated with tyrosine-like components（C2）and（C4）,but neg atively correlated with humic substances（C1）and（C3）.Conclusion:1.The PARAFAC method analyzed that Yinchuan wetland DOM has two humus-like components（C1 and C3）and two protein-like components（C2and C4）,which are divided into 5 regions by FRI,P _i,n value and fluorescence intensity Consistent with the fluorescence abundance,the wetland DOM in Yinchuan City is dominated by protein-like components.2.Through the spatial distribution of DOM and PCA analysis,it is found that there are significant di fferences in fluorescence intensity and component signals in each study area,which are mainly affected by the level of wetland development and utilization,lake water supply,and surrounding land use types.The difference in fluorescence intensity of wate r bodies in different years is not obvious,but the sediments are obviously higher than those of the water bodies,and the sediments have a large proportion of humus-like components.Generally speaking,the DOM type of wetland water bodies in Yinchuan is p rotein-like dominant type.3.According to the analysis of the characteristic parameters of the fluorescence spectrum,the source of DOM in Yinchuan wetland is dual characteristics of Autogenic and terrestrial sources,however,it is mainly self-generating source,and new DOM accounts for a relatively large proportion.4.The heavy metal ions in the surface water and sediments of the wetland in Yinchuan City are at a relatively low level,compared with several metal ions stipulated by national standards,th ey are all pollution-free and clean,low potential risk level,but certain points of As element may be moderately polluted and are at a medium potential ecological risk.5.There is a correlation between DOM in wetland sediments in Yinchuan and some uncommon trace elements in lake sediments,such as Ti and Tl,but the specific coupling mechanism remains to be studied.