Dynamic Changes And Influencing Factors Of Organic Matter In Typical Artificial Recharge Area Of Groundwater

Artificial recharge of groundwater can alleviate the continuous decline of groundwater level.Natural organic matter(NOM)has a good response to the natural recharge process of groundwater,but the dynamic change of dissolved organic matter(DOM)affected by artificial recharge of groundwater is still not clear.The research on the mutual transformation process of DOM and particulate organic matter(POM)in groundwater and the molecular response of DOM to artificial recharge is very scarce.In order to solve the above issues,222 groundwater and 40 surface water samples were collected from the reclaimed water(RWRA)and water from South to North Water Diversion(SNWRA)in Chaobai River Basin of Beijing Mihuaishun area,and 67 water particles were extracted by alkaline solution.Three dimensional fluorescence spectroscopy combined with parallel factor analysis(EEM-PARAFAC)and Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)were used to determine the apparent characteristics and molecular species of organic matter in surface water and groundwater and analyze the dynamic changes of organic matter in the process of recharge.The seasonal dynamics of organic matter,the apparent response of DOM and POM phase characteristics,and the DOM molecular response caused by groundwater recharge were studied in depth,which provided theoretical basis for biogeochemical process and risk assessment of artificial groundwater recharge.The main achievements are as follows:(1)The protein-like components have the potential to trace the recharge process of South to North Water Diversion.DOM of groundwater in RWRA is more abundant than that in SNWRA.DOM has the higher content,smaller molecular weight and higher biological activity in wet season.In the PARAFAC model of five DOM components,humic-like component(C3)can better distinguish surface water,shallow groundwater and deep groundwater;protein-like substance produced by microorganisms(C4)and protein-like substances utilized by microorganisms(C5)reflect the seasonal variation of surface water,shallow groundwater and deep groundwater.(2)The humic-like substances have the potential to respond to artificial groundwater recharge and to trace groundwater recharge process.In the PARAFAC model of four DOM-POM components,the DOM / POM partition ratio of humic-like components(C1 and C4)is greater than that of protein-like components(C2 and C3),indicating that refractory humic-like substances are easier to enter aqueous phase than protein-like substances.The results show that the concentration and composition of C1 have obvious gradient changes in the profiles of RWRA and SNWRA,indicating that humic-like C1 can significantly distinguish the two recharge areas.Moreover,the samples in the recharge area showed a gradient change with the depth along PC1.(3)The molecular response of dissolved organic matter can effectively track the recharge process of artificial groundwater recharge.The molecular diversity of groundwater DOM in RWRA is more abundant than that of SNWRA,and the occurrence rate of common molecules is higher.The molecular diversity of groundwater DOM in RWRA changed little with depth,and the molecular response sensitivity was low.The total molecular number of groundwater DOM in SNWRA increases with the depth,but the common molecular rate of deep groundwater is significantly lower than that of shallow groundwater.The results show that the occurrence rate of common molecules decreases with the increase of depth.