Quantitative source apportionment and origin analysis of Fe and Mn in the middle and lower reaches groundwater of Chaobai alluvial-proluvial fan,Beijing
In order to identify the sources and hydrochemical origin of groundwater with high concentration of Fe and Mn,principal component analysis method and absolute principal component-multiple linear regression model were used to analyze the sources of Fe and Mn in groundwater,and quantify the contribution of each source.Meanwhile,Durrov diagram,chlor-alkali index and mineral saturation index were used to reveal the influence,chemical characteristics and origin of Fe and Mn from different sources.The results showed that the ratio of Fe and Mn exceeding class III standard accounted for 45.6%and 59.4%,respectively.In addition,the concentration levels of Fe and Mn and the rates exceeding the standard were generally higher in wet season than that in dry season.The groundwater in the study area was in a reduction environment,and pH,TOC and sampling depth were the main environmental factors affecting the groundwater quality.Three main components about Fe and Mn were extracted by principal component analysis(PCA),namely,the migration-enrichment effect(F1),the natural dissolution effect of Fe and Mn oxides(F2),and the hydrochemical effect(F3).The main influencing factors of the three principal components were hydrogeological conditions,reduction environment and pH.F1 and F2 were the main reasons which lead to the excess of Fe and Mn in the first and second aquifers,and the low Fe and Mn groundwater formed by F3was distributed in all aquifers.Fe and Mn were easily enriched in HCO3-Ca·Mg groundwater(F1and F2),while the concentrations of Fe and Mn were low in HCO3-Na groundwater(F3).Source analysis results showed that 54.3%and 26.3%of Fe were mainly affacted by F1and F3;the corresponding values for Mn were 58.7%and 19.4%.Less than 7.50%of Fe and Mn were affected by F2.In summary,the migration-enrichment effect and the natural dissolution effect of Fe and Mn oxides are the main factors leading to the excess of Fe and Mn,and hydrogeological conditions and pH are the main variables affecting the concentration of Fe and Mn in groundwater.The influence of anthropogenic activities on the concentration of Fe and Mn in groundwater in the study area is limited.
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