| With the rapid economic development of the Nansi Lake basin,the water environment pollution caused by industrial sewage discharge and mining activities in the basin has received extensive attention,among which heavy metals are one of the most significant pollution sources.This study takes Nansi Lake as the research object and adopts high-resolution technology,highresolution dialysis(HR-Peeper)and diffusive gradients in thin films(DGT)technique,to realize the distribution and mobility of five typical heavy metals in the sediment-water interface(SWI)of Nansi Lake under the millimeter level.Research on distribution characteristics,diffusion flux,and release risk could provide a scientific basis for the treatment of metal pollution in the sediments of Nansi Lake and the restoration of the ecological environment in the future.The main research results are as follows:(1)The p H of the SWI of Nansi Lake is in a weakly alkaline environment between 7.49-8.16.At the junction of the overlying water and sediment,dissolved oxygen(DO)and oxidation-reduction potential(Eh)drop suddenly.The oxidizing environment gradually transitions to weakly alkaline reducing environment.The content of total nitrogen and organic carbon increases with depth.The content of Fe and Mn and the S fluxes suddenly increase below the interface,especially from the 0 mm to the position 40 mm below the interface.This also shows that the substance at this position is subject to Fe/Mn oxides and organic matter.(2)The metal content in the overlying water of Nansi Lake is relatively low.Except for the total dissolved Ni(24.86 mg/L > 20 mg/L),the content of other metals is lower than the second-class water standard.The heterogeneity of the distribution of metals in the SWI fluctuates greatly.The content distribution of HR-Peeper and DGT have similar changing trends,but the correlation is not significant.DGT,which represents the labile state,including the active ion state and the weak bound metals,and HR-Peeper measure the total amount of dissolved metals.The distribution characteristics of the two are mainly affected by environmental factors such as Fe/Mn oxides,C/N organic matter,and p H.Cd and Zn in Weishan Lake are enriched in the surface layer,which should arouse certain attention.(3)Except for Cd(0.4 mg/kg)and Zn(109.0 mg/kg)of Weishan Lake in the sediments,other elements are within the background value range,indicating that the management of Nansi Lake in recent years has been made initial progress.According to the results of BCR,the Ni,Cu,and Zn in the sediments at the interface are mainly composed of residual components,while Cd and Pb are mainly in the reduced fraction.The acid exchangeable fraction of Cd in the surface sediments accounts for the largest proportion,indicating that Cd has a higher potential mobility.The profile distribution can be divided into three categories according to the content change.The first kind is Cd,which is the main component of non-residue,the main component is the residue.The second kind is Pb,Ni,Cu,and the content of different components of them that gradually increase with depth.The third kind is Zn,and the change of Zn is not significant.The high Cd mobility coefficients of the two lakes indicate that although the Cd content is low but the activity is very strong,it is more likely to be released than other metals,which further illustrates the potential ecological risks in the overlying water.(4)According to the DGT-induced sediment flux(DIFS)model,the re-release ability of Cd and Zn in Dushan Lake is higher,and the re-release ability of Cu,Ni,and Pb in Weishan Lake is higher.In addition,the metal in Dushan Lake has a stronger effective supply capacity.According to the DIFS model,the mobility of the five metals from sediment to interstitial water is weak,but the risk of release in Nansi Lake is still worthy of attention,especially the high mobility of Cd and Ni in Dushan Lake.(5)The apparent diffusion flux indicates that the direction of release of Cd and Ni is from the sediment to the overlying water,and the sediment is the "source".The deposits are the "sink" of the labile Pb,Cu,and Zn.The release risk code(RAC)of Cd reached 18.5% in Dushan Lake,which was at a medium risk level,while Weishan Lake was at a low risk.The RAC of Ni was3.1% and 2.7% in the two lakes,which belonged to a low risk level.Both Cd and Ni exist the upward release trend from sediments,which should be taken seriously.In general,the current risk levels of the five metals in Nansi Lake are relatively low,but there are still potential release risks for Cd and Ni. |
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