Pollution Levels And Biological Effects Of Heavy Metals In Streambed Sediments Of The Weihe River Basin

Because of its high toxicity,non-degradation and bio-accumulation,heavy metals in streambed sediments not only damage water quality but also threaten the survival of macroinvertebrates.In recent years,the monitoring and assessment of heavy metal pollution in sediments have received much attention.The Weihe River Basin occupies a strategically important position in the Silk Road Economic Belt.In this study,the sediments and macroinvertebrates of 0-10 cm and 10-20 cm layers below the sediment-water interface were collected in the flood,dry and normal period of the Weihe River Basin?Weihe River-WR,Jinghe River-JR and Beiluohe River-LR?.The temporal and spatial distribution of six heavy metals in sediments and the macroinvertebrate community structure was analyzed.Based on heavy metal and biological index,heavy metal pollution in sediments was assessed.With ecological data processing software to analyze the biological effects of heavy metal pollution in sediments on macroinvertebrates,bioindicators corresponding to heavy metal pollution in streambed sediments were revealed at the river scale and vertical scale of sediments.Research indicates as following:1.The spatial and temporal distribution of heavy metal content in streambed sediments of the Weihe River Basin was clarified.The order of the average heavy metal content in streambed sediments of WR,JR and LR were:Cr>Zn>Ni>Cu>Pb>Cd,and the content of each heavy metal was basically as follows:WR>JR>LR,dry period>normal period>flood period,10-20 cm layer?0-10 cm layer.The average heavy metal contents in streambed sediments of these rivers were not only above the middle level in domestic and foreign rivers,but also higher than the background value.It reflects that streambed sediments in the WR Basin have been contaminated by heavy metals.2.The pollution degree of heavy metals in streambed sediments of the WR Basin was assessed.Based on Geo-accumulation index(I_geo),Potential ecological risk index(P_RI),Pollution load index?PLI?and mean Probable effect concentration quotient?m PECQ?,the assessment of heavy metal pollution in sediments was presented as:dry period>normal period>flood period,10-20 cm layer>0-10 cm layer,WR>JR>LR.I_geo showed that Cu,Zn,Cr,Ni,and Pb belong to mild pollution,and Cd pollution was the most prominent moderate pollution.P_RI were ranked as follows:Cd>Cu>Pb>Ni>Cr>Zn.And the sites contaminated with Cd were relatively the most,which was consistent with the results in I_geo.PLI and m PECQ indicated that WR,JR and LR sediments had been disturbed by heavy metals from outside,and the toxicity probability of heavy metals in sediments was between 15%and 29%.3.The macroinvertebrate community structure corresponding to the sediment layer in the WR Basin was analyzed.The macroinvertebrates identified mainly include:Mollusca,Annelida and Arthropoda.Among them,Arthropoda contain the most species,mainly Aquatic Insects.The WR and LR were very similar in species composition,and the WR and the JR had the same four main species.The average biomass in the 0-10 cm layer of the WR,JR and LR sediments was greater than the 10-20 cm layer.The dominant species were Oligochaetes.And the Oligochaetes in the WR occupied an absolute advantage.The JR also had the Ephemeroptera and Trichoptera that are more sensitive to pollutants in the environment.There were also Chironomid larvae in the LR that are more resistant to pollutants in the environment.Based on the Shannon-Wiener Diversity Index?H_S?and Maralef Species Richness Index?D_M?,it was shown that the community structure of WR was unstable and the degree of pollution was the largest,while the JR community was generally stable,and the LR was relatively unstable.The biological pollution index?BPI?and family biotic index?FBI?indicate that the sediments at each site were basically at a medium or higher pollution level.The overall pollution of the WR sediments was relatively more serious,the JR was relatively stable,while the LR was very unstable.This was consistent with the assessment results of the heavy metal index.4.Bioindicators corresponding to heavy metal pollution in streambed sediments of the WR Basin were revealed.Oligochaetes had strong resistance to Cd,Chironomid larvaeis had strong sensitivity to Ni and Cr,and D_M had a significant negative correlation with Ni and Cr,which was more common in the WR where the heavy metal pollution in streambed sediment was relatively serious.Aquatic insects had strong sensitivity to Zn,Ni,Cu and Pb.Gastropods had strong resistance to Zn,Ni,Cu and Pb.FBI and BPI had a significant positive correlation with Ni and Cr.This was more common in the JR and LR where the heavy metal pollution in streambed sediment was moderate.It shows that the pollution degree of heavy metals in streambed sediments at the river scale is different,and the response indexes corresponding to heavy metal pollution are also different.Oligochaetes active in deep sediments had strong resistance to Ni,Cu,Pb and were also the dominant species in the 10-20 cm layer.Gastropods active in surface sediments had strong resistance to Ni,Zn,Cd,Pb and were also the main species in the 0-10 cm layer.FBI had a significant positive correlation with Ni,Zn,Pb.This indicates that in addition to the accumulation degree of heavy metal on the vertical scale of sediment,the vertical distribution of main macroinvertebrates and dominant species will also lead to a certain difference in the response indicators corresponding to heavy metal pollution.Therefore,Oligochaetes,Chironomid larvaeis,Aquatic insects,Gastropods can be used as bioindicators corresponding to heavy metal pollution,and D_M,FBI,BPI can be used as bioindicators parameters.The results of this study can lay a foundation for the study of the ecological toxicity effects of heavy metals in the streambed sediments of the WR Basin,and provide technical support and reference basis for the monitoring and prevention of heavy metal pollution in streambed sediments and the restoration of aquatic ecological environment.