Study On The Relationship Between Metal Enrichment By Zooplankton And Eutrophication In Plateau Reservoir

This study conducted seasonal sampling of Hongfeng Reservoir,Baihua Reservoir and Aha Reservoir from January to December 2018.The samples mainly involved water eutrophication survey,quantitative and qualitative investigation of zooplankton,investigation of the metal content in the zooplankton.From July to August 2018,the enrichment experiment of five metal ions(Hg,Cd,Mn,Fe and Ca)was applied in the laboratory to explore the mechanism of metal enrichment by Cyclops and eutrophication.Results have shown that:(1)A total of 46 species(genus)metazooplankton were detected in Hongfeng Reservoir,including 30 species(genus)of rotifers,10 species(genus)of cladocerans,and 6 species(genus)of copepods.A total of 40species(genus)metazooplankton were detected in Baihua Reservoir,including 26 species(genus)of rotifers,10 species(genus)of cladocerans,and 4 species(genus)of copepods.A total of 40 species(genus)metazooplankton were detected in Aha Reservoir,including 29 species(genus)of rotifers,7 species(genus)of cladocerans,and 4 species(genus)of copepods.The dominant species(Y>0.02)of the three reservoirs are 8species(genus)of Hongfeng Reservoir,7 species(genus)of Baihua Reservoir,and 6 species(genus)of Aha Reservoir.The first and seconddominant species among the three reservoirs all are Keratella cochlearis and nauplii.(2)According to the comprehensive nutrition index(TLI(?))grading standard,Overall,Hongfeng and Baihua Reservoir is between medium nutrition-mild eutrophic level throughout the year.The whole of Aha Reservoir area should belong to medium nutrition-mediotrophic level.(3)The metal content of zooplankton in the three reservoirs was tested as follows: the average content of Hongfeng Reservoir was Ca(21.73±7.89mg/g),Fe(4.34±1.85 mg/g),Mg(2.15±1.18 mg/g),Mn(0.19±0.05 mg/g),Zn(0.17 ± 0.09 mg/g),Cu(18.91 ± 7.02 ug/g),Ni(16.83 ± 8.16 ug/g),As(8.53 ± 1.31 ug/g),Pb(8.13± 4.46 ?g/g),Cd(1.37±0.81 ?g/g)and Hg(0.11±0.03 ?g/g);the average content of Baihua Reservoir is Ca(36.52±10.27 mg/g),Fe(15.78±5.69 mg/g),Mg(2.48±0.89 mg/g),Mn(0.91±0.62 mg/g),Zn(0.16±0.10 mg/g),Ni(31.71±6.25)?g/g),As(14.28±3.99 ?g/g),Pb(5.06±3.46 ?g/g),Cu(2.62±1.34 ?g/g),Cd(1.99±1.30 ?g/g)and Hg(0.16±0.10 ?g/g);the average content of Aha Reservoir is Ca(21.28±10.56 mg/g),Fe(12.06 ± 10.37 mg/g),Mg(2.87 ±2.59 mg/g),Mn(0.60 ± 0.53mg/g),Zn(0.20 ± 0.06 mg/g),Pb(41.26±19.64ug/g),Ni(34.12±15.87 ?g/g),As(27.34±19.7 ?g/g),Cu(24.34±11.12 ?g/g),Cd(0.94±0.73 ?g/g)and Hg(0.43±0.37 ?g/g).Overall,the three reservoirs all showed that the necessary metal content of life activities was higher thanthat of non-living activities.At the same time,the vertical distribution of metal content in the metazooplankton of Hongfeng Reservoir(Daba),Baihua Reservoir(Yanjiaozhai)and Aha Reservoir(Zhongcaoshi)showed that the surface layer of the water body was higher and the middle layer was lower,but the bottom layer was rising.It indicates that the accumulation ability of metazooplankton to metal is related to its community structure and release of substrate metal ion.(4)There was no significant correlation between the number of zooplankton species(ZS),abundance(ZD)and biomass(ZB)and their enriched metal content in the three reservoirs(P>0.05,n=172).but there is a positive correlation between total nitrogen,total phosphorus,dissolved oxygen and conductivity in the environmental factors(r>0,n=172),indicating that eutrophication shows synergy to metal enrichments by zooplankton to a certain extent;while the water temperature is negatively correlated with most of the metals enriched by zooplankton,especially the Fe,Mg,etc.required for algae growth(r<0,n=172).And pH does not affect the enrichment of metal ions in this study.(5)The simulation experiment shows that the total accumulation of Hg,Cd,Mn,Fe and Ca in Cyclops is the highest in the life-requiring constant metal Ca at 72 h,followed by the trace metals Fe and Mn required for life activities,and finally the non-living activities.Essential metals Hg and Cd.At the same time,the experimental results also show that,under the same metal ion concentration,the enrichment ability of Cyclops is related to the different nutrient states of the water body,the metal species,the concentration of the metal and the enrichment time.The bio-enrichment coefficient(BCF)is also known.It shows that the enrichment ability of four metals,Hg,Cd,Mn and Ca,is that in eutrophic water is larger than oligotrophic water,while Fe shows that in oligotrophic water is larger than in eutrophic water.