Impacts Of Algae Bloom On The Variations Of Spatial Distribution Patterns Of Heavy Metals And Bacteria Communities In Sediments Across Chaohu Lake

In the present study,the impacts of algae-derived dissolved organic matter and its hydrophilic/hydrophobic fractions on the adsorption of Cr by kaolinite was investigated through simulated environment where intersection between Chaohu Lake and inflowing river.Simultaneously,we investigated the contents of Cr,Ni,Cu,As,Cd and Pb from surface sediments in Chaohu Lake before and after algae bloom,and evaluated the degrees of heavy metals’contamination and their potential ecological risk by the ratio of secondary phase and primary phase and ecological risk assessment methods.In addition,fluorescent components of water soluble organic matter and bacterial community structure from sediments were analyzed through fluorescent excitation-emission matrix and high-throughput sequencing.Based on the above findings,the response of bacteria communities to the change of heavy metals a nd water soluble organic matter was elucidated through redundancy analysis and structural equation model.There were major findings as following:The algae-derived dissolved organic matter,at intersections between Chaohu Lake and inflowing river,could be fractioned into aromatic proteins,fulvic acid-like,soluble microbial by-product-like and humic acid-like components by EEMs technology,which accounted for 8.32%,11.91%,8.45%and 71.32%of the total fluorescence intensity respectively.The algae-derived dissolved organic matter was also separated into the hydrophilic,hydrophobic and transphilic fractions according to the hydrophilicity and hydrophobicity,namely HPI-DOM,HPO-DOM and TPI-DOM.we also found that HPI-DOM was the main fraction,followed by HPO-DOM and TPI-DOM,which accounted for 74.22%,14.53%and 10.09%respectively.The adsorption dynamics of Cr on the kaolinite was influenced by the quantity and its composition of the algae-derived dissolved organic matter.With the increase of the algae-derived organic matter content,the adsorption capacity of Cr by kaolinite increased.We also found that the adsorption capacity of Cr by kaolinite decreased first and then increased with the increase of HPI-DOM content,and the adsorption capacity of Cr by kaolinite decreased with the increase of HPO-DOM and TPI-DOM.The contents of Cr,Ni,Cu,As,Cd and Pb from surface sediments in Chaohu Lake were 42.39 mg/kg-114.85 mg/kg,20.73 mg/kg-55.68 mg/kg,12.97 mg/kg-48.84 mg/kg,5.96 mg/kg-26.18 mg/kg,0.12 mg/kg-1.01 mg/kg and 14.65 mg/kg-107.54 mg/kg respectively.After algae bloom,the contents of Cr,Ni,Cu,As and Pb increased,and Cr,Ni and Cd were homogenized in sediments across Chaohu Lake compared to those before algae bloom.Meanwhile,the spatial patterns of the four species of heavy metal were varied after algal bloom.We found that the relative proportions of the six heavy metals’oxidizable speciation increased by 76.09%,43.46%,88.76%,86.81%,15.25%and 87.04%respectively after algae bloom,and the relative proportions of their residual ones decreased,in which the residual fractions of Cu,Cd and Pb decreased significantly by 53.81%,54.86%and 69.37%respectively.The WSOM quantities from sediments ranged from 95.52 mg/kg to 793.22mg/kg(measured by DOC)in Chaohu Lake,and their total fluorescence intensity ranged from 1062.82 R.U.·nm~2 to 6926.92 R.U.·nm~2.In which aromatic protein-like,fulvic acid-like,soluble microbial by-product-like and humic acids-like components accounted for 11.66%±3.18%,16.54%±2.83%,28.59%±8.96%and 43.20%±10.13%respectively.In addition,the relative proportions of aromatic protein-like and humic acid-like components were significantly decreased after algal bloom(P<0.01)by 3.31%and 11.16%respectively.However,the relative proportions of soluble microbial by-product-like substances were significantly increased(P<0.01)by14.37%.Moreover,the variation coefficients of fulvic acid-like,soluble microbial by-product-like and humic-like increased by 9.65%,8.40%and 11.00%.The high-throughput sequencing results showed that bacteria comprised of 32-41 phylum,57-71 class,70-90 order,130-168 family and 284-426 genus from sediments in Chaohu Lake.The relative abundance of Firmicutes and Actinobacteria were significantly increased(P<0.05 or 0.001),while the relative abundance of Acidobacteria,Aminicenantes,Verrucomicrobia and Bacteroidetes were significantly decreased after algae bloom(P<0.01 or 0.001).RDA and structural equation model results revealed that the key environmental factors affecting the bacterial community structure including the fulvic acid-like,soluble microbial by-product-like,Cr,Ni,Cu,As,Cd,the acid soluble fractions of As and Cd,the reducible fractions of Ni,Cu,As and Cd,and the oxidizable fractions of the six metals.In general,algae bloom not only affected the adsorption behaviors of heavy metals by clay minerals at the estuary of the lake,but also did change the spatial distribution patterns of WSOM and heavy metals in sediments.In addition,the bacterial community structure was altered by the WSOM and heavy metals.These results could improve theoretical and practical understanding for the remediation of heavy metals pollution in eutrophic lakes.