| Heavy metals,due to their persistence and non degradability,can be enriched in organisms,and have an important impact on the production and living of residents,the aquatic ecological environment,and the safety of drinking water.They are a class of important pollutants with potential hazards in environmental media.Therefore,heavy metal pollution in surface water has been highly concerned by researchers at home and abroad.Dissolved organic matter（DOM）is widely found in both natural and artificial environments,and it is easy to combine with heavy metals through electrostatic action and organic coordination complexation,thus affecting the distribution,migration and bioavailability of heavy metals.Nanyi Lake is one of the largest lakes in the Qingyi River and Shuiyang River systems.It belongs to a lake passing through the Yangtze River and is also the largest lake in southern Anhui.In recent years,with the rapid economic development of Nanyi Lake basin,as well as the comprehensive impact of hydrology,climate and surrounding village and town industries,Nanyi Lake is facing a series of ecological environmental problems such as agricultural non-point source pollution,industrial pollution,aquaculture pollution,flood disaster and soil erosion.In2019,the water quality of Nanyi Lake showed slight eutrophication,with fragile ecological functions and decreased biodiversity in the lake area.Based on the land use types around Nanyi Lake and the environmental characteristics of cage culture in the lake area,this study selected the East Lake purse seine culture area,the West Lake living area,and the main tributaries entering the lake as the study areas,and collected surface water,overlying water,and sediment samples of Nanyi Lake,respectively39×3 were tested to detect the content of heavy metals and organic matter in the water and sediment of Nanyi Lake,analyze the spatial occurrence characteristics of heavy metals and organic matter,and analyze their pollution sources,with a view to providing basic data for the comprehensive improvement of the ecological environment of Nanyi Lake and the protection of water resources in the Yangtze River basin.The main findings are as follows:1)The content range of heavy metals（As,Cr,Cu,Mn,Ni,Pb,Sb,Zn,Fe,Cd）in surface water was 1.00～7.78、0.40～5.59、0.20～4.52、20.00～269.50、0.40～5.56、0.20～5.06、1.00～7.64、20.00～252.50、60～590、0.04～0.6(unit:μg·L-1).Among them,Mn and Sb have sites exceeding the Class III limit specified in the Environmental Quality Standard for Surface Water in the East Lake seine aquaculture area,the West Lake living area,and the main tributaries entering the lake.Fe had sites exceeding the Class III limit specified in the Environmental Quality Standard for Surface Water in the West Lake area and tributaries.The spatial distribution characteristics of heavy metals（As,Cr,Cu,Mn,Ni,Pb,Sb,Zn,Fe,Cd）in surface water showed that the content around the lake was significantly higher than that in the center of the lake.The distribution characteristics of heavy metals in the overlying water were as follows:As is mainly distributed in the southern shore area of the lake,Cr,Cu,Ni and Cd were relatively high in the center of the lake,the maximum content of Fe was in the center of the west lake,and Sb was in the distribution trend of high in the center of the lake and low in the periphery.The maximum content of Zn appears in the places far away from the river mouth,while Pb was relatively high at some points near the Feili River in the East lake area and at the center of the East and West lakes,and Mn was at a maximum in the Beishan River in the West lake area.The distribution characteristics of heavy metals in interstitial water were that As concentration in the East Lake region was higher than that in the West lake region,and there was a certain concentration near the Langchuan River and Feili River.Cr,Cu,Ni and Cd were significantly enriched in the East Lake area,and Pb was significantly enriched.The concentration of As in the East Lake area was relatively high near the Feili River and Biqiao River,as well as some points in the center of the West Lake.2)The average content of As,Cr,Cu,Mn,Ni,Pb and Zn in the sediment exceeds the background value.Spatial analysis showed that heavy metals As,Cr,Mn,and Ni in sediments were significantly enriched in the bays of the East Lake aquaculture area,the maximum value of Cu content was distributed in the East Lake area,the maximum value of Zn was distributed in the vicinity of Langchuan River and Beishan River,and Pb was significantly enriched in the bay of the East Lake and the vicinity of Beishan River.The risk assessment of heavy metals in sediments indicates that:The comprehensive analysis of the risk assessment of heavy metals in sediments showed that the assessment results of the geoaccumulative coefficient method,the potential ecological risk method,the heavy metal distribution coefficient method and the correlation coefficient method all indicate that the potential ecological harm of heavy metal Pb was large.3)The fluorescence spectrum analysis of the water body of Nanyi Lake showed that the fluorescence intensity of both surface and overlying water was in the order of West Lake region>Tributaries>East Lake region.The main fluorescence peaks of dissolved organic matter in surface water and overlying water were A peak,C peak,B peak,and T peak.According to parallel factor analysis,the components in surface water and overlying water in the West Lake region are mainly ultraviolet region fulvic acid（fluorescence peak A）,tyrosine like（fluorescence peak B）,tryptophan like（fluorescence peak T）,and visible region fulvic acid（fluorescence peak C）.The fluorescence components in the surface water and overlying water of the East Lake region and its tributaries are mainly fulvic acid（fluorescence peak A）,tyrosine（fluorescence peak B）,and tryptophan（fluorescence peak T）in the ultraviolet region.The content of humic substances in the surface water of tributaries was high;The fluorescence region integral shows that the proportion of aromatic proteins（region II）in the water body of Nanyi Lake is the highest,with a proportion value of up to 56%.According to fluorescence parameters（FI,BIX,HIX,β:α,Fn（280）,Fn（355））,the organic matter in the water body of Nanyi Lake comes from the joint action of endogenous and exogenous sources,and the endogenous contribution was relatively large.The spatial distribution of organic matter content in sediments of Nanyi Lake was West Lake living area>Tributaries>East Lake aquaculture area,with the maximum value located in Feili River.The spatial distribution of TOC content in sediments of Nanyi Lake was West Lake living area>Tributaries>East Lake aquaculture area,with the maximum value located in Feili River.The average content of TN in sediments in the West Lake region is also higher than that in the East Lake region,and its maximum value was also at the tributary of the Feili River.4)According to C/N analysis,principal component analysis,correlation analysis,and comprehensive analysis of spatial distribution,it is showed that the water pollution of Nanyi Lake mainly comes from industrial wastewater collected by rivers entering the lake,aquaculture and aquatic biodegradation in the lake area,as well as non-point source input from surrounding agriculture and residents’lives.Figure [22] Table [18] Reference [119]... |
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