Spatial Distribution Characteristics And Source Analysis Of Heavy Metals In Sediments Of Typical Estuaries On The South Coast Of Laizhou Bay

Estuary is an important link between the river and the ocean,and also an important channel for land materials to enter the ocean.With the development of social economy,more and more pollutants are directly discharged into rivers.These pollutants eventually settle in the estuarine area or enter the ocean along with the river runoff movement.Among these pollutants,heavy metals are widely concerned because of their wide sources,difficult degradation and easy accumulation.Estuarine sediment is not only the habitat of many aquatic organisms,but also the natural "sink" of heavy metals.Heavy metals in sediment are easy to enter into aquatic organisms along with the food chain,and eventually harm human health along with the accumulation of food web.There are two main sources of heavy metals in estuarine sediments: natural sources and anthropogenic sources.The natural source mainly depends on the geochemical characteristics of the parent material during the weathering process.When the concentration of heavy metals changes within the range of environmental background value,it is considered to be affected by the natural background and belongs to the natural source.However,external human activities,such as industrial emissions,traffic emissions,coal fuel and agricultural activities,may also lead to the increase of heavy metals in the environment.Yu River and Xiaoqing River are two important rivers entering the sea on the South Bank of Laizhou Bay.They originate in Weifang City and Jinan City,Shandong Province,respectively.They flow from the south to the north in areas with rapid development of industry and agriculture.Both rivers have been seriously polluted.After centralized treatment,the pollution has been reduced.In this study,164 surface sediment samples and 43 surface sediment samples were collected from the Yu River and Xiaoqing River estuaries.Ten heavy metals such as As,Cd,Co,Cr,Cu,Hg,Mn,Ni,Pb and Zn were analyzed and tested.Descriptive statistical analysis,ordinary Kriging interpolation and geostatistical stochastic simulation(sequential Gaussian simulation,SGS and sequential indicator simulation,SIS),potential ecological risk index,single factors and Nemero index,index of geoaccumulation,as well as EPAPMF receptor model and WALSPMF receptor model were used to analyze heavy metal concentration,spatial distribution characteristics,pollution status and quantitative analysis of heavy metal pollution sources in the surface sediments of the estuary.The results are displayed as follows:(1)The average concentrations of heavy metals As,Cd,Co,Cr,Cu,Hg,Mn,Ni,Pb and Zn in the surface sediments of Yu River and Xiaoqing River estuaries were lower than the level I of national standard for marine sediments.The average concentrations of Cd and Zn in Yu River estuary were 1.4 and 1.3 times of the background value of elements in the coastal sediments in China.The average contents of As,Cd and Mn in Xiaoqing River estuary were higher than the background value of elements in the coastal sediments in China,and the concentrations of As and Cd were 1.2 and 1.6 times of the background value of elements in the coastal sediments in China,respectively.As a whole,the average contents of 8 heavy metals such as As,Cd,Co,Cr,Cu,Mn,Ni and Pb in Xiaoqing River estuary were slightly higher than those in Yu River estuary,while it was opposite for Hg and Zn.The concentrations of heavy metals in the two estuaries were generally lower than those in the Pearl River Estuary,Jiulong River Estuary,Bohai Bay,Yellow River Estuary,Laizhou Bay,the northern coast of Liaodong Bay,Luan River Estuary and the Yangtze River Estuary.The grain size of surface sediments in Yu River and Xiaoqing River estuaries was large.The average sand content was higher than 60%,the silt content is the second,the clay content is the smallest,and so it is not conducive to the enrichment of heavy metals.(2)The spatial distribution pattern of heavy metals in the surface sediments of Yu River and Xiaoqing River estuaries was mainly controlled by the grain size composition of the sediments.The areas with high concentration of heavy metals are concentrated in the areas with small grain size and high content of clay and silt.The pollution from human activities also has a certain impact on the spatial distribution pattern of heavy metals.As,Cd,Co,Cr,Hg,Mn and Zn in Yu River estuary are mainly controlled by sediment particle size,and Cu,Ni and Pb may be affected by both sediment particle size and anthropogenic pollutants;while Cd,Co,Cr,Cu,Hg,Mn,Ni,Pb and Zn in Xiaoqing River estuary are controlled by surface sediment particle size,and As may be affected by sediment particle size and human activity pollution source.The spatial distribution patterns of heavy metals obtained by ordinary Kriging,SGS well as SIS are basically the same.However,the smoothing effect of ordinary Kriging made the low value area of unsampled points overestimated and the high value area underestimated,so the results of SGS are more accurate.(3)The results of potential ecological risk assessment,single factor and Nemero index as well as index of geoaccumulation showed that the pollution level of heavy metals in Yu River estuary was at the level of light pollution,Cu was light pollution,and Cd,Hg and Zn belonged to moderate pollution.The areas where Cd,Hg and Zn were delineated as hazardous areas are 15.3%,24.6% and 46.75% of the study area,respectively.The pollution level of heavy metals in Xiaoqing River estuary was slightly lower than that in Yu River Estuary,which also belonged to light pollution level.As,Hg and Mn showed light pollution risk,and Cd showed moderate pollution risk.94.1% for As,12.5% for Cd,4.4% for Hg,and 47.6% for Mn of the total study areas were delineated as hazardous areas.(4)There are three sources of heavy metals in the application of EPAPMF model and WALSPMF model in two estuaries,and the results of the two models are basically the same.The weighted average contribution of the two receptor models was used as the final concentration contribution of the two estuarine heavy metal sources.The results show that,in the Yu River Estuary,As,Cd,Co,Cr,Cu,Mn,Ni and Pb were controlled by natural sources.Industrial,agricultural activities and atmospheric deposition related to coal combustion contributed 23.2%,53.1% and 45.4% to the concentration of Cd,Hg and Zn,respectively.Traffic emissions contributed 29.9%,27.3% and 24.2% to the contents of Cu,Ni,and Pb,respectively.In the Xiaoqing River estuary,As,Cd,Co,Cr,Cu,Hg,Ni,Pb and Zn were mainly from natural sources.32.8% of As and 48.1% of Mn were from agricultural activities,such as the use of pesticides,fertilizers and organic fertilizers.27.4% of Cu and 30.3% of Hg derived from industrial activities and atmospheric deposition related to coal combustion.