Spatial Distribution And Potential Ecological Risk Of Petroleum Hydrocarbons And Heavy Metals In Coastal Wetlands Of The Yellow River Delta

The Yellow River delta is one of the rare ecological wetlands in China,Shengli Oilfield is also distributed here.Oil development is as important as ecological protection.Therefore,it is of great significance to carry out environmental pollution research in this region,and it's conducive to sustainable development of the region.The study area of this paper was the coastal wetland in the Yellow River Delta.The contents of petroleum hydrocarbons and heavy metals in soil were investigated in this paper.The source of petroleum hydrocarbons in soil was explored by using characteristic parameters of petroleum hydrocarbons.Correlation analysis and principal component analysis were used to analyze the sources of heavy metals.What's more,the ecological risk of heavy metals was evaluated by using the land accumulation index and the potential ecological risk index.Moreover,in view of the widespread distribution of oil fields in the Yellow River Delta,this study analyzed the pollution status of petroleum hydrocarbons and heavy metals in the oil wells and non oil wells.The main results were as follows:(1)From the n-alkanes and its parameters,the n-alkanes content of point 19-46 and point 20-64 near oil well was greatly influenced by oil pollution;The soil of points20-44,19-16,and 20-26 near the mouth of the Yellow River might also be affected by a certain degree of crude oil pollution or other fossil fuel combustion;The n-alkanes in the soil of point 19-31 on the the Yellow River Beach might come from algae;The n-alkanes of point 19-9 and 20-69 covered with more vegetation might be mainly derived from higher plants;The n-alkanes of the samples 21-6 and 28-1 also covered with more vegetation showed the obvious characteristics of the input of terrestrial higher plants.Because the soil of point 19-46 and point 20-64 near oil wells and that of point20-69 near the oil field were directly or indirectly affected by oilfield development;And the point of 20-26 which was located near the the Yellow River Estuary might absorb anthropogenic pollutants from the Yellow River.So their total petroleum hydrocarbon content exceeded the national standard.(2)Most of the heavy metals in the surface soil of the study area were lower than the national standard,but the average value of the Cd element was close to the first level,and the average value of the As element was higher than that of the two grade standard.Furthermore,the potential ecological risk level of heavy metals Cd and As was calculated as mild or moderate pollution,which should be paid attention to.Overall,near the old Yellow River Estuary,Yellow River Estuary,chemical plants and some wells,the content of heavy metal was relatively high.And the potential ecological risk index and the land accumulation index of these areas were also higher,which meant that the degree of pollution was relatively high,so it should be paid attention to.Heavy metals Zn,Pb,Cr and Cu in surface soil might come from a source of pollution,well Ni and As might come from another one.Their distribution might be affected by industrial and agricultural pollution,such as pesticides,chemical fertilizers,petroleum industry and so on.The distribution of heavy metals in surface soil was affected by soil particle size.(3)The contents of the heavy metals in most soil profiles of the study area were under the soil background values of Shandong province and the first class national standard.The content of heavy metals As and Cd near oil wells and non oil wells was higher than the national standard.This conclusion was close to that of the surface soil.The heavy metal content in the soil profile of oil well decreased with the increase of depth,but not in the non oil wells.Because of the strong correlation among Cd,Pb,Cu and Zn,they might come from the one source of pollution;And heavy metals Ni and As might come from another source of pollution.Heavy metals near oil wells and non oil wells might come from industrial and agricultural pollution.This conclusion was close to that of the surface soil.The potential ecological risk index and the land accumulation index of heavy metal Cd and As in the soil profiles was relatively high,but all were moderate and low,and the pollution was not serious.The pollution levels of other heavy metals were very low.(4)Generally speaking,there was little correlation between petroleum hydrocarbon and heavy metal content in the studied samples,and most of them were weakly negative correlation.However,there was a positive correlation between petroleum hydrocarbon and heavy metals Pb and As.The petroleum hydrocarbon in the soil might affect the migration of heavy metals.As a result,the content of heavy metals near oil well along with the increase of the depth of the soil decreased gradually,rather than that of the non oil well.