Responses Of Human Activities To Historical Reconstruction Of Polycyclic Aromatic Hydrocarbons In Typical Lake Sediments In Northern China

With the development of social economy,the increasing of population,the strengthening of human activities,environmental pollution is a problem that human must face,polycyclic aromatic hydrocarbons（PAHs）as a kind of persistent organic pollutants can be widespread in the environment,because of its toxicity（mutagenic,carcinogenic and teratogenic）,persistence,and the characteristics of long distance migration ability,huge potential risk to the ecological environment and human health,and the greenhouse effect and ozone depletion and listed as one of the three big environment problems affect human health and survival.The lacustrine sediments have the characteristics of intact section preservation,good continuity,high resolution and fast deposition rate.They are important carriers for restoring the regional historical climate,inverting the environmental behavior of pollutants,and quantitatively describing the relationship between human activities in the basin and the environmental evolution of the lake area.PAHs are highly hydrophobic,which are easily adsorbed on particulate matter,enter lake water body with atmospheric deposition and surface runoff,and then accumulate in sediments.Therefore,regional PAHs pollution history can be reconstructed based on lake sediments,and pollution sources can be identified,reflecting the influence of human activities on PAHs pollution in the region.Based on the analysis of the concentration and composition of PAHs in the core sediments of typical lakes in northern China,combined with ²¹⁰Pb and ¹³⁷Cs dating,the PAHs pollution history in the study area was reconstructed,the source and relative contribution of PAHs were studied qualitatively and quantitatively by correlation analysis,characteristic ratio and positive definite Matrix factorization model（PMF）,the difference of PAHs pollution in Lake areas of Chagan Lake,Hulun Lake,Wuliangsu Lake,and Bosteng Lake was compared and analyzed with economic data Combined with climate model,the backward trajectories of PAHs input and potential pollution sources in typical lakes of northern China under different air masses were analyzed by using the backward trajectories of air masses,and a stochastic impact model was constructed,quantitative study on the driving mechanism of PAHs deposition and evolution under different human activity intensities.The main results achieved are as follows:（1）The spatial distribution of PAHs in the sediments of typical lakes in northern China showed a decreasing trend from east to west,especially Chagan Lake（305.90～1214.42 ng/g,596.53 ng/g on average）>Hulun Lake（282.87～1056.87 ng/g,Average596.47 ng/g）>（57.44～515.35ng/g,average 216.91ng/g）>Bosten（51.07～583.73ng/g,average 197.57ng/g）,The content of PAHs in the sediments of northern lakes is significantly lower than that of Taihu Lake and Chaohu Lake in the economically developed areas of eastern China.Among the components of PAHs,3-4 ring PAHs were the dominant components in the sediments of four lakes,which were significantly higher in Chagan Lake and Hulun Lake than in Wulangsu Lake and Bosten Lake.2-ring of PAHs in the sediments of Hulun Lake and 6-ring of PAHs in the sediments of Chagan Lake were significantly higher than those of the other three lakes.The ecological risk assessment showed that there was no serious ecological risk of PAHs in the sediments of typical lakes in northern China,but the monomer Ace and Flu had certain potential risk in the four lakes.In terms of health risks,both carcinogenic risks（TEQs）and teratogenic risks（MEQs）are at a low level compared with the world average.However,since the beginning of the 21st century,the content of CPAHs in the sediments of Chagan Lake has increased rapidly,and the TEQs and MEQs in the sediments of Wulangsuhai and Bosten Lake are relatively high,which should be paid attention.（2）The pollution history of PAHs in typical lake sediments in northern China was established by ²¹⁰Pb and ¹³⁷Cs specific activity measurements.The study of PAHs pollution history in the sediments of four lakes showed that the PAHs content in the sediments of typical lakes in northern China was in the order of Hulun>Chagan>Wulangsu>Bosten before 1970s.The content of PAHs in the sediments of Chagan Lake increased rapidly after 1980s,and the pollution degree of PAHs was higher than that of Hulun Lake,Wuliangsuhai Lake and Bosten Lake.Since the beginning of the 21st century,due to the economic development of cities around the lakes and the increase of human activities,the content of PAHs in the sediments of the four lakes has entered a stage of rapid growth,and the increase of PAHs in the high ring is particularly significant.In particular,the monomeric Dah A,Icdp and Bghi P in the sediments of Chaganhu Lake were significantly higher than those of the other three lakes,indicating the change of fuel consumption from wood to coal and liquid fossil fuels.The pollution history of PAHs in the sediments of typical lakes in northern China is significantly different.The first peak value of PAHs pollution in Chagan Lake and Hulun Lake occurred in the early 1980s,and the first peak value of PAHs pollution in the sediments of Wuliangsu Sea appeared in the late 1980s.The first peak value of PAHs in the sediments of Bosten Lake occurred in the late 1990s,and PAHs pollution in the sediments of four lakes lagged behind the first peak value of PAHs in the lake subsidence column in the eastern coastal area of China by 10 to 20 years.（3）There is a strong positive correlation between the content of PAHs and TOC in typical lake sediment cores in northern China（P<0.01）.At the same time,there is also a good correlation between the content of PAHs and TOC in the middle and high ring regions,while there is no or weak correlation between the content of PAHs and TOC in the low ring regions.The main reason is that the adsorption capacity of cyclic and high-cyclic PAHs to organic matter is stronger.The correlation between the mechanical composition of grain size and the total amount of PAHs in the sediments of typical lakes in northern China showed a good positive correlation（P<0.05）between PAHs and silt with particle size composition（except Wulangsu）,and PAHs in the sediments were more likely to be adsorbed on coarse-grained particles and subsided into the lakes with atmospheric precipitation.PMF method was used to analyze the source of PAHs in the sediment cores of each lake.The source of PAHs in the typical lake sediments in the north of China was mixed with combustion sources.In the sediments of Chagan Lake,biomass combustion source accounted for 16.39%,oil spill/low temperature combustion source accounted for 32.32%,traffic source accounted for 16.58%,and fossil fuel combustion source accounted for 34.71%.In the sediments of Hulun Lake,the traffic source accounted for 17.57%,the combustion source of petroleum products accounted for 11.52%,the mixed source of biomass/high temperature combustion accounted for10.11%,and the mixed source of oil spill/coal combustion accounted for 60.80%.In the sediments of Wuliangsu,fossil fuel combustion sources accounted for 58.12%,traffic sources accounted for 10.79%,oil leakage/biomass combustion sources accounted for31.09%;The fossil fuel combustion source,oil spill,biomass combustion mixed source and traffic source accounted for 53.02%,28.16%and 18.82%respectively in the sediments of Bosten Lake.（4）The environmental sensitive components were extracted from four typical lake sediments by particle size standard deviation method,and the contribution rate of combustion source of PAHs was positively correlated with the contribution rate of F2（8.71～52.84μm）in the sediments analyzed by PMF（P<0.01）.That is,it has excellent correlation with close regional atmospheric transport（local input）.PAHs generated from industrial production,residential life,waste incineration,fuel combustion and other production activities around the four lakes are easy to combine with fine particulate matter under the action of wind,and enter the water through atmospheric migration and settlement,and then accumulate.（5）The results of HYSPLIT showed that there was a local air mass with a short transport distance in the input track of PAHs in typical lake sediments in northern China.The air mass input directions of Chagan Lake,Hulun Lake,Wulangsuhai Lake and Boston Lake were southeast,east,southwest and northwest,respectively.The specific input tracks are as follows:from the central part of Jilin,from the southwest to Chagan Lake through Songyuan City;From the Daxing’anling region to the west through the Inner Mongolia Plateau Hulun Buir City to reach the Hulun Lake;From the west of Inner Mongolia,it turns to the east and passes Bayannur and other cities,then arrives at Wuliangsuhai;The air mass from the northwest of Bosten Lake reaches the lake through Hejing County,Yanqi County and Bohu County.（6）STIRPAT model analyzes the population size,the level of economic development,the industry development and energy consumption as a share of GDP and other factors on the influence of typical PAHs contents in lake sediments in the north,through the study found that songyuan,hulun buir city industrial production and GDP energy consumption,bayinnaoer city GDP per capita and bazhou city industrial added value of chagan lake,lake called Aaron and wu liang,the sea and the characters of the main content of PAHs in sediment change driving factor,The PAHs content in sediments will increase by 0.521%,0.2001%,0.4114%and 0.5178%when the index increases by 1%.