| With the development of social economy and the intensification of human activities,The reduction of area and pollution aggravate eutrophication,ecology and environment deterioration has become a serious problem for lakes.Fuxian Lake is a poor nutrient lake.Due to the imbalance between economic development and environmental protection in past,the water pollution in Fuxian Lake is increasing day by day.Polycyclic aromatic hydrocarbons?PAHs?are a class of persistent organic pollutants that pose great harm to the environment due to their widespread presence in the environment due to their high degradability and toxicity.In recent years,due to the implementation of pollution prevention measures in Fuxian Lake area,the water quality of Fuxian Lake has been better protected,but the persistent organic pollutants PAHs in sediments are still important factors and potential threats to its lake ecosystem.Therefore,it is very important to study the pollution characteristics,sources and ecological risks of PAHs in the sediments of Fuxian Lake for the environmental protection of Fuxian Lake and the control of organic pollution.In addition,lake sediments are the result of long-term surface material migration and atmospheric subsidence,so it continuously and accurately records rich geographic environment information.Through research and analysis of the temporal changes of PAHs content in sedimentary columns,the historical sources of PAHs in the area provide scientific basis for the monitoring and prevention measures of PAXs in Fuxian Lake,which is of great significance for protecting the ecosystem of Fuxian Lake and the health of surrounding residents.From the perspective of the deposition history of PAHs in Fuxian Lake,this paper comprehensively analyzes the content and composition characteristics of PAHs in different spatial and temporal sediments of Fuxian Lake.The sources of PAHs in different historical periods,and the influencing factors of PAHs burial distribution in the sediments of Fuxian Lake and their ecological risk levels were discussed.The main conclusions are as follows:?1?The content of 16 types of controlled PAHs in the surface sediments of Fuxian Lake ranged from 132.4 to 386.3 ng g-1,with an average content of 223.8±69.9 ng g-1.Its main composition was low-ring PAHs,accounting for 53.0%.Because low ring number PAHs have a lower Octanol-Water Partition Coefficient,the proportion of low ring number PAHs in the air is higher than that of middle and high ring numbers,and it is easier to transmit to remote areas through the long distance of the atmosphere.The content of?PAHs and PAHs in each ring in the southern part of Fuxian Lake are significantly higher than that in the northern and central sediments.?2?Based on the 210Pb dating results,the deposition history of PAHs in the 100-year s of Fuxian Lake was studied.The PAHs content in the sedimentary columns from north to south was FX-2(51.5?325.9 ng g-1,average 152.2±52.2 ng g-1),FX-3(32.6?451.5 ng g-1,average 148.9±63.4 ng g-1),FX-4(73.4?536.9 ng g-1,average198.7±79.3 ng g-1),and FX-6(64.0?565.6 ng g-1,average 295.6±129.0 ng g-1).Based on the historical trends of PAHs and human activities,the PAHs deposition history in4 different periods of Fuxian Lake was studied and analyzed.It was found that the content and composition of PAHs in different time periods showed different trends,mainly due to human activities and energy.Take advantage of structural influences,the main components of PAHs in the sedimentary column of Fuxian Lake are Phe of 3 rings,Nap of 2 rings,and Fla and Pyr of 4 rings,and mainly PAHs of low rings.It is consistent with the composition of PAHs in lake sedimentary columns in other remote areas.?3?The PCA-MLR model analyzes the sources of PAHs pollution in the sediments of Fuxian Lake in different periods including coal combustion,biomass combustion,and transportation sources.The contribution rate of each source in different periods has changed,which is related to the economic development and human activities in the region.Before 1950,the source contribution rate of coal combustion analyzed by PCA-MLR model?49.8%?was higher than that of PMF model?29.1%?,while the source contribution rate of biomass combustion analyzed by PCA-MLR model?44.7%?was lower than that of PMF model?52.6%?.During the period from 1950 to 1978,the contribution rates of coal combustion source,biomass combustion source and traffic source analyzed by PCA-MLR model were 39.7%,56%and 4.3%respectively,not much different from the contribution rates of coal combustion source?43.3%?,biomass combustion source?54.4%?and traffic source?2.3%?analyzed by PMF model.The results of both models indicated that the proportion of biomass burning sources increased during this period,and the biomass burning source was the main source of PAHs in the sediments of Fuxian Lake during this period.From 1978 to 2000,the contribution rate of each source of PAHs analyzed by the two models was small,and the contribution rate of biomass combustion sources analyzed by the two models was above 40%.During this period,biomass combustion was still the main source of PAHs in the sediments of Fuxian Lake.After 2000,the fossil fuel combustion sources analyzed by PCA-MLR model and PMF model were 62%and 55.5%respectively.During this period,the main source of PAHs in the sediments of Fuxian Lake changed from biomass combustion to coal combustion,automobile exhaust emission and other fossil fuel combustion sources.Compared with PCA-MLR model,PMF model has higher fitting degree and lower error,and the source of source analysis is more detailed and reliable,but the results of source analysis of the two models are consistent on the whole.?4?With the TN,TP,the correlation of total organic carbon and its internal and external source research analysis found that because of Fuxian Lake in poverty level leads to lower water of planktonic algae biomass such as did not happen"biological pump"effect,nutrient concentrations of PAHs in fuxian lake sediment deposition buried less affected,and only fuxian department of hubei province affected by the sediment TOC content of PAHs in sediment distribution.Further research on the correlation between PAHs content in the sediments of Fuxian Lake and climate data and economic data found that changes in precipitation and days of precipitation have a greater impact on the buried flux of PAHs in Fuxian Lake.In addition,agricultural production activities have always been the main source of PAHs sources in the Fuxian Lake area environment,and human activities,especially industrial and agricultural production,will significantly increase PAHs pollution emissions in the environment.?5?The ecological risk of PAHs in the surface sediments of Fuxian Lake was evaluated using the sediment quality benchmark method and risk quotient.The overall PAHs in the surface sediments of Fuxian Lake are at a low ecological risk level.But Nap,Flu,Phe and Pyr,the four low rings PAHs,are at a medium risk level,and it is necessary to strengthen the control of oil leakage and biomass combustion input source. |
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