Ecological Threshold Of Polycyclic Aromatic Hydrocarbons To Baiyangdian Lake Based On Ecological Model

Polycyclic aromatic hydrocarbons（PAHs）are a kind of persistent organic compounds,which have the characteristics of"carcinogenic,lethal and mutagenic"effect,stability and difficult degradation.With the rapid development of our country’s economy and society,a large number of lakes are polluted by polycyclic aromatic hydrocarbons.These problems become the concern of many ecologists:maintaining the stability of the ecosystem and ensuring the health and safety of the ecosystem under the stress of polycyclic aromatic hydrocarbons.At present,the research on the toxic effects and ecological threshold of polycyclic aromatic hydrocarbons mainly focuses on the individual and population level,and there are few studies based on the community system level.There are many studies on direct toxic effects,but few studies on indirect toxic effects based on food web relationship.In this study,Baiyangdian Lake is taken as an example,combined with laboratory analysis and literature research methods,the pollution concentration and distribution of PAHs in environmental media and organisms were obtained;In this study,a Baiyangdian ecosystem model based on Aquatox was constructed by combining meteorological,hydrological,water quality,aquatic organisms and toxicological data.Select the system response index,set different PAHs concentrations,and obtain the concentration-response empirical relationship.Identify and determine the ecological threshold according to the shape of empirical function.The main research contents and conclusions are as follows:（1）The distribution of PAHs in environmental media and organisms in Baiyangdian Lake is clarified.Data on PAHs contamination were obtained through field investigation and laboratory analysis.The total amount of PAHs in the water is between 40.48～187.69ng/L,with an average value of 138.77±64.12ng/L;the total amount of PAHs in the sediment is between 1.79～1618.90μg/kg,with an average value It was 411.12±393.77μg/kg;the total amount of macrophyte PAHs was 152.22～331.61μg/kg,the mean value was241.20μg/kg.Referring to relevant literature,the total amount of PAHs in the atmosphere is 84.40～982.60ng/m³,the average is 417.20±299.80ng/m³;The total amount of PAHs in fish is 1.95～804.05μg/kg,the average is 58.35±129.94μg/kg.Compared with other regions,the concentration of PAHs in Baiyangdian Lake is at a medium level and the pollution degree is general.（2）Based on Aquatox,the Baiyangdian lake ecological simulation system was constructed by using the methods of mechanism modeling and box model.Then carry out parameter setting and calibration,and carry out parameter sensitivity analysis.Sensitivity analysis shows that the simulated species were most sensitive to the parameters of optimal temperature（T₀）and temperature response slope(T_rs).The calibration results show that the simulated values of all indicators are in good agreement with the measured values.The relative error between the simulated value and the measured value of hydrodynamics is0.079%～14.15%;the relative error between the simulated value and the measured value of water quality is 1.98%～17.49%;the relative error between the simulated value and the measured value of the annual average biomass of each species is 4.32%～66.04%,the seasonal trend is more consistent with the actual situation.The relative error between the simulated value of toxicant concentration in the organism and the current distribution value of PAHs in the organism is 49.40%～179.29%.The accuracy of model simulation results is high.（3）Biomass,P/R,and eco-exergy are determined as response indicators driven by toxicant concentrations.Eight scenarios are designed.Running the Baiyangdian ecological simulation model,and output the response index changes.The results show that with the increase of PAHs concentration in water,the change of each response index is slow first,then rapid,and then tends to be slow.In terms of biomass changes of various species,rotifers are the most sensitive,with a biomass decrease observed（-20.34%）at lower pollution levels（0.328μg/L）.At low pollution levels,organisms may have a tolerance period to poisons,which changes violently at a moderate pollution level.At a high concentration,the biomass changes to a higher value,and the change is not obvious when the concentration continues to increase.From the changes of P/R and Ex indexes,with the increase of PAHs concentration,ecosystem maturity and health decreased,slowly at low concentration,sharply at medium concentration,and no longer significantly at high concentration.（4）Determining ecological thresholds.According to the threshold definition and curve shape to determined the threshold point or threshold interval.The threshold results determined based on the three indicators are:population biomass is 2.68μg/L,P/R index is 3.80μg/L and eco-exergy quality is 4.40μg/L.Compared with domestic and foreign environmental benchmarks or environmental standards,the ecological thresholds in this paper are 10²～10³ larger.Compared with concentration threshold by species sensitivity distribution（SSD）,the ecological thresholds in this paper are consistent with their larger values.The reasons are different expected objectives,different ecosystems and model errors.