Spatial Distribution And Ecological Risk Assessment Of Polycyclic Aromatic Hydrocarbons In Snowmelt Runoff In Harbin City

In recent years,in the process of accelerating the development of social economy and urbanization,people have increased the rate of urban surface hardening,and the original natural hydrological circulation mechanism has changed.The meltwater runoff of urban surface has become the main source of pollution of urban surface water bodies.Related studies have shown that surface runoff contains various pollutants such as heavy metals,polycyclic aromatic hydrocarbons and other nutrients such as nitrogen and phosphorus.Among them,POPs have received extensive attention due to their high concentration and toxicity.The sources of pollution in urban environments are mainly sources of vehicle exhaust emissions,fuel leaks,tire friction and road wear.Polycyclic aromatic hydrocarbons in urban environments enter the urban environment mainly through dry and wet deposition of the atmosphere.Surface rainfall runoff from the erosion of dust and rain on urban roads is one of the important factors that cause pollutants in the urban surface environment to enter the water body and pose a potential threat to the receiving water body.Snow can effectively remove organic chemicals from the atmosphere to the ground,and it can be stored in the snow for many weeks or even months.On the other hand,urban underlying surface change is the main driving force for runoff variation in the Songhua River Basin.The impervious underlying surface blocks the infiltration of runoff,and the pollutants accumulated on the surface are flushed into the drainage pipe during the runoff formation process.Finally,it enters the receiving water body and finally flows into the receiving water body or is adsorbed by the sediment.In this paper,the SWMM model is used to divide the study area,and the snowmelt runoff model of Harbin is established.The model parameters are determined and verified.The model after application rate simulation analyzes the spatial distribution of snowfall runoff and different ring numbers,different catchments,different drainage outlets and different underlying surfaces in different catchments,different drainage openings,different underlying surfaces,and Conduct ecological risk assessment.The results show that the hydrological verification of the snowmelt runoff model in Harbin has a Nash efficiency coefficient of 0.79,which is greater than 0.7.The water quality verification has a concentration deviation of less than 10%,which satisfies the accuracy requirements,and can be used to reflect the process of snowmelt flow in Harbin.In the spring of 2018,the total amount of snowmelt runoff was 12.65 million m3,and the average production flow was 380,600 m3.The spatial distribution of snowmelt runoff of different outlets can be: Hejiagou discharge> Ash River discharge> Songbei discharge> Majiagou discharge> Daoli discharge.Roof runoff output is the largest,46 times the sidewalk with the smallest runoff output,mainly because the roof of the central city is the largest underlying surface type in the impervious surface.The throughput of internal road path flow is higher than that of urban roads mainly due to the runoff caused by artificial snow clearing of urban roads after snowfall.The spatial distribution of polycyclic aromatic hydrocarbons with different ring numbers tends to decrease from four weeks to the center.The concentration is 2 rings > 3 rings > 4 rings > 6 rings > 5 rings.The output of polycyclic aromatic hydrocarbons in the five sewage outlets generally showed a high and low order of P5>P4>P2>P3>P1.The total concentration of PA16 PAHs in urban roads,internal roads and sidewalk snowmelt runoff is relatively large,and high-value areas appear at the junction of Daoli,Daowai and Nangang Districts and near the Songbei Ring Expressway,and are presented from the central city to the suburbs.Declining trend.The aquatic organisms in the main stream of the Songhua River are most sensitive to Flu,with an equivalent coefficient of 10.457;the tolerance to Nap is the strongest,and the equivalent coefficient is 0.003;the order of tolerance is: Nap > Ace> Chr > Ant > Pyr > Fla> BaP > Phe >Flu;that is,Flu is most toxic to aquatic organisms,Nap is the least toxic,and Pyr is centrally toxic.