Effects Of Landscape On The Distributions Of Polycyclic Aromatic Hydrocarbons And Water Quality Indices In An Urban River System

Urban river systems have large potentials for determining the fate,distribution,and transport of water contaminants.This study was conducted to investigate the distribution and identify the sources of 16 Environmental Protection Agency priority polycyclic aromatic hydrocarbons with respect to four different urban river landscapes（river channels managed with hard revetment,unmanaged,with wetland construction,and in city park）.The significant differences of water nutrient physicochemical indices in the four landscapes were also compared with the general linear model,and their relationships with polycyclic aromatic hydrocarbons were analyzed using principal component analysis.Specifically,the main results of this research are as follows:1.COD and NH₃-N indices reached Criterion I of Chinese quality standards for surface water,both in river channels with wetland construction and in city park.2.The concentrations of∑16 PAHs of Jialu River of Zhengzhou City in this present study ranged from 827.5 ng/g d.w.-1514.3 ng/g d.w.,with an average concentration of1140.8 ng/g d.w.,which was lower than most of parallel studies on urban rivers.3.Analysis of isomeric ratios and LMW PAHs distributions in most sampling sites indicate that coal combustion was probably the main source of PAHs pollutions in Zhengzhou City.Specifically,for this study,the ratio of LMW PAHs stayed lowest in urban river channel in city park,followed by urban river channel with wetland construction,which may indicate better dissipation effects of PAHs in these two urban river landscapes.4.PCA analysis shows that sediment∑16 PAHs correlated closely with water NH₃-N,COD,TN,and TP and far from water NO₃-N.All in all,this present study shows that wetland and city park exert better environmental and social benefits for the management of urban river systems.The results show that the practice of constructing landscapes of city park and wetland in the Jialu River section of Zhengzhou City can significantly improve water quality indicators such as chemical oxygen demand（COD）and ammonia nitrogen（NH₃-N）,making these two water quality indicators meet Criterion I water standards prescribed by Chinese government.The average concentration of 16 total polycyclic aromatic hydrocarbons（∑16 PAHs）in the sediments of the Jialu River in the urban area of Zhengzhou city was 1140.8 ng/g d.w.,which was lower than the concentration of polycyclic aromatic hydrocarbons in similar researches on rivers of other cities.Besides,the main pollution source of polycyclic aromatic hydrocarbons（PAHs）in the Jialu River of Zhengzhou City may be coal combustion.The proportion of low molecular weight polycyclic aromatic hydrocarbons（LMW PAHs）to the total polycyclic aromatic hydrocarbons was lower in the urban river channels in the park and constructed wetland area,which maybe indicated that polycyclic aromatic hydrocarbons（PAHs）in these two urban river landscapes were digested and removed better.In summary,the two urban river channel landscapes,urban river in city park and urban river in wetland construction river,can significantly improve water quality and accelerate the removal of pollutants such as polycyclic aromatic hydrocarbon.