Distribution Characteristics Of Typical Pollutants In The East Tiaoxi River And Its Comprehensive Assessment Using A Monte-carlo Model

At present,China has begun to shift from pollution monitoring to pollution control and further improving water quality in response to river pollution.As a representative of the river basin in Southeast China,conventional pollutants such as nitrogen and phosphorus in the East Tiaoxi River has attracted a lot of attention,while some new pollutants and the comprehensive pollution degree has not received enough attention.In this paper,20monitoring sections are divided according to the water system conditions and watershed functions of the East Tiaoxi River.The concentrations of nitrogen,phosphorus,n-alkane（n-Alks）,polycyclic aromatic hydrocarbons（PAHs）and 3 types of 21 variety of antibiotics in the river were detected,and their concentration levels and spatial-temporal distribution were analyzed.A comprehensive pollution index based on five factors such as TN,NH₄⁺-N,TP,∑n-Alks and∑PAHs was established.The Monte-Carlo model is used to simulate and predict the comprehensive pollution index,so as to carry out comprehensive water quality analysis on the East Tiaoxi River.The purpose of this study is to fully investigate the types,distribution,scale,and nature of pollution in the East Tiaoxi River,while improving the database of new pollutant levels and comprehensive pollution status for this river,so that to provide data and theoretical support for the formulation of new environmental quality standards and control technologies.The main research conclusions are as follows:（1）For the 20 monitoring sections of East Tiaoxi River,the annual average concentrations of TN are 0.80～1.50 mg/L（Class Ⅲ water quality standard TN concentration is 1.00 mg/L）,and the annual average concentrations of NH₄⁺-N are 0.03～0.61 mg/L（Class Ⅲ water quality standard NH₄⁺-N concentration is 1.00 mg/L）.The annual average concentrations of TP are 0.07～0.26 mg/L（Class Ⅲ water quality standard TP concentration is 0.20 mg/L）,the annual average of dissolved total phosphorus（DTP）are 0.05～0.21 mg/L,and the annual average of particulate phosphorus（PP）are 0.02～0.06 mg/L.The overall concentration of TN in East Tiaoxi River is relatively high,causing serious pollution.The concentration of TP is higher in the middle and lower reaches of East Tiaoxi River.（2）The annual averagelevels of the 20 monitoring sections range from 190.15ng/L to 276.79 ng/L.The main PAHs are naphthalene and phenanthrene,with average concentrations of 52.14 ng/L～112.13 ng/L and 75.93 ng/L～108.86 ng/L,respectally.The annual average∑n-Alks levels range from 140.36μg/L to 234.16μg/L,and C39 is the main n-Alks with an average concentration of 47.24μg/L～127.76μg/L.The CPI index shows that the n-alkanes in East Tiaoxi River are mainly derived from fossil fuels.The overall concentration of antibiotics was basically at the ng level.The highest detection rates and concentrations are trimethoprim（TMP）and erythromycin（ERY）.During the 12-month monitoring of ERY,the concentration of ERY was higher in May and June,and a higher value appeared in the middle and lower reaches of East Tiaoxi River,with the highest concentration of 13 ng/L.（3）Monte-Carlo simulation prediction of the comprehensive pollution index based on the five factors of TN,NH₄⁺-N,TP,（16 types）,and the predicted values of CWQI for each monitoring section in East Tiaoxi River are above 0.7.Most of the monitoring sections are moderately polluted,and some sections are heavily polluted.The water quality in the upper reaches of the East Tiaoxi River is relatively better,with moderate pollution.The best water quality is in the North Tiaoxi River.In the middle and lower reaches of the East Tiaoxi River,the water quality is relatively worse,and some sections are heavily polluted.（4）In the middle and upper reaches of East Tiaoxi River,theand TN showed greater impact on the comprehensive pollution index.The SRCC values ofin the 9monitoring sections are all greater than 0.5.The situation in the middle and lower reaches of the East Tiaoxi River is more complex,and the comprehensive pollution index is mainly affected by TN and∑n-Alks.Compared with the upper and middle reaches of the East Tiaoxi River,the∑n-Alks in the middle and lower reaches of East Tiaoxi River have a significant impact on the comprehensive pollution index,which indicates the significant impact of shipping on water quality in the lower reaches of the East Tiaoxi River.