Study On The Causes Of Water Pollution In Jiashan Pond-Fengjing Pond

Jiashan,as a county incorporated into the demonstration zone of green and integrated ecological development of the Yangtze River Delta,is located in the Hangjiahu Plain of Taihu Lake Basin,situated in the northeastern side of Jiaxing,where intersects with both Jiangsu Province and Shanghai.Inside of Jiashan,Jiashan Tang-Feng Jing Tang is the most crucial mainstream flowing through Jiashan’s Witang,Luoxing and Huimin districts with a total length of 25 kilometres.And eventually,it flows into Shanghai through one state-controlled water quality monitoring station-Feng Nan Qiao.According to the station’s records,while the annual average continually reaches the standard,sometimes the dissolved oxygen(DO)or the total phosphorus(TP)of the water quality index would exceed the standard in monthly monitoring.This study conducted intensive water quality monitoring four times in September 2020(regular season),December 2020(dry season),June 2021(flood season)and December 2021(dry season).It studies the temporal and spatial variations based on the conventional water quality index,heavy metal pollution index,and threedimensional fluorescent fingerprints.Combining the results of the principal component/factor analysis(PCA/FA)and the positive definite matrix receptor model analysis(PMF),it analyzes the potential pollution sources in Jiashan Tang-Feng Jing Tang and their contribution rates.Eventually,it provides a scientific basis for further improving the water quality.The main conclusions of this study are as follows:(1)The ammonia nitrogen and permanganate index of Feng Nan Qiao usually could reach the standard.Still,the chance of the DO index exceeding is significant during Summer and autumn and the TP index during Summer.The water monitoring results show that the upstream water is not why the DO and TP indexes degrade.It happens at the section between #7 and #13 monitoring points,which is likely the reason causing Feng Nan Qiao sometimes exceeds the standard in monthly monitoring.(2)The PCA/FA analysis shows that agricultural non-point sources and domestic sources are the ones causing water pollution in Jiashan Tang-Feng Jing Tang.The PMF analysis results further reveal that the contribution rates of two water pollutions sources would vary through different seasons and water levels.Domestic sources play a more significant role than agricultural sources during the dry season and vice versa during the regular and dry seasons.(3)There are higher concentrations of heavy metal elements,including V,Cr,Co,Rb,Sr,Mo,Cu,Zn,Ni,As,Fe and Mn,at the upstream monitoring points #1,#2,#4,and #6.The number decreases when it turns to the downstream points,starting at #7.Considering both banks of this section of the river are farmland,the heavy metal elements most likely originated from the agricultural non-point sources.The PMF analysis result seems to support this hypothesis,as it ranks the contribution rates in this way: natural sources(33.7%)> agricultural non-point sources(23.8%)> other sources(23.6%)> industrial point sources(18.9%).(4)TP concentration in sediment is generally greater than 500 mg/kg at both Jiashan Tang-Feng Jing Tang and its tributaries’ monitoring points.When the DO concentration reaches a low level during Summer,there is a risk of releasing phosphorus pollutants into the waterbody.In addition,the mud sample contains a large amount of reducing substance that makes it appear black,which resides a likelihood to consume DO in some circumstances.(5)In conclusion,the sub-standard DO and TP index of Jiashan Tang-Feng Jing Tang is majorly due to domestic sources and sediment release.At the same time,the TP index is also affected by upstream runoff.