Study On The Distribution Characteristics Of Sediment Pollution In The North Canal And The Influence Of Reclaimed Water On The Release Of Endogenous Pollution

With the increasingly serious water pollution problem,the endogenous pollution caused by the release of pollutants in the sediments has received widespread attention.Various pollutants in the sediment enter the overlying water through physical,chemical and biological effects,posing a serious threat to the water environment.This research takes the North Canal of the Haihe River System as the research object.Through the study of the distribution characteristics of sediment pollution and the release regularity of endogenous pollution,at the same time,according to the characteristics of the North Canal's own unconventional water source replenishment,the impact of reclaimed water replenishment on the release of endogenous pollution is studied.Lay a theoretical foundation for the water environment management of the North Canal and provide new ideas for the control of endogenous pollution.The main conclusions of this study are as follows:(1)The concentration of phosphorus nutrients in the overlying water of the main stream of the North Canal during the flood season and the non-flood season has little difference.The concentration of NH₄⁺-N in the flood season is higher than that in the non-flood season,while the concentrations of NO₃^--N and TN are higher in the non-flood season.Along the main stream,the concentration of nitrogen and phosphorus in the overlying water of the Shahe Reservoir in the source area of the North Canal is relatively higher,and the concentration in the midstream and downstream has decreased.The characteristics of the temporal and spatial distribution of nutrient pollution in sediments are as follows:the degree of nutrient pollution in non-flood season is higher than that in flood season;in the horizontal direction,the total nitrogen(TN)content is higher in the upstream,gradually decreased in the midstream and downstream,and the most downstream content has increased,and the total phosphorus(TP)content gradually decreases along the main stream.In the vertical direction,the nutrient content gradually decreases or remains stable with the increase of depth.At some sampling points,the content first increases and then decreases with the increase of depth.(2)The dissolved organic matter in the sediment interstitial water of the North Canal is mainly proteinaceous substances such as tyrosine,tryptophan,and soluble microbial metabolites.The main source of dissolved organic matter is the new authigenic source,which is produced by biological metabolism.Correlation analysis shows that there is a significant positive correlation between most of the fluorescent components,with similar sources,and there is also a certain correlation between nutrients and organic matter.(3)The average content of Zn,Cr,Cu,and Pb in the surface sediments exceeds the Beijing soil background value.In the horizontal direction,the most serious heavy metal pollution in sediments is the core area of the Shahe Reservoir;in the vertical direction,the pollution status is upper layer>lower layer>middle layer.Based on the evaluation of the geo-accumulation index and the potential ecological risk index,Zn in the sediments is moderately polluted,Cr and Cu are lightly polluted,all sampling points are mild ecological hazards,and heavy metals mainly exist in the speciation of residues.(4)In the Shahe Reservoir in the source area of the North Canal,the NH₄⁺-N release rate of was 233.73 mg/(m²·d),and the release rate of PO₄^3--P was 6.64 mg/(m²·d).Simulation experiment results show that a neutral p H and maintaining aerobic conditions can reduce the release rate of sediment nutrients.Reclaimed water has a certain inhibitory effect on the release of TP and TOC in the sediment.In view of the characteristics of the North Canal that reclaimed water is mainly used as supplementary water,reasonable use of the input of reclaimed water can inhibit the release of phosphorus in river sediments.