Distribution Characteristics Of Phosphorus Forms And Its Ecological Risk Assessment In Sediments In The Zhanghe River Upstream

The construction of water conservancy projects and human activities in the Zhanghe River Upstream have changed the water environment and water ecology of the Zhanghe River Basin,and affected the sediment of river and biological material cycle process.In order to reveal the distribution characteristics and influencing factors of phosphorus(P)and its forms in sediments disturbed by human activities.This study took the Zhanghe River Upstream as the research object and systematically studied the occurrence forms of P in the surface sediments of the Zhanghe River Upstream:loosely sorbed P(Ex-P),reductant-soluble P(BD-P),metal oxide-bound P(NaOH-P)and calcium-bound phosphorus(HCl-P),analyzed the main factors affecting the P forms in the sediments,and explored the sediments by assessing the pollution risk and release risk of P.The ecological risk of P,the research results can be used to reflect the impact of strong human activities on the cycle in the Zhanghe River Upstream,so as to provide a scientific basis for the management of the water environment in the Zhanghe River Upstream.The main research conclusions are as follows:(1)The sediment particles at the source of the Zhanghe River Upstream were mainly silt,while the sedim2ents in the main stream were mainly sandy;the total phosphorus(TP)content in the sediments showed that Qingzhang River>Zhuozhang River>Zhang River.The main stream of the river,and the overall trend of decreasing distribution from the source to the main stream of the Zhanghe River.The geological conditions at the source and human activities in the main stream were the reasons for the higher TP content;the spatial variation of iron(Fe),aluminum(Al)and manganese(Mn)in the sediments is similar,while the Zhuozhang River Basin was due to industrial pollution.As a result,the metal content of the Zhuozhang River was greater than that of the Qingzhang River;the total nitrogen(N)content of the Zhuozhang River was higher than that of the Qingzhang River,while the total carbon(C)content and C/N was lower than those of the Qingzhang River.(2)Except for the content of NaOH-P,which showed that Zhuozhang River>main stream of Zhanghe River>Qingzhang River,the content of other P forms showed the content of Qingzhang River>Zhuozhang River>the main Zhanghe River.Only the HClP content from the west source of Qingzhang to the main stream of the Zhanghe River and the BD-P content from the west source of Qingzhang and Zhuozhang to the main stream of the Zhanghe River did not increase significantly,and the content of other phosphorus forms decreased from the source to the main stream.(3)In the sediments of the Zhanghe River Upstream,only NaOH-P was significantly related to fine particles.The P content in the Zhanghe River Upstream was greatly affected by human input,thus concealing the effect of particle size;the total amount of extracted metal and the phosphorus form.The correlations between them were not significant;TP and N in the sediments are significantly positively correlated,indicating that the N-P deposition in the sediments was synchronized.C,N,Ex-P and NaOH-P were all significantly positively correlated,indicating that C and N were simultaneously deposited in the active state of P,and P was released along with C mineralization;BD-P and NaOH-P were the main source of TP,and there was a certain transformation relationship between Ex-P and HCl-P.(4)The content of TP in the surface sediments of the Zhanghe River Upstream was equivalent to that of Dongting Lake and Poyang Lake,but lower than that of sediments in other parts of China.Only the average PEI of the main stream of the Zhanghe River after the merge was less than 1.The percentage of BAP/TP in the sediments ranged from 38.36%to 52.04%,and the risk of BAP being released from the surface sediments was higher.NaOH-P was significantly positively correlated with BD-P and BAP,indicating that NaOH-P and BD-P were important factors that control the potential release of BAP in the surface sediments of the study area.(5)The EPC0 values of the sediments in the Zhanghe River Upstream presented the Zhuozhang River>Qingzhang River>main stream of the Zhanghe River.The distribution of the EPC0 values were significantly related to the composition of fine particles in the sediments,and the fine particles in the sediments would absorb higher P content.There is a significant correlation between Qmax and TP in the sediments,and the pollution of the Zhanghe River Upstream leads to serious human disturbance of Qmax in the sediments.(6)The Zhanghe River Upstream basin had high phosphorus load and high pollution potential,which highlighted the importance and urgency of treating phosphorus pollution in Zhanghe River Upstream.The analysis of the sediment P enrichment index showed that the Qingzhang River should have a higher priority than the Zhuozhang River in the prevention and control of eutrophication risks;The Zhuozhang River should control the discharge of point and non-point sources from industry and agriculture.