Distribution Of Phosphorus Forms In The Minjiang River And Tuojiang River

Phosphorus?P?,as a limiting factor and vital nutrient in freshwaters,was mainly transported by rivers.In this study,the spatial characteristics of the total phosphorus?TP?pollution in the Yangtze River Basin were investigated.The most significant phosphorus sources were explored in the Minjiang River and Tuojiang River,which were the upper reaches of the Yangtze River Basin.The distribution of phosphorus forms in water-suspended particulate matter-sediment posed a significant effect on freshwater ecological environment.In order to analyze the form component and spatial distribution of phosphorus in water and phosphorus forms in suspended and sediments solids,thirty surface water samples,and 14 suspended and sediments were collected in the main stream and tributary of the Minjiang River.While,twenty-eight surface water samples,and 15 suspended and sediments were collected in the main stream and tributary of the Tuojiang River.The potential risk of phosphorus release was determined by the ratio of bioavailable phosphorus?BAP?and calcium binding phosphorus(P_Ca)in suspended solids.The phosphorus forms composition and potential characteristics of phosphogypsum release were studied.The main results were as follows:?1?The average concentration of TP in the water of Minjiang nd Tuojiang River were 0.20 mg/L and 0.30 mg/L respectively,which indicated the total phosphorus pollution of Tuojiang River was relatively heavy.The main phosphorus forms in water of the Minjiang and Tuojiang River were total dissolved phosphorous?TDP?,and most of TDP exist in the form of phosphate PO₄^3-.The proportion of total particulated phosphorus?TPP?in the water body was occupied more than 20%.TP concentrations in water at the Meishan to Leshan sections?the middle reach of the Minjiang River?and the Deyang to Ziyang sections?the middle reach of the Tuojiang River?were higher than that in the other sections.Most of the tributaries of the Minjiang River?such as Jinniu River,etc.?flowed through the urban area in Meishan.The pollution sources were relatively concentrated.TDP concentration in the water accounted for more than 85%of TP concentration in the tributaries.The large amount of phosphorus containing sewage flowed into the river causing TDP and PO₄^3-rise.However,there were some large phosphate mines in Leshan.Thus,and the proportion of TPP in the water body of Mabian River?the tributary of Minjiang River?occupied more than 80%.The combination of water phase phosphorus and organic particles in Leshan has led to the increase of TPP.Meanwhile,the proportion of TPP in the tributary water of Tuojiang River is more than50%,and the average proportion of the TPP is rising in the downstream.?2?The average concentration of TP in suspended matter of Minjiang and Tuojiang River was 1571.80?g/g and 1946.39?g/g respectively.Inorganic phosphorus?IP?was the main content in particulate matter.Among them,iron-bound phosphorus?Fe-P?,authigenic phosphorus?Ca-P?,and detrital phosphorus?De-P?are the main components of IP,and organic phosphorus?OP?is the main component of exchangeable organic phosphorus?Org-P?.The BAP contents in Tuojiang River were relatively heavy,the main bioavailable phosphorus forms were Fe-P and Org-P.In addition,the values of??BAP?/?(P_Ca)in sites were higher than 0.5 indicating that it has a severe potential risk that can causing eutrophication.?3?The results indicated that the contents of total phosphorus?TP?in surface sediments of Minjiang and Tuojiang River ranged from 522.17?g/g to 979.22?g/g,and838.20?g/g to 1687.55?g/g,respectively.The particles in the surface sediments of the river water system were mainly composed of coarse grains such as sand grains,which were beneficial to the enrichment of self-generated apatite phosphorous Ca-P and clast phosphor De-P in IP.The concentration of organic phosphorus in sediments were low and mainly in the form of Ca-P and De-P.The BAP in the sediments of Minjiang River was concentrated in meishan and Leshan areas.The BAP content was high in the middle and lower reaches of Tuojiang River to Luzhou.The high concentration of phosphate in the water bodies of Minjiang and Tuojiang River were due to the high concentration of Org-P and Fe-P in the suspended solids and sediments.?4?The maximum release rate of phosphorus in phosphogypsum was 3.52 mg/?g·h?,and the Q_max was 2.30 mg/?g·h?under this experimental condition.The TP content of phosphorus gypsum was 3.70 mg/g,and the release of phosphorus gypsum was mainly carried out by EX-P,Org-P and Fe-P.Among them,EX-P and Fe-P accounted for a large proportion.Acidic or alkaline water environment was conducive to the release of phosphate.Acid rain had an effect on phosphorus loss.At the same time,since the water system itself was weak alkaline,it facilitated the release of phosphorus gypsum as well.In general,the release of phosphate had a weak sensitivity to water salinity.However,it had a strong sensitivity to the changes of water phase temperature.