Research On The Migration And Transformation Mcchanism Of Nitrogen And Phosphorus In Water And Sediment Of A Sea-going River

Research and exploration on the migration and transformation mechanism of nitrogen and phosphorus have significant meaning to the realization of the removal of nitrogen and phosphorus.This paper searched the Duliujian River of Tianjin,collected water and sediment samples,analyzed the temporal and spatial distribution of nitrogen and phosphorus,studied the effects of water environmental factors and sedimentary physical properties on the spatial and temporal distribution pattern of nitrogen and phosphorus,and described the migration and transformation between nitrogen and phosphorus in water and sediment by correlation analysis(CA).On this basis,the mechanism of nitrogen and phosphorus migration and transformation is discussed.The results show that:(1)The phosphorus of river entering the sea had a downward trend along the river direction.The removal rates of phosphorus in the total phosphorus(TPw)of the four seasons were 76.28%,82.81%,32.37%and 22.53%,respectively.Hence,the removal effect of phosphorus in spring and summer were better.Phosphorus was mainly dissolved in summer and autumn,and granular in spring and winter.Among them,dissolved phosphorus was mainly composed of active phosphate(SRP)in summer,autumn and winter.TPw and phosphorus have significant differences on time and space scales:TPw,total dissolved phosphorus(TDP)and particulate phosphorus(PP)had significant spatial variation characteristics;the time variation of TPw and various forms of phosphorus on time scale was very significant.CA results showed water temperature(WT),conductivity(C),salinity(SAL),turbidity(TUR),pH,redox potential(Eh),chlorophyll(Chl-a)and water Total calcium(Ca)had significant effects on phosphorus form and phosphorus migration and transformation in water.(2)The content of total phosphorus(TP)in sediments ranged from 460.35 to 1148.19 mg/kg in the four seasons.Phosphorus was mainly composed of inorganic phosphorus.which commonly consisted of Ca-P.The order of phosphorus content was Ca-P>Org-P>Al-P>Ex-P>Fe-P,BD-FePO4,BD-AIPO4.The spatial variation of phosphorus in sediments on the time and spatial scale were very significantt.On the time scale.Ex-P,Al-P,BD-FePO4 and BD-AIPO4 were significantly affected by time variation,on the spatial scale,except Fe-P,TP and other forms of phosphorus were significantly affected by time variation.CA results showed that WT,C,SAL,Ca,TUR,pH and Eh and sediment organic matter(OM),cation exchange capacity(CEC),total iron(Fet),total aluminum(Alt),total zinc(Znt),total manganese(Mnt),active aluminum(Alac),active calcium(Caac),active iron(Feac)and sediment particle size had significant effects on sediment phosphorus form and phosphorus migration and transformation.(3)The removal effect of nitrogen in water was not obvious,and the nitrogen content of the whole river remained high.Total nitrogen(TNw),total dissolved nitrogen(TDN)and nitrate nitrogen(NO3--N)in water were not affected by spatial changes,while ammonia nitrogen(NH4+-N)varies spatially.In addition,the temporal variations of various forms of nitrogen in water were significant on time scale.Nitrogen in water mainly existed in the dissolved state,with TDN accounting for 70.54%of TNw and NH4+-N as the main dissolved inorganic nitrogen,accounting for 15.97%of TDN.The results of CA showed that WT,C,SAL,Ca,pH,DO,Eh and Chl-a had significant effects on nitrogen migration and transformation.(4)The content of total nitrogen(TN)in sediments ranged from 192.89?3774.00 mg/kg in the four seasons.Most of the sites were polluted by nitrogen.On the whole,the TN content in the upper and middle reaches fluctuated up and down,while in the lower reaches showed a relatively gentle distribution trend.The content of exchangeable total nitrogen(ETN)was very low,ranging from 4.84 mg/kg to 120.77 mg/kg in four seasons,accounting for 3.20%of TN.Among them,exchangeable ammonia nitrogen(ENH4+-N)was the main form of exchangeable nitrogen,accounting for 60.04%of the average content of ETN.The exchangeable state of nitrate nitrogen(ENO3--N)and exchangeable organic nitrogen(EON)were extremely low.TN and ETN varied significantly on a spatial scale;TN.ETN.ENH4+-N,and ENO3--N varied significantly on a time scale.The results of CA showed that C,SAL.Ca,pH,Chl-a.OM,CEC,Fet,Alt,Znt,Feac and Caac had significant effects on sediment nitrogen migration and transformation.(5)The results showed that TPw.TDP and SRP in water were related to Al-P and BD-FePO4 in sediments.Phosphorus in water and sediments mainly migrates and transforms through SRP in dissolved phosphorus,The water body TDN and the sediment TN,the water body TNw and TDN,the sediment ETN,ENH4+-N had a mutual transformation relationship,and the water and sediment nitrogen were mainly TDN and ENH4+-N for migration and transformation.This study revealed the distribution characteristics and migration and transformation of nitrogen and phosphorus in the waters and sediments of rivers entering the sea,and provided theoretical basis and data support for the ecological engineering construction and eutrophication of the rivers.