Study On Vertical Distribution Regularity Of Phosphorus In The Middle Reaches Of The Changjiang River At Wuhan

Phosphorus is an essential element for the growth and reproduction of aquatic organisms in river.The continuity of its transport plays an irreplaceable role in maintaining the health and stability of watershed ecosystems.The phosphorus in water body with sediment in the middle reaches of the Changjiang River is mostly in the form of particulate phosphorus,and has the characteristics of vertical distribution inhomogeneity.The construction of large reservoirs in the upper reaches of the Changjiang Riverhas intercepted a large amount of sediment,resulting in the decrease of the suspended sediment in the middle reaches,changing the vertical distributionof suspended sediment concentration.The vertical distribution of particulate phosphorus which is closely related to the suspended sediment has also changed,which has an effect on the habitat of aquatic organisms in the middle reaches of the Yangtze River.As a large river,the Changjiang River's cross section is very large,which makes the suspended sediment concentration and phosphorus concentration different from the surface to the bottom.Therefore,it is necessary to carry out research on the vertical distribution of phosphorus concentration in river,and further study the calculation method of river phosphorus flux,forproviding scientific basis for accurately understanding the impact of reservoir engineering on river nutrient transport.In this paper,the phosphorus distribution in sandiness water of the middle typical river reaches of the Changjiang River is studied.The vertical distribution characteristic of the phosphorus is studied through field investigation.The vertical distribution formula of suspended sediment in the middle reaches of the Changjiang River is selected,and the vertical distribution model of particulate phosphorus and total phosphorus concentration in sandy water was established,by introducing the quantitative relationship between the concentration of particulate phosphorus and suspended sediment,.The calculation method of phosphorus flux was established according to the vertical distribution of the total phosphorus concentration.The main conclusions of this paper are as follows:(1)According to the analyses of the survey data of the suspended sediment at Wuhan section in the middle reaches of the Changjiang River,the suspended sediment concentration and particlesize in Wuhan section increase along with the increase of water depth both at the wet period and normal period.The vertical increase of suspended sediment concentration is from 3.93% to 52.6%,and the vertical increase of suspended sediment particle size is from 3.6%to 13.06%.(2)According to the survey data of phosphorus at Wuhan section in the middle reaches of the Changjiang River,the total phosphorus and particulate phosphorus in Wuhan section are increasing from the surface to the bottom,and the dissolved phosphorus is evenlydistributed in the vertical direction.The concentration of total phosphorus in Wuhan section is from 0.071 to 0.223mg/L,and the vertical increase is from 6.5% to 82.9%;the concentration of phosphorus is from 0.031 to 0.178 mg / L,and the vertical increase is from 4.1% to85.5%;the dissolved phosphorus concentration is from 0.021 to 0.128 mg / L,and the vertical distribution is uniform.(3)The vertical distribution model of suspended sediment in the middle reaches of the Changjiang Riveradopts Rouse's formula.Based on the measured data of suspended sediment in Wuhan section,the average value of the determination coefficient of this model formula is 0.945,and the fitting precision is high.(4)Based on Langmuir adsorption isotherm,the quantitative relationship between grain phosphorus and sediment concentration is obtained by using the measured values of particulate phosphorus and sediment concentration in Wuhan section,and combined with the above suspended sediment model,the vertical distribution model of the particulate phosphorus and total phosphorus in the middle reaches of the Changjiang River is deduced.The relative error between the calculated value and the measured data is 1.4%-25.1% and the accuracy is relatively high.(5)Based on the vertical distribution model of total phosphorus,the formula of phosphorus flux calculation model for sandy water in the middle reaches of the Changjiang River is deduced.The relative error between the formula and the measured value is 0.3%-11.1%,and the phosphorus flux calculation accuracy is high.