| To research the endogenous pollution intensity of the East Taihu Lake, we have investigated the characteristics of the distribution of P in East Taihu Lake sediment and observed the environmental factors, such as dissolved oxygen, water temperature and the flow, which could have an effect on the nitrogen, phosphorus release from sediment of the East Taihu Lake. Then we studied the effect of waterweed and eel grass on the purification of N and P in East Taihu Lake. The results showed that:Study on the characteristics of the distribution of phosphorus in East Taihu Lake sediment is test one.Using the chemical method of sequential extraction to extract different forms of phosphorus in sediments from East Lake, and then analyzed the spatial and vertical distribution characters of different forms of phosphorus in sediments from East Lake. The results showed that the forms of phosphorus in sediments of East Lake are mainly debris phosphorus (Ca-P), organic phosphorus (Or-P), authigenic P (De-P) and the average contents were 188.6,73.1,45.2g/kg; iron bounded phosphorus (Fe-P) followed with an average of 34.3g/kg; occluded P (Oc-P) and aluminum bounded phosphorus (Al-P) content was lower, which were 4.0,1.3g/kg. The aggregation of the average contents of different forms of phosphorus is 353.1g/kg. The four kinds of phosphorus, Ca-P, Or-P, De-P, Oc-P which can not easily release accounted for 88%, while the other three kinds, Fe-P, Ex-P, Al-P which are easy to release only accounted for 12%. Except the fact that the content of Ca-P increases with the increase of sediment depth, the content of Al-P was low and has no significant change with the increase of sediment depth, the content of other forms of phosphorus decreased approximately with the increase of depth, showing the phenomenon of "surface concentration". Effect of dissolved oxygen, water temperature and currents on the release of nitrogen and phosphorus from sediment of the East Taihu is test two.In different dissolved oxygen (DO) and water temperature conditions, the concentrations of nitrogen and phosphorus in the overlying water were increased linearly with time.When dissolved oxygen are 3.0,5.5,8.0mg/L respectively, the average release rate of nitrogen and phosphorus accordingly reached 443,239,153 and 33.2,17.8,12.1mg/(m2×d); when the water temperature were in 15,25 and 35℃, the average release rate of nitrogen and phosphorus respectively reached 81,169,301 and 8.7,15.8,19.3 mg/(m2 X d); when the flow rate was different, the concentrations of nitrogen and phosphorus in the overlying water would increase linearly with time at the beginning, then tended to balance after 120 hours; when the water flow at the rate of 0.02,0.04 and 0.08m/s, the average release rate of nitrogen and phosphorus were 45,78,161 and 1.8,7.5,16.8 mg/(m2 X d) in 96 hours.The effcet purification nitrogen and phosphorus of the Elodea in the water is test three.The rate of nitrogen and phosphorous in this experiment was 10:1. Study found that when N concentration were 0,2.5,5,10mg/L, Elodea grown faster in Spring and the growth rates were 157.2,185.7,139.0,76.2%, respectively; the average purification rates of N were-35.30,150.48,414.12,720.75mg/(kg-Day), respectively; and the average purification rates of P were-2.88,19.84,47.11,111.56mg/(kg-Day), respectively. The average purification rates of N and P of each group were significant higher with N concentration increased. During Summer, the growth rates were 145.3, 200.4,178.3,111.5%, respectively; the average purification rates of N were 9.21, 181.35,338.07,526.97mg/(kg·Day), respectively; and the average purification rates of P were 1.54,17.35,34.74,65.18mg/(kg·Day), respectively. The relationship between N concentration increased and the purification rates of N and P was the same as during spring. (The average purification rates of N and P of each group are also significant higher with N concentration increased.) During autumn, the average growth rates of each group were 97.4,78.6,99.9,71.9%, respectively; the average purification rates of N were-24.57,191.02,360.25,831.03mg/(kg·Day), respectively; and the average purification rates of P were 3.29,19.90,51.94,110.2mg/(kg-Day), respectively. Also, with the N concentration increased, the purification rates of N and P were significant higher (P<0.05). During winter the growth rates were 25.9,23.5,14.5,7.1%, respectively; the average purification rates of N were 3.77,26.38,77.10,134.96 mg/(kg·Day), respectively; and the average purification rates of P were-0.06,4.11,7.07, 13.69mg/(kg·Day), respectively. The purification rates of N and P of each group were still higher with the increasement of N concentration.The effcet purification nitrogen and phosphorus of the Vallisneria natans in the water is test four.The rate of nitrogen and phosphorous in this experiment was 10:1. Study found that when N concentration were 0,2.5,5, 10mg/L, Vallisneria natans grown faster in Spring and the growth rates were 110.8,144.1,34.9,39.4%, respectively; the average purification rates of N were -19.3,136.89,262.11,358.41mg/(kg·Day), respectively; and the average purification rates of P were 0.19,11.92,28.56,51.34 mg/(kg·Day), respectively. The purification rates of N and P of each group were significant higher with N concentration increased (P<0.05). During Summer, the growth rates were 146.3,145.3,136.4,60.7%, respectively; the average purification rates of N were 8.73,86.17,156.04,223.97mg/(kg·Day), respectively; and the average purification rates of P were 0.01,9.77,20.88,47.7mg/(kg·Day), respectively. The relationship between N concentration increased and the purification rates of N and P was the same as during spring. The average purification rates of N and P of each group are also significant higher with N concentration increased (P<0.05). During autumn, the average growth rates of each group were 62.8,73.6,71.4,64.6%, respectively; the average purification rates of N were 1.09,65.00,117.14,223.47mg/(kg·Day), respectively; and the average purification rates of P were 0.88,8.14,17.56,46.44mg/(kg·Day), respectively. Also, with the N concentration increased, the purification rates of N and P were significant higher (P<0.05). During winter Vallisneria natans started and gradually death, the growth rates were -13.0,-14.9,-20.8,-28.2%, respectively; the average purification rates of N were 1.39,38.5,62.15,68.81mg/(kg·Day), respectively; and the average purification rates of P were 0.85,6.26,12.54,18.72mg/(kg·Day), respectively. The purification rates of N and P of each group were still higher with the increasement of N concentration. As a result, the content of internal phosphorus in East Lake is low.In static conditions, the water temperature is 15℃, the endogenous N, P release of East Lake which is 130km2 approximately reached 3827,441.7t.To prevent endogenous pollution caused by N and P of sediment releasing from happening, the biomass of Elodea which are 0.4-0.5,0.8-0.9,0.7-0.9,2.1-3.1kg/m2 respectively from spring to winter is suggested, the biomass of Vallisneria natans which are 0.6-0.7,1.8-2.6,1.5-2.0, 1.8-2.6kg/m2 respectively from spring to winter is suggested. |
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