The Research Of River Evaluation And Eutrophication Drived By Its Sediment In Wenzhou

Compared with the urban construction and the population expansion, the environmental infrastructure is seriously lagging behind, so most of the sewage has been discharged into the river directly without any collection and treatment, which polluted river severely. Considering the local situation, many cities have taken a series of measures to control pollution and improve the water quality. However, due to long time and complex pollution, accumulation of sediment load is becoming more and more serious, from "source" to "sink". When the overlying water gets better, sediments will start to release nitrogen and phosphorus to overlying water to cause endogenous pollution. Thus, it is important to predict eutrophication and other secondary disasters according to the characteristics of overlying water and release law of nitrogen and phosphorus in sediments.This research took two rivers, Shanxia and Jiushanwai River, Wenzhou, as examples. The objective of this study was to assess water quality of overlying water in these rivers from April,2013 to March,2014, and to analyse physicochemical property and adsorption or release rule of orthophosphate and ammonia nitrogen in sediments in January, May, July, and October,2013. Taking fresh sediments in July, 2013 as an example, AGP experiment was conducted to study effector mechanism of eutrophication drived by sediments. The goal of this study was to provide reference for water environmental government and control of secondary disaster.(1) According to four methods of water quality assessment, both rivers were polluted. Shanxia River was seriously polluted and Jiushanwai was mild polluted. This demonstrates that control of exogenous pollution is not enough, and operation of clarifying facility is abnormal.(2) SMT was adopted to analyse TP, IP(Fe/Al-P, Ca-P) and OP in sediments. The quantity of TP in Shanxia River ranged from 1.36 g/kg to 2.73g/kg, where January was the highest, followed by May, October and July. The quantity of TP in Jiushanwai River ranged from 0.69 g/kg to 1.14 g/kg, where January was the highest, followed by May, October and July. TP contained more Fe/Al-P, less OP. The mean quantity of OM, TN and NH4+-N was 95.70g/kg,3.63 g/kg and 2.33 g/kg in Shanxia River, and 34.70 g/kg,0.49 g/kg, and 0.23 g/kg in Jiushanwai River.(3) In the setting of initial phosphorus concentration range, the sediments adsorbing phosphate and phosphorus in both rivers had a good linear relationship with 1/Q= (1/KLQmax) in Freundlich isotherm model and Langmuird each month. Moreover, they showed a significant correlation with organic matter and different forms of phosphorus content in the sediments. When the initial concentration was constant, phosphate and phosphorus in sediments released increasingly with increase of oscillating time, and then tended to be stable in 24h.(4) By linear regression, the thermodynamic process of sediments adsorbing ammonia were consistent with Henry and Langmuir models in both rivers. With initial ammonia concentration increasing, the adsorption rate had no obvious change. In addition, when the temperature and initial concentration were constant, adsorption or release kept stable.(5)The ammonia nitrogen of interstitial water was primary in sediments of both rivers, which accounted for 90% of TN. In Shanxia River, the highest quantity was 51.23 mg/L in January 2013, and in Jiushanwai River, it was 29.01 mg/L in May 2013. The nitrate nitrogen and nitrite nitrogen were lower than ammonia nitrogen. The sediments adsorbing or releasing nitrogen and phosphorus reached equilibrium in 20h generally. The higher the value of nitrogen and phosphorus was in sediments, the more the release was.(6) Under suitable conditions of light and temperature, the growth of chlorella increased more when nitrogen and phosphorus released more from sediments to overlying water. When there were no extra nutrients, the adjustment period of chlorella was 1 day. It went to logarithmic growth period quickly (3 days) and then to stable period and death period successively. The whole process lasted 8 to 10 days totally.(7) It’s necessary to dredging for polluted river in cities, when in project management. After treatment, we had better insist scientific management on avoiding eutrophication problems of secondary disasters.