Dissolved Oxygen In Lowland Jiaxing Rivers

Dissolved oxygen (DO) is essential for aquatic organisms to live. When low dissolved oxygen levels occur, ecosystem can be impacted and the self-purification slows down and dominated organisms change from aerobic organisms to anaerobic organisms. Few studies on dissolved oxygen have been conducted in lowland rivers of China. We monitored and modeled the change of dissolved oxygen in Jiaxing rivers in order to provide some advises for river restoration.A field study was conducted to study the DO diel variation in Jiaxing urban rivers. By analyzing the diurnal oxygen variation, reaeration coefficients, the oxygen supplied by plants and the atmosphere, and the oxygen demand were calculated. The results showed that the DO levels in Jiaxing urban rivers were very low and primary productions were small while the oxygen demands were large. Comparing to different methods, DO balance methods resulted to reliable values of reaeration coefficient. In the study, the influx of rainwater was found to decrease both the DO concentration and the reduction of photosynthesis.Sediment oxygen demand (SOD) was measured by using both laboratory method and in situ method. In the experiments of SOD in Jiaxing rivers, high values of SOD were observed. It also found that SOD value of rivers after dredging were smaller than rivers before dredging. The in situ SOD experiment indicated that particle size of sediment and content of organic matter related to SOD while the liquid water content was weakly correlated.The value of reaeration coefficients and values of primary productions and sediment oxygen demand were used to build and calibrate QUAL2Kw model to research the DO in a Zhuqiaogang river. Sensitivity of some parameters was also discussed. Changing the max growth rate of bottom algae and reaeration coefficient would cause large disturbances in DO.A passage about the methods for rivers restoration was included in this thesis. It reviewed cases about different methods that people used to treat the polluted rivers at home and summarized the methods. It introduced the main features of these methods and their scope of application so it can be a useful reference for Jiaxing rivers restoration.