| In order to research on the seasonal variations of water stratification and water quality responses in canyon-shaped stratified reservoirs,some water quality index of Jinpen reservoir including water temperature,dissolved oxygen,chlorophyll a,nitrogen and phosphorus were investigated through continuous on-site monitoring.And the influence of the water-lifting aerators on hypolimnetic oxygen demand and the connection conditions of artificial forced mixing and natural mixing were researched.Meanwhile,a three-dimensional water quality model of DO/CODMn of the Jinpen reservoir was established using MIKE3 simulation software.The main results and conclusions of this study are as follows:?1?Heihe Jinpen reservoir is a typical stratified source reservoir.From April to September,the water body was thermal stratification,and the boundaries between thermocline and hypolimnion were obvious.During the stable period of thermal stratification,the vertical dissolved oxygen also showed“oxygen stratification”,and the bottom anaerobic region reached 13.82 m in maximum,while the anoxic region also reached 19.63 m.The prolonged anaerobic environment led to the release of nutrients from the bottom sediment,and the total nitrogen as well as total phosphorus increased to1.55 mg/L and 0.042 mg/L,respectively.?2?According to the cluster analysis of the density gradient of the Jinpen reservoir,the results indicated that the vertical water body density gradient of 0.02 kg/m3 is the most representative index of the thermocline position of the water body.According to the results,the trend of designing HOD?hypolimnetic oxygen demand?during the three-year operation was not obvious.However,the average HOD had a significant decrease from2722.1752 kg/d to 1316.2997 kg/d,which showed that the long-term operation of the Water-Lifting Aerators system could reduce the average HOD,thereby reducing the amount of oxygen needed to be provided during the manual forced mixing period.?3?Based on the comparative analysis of variations of water temperature as well as dissolved oxygen during the artificial forced mixing period of reservoirs in the past three years,the results showed that when the artificial forced mixing was finished,the depth of the thermocline was still at a higher position,which could affect the natural mixing,and the thermocline would hinder the oxygen transformation in the bottom water body.At the same time,the dissolved oxygen supplemented by the previous system would be quickly consumed and hypolimnion would be re-entered into the hypoxic state.Therefore,to obtain an optimal joint,the thermocline depth should be controlled to the bottom layer.?4?Based on MIKE3 software,the DO/CODMn model of Jinpen reservoir was established.The average relative error of DO and CODMn measured was 7%and 9.82%,respectively.The results showed the large differences of the parameters under different water depth conditions as well as the good consistency between the total sensitivity and the first-order sensitivity.Also,the temperature-related parameters should be prioritized due to the significant effect on DO/CODMn in surface waters.During the study,with the increase of water depth,the influence of temperature was gradually weakened,and the first-order degradation rate?K2?of permanganate was the largest contribution parameter.?5?By Application of simulation to research oxygenation process and oxygenation capacity of water-lifting aerators system,having a superior oxygenation effect on the bottom water body,and ending the anoxic phenomenon caused by thermal stratification of water body about 17 days ahead of schedule.The operation of the system can greatly increase the dissolved oxygen in the bottom layer,and the water in the middle and upper layers can also increase by about 10%to 30%.Its forced mixing and oxygenation function can effectively improve the dissolved oxygen in the water,inhibit the release of endogenous pollutants,and improve or maintain water quality. |
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