Study On The Growth Process Of Reservoir Ice Sheet And Its Influence On Water Quality

As the main water supply source in the northern cities,eutrophication is still one of the main environmental problems.The northern region is located in the middle and high latitudes,affected by geographical location and climate,there is a months-long ice-sealing process,which makes the reservoir relatively closed at this time,that is,the formation of ice-water-sediment multi-media pattern,directly changed the reservoir water nitrogen phosphorus migration process,and because of the limitations of the frozen environment,it is difficult to grasp the water quality state of the reservoir system at this time.The existing research has carried on beneficial exploration around the shallow lake,but the research on deep water reservoir is rare,which brings the hidden danger to the water supply safety of the reservoir in the frozen environment.Taking the Biliu river reservoir as an example,this paper makes a collated analysis of the basic data such as temperature and ice characteristics in the reservoir area,selects the ice-water interface as the main research process,clarifies the nitrogen migration process in the reservoir ice-blocking process,and lays a foundation for the water environment management and research in the frozen environment of the subsequent reservoir.The main research contents are as follows:(1)Collecting temperature data from 1986-2020 in the reservoir area for nearly 35 years,using the freezing method and heat flux method to estimate the number of freezing days and maximum ice thickness of the reservoir,and comprehensively using trend analysis and wavelet analysis to analyze the average temperature of the reservoir,the number of freezing days,the changing characteristics of ice thickness and periodic laws.The results show that the multi-year averages of the three time series are-4.1℃,115 days and 36.7cm.The sequence trend is down,down and up respectively.Mutation points were in 2003,2009 and 2008,respectively;The periodic changes are 9a,12 a and 13 a.The analysis suggests that in addition to the temperature,ice thickness may also be affected by other factors such as the number of days of freezing,the size of the wind and solar radiation.(2)Through the analysis and testing of the sub-ice water samples of the reservoir during the ice-sealed period,it is found that the concentration of pollutants in the surface water body under the ice of the reservoir is greater than that of the middle water body,which proves that there is a phenomenon of pollutant discharge during the growth of the ice sheet,and the total nitrogen(TN)is selected to carry out indoor simulation experiments for the research index,and the change of the TN content of the water body under different initial concentrations and different frozen volumes is explored.The experimental results were shown by scale comparison table,which provided reference for reservoirs to predict the concentration of pollutants in subglial water during ice-covered period.(3)Based on the scale comparison table of the predicted concentration obtained in the experimental part,the TN concentration of the water body after considering the nitrogen discharge effect is predicted,and the water quality data before and after the prediction are processed by SPSS,MATLAB and other software,and the water quality rating evaluation is carried out by variable fuzzy method.The evaluation results show that the nitrogen icing effect of ice will increase the concentration of reservoir surface water TN obviously and the water quality level decrease.After considering the nitrogen icing effect,the TN concentration of reservoir surface water increased by 1.64 times,while the corresponding water quality evaluation grade increased from 2.55 to 2.7,an increase of 6%.Then the nitrogen removal effect in the growth of ice sheet has an effect on reservoir surface water.