Study On Change Characteristics And Metabolic Rate Of Dissolved Oxygen In Lakes Ice-Covered Period

The ice-covered period refers to the period from when the rivers and lakes are completely covered by the ice cap to the time when the ice cap melts and the water surface is exposed.The gas exchange between lakes and the atmosphere during the glacial period was hindered by ice sheets,which had a huge impact on the lake environment,resulting in a decrease in the dissolved oxygen(DO)content and deterioration of water quality in the lake.In order to explore the change characteristics and influencing factors of dissolved oxygen and metabolic rate in lakes during the ice-covered period,In this study,high-frequency dissolved oxygen meter and environmental photometer were used to monitor the dissolved oxygen,water temperature and photosynthetically active radiation(PAR)at different depths in typical seasonal frozen shallow lakes.Combined with the results of water quality testing,redundancy analysis and Pearson correlation analysis were used.To explore the relationship and influencing factors of dissolved oxygen and environmental factors in lakes during ice-covered and non-ice-covered periods.In addition,this study also improved the calculation method of the lake’s daily metabolic rate,estimated the lake’s metabolic rate during the ice-covered period,analyzed the main factors affecting the lake’s metabolic rate during the ice-covered period,and finally compared different lakes at the same latitude during the ice-covered period.Dissolved oxygen change characteristics,explore the reasons for the lack of oxygen in the lake during the ice-covered period,and design an indoor experiment to test.The object of this study is the Daihai ice-covered period in 2021,the results showed that the dissolved oxygen was in a supersaturated state during the Daihai ice-covered period,with an average value of 15.49 mg/L.The results of water quality testing showed that the water in the Daihai Lake was in a state of mild eutrophication.Compared with the non-freezing period,the concentrations of total nitrogen,p H,and soluble phosphorus in the Daihai Lake waters all increased further,while the concentrations of total dissolved solids(TDS)and chlorophyll a decreased,and the electrical conductivity and salinity did not change significantly.The dissolved oxygen in Daihai Lake experienced diurnal changes and stratification during January 10,2021 to March 11,2021.The dissolved oxygen change curve shows a gradual increase first(January 10,2021 to February 5,2021),Then keep it stable(February6,2021 to March 1,2021),Entering the ablation period(March 2,2021 to March 11,2021),the regularity of the disappearance of the delamination phenomenon.Vertically,the water temperature shows a transition from a uniformly mixed state(January 10,2021 to February5,2021)to a stratified state(February 6,2021 to March 11,2021).The average values of total primary productivity,net primary productivity and ecosystem respiration rate were 0.21 mg/L·d,0.11 mg/L·d and 0.10 mg/L·d,respectively,during the Daihai Lake ice-covered period,and the metabolic rate was at a low level.Water temperature and snow cover have a significant effect on metabolic rate: increased water temperature leads to increased respiration,which affects the accumulation of oxygen;Snow cover affects metabolic rates by affecting subglacial light and effective radiation.Statistical analysis shows that water temperature,photosynthetically active radiation(PAR),total nitrogen and p H have obvious effects on the dissolved oxygen concentration in Daihai Lake during the ice-covered period.By comparing the changes of dissolved oxygen in the Daihai Lake and the Wuliangsuhai Lake during the ice-covered period,we found that background conditions such as snowfall,water depth,particulate organic matter(POM)concentration,and heat flux at the water-sediment interface would have an impact on the change trend of dissolved oxygen.Through the indoor simulation test,the study found that the p H and nutrient salt concentration of water body with different dissolved oxygen concentration are different in low temperature environment;The decomposition of particulate organic matter is the main factor for the oxygen consumption of the Daihai Lake during the ice-covered period,and the possibility of hypoxia in the Daihai Lake during the ice-covered period is low.