Statistical Study On The Variation Of Water Temperature And Dissolved Oxygen Concentration In High Latitude Lakes During Ice-free Period

Lake water temperature is an important condition for the rationalization process of various dynamic phenomena of lake water,It is one of the most important survival factors in the lake biological field,Dissolved Oxygen(DO)is the oxygen in which the water body is dissolved in the molecular state after exchange with atmospheric oxygen or chemical and biochemical reactions.Dissolved oxygen(DO)is the molecular state of water dissolved in water after exchange of oxygen with atmosphere or chemical and biochemical reactions.There are many factors that affect the concentration of dissolved oxygen.It is found that the atmospheric pressure,gaseous oxygen in the atmosphere,photosynthesis and temperature of aquatic plants have great influence on the concentration of dissolved oxygen.The change of dissolved oxygen is very complicated.This paper is mainly based on the field observation data of water temperature and dissolved oxygen concentration in different water layers of Valkea-Kotinen Lake from 1990 to 2017,provided by Rami Biological Station,University of Helsinki,Finland.The variation trend of water temperature and dissolved oxygen concentration in the lake in recent decades were studied.Firstly,this paper selects the field observation data of different depth water temperature of Valkea-Kotinen Lake from 1990 to 2017,and calculates the Kendall rank correlation test statistic for the time series analysis of the highest water temperature in the past year and the average water temperature of each month in each month.The results of test and analysis show that the water temperature below the surface layer of the lake has not decreased significantly in the past28 years,but the water temperature in the surface layer(0m~1m)and in May and October of the lake generally showed an upward trend.The results are in good agreement with the observed data of the days of ice-free period of lake water in the past years.Secondly,the field observation data of dissolved oxygen concentration in the ice-free period from 1990 to 2017 of the lake are selected and the Spearman rank correlation test is used to test and analyze the two time series of the mean dissolved oxygen concentration and the corresponding temperature average of the different water layers in the lake in the past years.It is concluded that there is a significant negative correlation between the dissolved oxygen concentration in the surface layer of the lake(0m~1m)and the temperature in the surface layer,but there is no significant positive correlation between the concentration of dissolved oxygen in the subsurface layer(2m~5m)and the temperature.Finally,the maximum and minimum values of dissolved oxygen concentration in different aquifers of the lake during the calendar years are fitted to the date of observation from 1990 to2017(the number of days starting on the first day of the year).The curve of the maximum and minimum dissolved oxygen concentration in different water layers of 0m~5m depends on the time(days),and the variation rule of dissolved oxygen concentration in different water layers of Valkea-Kotinen Lake during the ice-free period of Valkea-Kotinen Lake is obtained by fitting the curves of the maximum and minimum values of dissolved oxygen concentration in different water layers.It has important reference value for the aquaculture industry such as frozen lake,pond and so on in the north of China.