Study On Dynamic Variation Characteristics And Law Of Dissolved Oxygen Concentration In Wuliangsuhai Lake

Dissolved oxygen plays a key role in the biochemical cycle of surface water and is a sensitive index for changes in biochemical conditions of lake and reservoir water ecosystem.Taking Wuliangsuhai as the study area,this study analyzed the dynamic characteristics of dissolved oxygen concentration in the water of Wuliangsuhai from 2015 to 2020 on the basis of field investigation,monitoring and laboratory experiment analysis,so as to understand the spatial pattern and vertical change characteristics of dissolved oxygen.At the same time,based on the wavelet changes,the relationship between water temperature and dissolved oxygen concentration under the ice in January 2019 was explored to predict the change trend of dissolved oxygen concentration in the water,and the following conclusions were drawn:1.The annual variation of dissolved oxygen in the Wuliangsu seawater has a certain pattern,showing a"U"-shaped pattern.When the water temperature is in the range of 22.1-24.8°C,the dissolved oxygen concentration value is small;if it is within-0.21-6.34°C,the dissolved oxygen concentration increases.When the water temperature gradually decreases,the dissolved oxygen value gradually increases and reaches its maximum value in November each year.Divided by season,the dissolved oxygen concentration in 2015-2020 is basically the largest in winter,followed by autumn.2.Dissolved oxygen in water has a significant correlation with TN,TP,p H,conductivity,ORP,etc.in different seasons and water depths.Dissolved oxygen concentration in surface water has a significant correlation with ORP in spring,Chl-a and p H in summer,and con-ductivity and ORP in autumn.The concentration of dissolved oxygen in the bottom water body has a significant correlation with conductivity and ORP in spring;it is significantly correlated with TN,TP,p H,conductivity and ORP in autumn.3.There is stratification phenomenon in the water temperature of the lake during the icebound period,and the concentration of dissolved oxygen also presents stratification phe-nomenon in different degrees.The concentration of dissolved oxygen in the surface layer remained unchanged for nearly a month.The concentration of dissolved oxygen in the mid-dle layer and the bottom layer began to decrease with the increase of freezing time.The rate of decrease in the middle layer was 0.32 mg·(L-1·d^-1),and the rate of decrease in the bottom layer was 0.05 mg·(L^-1·d^-1).4.The water temperature and dissolved oxygen concentration of the three-layer water body of Wuliangsu Sea in 2017 and 2019 have similar cycles on the characteristic time scale.The two-year similar cycle is mainly due to the fact that the phytoplankton species during the freezing period are mainly composed of green algae,diatoms and cyanobacteria.The sum of the three algae accounts for more than 80%,and the types all show green algae>diatoms>cyanobacteria.The general growth characteristics of cyanobacteria:the growth cycle is about 30 days,and the life cycle can be divided into three stages:growth,peak,and aging.In addition,the number of cyanobacteria species accounted for the highest proportion in winter compared with other seasons,reaching 21.60%.At the same time,the freezing period and the change cycle of dissolved oxygen concentration in the Wuliangsu Sea are basically consistent with the growth cycle of cyanobacteria.It is speculated that the life cycle evolution process of this cyanobacteria exists in the subglacial water body during the freez-ing period.5.The wavelet coherence spectrum results show that there is a complex relationship between the lake water temperature and the dissolved oxygen concentration:the surface layer,bottom layer and the dissolved oxygen concentration have an inverse phase relation-ship;on the 2～4d period scale,the middle layer change leads the dissolved oxygen concen-tration change by about 2～4h.6.Based on the time series ARIMA model,the prediction effect of dissolved oxygen in the water body is better,which can provide a reference for the selection of the prediction model of dissolved oxygen in the subglacial water in the study area.