Equilibrium Simulation And Driving Factors Analyze Of Dissolved Oxygen In Lake Wuliangsuhai

Dissolved oxygen in water is a key influence on biogeochemical cycles and maintains the stability of lake water ecosystems.The dynamic changes of dissolved oxygen content reflect the water quality condition of the lake environment and the ability of all biological activities in the food web structure to proceed normally.Therefore,it is of great practical importance to explore the equilibrium mechanism and driving factors of dissolved oxygen in lakes.In the thesis,the Wuliangsuhai,a shallow lake in the cold and arid region of northern China,is used as the research object.A combination of long-term sampling and detection and high-frequency in situ monitoring was used to mechanistically investigate the sources and consumption of dissolved oxygen in the lake.The study was based on the characteristics of lakes in cold and arid regions,in view of the difference between non-ice-bound period and ice-bound period,the dynamic change trend of dissolved oxygen in Lake Wuliangsuhai was simulated respectively,and the intrinsic equilibrium relationship of dissolved oxygen in water was qualitatively analyzed.Firstly,the field monitoring and sampling test data of the Wuliangsuhai from2014-2021 were analyzed.During the spatial and temporal variation of dissolved oxygen in water bodies,dissolved oxygen exhibits significant seasonal variation.The overall pattern of change in concentration is: winter > autumn > spring > summer.During the interannual variation,the overall dissolved oxygen concentration in Lake Wuliangsuhai first decreases with time and then stabilizes.Spatially dissolved oxygen concentrations migrate from north to south over time and gradually form multiple high dissolved oxygen distribution areas.In the response analysis with environmental factors,it was found that most of the water environmental indicators in Lake Wuliangsuhai showed moderate or weak correlation with dissolved oxygen.And seasonal correlations were generally higher than interannual correlations,suggesting that increasing the correlation between impact indicators with time step.Among them,the correlation between dissolved oxygen and p H was least influenced by seasonal and interannual variations.And showed significant correlation differences with other water environment indicators at long time series.The water environment factors did not show highly correlated covariance with dissolved oxygen,establishing a theoretical basis for the dissolved oxygen kinetic model.Then,a set of water quality intelligent monitoring platform deployed in the center of the lake,combined with automatic meteorological facilities to collect meteorological data,to establish and improve a set of non-freezing period dissolved oxygen kinetic model.A particle swarm optimization algorithm was used to determine the optimal calibration parameters for the dissolved oxygen model of the Wuliangsuhai.The coefficient of determination and the Nash efficiency coefficient of the improved model prove the feasibility of the model.Following that,the main driving variables affecting the dissolved oxygen balance in the lake were identified.Photosynthesis,aeration and runoff recharge accounted for 49.28%,14.72% and 36% of the dissolved oxygen sources,respectively.In contrast,respiration and sediment oxygen consumption accounted for 1.56% and 98.44%of dissolved oxygen consumption,respectively.This suggests that photosynthesis and sediment oxygen consumption dominate the dissolved oxygen balance in Lake Wuliangsuhai.In addition,the analysis of the average oxygen production rate per unit time showed that the maximum values of photosynthesis and sediment oxygen consumption rates were 0.22 mg/L·h and 0.20 mg/L·h,respectively.The average daily oxygen production and consumption rate showed the highest daily oxygen production rate of 8mg/L·d and oxygen consumption rate of 7.84 mg/L·d.The lowest daily oxygen production rate was 1.99 mg/L·d and the oxygen consumption rate was 1.79 mg/L·d.In further correlation analysis,water temperature was found to change the dissolved oxygen level in the lake mainly by affecting the oxygen consumption reaction process.The comparative analysis revealed that solar radiation has some uncertainty in simulating photosynthetic oxygen production.Finally,still using the water quality intelligent monitoring platform to collect data and combined with meteorological information to build a model of dissolved oxygen changes during the ice storm.The wavelet transform principle is used to determine the wavelet function and perform noise reduction,and the measured dissolved oxygen concentration is used as the model input variable.The analysis determined that the maximum values of the average oxygen production rate per unit time in the lake were 0.55 mg/L·h and 0.36mg/L·h,respectively.The average daily maximum oxygen production rate was 7.19mg/L·d and oxygen consumption rate was 7.13 mg/L·d.The minimum oxygen production rate was 2.01 mg/L·d and the oxygen consumption rate was 2.37 mg/L·d.This suggests that the unbalanced replenishment and depletion of dissolved oxygen at small time scales during the freezing period leads to the imbalance of dissolved oxygen at large time scales,which in turn causes the oxygen deficit in the lake during winter.Further in the response relationship analysis,turbidity and water temperature were found to be significantly negatively correlated with oxygen production rate,and chlorophyll-a was found to be significantly positively correlated with both oxygen production rate and oxygen consumption rate.It is demonstrated that these limiting aquatic environmental factors affect the dissolved oxygen balance of subglacial waters to some extent.