Developing an Hourly Water Quality Model to Simulate Diurnal Water Temperature and Dissolved Oxygen Variations in Shallow Lakes
Type of DegreeMaster's Thesis
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Water quality related problems are serious concerns in most part of the world in the 21st century. Previous studies conducted on lakes have usually tried to develop models for deep strongly stratified lakes. Moreover, all these models developed previously are on daily time steps. However, the water quality parameters in shallow lakes could have relatively large changes during the day. Therefore, the previous models cannot catch the diurnal fluctuations of water temperature and dissolved oxygen which are common in shallow polymictic lakes. To capture these fluctuations, an hourly model MINLAKE2018 is developed based on a one-dimensional, deterministic daily-time-step water quality model “MINLAKE2012”. The time step and coefficients of MINLAKE2012 were modified to give it the capability of predicting the hourly water temperature and dissolved oxygen. The diffusion coefficient at the epilimnion was refined. Necessary changes were applied to the sediment temperature model. Some of the model parameters were calibrated for five shallow Minnesota lakes and University Lake in Louisiana. The hourly model was applied to the seven study lakes (including a deep lake for comparison). The accuracy of the model was assessed by comparing the output from each source and sink terms with the ones from the daily MINLAKE model and comparing the simulated water temperature and dissolved oxygen with the observed ones at the study lakes. The overall results from the hourly model are satisfactory with shallow lakes (smaller RMSE and larger NSE). However, with the deep lakes such as Lake Carlos, the daily model is good enough to predict stronger vertical season stratification.