Dissolved Oxygen in an Ecosystem

Two sources of dissolved oxygen is contact with the atmosphere and plants in the water. Throughout the day, the levels of oxygen and carbon dioxide fluctuates. When the sun is up, the levels of oxygen increases as plants undergo photosynthesis while the levels of carbon dioxide decrease as a result of the plants absorbing it. During the night however, levels of CO2 increases while O2 decreases. This is because even though production of oxygen by plants ceased for the day, other organisms are still undergoing cellular respiration, using the remaining oxygen while producing CO2.