3c pH: dioxide and produce oxygen. Carbon dioxide will lower the pH of water, as when CO2 is dissolved in water, a part of it reacts with water to form carbonic acid (H2CO3). The hydrogen ions present in carbonic acid will make water acidic, meaning that the pH will be lowered. Thus, when aquatic plants absorb carbon dioxide and remove it from water, the pH will rise slightly as there is less hydrogen ions present in the water (Orenda Technologies, 2022). On the other hand, plants also absorb ammonia and other nitrogen compounds. These compounds cause biological reactions that produce free hydrogen ions, which lower the pH as the formula for calculating pH is -log[H ⁺]. This has a much larger effect on pH compared to the aforementioned effect of plants absorbing carbon dioxide in water . The control in the experiment as represented by the blue line indicates that there is no clear correlation between DO levels and time when in contact with a macrophyte. This is likely due to environmental factors as the amount of oxygen that can be dissolved in water depends on water temperature, the amount of dissolved salts present in the water which is salinity, and the atmospheric pressure . Nevertheless, these variables accurately reflect the practical usage of macrophytes in a constructed wetland as the environmental factors may vary daily and thus lead to mixed results in DO concentration in water. In addition, different macrophytes can have different impacts on DO concentration. Oxygen release rates from roots depend on the internal oxygen concentration, the oxygen demand of the surrounding medium and the permeability of the root-walls . Macrophytes release oxygen from their roots as rates of oxygen leakage are generally highest in the sub-apical region of roots and decrease with distance from the root-apex . In addition, research shows that aquatic plants with an internal convective throughflow ventilation system have higher internal oxygen concentrations in the roots compared to aquatic plants that rely on the diffusive transfer of oxygen . Thus, aquatic plants with a convective throughflow mechanism, such as the Typha, have the potential to release more oxygen from their roots compared to species without convective throughflow which will impact the DO concentration in water as seen in the results of the experiment .