It is also affected by a third reaction involving the amount of carbonate minerals, or alkalinity, present in lake water. Alkalinity is discussed in another section. Carbon dioxide is essential to plant growth. It is the basic carbon source from which plants produce sugar and more complex organic matter.
Values often fluctuate, being highest late at night and lowest early in the evening.
Carbon Dioxide Reactions. As carbon dioxide changes from morning to evening, so does water's pH, especially in low alkaline, productive lakes. When carbon dioxide reacts with water, it forms carbonic acid. Acidity regulates the solubility of many minerals. Values above 7 are alkaline or basic.