Humic Acid and other leached compounds from floating or benthic organic waste are responsible for dark-brown discoloured water in wetlands. The amount of staining will be greatest in wetlands with low flow and a high organic matter concentration. The majority of nonmarine wetlands have an acidic water column due to the reactivity of organic molecules and carbon dioxide with water. Wetlands that are immediately carved into carbonate bedrock or those with groundwater flows that are mineral-rich can also be notable exceptions.
Hence, the pH of the Humic Acid system is ultimately determined by the equilibrium of carbonate ions, carbon dioxide, and dissolved organic molecules in the water column. The availability of nutrients and the conditions of vegetative growth depend on this equilibrium. With less carbon dioxide available to react with water and form carbonic acid, photosynthesis causes a net removal of dissolved carbon dioxide from the water column. In contrast, breathing at night causes dissolved carbon dioxide to rise and accelerates carbonic acid reactions in wetlands.
