Dissolved Oxygen

 

Although water is a liquid, it usually contains a significant amount of dissolved oxygen (DO) plus small amounts of other gasses.  Icy cold water (0^oC) can hold as much as 4.9% oxygen by volume.  However, as the water’s temperature increases its ability to hold oxygen decreases.  The chart below lists the maximum amount of oxygen that can be dissolved in water at different temperatures:

DO is highest in cold mountain streams where the water is aerated by waterfalls and rapids.  Insects living here can usually rely on gills, plastrons, or cuticular respiration to meet their metabolic demand for oxygen.  Shallow lakes and ponds with warm, quiet water have less potential to hold DO so insects may need to rely more heavily on air bubbles or snorkel-like breathing tubes.  In water polluted by organic wastes, bacteria consume nearly all of the DO and create a near-anaerobic environment.  Insects that manage to survive under these conditions usually get all of their oxygen directly from the atmosphere.