At left: Caney Fork. Photo by Chuck Sutherland.
In fast-moving streams, rushing water is aerated by bubbles as it churns over rocks and falls down hundreds of tiny waterfalls, saturating these streams with oxygen. In slow, stagnant waters, oxygen only enters the top layer of water, and deeper water is often low in dissolved oxygen concentration due to decomposition of organic matter by bacteria that live on or near the bottom of the reservoir. Dams slow water down, and therefore can decrease the dissolved oxygen concentration of water downstream.
Additionally, bacteria decompose organic wastes, including leaves, grass clippings, dead plants or animals, animal droppings, and sewage, removing dissolved oxygen from the water when they breathe. Bacteria also use oxygen to digest dead algae, which bloom when fertilizers run off into waterways. If more food (organic waste or algae) is available for the bacteria, more bacteria will grow and use oxygen, and the dissolved oxygen concentration will drop.
Removing trees can also affect dissolved oxygen concentrations in different ways. In general, as water temperature increases, dissolved oxygen drops. The bare soil exposed from removing the tree can erode, increasing the amount of dissolved and suspended solids in the water and decreasing dissolved oxygen concentrations.
Depleted dissolved oxygen in water will restrict or eliminate aquatic life. While some species of fish and aquatic insects can tolerate lower levels of oxygen for short periods, prolonged exposure will affect biological diversity and in extreme cases, cause massive fish kills.
How To Help (And Who Can Help You)1. Remove unused dams.2. Limit fertilizers.3. Plant natives.4. Allow for natural growth near waterways.5. Compost or recycle yard debris.6. Conserve water.7. Pick up after your pet.8. Limit impervious surfaces.9. Plant a rain garden.10. Plan for a better future.11. Contact your representatives.12. Support your local watershed stewards.13. Spread the word.Ready To Make A Difference?Pledge to do one or more of these mitigation activities!