Skip to main content
In partnership with the NYS Housing Trust Fund Corporation, Housing Action Council and select municipalities, Habitat for Humanity will coordinate the construction of accessory apartments on the properties of low- to moderate-income residents of Bedford, Dobbs Ferry, Hastings-on-Hudson, Irvington, Cortlandt, Croton-on-Hudson and Yorktown. 

For additional information please visit Plus One ADU - Habitat NYC and Westchester

Dissolved Oxygen

Fish and other animals that live in water need oxygen to breath, just like humans and other animals that live on land. How do these animals breathe oxygen if they are under water and where does the oxygen come from?

Oxygen does not come from
The chemical composition of water is two parts hydrogen bonded with one part oxygen. The oxygen component of water is not what animals breathe, because the oxygen cannot easily be separated from the hydrogen component.

Oxygen does come from
Animals do breathe oxygen that is naturally dissolved in the water. Aquatic plants release oxygen into water and it is then dissolved and made available to animals. Plant "breathing" is the exact opposite of human breathing; plants need carbon dioxide and give off oxygen. Aquatic plants "exhale" this oxygen into the water where fish and other aquatic animals breathe it in. 
    
Percent dissolved oxygen
Like a glass of water can only dissolve a certain amount of lemonade powder, water can only dissolve a set amount of oxygen. If water has dissolved all the oxygen it can, it is said to be 100% saturated. The amount of oxygen water can dissolve is dependent on temperature. As water warms up, its ability to hold oxygen decreases, and likewise as water cools it can dissolve more oxygen. 

Biochemical oxygen demand
The biochemical oxygen demand is the amount of oxygen used by bacteria and other decomposers in the breakdown of organic material. A biochemical oxygen demand test measures how much oxygen decomposers and bacteria are consuming. This data helps to determine if low oxygen measurements are caused by pollution, such as inputs of nutrients and/or organic matter. Unpolluted waters have a normal biochemical oxygen demand of around 5 mg/L or less, while polluted waters have a much higher biochemical oxygen demand. For example, waters with raw sewage inputs may have biochemical oxygen demand levels between 150-300 mg/L.