Dissolved Oxygen As Essential For A Healthy Aquatic Ecosystem

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Dissolved Oxygen is highly essential for a healthy aquatic ecosystem. Aquatic organisms need oxygen dissolved in water to stay alive. The need for Oxygen is dependent on species and life stage. While some organisms adapt to low oxygen level, others do not. Amount of dissolved Oxygen in a system can affect the solubility and availability of nutrients (Fondriest Environmental, 2014). The Oxygen content of water bodies varies with temperature, turbulence, salinity, photosynthetic ability of algae and plants and atmospheric pressure, decreasing with rising temperature and salinity, and increasing with rising atmospheric pressure (National Oceanic and Atmospheric Administration, NOAA, 2012). In water it usually is expressed in milligrams per…show more content…
The lower the concentration, the greater the stress, Oxygen levels that remain below 1-2 mg/l for a few hours can result in death of fish. DO analysis measures the amount of gaseous oxygen (O2) dissolved in an aqueous solution. Oxygen gets into water by diffusion from the surrounding air, by aeration and as a waste product of photosynthesis. For proper maintenance of aquatic health, DO concentrations should approach saturation that is the concentration which is in equilibrium with the partial pressure of atmospheric oxygen. Freshwater at sea level has a saturation dissolved oxygen concentration of about 14.6 mg/l at 0C (32F) and 8.2 mg/l at 25C (77F).
1.2 Causes of Low Dissolved Oxygen

Low dissolved oxygen (DO) mainly is as a result of excessive algae growth caused by phosphorus (Minnesota Pollution Control Agency, 2009). Nitrogen can also contribute to algae growth. The death and decomposition of algae consumes dissolved oxygen resulting in a deficiency.
Decomposition of submerged plants may also contribute to low level of dissolved oxygen, Phosphorus can be introduced into water system by discharges from municipal and private wastewater treatment, cropland and urban storm water runoff, and natural decay of vegetation. The discharge of pollutants from different point sources and nonpoint sources into a river segment can add to its Carbonaceous Biological Oxygen Demand (CBOD) loadings, leading to an oxygen demand that may decrease DO below useable
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