| Hypoxia (water) |
Website Links For Oxygen |
Information AboutHypoxia (water) |
|
Hypoxia or '''oxygen depletion''' is a phenomenon that occurs in aquatic environments as Dissolved Oxygen ('''DO'''; molecular oxygen dissolved in the water) becomes reduced in concentration to a point detrimental to aquatic organisms living in the system. Dissolved oxygen is typically expressed as a percentage of the oxygen that would dissolve in the water at the prevailing temperature and salinity (both of which affect the solubility of oxygen in water; see Oxygen Saturation and Underwater ). An aquatic system lacking dissolved oxygen (0% saturation) is termed Anaerobic , Reducing , or '''anoxic'''; a system with low DO concentration—in the range between 1 and 30% DO saturation—is called '''hypoxic'''. Most fish cannot live below 30% DO saturation. A "healthy" aquatic environment should seldom experience DO less than 80%. Causes of hypoxia Oxygen depletion could be the result of a number of factors including natural ones, but is of most concern as a consequence of Pollution and as a highly detrimental outcome of a process known as Eutrophication . Where Plant Nutrients enter a river, lake, or ocean, Phytoplankton blooms are encouraged. While phytoplankton, through photosynthesis, will raise DO saturation during daylight hours, the dense population of a Bloom reduces DO saturation during the night. When phytoplankton cells die, they sink towards the bottom and are decomposed by Bacteria , a process that further reduces DO in the water column. If oxygen depletion progresses to hypoxia, fish kills can occur and invertebrates like Worm s and Clam s on the bottom may be killed as well. Natural occurrences of hypoxia have been observed. Water flowing from a river into the sea is less dense than salt water. When this water does not mix with the underlying saline water, the oxygen concentration in the bottom layer may become low enough for hypoxia to occur. Hypoxia is particularly problematic in shallow waters of semi-enclosed bodies of water like the Waddenzee or the Gulf Of Mexico where land runoff is substantial. In these areas, a so-called " Dead Zone " can be created. Solutions To combat hypoxia, it is essential to reduce the amount of land-derived nutrients reaching rivers in runoff. Defensively this can be done by improving sewage treatment and by reducing the amount of fertilizers leaching into the rivers. Offensively this can be done by restoring natural environments along a river; marshes are particularly effective in reducing the amount of phosphorus and nitrogen (nutrients) in water.
See also
External link |