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In 2021, the low-oxygenated waters caused a mass-kill event of freshwater drum fish species (also known as sheepshead fish). [48] Water from the lake is also used for human drinking. [49] Water from the lake has been said to acquire a pervasive odor and discoloration when the dead zone is active in the late summer months. [50]
Oxygen diffuses into water from air and therefore the top layer of water in contact with air contains more oxygen. This is true only in stagnant water; in running water all layers are mixed together and oxygen levels are the same throughout the water column. One environment where ASR often takes place is tidepools, particularly at night. [34]
In some fish, capillary blood flows in the opposite direction to the water, causing countercurrent exchange. The muscles on the sides of the pharynx push the oxygen-depleted water out the gill openings. In bony fish, the pumping of oxygen-poor water is aided by a bone that surrounds the gills called the operculum. [6]
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 worms and clams on the bottom may be killed as well. Still frame from an underwater video of the sea floor.
When the oxygen in a parcel of water is consumed, the oxygen cannot be replaced without the water reaching the surface ocean. When oxygen concentrations drop to below <10 nM, microbial processes that are normally inhibited by oxygen can take place like denitrification and anammox. Both processes extract elemental nitrogen from nitrogen ...
When oxygen is depleted in a basin, bacteria first turn to the second-best electron acceptor, which in sea water, is nitrate. Denitrification occurs, and the nitrate will be consumed rather rapidly. After reducing some other minor elements, the bacteria will turn to reducing sulfate .
Consequently, decomposition of organic matter in the water column and sediments can cause oxygen concentrations to decline to the point of hypoxia (low oxygen) or anoxia (no oxygen). [5] In dimictic , eutrophic lakes, the hypolimnion is often anoxic throughout a majority of the stratified period. [ 6 ]
Nitrate – a water-soluble molecule made up of nitrogen and oxygen, commonly found in agricultural fertilizers, and therefore in land runoff. Too much nitrate concentration is can be toxic to marine life. Nursery – The part of a fish or animal habitat where the young grow up.