What is a dead zone? A dead zone is an area of water with little to no dissolved oxygen present. Without dissolved oxygen, aquatic organisms cannot survive. Dead zones often occur near heavy human populations, such as estuaries and coastal areas off the Gulf of Mexico, the North Sea, the Baltic Sea, and the East China Sea. These zones are usually a result of a fertilizer-fueled algae and phytoplankton growth boom. While these algal blooms initially boost dissolved oxygen levels, the consequences are further reaching. As the algae and phytoplankton die, the microbes at the seafloor decompose the organic matter. The decomposition process often uses up all of the dissolved oxygen in the area. These anoxic (no oxygen) conditions are usually stratified, occurring only in the lower layers of the water. While some fish and other organisms can escape, shellfish, young fish and eggs usually die. Naturally occurring hypoxic (low oxygen) conditions are not considered dead zones. The local aquatic life (including benthic organisms) have adjusted to the recurring low-oxygen conditions, so the adverse effects of a dead zone (mass fish kills, sudden disappearance of aquatic organisms, and growth/development problems in fish and invertebrates) do not occur. Learn more about the importance of dissolved oxygen here: fondriest/environmental-measurements/parameters/water-quality/dissolved-oxygen/
Posted on: Fri, 02 May 2014 18:24:11 +0000
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