A dead zone is an area of depleted oxygen, whether hypoxic (low oxygen) or anoxic (no oxygen). Dead zones result from an excess of nutrients in the water, such as nitrogen and phosphorus, which in turn lead to an increase in levels of harmful bacteria. This process is called eutrophication.
The reduction of oxygen also fosters the growth of algae blooms. These blooms block sunlight, further blocking oxygen from reaching marine life beneath them.
A variety of causes can lead to the excess nutrients that result in oxygen level changes, including agricultural runoff from fields, burning of fossil fuels, wastewater from sewage facilities, and, in the case of certain types of fish farming, an overabundance of feed and fish feces beneath pens.
A lack of sufficient oxygen can alter the habits of creatures as they attempt to circumvent these conditions, and further, can lead to mass die-offs.
in Environmental Impacts
