Dead zones are so named because they are areas in the ocean without any oxygen. Any animals that cannot swim or move out of the area quickly enough will die. There are about 550 dead zones in the oceans today, including several off the Oregon coast. Some of these dead zones stretch for a hundred miles. Some scientists think that once a die off happened because of a dead zone, that it could take many years, perhaps hundreds before a healthy marine ecosystem can be re-established.
What causes dead zones are algal blooms. Most of the time algae and other types of phytoplankton are useful because it creates oxygen and provides the food source for thousands of different zooplankton which then becomes food for larger fish and other animals.
But all things in moderation. Sometimes the algae create toxins which will poison everything up the food chain. Some types of “red tide” will affect the brains of the animals that are higher up the food chain like sea lions and birds and they will act erratically or die.
When there is too much algae, the algae will die off and sink to the bottom where it is consumed by bacteria which eats up all of the oxygen in the water. This is a process called eutrophication.
When there are large areas of algal blooms it can create dead zones. Most of these dead zones are near the mouths of rivers, and the algal blooms are the result of too much nitrates and phosphates in the river. Most of the excess fertilizer is from agricultural runoff but some is also because of sewage from humans and also animal feedlot wastes discharged into the waterways.
The dead zones have been growing with increased population and increased use of artificial fertilizers. Dead zones can decimate fish and shellfish populations, and destroy habitat for thousands of other species.
So how can we reduce or eliminate dead zones? For one thing all cities should have a decent tertiary treatment system. This is a three stage system. The first stage is simply a settling tank that allows the solids to precipitate out. The second is anaerobic digestion, and the third is aerobic digestion. The resultant solids could be used for non food plantings. The filtered liquids should go into an estuary for final processing.
The use of concentrated fertilizers destroy the fertility of the land in the long run. Organic farming and Permaculture practices would build up the soil and prevent erosion and runnoff.
“The most devastating pollutants are the nitrogen and phosphorus found in our fertilizer and sewage. When too much of either washes downstream, coastal waters become choked with heavily fertilized algae, which then dies and decomposes, consuming the oxygen in the water and asphyxiating animal life. This process, called eutrophication, has created at least 405 “dead zones” worldwide.”
“Over the past two and a half decades, farmers have adopted “no-till” methods on 36 percent of U.S. cropland…In doing so, they reduce phosphorus runoff by about 40 percent, atmospheric nitrogen release by about half, and overall erosion by up to 98 percent—and achieve equal yields using just half the energy.” https://www.popsci.com/science/article/2011-04/reducing-fertilizer-runoff-resurrect-ocean-dead-zones
Here are some videos that discuss dead zones and eutrophication:
Dead Zones 5min. https://www.youtube.com/watch?v=rc4f8K4cgyo
Marine Dead Zones 4:48 min https://www.youtube.com/watch?v=SmETlQ0E_rE
Eutrophication and Dead Zones 5:50 min. https://www.youtube.com/watch?v=AxaWXWd2pw4
05 Final Ocean Dead Zones
Harmful Algal Blooms (HAB)
10 min. https://www.youtube.com/watch?v=bBcaFoR1ZUs
What Is Eutrophication 1:30 min| Biology for All | FuseSchool https://www.youtube.com/watch?v=6LAT1gLMPu4
Dead Zones Can Be Reversed 3:40 min https://www.youtube.com/watch?v=pKfj6tr-7IM
Red Tides, Hypoxia and Dead Zones explained by Dr. Nancy Rabalais of LUMCON at the Gulf of Mexico
BioGold/BioRed…Positive Influences for Dead Zone Problem https://www.youtube.com/watch?v=JeiAV88tiug
BioGold Promo https://www.youtube.com/watch?v=fN2UrD4tOaM