What Is A ‘Dead Zone’?

A dead zone is an area within a body of water where the oxygen level is too low to support aquatic life. The lack of adequate oxygen is caused by an excess of nutrient pollution. In the Arabian Sea, there is an area of 63,700 square miles (almost the entire Gulf of Oman) that is considered today to be the largest dead zone in the world. Second place belongs to the Gulf of Mexico, located in the United States. It is a dead zone measuring approximately 6,000 square miles.

Intense study of dead zones began in 1950 when the amount of nitrates in water tripled. By 1970, in areas around the world, the impact on the earth’s natural ecological balances from agricultural practices and industrial activities had worsened. At that time, dead zones were detected in Chesapeake Bay off Maryland and at the mouth of the Baltic Sea, the Black Sea and the Northern Adriatic. Conditions continued to deteriorate and by 2008 the number of dead zones worldwide (including China, South America, Japan and Australia) totaled 400+, with no sign of stopping. Levels of nitrogen and phosphorous from sewage, animal waste and automobile emissions were contributing to the pollution and the pollution was responsible for dying fish and crustaceans; a valuable resource.

Photo by/ Jonathan Larson

Have you ever wondered why it became so important to eliminate phosphorous from household products such as dish soaps, detergents, fertilizers? It was discovered that the heavy use of phosphorous in those products leads to a proliferation of algae blooms. Nitrogen and other chemical nutrients promote the creation and growth of phytoplankton, seaweed and related tiny green plants which take up residence upon the surface of the pond, lake, sea, ocean. This growth prevents sunlight from reaching below the water’s surface. It also stops the absorption of oxygen by organisms beneath the growth. The green scum formed by these algae blooms destroys the beauty, the health, and the productivity of the area. The water no longer can be used for recreation. The wildlife disappears. The economies that rely upon fishing and tourism collapse.

When the algae blooms eventually die, the existing bacteria will decompose the dead algae. This process depletes the oxygen from the water and at the same time releases carbon dioxide into the water. From start to finish, the cycle of degradation involved in the production of a dead zone is titled Eutrophication; a real and tangible threat to humans. The algal bloom contaminates the drinking water, which then causes a rash; stomach and liver disease; difficulties in breathing and neurological complications. When did this start becoming such a serious problem and what is being done by way of recovery and prevention?

Photo by / T. Mohamed

In 2010, research teams at work in the State of Oregon, discovered pools of low oxygen close to the shores of the Pacific Northwest coastline. The pools had expanded from the continental shelf. Scientists wanted to know how this expansion occurred. Is there is a relationship between climate change and coastal dead zones they asked. Scientists are still debating this question. Before 2010, it was known that there were physical, chemical and biological reasons why dead zones existed. Nutrient pollution was something new and the result of human activity. What these world renowned scientists do agree on is that some dead zones occur seasonally; some are permanent.

Forward seven years to 2017 and we have the arrival of a report which suggests that the meat industry and agro-economic systems are the main sources of the contaminated water from the Heartland to the Gulf of Mexico. Also during 2017 the experts decide on a table of classifications for dead zones. In order of length of occurrence, there are 4 types: 1) Permanent dead zones – these are found in deep water and are approximately two milligrams per liter 2) Temporary dead zones– the duration of these zones is from a few hours up to a few days 3) Seasonal dead zones– these zones are found in the warm months of summer and autumn every year 4) Diel cycling hypoxia-this is an exact type of seasonal dead zone that becomes toxic only at night.

Around the world, the prevalence of dead zones and the decimation of the surrounding environment had by 2021 become of great concern to ecologists of all ages and nationalities. To report on all that has happened since 1950 up until 2021 would take many pages and those pages would consist of diagrams and statistics. Hopefully I have included enough to answer the question of what are dead zones and when did these zones get identified as problematic. Next, let’s see what is being done (if anything) to manage these dangerous areas.

Photo by / Maria Battazzi

At this point of researching ‘dead zones’ I became alarmed. Why? Not much is being done to recover these areas. ‘Dead zones’ are reversible if their causes are eliminated. In 1990, following the end of the Soviet Union, a shortage of chemical fertilizers and the rise in price of available fertilizers were a combined force behind the disappearance of an extremely large dead zone located in the Black Sea. Fishing was re-instated and once again is a major contributor to the region’s economy. Another example? In the North Sea dead zone, nitrogen was reduced by 37%. How? Sewage and industrial emissions from numerous areas along the Rhine River was lowered through policy efforts initiated by local governments. Similar actions were taken in territories along the Hudson River and San Francisco Bay. Phosphorous removal measures started in Finland around 1975. A number of contaminated rivers and lakes were selected for recovery. The effort resulted in 90% removal efficiency. Other changes include upgrading sewage treatment facilities, more laws regulating the discharge of nutrients into the surrounding ecosystems, introduction of improved technology for the safe and efficient reuse of wastewater, planting trees, shrubs and grasses along edges of fields to catch and absorb nutrients before entry into nearby bodies of water.

The available articles citing recovery projects are limited. The subject of dead zones is not of interest to a large section of the general public. It should be because as things stand many of us are part of the problem. The general public has an important and vital role in the prevention of ‘dead zones’. One article I read while doing the research for this introductory article had this admonition: “the public must be aware of their contribution to the problem…” (author unnamed). I agreed.


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