Site icon Conservation news

Ocean dead zones have nearly quadrupled since 1994

Ocean dead zones have nearly quadrupled since 1994

Ocean dead zones have nearly quadrupled since 1994
Coastal ecosystems threatened worldwide by nutrient-rich runoff
Jeremy Hance,
April 3, 2008

Coastal areas worldwide are suffering from over-enrichment of their waters by nitrogen and phosphorus, finds a new study from the World Resources Institute (WRI). This over-enrichment, known as eutrophication, causes numerous environmental problems, eventually devastating coastal environments. In overly nutrient-rich waters phytoplankton, micro- and macroalgae grow to excessive portions; these ‘algal blooms’ diminish subaquatic vegetation, damage coral reefs, and deplete populations of fish, shellfish, marine mammals, and sea birds. In the worst case scenarios the massive algal blooms form hypoxic or dead zones due to loss of oxygen in the water, essentially condemning the ecosystem.

Eutrophication is human-caused. The culprits are agricultural fertilizer, domesticated animal manure, industrial and urban runoff, sewage, and atmospheric nitrogen. These waste products have caused nitrogen and phosphorus to triple in coastal areas in the last fifty years alone. In Europe and the U.S. fertilizer and manure are the main sources, because much of their sewage is treated before entering the water system. In regions like Africa, Latin America, and Asia where sewage and industrial waste are rarely treated, these wastes provide larger sources of nitrogen and phosphorus.

This map identifies 415 eutrophic and hypoxic coastal systems worldwide. Of these, 169 are documented hypoxic areas, 233 are areas of concern and 13 are systems in recovery. The map is based on research conducted by WRI’s NutrientNet program and Dr. Bob Diaz at the Virginia Marine Institute.

Agriculture, growing industry, fossil fuel combustion, and population growth are together causing significant growth in areas receiving nitrogen and phosphorous endflows. Over the past 50 years, nitrogen flux has doubled and phosphorus has tripled, according to the Millennium Ecosystem Assessment. These cumulative changes are, quite literally, choking coastal waters around the world.

The study found 415 sites globally that are suffering from eutrophication. In Europe 65 percent of its Atlantic coast suffers from eutrophication in some degree or another. The news is worse for the United States: 78 percent of the assessed areas showed eutrophication.

“A significant portion of the world’s population – nearly half of which lives within 40 miles of a coast – is vulnerable to harmfully over-enriched ecosystems,” said Mindy Selman, lead author of the study. As well as marine animals, the problem greatly affects human communities, which rely on the coast and its resources for their livelihoods. For example, according to the study a massive algae bloom in 1998 cost Hong Kong $40 million USD as it wiped out almost the entirety of Hong Kong’s fish farms.

Hypoxic regions have risen rapidly in less than two decades. The last count showed 44 dead zones in 1994. The WRI study found 169. Two infamous hypoxic regions are the Gulf of Mexico, fed by the overly-enriched Mississippi, and the Black Sea, which is currently recovering from a spike in fertilizer-use during the Soviet area.

Even these numbers: 415 areas globally effected by nutrient-rich runoff, 169 of which can be classified as hypoxic, are under-estimations. The WRI was only able to take into account areas that possessed reliable data on their water. “The number of degraded coastal areas around the world is sure to be a much greater problem than even our study of 415 areas suggests,” Selman said. The report states that Africa, Latin America, the Caribbean, and Asia do not monitor their coastal water-quality closely.

The study recommends the first step in confronting this problem is increasing research on eutrophication, including studies in areas that lack information. The study also urges global society to become more aware and involved. “Eutrophication is an issue that requires greater attention by governments and society in general. Left untouched, it may have dire consequences for many ecosystems, the food webs that they support, and the livelihoods of the populations that depend on them.”

Exit mobile version