In the 1970s, marine dead zones were first noted in settled areas where intensive economic use stimulated scientific scrutiny: in the U.S. East Coast's
Chesapeake Bay, in Scandinavia's
strait called the
Kattegat, which is the mouth of the
Baltic Sea and in other important Baltic Sea fishing grounds, in the
Black Sea, and in the northern
Adriatic. Other marine dead zones have appeared in coastal waters of
South America,
China,
Japan, and
New Zealand. A 2008 study counted 405 dead zones worldwide. Some of the causes behind the elevated increase of dead zones can be attributed to the use of fertilizers, large animal farms, the burning of
fossil fuels, and effluents from municipal wastewater treatment plants. With its massive size, the Baltic Sea is best analyzed in sub-areas rather than as a whole. In a paper published in 2004, researchers specifically divided the Baltic Sea into 9 sub-areas, each having its own specific characteristics. The 9 sub-areas are discerned as follows: Gulf of Bothnia, Archipelago region, Gulf of Finland, Gulf of Riga, Gulf of Gdansk, Swedish East-coast, Central Baltic, Belt Sea region, and Kattegat. The Chesapeake Bay experiences seasonal hypoxia due to high nitrogen levels. These nitrogen levels are caused by urbanization, there are multiple factories that pollute the atmosphere with nitrogen, and agriculture, the opposite side of the bay is used for poultry farming, which produces a lot of manure that ends up running off into the Chesapeake Bay. From 1985–2019, there were efforts from the caretakers of Chesapeake Bay to reduce the annual hypoxic volumes. There was significant improvement in 2016–2017 that gave assurance to the caretakers that the efforts were successful, however recent data has shown that further efforts are needed to continuously curb the effects of global warming. From 2015-2019, 11 different conditions were measured in various areas of the Elizabeth River. Throughout the river, there were consistently high levels of nitrogen and phosphorus, along with high levels of other contaminants contributing to the poor quality of life for bottom feeders along the river. The main cause of the pollution to the Elizabeth river has been the military and industrial activities through the 1990s. In 2006, Maersk-APM, a major shipping company, wanted to build a new port on the Elizabeth River. By 2012, they were able to restore over 7 acres of tidal marsh, 3 acres of oyster reef and created a new shoreline. In 2019, the Money Point Project received the "Best Restored Shore" award from the American Shore and Beach Preservation Association.
Lake Erie A seasonal dead zone exists in the central part of
Lake Erie from east of
Point Pelee to
Long Point and stretches to shores in Canada and the United States. Between the months of July and October the dead zone has the ability to grow to the size of 10,000 square kilometers. Lake Erie has an excess of
phosphorus due to
agricultural runoff that quickens the growth of algae which then contributes to
hypoxic conditions. The superabundance of phosphorus in the lake has been linked to
nonpoint source pollution such as urban and agricultural runoff as well as
point source pollution that includes sewage and wastewater treatment plants. The zone was first noticed in the 1960s amid the peak of eutrophication occurring in the lake. After public concern increased, Canada and the US launched efforts to reduce
runoff pollution into the lake in the 1970s as means to reverse the dead zone growth. The commercial and recreational fishing industry have been significantly impacted by the hypoxic zone. Water from the lake is also used for human drinking. Water from the lake has been said to acquire a pervasive odor and discoloration when the dead zone is active in the late summer months.
Lower St. Lawrence Estuary A dead zone exists in the Lower
St. Lawrence River area from east the
Saguenay River to east of
Baie Comeau, greatest at depths over and noticed since the 1930s. The main concern for Canadian scientists is the impact on fish found in the area.
Oregon There is a hypoxic zone covering the coasts of Oregon and Washington that reached peak size in 2006 at an area of over 1,158 square miles. Strong surface winds between April and September cause frequent upwelling that results in an increase of algae blooms, rendering the hypoxia a seasonal occurrence. The upwelling has contributed to lower temperatures within the zone. The dead zone has resulted in sea organisms such as crabs and fish relocating and an interference with
commercial fishing. In 2009, one scientist described "thousands and thousands" of suffocated, crabs, worms, and sea stars along the seafloor of the hypoxic zone. In 2021, 1.9 million dollars were put into monitoring and continuing to study the hypoxic conditions in the area that the dead zone occurs in. is the largest recurring hypoxic zone in the United States. It occurs only during the summer months of the year due to summer warming, regional circulation, wind mixing and high freshwater discharge. The
Mississippi River, which is the drainage area for 41% of the continental United States, dumps high-nutrient runoff such as
nitrates and
phosphorus into the Gulf of Mexico. According to a 2009 fact sheet created by
NOAA, "seventy percent of nutrient loads that cause hypoxia are a result of this vast
drainage basin", which includes the heart of U.S.
agribusiness, the
Midwest. The discharge of treated sewage from urban areas (pop. c 12 million in 2009) combined with agricultural runoff deliver c. 1.7 million tons of phosphorus and nitrogen into the Gulf of Mexico every year. Even though
Iowa occupies less than 5% of the Mississippi River drainage basin, average annual nitrate discharge from surface water in Iowa is about 204,000 to 222,000 metric tonnes, or 25% of all the nitrate that the Mississippi River delivers to the Gulf of Mexico. Export from the Raccoon River Watershed is among the highest in the United States, with annual yields at 26.1 kg/ha/year, which ranked as the highest loss of nitrate out of 42 Mississippi subwatersheds evaluated for a Gulf of Mexico hypoxia report. In 2012, Iowa introduced the Iowa Nutrient Reduction Strategy, which "is a science and technology-based framework to assess and reduce nutrients to Iowa waters and the Gulf of Mexico. It is designed to direct efforts to reduce nutrients in surface water from both point and nonpoint sources in a scientific, reasonable and cost effective manner." The strategy continues to evolve, using voluntary methods to reduce Iowa's negative contributions through outreach, research, and implementation of nutrient holding practices. In order to help reduce agricultural runoff into the Mississippi Basin, Minnesota passed MN Statute 103F.48 in 2015, also known as the "Buffer Law", which was designed to implement mandatory
riparian buffers between farmland and public waterways across the State of Minnesota. The Minnesota Board of Water and Soil Resources (BWSR) issued a January 2019 report stating that compliance with the 'Buffer Law' has reached 99%.
Size The area of hypoxic bottom water that occurs for several weeks each summer in the Gulf of Mexico has been mapped most years from 1985 through 2024. The size varies annually from a record high in 2017 when it encompassed more than 22,730 square kilometers (8,776 square miles) to a record low in 1988 of 39 square kilometers (15 square miles). The 2015 dead zone measured 16,760 square kilometers (6,474 square miles).
Nancy Rabalais of the
Louisiana Universities Marine Consortium in
Cocodrie, Louisiana predicted the dead zone or
hypoxic zone in 2012 will cover an area of 17,353 square kilometers (6,700 square miles) which is larger than Connecticut; however, when the measurements were completed, the area of hypoxic bottom water in 2012 only totaled 7,480 square kilometers. The models using the nitrogen flux from the Mississippi River to predict the "dead zone" areas have been criticized for being systematically high from 2006 to 2014, having predicted record areas in 2007, 2008, 2009, 2011, and 2013 that were never realized. In late summer 1988 the dead zone disappeared as the great drought caused the flow of Mississippi to fall to its lowest level since 1933. During times of heavy flooding in the Mississippi River Basin, as in 1993, "the "dead zone" dramatically increased in size, approximately larger than the previous year".
Economic impact Some assert that the dead zone threatens lucrative commercial and recreational fisheries in the Gulf of Mexico. "In 2009, the dockside value of commercial fisheries in the Gulf was $629 million. Nearly three million recreational fishers further contributed about $10 billion to the Gulf economy, taking 22 million fishing trips." The seafood production is not only hurting states located on the Gulf of Mexico but the U.S. as a whole. It is reported that the Gulf of Mexico dead zone is costing the U.S. seafood and tourism industries about $82 million a year. Louisiana is ranked second in seafood production behind Alaska, and this impact can be devastating for the nations seafood production since the Gulf of Mexico sources 40% of the nations seafood. Scientists are not in universal agreement that nutrient loading has a negative impact on fisheries. Grimes makes a case that nutrient loading enhances the fisheries in the Gulf of Mexico. Courtney et al. hypothesize that nutrient loading may have contributed to the increases in red snapper in the northern and western Gulf of Mexico. In 2017, Tulane University offered a $1 million challenge grant for growing crops with less fertilizer.
History Shrimp trawlers first reported a 'dead zone' in the Gulf of Mexico in 1950, but it was not until 1970 when the size of the hypoxic zone had increased that scientists began to investigate. After 1950, the conversion of forests and wetlands for agricultural and urban developments accelerated. "Missouri River Basin has had hundreds of thousands of acres of forests and wetlands (66,000,000 acres) replaced with agriculture activity [. . .] In the Lower Mississippi one-third of the valley's forests were converted to agriculture between 1950 and 1976."
Korea Jinhae Bay Jinhae Bay is the first of Korea's two major dead zones. Hypoxia was first reported in Jinhae Bay in September 1974. In 2011, a joint study was done to observe and record causes, effects, and what can be done about Korea's hypoxic zones. It was discovered that Jinhae Bay exhibits a seasonal dead zone from early June to late September. This dead zone is caused by "domestic and land use waste and thermal stratification". Jinhae Bay experiences hypoxia largely at the bottom of its bay. The ratio of phosphorus to nitrogen is imbalanced at the bottom, where it is otherwise balanced at the top, with the exception of early June to late September where the Bay experiences eutrophication as a whole. The effects of Jinhae Bay's hypoxia is seen in the marine system surrounding Korea, with a loss of biological diversity, particularly of the
calcareous shelled organisms.
Shihwa Bay Shihwa Bay is a coastal reservoir created in 1994 to supply surrounding agricultural lands with water, and act as a run-off lake for nearby industrial plants. The Bay was made without much environmental consideration, and by 1999, water quality saw a significant drop. This drop in water quality is attributed to the bay not having enough circulation or new water flow to accommodate the domestic and industrial waste being dumped. In response, the Korean government set up a pollution management system within the bay, and has installed a gate system that allows the Bay to mix with water from the sea. Shihwa Bay is also experiencing an imbalance of phosphorus to nitrogen, but also large influxes of ammonium. ==Energy Independence and Security Act of 2007==