![]() ![]() When production increases in an ecosystem, organic matter, such as algal cells and fecal pellets, increases. Consequently, if the hypoxic zone continues or worsens, fishermen and coastal state economies will be greatly impacted. harvested shrimp, 66% of harvested oysters, and 16% of commercial fish (Potash and Phosphate Institutes of the U.S. The Gulf of Mexico is a major source area for the seafood industry. Hypoxic water supports fewer organisms and has been linked to massive fish kills in the Black Sea and Gulf of Mexico. Nutrient overloading and algal blooms lead to eutrophication (link to USGS definition), which has been shown to reduce benthic (link to definition) biomass and biodiversity. It is also affected by weather events such as flooding and hurricanes. The size of the dead zone fluctuates seasonally, as it is exacerbated by farming practices. Consequently, algal blooms develop, the food chain is altered, and dissolved oxygen in the area is depleted. However, with anthropogenically increased nitrogen and phosphorus input, algae growth is no longer limited. In a natural system, these nutrients aren't significant factors in algae growth because they are depleted in the soil by plants. Nitrogen and phosphorous enter the river through upstream runoff of fertilizers, soil erosion, animal wastes, and sewage. Most of the nitrogen input comes from major farming states in the Mississippi River Valley, including Minnesota, Iowa, Illinois, Wisconsin, Missouri, Tennessee, Arkansas, Mississippi, and Louisiana. Watersheds within the Mississippi River Basin drain much of the United States, from Montana to Pennsylvania and extending southward along the Mississippi River. The dead zone is caused by nutrient enrichment from the Mississippi River, particularly nitrogen and phosphorous. Dead zones may also be found in lakes, such as Lake Erie. Marine dead zones can be found in the Baltic Sea, Black Sea, off the coast of Oregon, and in the Chesapeake Bay. The Gulf of Mexico dead zone is one of the largest in the world. Photo courtesy of NOAA.ĭead zones can be found worldwide (link to NASA dead zone page). The Gulf of Mexico dead zone varies in size annually, but may extend from the Louisiana/Alabama coast to the westernmost Texas coast. ![]()
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