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From Farmer to Shrimper: The Dead Zone
(pg 2 of 8)

The dead zone is caused by an excess of nitrogen flushing down the Mississippi, and the primary source of that nitrogen is the farms of the upper Midwest, mainly Minnesota, Iowa, Illinois, and Indiana.

Freshwater flushing from the Mississippi River spreads into the Gulf, trapping the denser saltwater beneath it. Phytoplankton such as algae growing in these shallow fecund waters die and settle to the bottom. Bacteria degrade the organic matter, consuming dissolved oxygen from the water. The stratification of saltwater and freshwater prevents wave action from mixing and reoxygenating the bottom layer, and a dead zone spreads along the seabed.


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