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Dead ZonesThe Loss of Oxygen from Rivers, Lakes, Seas, and the Ocean$
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David L. Kirchman

Print publication date: 2021

Print ISBN-13: 9780197520376

Published to Oxford Scholarship Online: February 2021

DOI: 10.1093/oso/9780197520376.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 24 September 2021

What Happened in 1950?

What Happened in 1950?

(p.52) 4 What Happened in 1950?
Dead Zones

David L. Kirchman

Oxford University Press

This chapter discusses what happened around 1950 that led to the expansion of dead zones. For the Gulf of Mexico, there are many reasons to think the flow of the Mississippi River has changed since the days of Mark Twain, considering the construction of so many levees, dikes, floodways, spillways, weirs, and revetments. Rain-absorbing grasslands and forests have been replaced by asphalt, roof shingles, and other hydrophobic material that hasten rainwater to the Gulf. But the flow of the Mississippi has not changed enough to explain why the Gulf dead zone grew around 1950. As the chapter discusses, what did change was nutrients. It shows that concentrations doubled in the Mississippi River from the 1930s to the 1990s, which stimulated algal growth and production of organic material that eventually led to depletion of dissolved oxygen. In addition to creating dead zones, the increase in nutrients has stimulated harmful algal blooms, leading to fish kills and beach closings.

Keywords:   eutrophication, stratification, plant nutrients, harmful algal blooms, wetlands, Mississippi River

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