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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: 16 September 2021

The Case for Phosphorus

The Case for Phosphorus

(p.106) 7 The Case for Phosphorus
Dead Zones

David L. Kirchman

Oxford University Press

As this chapter explains, one approach to evaluate nutrient limitation is to compare nutrient concentrations with the Redfield ratio. Alfred Redfield had no formal background in oceanography, yet he made one of the most fundamental discoveries in the field. He found that the ratio of nitrogen to phosphorus in marine microorganisms is the same as the ratio of the two elements in nutrients dissolved in the oceans. Because of work with the ratio, the current Hypoxia Action Plan for the Gulf of Mexico mentions phosphorus as well as nitrogen. In the Baltic Sea, it was argued that the focus should be solely on phosphorus to limit toxic cyanobacterial blooms, but other work demonstrates the importance of limiting nitrogen for minimizing eutrophication. Once considered to be a dead lake, Lake Erie improved after the construction of wastewater-treatment plants and the banning of phosphorus-rich detergents, as the chapter shows. But the lake continues to have problems with hypoxia and harmful algal blooms, because of continuing inputs of phosphate and organic nitrogen. The chapter ends by arguing that both nitrogen and phosphorus must be considered in efforts to solve the dead-zone problem.

Keywords:   cyanobacteria, Redfield ratio, phosphorus detergents, phosphate, microcystin

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