Hypoxia or dead zones in aquatic systems
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Hypoxia or “Dead Zones” in Aquatic Systems. Katlynd Reese Aquatic Ecology 9 November 2011. Outline. Introduction and background information Some effects of hypoxia Examples Lake Erie The Gulf of Mexico Causes Prevention Recent article. What is Hypoxia?.

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Hypoxia or “Dead Zones” in Aquatic Systems

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Hypoxia or “Dead Zones” in Aquatic Systems

Katlynd Reese

Aquatic Ecology

9 November 2011


  • Introduction and background information

  • Some effects of hypoxia

  • Examples

    • Lake Erie

    • The Gulf of Mexico

  • Causes

  • Prevention

  • Recent article

What is Hypoxia?

  • Hypoxia is defined as a condition where the DO is less than 2-3 ppm

  • Often referred to as a “dead zone” in a body of water

  • A complete lack of oxygen is referred to as “anoxic”


Background Information

  • Dead zones have always existed historically

  • Currently appearing in shallow coastal and estuarine waters

  • Dead zones are being found in larger and larger areas of water

  • Lasting for a longer time

Effects of Hypoxia

  • Kills sedentary animals

  • Severely decreases animal and plant diversity

  • Habitat loss

  • Weakening or loss of populations

  • Significant loss in coastal regions with high natural diversity

Examples of Harmful Dead Zones

  • The Gulf of Mexico

  • Lake Erie


Examples: Gulf of Mexico


Examples: Gulf of Mexico

  • Occurs where the Mississippi River meets the Gulf

  • Water stratifies due to salinity differences

    • Epilimnion: fresh water is less dense

    • Hypolimnion: salt water is more dense

    • Crates stratification

  • Results in anoxic conditions in more dense waters

  • Nutrient loading into the Mississippi is another possible cause

  • A high biodiversity area

Examples: Lake Erie


Examples: Lake Erie Central Basin

  • Sever eutrophication

  • Stratification

    • Before fall mixing…

    • Warm epilimnion and cold hypolimnion

    • Shallow central basin cannot hold very much oxygen

  • Not only affects ecosystem but also the fishing industry and therefore economy

Causes of Hypoxia


Causes of Hypoxia

  • Algal blooms and nutrient loading

    • When large amounts of algae die they sink to bottom

    • Decomposition uses up a lot of DO

  • Abiotic conditions of body of water

    • Depth and shape

    • Wind and weather

    • Flow strength and direction

  • Global Warming

    • Temperature increase can decrease the maximum amount of DO

    • Exacerbates the eutrophication problem


  • Reduce use of fertilizers and manage their use

  • Practice clean boating

  • Preserve land adjoining rivers and streams


Recent Article: Diaz and Rosenberg

  • “Spreading dead zones and consequences for marine ecosystems”

  • Diaz and Rosenberg in Science 2008

  • Recorded the growth of dead zones across the planet

  • Found over 400 hypoxic zones in the world

  • Tracked energy flow and community maturity to determine health of the aquatic ecosystems


  • Diaz, Robert J. et al. 2008. “Spreading dead zones and consequences for marine ecosystems”. Science 321: 926.

  • http://water.epa.gov/type/watersheds/named/msbasin/hypoxia101.cfm

  • http://www.eoearth.org/article/Hypoxia_fact_sheet

  • http://toxics.usgs.gov/hypoxia/hypoxic_zone.html

  • http://www.esa.org/education/edupdfs/hypoxia.pdf

  • http://water.epa.gov/type/watersheds/named/msbasin/upload/diaz_article.pdf

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