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?
 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”
http://www.edupic.net/fish.htm
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
http://www.scientificamerican.com/article.cfm?id=oceanic-dead-zones-spread
Examples: Gulf of Mexico
http://www.greendiary.com/entry/dead-zone-in-the-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
http://www.noaanews.noaa.gov/stories2005/s2427.htm
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
http://water.epa.gov/type/watersheds/named/msbasin/hypoxia101.cfm
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
Prevention
 Reduce use of fertilizers and manage their use
 Practice clean boating
 Preserve land adjoining rivers and streams
http://www.dbw.ca.gov/Pubs/CleanBoatingHabits/Default.aspx
Recent Article: Diaz and Rosenberg
 “Spreading dead zones and consequences for marine
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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
References
 Diaz, Robert J. et al. 2008. “Spreading dead zones
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and consequences for marine ecosystems”.
Science 321: 926.
http://water.epa.gov/type/watersheds/named/msba
sin/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/msba
sin/upload/diaz_article.pdf