katlynd reese aquatic ecology 9 november 2011 hypoxia or “dead zones” in aquatic systems
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KATLYND REESEAQUATIC ECOLOGY9 NOVEMBER 2011
Hypoxia or “Dead Zones” in Aquatic Systems
Outline
Introduction and background informationSome effects of hypoxiaExamples
Lake Erie The Gulf of Mexico
CausesPreventionRecent 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 historicallyCurrently appearing in shallow coastal and
estuarine watersDead zones are being found in larger and
larger areas of waterLasting for a longer time
Effects of Hypoxia
Kills sedentary animals Severely decreases animal and plant diversityHabitat lossWeakening or loss of populationsSignificant loss in coastal regions with high
natural diversity
Examples of Harmful Dead Zones
The Gulf of MexicoLake 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 eutrophicationStratification
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 boatingPreserve 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 ecosystems”
Diaz and Rosenberg in Science 2008Recorded the growth of dead zones across
the planetFound over 400 hypoxic zones in the worldTracked energy flow and community maturity
to determine health of the aquatic ecosystems
References
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.htmlhttp://www.esa.org/education/edupdfs/
hypoxia.pdfhttp://water.epa.gov/type/watersheds/named/
msbasin/upload/diaz_article.pdf
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