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