Hypoxia or “Dead Zones” in Aquatic Systems

1. Hypoxia or “Dead Zones” in Aquatic Systems Katlynd Reese Aquatic Ecology 9 November 2011

2. Outline • Introduction and background information • Some effects of hypoxia • Examples • Lake Erie • The Gulf of Mexico • Causes • Prevention • Recent article

3. 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

4. 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

5. 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

6. Examples of Harmful Dead Zones • The Gulf of Mexico • Lake Erie http://www.scientificamerican.com/article.cfm?id=oceanic-dead-zones-spread

7. Examples: Gulf of Mexico http://www.greendiary.com/entry/dead-zone-in-the-gulf-of-mexico/

8. 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

9. Examples: Lake Erie http://www.noaanews.noaa.gov/stories2005/s2427.htm

10. 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

11. Causes of Hypoxia http://water.epa.gov/type/watersheds/named/msbasin/hypoxia101.cfm

12. 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

13. 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

14. 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

15. 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.html • http://www.esa.org/education/edupdfs/hypoxia.pdf • http://water.epa.gov/type/watersheds/named/msbasin/upload/diaz_article.pdf