MODIFIED BY J.SHANNON The Coast: Dead Zones

Dead zones are regions in fresh and marine aquatic environments in which dissolved oxygen concentrations drop to extremely low levels What is a Dead Zone?

Around the world in both fresh and saltwater systems For example: Lake Erie, Chesapeake Bay, Northern Gulf of Mexico and the Baltic Sea Worldwide there is an increase espically in coastal areas next to heavily populated areas. Where do they occur?

Combination of biological and physical factors Nutrients from farming and urban development are washed into lakes, rivers and the ocean Microscopic plant populations quickly grow from the nutrients This is referred to as eutrophication How Are Dead Zones Created?

These plants are called phytoplankton. When they use all the nutrients, they die and sink to the bottom Bacteria decompose the dead plants and consume oxygen in the process New oxygen cannot get to the bottom of the ocean Hypoxia happens which is a lack of oxygen and dead zones are created How are Dead Zones Created? Continued

Nutrient Pollution This increase has been attributed to the increased use of nitrogen and phosphorous fertilizers, nitrogen fixation by leguminous crops, and atmospheric deposition of oxidized nitrogen from the combustion of fossil fuel. 7

Fish and mobile invertebrates (shrimp, crabs etc) leave the areas Plants and slow moving animals (seagrass, worms and clams) cannot escape and die from lack of oxygen What are the effects of hypoxia?

Permanent Hypoxia Some areas experience essentially constant hypoxia 9

Temporary Hypoxia In others, hypoxia lasts from hours to days 10

Seasonal Hypoxia Seasonal hypoxia occurs every year, during the warm months 11

In groups of two, brainstorm as many ways that we can prevent dead zones. Write them down for a class discussion. In the same group, brainstorm as many ways as possible that we can clean up dead zones that already exist. (Natural ways and man made ways) What could happen if nothing is done to stop dead zones from happening? How can we prevent dead zones?

Recent Episodes Chris Paschenko reported in The Galveston Daily News on August 13, 2012, “Low oxygen levels are believed to have killed possibly hundreds of thousands of Gulf menhaden fish found littering beaches and shorelines from Matagorda to Galveston, officials said Sunday.” (August12) 13

Gulf of Mexico,

Other Sites Around the world Black Sea 15 High nutrient loads cause major phytoplankton blooms on the Black Sea in the 1970’s

In the mid-1990’s, the dead zone of the Black Sea all but disappeared Gives hope that reductions in nutrient load will reduce the frequency of dead zones 16

Baltic Sea Northern European body of water is salty and deep. Affected by humans for centuries Following World War II, increasing fertilizer use and a growing population led to high inputs of nutrients to the Baltic. 17

Baltic Sea Decline Increased nutrient load causes algae blooms which eventually caused low oxygen conditions Efforts to decrease nutrient loads to the Baltic were successful in minimizing the size of the dead zone in the mid-1990s 18

Baltic Sea Hypoxia Area Decreases in nutrient loading helped 19