dead zones 1

8/7/2019 Dead Zones 1

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The Ocean Dead Zones


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What are Dead Zones?

y Dead Zone or otherwise known as eutrophication. Process involvingremoval of oxygen from water bodies

y Two Causes: Natural and Anthropogenic.

y Main difference is anthropogenic eutrophication occurs much morerapidly.


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The Problem

Non-point source pollution

Point source pollution


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Non-point source pollution

y Pollution that arise from many dispersed areas and it is not traceable toany single discrete source (e.g., cars leaking oil, excess fertilizers infarms)


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Point source pollution

y Pollutants discharged from a single identifiable location (e.g., pipes,ditches, channels, sewers, tunnels)


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Sources

y Natural

y Anthropogenic


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Natural

y Stratification of fresh water over salt water.

y Warming ocean waters.

y Increased concentrations of CO2 in ocean.


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Anthropogenic

y Agriculture and Municipal are main human sources

y Rapidly stimulates phytoplankton growth.

y The natural decomposition of phytoplankton depletes O2 from Gulf.


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NitrogenNitrogen PhosphorousPhosphorousy Nitrates (fertilizers containing

NO3- ) are highly water soluble,.

y Only 18% applied N is taken upby produce.

y Fertilizers make up 70 percentof the N in Gulf.

y Nitrogen delivered to Gulf hastripled in the last 4 decades.

y Not water soluble, moves onlywith soil movement.

y Erodes on soils fromagricultural fields, where it is

non-recoverable.y Net P storage in soil and fresh

water ecosystems is 75% higherthan preindustrial times

Main Pollutants


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Ecological effects

y Increased biomass of phytoplanktony Toxic or inedible phytoplankton speciesy Increases in blooms of gelatinous zooplanktony Decreased biomass of benthic and epiphytic algae

y Changes in macrophyte species composition and biomassy Decreases in water transparencyy Colour, smell, and water treatment problemsy Dissolved oxygen depletiony Increased incidences of fish killsy Loss of desirable fish speciesy Reductions in harvestable fish and shellfishy Decreases in perceived aesthetic value of the water body


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The program noted preventive steps can be taken

y European nations along the Rhine agreed to halvedischarged nitrogen levels, reducing the dischargeinto the North Sea.

y Planting new forests and grasslands will help soak upexcess nitrogen, keeping it out of waterways.

y Requiring vehicles to reduce nitrogen emissions.

y Fostering alternative energy sources that are not

based on burning fossil fuels.

y Better sewage treatment would reduce nutrientdischarges to coastal waters.


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