ecological succession and dredging
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ecological succession – the replacement of one community with another over time
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pioneer species – first organisms to come into a new area
• change ecosystem slightly• can then be outcompeted by another species
• next species replaces pioneer species
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• climax species/community – dominant organisms or community in a mature stable area – outcompete others
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pioneer species
climax species
typical ecological successionon land:
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disturbance - any kind of disruption to community that sends it back to an earlier successional stage
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disturbances to forest ecosystem:
forest fire volcano
land slide
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disturbances to forest ecosystem:
farmer plowing field – if the farmerlets the field lie fallow, ecologicalsuccession will occur
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• ecological succession also occurs in the ocean
• usually changes in animal community, not plant community
• ecological succession affects biodiversity
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benthic communities includemany types of organisms
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• Over time, one community changes the environment slightly and is outcompeted by members of another community.
• The dominant community has changed – ecological succession is occurring.
• The community will remain until it is outcompeted or there is a disturbance.
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example of organismschanging the sediments:
some amphipods and worms (deposit feeders) build tubes in sediments
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• tubes stabilize sediments• makes it easier for other
organisms (suspension feeders) to survive
• suspension feeders outcompete original deposit feeders
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example of organisms changing the sediments:
• some organismsbuild burrows inanoxic (no oxygen)sediments
• pump oxygen-rich water throughburrows
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• brings oxygen into sediments• aerobic bacteria can now survive• changes and increases nutrient
cycling
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• dredging disturbs benthic habitat- when sediments are dredged up- when dredge spoils are deposited
Human Disturbance – Dredging:underwater excavation of bottom sediments
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dredging is often for navigation – sediments settle andbuild up on bottom
> 500 million cubic yards per year in U.S
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• ecological succession may start over after dredging occurs
• sediment types may change from original• therefore species may change from what
was originally there
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Dredge Disposal• Dredged material must be disposed
somewhere – LIS, ocean, on land?• Disposal site depends on level of toxic
contamination of sediments• Uncontaminated
dredged material may be used forbeach nourishment, fill, construction, cap landfills
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• dredging may also occur to removecontaminated sediment
• ecological succession may also occurafter dredge spoils are dumped
• may change sediment grain size
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• can smother existing organisms• can impact species that
reproduce when dredging is occurring
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• sediments often contain toxic
contaminants • sediments can harm eggs and larvae
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sediments can harm coral reefs:• clog feeding apparatus• block sunlight for photosynthesis• make it hard for new larvae to
settle and attach
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Dredge Disposal - OPTIONS
• Cap disposal sites to prevent leaching of contaminants to water and isolate contaminants from organisms
• Dredge from inner harbor (more polluted) to outer harbor (less polluted) – less polluted covers more polluted sediments
• Locate dump sites in deeper water
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Dredge Disposal - OPTIONS
• Restrict dredging and disposal to fall and winter (less biological activity)
• Can use on-land sites or containment islands instead
• Put dump sites in areas with high natural rate of deposition – less likely to erode