Ecological Succession And Dredging


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Ecological Succession And Dredging

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