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Aquatic Pollution - Keynote pdf
Kaneohe Bay - Keynote pdf

Aquatic Pollution

Aquatic Pollution

All watersheds have runoff; however urbanization can alter the dynamics of runoff.

Urbanization can affect the dynamics of runoff:

  1. Total runoff volume
  2. Speed of running water

Changes are the results of the hardening of the surface.
Nonporous surfaces prevent infiltration.

Urban runoff can contain many contain pollution from urban area, such as:

  1. Nutrients
  2. Oxygen-consuming wastes
  3. Pathogens
  4. Toxic substances (pesticides, heavy metals, or oils)

Urban runoff is nonpoint source pollution.
This is a significant source of pollution in Hawaii.

Kaneohe Bay

Things to remember:

  1. Cultural eutrophication from sewage discharge.
  2. Reefs flat benthic communities became heterotrophic
  3. Quick recovery time because of short residence time of water
  4. Storm runoff might be the current major pollution source

Kaneohe Bay is subtropical estuary.
46 km2 and mean depth is 6 m (averages 12.5 in SE sector).
Salinity generally 33-35 ppt
Barrier reef restricts circulation: SE sector has most restricted circulation.
Residence time: SE sector = 24 d; rest of bay 12 d.

Causes of Pollution Problem

Pollution is related to urbanization: land runoff and sewage discharge.
Population: 1940 - 5,000
1980 - 70,000 5.3% annual growth.

Runoff

Greatly increased with urbanization.

  1. Land clearing for construction
  2. Creation of impervious surfaces

Rapid runoff increased total runoff and erosion.
Freshwater can damage reef.
Corals can tolerate 27-40 ppt.
Can get freshwater lenses with salinities as low as 23 ppt. Has kills corals to a depth of 1.5 m.

Sedimentation rate increased after 1927, now have soft mud bottom in places.
At present rate bay will fill up in 300 years.

Sewage Discharge

Sewage was released into the most stagnant part of the bay so that mixing was minimized and residence time maximized.

Realization of Pollution Problem

  1. Deterioration of coral reef
  2. Decline of water clarity
  3. Possible contamination by sewage pathogens

Deterioration of coral reef

Drastic decrease in coral cover from 1951-1972.
SE sector - 99.9% of coral died.
Transition sector- 87% of coral died.
NW sector - 26% of coral died.

Possible Contamination by Sewage Pathogens

Contamination of aquaculture shellfish.
Possible human infections.

Extent of the Pollution Problem

Sewage affected reef community in three ways:

  1. Reduction of water clarity
  2. Eutrophication - favorable to filter feeders
  3. Stimulation of bubble algae

Reduction of Water Clarity

Decreased water clarity because of increased phytoplankton biomass.
Hermatypic corals need light to photosynthesis - dinoflagellate symbionts.
Also slower coralline algae growth.

Eutrophication

Increased phytoplankton created conditions favorable to filter feeders such as sponges and zoanthids.
These organisms overgrew many corals.
Corals compete best in oligotrophic systems where P = R.
Increased production cause system reef community to switch from autotrophic to heterotrophic.
Photosynthetic and calcification rates low compared to typical reef.
Respiration higher by 85% than typical reef
P < R - greater phytoplankton production, more food for filter feeders

Stimulation of Bubble Algae

Bubble algae stimulated by eutrophication, grows on and kills coral.
Gazed in NW sector and did not grow well in SE, but estimated to have kill 24% of corals in Transition sector.

Solving Pollution Problem

1977-1978 diverted both secondary STP to seaward of Mokapu peninsula.
Diverted Ahuimanu effluent to Mokapu outflow in

Prospects for Kaneohe Bay

Short residence time so expected fast recovery.
Phytoplankton decreased in SE sector by 45%
Decrease in benthic filter feeder bubble algae population.
Secchi depth increased 30%.
Coral growth was faster than expected, in SE sector by 0-20% by 1990.

Notes of the final exam are continued in Biomes

 

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