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Hypereutrophication of the Ala Wai Canal, Oahu, Hawaii: Prospects for Cleanup

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Title:Hypereutrophication of the Ala Wai Canal, Oahu, Hawaii: Prospects for Cleanup
Authors:Laws, Edward A.
Doliente, Dominador
Hiayama, Jamelle
Hokama, Mai-Li
Kim, Kay
show 3 moreLi, DeWang
Minami, Shigehiro
Morales, Christina
show less
Date Issued:Jan 1993
Publisher:University of Hawaii Press
Citation:Laws EA, Doliente D, Hiayama J, Hokama M, Kim K, Li D, Minami S, Morales C. 1993. Hypereutrophication of the Ala Wai Canal, Oahu, Hawaii: prospects for cleanup. Pac Sci 47(1): 59-75.
Abstract:Studies of trophic conditions in the Ala Wai Canal were carried
out during a 6-week period during the summer of 1991. The canal is a partially
mixed estuary whose water quality and trophic status are impacted to a large
extent by run-off from residential and light industrial portions of the City of
Honolulu. Gross photosynthetic rates are about 5.5 g C m-2 d-1 and increase
by a factor of three from the mouth to the head of the estuary. Photosynthesis
appears to be limited only by the availability of light and the concentration of
phytoplankton. Allochthonous inputs of organic carbon exceed photosynthetic
rates by about 60%. Of the total allochthonous plus autochthonous organic
carbon input to the system, respiration consumes about 70%,18% accumulates
in the sediments, and about 12% is flushed out at the mouth of the canal.
Sedimentation amounts to about 7-8 x 10 3 m3 yr-1 and has greatly altered the
bathymetry of the canal. Concentrations of particulate carbon, particulate
nitrogen, and chlorophyll a are comparable to values reported 20 yr ago, despite
dredging of the canal in 1978-1979. Surface waters are supersaturated with
oxygen during the day and undersaturated at night. Shallow subsurface waters
undergo even greater diel oxygen changes because of inefficient oxygen exchange
with the atmosphere. Oxygen concentrations below a depth of 3 m frequently
violate Environmental Protection Agency water quality criteria. Flushing the
canal by pumping in seawater at its head at a rate of about 104 m3 hr-1 will
probably do much to improve the aesthetic condition of the canal and increase
oxygen concentrations in the bottom waters.
Appears in Collections: Pacific Science Volume 47, Number 1, 1993

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