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Determining factors that influence Turbidity in Kaneohe Bay, Oahu

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Title:Determining factors that influence Turbidity in Kaneohe Bay, Oahu
Authors:Ohta, Everett
Contributors:Pawlak, Geno (advisor)
Oceanography (department)
Global Environmental Science (department)
Keywords:water quality
Date Issued:2006
Publisher:University of Hawaiʻi at Mānoa
Place of Publication:Honolulu
Abstract:In recent years, much attention has been given to suspended particulate matter
(SPM) concentrations, or suspended load, due to its potential impact on reef ecosystems.
Solids are transported through the ocean and can have both detrimental (through
sedimentation) and beneficial (supplying nutrients) effects on a coral reef community.
This project seeks to identify the marine physical mechanisms that influence SPM
concentrations in the reef environment of Kaneohe Bay. An acoustic Doppler current
profiler (ADCP) was used to measure a number of water properties over the coral reef
that extends across the mouth of Kaneohe Bay. The benefit of the ADCP is that it allows
researchers to not only measure water current velocities throughout the entire water
column, but it also enables this sampling to occur over extended periods of time.
Sampling occurred during three separate deployments. The third ADCP
deployment occurred in conjunction with field sampling with a Niskin bottle in hopes of
calibrating measured ADCP values of acoustic backscatter with SPM concentration from
filtered samples.
Analysis of the ADCP data showed significant variation in the echo intensity (EI)
signal, which can be used as an analogue for turbidity, between the ADCP sites. Current
speed and wave height exhibited a covariant relationship with EI data, with higher EI
values typically associated with higher waves and faster currents. Surprisingly, Sites 0-2
exhibited a diurnal cycle in EI levels, suggesting that marine biota may constitute a
significant portion of the scatterers responsible for the EI data. It was not possible to
confirm this hypothesis however, due to minimal data regarding the actual composition
of the SSC at the time of deployments. The strongest relationship was found to be the EI
response to vertical current velocities, themselves exhibiting a diurnal cycle. This
relationship was not present at Site 3. The mechanism for vertical currents appears to be
related to the incoming tide. There was a poor correlation between EI, as measured by the
ADCP, and the filtered water samples from the third experiment. This was likely due to
high spatial variations in reef characteristics and the inherent difficulty in measuring
relatively small changes in suspended load.
Pages/Duration:49 pages
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Rights Holder:Ohta, Everett
Appears in Collections: Global Environmental Science Theses

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