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Kū Hou Kuapā: Increase of Water Exchange Rates and Changes in Microbial Source Tracking Markers Resulting from Restoration Regimes at He‘eia Fishpond.

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Title:Kū Hou Kuapā: Increase of Water Exchange Rates and Changes in Microbial Source Tracking Markers Resulting from Restoration Regimes at He‘eia Fishpond.
Authors:Moehlenkamp, Paula
Contributors:Oceanography (department)
Keywords:Heʻeia Fishpond
community restoration
conservation ecology
Date Issued:Aug 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:Anthropogenic activities have changed island ecosystems throughout history. Hawaiʻi’s natural
environment has been dramatically altered by land use change, urbanization, pollution, and the
introduction of invasive species causing a demise of traditional Hawaiian fishponds across the
state over the last century. Heʻeia fishpond is currently being restored and provides- embedded
between land and sea- a unique opportunity to examine how historical land use change has
altered the functions of coastal habitats and how restoration can help to maintain and improve the
integrity of coastal ecosystems in the face of rapid global change.
He‘eia fishpond is an example of a traditional Hawaiian aquaculture system at the terminus of
He‘eia ahupuaʻa on the windward site of Oʻahu, Hawaiʻi. It is a natural embayment that is
enclosed by a constructed wall (kuapā) with sluice gates (mākāhā) facilitating water exchange
crucial for fish survival. This study examines how major restoration regimes, as the removal of
invasive mangroves, and the reconstruction of a 50 m section of the kuapā known as “Ocean
Break”, impacted water exchange rates, residence times, salinity distribution, as well as
abundance of microbial source tracking markers.
Our study revealed that Heʻeia fishpond’s physical environment is largely tidally driven during
baseline (non-storm) conditions with wind forcing and river flux being secondary drivers. Postrestoration,
two (OM1/Mākāhā Nui, Kahoʻokele (former OB)) of six mākāhā accounted for over
80% of relative flux together, making the northeastern region of the fishpond the dominant flow
pathway of water into and out of the fishpond. The repair of Ocean Break increased water
exchange rates ~5% during spring tide and ~16% during neap tide and similarly decreased
minimum water residence time in the fishpond from 38 hours to 32 hours and maximum
residence time from 102 hours to 64 hours. Salinity distribution displayed a spatial gradient
across the fishpond with higher salinities on the ocean side of the fishpond and lower salinities
towards the fresh water dominated site. Comparison of pre- vs. post-restoration salinity revealed
significantly lower average salinities post-restoration, an indication for increased fresh water flux
due to mangrove removal around the northern fishpond periphery. Spatial distribution of
microbial source tracking markers was inversely correlated with salinity. Despite decreased
residence times, average abundance of Enterococcus and Bacteroidales did not significantly
change after restoration efforts. As these microbes are introduced through freshwater from
terrigenous runoff, the increase in fresh water flushing post-restoration presents a mechanism
increasing overall abundance, hence counteracting the positive impact increased exchange rates
may have on water quality. However, average abundance of Fusobacteria, a biomarker specific
to fecal contamination from cattle egrets living at the fishpond, decreased significantly after
restoration. The source of bird microbial contamination lies in the fishpond and is less dependent
on terrigenous freshwater input suggesting that increased flushing affected bird biomarker
abundance. Taken together microbial source tracking is a promising avenue to pursue further in
understanding how restoration and changes in circulation relate to microbiological water quality
assessments.
Repairing the wall restored the fishpond to its traditional nature: A loko kuapā - a seashore
fishpond with an artificial stone wall enclosing the system during all tidal states and sluice gates
facilitating rigorous water exchange in particular in the eastern portion of the fishpond. To avoid
events with mass fish mortality in the future, we recommend moving fish pens strategically to
the eastern region of the fishpond (close to Kahoʻokele and OM1), which exhibit the highest
flushing rates with favorable conditions for fish to thrive. This study clearly demonstrates the
positive impact restoration regimes have had on water flushing and water quality parameters
encouraging the prospect of revitalizing this culturally and economically significant site for
sustainable aquaculture in the future.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2018.
URI:http://hdl.handle.net/10125/62654
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.
Appears in Collections: M.S. - Oceanography


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