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Water Quality Characteristics of Honokohau Harbor: A Subtropical Embayment Affected by Groundwater Intrusion

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Title:Water Quality Characteristics of Honokohau Harbor: A Subtropical Embayment Affected by Groundwater Intrusion
Authors:Bienfang, P.
Date Issued:Jul 1980
Publisher:University of Hawaii Press
Citation:Bienfang P. 1980. Water quality characteristics of Honokohau Harbor: a subtropical embayment affected by groundwater intrusion. Pac Sci 34(3): 279-291.
Abstract:This study describes the water quality characteristics of a
subtropical embayment that is markedly affected by the infiltration of cold,
nutrient-rich groundwater. The spatial, vertical, and tidal variations of physicochemical
characteristics (e.g., temperature, salinity, oxygen, turbidity) and
nutrients (e.g., nitrate, phosphate, ammonium) are depicted and show conditions
of pronounced stratification. The harbor supports an unusual two-layered
structure of cold, brackish, nutrient-rich waters overlying a warm, low-nutrient,
oceanic layer. Temperature and salinity range from 20.5 to 24.5°C
and from 18.1 to 35%0 at the surface and bottom (5.5 m), respectively. High
nutrient levels in the surface layer (about 30 ug-atoms N03 -/liter and 2 ug-atoms
PO4 3 -/liter and the close correlation with thermohaline parameters
identify groundwater intrusion as the major nutrient source.
The prolific (1.5-2 million gallons per day) and continual groundwater
influx produces persistent flow out of the harbor irrespective of the tidal
condition and produces harbor flushing rates six to ten times those calculated
for tidal flushing alone. The potential eutrophying effects of the groundwater
nutrients are avoided as a result of the rapid harbor flushing. This study
details the potential impact of groundwater nutrients on the aesthetic and
water quality character of island coastal developments, indicates that consideration
of terrestrial features (e.g., land slope, rainfall) cannot be used to predict
the likelihood or extent of groundwater effects, and describes the importance
of infrastructure design to optimize flushing as a critical criterion in maintaining
good water quality in such embayments.
Appears in Collections: Pacific Science Volume 34, Number 3, 1980

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