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Introduction

Excavation of the Wai Kai Lagoon began late in 2003 and was completed in August 2008. Monitoring of the water quality in the Lagoon began in January 2005, in accordance with the methodology approved by the State of Hawai`i Department of Health and pursuant to Haseko’s Department of the Army Water Quality Certification (WQC 137) for the original marina project. Preliminary biological monitoring of the Lagoon flora and fauna began in 2012. Results of this work are summarized in the environmental impact statement published for Haseko’s zone change application.  In mid-2014, Haseko initiated monthly biological surveying in the Lagoon to complement ongoing monthly water quality monitoring. This work continues, with results shown to July 31, 2023. The available results for this water quality and biological monitoring program from 2015 to present are summarized here graphically after a description of the methods used. Sample station locations used for routine monitoring are shown below.

Monitoring Station Locations. Prepared by Planning Solutions, Inc.

Water Quality Measurements

Lagoon water samples are collected from surface water (within 6 inches of the surface) and near-bottom water (within 1 foot of the Lagoon floor). Stations 1-12 in the Lagoon have been sampled for water quality since 2006. Sampling at Stations 14 and 15, which are the Mauka and Makai water quality lakes, began in April 2019.

All Lagoon samples are collected from a small, inflatable boat. Surface samples in the Lagoon are collected by filling bottles by hand over the side of the boat. Near-bottom samples are collected using a 2L Niskin oceanographic sampling bottle, which is lowered to the desired sampling depth with spring-loaded end-caps held open so water can pass freely through the bottle. A weight hung below the bottle signals the designated sampling depth above the bottom. At the desired sampling depth, a weighted messenger released from the surface triggers closure of the end caps, isolating a volume of water from depth. Upon retrieval, water from the Niskin bottle is poured into 250 ml, acid washed and triple-rinsed polyethylene bottles.

Samples from the water quality lakes are collected only from the near-surface. This is done using a sample bottle attached at the end of a long pole to minimize the possibility of contaminating the sample with material dislodged from the lake edges. At times, surface samples are collected from the middle of the water quality lakes off the side of an inflatable stand up paddleboard.

Water quality parameters evaluated for the Lagoon include all of those for which Chapter 11-54 of the State of Hawai`i Department of Health (DOH) Water Quality Standards establish specific criteria. These parameters include: total nitrogen (TN), nitrate + nitrite nitrogen (NO3 + NO2), hereinafter referred to as NO3, ammonium nitrogen (NH4), total phosphorus (TP), chlorophyll-a (Chl-a), turbidity, pH and salinity. In addition, ortho-phosphate (PO4) and silica (SiO2) are measured, because these parameters are sensitive indicators of biological activity and the degree of groundwater mixing.

Following collection, samples for nutrient analysis are immediately stored on ice. Analyses for NH4, PO4, Si and NO3 are performed with a Seal Analytical segmented flow autoanalyzer (AA3) using EPA approved standard methods for seawater analysis (Strickland and Parsons 1968, Grasshoff 1983). TN and TP are analyzed in a similar fashion following oxidative and UV digestion. Total organic nitrogen (TON) and total organic phosphorus (TOP) are calculated as the difference between TN and dissolved inorganic N and between TP and dissolved inorganic P, respectively.

Water for additional testing is subsampled from the polyethylene bottles and kept chilled until analysis. Chl-a is measured by filtering 150 ml of water through glass-fiber filters (Whatman GFF); pigments on filters are extracted in 90% acetone in the dark at 20° C for 24 hours. Chlorophyll concentration is determined using the modified fluorometric technique (EPA Method 445.0 rev 1.2) and a Turner Trilogy Laboratory Fluorometer. Salinity is determined using a Mettler Toledo InLab-731 ISM conductivity probe and pH is measured using a Mettler Toledo InLab Expert Pro-ISM probe. Turbidity is measured on 20 ml subsamples using a Hanna Instruments HI88703 Turbidimeter. Laboratory testing for water quality variables was conducted by Marine Consulting and Analytical Resources, LLC.

In situ field measurements of water temperature, dissolved oxygen, pH and salinity are acquired using an RBR Maestro3 CTD (Conductivity, Temperature, Depth) profiling instrument, calibrated to factory specifications. The CTD has a readability of 0.001°C, 0.001 pH units, 0.001% oxygen saturation, and 0.001 parts per thousand (salinity). The instrument is lowered slowly through the water column and automatically records data eight times per second.

Prior to December 2019, screening for Enterococci bacteria as a fecal indicator was conducted using the membrane filtration EPA Method 16003. Since late 2019, the Enterolert® method for Enterococci is run concurrent with the membrane filtration method. For both analytical methods, water samples are collected from just under the surface directly into a sterile container. Collected samples are placed in a cooler containing an ice pack and then transported to the lab for immediate processing.

For EPA Method 1600, Standard Method 9230C, membrane filtration procedure (mE1 Agar, 24-hour incubation at 41°C) was used for the detection and enumeration of Enterococci bacteria in water as described in Standard Methods for the Examination of Water and Wastewater. The units for the EPA 1600 Method are “colony forming units” (CFU) per 100 ml.

The Enterolert® test employs a proprietary nutrient indicator to detect Enterococci. It does not require bacterial culturing of the water sample to estimate Enterococci, but instead relies on colorimetric tagging to detect the active enzymes that indicate the presence of these bacteria (24-hour incubation at 41°C). The units for the Enterolert® method are “most probable number” (MPN) per 100 ml.

Enterocci data are compared with the Beach Action Value (BAV). A BAV of 130 CFU or MPN per 100 ml is the HDOH Clean Water Branch equivalent of the EPA recommended threshold value and triggers a resampling the next workday and issuance of an advisory until testing indicates action is no longer needed (https://health.hawaii.gov/cwb/files/2020/09/Hawaii-Beach-Monitoring-Program-FINAL_9-1-20.pdf).

Chara Percent Coverage and Canopy Height

The canopy-forming macroalga Chara zeylanica (Chara) covers most of the Lagoon bottom. Estimates of percent Chara coverage on the Lagoon bottom and average canopy height above the bottom are made monthly by Aquatic Research Consultants LLC at designated stations using SCUBA diving transects 50 meters (~165 feet) in length, starting from each station marker buoys and continued along fixed, predetermined headings. At each site, the GPS location is noted at the beginning and end of each transect. The percent cover of Chara is determined using the point contact method. The presence/absence of Chara is measured at every 1-meter increment, for a total of 50 points sampled. The percent cover of Chara is calculated as the percentage of the points sampled where Chara is present. For example, if a diver noted that Chara is present at 14 of 50 points sampled along the transect, then the coverage equals 28%. The Chara canopy height is measured every 5 meters, if present, along the transect.

Chara Nitrogen Stable Isotope Ratios

The ratio found in Chara tissue between the stable heavy isotope of nitrogen (15N) and the more commonly occurring isotope (14N) is related to the potential sources of the nitrogen nutrients assimilated into the alga from the ambient water. The indicator variable used, δ15N, is normalized to the ratio of these two isotopes found in the atmosphere. The apical, new growth of the alga (upper 3-5 cm) was used for analyses. Samples were processed according to Strait and Spalding (2021)4 and left calcified to limit nitrogen degradation resulting from the acidification process. The δ15N values for this monitoring effort are determined at the Biogeochemical Stable Isotope Facility for Stable Isotopes at the University of Hawai`i.5

Chara Tissue Nitrogen Concentration

Dry-weight nitrogen concentrations are analyzed for Chara tissue samples by the Biogeochemical Stable Isotope Facility at the University of Hawaiʻi at Mānoa. Relatively high concentrations suggest plentiful nitrogen nutrient availability. The apical, new growth of the algal thallus (upper 3-5 cm) is used for analyses.

Tilapia Nest Occurrence

During the Chara coverage and height surveys, the number of Tilapia (Oreochromis mossambicus) nests are counted within a distance of 1 m from the transect along one side of the 50 m transect. Visibility at depth is also noted along the transect line over unvegetated (bare sediment) and vegetated areas.

Irradiance Profiles

Measuring irradiance (µE m-1 s-1), or light, in the Lagoon water column allows for the comparison of changes in the attenuation of light in the water over time due to increases or decreases in phytoplankton and other particulate matter in the water. Irradiance profiles are measured mid-day at 0.5 m depth increments from just below the water surface to the Lagoon bottom (or top of the Chara canopy, as determined when the profiling line becomes slack). Measurements are only taken when weather conditions are clear and sunny. Profiles are conducted on the sunny side of the boat to minimize the effect of boat shadow. A LI-COR LI-1400 data logger coupled with a LI-COR underwater spherical quantum sensor mounted on a profiling frame with a 10 m LI-COR underwater cable is used to measure irradiance. Depth is measured with a line marked at 0.5 m increments. A spherical sensor is used instead of a cosine sensor because the spherical sensor more accurately measures light in a manner consistent with how Chara absorbs light at depth. The Secchi depth is also recorded at each site to compare with the diffuse attenuation coefficient.

Plankton Assemblages

Samples for analysis of the plankton assemblage are collected to evaluate temporal and spatial variability, the stability of the microbial system, and to complement water chemistry measurements. Whole water samples6 or phytoplankton and zooplankton determinations are collected in 1L dark bottles and 5 x 1- gallon plastic jugs respectively, from the surface waters of each station. Zooplankton samples are filtered onto a 93-µm mesh and preserved on site; phytoplankton samples are immediately taken to the laboratory on ice and preserved within 2 hours for subsequent analysis. Because the size range of the plankton assemblage spans four orders of magnitude (<1 μm to >1 mm), a suite of different preservatives and methods is necessary to address each segment of the population. Detailed descriptions of these methods are available from Marine Consulting and Analytical Resources, LLC7.