Dataset: Water quality parameters from discrete sampling of West Maui shoreline following the Lahaina Wildfires from Aug 2023 to Oct 2024

Sample Collection

Boat transect sampling was done twice a day on two dates, 2023-10-07 and 2024-01-27. These were done at sites L1-L5. Between 2023-10-07 and 2024-10-23 shoreline samples were taken for sites SH1-SH11. Between 2023-10-07 and 2024-08-04, an autosampler was used at Kahekili Beach Park (KBP) and Mala Point (M).

Sample Analysis

a. Carbon Chemistry (μmol/L): One sample is collected for the analysis of TA and DIC and a second is collected for DOC. TA/DIC is collected by submerging a niskin bottle just below the surface of the water and collecting a sub sample. A piece of PharMed BPT tubing is attached to the niskin bottle and placed on the bottom of a 250mL VWR narrow mouth glass bottle and rinsed and dumped three times. Each sample is poisoned with 0.1 mL of mercuric chloride and the glass topper is sealed with Apiezon L Vacuum Grease and a snap-grip clamp.

a.1.Total Alkalinity (TA): Alkalinity determination using the Gran titration method. Alkalinity is determined by the amount of acid (in mol/kg or mol/L) needed to titrate a water sample to the CO2 equivalence point (about 4.4) at which all inorganic carbon species are converted to CO2 in seawater. Measurements validated with Dickson CO2 Certified Reference Material.

a.2. Dissolved Inorganic Carbon (DIC): All species of carbon are transformed into CO2 and the resulting CO2 gas is purged from the water sample by the pure nitrogen (N2) carrier gas and use only a single certified reference material to make a three-point calibration line or broken line. Apollo Dissolved Inorganic Carbon Analyzer Model AS-C5 was calibrated with Dickson CO2 Certified Reference Material.

a.3. Dissolved Organic Carbon (DOC): Water for TOC analysis was collected in 40 ml amber Volatile Organic Analysis (VOA) vials with silicone septum caps. TOC was measured on a Shimadzu TOC-L Combustion analyzer. Water samples were not filtered prior to collection and included both dissolved and particulate organic carbon.

a.4 Total Organic Carbon (TOC): Water samples were analyzed for total organic carbon (TOC). Water for TOC analysis was collected in 40 ml amber Volatile Organic Analysis (VOA) vials with silicone septum caps. Prior to sampling, vials and caps were acid washed with 10% HCl and vials were combusted at 450°C for 4 hours. Prior to collection, sample vials and caps were triple rinsed with sample water. Vials were filled to the shoulder with sample water and then acidified to a pH of ~2 via dropwise addition of 12M hydrochloric acid.

b. Trace Metals: Samples for dissolved and total dissolvable metal concentrations were collected in acid washed polyethylene bottles, which were rinsed 3 times before filling. During offshore sampling, a 10' polyvinylchloride pole was assembled to collect non-contaminated samples away from the vessel. During shore sampling, bottles were fill from upstream waters and closed immediately after filling. Samples for dissolved metals were vacuum filtered using a 0.2 um polyethersulfone membrane. Samples for total dissolvable metals were not filtered. Both filtered and unfiltered samples were acidified to a pH of 1.8 using ultra high purity hydrochloric acid and stored for several weeks prior to analysis.

For dissolved iron, zinc, nickel, copper, cadmium, and lead, samples were subject to preconcentration using a SeaFAST S2 system (Elemental Scientific) after addition of an isotope spike to track sample recover. 10 mL of samples were preconcentration into 0.75 mL and analyzed by inductively coupled plasma mass spectrometry (ICP-MS) using an iCAP-TQ instrument (Thermo Fisher Scientific) using O2 as a collision gas. Pre-concentration blanks were assessed by measuring high purity (18.2 M-Ohm cm-1) water after passing through the SeaFAST system and subtracted from measured values.

For dissolved Mn, Ba, V, and As, and all total dissolvable measurements, samples were also measured by ICP-MS, but after dilution in 0.1 M nitric acid with In as an internal standard. These samples were calibrated diluted multi-element standard (Inorganic Ventures) with matrix-matched seawater collected from offshore waters in the North Pacific Subtropical Gyre. 

For dissolved metals analyzed by both procedures, CASS7 and NASS5 seawater reference materials were measured to ensure accuracy of calibrations. No standards are available for total dissolvable metal measurements. 

c. Metabolomics: For untargeted LC-MS/MS, 200 ml water samples were acidified to pH2 and collected on solid phase extraction cartridges with a 60mg HLB resin bed. Cartridges were eluted using 2 mls of LC/MS grade methanol, evaporated to dryness, and redissolved in 100 µl of 80:20:1 Methanol/water/formic acid. Samples were run in data dependent acquisition mode on an Orbitrap Exploris MS/MS coupled to a Vanquish Flex UHPLC using a Kinetex® 1.7 µm C18 150 x 2.1 mm Column and C18 guard column. 

d. Nutrients: Nutrient samples were collected by rinsing a previously acid washed 125 mL Nalgene HDPE bottle three times with surface water and next filled leaving room on the top to allow freezing. Samples are immediately placed in a dark cooler on ice and frozen at the end of the sampling day. Samples are removed from the freezer the night before analyzing and are slowly defrosted in a dark environment. Measurements were validated with Kanso Certified Reference Material.

d.1. Nitrate and Nitrite: Method no. A-044-19 Rev.5: Nitrate is reduced to Nitrite at pH 7.5 in a copperized cadmium coil. Nitrite is reduced with sulfanilamide to form a diazo compound that then couples with N-(1-Naphthyl)ethylenediamine dihydrochloride to form an azo dye that is measured at the absorbance of 540 nm.

d.2 Phosphate: Method no. A-005-19 Rev.3:ortho-phosphate, molybdate, and antimony form a blue color followed by the reduction with ascorbic acid at pH <1. This reduced blue phospho-molybdenum complex is read at the absorbance of 880nm.

d.3 Silicate: Method no. A-006-19 Rev.4: silico-molybdate is reduced in an acidic solution of molybdenum blue by ascorbic acid. Oxalic acid is added prior to ascorbic acid to reduce interference from phosphates.

d.4 Ammonia: G-327-05 Rev 9: sample is reacted with o-phthalaldehyde at 75C with a borate buffer and sodium sulfite and analyzed at an absorbance of 460 nm following excitation at 370 nm.

e. Fluorescence Dissolved Organic Matter (fDOM): Water for fDOM analysis was collected in acid washed 20 ml glass vials with urea caps. Vials and caps were triple rinsed with sample water prior to collecting each sample and stored at 4° C . 3 ml subsamples were transferred into 1 cm quartz cuvettes, which were then loaded into the fluorometer. Excitation-Emission Matrices (EEMS) were generated with excitation values ranging from 240 nm to 500 nm and emission values were measured ranging from 250 nm to 825 nm. These included M:C (Burdigee et al. 2004), FI (McKnight et al. 2001), BIX (Huguet et al. 2009), HIX (Zsolnay et al. 1999), M, A, C, T, and B (Coble 1996).

f. Flow cytometry: Water samples were analyzed for bacterial counts using flow cytometry. Water for flow cytometry was subsampled from triple rinsed and acid washed 1L polycarbonate bottles. For each sample, a 1 ml subsample was transferred via pipette to a 2ml screw cap tube. Samples with17 µl of 32% paraformaldehyde, for a final concentration of 0.5% paraformaldehyde in each sample. During field collection, samples were stored on ice in the dark. To avoid repeated freeze-thaw cycles, flow cytometry samples were preserved at 4°C for a period of up to 48 hours while in the field prior to long term storage at -80°C. For analysis, 275 µl aliquots from each sample were transferred to 96-well optically clear flat bottom plates. Each sample was stained with 7 µl of Hoechst stain following Selph et al. (Selph 2021 CITE). Samples were analyzed on a CytoFlex flow cytometry. Gates were established empirically to generate counts of 4 distinct populations of marine microorganisms: heterotrophic bacteria, large autotrophs, small autotrophs, all autotrophs.