Dataset: Biological degradation rate constants for acetaldehyde and ethanol (and associated water quality parameters) in surface waters of the Upper Newport Back Bay estuary in California from May 2021 to July 2022

The Newport Back Bay (NBB) is an estuary in Orange County, Southern California, USA. It includes the Upper Newport Back Bay, a ~1000-acre ecological preserve managed by the U.S. Fish and Wildlife Service and the California Department of Fish and Game. This estuary includes salt marshes and mudflats. The primary freshwater input is the San Diego creek which drains a ~150 square mile watershed, with  additional freshwater inputs from some storm-water drains.  Water samples were collected from 3 sites: Site 1 (inlet; 33.650327, -117.8671967); site 2 (mid-estuary; 33.6302266, -117.8859726); site 3 (near the outlet into the Pacific Ocean; 33.6181867, -117.9051099). When freshwater inflow is significant, site 1 has lower salinity water with higher dissolved organic content.

Surface water (<5 cm) was sampled in the morning from the shore, stored in amber glass bottles and transported to the laboratory.  Water quality measurements were made in-situ (Hanna Instruments HI 9829 multiparameter probe with a double junction pH/oxidation reduction potential (ORP) sensor (HI7609829-1), galvanic dissolved oxygen (DO) sensor (HI7609829-2), conductivity/turbidity sensor (HI7609829-4) and a temperature sensor. 

Absorbance was measured to assess the dissolved organic content of the sample and allow for calculations of estimated photochemical production rates of ethanol and acetaldehyde. Samples were first filtered through 0.2 micron Durapore filters to remove microorganisms. Spectra were obtained in a 1 cm quartz cell using a Horiba Aqualog spectrofluorometer.  Excitation-emission matrices (EEMs) were also collected (excitation 250-450 nm; emission 250 to 830 nm).  Nanopure water was used as the blank.  Raw absorbance data were used to calculate absorption coefficients (Juetten et al., 2025). 

Aerobic bacterial counts were measured by adding 1 mL of a 1:100 mL mixture of seawater and artificial seawater to Petrifilm Aerobic Count Plates (3M Corporation), incubating at 37oC for 48 hours and then counting the number of colony-forming units on the plates. This provides a measurement of culturable colonies and would be expected to underestimate the true aerobic microbial population. For total bacteria counts, 20 mL was filtered through black 0.2 µm polycarbonate filters (Whatman Cyclopore), fixed with glutaraldehyde (2% in 0.1 M phosphate buffer; pH 7.4; Poly Scientific) and stored in aluminum foil packets at 4oC. These filters were shipped on dry ice to Western Washington University where they were placed on microscope slides, DAPI stained and particles counted using a fluorescence microscope. 

Filtered samples were acidified to pH <2 using 6 M hydrochloric acid before measuring DOC concentrations with a Shimadzu TOC analyzer.

Chlorophyll a levels were determined with EPA method 445.0. Briefly, 200 mL were buffered saturated magnesium carbonate solution, filtered through GF/F filters (Cytiva), sealed in aluminum foil packets and stored at -80oC in the dark. Samples were shipped on dry ice to Western Washington University’s Institute for Watershed Studies laboratory where the GF/F filters were ground and chlorophyll extracted with acetone before determining chlorophyll levels by measuring  fluorescence before and after acidification with 0.1 N HCl using a Turner Designs TD700 or 10 AU.  

The measurement of acetaldehyde and ethanol uptake rates has been described in detail in de Bruyn et al. (2021). Briefly, samples were split into two aliquots; one aliquot was filtered through 0.2 µm filters (Millipore) to remove abiotic particles and microorganisms to serve as abiotic controls for biological uptake.  About 150 mL from the other unfiltered aliquot was placed in a glass syringe, spiked with deuterated acetaldehyde or ethanol (d-4; Aldrich 98% deuterated; 40-100 nM)) and used to measure acetaldehyde or ethanol  biological degradation rates.  Syringes were kept in the dark in a water bath set to the temperature of the water when sampled. Degradation rates were determined from changes in deuterated acetaldehyde or ethanol concentrations over 4 to 5-hours.  Every ~45 minutes, samples were removed from the syringe and deuterated acetaldehyde or ethanol measured by purge and trap gas chromatography mass spectrometry (Shimadzu GC-14A/HP5973MSD).  Details of this measurement are given in de Bruyn et al. (22021). In brief, deuterated acetaldehyde or ethanol is sparged using ultrapure He, trapped in a glass bead trap at liquid nitrogen temperatures, thermally desorbed, and analyzed on a Poroplot Q column (Shimadzu, 14A) with MS detection (Agilent 5973).