Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

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).

Acetaldehyde and ethanol concentrations in unfiltered incubations decreased exponentially with time consistent with first-order or pseudo-first-orde rkinetics. For first order or pseudo first order kinetics the rate of reaction depends only on the concentration of a single species, in this case acetaldehyde or ethanol: Reaction rate = -dA/dt = k [A]      where [A] is the acetaldehyde or ethanol concentration and k is the first order rate constant. Separating variables and integrating results in the integrated rate law: ln [A]t/[A]t=0 = - kt        Where [A]t is the concentration of acetaldehyde or ethanol at time t and [A]t=0 is the concentration of acetaldehyde or ethanol at t=0.  Therefore a plot of the natural log of the acetaldehyde concentration at time t divided by the concentration at time t=0 is linear and the slope is the first-order rate constant with units of time-1.  This is summarized from De Bruyn et al. (2021).

Absorbance was converted to absorption coefficient at a particular wavelength by dividing the absorbance by 0.01 and multiplying by 2.303. This is described in Juetten et al. (2025).

* adjusted parameter names to comply with database requirements
* added lat/lon of sampling sites to dataset
* converted sampling date to ISO format

NSF Award Abstract

Ethanol is added to gasoline to increase octane levels and lower the concentrations of carbon monoxide and surface ozone in the atmosphere. As a renewable fuel, ethanol may also help decrease our dependence on gasoline. Increased use of ethanol in the United States and globally as a fossil fuel substitute and additive is expected to increase ethanol levels in the atmosphere. Atmospheric ethanol is converted to acetaldehyde which is a hazardous pollutant. To understand the impact of increasing ethanol usage, it is important to understand the cycling of ethanol and acetaldehyde in the environment--how they are produced, consumed, and interconverted. Because these compounds can cross from air into water, this requires understanding what happens to these compounds in both the atmosphere and in seawater and other surface waters. This proposal focuses on improving our understanding of processes that produce and consume ethanol and acetaldehyde in coastal seawater and other coastal surface waters like estuaries and salt marshes. This project will measure the rates of photochemical production of ethanol and acetaldehyde, as well as their chemical and biological degradation rates. The project will also measure the rate and efficiency of the biological production of acetaldehyde from ethanol by microbial organisms in these waters. The scientists have an excellent track record of involving undergraduate students, including underrepresented minorities, in their research and as co-authors on publications, a trend they plan to continue with this project. These students would be trained in analytical chemistry and environmental research and would present their research findings at local and national conferences. Lastly, the PIs also plan outreach activities with high school STEM programs to improve student diversity in environmental research.

The primary sink for ethanol in the troposphere is reaction with OH to produce acetaldehyde. Acetaldehyde levels in the troposphere are also expected to increase with increased use of ethanol. Changes in the atmospheric concentrations of these species are expected to have a significant impact on the oxidative capacity of the troposphere. To understand future impacts, it is important to understand current tropospheric budgets which have significant uncertainties for both species. One of the largest sources of uncertainty is the role of the oceans and surface waters in cycling these species into and out of the troposphere. The current understanding is limited by the very small database of ambient concentration measurements in both air and water and an incomplete insight into the processes that control concentrations in seawater and surface waters; these processes represent a complex interplay between biological and photochemical sources and sinks, and air-water exchange. To improve the current understanding of the cycling of ethanol and acetaldehyde in coastal seawater and surface waters, this project will measure: 1) chemical and biological degradation rates of ethanol and acetaldehyde in coastal waters; 2) the rate and efficiency of the biological production of acetaldehyde from ethanol by microbial organisms; 3) ethanol and acetaldehyde concentrations in air and surface waters; 4) the ethanol and acetaldehyde source strength of estuary and saltmarsh sediments; and 5) ethanol and acetaldehyde photochemical production rates in surface waters.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.