Dataset: Dissolved organic matter (DOM) optical properties 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, transported to the laboratory, filtered through 0.2 micron Durapore filters and stored in the fridge.  Optical properties were measured to assess the dissolved organic content of the sample and allow for the estimation of the photochemical production rates of ethanol and acetaldehyde. Samples were 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. EEMs were corrected for inner filter effects and 1st order Rayleigh scattering using post-measurement routines of the Aqualog. Raw absorbance data were used to calculate absorption coefficients. 

These methods are described in more detail in Juetten et al. (2025).