Assessing Riverine Inputs Versus in situ Production as Sources of Chromophoric Dissolved Organic Matter in Bellingham Bay in the Salish Sea

Authors

• Caleb D. R. Jansen, Western Washington University
• Erika McPhee-Shaw, Western Washington University
• Joseph Loughren, Western Washington University
• Jefferson Crosland, Western Washington University
• Ashley Yamamaura, Western Washington University
• Aaron Harrison, Trinity University
• Aquila Flower, Western Washington University
• Warren de Bruyn, Chapman UniversityFollow
• Catherine D. Clark, Western Washington University

Document Type

Article

Publication Date

1-18-2026

Abstract

Differences in lability between allochthonous and autochthonous dissolved organic matter (DOM) can drive changes in bacterial community composition and metabolism. To assess riverine inputs versus in situ production as DOM sources, we measured optical properties in Bellingham Bay, Washington (USA) over 1 year (n = 38 measurements). Optical indices were consistent with riverine inputs as the primary source of chromophoric DOM (CDOM) throughout the year. Three components were identified by parallel factor analysis of the excitation–emission matrices (EEMs). The major terrestrial humic-like component from riverine inputs dominated all samples. A secondary component was attributed to microbial degradation of the terrestrial humic material. A minor protein-like component was present in 70% of samples. The highest absorption coefficient at 300 nm (a300; increases with increasing chromophoric DOM amount) and lowest spectral slope (S; 300 to 400 nm; higher for more photochemically and biologically processed material) occurred in the fall with increased river discharges. This increase was attributed to high levels of freshly-produced terrestrial CDOM washing in from the watershed with the first rainfall after the summer dry season. S occasionally increased with low river discharges, which was attributed to the influence of seawater. There was evidence of sporadic instances across all seasons when in situ production was significant. Variability in the optical parameters suggested monthly sampling would miss events with increased CDOM levels and indicators of different CDOM sources. Impacts of climate change on rainfall, river discharges and hydrodynamics may change the relative contributions of riverine and in situ sources, affecting the biological community.

Comments

This article was originally published in Aquatic Sciences, volume 88, in 2026. https://doi.org/10.1007/s00027-025-01264-1

Recommended Citation

Jansen, C.D.R., McPhee-Shaw, E., Loughren, J. et al. Assessing riverine inputs versus in situ production as sources of chromophoric dissolved organic matter in Bellingham Bay in the Salish Sea. Aquat Sci 88, 27 (2026). https://doi.org/10.1007/s00027-025-01264-1

Copyright

Springer