Seasonal differences in the optical properties of chromophoric dissolved organic matter (CDOM) in the coastal waters of Puget Sound in northern Washington State

Dissolved organic matter (DOM) is an active part of marine ecosystems and plays a key role in the carbon cycle. The optical properties of chromophoric dissolved organic matter (CDOM) were measured in the coastal waters of Puget Sound in Bellingham, Washington State. Weekly samples were analyzed over multiple years to evaluate seasonal differences in CDOM sources and processing. Absorption coefficients, HIX and BIX indices showed little difference seasonally. FI values and the ratio of the fluorescence intensities of EEM peaks A/C were statistically different between winter and spring. Peak M was not observed in the EEMs. FI values were consistent with a terrestrial source of CDOM. BIX values did not indicate fresh biological production was occurring. This suggests that autochthonous microbial sources do not dominate the CDOM pool in these waters. In some water samples, additional peaks, characteristic of oil, were also observed in the EEMs . A leachate of seagrass collected near the sample site was evaluated pre and post-irradiation. Humic peaks A and C and protein peaks were observed in the leachate EEMs pre- and post-irradiation. Intensities decreased with increasing irradiation time. In future studies, we plan to examine leachates from additional marine plants found in the region and river waters entering this coastal region to further evaluate CDOM sources in this water system.