Dissolved organic matter (DOM) is a heterogeneous mixture of water-soluble chemical compounds. It contains organic carbon, nitrogen, and phosphorus from various biotic and abiotic sources with a wide range of chemical reactivities. DOM plays a vital role in many biogeochemical processes in estuarine sediments and is the largest reactive organic carbon reservoir across the Earth’s aquatic ecosystems. Even though coastal marine sediments are globally a significant source of DOM to the water column, their role in the marine DOM cycle is unclear because the transformation of porewater DOM that diffused to the water column remains largely unexplored. In this study, we investigate the changes in porewater DOM chemical structures during irradiation experiments. The samples were collected from six different stations from a semi-arid bay (Baffin Bay, Texas) on four different seasons. DOM sources of Baffin Bay are more dominated by phytoplankton/microbes and benthic fluxes than terrestrial sources. During all the irradiation experiments, we observed ammonia photoproduction (2-6µM). We analyzed porewater DOM using a state-of-the-art Orbitrap Fusion Mass Spectrometer coupled with both Ion chromatography and Liquid Chromatography. Preliminary structural elucidation results indicate that specific peptides and deaminated peptides with conjugated double bonds systems could lose their terminal amine functional groups as ammonia and break down into organic acids and free amino acids during irradiation experiment. This work highlights the critical connections between the marine water column and sedimentary carbon and nitrogen cycles. It will provide a better estimate of the nitrogen (N) loading to the coastal regions.

Mechanistic understanding of photo-ammonification of porewater dissolved organic matter in Baffin Bay - Texas

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.