The subterranean estuary (STE) has been recognized as a reactive biogeochemical zone at the groundwater–seawater interface in coastal areas. In this study, we conducted controlled laboratory experiments to elucidate dissolved organic matter (DOM) processing and microbial community dynamics in STEs under various particle size distributions, salinity regimes, and incubation times. Incubations with silt-dominated sediments generated pore water characterized by high dissolved organic carbon (DOC)-to-dissolved organic nitrogen (DON) ratio, while the addition of high-ionic-strength treatments to the incubations led to reduced DOC solubility, selective removal of aromatic compounds, and altered ammonium (NH₄⁺) generation pathway from predominantly biological (mineralization) to abiotic (ion exchange) pathways. Our experiments further indicated that the long incubation time caused the enrichment of DOC, DON, and bulk DOM consisting of degraded DOM compounds. Regarding the microbial community, Firmicutes, Proteobacteria, and Desulfobacterota were the most abundant phyla in incubated sediments. Although some phyla’s relative proportions were affected by different treatments, the taxonomic assemblages at the phylum level were similar across all samples. We observed a strong correlation between Bacillus and Verrucomicrobiae with highly refractory DOM, suggesting their role in the degradation process. Our results illustrate the sensitivity of DOM cycling in STEs to climate change variables, consequently affecting the quantity and quality of DOM transported to coastal waters worldwide.

Primary Presenter: Dini Adyasari, University of Alabama (dadyasari@ua.edu)

Authors:

Dini Adyasari, University of Alabama  (dadyasari@ua.edu)

Natasha Dimova, University of Alabama  (ntdimova@ua.edu)

Hannelore Waska, ICBM, University of Oldenburg  (hannelore.waska@uni-oldenburg.de)

Sinead Ni Chadhain, University of South Alabama  (snichadhain@southalabama.edu)