Biodegradation-induced signatures in sediment pore water dissolved organic matter: Implications from artificial sediments composed of two contrasting sources.

Biodegradation is one of the main processes causing the changes in amount, composition and properties of organic matter in sediment and water-sediment interface. The degradation processes of sediment organic matter lead to a release of dissolved organic matter (DOM) into the pore water via hydrolysis and depolymerization of particulate organic matter (POM). Whereas the pore waters represent a reactive zone in sediment closely linked to biogeochemistry of the substrate, they are still poorly characterized under diagenetic processes. In this study, we examined the DOM alterations in sediment pore water originating from the mixtures of two contrasting POM sources at known ratios through controlled incubation experiments with two different oxygen conditions (i.e., oxic versus anoxic). The changes in pore water DOM were tracked using fluorescence and absorbance spectroscopy and size exclusion chromatography. The results based on the sediments artificially mixed of two end-member sources (e.g., soil and algae) showed that the most affected parameter during the biodegradation process was the amount of the pore water DOM. It was also demonstrated that the changes in the spectroscopic and molecular properties were more dependent on the POM sources and the mixing ratios rather than on the oxygen conditions. This study provides insights into the responding features of DOM in a reactive sediment zone as pore water to the main biogeochemical process.