Hydroxyl Radicals in Marine Sediments

In spite of evidence suggesting hydroxyl radicals (OH ·) may form at the oxicanoxic interface in marine sediments, their existence has never been shown. The dissertation goal was to detect OH· in marine sediments and its potential effects on sedimentary organic matter (SOM). OH· was detected using disodium terephthalate (TPA). OH· formation rates were determined in oxic surface sediment.;The effect of OH· on bulk C and N and compound-specific SOM composition was evaluated in slurry incubations by addition of Fenton reagents, which produce OH·. Samples included Elliott soil standard (ES), live marine sediment, and biocide-amended marine surface sediment.;OH· affected compound-specific concentrations of both biologically labile organic matter (OM) and refractory OM. OH · selectively increased dissolve organic N (DON) concentrations over dissolved organic C (DOC) concentrations, possibly a result of desorption of organic N from sediment surfaces. Further evaluation showed that OH · increased amino acid (AA) concentrations and AA-like fluorescence in live sediment. OH· increased mol fractions of non-protein AA in biocide-treated sediment and ES. OH· decreased humic material fluorescence and also decreased sediment lignin phenol concentrations, indicating that OH· degradation may be a sink for these refractory OM compound groups. Additionally, increased OH· concentrations also affected the relative abundance of lignin phenol families, selectively degrading vanillyl. The selective degradation of specific lignin phenol families increased cinnamyl: vanillyl, syringyl:vanillyl, and the lignin phenol vegetation index.;The diagenetic effects of OH· on AA, NS, and lignin were mitigated in live sediments, presumably by microbial activity. The AA degradation index showed that AA in the biocide-treated sediment and ES were degraded by OH·, while there was no effect on live sediment. Similarly, lignin phenol composition was less affected by OH· in the biocide-treated sediment than in the live sediment. Initial diagenetic state of the OM also affected the extent of OH· degradation: OH· decreased fluorescence of terrestrially-derived humic material in ES, but had no effect on total AA, LOP or NS.