Sequestration of organic nitrogen in the sapropel from Mangrove Lake, Bermuda

Humic isolates from different layers of an organic-matter-rich algal saprop el from Mangrove Lake, Bermuda, were subjected to solid-state N-15 nuclear magnetic resonance (NMR) spectroscopy in order to reveal chemical structura l interrelationships that allow delineation of diagenetic pathways. Amide-N , most likely from peptide-like material, was found to represent the main o rganic nitrogen form in all humic fractions at all depths of the sapropel. Amides were also identified in the residues from 6 M HCl hydrolysis of the alkaline insoluble extract (formerly called humin). These results indicate that some peptide-like material resists both alkaline and acid hydrolysis. We suggest that the chemical, and also the biological recalcitrance of pept ide-like material, is related to encapsulation into the paraffinic network of algaenans. Being hydrophobic in nature, algaenan biomacromolecules may r epresent an effective means of protection against the attack of hydrophilic enzymes and aqueous extraction solutions. (C) 2001 Elsevier Science Ltd. A ll rights reserved.