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

Humic isolates from different layers of an organic-matter-rich algal sapropel from Mangrove Lake, Bermuda, were subjected to solid-state 15N nuclear magnetic resonance (NMR) spectroscopy in order to reveal chemical structural interrelationships that allow delineation of diagenetic pathways. Amide-N, most likely from peptide-like material, was found to represent the main organic 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 peptide-like material, is related to encapsulation into the paraffinic network of algaenans. Being hydrophobic in nature, algaenan biomacromolecules may represent an effective means of protection against the attack of hydrophilic enzymes and aqueous extraction solutions.