Export of dissolved organic matter from a mangrove swamp ecosystem: evidence from natural fluorescence, dissolved lignin phenols, and bacterial secondary production

Export of dissolved organic matter (DOM) from an island mangrove swamp was traced and quantified by analysis of dissolved lignin-derived humic substances and naturally fluorescing compounds. Concentrations of both lignin phenols and fluorescent compounds indicated the tidally-mediated movement of DOM offshore from the swamp to distances at least 1 km seaward. Laboratory studies documented the formation of significant amounts of DOM from degrading mangrove leaves, about 20 % of which was highly-fluorescent humic substances. At the 1 km station, vascular plant-derived material was calculated to account for about 10 % of the total DOM, based on simple mixing models. A correlation between apparent concentrations of vascular plant-derived DOM and rates of bacterial secondary production suggests that some components of exported DOM are available for bacterioplankton growth in offshore environments.