Tracking spatiotemporal variations in porewater dissolved organic matter in a planted mangrove chronosequence using FT-ICR MS

This is the authors' abstract. We don't add key points for this paper.

Mangroves are important sources of Dissolved Organic Matter (DOM) that contribute to marine carbon sequestration. Porewater acts as a key intermediate reservoir through which mangrove-derived DOM is mobilized and transported to adjacent coastal waters. Despite this importance, the spatiotemporal variability in porewater Dissolved Organic Carbon (DOC) concentration and molecular composition within mangrove ecosystems remains poorly understood. This study applied a chronosequence approach across four mangrove plantations of different ages (10–18 years) in Thailand to investigate the spatiotemporal variability in DOC concentration and molecular composition using ultrahigh-resolution mass spectrometry (FT-ICR MS). Temporal variation was inferred across this 10–18-year age sequence, including mudflats as a reference, while spatial variation was assessed along seaward-to-landward transects within each plantation. DOC concentrations increased landward but showed no significant dependence on forest age, indicating that porewater DOC is primarily regulated by spatial gradients associated with tidal dilution and vegetation distribution rather than by forest development. In contrast, DOM molecular composition responded to both distance from the seaward edge and forest age. At landward sites in older forests, the relative abundances of aromatic and sulfur-containing compounds increased, coinciding with a molecular index indicative of sulfidic porewater. The enrichment of sulfur-containing compounds and high values of the molecular index under sulfate-reducing redox conditions are consistent with abiotic sulfurization of porewater DOM. This study shows that mangrove forest development alters the quality of porewater DOM, with implications for the contribution of mangrove-derived recalcitrant carbon to porewater pools, carbon cycling, and long-term carbon persistence in blue carbon ecosystems.