Abstract
Mangroves play a critical role in shaping the composition of dissolved organic matter (DOM) in tropical estuarine systems. They act as bioreactors that transform and degrade imported organic matter before releasing it as DOM and export large amounts of leaf litter that leach additional DOM into estuarine waters. These processes are coupled with highly dynamic hydrological conditions in estuaries, creating complex systems that remain poorly understood. In this study, we used ultra high-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to characterize the molecular composition of solid-phase extracted DOM along the Jaguaripe River estuary, Bahia, Brazil, and from mangrove leaf leachates in combination with environmental parameters. Our findings indicate that mangroves fringing the estuary are a significant source of dissolved organic carbon (DOC). DOM derived from mangroves was rich in sulfur-containing and saturated compounds with low oxygen-to-carbon (O/C) ratios, particularly during the dry season. Interestingly, during the rainy season, mangroves also appeared to act as a sink for total dissolved nitrogen (TDN), and aliphatic nitrogen-containing compounds. Mangrove leaf leachate DOM exhibited elevated levels of highly unsaturated compounds with low O/C ratios. We identified 432 unique compounds as indicators of DOM leached from mangrove leaf litter. Furthermore, we developed a novel molecular tracing index, IManL, which allowed us to successfully track mangrove leaf–derived DOM within the estuary and beyond. By combining our index with other established DOM indices, we gained a deeper understanding of how diverse DOM sources shape estuarine DOM pools, underscoring the significant influence of fringing mangroves in these systems.
Published Version
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