Elucidating the Composition and Transformation of Dissolved Organic Matter at the Sediment-Water Interface Using...

Area of Science:

• Environmental Chemistry
• Biogeochemistry
• Analytical Chemistry

Background:

• Dissolved organic matter (DOM) exchange at the sediment-water interface is key to watershed biogeochemistry.
• DOM molecular composition dictates its transformation processes.
• High-resolution mass spectrometry (HRMS) is vital for analyzing DOM composition.

Purpose of the Study:

• To analyze DOM compositional characteristics at the sediment-water interface across varying salinities.
• To understand how salinity influences DOM molecular diversity, weight, saturation, and bioavailability.
• To elucidate DOM transformation pathways under different salinity conditions.

Main Methods:

• Analysis of DOM composition at the sediment-water interface using high-resolution mass spectrometry (HRMS).
• Comparison of DOM characteristics across three different salinity levels in northern China.
• Calculation of H/C and O/C ratios to characterize chemical transformations.

Main Results:

• Low-salinity inland waters exhibited greater DOM molecular diversity and higher molecular weights compared to high-salinity seawaters.
• High-salinity seawaters showed increased DOM saturation and bioavailability.
• CHOS substances were more prevalent in low-salinity waters (terrestrial/anthropogenic influence), while CHO and CHNO substances dominated high-salinity waters (microbial influence).
• Chemical transformations including methylation, hydrogenation, decarboxylation, and reduction were identified.

Conclusions:

• HRMS provides refined insights into DOM processes at the sediment-water interface under diverse environmental conditions.
• Salinity significantly alters DOM molecular composition and transformation pathways.
• Findings enhance understanding of the source-sink mechanisms of sediment organic matter.