Decomposition of plankton-derived dissolved organic matter in permeable coastal sediments

• Published in: Limnology and oceanography Vol. 55; no. 2; pp. 857 - 871
• Main Authors: Chipman, Lindsay, Podgorski, David, Green, Stefan, Kostka, Joel, Cooper, William, Huettel, Markus
• Format: Journal Article
• Language: English
• Published: Waco, TX American Society of Limnology and Oceanography 01.03.2010
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Earth sciences; Earth, ocean, space; Exact sciences and technology; Firmicutes; Fundamental and applied biological sciences. Psychology; Marine; Marine and continental quaternary; Planctomycetes; Sea water ecosystems; Surficial geology; Synecology; Gulf of Mexico; ASW, Mexico Gulf; Organic matter; Sand; surface sediments; subsurface flow; Fluorescence; Decomposition; Interstitial water; Marine environment; Heterokontophyta; diatom flora; Emission spectrometry; Bacillariophyta; Plankton; Mineralization; Bacteria; Saint George Island; Thallophyta; Filtration; Algae; Plantae; Experimental study; Protein; Dissolved matter; diatoms; Adsorption; Nutrient; Fulvic acid; Humic acid; dissolved organic carbon
• ISSN: 0024-3590; 1939-5590; 0024-3590
• DOI: 10.4319/lo.2009.55.2.0857

We tested the hypothesis that dissolved organic carbon (DOC) is degraded when filtered through permeable shelf sediments. In a laboratory flume experiment the concave shape of DOC profiles observed in the upper 10 cm of Gulf of Mexico sublittoral sands was reproduced by the combination of DOC filtration and production in the sediment surface layer and mineralization and adsorption in the subsurface layer. Six percent to 14% of ¹³C-labeled, highly degradable DOC was mineralized during filtration through 5.8-cm-long sand-filled column reactors, up to nine times more than in dark, water-filled column reactors. Filtration through 50-cm-long sand columns removed all highly degradable DOC pumped through the sediment, translating to fluxes of up to 379 mmol DOC m⁻² d⁻¹, corresponding to DOC removal from an approximately 1-m-deep water layer each day. Bacterial incorporation of ¹³C identified a diverse group of sedimentary aerobic and anaerobic microbes processing DO¹³C filtered through sand columns, dominated by Gammaproteobacteria, Deltaproteobacteria, Firmicutes, Barter oidetes, and Planctomycetes. Excitation-emission matrix spectroscopy analysis of chromophoric dissolved organic matter contained in diatom-derived DOC indicated that microbes preferentially removed components around the fluorescence peak of tryptophan or protein-like substances, which may have the highest nutrient value. Mass spectra analysis revealed that filtration through sand also removes a broad spectrum of substances from less degradable humic and ful vie acid-like DOC and produces new DOC components. The flushed sand layer between the water column and deeper anoxic sediment layers acts as an effective DOC filter, with subsurface horizontal pore-water flows promoting decomposition of DOC.