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

Abstract

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, Bacteroidetes, 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 fulvic 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.

Planctomycetes diversity associated with macroalgae

“…Here, we enlarge the geographical regions of P. brasiliensis to the north Atlantic coast and the kind of habit to the biofilm community of macroalgae. Typically, Planctomycetes appear in low percentage in natural populations, being more represented in marine sediments (Rusch et al, 2003;Musat et al, 2006;Chipman et al, 2010;Hu et al, 2010) when compared with coastal waters or also to the marine pelagic environment (Rusch et al, 2007). Even though we have not carried out any numerical study of the percentage of Planctomycetes in the macroalgae biofilm, the significant diversity encountered both in the number of isolates and in phylotypes indicates their ecological relevance.…”

Minor impact of ocean acidification to the composition of the active microbial community in an Arctic sediment

“…They have been found associated with micro-algae, seaweeds and detrital material (Morris et al, 2006;Longford et al, 2007;Bengtsson and Ovreås, 2010) where they are thought to be specialized degraders of sulphated polysaccharides produced by algae (Glöckner et al, 2003). It is likely that they perform a similar role within coastal sediments where they are also found in high abundance (Muscat et al, 2006;Chipman et al, 2010). Several moderately acidophilic Planctomycetes of the genera Schlesneria, Singulisphaera and Zavarzinella have been isolated from peat (Kulichevskaya et al, 2007;, but the diverse range of Planctomycetaceae found that only within cores receiving 3000 μatm CO 2 seawater could imply that the ability to take advantage of changing pH or CO2 conditions may be a feature of the family.…”

Hydrocarbon-Degrading Bacteria and the Bacterial Community Response in Gulf of Mexico Beach Sands Impacted by the Deepwater Horizon Oil Spill

“…Marine sands act as efficient biocatalytic filters that play an important role in the biogeochemical cycles of carbon and nutrients in shallow Gulf waters (11,19,20). Marine sands in the Gulf are covered with biofilms of highly diverse microbial communities (30,53), and the bacterial abundance in sands exceeds that of the overlying seawater by orders of magnitude (7,35,38).…”