Cross-Shore and Depth Zonations in Bacterial Diversity Are Linked to Age and Source of Dissolved Organic Matter across the Intertidal Area of a Sandy Beach

Abstract

Microbial communities and dissolved organic matter (DOM) are intrinsically linked within the global carbon cycle. Demonstrating this link on a molecular level is hampered by the complexity of both counterparts. We have now investigated this connection within intertidal beach sediments, characterized by a runnel-ridge system and subterranean groundwater discharge. Using datasets generated by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and Ilumina-sequencing of 16S rRNA genes, we predicted metabolic functions and determined links between bacterial communities and DOM composition. Four bacterial clusters were defined, reflecting differences within the community compositions. Those were attributed to distinct areas, depths, or metabolic niches. Cluster I was found throughout all surface sediments, probably involved in algal-polymer degradation. In ridge and low water line samples, cluster III became prominent. Associated porewaters indicated an influence of terrestrial DOM and the release of aromatic compounds from reactive iron oxides. Cluster IV showed the highest seasonality and was associated with species previously reported from a subsurface bloom. Interestingly, Cluster II harbored several members of the candidate phyla radiation (CPR) and was related to highly degraded DOM. This may be one of the first geochemical proofs for the role of candidate phyla in the degradation of highly refractory DOM.

Microbial Assemblages and Metabolic Activity in Organic‐Rich Subterranean Estuaries: Impact of Climate and Land Use Changes

“…In summary, our results indicated that microbial metabolic pathways, specifically DOC and DON degradation, were not overly sensitive to environmental changes when (a) most of the processes were performed by resilient, core STE communities and thus promoted functional redundancy, and (b) there was an abundance of electron donors (i.e., high DOC concentration) and recipients (i.e., $${{\text{NO}}_{3}}^{-}$$ or $${{\text{SO}}_{4}}^{2-}$$) for such metabolisms to occur. In fact, the anomalously high DOC concentration originating from vascular plant microbial degradation is a distinctive signature of organic‐rich STE sediments, as other microbial studies performed in relatively sandy STE layers resulted in an elevated metabolic prediction of marine DOM origins, for example, as a result of phytoplankton metabolisms (Degenhardt et al., 2021).…”

“…2 ) for such metabolisms to occur. In fact, the anomalously high DOC concentration originating from vascular plant microbial degradation is a distinctive signature of organic-rich STE sediments, as other microbial studies performed in relatively sandy STE layers resulted in an elevated metabolic prediction of marine DOM origins, for example, as a result of phytoplankton metabolisms (Degenhardt et al, 2021).…”

“…Lignin‐degrading genes are shared among Actinobacteria, Gammaproteobacteria, Alphaproteobacteria, and Cyanobacteria (Bugg et al., 2011). More recent studies using 16S rRNA sequencing and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICRMS) have linked tannin‐ and lignin‐like structure decarboxylation to heterotrophic bacteria and candidate phyla radiation group in coastal sediments (Degenhardt et al., 2021; Oni et al., 2015).…”

The DynaDeep observatory – a unique approach to study high-energy subterranean estuaries

“…Together with the previous biogeochemical studies from the shallow subsurface of Spiekeroog beach (Beck et al, 2017;Reckhardt et al, 2017;Waska et al, 2019;Ahrens et al, 2020;Degenhardt et al, 2020;Degenhardt et al, 2021a;Degenhardt et al, 2021b;Seibert et al, 2021;Waska et al, FIGURE 1 Proposed conceptual model of the STE as a biogeochemical reactor with general features and groundwater salinities (saltwater red, freshwater blue). Major biogeochemical processes expected along flow paths (#1) and at interfaces (#2) are listed.…”

“…Moreover, since Spiekeroog belongs to the Wadden Sea National Park of Lower Saxony, the anthropogenic influence is relatively small, ensuring that a nearnatural system is investigated. The site has the further advantage that it has previously been studied with regard to the shallow beach subsurface (e.g., Beck et al, 2017;Waska et al, 2019;Ahrens et al, 2020;Grünenbaum et al, 2020a;Waska et al, 2021;Grünenbaum et al, 2020b, Degenhardt et al, 2020Degenhardt et al, 2021a, Degenhardt et al, 2021b as well as the freshwater end-member (i.e., freshwater lens) underneath the island (Röper et al, 2012;Seibert et al, 2018;Seibert et al, 2019b;Reckhardt et al, 2021;Seibert et al, 2021), which is also used for local drinking water production (Figure 6). Marine and aeolian processes have strongly shaped and transformed Spiekeroog over the past centuries.…”