Geochemical factors impacting nitrifying communities in sandy sediments

Synchronous control of nitrogen and phosphorus release from sediments in shallow lakes under wind disturbance by modified zeolite and Ca/Al-based sludge combination

To inhibit eutrophication caused by endogenous pollutants release, the experiment explored the efficiency and mechanism of the synchronous control of nitrogen (N) and phosphorus (P) release from sediments in shallow lakes under wind disturbance by modified Ca/Al-based sludge (MS) and modified zeolite (MZ). High-temperature calcination and NaCl impregnation increased the pore volume of MS and Na+ content of MZ, and the adsorption capacity of MS for PO43--P and MZ for NH4+-N was as high as 42.01 and 20.28 mg g-1. The results of a 90-day incubation experiment showed that the addition of MS and MZ increased the abundance of Thauera, Nitrospira, Denitratisoma, and Clostridium, while decreasing the proportion of Proteus Hauser and Saccharimonadales, thereby reducing the active N and P contents in sediments through microbial transformation. At the same time, the efficient adsorption performance of the MS and MZ resulted in a significant decrease in pollutants in the interstitial water and sediments. In addition, sediment resuspension caused by wind disturbance increased the contact between sediments and remediation agents, resulting in the action depth of covering materials exceeding 100 mm. Compared to adding MS or MZ alone, the combination of the two (MSZG) could synchronously, efficiently, and stably inhibit N and P release. Under the coupling effects of physical interception, physicochemical adsorption, and biotransformation, the average TN, NH4+-N, TP, and PO43--P in the overlying water of the MSZG decreased by 72.13%, 88.92%, 69.28%, and 81.26%, respectively, compared to Control, which satisfying the Class III standard for surface water. Therefore, this study could provide reference for controlling endogenous release, improving eutrophication in shallow lakes under wind disturbance, and recycling residual sludge from sewage plants.

Novel database for accA gene revealed a vertical variability pattern of autotrophic carbon fixation potential of ammonia oxidizing archaea in a permeable subterranean estuary

The autotrophic carbon fixation pathway of ammonia-oxidizing archaea (AOA) was the 3-hydroxypropionate/4-hydroxybutyrate (3-HP/4-HB) cycle, of which the acetyl-CoA carboxylase α-submit (accA) gene is widely recognized as the indicator. To date, there is no reference database or suitable cut-off value for operational taxonomic unit (OTU) clustering to analyze the diversity of AOA based on the accA gene. In this study, a reference database with 489 sequences was constructed, all the accA gene sequences was obtained from the AOA enrichment culture, pure culture and environmental samples. Additionally, the 79% was determined as the cut-off value for OTU clustering by comparing the similarity between the accA gene and the 16S rRNA gene. The developed method was verified by analyzing samples from the subterranean estuary and a vertical variation pattern of autotrophic carbon fixation potential of AOA was revealed. This study provided an effective method to analyze the diversity and autotrophic carbon fixation potential of AOA based on accA gene.

Microbiome mediating methane and nitrogen transformations in a subterranean estuary

Subterranean estuaries (STEs) are important coastal biogeochemical reactors facilitating unique niches for microbial communities. A common approach in determining STE greenhouse gas and nutrient fluxes is to use terrestrial endmembers, not accounting for microbially mediated transformations throughout the STE. As such, the microbial ecology and spatial distribution of specialists that cycle compounds in STEs remain largely underexplored. In this study, we applied 16S rRNA amplicon sequencing with paired biogeochemical characterisations to spatially evaluate microbial communities transforming greenhouse gases and nutrients in an STE. We show that methanogens are most prevalent at the terrestrial end (up to 2.81% relative abundance) concomitant to the highest porewater methane, carbon dioxide and dissolved organic carbon concentrations (0.41 ± 0.02 μM, 273.31 ± 6.05 μM and 0.51 ± 0.02 mM, respectively). Lower ammonium concentrations corresponded with abundant nitrifying and ammonia-oxidising prokaryotes in the mixing zone (up to 11.65% relative abundance). Methane, ammonium and dissolved organic carbon concentrations all decreased by >50% from the terrestrial to the oceanic end of the 15 m transect. This study highlights the STE's hidden microbiome zonation, as well as the importance of accounting for microbial transformations mitigating nutrient and greenhouse gas fluxes to the coastal ecosystems.