Planktonic Bacterial and Archaeal Communities in an Artificially Irrigated Estuarine Wetland: Diversity, Distribution, and Responses to Environmental Parameters

Ecological degradation of a fragile semi-arid wetland and the implications in its microbial community: The case study of Las Tablas de Daimiel National Park (Spain)

Las Tablas de Daimiel National Park (TDNP, Iberian Peninsula) is a semi-arid wetland of international significance for waterfowl and serves as a migratory route for various bird species. However, TDNP presents strong anthropization and fluctuating water levels, making it a highly fragile ecosystem. Water physico-chemical parameters and microbial diversity of the three domains (Bacteria-Archaea- Eukarya) were analysed in Zone A and Zone B of the wetland (a total of eight stations) during spring and summer, aiming to determine how seasonal changes influence the water quality, trophic status and ultimately, the microbial community composition. Additionally, Photosynthetically Active Radiation (PAR) was used to determine the trophic status instead of transparency using Secchi disk, setting the threshold to 20-40 μmol/sm2 for benthic vegetation growth. In spring, both zones of the wetland were considered eutrophic, and physico-chemical parameters as well as microbial diversity were similar to other wetlands, with most abundant bacteria affiliated to Actinobacteriota, Cyanobacteria, Bacteroidota, Gammaproteobacteria and Verrumicrobiota. Methane-related taxa like Methanosarcinales and photosynthetic Chlorophyta were respectively the most representative archaeal and eukaryotic groups. In summer, phytoplankton bloom led by an unclassified Cyanobacteria and mainly alga Hydrodictyon was observed in Zone A, resulting in an increase of turbidity, pH, phosphorus, nitrogen, chlorophyll-a and phycocyanin indicating the change to hypertrophic state. Microbial community composition was geographical and seasonal shaped within the wetland as response to changes in trophic status. Archaeal diversity decreases and methane-related species increase due to sediment disturbance driven by fish activity, wind, and substantial water depth reduction. Zone B in summer suffers less seasonal changes, maintaining the eutrophic state and still detecting macrophyte growth in some stations. This study provides a new understanding of the interdomain microbial adaptation following the ecological evolution of the wetland, which is crucial to knowing these systems that are ecological niches with high environmental value.

The diversity of planktonic bacteria driven by environmental factors in different mariculture areas in the East China Sea

Planktonic bacteria play a crucial role in sustaining the ecological balance of aquatic ecosystems. However, their seasonal variations in different aquaculture areas within the East China Sea, along with their correlation to environmental factors, have not been extensively explored. In this study, each area with 3 sample points were set up to represent the fish aquaculture area, shellfish aquaculture area and non-aquaculture area. In 2019, we undertook four marine surveys along the Xiasanhengshan uninhabited island, during which we gathered surface seawater samples for both physicochemical analysis and high-throughput sequencing. This allowed us to obtain data about the physicochemical properties and microbial composition in each surveyed region. A short-term eutrophication phenomenon was present in the sea, and the spatial and temporal distribution of planktonic bacteria differed based on the mariculture area. At the phylum level, Proteobacteria accounted for >50 % of the community abundance in winter, spring, and autumn, while Cyanobacteria accounted for >30 % of the community abundance in summer. Because Cyanobacteria blooms are likely in summer, the relationship between Cyanobacteria and environmental factors was studied. Redundancy analysis showed that Cyanobacteria were consistently positively correlated with phosphate. Eutrophication and abnormal proliferation of Cyanobacteria in the study area necessitate ameliorations in the mariculture structure. The variation of genus in Proteobacteria is consistent with that of eutrophication, so some genera in Proteobacteria have the potential to become biological indicator species.

Water diversion induces more changes in bacterial and archaeal communities of river sediments than seasonality

Previous studies have demonstrated that seasonal variation is often the most important factor affecting aquatic bacterial assemblages. Whether anthropogenic activities can dominate community dynamics remains unknown. Based on 16S rRNA high-throughput sequencing technology, this study revealed and compared the relative influence of water diversions and seasonality on bacterial and archaeal communities in river sediments from a region with obvious seasonality. The results indicate that the influence of water diversion on bacteria and archaea in water-receiving river sediments exceeded the influence of seasonal variation. Water diversion affected microbes by increasing EC, salinity, water flow rate, and organic matter carbon and nitrogen contents. Seasonal variations affected microbes by altering water temperature. Diversion responders but no season responders were classified by statistical methods in the microbial community. Diversion responder numbers were related to nitrogen concentrations, complex organic carbon contents and EC values, which were mainly affected by water diversion. With the joint impact of water diversion and seasonality, the correlations of bacterial and archaeal numbers with environmental factors were obviously weakened due to the increases in the ecological niche breadths of microorganisms. Natural seasonal changes in bacterial and archaeal communities were totally altered by changes in salinity, nutrients, and hydrological conditions induced by anthropogenic water diversions. These results highlight that human activity may be a stronger driver than natural seasonality in the alteration of bacterial and archaeal communities.

Microorganisms that participate in biochemical cycles in wetlands

Several biochemical cycles are performed in natural wetlands (NWs) and constructed wetlands (CWs). The knowledge of the microorganisms could be used to monitor the restoration of wetlands or the performance of the wastewater treatment. Regarding bacteria, Proteobacteria phylum is the most abundant in NWs and CWs, which possesses a role in N, P, and S cycles, and in the degradation of organic matter. Other phyla are present in lower abundance. Archaea participate in methanogenesis, methane oxidation, and the methanogenic N2 fixation. Sulfur and phosphorus cycles are also performed by other microorganisms, such as Chloroflexi or Nitrospirae phyla. In general, there is more information about the N cycle, especially nitrification and denitrification. Processes where archaea participate (e.g. methane oxidation, methanogenic N2 fixation) are still unclear their metabolic role and several of these microorganisms have not been isolated so far. The study can use 16S rDNA genes or functional genes. The use of functional genes gives information to monitor specific microbial populations and 16S rDNA is more suitable to perform the taxonomic classification. Also, there are several Candidatus microorganisms, which have not been isolated so far. However, it has been described their metabolic role in the biochemical cycles in wetlands.