From Surface to Subsurface: Diversity, Composition, and Abundance of Sessile and Endolithic Bacterial, Archaeal, and Eukaryotic Communities in Sand, Clay and Rock Substrates in the Laurentians (Quebec, Canada)

Microbial communities play an important role in shallow terrestrial subsurface ecosystems. Most studies of this habitat have focused on planktonic communities that are found in the groundwater of aquifer systems and only target specific microbial groups. Therefore, a systematic understanding of the processes that govern the assembly of endolithic and sessile communities is still missing. This study aims to understand the effect of depth and biotic factors on these communities, to better unravel their origins and to compare their composition with the communities detected in groundwater. To do so, we collected samples from two profiles (~0–50 m) in aquifer sites in the Laurentians (Quebec, Canada), performed DNA extractions and Illumina sequencing. The results suggest that changes in geological material characteristics with depth represent a strong ecological and phylogenetical filter for most archaeal and bacterial communities. Additionally, the vertical movement of water from the surface plays a major role in shallow subsurface microbial assembly processes. Furthermore, biotic interactions between bacteria and eukaryotes were mostly positive which may indicate cooperative or mutualistic potential associations, such as cross-feeding and/or syntrophic relationships in the terrestrial subsurface. Our results also point toward the importance of sampling both the geological formation and groundwater when it comes to studying its overall microbiology.

Local-Scale Damming Impact on the Planktonic Bacterial and Eukaryotic Communities in the Upper Yangtze River

Dam construction and reservoir formation alters hydro-morphology of rivers, thereby restructuring microbial communities and biogenic element cycles in river ecosystems. The ecological responses and mechanisms of planktonic communities showed notable changes upstream and downstream of dams. Yet, less is reported about how the ecological mechanisms structuring planktonic communities at the closest area upstream and downstream of dams. In this study, we hypothesized that planktonic communities remained the connectivity or similarities but show distinctive ecological responses to changing environment at the closes area upstream and downstream of dams. Three large dams in the upper Yangtze River were chosen in the study. Field data revealed that the alpha diversity indexes slightly increased downstream of the dams. In addition, more eukaryotic ASVs solely occurred downstream of the dams, indicating that a large proportion of eukaryotes was formed downstream of the dams. Co-occurrence network analysis demonstrated that the keystone species of planktonic bacteria and eukaryotes decreased downstream of the dams, and the modularity increased. The robustness of the co-occurrence relationships among the eukaryotic communities was more strongly influenced by these dams than that among the planktonic bacteria. The variance partitioning analysis results indicated that dam-related variables and local environmental variables mainly shape the assembly of the planktonic microbial communities closest to the dams. In conclusion, dams exert a greater impact on planktonic eukaryotes than on bacteria in near-dam areas, and planktonic bacteria can better adapt to changing environments. Our study provides a better understanding of the ecological effects of river damming.

Planktonic communities in a small post-peat reservoir (Ustka Forest District, Poland)

The aim of this study was to evaluate the present state of a small (area of 0.2 ha), shallow (mean depth of 2 m) and approximately 30-year-old post-peat reservoir located in Bruskowskie Bagno, a Baltic raised mire in northern Poland. The study was conducted during all seasons of the year (August 2019–July 2020). The reservoir was characterised by a yellow to brown water colour, low pH (5.4) and quite low conductivity (40.4 μS cm-1), which are the main features of dystrophic water bodies. Similar to natural, dystrophic lakes and ponds, the phytoplankton was mainly composed of mixotrophic species like Dinobryon sp. and Gonyostomum semen. The only numerous non-flagellate group within the phytoplankton was desmids, which indicated that the water was influenced by the mire. The reservoir was characterised by a high abundance of ciliates (annual mean of 55.6 cells ml-1) and a very high abundance of rotifers (annual mean of 3.72 ind. ml-1). Among ciliates, the most important were prostomatids, accounting for 53% of the mean annual ciliate abundance. The results of our study indicate that artificial, approximately 30-year-old, post-peat reservoir resembled a natural dystrophic water body.

The state of zooplankton communities in the lower Dniester area under the conditions of river regulation and actual climatic changes

The study focuses on zooplankton communities of the Lower Dniester. The quantitative indicators of plankton are given and the annual dynamics is described. An assessment of the current state of the river according to the state of zooplankton communities is presented, together with a comparison with historical data, at different stages of river regulation. The changes that occurred in the river zooplankton since the 1950s were analyzed. The relationships between individual characteristics of planktonic communities and the physical and chemical characteristics of the river was also investigated. A comparison of actual data with those collected during 70-80s revealed no significant changes in the structure of the zooplankton community. The proportion of different groups of zooplankton organisms changed insignificantly, the saprobity indices improved slightly, and the average zooplankton biomass did not change. However, compared to the period before 1950s, prior to river regulation for hydropower purposes the role of rotifers in the community was reduced. It might be difficult to identify the main factor determining the development of zooplankton in the Lower Dniester, in order to understand the processes taking place in planktonic communities, it is necessary to analyze the complex impact of hydrological and hydrochemical factors on planktonic communities.