Structure and succession dynamics of a Neotropical freshwater periphyton community, with emphasis on ciliates and their association with bacterial taxa

Periphyton communities in freshwater systems play an essential role in biogeochemical processes, but knowledge of their structure and dynamics lags far behind other environments. We used eDNA metabarcoding of 16S and 18S rRNA markers to investigate the formation and establishment of a periphytic community, in addition to morphology-based analyses of its most abundant group (peritrich ciliates). We sampled two nearby sites within a large Neotropical lake at four time points, aiming to assess whether periphyton establishment can be replicated on this local scale. Producers and denitrifiers were abundant in the community, illustrating the relevant role of biofilms in freshwater nutrient recycling. Among microeukaryotes, peritrich ciliates dominated the community, with genera Epistylis and Vorticella being the most abundant and showing a clear succession at both sites. Other ciliates were identified and, in some cases, their occurrence was strongly related to bacterial abundance. The structure and succession dynamics of both prokaryotic and eukaryotic components of periphyton differed between the two sites, in spite of their adjacent locations and similar abiotic properties, indicating that the establishment of these communities can vary even on a local scale within a lake ecosystem.

Distribution and Driving Mechanism of N2O in Sea Ice and Its Underlying Seawater during Arctic Melt Season

Nitrous oxide (N2O) is the third most important greenhouse gas in the atmosphere, and the ocean is an important source of N2O. As the Arctic Ocean is strongly affected by global warming, rapid ice melting can have a significant impact on the N2O pattern in the Arctic environment. To better understand this impact, N2O concentration in ice core and underlying seawater (USW) was measured during the seventh Chinese National Arctic Research Expedition (CHINARE2016). The results showed that the average N2O concentration in first-year ice (FYI) was 4.5 ± 1.0 nmol kg−1, and that in multi-year ice (MYI) was 4.8 ± 1.9 nmol kg−1. Under the influence of exchange among atmosphere-sea ice-seawater systems, brine dynamics and possible N2O generation processes at the bottom of sea ice, the FYI showed higher N2O concentrations at the bottom and surface, while lower N2O concentrations were seen inside sea ice. Due to the melting of sea ice and biogeochemical processes, USW presented as the sink of N2O, and the saturation varied from 47.2% to 102.2%. However, the observed N2O concentrations in USW were higher than that of T-N2OUSW due to the sea–air exchange, diffusion process, possible N2O generation mechanism, and the influence of precipitation, and a more detailed mechanism is needed to understand this process in the Arctic Ocean.

The ecological characteristics of small rivers in the Shilka river basin by zoobenthos organisms

Zoobenthos organisms are directly related to the biogeochemical processes occurring at the bottom and in the water column of the channel. The paper presents the results of studies of the quantitative characteristics of the zoobenthos and the water quality of small rivers in the river basin of Shilka in the area of gold mining enterprises.

Quantifying functional consequences of habitat degradation on a Caribbean coral reef

Coral reefs are declining worldwide. The abundance of corals has decreased alongside a rise of filter feeders, turf, and algae in response to intensifying human pressures. This shift in prevalence of functional groups alters the biogeochemical processes in tropical water ecosystems, thereby influencing reef functioning. An urgent challenge is to understand the functional consequences of these shifts to develop suitable management strategies that aim at preserving the biological functions of reefs. Here, we quantify biogeochemical processes supporting key reef functions (i.e. net community calcification (NCC) and production (NCP) and nutrient recycling) in situ for five different benthic assemblages currently dominating shallow degraded Caribbean reef habitats. To this end, a transparent custom-made enclosure was placed over communities dominated by either one of five functional groups – coral, turf and macroalgae, bioeroding sponges, cyanobacterial mats, or sand – to determine chemical fluxes between these communities and the overlying water, during both day and night. To account for the simultaneous influence that distinct biogeochemical processes have on measured variables, the rates were then derived by solving a model consisting of differential equations describing the contribution of each process to the measured chemical fluxes. Inferred rates were low compared to those known for reef flats worldwide. Reduced accretion potential was recorded, with negative or very modest net community calcification rates for all communities. Net production during the day was also low, suggesting limited accumulation of biomass through photosynthesis and remineralisation of organic matter at night was relatively high in comparison, resulting in net heterotrophy over the survey period for most communities. Estimated recycling processes (i.e. nitrification and denitrification) were high but did not fully counterbalance nutrient release from aerobic mineralisation, rendering all substrates sources of nitrogen. Results suggest similar directions and magnitudes of key biogeochemical processes of distinct communities on this shallow Curaçaoan reef. We infer that the amount and type of organic matter released by abundant algal turfs and cyanobacterial mats on this reef likely enhances heterotroph activity and stimulates the proliferation of less diverse copiotrophic microbial populations, rendering the studied reef net heterotrophic and drawing the biogeochemical “behaviour” of distinct communities closer to each other.

Tidal frequencies and quasiperiodic subsurface water level variations dominate redox dynamics in a salt marsh system

Salt marshes are hotspots of nutrient processing en route to sensitive coastal environments. While our understanding of these systems has improved over the years, we still have limited knowledge of the spatiotemporal variability of critical biogeochemical processes within salt marshes. Sea-level rise will continue to force change on salt marsh functioning, highlighting the urgency of filling this knowledge gap. Our study was conducted in a central California estuary experiencing extensive marsh drowning and relative sea-level rise, making it a model system for such an investigation. Here we instrumented three marsh positions with different degrees of inundation (6.7%, 8.9%, and 11.2% of the time for the upper, middle, and lower marsh positions, respectively), providing locations with varied geochemical characteristics and hydrological interaction at the site. We continuously monitored redox potential (Eh) at depths of 0.1, 0.3, and 0.5 m, subsurface water levels (WL), and temperature at each marsh position to understand how drivers of subsurface biogeochemical processes fluctuate across tidal cycles, using wavelet analyses to explain the interactions between Eh and WL. We found that tidal forcing significantly affects biogeochemical processes by imparting controls on Eh variability, likely driving subsurface hydro-biogeochemistry of the salt marsh. Wavelet coherence showed that the Eh-WL relationship is non-linear, and their lead-lag relationship is variable. We found that precipitation events perturb Eh at depth over timescales of hours, even though WL show relatively minimal change during events. This work highlights the importance of high-frequency measurements, such as Eh, to help explain factors that govern subsurface geochemistry and hydrological processes in salt marshes.

Tidal frequencies and quasiperiodic subsurface water level variations dominate redox dynamics in a salt marsh system

Salt marshes are hotspots of nutrient processing en route to sensitive coastal environments. While our understanding of these systems has improved over the years, we still have limited knowledge of the spatiotemporal variability of critical biogeochemical processes within salt marshes. Sea-level rise will continue to force change on salt marsh functioning, highlighting the urgency of filling this knowledge gap. Our study was conducted in a central California estuary experiencing extensive marsh drowning and relative sea-level rise, making it a model system for such an investigation. Here we instrumented three marsh positions with different degrees of inundation (6.7%, 8.9%, and 11.2% of the time for the upper, middle, and lower marsh positions, respectively), providing locations with varied geochemical characteristics and hydrological interaction at the site. We continuously monitored redox potential (Eh) at depths of 0.1, 0.3, and 0.5 m, subsurface water levels (WL), and temperature at each marsh position to understand how drivers of subsurface biogeochemical processes fluctuate across tidal cycles, using wavelet analyses to explain the interactions between Eh and WL. We found that tidal forcing significantly affects biogeochemical processes by imparting controls on Eh variability, likely driving subsurface hydro-biogeochemistry of the salt marsh. Wavelet coherence showed that the Eh-WL relationship is non-linear, and their lead-lag relationship is variable. We found that precipitation events perturb Eh at depth over timescales of hours, even though WL show relatively minimal change during events. This work highlights the importance of high-frequency measurements, such as Eh, to help explain factors that govern subsurface geochemistry and hydrological processes in salt marshes.

The meta-gut: community coalescence of animal gut and environmental microbiomes

All animals carry specialized microbiomes, and their gut microbiota are continuously released into the environment through excretion of waste. Here we propose the meta-gut as a novel conceptual framework that addresses the ability of the gut microbiome released from an animal to function outside the host and alter biogeochemical processes mediated by microbes. We demonstrate this dynamic in the hippopotamus (hippo) and the pools they inhabit. We used natural field gradients and experimental approaches to examine fecal and pool water microbial communities and aquatic biogeochemistry across a range of hippo inputs. Sequencing using 16S RNA methods revealed community coalescence between hippo gut microbiomes and the active microbial communities in hippo pools that received high inputs of hippo feces. The shared microbiome between the hippo gut and the waters into which they excrete constitutes a meta-gut system that could influence the biogeochemistry of recipient ecosystems and provide a reservoir of gut microbiomes that could influence other hosts. We propose that meta-gut dynamics may also occur where other animal species congregate in high densities, particularly in aquatic environments.