Periphytic Communities Research Articles

Does exposure timing of macrolide antibiotics affect the development of river periphyton? Insights into the structure and function

Discharged sewage is the dominant source of urban river pollution. Macrolide antibiotics have emerged as prominent contaminants, which are frequently detected in sewage and rivers and pose a threat to aquatic microbial community. As a typical primary producer, periphyton is crucial for maintaining the biodiversity and functions of aquatic ecosystem. However, effects of antibiotic exposure time as well as the recovery process of periphyton remain undetermined. In the present study, five exposure scenarios of two typical macrolides, erythromycin (ERY) and roxithromycin (ROX) were investigated at 50 µg/L, dose to evaluate their potential detrimental effects on the structure and function of periphyton and the subsequent recovery process in 14 days. Results revealed that the composition of periphytic community returned to normal over the recovery period, except for a few sensitive species. The antibiotics-caused significant photodamage to photosystem II, leading to continuous inhibition of the photosynthetic capacity of periphyton. Furthermore, no significant difference in carbon metabolism capacity was observed after direct antibiotic exposure, while the amine carbon utilization capacity of periphyton remarkably increased during the recovery process. These results indicated that periphyton community was capable of coping with the periodic exposure of antibiotic pollutants and recovering on its own. However, the ecological functions of periphyton can be permanently disturbed due to macrolide exposure. Overall, this study sheds light on the influence of macrolide exposure on the development, structure and function of the periphytic microbial community in rivers.

Removal of PAHs in paddy fields: How natural periphytic biofilm enhances the removal process and the mechanisms involved

Previous studies on the removal of polycyclic aromatic hydrocarbons (PAHs) from farmland have mostly relied on anthropogenic biotic or abiotic amendments. Here, an indigenous paddy periphytic biofilm (PB) composed of complex symbolic communities was enriched, and its essential role, as well as the potential mechanisms of PAHs dissipation, was investigated. A pot experiment revealed that PB achieved 92.87% and 92.76% removal of the USEPA priority PAHs from the overlying water and soil of a heavily PAHs-contaminated paddy field, respectively. This subsequently decreased ΣPAHs accumulation in rice shoots to 4.12 ± 1.08 ng g-1, under the thresholds based on food safety standards. The physiology of PB in an aquatic culture with PAHs was assessed to understand the toxicity and removal mechanism. Extracellular polymeric substances (EPS) adsorption occurred in the early stage, followed by late biodegradation, which was considered the primary mechanism for removing PAHs. In this process, the PB contributed more to the high molecular weight PAHs compared to the low molecular weight. Furthermore, 16S-rRNA sequencing demonstrated specific functional phyla (Proteobacteria, Ascomycota, and Chloroplastida) with significantly higher relative abundances in periphytic communities with PAHs, which facilitated PAHs degradation. The predicted synergetic metabolic pathway involved 33 PAHs-degrading genes as inferred by PICRUSt. These findings suggest that PB could provide a promising strategy for target PAHs remediation in situ and food safety in contaminated paddy fields.

Assessment of extracellular polymeric substances production and antioxidant defences in periphytic communities exposed to effluent contaminants.

Periphyton is frequently used in the evaluation of the ecological status of aquatic ecosystems using diatoms as a proxy. However, periphyton has a particularity, the production of extracellular polymeric substances (EPS), which might play a protective role against exposure to harmful environmental contaminants. Effluents originating in wastewater treatment plants (WWTPs) constitute some of the most complex mixtures of contaminants, to which aquatic ecosystems are frequently exposed, often containing tens to hundreds of different chemicals. In such challenging scenarios, a putative protective role of EPS may obscure the bioindicator value of diatoms. To address this problem, we sampled periphyton upstream and downstream of the effluent outfall from three different WWTPs, quantifying EPS production and simultaneously evaluating general stress responses in the community (protein and sugar content, photosynthetic pigments, antioxidant enzyme activity and oxidative damage). By combining these endpoints with a characterization of the sediments of the riverine systems receiving the effluents made in a previous study (metals, polycyclic aromatic hydrocarbons, pharmaceuticals and personal care products), we aimed to elucidate whether effluent contaminants trigger negative effects, which may be mitigated by EPS layers protecting the communities. Our results indicated that under a comparatively milder contamination burden, EPS production is enhanced in samples collected downstream of the effluent outfall; under a higher contamination burden, EPS production is hampered. Stress-coping mechanisms were activated by environmental contaminants, including the antioxidant defense, particularly through catalase and superoxide dismutase activity. The findings support the generally assumed protective effect of EPS, but also suggest that EPS production depends on the contamination burden and that protective effects should be in place under specific scenarios of, for example, relatively low contamination levels. Overall, the integrative approach used in this study contributes to a better understanding of the complex interplay of interactions between effluent-driven contamination and thriving periphytic communities inhabiting recipient waterways, including evolved protection mechanisms.

Seasonal variation of gross ecosystem productivity of periphyton in three post-mining lakes in the Czech Republic, Europe

We investigated the seasonal variation of gross ecosystem productivity (GEP) of periphyton biomass in three post-mining lakes in the Czech Republic. These lakes were established as part of recultivation efforts after coal mining activities and resulted in a unique series of anthropogenic oligotrophic lakes of gradual successional age. Periphyton is ubiquitous in aquatic habitats and performs numerous environmental functions such as nutrient cycling and self-purifying of aquatic ecosystems. Well-developed periphyton mat can be formed within a few weeks, so it can quickly become the dominant of littoral zone of newly established lakes. In studied post-mining lakes, the highly developed periphytic community covers the littoral zone of each lake to the depth of 2m (Bešta et al. 2022, Konopáčová et al. 2023) Fig. 1. We aimed to shed some new light on the processes controlling the dynamics of primary productivity in oligotrophic lakes. The accurate estimation of primary productivity is crucial for understanding the functioning of aquatic ecosystems, as primary productivity serves as the primary source of autochthonous carbon in these systems. In addition to phytoplankton, periphyton can significantly contribute to primary productivity in littoral zones, known for their high productivity and biodiversity. Conducting in situ measurements provides the most accurate means of inferring the metabolic activity of primary producers in littoral zones. We conducted detailed seasonal in-situ periphyton gross primary production (GPP) measurements in three post-mining lakes with different successional ages (Čapková et al. 2022). GPP and NPP of periphytic biomass were determined using direct in-situ measurement of O2 fluxes. O2 production and consumption were measured over 5 hours of in-situ light and dark gas-tight glass bottle incubation. Bottles were filled with the lake water from the corresponding depth, and a similar amount of periphytic biomass was enclosed Fig. 2. We used the Fibox3 fibre-optic oxygen meter coupled with a PSt3 oxygen sensor (PreSens, Regensburg, DE) to measure changes in O2 concentration. The O2 fluxes were normalized to periphytic biomass in each bottle (measured as total organic carbon). Data were corrected for O2 concentration changes in dark and light gas-tight bottles containing lake water without periphytic communities. This setup enabled us to monitor online oxygen flux, therefore, insights into metabolic activities. The primary productivity was measured in real-time, allowing us to capture the quantitative effect of various environmental drivers on periphyton productivity, i.e. phosphorus concentration and light intensity, as they are known to play significant roles in primary productivity. We showed that the primary production of periphyton mats exhibited seasonal variations, with higher productivity observed in spring compared to other seasons. This observation could be attributed to the occurrence of winter/spring upwelling events and vertical mixing, which resupply nutrients from the deeper strata. Furthermore, the physiological activity of periphyton was strongly influenced by the seasonal changes in light intensity, temperature, and nutrient concentration. We provided the first insight into the seasonal variation of primary productivity of the periphyton assemblage dominating the littoral zone of newly established post-mining lakes. We stress the importance of periphyton in aquatic ecosystems, particularly in anthropogenic oligotrophic lakes.

Mixed light photoperiod and biocide pollution affect lipid profiles of periphyton communities in freshwater ecosystems

Environmental factors, such as light intensity and exposure to contaminants, may significantly influence the lipid composition of algae in periphytic communities. In this study, we investigated the joint effects of dodecylbenzyldimethylammonium chloride (BAC 12), as biocide, and light photoperiods on the polar lipidome of a freshwater biofilm. Exposure to BAC 12 in a microcosm experiment increased the heterotrophic compartment, while phototrophic organisms were severely affected, with corresponding shifts in lipid composition. The overall decrease in polyinsaturated fatty acids suggested a significant impact of the biocide on biofilm microalgae. However, it was difficult to distinguish the influence of light from that of contamination, as there was no observable effect of photoperiod on conventional fatty acid determination. Thus, the molecular species compositions of both glycolipids and phospholipids were explored in additional multivariate analyzes. The results suggested that certain molecular species can serve as more specific markers of light duration at the biofilm scale, independently of the chemical pressure caused by other pollutants.

Structure and Dynamics of Periphyton in a Neotropical Freshwater Lake, with Emphasis on Ciliates and Their Relationships 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 a morphology-based approach for peritrich ciliate determinations, its most abundant group. 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 morphologically identified and, in some cases, their occurrence was strongly related to bacterial abundance. The structure of both prokaryotic and eukaryotic components of periphyton was not different, while the turnover dynamics differed between the two sites, in spite of their adjacent locations and similar abiotic properties. This indicates that the establishment of these communities can vary even on a local scale within a lake ecosystem.

Community Composition and Assessment of the Aquatic Ecosystem of Periphytic Algae in the Yangtze River Basin

To explore the periphytic algae community structure in the Yangtze River basin, samples were collected from 130 sampling sites, including the source to the estuary along the mainstream of the Yangtze River, eight primary tributaries, and the tributary of the Three Gorges area. The periphytic algae densities of different areas in the mainstream of the Yangtze River ranked from high to low were the upstream area, source area, middle and lower area, and the Jinsha River. The high periphytic algae density in the upstream area was associated with the shift in nutrition level, and the high periphytic algae density in the source area was associated with human activity. The spatial pattern of the periphytic algae community in the whole main stream from west to east presented the alternating dominance of Bacillariophyta and Cyanophyta; the Bacillariophyta (Navicula) had a competitive advantage in the main stream, and the distribution of the periphytic algae community was driven by total nitrogen, total phosphorus, and pH. For the tributary of the Yangtze River, the periphytic algae density in the Three Gorges tributary area was far higher than those in the eight primary tributaries; the periphytic algae community was dominated by Cyanophyta (Lyngbya), which had a competitive advantage in the tributaries of the Yangtze River. The distribution of the periphytic community was driven by dissolved oxygen and pH. According to the diversity analysis and assessment, the periphytic algae community in the source area showed lower species richness and higher evenness, thus leading to a high α-diversity and good assessment result (mesosaprobic zone). The middle and lower reaches of the Yangtze River also showed the same assessment result, the mesosaprobic zone. However, the community evenness of the middle and lower reaches was significantly lower than that of the source area, thus making the middle and lower reaches of the Yangtze River have a significantly lower α-diversity than that of the source area. All areas of the Yangtze River showed good water quality assessment; however, different areas had different WQI index numbers, and the assessment results of the WQI index were inconsistent with the results of the aquatic assessment. Therefore, a comprehensive assessment of aquatic ecosystem health should use both aquatic assessments and water quality assessments.

Distribution and photosynthetic potential of epilithic periphyton along an altitudinal gradient in Jue River (Qinling Mountain, China)

Abstract Periphyton in aquatic ecosystems play a crucial ecological role in element cycling and are susceptible to natural disturbances and anthropogenic activities. To understand the responses of periphytic communities to water quality factors and altitude gradients, DNA metabarcoding was employed to investigate the distribution characteristics of epilithic periphyton (comprising prokaryotes and eukaryotes). Epilithic periphyton and water were sampled at 26 sampling sites with an altitude ranging from 445 to 1,565 m in the Jue River and its three tributaries in Qinling Mountain, China. The altitudinal patterns of water quality variables were initially investigated, followed by redundancy analysis and distance‐based linear models to explore the responses of community structure to altitudes and water quality. Meanwhile, the relationship between these variables and fluorescence parameters to reflect the photosynthesis of epilithic periphyton along an altitudinal gradient was examined. The results indicated that with decreasing elevation, water quality variables including total dissolved solids (TDS), water temperature, conductivity, salinity, and concentrations of ‐N, total nitrogen, and ‐N increased. This pattern was closely associated with the intensification of anthropogenic disturbance downstream. Specifically, higher salinity and water temperature downstream may reduce the prokaryotic biodiversity but promote the diversity and evenness of eukaryotes; higher concentrations of total nitrogen may increase the diversity, richness, and evenness of the whole periphyton community. Furthermore, salinity, nutrients, and TDS were identified as crucial variables shaping periphyton community structure, especially salinity and TDS, which were linked to the growth of chlorophytes. The attenuated maximum photochemical efficiency of periphyton at high altitudes indicated that photosystem II was inhibited, while the enhancement of maximum photochemical efficiency at low altitudes may be attributed to the reduced abundance of synurophyceae and increased chlorophyte abundance with strong photosynthetic capacity. The spatial distribution of the structure and photosynthetic activity of the periphyton community along the altitudinal gradient of the Jue River and its tributaries showed that most water quality variables were negatively correlated with altitude. The photosynthetic efficiency of periphyton declined at high altitudes because the abundance of chlorophytes was lower at higher altitude reaches. This pattern of periphyton structural composition and function with altitude may also exist in other alpine rivers influenced by anthropogenic impacts.

Structural Characteristics of Periphytic Algal Community and Its Relationship with Environmental Factors in the Taiyuan Region of the Fenhe River

In order to explore the characteristics of the periphytic algae community structure and its relationship with environmental factors in the Taiyuan region of the Fenhe River, a total of six sampling sites were investigated in July and December 2021. The effects of water quality status and environmental factors at each sampling point on the community structure of epiphytes were detected. The results showed that a total of 7 phyla and 54 genera of periphytic algae were identified in the Taiyuan region of the Fenhe River, and the species composition was mainly Bacillariophyta, Cyanophyta, and Chlorophyta. According to the analysis results of the biodiversity index, the water body of the Taiyuan region of the Fenhe River is in a state of moderate pollution. The correlation analysis between the epiphytic algae and environmental factors showed that the cell density of algae was significantly correlated with dissolved oxygen (DO), phosphate (PO43−-P), chemical oxygen demand (COD), total phosphorus (TP), and transparency (SD) in the wet season. The algal cell density in the dry season was significantly correlated with water temperature (WT), TP, PO43−-P, and COD. According to the redundancy analysis, the community distribution of the epiphytic algae in the Taiyuan region of the Fenhe River was closely related to physical and chemical factors such as COD, nitrate nitrogen (NO−3 -N), WT, dissolved organic carbon (DOC), total nitrogen (TN), and TP, and COD is the main environmental factor driving the change in the community distribution of the periphytic algae in the wet season. TN is the main control factor driving the change in the biological community distribution of periphytic algae in the dry season.

Succession and Driving Factors of Periphytic Community in the Middle Route Project of South-to-North Water Division (Henan, China).

The Middle Route Project of the South-to-North Water Diversion is an artificially independent system that does not connect to other surface waters. Excessive periphyton proliferation causes a series of environmental problems in the canal. In this study, the periphyton community and environmental factors on the left and right banks of the canal in the algal growing area were investigated and sampled six times (June, September, and November of 2019 and 2020). The succession pattern of the attached organism community in the artificial canal was analyzed, and the key factors affecting the algal community were analyzed using RDA and GAM. The results showed that the seasonal variability of the environmental factors was more significant than the spatial variability. A total of 114 taxa of periphytic algae were found, belonging to seven phyla and 69 genera, and mainly composed of Bacillariophyta. Species richness was ranked as Bacillariophyta (60 taxa), Chlorophyta (31 taxa) and Cyanobacteria (15 taxa), and higher in autumn than in summer. The dominant taxa were Cymbella sp., Fragilaria sp., Navicula sp. and Diatoma sp. The abundance of periphytic algal varied from 0.07 × 105 to 8.99 × 105 ind./cm2, with trends similar to that of species richness. The redundancy analysis and generalized additive model showed that water temperature and nutrient concentration were the key factors influencing the structure of the algal community, followed by discharge rate and velocity, which were the determinants of the spatial and temporal patterns of the algal community. In view of the influence of discharge and velocity on the structure of algal communities, it is suggested that ecological scheduling could be used to regulate the structure of the algal community on the canal wall in the operation of later water division projects to ensure the safety of water division.

Population structure and diversity of the periphyton community in the glacier-fed stream Balkhila at Siron from Garhwal Himalaya

The stream Balkhila is a glacier-fed and originates at higher altitudes from the Lal Mati glacier, flows through the famous Mandal valley of Garhwal Himalaya and finally merges with the Alaknanda River in Chamoli district of Uttarakhand. The present study aimed to assess the population structure, density and diversity of the periphyton community along with some detrimental ecological parameters in the glacier fed stream Balkhila for a period of two years on a monthly basis from November 2018 to October 2020. The stream Balkhila was represented by 17 periphytic genera belonging to 3 classes, namely, Bacillariophyceae, Chlorohyceae and Cyanophyceae. The class Bacillariophyceae was represented by 10 periphytic genera (Cymbella, Navicula, Fragilaria, Nitzschia, Ampohora, Diatoma, Synedra, Tabellaria, Cocconeis and Meridion), and Chlorophyceae (green algae) was represented by 6 algal genera (Chlorella, Ulothrix, Zygnema, Oedogomium, Spirogyra and Stigeoclonium). The class Myxophyceae was represented by a single genus (Phormidium). The maximum periphytic density (individuals/cm2) was found to be 316.7±7.1 x 103 in January, and the minimum density (12.5±3.5 x 103) was recorded in August. The SIMPLER test indicated 18.58% dissimilarity of periphytic communities between the two years of study. The Shannon–Wiener diversity index values were high (2.358 and 2.388) in December and January and minimum (0.2484 and 0.3534) in July and August during the first and second years of the study, respectively. Multivariate canonical correspondence analysis (CCA) suggested that most of the periphytic genera were closely associated with the winter season (December, January and February). The various ecological parameters of our study indicated that the Balkhila stream is a conducive habitat for periphyton communities.

Environmental Factors Drive Periphytic Algal Community Assembly in the Largest Long-Distance Water Diversion Channel

Periphytic algae exist widely in different waters. However, little is known about periphytic algae in long-distance water diversion channels across watersheds. We investigated the periphytic algae and the environmental factors at twenty sampling sites in the middle route of the South-to-North Water Diversion Project (MRP). The dominant species were Desmodesmus intermedius (Hegewald), Calothrix thermalis (Bornet & Flahault), Calothrix parietina (Bornet & Flahault) and Leptolyngbya benthonica (Anagnostidis) (dominance > 0.02) as measured in a whole year. Habitat heterogeneity in the MRP led to lower spatial heterogeneity and higher temporal heterogeneity of the periphytic algal community. Stochastic processes are the major process in periphytic community assembly. In deterministic processes, homogeneous selection had the major role in structuring the periphytic community, whereas the role of heterogeneous selection was less significant. In stochastic processes, dispersal limitations had the major role in structuring the periphytic community, whereas the role of homogenizing dispersal and drift were less significant. The variation in total nitrogen and total phosphorus promoted more stochastic processes (−1.96 < βNTI < 1.96). The variations in water temperature and water velocity promoted more heterogeneous selection (βNTI > 1.96). In integrating all of this empirical evidence, we explore the role of environmental factors in the action of ecological processes shaping thecommunity assembly of the periphytic algal community.

Diatom eDNA metabarcoding and morphological methods for bioassessment of karstic river

Karst ecosystems play a unique role as exceptional natural habitats in sustaining biodiversity. This study focuses on diatoms, a diverse group of microeukaryotes in the periphytic community of a karstic river. In a multi-microhabitat study along the Krka River (Croatia), our goal was to obtain a detailed overview of diatom diversity and community structure using morphological and molecular approaches, and to assess the applicability of eDNA metabarcoding as a reliable tool for biomonitoring assessment. The results revealed a relatively low agreement in the diatom community composition between the two approaches, but also provided complementary information, with no differences in beta diversity detected between microhabitats. The SIMPER analysis underlined the importance of the molecular approach in identifying diatom community composition, due to errors in distinguishing between deposited diatom cells that occurred in the morphological analysis. In contrast, the morphological approach indicated a clear diatom community separation along the river with a strong location effect. Despite certain differences, both approaches provided a feasible assessment of the ecological status according to the relationship to environmental pressures, classifying the Krka River as High (morphological approach) or Good (molecular approach) throughout the most of its course. Moreover, diatom diversity based on both approaches provides a reliable dataset applicable in routine monitoring assessment and offers a deeper understanding of the presented ecological status. The incompleteness of a reference database presents one major drawback of the molecular approach, which needs further updating in order to improve routine diatom metabarcoding.

Effect of different substrates on growth and biochemical composition of the ornamental “red cherry” caridean shrimp, Neocaridina davidi (Atyidae)

The effect of different substrates on growth, sexual ratio, number of ovigerous females and survival of the red cherry shrimp, Neocaridina davidi, was analysed to enhance its culture. Recently hatched juvenile shrimps were exposed to 4 different substrates: Vesicularia sp., Ceratophyllum sp., Cabomba sp. and a green plastic net. Growth was analysed over 90 days with shrimps being weighed every 30 days. While maximum size was similar for all treatments, maximum relative growth rate and instantaneous growth was significantly greater and peaked earlier, respectively, in shrimps cultured with Vesicularia sp. Additionally, substrate had no effect on female and male final body weights or their biochemical composition (lipid and protein content). Sexual proportion was slightly biased towards males in all treatments. Survival was highest with Vesicularia sp. (90%) and similar among the remaining treatments (nearly 60%). Shrimps grown with Ceratophyllum sp. presented the lowest proportion of ovigerous females at 10% compared to 30–48% for other treatments. Overall, shrimp culture was significantly influenced by substrates. We hypothesize that Vesicularia sp. could enhance shrimp survival by supporting an environment free of pathogens; or that the periphytic community itself could provide benefits.

Responses of benthic diatoms to waters affected by post-fire contamination

Wildfire effects go beyond direct impact in terrestrial ecosystems. Specifically, the periphytic communities of aquatic ecosystems standing within and downstream the burnt areas are relevant ecological receptors of post-fire runoff contamination. Nevertheless, the off-site impacts of wildfires in these communities are limitedly studied so far. The present study aimed to assess the effects of river water contaminated with ash-loaded runoff in the growth benthic diatom Navicula libonensis (Schoeman 1970). Four surface water samples were collected approximately one year after the wildfire for laboratory testing with the diatom: one was collected from a site upstream the burnt area, within the Unhais river (UU); three were collected from sites standing within the burnt area, one in the Unhais river (UB) and two in the Zêzere river (Z1 and Z2), reflecting different hydrological regimes. N. libonensis was proven able to discriminate among river sites affected and unaffected by wildfire runoff, reflecting, in general, the expected trends considering the physico-chemical characterization of the water samples. The water samples from the sites standing within the burnt area inhibited the biomass yield and growth rate of the tested diatom, ranking the samples regarding toxicity as follows: Z1 > UB > Z2 > UU. However, UB rather than Z1 presented the highest contaminant burden, namely metal elements, and some were found above widely accepted safety benchmarks (polycyclic aromatic hydrocarbons were not detected). This inconsistency can be linked to unknown interactions among metals within each water sample, to differential nutrient enrichment of samples, as well as hydrological factors. Overall, our results suggest that monospecific laboratory assays with sensitive diatoms can be valuable as cost-effective screening tools to prioritize sites affected by wildfires runoff requiring in-depth monitoring of negative effects in benthic producer communities.

Ecological thresholds of periphytic communities and ecosystems integrity in lower Doce River basin

Freshwater biodiversity has been impacted by several stressors such as eutrophication, turbidity and metals. Besides these frequent impacts, large-scale accidents occasionally affect aquatic systems, input an intense load of contaminants to the water bodies, as in the case of the Fundão tailing dam collapse (Brazil), which launched millions of meters cubic of iron ore tailing in the Doce River Basin. Our aim in this study was to assess how much stress the environmental conditions of lentic and lotic environments in the lower region of this basin impact the periphytic community. In addition, we intend to verify whether the limits of changes of the periphytic communities agreed with Brazilian legislation for the protection of aquatic life. For that, monthly samplings were carried out in seven sampling stations in lentic environments and five in lotic environments, including the Doce River channel, between October/2018 and March/2021 (except in October/2019). Concentrations of metals (iron, aluminum, manganese and chromium), total nitrogen, total phosphorus, conductivity, and suspended particulate material were determined. The periphytic community was collected from natural substrates (macrophytes or pebbles) and quantified by the sedimentation chamber method. From these data, thresholds of concentrations of variables that caused changes in periphytic communities were determined by the Threshold Indicator Taxa ANalysis (TITAN). We concluded that evidence of chronic impact of iron ore tailing should be revealed and that the standards established by Brazilian legislation may be incompatible with the protection of aquatic life. Moreover, we found that the Doce River mouth and surrounding environments were the most stressful environments for the periphytic communities.

Caffeine as a contaminant of periphyton: ecological changes and impacts on primary producers.

Every day, tons of caffeine is consumed by humans in beverages, medications or supplements, and a significant amount of this stimulant is released in domestic sewage. Once in aquatic environments caffeine interacts directly with the periphytic community, which is responsible for a significant part of primary production in aquatic ecosystems. However, the effects of exposure to caffeine are mostly unknown for both the periphyton and their predators. Aiming to comprehend the interaction between caffeine and the periphytic community, ecotoxicological experiments were performed by exposing a periphytic biofilm cultivated in the laboratory to different concentrations of caffeine, following concentrations found in domestic sewers. The impact of exposure to this contaminant was observed on the structure of the community through taxonomic evaluation, as well a set of physiological variables linked to primary production. After exposure to the highest caffeine concentration (300 µg L-1), the density of the genus Scenedesmus was severely affected, leading to an increase in cyanobacteria and diatoms. Both richness and diversity decreased after exposure, and there was lower photosynthetic activity, with light saturation point changing from 186 µmol m-2 s-1 in the control treatment to 108 µmol m-2 s-1 after exposure. Caffeine accumulation within the biofilm was also observed during the first 24 h, in the concentration of 0.14 µg /cm².

Microbial Diversity and Mercury Methylation Activity in Periphytic Biofilms at a Run-of-River Hydroelectric Dam and Constructed Wetlands.

ABSTRACTPeriphytic biofilms have the potential to greatly influence the microbial production of the neurotoxicant monomethylmercury in freshwaters although few studies have simultaneously assessed periphyton mercury methylation and demethylation rates and the microbial communities associated with these transformations. We performed a field study on periphyton from a river affected by run-of-river power plants and artificial wetlands in a boreal landscape (Québec, Canada). In situ incubations were performed on three sites using environmental concentrations of isotopically enriched monomethylmercury (MM198Hg) and inorganic mercury (200Hg) for demethylation and methylation rate measurements. Periphytic microbial communities were investigated through 16S rRNA gene analyses and metagenomic screenings for the hgcA gene, involved in mercury methylation. Positive mercury methylation rates ([5.9 ± 3.4] × 10−3 day−1) were observed only in the wetlands, and demethylation rates averaged 1.78 ± 0.21 day−1 for the three studied sites. The 16S rRNA gene analyses revealed Proteobacteria as the most abundant phylum across all sites (36.3% ± 1.4%), from which families associated with mercury methylation were mostly found in the wetland site. Metagenome screening for HgcA identified 24 different hgcA sequences in the constructed wetland site only, associated with 8 known families, where the iron-reducing Geobacteraceae were the most abundant. This work brings new information on mercury methylation in periphyton from habitats of impacted rivers, associating it mostly with putative iron-reducing bacteria.IMPORTANCE Monomethylmercury (MMHg) is a biomagnifiable neurotoxin of global concern with risks to human health mostly associated with fish consumption. Hydroelectric reservoirs are known to be sources of MMHg many years after their impoundment. Little is known, however, on run-of-river dams flooding smaller terrestrial areas, although their numbers are expected to increase considerably worldwide in decades to come. Production of MMHg is associated mostly with anaerobic processes, but Hg methylation has been shown to occur in periphytic biofilms located in oxic zones of the water column. Therefore, in this study, we investigated in situ production of MMHg by periphytic communities in habitats impacted by the construction of a run-of-river dam by combining transformation rate measurements with genomic approaches targeting hgcAB genes, responsible for mercury methylation. These results provide extended knowledge on mercury methylators in river ecosystems impacted by run-of-river dams in temperate habitats.

Ciliates as bioindicators of environmental pressure in a karstic river

Ciliates (protozoa) are a very large and diverse group of microeukaryotes that occupy a central position in the trophic web of freshwater ecosystems. Ciliates exhibit high ecological sensitivity and have tremendous bioindicator potential, but they are largely ignored in routine biomonitoring, mainly due to limitations in morphological diagnosis, which is both time-consuming and costly. In this study, we combined molecular (Illumina sequencing of the hypervariable V9 region of the SSU rRNA gene) and morphological approaches to get a detailed insight into the periphytic ciliate community structure and function within a karst, tufa-precipitating hydrosystem (National Park Krka, Croatia). Periphyton (biofilm) was sampled from light- and dark-exposed lithified tufa/stones at four representative locations within the Krka River, including upstream, midstream, and downstream river sections. We identified hydrological parameters and saprobiological classification of the sampling locations as the main structuring factors for ciliate communities. The molecular approach showed a clear separation of sampling locations in beta diversity analyses, as confirmed by PERMANOVA test. In contrast, alpha diversity was mostly affected by light exposition of the lithified tufa/stones, as confirmed by morphological approach. Environmental conditions consistently affected ciliate community composition at all locations, resulting in clear separation of periphyton samples. Our results indicate that ciliates should be considered as important bioindicators in monitoring tufa-forming rivers and streams, and the molecular approach (V9 region) proved to be applicable because as it efficiently captured the diversity of ciliates in periphyton. Validation of such an approach would lead to significant progress in extending monitoring to a broader range of indicator organisms than those now included in standard monitoring.

Responses of periphyton communities to abrupt changes in water temperature and velocity, and the relevance of morphology: A mesocosm approach

Sudden instream releases of water from hydropower plants (hydropeaking [HP]) can cause abrupt temperature variations (thermopeaking [TP]), typically on a daily/sub-daily basis. In alpine rivers, hydropeaking and thermopeaking waves usually overlap, which leads to a multiple stressor of flow velocity pulses and temperature alteration. Periphytic communities could give important insights into the effects of combined thermo- and hydropeaking (THP) in stream ecosystems. Thus, the study's first aim was to assess the combined effects of thermo-hydropeaking on structural (composition, biomass) and functional (photosynthesis, enzyme activity) properties of periphyton. The second aim was to assess the interaction between periphytic algae and the heterotrophic communities (bacteria) and determine how biotic and abiotic factors explain the variability of bacterial enzymatic activities in the periphyton. We assessed the effects of repeated cold and warm thermo-hydropeaking for 24 days on periphyton, by manipulating discharge and temperature in six experimental flumes directly fed by an Alpine stream. Our study revealed that THP had structural and functional effects on periphyton in oligotrophic streams, where the effects depending on the direction of the temperature change (cold/warm) and on the morphological setting (pool/riffle). The results showed that even a short-term increase in flow velocity and temperature decrease could induce better growth conditions for diatoms. Additionally, an increase in the interaction between periphytic algae and bacteria during thermo-hydropeaking was also shown, this coupling being more pronounced in pool than in riffle sections. Our results clearly showed that riffle sections develop less periphytic algal biomass and activity and therefore, THP can reduce biomass availability for primary consumers in large areas of impacted streams. These findings highlight the importance of mitigation measures, focusing on establishing heterogeneous stream bed areas, with frequent pool and riffle sequences.