Stream Biofilms Research Articles

Spatial patterns of benthic biofilm diversity among streams draining proglacial floodplains.

Glacier shrinkage opens new proglacial terrain with pronounced environmental gradients along longitudinal and lateral chronosequences. Despite the environmental harshness of the streams that drain glacier forelands, their benthic biofilms can harbor astonishing biodiversity spanning all domains of life. Here, we studied the spatial dynamics of prokaryotic and eukaryotic photoautotroph diversity within braided glacier-fed streams and tributaries draining lateral terraces predominantly fed by groundwater and snowmelt across three proglacial floodplains in the Swiss Alps. Along the lateral chronosequence, we found that benthic biofilms in tributaries develop higher biomass than those in glacier-fed streams, and that their respective diversity and community composition differed markedly. We also found spatial turnover of bacterial communities in the glacier-fed streams along the longitudinal chronosequence. These patterns along the two chronosequences seem unexpected given the close spatial proximity and connectivity of the various streams, suggesting environmental filtering as an underlying mechanism. Furthermore, our results suggest that photoautotrophic communities shape bacterial communities across the various streams, which is understandable given that algae are the major source of organic matter in proglacial streams. Overall, our findings shed new light on benthic biofilms in proglacial streams now changing at rapid pace owing to climate-induced glacier shrinkage.

Effects of intermittent flow on biofilms are driven by stream characteristics rather than history of intermittency

Intermittent streams are found all over the world, however most studies focus on intermittency in hot, arid climates. As flow intermittency is expected to increase with climate change, it is important to understand how stream biofilms in temperate regions respond to these changing conditions. In this study, 20 different streams from around Austria were sampled under flowing and non-flowing conditions to evaluate the effect of intermittency on temperate stream biofilms. These streams encompassed two distinct stream types: fine-grained with high agricultural land use and coarse sediments from relatively pristine areas. Half of these streams were historically intermittent and half historically perennial. Samples were taken from all streams during the spring and fall, when the intermittent streams were flowing and dry, respectively. Subsets of the sediments were subjected to controlled drying to evaluate the effects of history of intermittency on the biofilms. Samples were analyzed for respiration, extracellular enzyme activities, and extracellular polysaccharides in the wet and dry sediments from the field, as well as the lab-dried sediments. This study found that lab-dried perennial sediments showed similar responses to the intermittent sediments, indicating that history of intermittency does not affect biofilm response to drought. This study also found that the effects of grain size, seasonal growth, and nutrient levels have a larger impact on the biofilms than moisture content and history of intermittency.

Polyphosphate Accumulation Tracks Incremental P-Enrichment in a Temperate Watershed (Pennsylvania, United States) as an Indicator of Stream Ecosystem Legacy P

Legacy phosphorus concentrations resulting from historic additions of phosphorus (P) to the landscape may impede rapid remediation of P pollution and achievement of water quality management goals. Herein, we hypothesized that the capacity of stream biofilms to assimilate new polyphosphate (polyP) will vary as a function of stream legacy phosphorus. To test this hypothesis, we deployed a series of in situ enrichment experiments at five sites of varying land cover in central Pennsylvania, United States. Incremental P-loading was delivered using vials fitted with porous lids, that contained agar enriched with six levels of P (as Dissolved inorganic phosphorus, dissolved inorganic P) loading with rates ranging from 0 to 1,540 µg PO4−3/day; these loading rates mimicked natural stream P loadings. Substrata were incubated at stream sites for a relatively short incubation period (12 days), to measure uptake rates; after which, biofilms growing on the lids were removed and their tissue content was analyzed for biomass (as chlorophyll) and various forms of particulate phosphorus. Polyphosphate (polyP) accumulated by stream biofilms at all sites closely tracked the release of dissolved inorganic P from experimental enrichment assays. Comparatively, biofilms accumulated relatively small amounts of Particulate inorganic phosphorus and other forms of organic P that we assume constitute a third group of P-rich biochemicals (e.g., DNA, RNA, lipids, proteins). Viewed at the watershed scale, land use appeared to affect P accumulation, where sites dominated by forest cover had a higher capacity for P storage, while sites dominated by agriculture did not; this underscores the importance of polyP storage as an indicator of legacy P pollution.

Benthic Biofilms in Glacier-Fed Streams from Scandinavia to the Himalayas Host Distinct Bacterial Communities Compared with the Streamwater.

Microbial life in glacier-fed streams (GFSs) is dominated by benthic biofilms which fulfill critical ecosystem processes. However, it remains unclear how the bacterial communities of these biofilms assemble in stream ecosystems characterized by rapid turnover of benthic habitats and high suspended sediment loads. Using16S rRNA gene amplicon sequence data collected from 54 GFSs across the Himalayas, European Alps, and Scandinavian Mountains, we found that benthic biofilms harbor bacterial communities that are distinct from the bacterial assemblages suspended in the streamwater. Our data showed a decrease in species richness in the benthic biofilms compared to the bacterial cells putatively free-living in the water. The benthic biofilms also differed from the suspended water fractions in terms of community composition. Differential abundance analyses highlighted bacterial families that were specific to the benthic biofilms and the suspended assemblages. Notably, source-sink models suggested that the benthic biofilm communities are not simply a subset of the suspended assemblages. Rather, we found evidence that deterministic processes (e.g., species sorting) shape the benthic biofilm communities. This is unexpected given the high vertical mixing of water and contained bacterial cells in GFSs and further highlights the benthic biofilm mode of life as one that is determined through niche-related processes. Our findings therefore reveal a "native" benthic biofilm community in an ecosystem that is currently threatened by climate-induced glacier shrinkage. IMPORTANCE Benthic biofilms represent the dominant form of life in glacier-fed streams. However, it remains unclear how bacterial communities within these biofilms assemble. Our findings from glacier-fed streams from three major mountain ranges across the Himalayas, the European Alps and the Scandinavian Mountains reveal a bacterial community associated with benthic biofilms that is distinct from the assemblage in the overlying streamwater. Our analyses suggest that selection is the underlying process to this differentiation. This is unexpected given that bacterial cells that are freely living or attached to the abundant sediment particles suspended in the water continuously mix with the benthic biofilms. The latter colonize loose sediments that are subject to high turnover owing to the forces of the water flow. Our research unravels the existence of a microbiome specific to benthic biofilms in glacier-fed streams, now under major threats due to global warming.

Hypersaline mining effluents affect the structure and function of stream biofilm

The salinisation of freshwater ecosystems is a global environmental problem that threatens biodiversity, ecosystem functioning and human welfare. The aim of this study was to investigate the potential impact of a realistic salinity gradient on the structure and functioning of freshwater biofilms. The salinity gradient was based on the real ion concentration of a mining effluent from an abandoned mine in Germany. We exposed biofilm from a pristine stream to 5 increasing salinities (3 to 100 g L−1) under controlled conditions in artificial streams for 21 days. We evaluated its functional (photosynthetic efficiency, nutrient uptake, and microbial respiration) and structural responses (community composition, algal biomass and diatom, cyanobacteria and green algae metrics) over time. Then we compared their responses with an unexposed biofilm used as control. The functionality and structure of the biofilm exposed to the different salinities significantly decreased after short-term and long-term exposure, respectively. The community composition shifted to a new stable state where the most tolerant species increased their abundances. At the same time, we observed an increase in the community tolerance (measured as Pollution-Induced Community Tolerance) along the salinity gradient. This study provides relevant information on the salt threshold concentrations that can substantially damage algal cells (i.e., between 15 and 30 g L−1). The results provide new insights regarding the response and adaptation of stream biofilm to salinity and its potential implications at the ecosystem level.

Dark matters: Contrasting responses of stream biofilm to browning and loss of riparian shading.

Concentrations of terrestrial‐derived dissolved organic carbon (DOC) in freshwater ecosystems have increased consistently, causing freshwater browning. The mechanisms behind browning are complex, but in forestry‐intensive regions browning is accelerated by land drainage. Forestry actions in streamside riparian forests alter canopy shading, which together with browning is expected to exert a complex and largely unpredictable control over key ecosystem functions. We conducted a stream mesocosm experiment with three levels of browning (ambient vs. moderate vs. high, with 2.7 and 5.5‐fold increase, respectively, in absorbance) crossed with two levels of riparian shading (70% light reduction vs. open canopy) to explore the individual and combined effects of browning and loss of shading on the quantity (algal biomass) and nutritional quality (polyunsaturated fatty acid and sterol content) of the periphytic biofilm. We also conducted a field survey of differently colored (4.7 to 26.2 mg DOC L−1) streams to provide a ‘reality check’ for our experimental findings. Browning reduced greatly the algal biomass, suppressed the availability of essential polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA), and sterols, but increased the availability of terrestrial‐derived long‐chain saturated fatty acids (LSAFA). In contrast, loss of shading increased primary productivity, which resulted in elevated sterol and EPA contents of the biofilm. The field survey largely repeated the same pattern: biofilm nutritional quality decreased significantly with increasing DOC, as indicated particularly by a decrease of the ω‐3:ω‐6 ratio and increase in LSAFA content. Algal biomass, in contrast, was mainly controlled by dissolved inorganic nitrogen (DIN) concentration, while DOC concentration was of minor importance. The ongoing browning process is inducing a dramatic reduction in the nutritional quality of the stream biofilm. Such degradation of the major high‐quality food source available for stream consumers may reduce the trophic transfer efficiency in stream ecosystems, potentially extending across the stream‐forest ecotone.

Time after time: detecting annual patterns in stream bacterial biofilm communities.

SummaryTo quantify the major environmental drivers of stream bacterial population dynamics, we modelled temporal differences in stream bacterial communities to quantify community shifts, including those relating to cyclical seasonal variation and more sporadic bloom events. We applied Illumina MiSeq 16S rRNA bacterial gene sequencing of 892 stream biofilm samples, collected monthly for 36‐months from six streams. The streams were located a maximum of 118 km apart and drained three different catchment types (forest, urban and rural land uses). We identified repeatable seasonal patterns among bacterial taxa, allowing their separation into three ecological groupings, those following linear, bloom/trough and repeated, seasonal trends. Various physicochemical parameters (light, water and air temperature, pH, dissolved oxygen, nutrients) were linked to temporal community changes. Our models indicate that bloom events and seasonal episodes modify biofilm bacterial populations, suggesting that distinct microbial taxa thrive during these events including non‐cyanobacterial community members. These models could aid in determining how temporal environmental changes affect community assembly and guide the selection of appropriate statistical models to capture future community responses to environmental change.

Wastewater microorganisms impact the micropollutant biotransformation potential of natural stream biofilms

Biotransformation is the most important process removing manmade chemicals from the environment, yet mechanisms governing this essential ecosystem function are underexplored. To understand these mechanisms, we conducted experiments in flow-through systems, by colonizing stream biofilms under different conditions of mixing river water with treated (and ultrafiltered) wastewater. We performed biotransformation experiments with those biofilms, using a set of 75 micropollutants, and could disentangle potential mechanisms determining the biotransformation potential of stream biofilms. We showed that the increased biotransformation potential downstream of wastewater treatment plants that we observed for specific micropollutants contained in household wastewaters (downstream effect) is caused by microorganisms released with the treated effluent, rather than by the in-stream exposure to those micropollutants. Complementary data from 16S rRNA amplicon-sequencing revealed 146 amplicon sequence variants (ASVs) that followed the observed biotransformation patterns. Our results align with findings for community tolerance, and provide clear experimental evidence that microorganisms released with treated wastewater integrate into downstream biofilms and impact crucial ecosystem functions.

Viral diversity is linked to bacterial community composition in alpine stream biofilms

Biofilms play pivotal roles in fluvial ecosystems, yet virtually nothing is known about viruses in these communities. Leveraging an optimized sample-to-sequence pipeline, we studied the spatiotemporal turnover of dsDNA viruses associated with stream biofilms and found an astounding diversity to be structured by seasons and along the longitudinal gradient in the stream. While some vOTUs were region- or season-specific, we also identified a large group of permanent biofilm phages, taxonomically dominated by Myoviridae. Comparison of the observed viral distribution with predictions based on neutral community assembly indicated that chance and dispersal may be important for structuring stream biofilm viral communities. Deviation from neutral model predictions suggests that certain phages distribute efficiently across distant locations within the stream network. This dispersal capacity appears to be linked to EPS depolymerases that enable phages to efficiently overcome the biofilm barrier. Other phages, particularly vOTUs classified as Siphoviridae, appear locally overrepresented and to rely on a lysogenic life cycle, potentially to exploit the spatial distribution of bacterial populations in stream biofilms. Overall, biofilm viral and bacterial community turnover were significantly coupled. Yet, viral communities were linked to the presence of the most abundant bacterial community members. With this work, we provide a foundational ecological perspective on factors that structure viral diversity in stream biofilms and identify potentially important viral traits related to the biofilm mode of life.

Natural and anthropogenic influences on benthic cyanobacteria in streams of the northeastern United States

Benthic cyanobacteria are widespread in streams and rivers and have the potential to release toxins. In large numbers, these microorganisms and their toxins present a risk to human health. Cyanobacterial abundance in stream biofilms is typically related to single or a limited set of environmental factors, mainly light availability, water temperature, and nutrient concentrations. However, these factors may act synergistically with watershed characteristics and other stressors, such as anthropogenic pollutants, to affect cyanobacteria. We investigated the influence of multiple regional and local variables on the abundance of benthic cyanobacterial genera in streams using all subsets generalized additive modeling. We examined watershed factors (topography, geology, and climate) alongside in-stream factors (geomorphology, hydrology, pH, specific conductance, nutrients, organic contaminants, and dissolved metals) from 76 sites along an urban gradient in the northeast United States. Each genus responded to a distinct combination of environmental variables, demonstrating strong intergeneric variation in environmental selection of realized niches. Four of the 7 potentially toxigenic genera that we modeled were positively influenced by water temperature or nutrients. Nonetheless, watershed characteristics, streamflow, and/or other water quality pollutants were equally or more influential for the potentially toxigenic genera. Additionally, the relationships between cyanobacterial abundance and environmental factors varied in shape and direction across many genera. In particular, with increasing concentrations of herbicides, polychlorinated biphenyls, or metals, the abundance of roughly half of the affected genera decreased, while the others increased. These results likely demonstrate novel toxic effects of the pollutants on cyanobacterial genera in the environment, while indicating that unmeasured biotic interactions may lead to positive responses for other genera. Our results emphasize the need to consider variables beyond those that are most frequently measured or implicated (e.g., water temperature and nutrients) to more fully understand the environmental conditions that influence the distributions and abundance of potentially harmful cyanobacteria.

Biogeochemical consequences of grassland degradation on linked soil, stream, and lake ecosystems in watersheds: A short review

Grasslands are among one of the largest terrestrial biomes in the world, suffering severe threat from ongoing degradation. Grassland degradation not only alter terrestrial biogeochemical processes but also have strong potential to affect nutrient limitation and stoichiometry in aquatic ecosystems. Moreover, the impacts of grassland degradation are likely to differentially affect the cycling of carbon (C), nitrogen (N), and phosphorus (P) in the linked terrestrial-aquatic ecosystems in the watershed, leading to multiple possible scenarios of nutrient stoichiometry and limitation in soil, stream, and lake ecosystems. However, we lack of integrated studies to consider biogeochemical consequences of grassland degradation transferring from soil to stream, and finally to the lake ecosystems. An integrated case study was conducted in the Qinghai Lake Watershed on the Qinghai-Tibet Plateau to reveal the influences of grassland degradation on soil, stream, and lake ecosystems from the perspectives of C:N:P stoichiometry , nutrient limitation, and bacterial communities. This case study demonstrated a clear cascading influence from terrestrial to aquatic ecosystem, that grassland degradation differentially influenced N and P in soil with soil N decreased but P did not change (N:P decreased in soil), influencing the nutrients delivered to streams with streamwater N decreased but P increased (N:P decreased in stream), alleviating P limitation of stream biofilms which are sensitive to P variation, and ultimately stimulating phytoplankton growth in the P-limited Qinghai Lake. This case study supported one scenario of biogeochemical consequences of grassland degradation, and other scenarios might be also possible in watersheds with different geochemistry background, different landcover, and/or different lake trophic status. Integrated studies considering the coupled terrestrial-aquatic ecosystems can provide insights for protection and management of grassland watersheds in the rapidly changing world.

Epiphyton in Agricultural Streams: Structural Control and Comparison to Epilithon

Stream biofilms play an important role in the structure, functioning, and integrity of agricultural streams. In many lowland streams, macrophyte vegetation is abundant and functions as an important substrate for biofilm (epiphyton) in addition to the gravel and stone substrate for epilithon on the stream bed. We expect that reach-scale habitat conditions in streams (e.g., nutrient availability, hydraulic conditions) affect the epiphyton and epilithon biomass and composition, and that this effect will be substrate-specific (macrophytes and stones). The objectives of our study were (i) to describe concurrent changes in epiphyton and epilithon biomass and composition over a year in agricultural streams, and (ii) to determine the substrate specific reach-scale habitat drivers for the epiphyton and epilithon structure. We monitored epiphyton and epilithon biofilm biomass and composition at three-week intervals and reach-scale environmental conditions daily during a year for two agricultural steams. The results showed that epiphyton and epilithon communities differed in biomass, having high substrate specific biomass in epilithon compared to epiphyton. Epiphyton was mainly composed of diatom and green algae, while cyanobacteria were more important in epilithon, and the diatom species composition varied between the two biofilm types. Epiphyton structural properties were less influenced by reach-scale hydrology and nutrient availability compared to epilithon. The overall explanatory power of the measured environmental variables was low, probably due to micro-scale habitat effects and interactive processes within stream biofilms. Knowledge of biofilm control in agricultural streams is important in order to improve management strategies, and future studies should improve the understanding of micro-scale habitat conditions, interactive relationships within biofilms and between the biofilm and the substrates.

Seasonal and temporal variation in the effects of forest thinning on headwater stream benthic organisms in coastal British Columbia

Removal of riparian trees can alter aquatic ecosystem structure and function by influencing factors such as light availability, sediment input, and stream temperature. Contemporary forest practices such as variable retention harvest are used to mitigate the effects of clear-cut forest harvest on stream communities, but few studies have examined the effects of these techniques on aquatic ecosystems. We examined the effects of variable retention harvest on light, temperature, biofilm biomass and macroinvertebrate consumers in three coastal headwater streams in British Columbia, Canada and compared them to three nearby reference streams with unlogged riparian stands. Variable retention harvest increased light and stream temperature variability. Harvested catchments had higher stream biofilm biomass in all seasons except winter and higher invertebrate abundance in summer. Variable retention harvest altered invertebrate community composition, largely driven by increasing Chironomidae abundance and decreasing Simuliidae abundance. In conclusion, we found that variable retention harvest modified stream benthic communities, but responses varied seasonally and among taxa. This is one of few studies to investigate the impacts of variable retention harvest on multiple trophic levels over multiple seasons and years. Understanding the cascading effects of forest harvest over multi-year time scales is important for management decisions.

Feedback between bottom-up and top-down control of stream biofilm mediated through eutrophication effects on grazer growth

Algal biofilms in streams are simultaneously controlled by light and nutrient availability (bottom-up control) and by grazing activity (top-down control). In addition to promoting algal growth, light and nutrients also determine the nutritional quality of algae for grazers. While short-term experiments have shown that grazers increase consumption rates of nutrient-poor algae due to compensatory feeding, nutrient limitation in the long run can constrain grazer growth and hence limit the strength of grazing activity. In this study, we tested the effects of light and phosphorus availability on grazer growth and thus on the long-term control of algal biomass. At the end of the experiment, algal biomass was significantly affected by light, phosphorus and grazing, but the interactive effects of the three factors significantly changed over time. At both high light and phosphorus supply, grazing did not initially reduce algal biomass, but the effect of grazing became stronger in the final three weeks of the experiment. Snail growth was enhanced by light, rather than phosphorus, suggesting that algal quantity rather than quality was the main limiting factor for grazer growth. Our results highlight the role of feedback effects and the importance of long-term experiments in the study of foodweb interactions.

Wastewater constituents impact biofilm microbial community in receiving streams

Microbial life in natural biofilms is dominated by prokaryotes and microscopic eukaryotes living in dense association. In stream ecosystems, microbial biofilms influence primary production, elemental cycles, food web interactions as well as water quality. Understanding how biofilm communities respond to anthropogenic impacts, such as wastewater treatment plant (WWTP) effluent, is important given the key role of biofilms in stream ecosystem function.Here, we implemented 16S and 18S rRNA gene sequencing of stream biofilms upstream (US) and downstream (DS) of WWTP effluents in four Swiss streams to test how bacterial and eukaryotic communities respond to wastewater constituents. Stream biofilm composition was strongly affected by geographic location – particularly for bacteria. However, the abundance of certain microbial community members was related to micropollutants in the wastewater – among bacteria, micropollutant-associated members were found e.g. in Alphaproteobacteria, and among eukaryotes e.g. in Bacillariophyta (algal diatoms). This study corroborates several previously characterized responses (e.g. as seen in diatoms), but also reveals previously unknown community responses – such as seen in Alphaproteobacteria. This study advances our understanding of the ecological impact of the current wastewater treatment practices and provides information about potential new marker organisms to assess ecological change in stream biofilms.

Microbial biofilm community dynamics in five lowland streams

Stream biofilms are complex aggregates of diverse organism groups that play a vital role in global carbon and nitrogen cycles. Most of the current studies on stream biofilm focus on a limited number of organism groups (e.g., bacteria and algae), and few have included both prokaryote and eukaryote communities simultaneously. In this study, we incubated artificial substrates in five Danish lowland streams exhibiting different hydrological and physico-chemical conditions and explored the dynamics of community composition and diversity of the benthic biofilm, including both prokaryotes and eukaryotes. We found that few phyla in the prokaryote (Gammaproteobacteria and Bacteroidetes) and eukaryote (Cercozoa) communities accounted for over two-thirds of the total abundance at most of the sites. Both prokaryotic and eukaryotic diversity displayed the same temporal patterns, i.e., diversity peaked in July and January. We also found that hydrological and physico-chemical variables significantly explained the variation in the community composition at phylum level for both prokaryotes and eukaryotes. However, a large proportion of variation remained unexplained, which can be ascribed to important but unmeasured variables like light intensity and biological factors such as trophic and non-trophic interactions as revealed by network analysis. Therefore, we suggest that use of a multitrophic level perspective is needed to study biofilm i.e., the “microbial jungles”, where high occurrences of trophic and non-trophic interactions are expected.

Glyphosate-degrading behavior of five bacterial strains isolated from stream biofilms

The present study investigates the individual degrading behavior of bacterial strains isolated from glyphosate-degrading stream biofilms. In this aim, biofilms were subjected to enrichment experiments using glyphosate or its metabolite AMPA (aminomethyl phosphonic acid) as the sole phosphorus source. Five bacterial strains were isolated and taxonomically affiliated to Ensifer sp. CNII15, Acidovorax sp. CNI26, Agrobacterium tumefaciens CNI28, Novosphingobium sp. CNI35 and Ochrobactrum pituitosum CNI52. All strains were capable of completely dissipating glyphosate after 125–400 h and AMPA after 30–120 h, except for Ensifer sp. CNII15 that was not able to dissipate glyphosate but entirely dissipated AMPA after 200 h. AMPA dissipation was overall faster than glyphosate dissipation. The five strains degraded AMPA completely since formaldehyde and/or glycine accumulation was observed. During glyphosate degradation, the strain CNI26 used the C-P lyase degradation pathway since sarcosine was quantitatively produced, and C-P lyase gene expression was enhanced 30× compared to the control treatment. However, strains CNI28, CNI35 and CNI52 accumulated both formaldehyde and glycine after glyphosate transformation suggesting that both C-P lyase and/or glyphosate oxidase degradation pathways took place. Our study shows different and complementary glyphosate degradation pathways for bacteria co-existing in stream biofilms.

Dumpster diving for diatom plastid 16S rRNA genes.

High throughput sequencing is improving the efficiency of monitoring diatoms, which inhabit and support aquatic ecosystems across the globe. In this study, we explored the potential of a standard V4 515F-806RB primer pair in recovering diatom plastid 16S rRNA sequences. We used PhytoREF to classify the 16S reads from our freshwater biofilm field sampling from three stream segments across two streams in south-eastern Australia and retrieved diatom community data from other, publicly deposited, Australian 16S amplicon datasets. When these diatom operational taxonomic units (OTUs) were traced using the default RDPII and NCBI databases, 68% were characterized as uncultured cyanobacteria. We analysed the 16S rRNA sequences from 72 stream biofilm samples, separated the chloroplast OTUs, and classified them using the PhytoREF database. After filtering the reads attributed to Bacillariophyta (relative abundance >1%), 71 diatom OTUs comprising more than 90% of the diatom reads in each stream biofilm sample were identified. Beta-diversity analyses demonstrated significantly different diatom assemblages and discrimination among river segments. To further test the approach, the diatom OTUs from our biofilm sampling were used as reference sequences to identify diatom reads from other Australian 16S rRNA datasets in the NCBI-SRA database. Across the three selected public datasets, 67 of our 71 diatom OTUs were detected in other Australian ecosystems. Our results show that diatom plastid 16S rRNA genes are readily amplified with existing 515F-806RB primer sets. Therefore, the volume of existing 16S rRNA amplicon datasets initially generated for microbial community profiling can also be used to detect, characterize, and map diatom distribution to inform phylogeny and ecological health assessments, and can be extended into a range of ecological and industrial applications. To our knowledge, this study represents the first attempt to classify freshwater samples using this approach and the first application of PhytoREF in Australia.

Impacts of volcanic eruptions and early recovery in freshwater environments and organisms.

Volcanic eruptions modify environments physically and chemically with serious consequences for the biota. In this review, we analysed 80 papers reporting the effects of volcanic eruptions in freshwater environments and on freshwater organisms. An increase in water turbidity is the most common reported physical effect while increases in concentrations of inorganic elements, many representing nutrients for primary producers, are the most common chemical effects. Bacterial growth is usually stimulated, while autotrophs can be either positively or negatively affected depending on the type of impact. A persistent effect reported in the biota is changes to the assemblage, which could generate further changes in terms of ecosystem functions. This analysis also identifies some information gaps, particularly involving the effects of eruptions on heterotrophic biofilms in streams and on invertebrates and fish in lakes. Most studies were carried out soon after the volcanic eruption, so it is difficult to assess the recovery of the ecosystems. Eruptions present unique opportunities for scientific discovery, although such studies are often hindered by a lack of pre-eruption data, which would allow for a more comprehensive assessment of the effects.

Low-level pharmaceuticals alter stream biofilm structure and function

ABSTRACT Pharmaceuticals and personal care products (PPCPs) are a contaminant class of worldwide concern and a potential source of global change. To better understand the impact of low levels of PPCPs on stream biofilm structure and function, we conducted laboratory mesocosm experiments in which biofilms cultivated in streams draining areas of different land use (natural, agricultural, and urban) were exposed to low levels (5 µg L−1) of several common pharmaceuticals. We performed several functional assays and assessed differences in biofilm bacterial community composition among pharmaceutical treatments and streams. Pharmaceutical treatments altered the functional capacity and diversity of biofilms, but had no significant effect on carbon uptake or photosynthetic potential. Biofilm bacterial communities differed with land use, and pharmaceutical treatments decreased the relative abundances of Alcanivorax and Halioglobus and increased the relative abundance of Pseudomonas, indicating a shift to more drug-tolerant groups. Overall, our results provide evidence that PPCPs may act as ecological disruptors even at low levels, altering biofilm structure and some aspects of ecosystem function, and potentially influencing important biogeochemical processes in streams.