Modelling epilithic biofilms combining hydrodynamics, invertebrate grazing and algal traits

AbstractNitrogen (N) uptake is a key process in stream ecosystems that is mediated mainly by benthic microorganisms (biofilms on different substrata) and has implications for the biogeochemical fluxes at catchment scale and beyond. Here, we focused on the drivers of assimilatory N uptake, especially the effects of hydromorphology and other environmental constraints, across three spatial scales: micro, meso and reach. In two seasons (summer and spring), we performed whole-reach 15N-labelled ammonium injection experiments in two montane, gravel-bed stream reaches with riffle–pool sequences. N uptake was highest in epilithic biofilms, thallophytes and roots (min–max range 0.2–545.2 mg N m−2 day−1) and lowest in leaves, wood and fine benthic organic matter (0.05–209.2 mg N m−2 day−1). At the microscale, N uptake of all primary uptake compartments except wood was higher in riffles than in pools. At the mesoscale, hydromorphology determined the distribution of primary uptake compartments, with fast-flowing riffles being dominated by biologically more active compartments and pools being dominated by biologically less active compartments. Despite a lower biomass of primary uptake compartments, mesoscale N uptake was 1.7–3.0 times higher in riffles than in pools. At reach scale, N uptake ranged from 79.6 to 334.1 mg N m−2 day−1. Highest reach-scale N uptake was caused by a bloom of thallopyhtes, mainly filamentous autotrophs, during stable low discharge and high light conditions. Our results reveal the important role of hydromorphologic sorting of primary uptake compartments at mesoscale as a controlling factor for reach-scale N uptake in streams.

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Assessing arsenic bioremediation potential of epilithic biofilms affected by acid-mine drainage

10.5194/biofilms9-81 ◽

2020 ◽

Author(s):

Sarah Zecchin ◽

Nicoletta Guerrieri ◽

Evelien Jongepier ◽

Leonardo Scaglioni ◽

Gigliola Borgonovo ◽

...

Keyword(s):

Microbial Community ◽

Acid Mine Drainage ◽

Mine Drainage ◽

Heterotrophic Bacteria ◽

16S Rrna Genes ◽

Rrna Genes ◽

Sampling Point ◽

Epilithic Biofilm ◽

Acid Mine ◽

Epilithic Biofilms

Arsenic is a toxic but naturally abundant metalloid that globally leads to contamination in groundwater and soil, exposing millions of people to cancer and other arsenic-related diseases. In several areas in Northern Italy arsenic in soil and water exceeds law limits (20 mg kg-1 and 10 mg L-1, respectively), due to both the mineralogy of bedrock and former mining activities. The Rio Rosso stream, located in the Anzasca Valley (Piedmont) is heavily affected by an acid mine drainage originated from an abandoned gold mine. Arsenic, together with other heavy metals, is transferred by the stream to the surrounding area. The stream is characterized by the presence of an extensive reddish epilithic biofilm at the opening of the mine and on the whole contaminated waterbed. The aim of this study was to characterize the mechanisms allowing the biotic fraction of this biofilm to cope with extreme arsenic concentrations. The composition and functionality of the microbial communities constituting the epilithic biofilms sampled in the close proximity and downstream the mine were unraveled by 16S rRNA genes and shotgun Illumina sequencing in relation to the extreme physico-chemical parameters. In parallel, autotrophic and heterotrophic microbial populations were characterized in vivo by enrichment cultivation and isolated strains were tested for their ability to perform arsenic redox transformation. Preliminary analyses indicated that the biofilm accumulated arsenic in the order of 6 &#183; 103 mg kg-1, in contrast to 0.14 mg L-1, measured in the surrounding water. The main chemical parameter affecting the composition of the microbial community was the pH, being 2 next to the mine and 6.7 in the downstream sampling point. In both sampling sites iron- and sulfur-cycling microorganisms were retrieved by both cultivation and molecular methods. However, the diversity of the microbial community living next to the mine was significantly lower with respect to the community developed downstream. In the latter, autotrophic Cyanobacteria belonging to the species Tychonema were the dominant taxa. A complete arsenic cycle was shown to occur, with heterotrophic bacteria mainly responsible for arsenate reduction and autotrophic bacteria performing arsenite &#160;oxidation. These observations indicate that the epilithic biofilm living in the Rio Rosso stream represents a peculiar ecosystem where microorganisms cope with metalloid toxicity likely using diverse mechanisms. Such microbial metabolic properties might be exploited in bioremediation strategies applied in arsenic-contaminated environments.

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Faecal indicator bacteria in river biofilms

Water Science & Technology ◽

10.2166/wst.2010.022 ◽

2010 ◽

Vol 61 (5) ◽

pp. 1105-1111 ◽

Cited By ~ 29

Author(s):

M. Balzer ◽

N. Witt ◽

H.-C. Flemming ◽

J. Wingender

Keyword(s):

Total Coliform ◽

Cell Number ◽

Indicator Bacteria ◽

Coliform Bacteria ◽

Plate Count ◽

Overlying Water ◽

Faecal Indicator Bacteria ◽

Epilithic Biofilms ◽

Cell Densities ◽

A Minor

Biofilms in surface waters primarily consist of allochthonous microorganisms. Under conditions of pollution faecally derived bacteria may interact with these biofilms. Total coliform bacteria, Escherichia coli and intestinal enterococci are used to monitor source water quality, indicating faecal pollution and the possible presence of enteric pathogens. In the present study the occurrence of faecal indicators was investigated in biofilms (epilithic biofilms, sediments) of German rivers. All of the biofilms contained significant concentrations of these bacteria, which were several orders of magnitude lower compared with the total cell number and the number of culturable heterotrophic plate count bacteria indicating that faecal indicator bacteria represented a minor fraction of the whole biofilm communities. The biofilms displayed approximately two orders of magnitude higher concentrations of total coliforms, E. coli and enterococci compared with the overlying water. Identification of coliform and enterococcal isolates from the biofilms revealed the presence of species which are known to be opportunistic pathogens. Overall, the results of the present study show that faecal indicator bacteria can survive in the presence of high cell densities of the authochthonous microflora in epilithic biofilms and sediments, suggesting that these biofilms may act as a reservoir for bacterial pathogens in polluted rivers.

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