59 research outputs found
Colonization dynamics and grazing activity of ciliates in stream biofilms
Cross-barriers such as small dams cause local flow velocity heterogeneities, which might
affect the formation, structure, and function of biofilms. The main objective of this thesis was
to investigate the impact of flow velocity on colonization dynamics, grazing activity, and
behavioral changes of biofilm associated ciliates. In addition, the effect of protists grazing
activity on spatial biofilm morphology was examined at slow flow velocities. Surfaces were
rapidly colonized by ciliates at a slow flowing reservoir of the third order Ilm stream
(Thuringia, Germany) and in slow flowing flow channels. Initial stream biofilms inhabited all
functional groups of ciliates irrespective of flow velocity implementing all trophic links
within the microbial loop. The low abundance of sessile filter feeders at faster flow velocities
suggested that the attachment of these cells was inhibited. Grazing activity of a previously
attached filter feeder seemed to be inhibited at faster flow velocities since cells remained
about 45% of the observed time in a contracted state. Vagile flattened gulper feeder tolerated
faster flow velocities and responded with a positive rheotactic movement. Grazing activity
and motility of ciliates altered spatial biofilm morphology. Mushroom shaped microcolonies,
a higher porosity, and a higher biofilm surface area to volume ratio indicated that nutrient
exchange between biofilm and the surrounding fluid was improved and bacterial growth
might be accelerated. With respect to restoration ecology the data indicated that flow velocity
differences at small low-head dams increased the diversity of biofilm associated ciliates,
which might contribute to enhanced ecosystem resilience
Streambed migration frequency drives ecology and biogeochemistry across spatial scales
The bed of fluvial ecosystems plays a major role in global biogeochemical cycles.
All fluvial sediments migrate and although responses of aquatic organisms to
such movements have been recorded there is no theoretical framework on how
the frequency of sediment movement affects streambed ecology and biogeochemistry.
We here developed a theoretical framework describing how the
moving-resting frequencies of fine-grained sediments constrain streambed communities
across spatial scales. Specifically, we suggest that the most drastic
impact on benthic and hyporheic communities will exist when ecological and
biogeochemical processes are at the same temporal scale as the sediment
moving-resting frequency. Moreover, we propose that the simultaneous occurrence
of streambed patches differing in morphodynamics should be considered
as an important driver of metacommunity dynamics. We surmise that the frequency
of patch transition will add new dimensions to the understanding of biogeochemical
cycling and metacommunities from micro-habitat to segment
scales. This theoretical framework is important for fluvial ecosystems with frequent
sediment movement, yet it could be applied to any other dynamic habitat.German Research Foundation joint funding
grant RI 2093/2-1 and MU 1464/7-1Carl Zeiss Foundation, P2021-00-004Israel Science
Foundation, grant 682/17),NSF-BSF joint funding grant EAR-1734300UK-Israel Science Fellowship Scheme 2018–2019Israeli Science Foundation, grant 944\2
Two microcrustaceans affect microbial and macroinvertebrate-driven litter breakdown
1. Leaf litter degradation in fresh waters is a fundamental ecosystem process performed by a wide array of decomposers. The meiofauna is an important component of aquatic heterotrophic assemblages, which can provide a trophic link between plant detritus and associated microbial and macroinvertebrate communities, but their contribution to leaf breakdown remains poorly understood. 2. We hypothesised that, through their feeding activity, microcrustaceans influence the structure of fungal assemblages and consequently microbially mediated litter breakdown. Litter-associated microcrustaceans were predicted to change the pathways of energy transfer in the food web according to the positive (e.g. complementarity) or negative (e.g. predation) interactions with macroinvertebrate detritivore taxa.
3. We evaluated experimentally in the laboratory, over 6 and 13 days, the potential contribution of two freshwater microcrustaceans (a cladoceran and a copepod) to litter breakdown in the presence of microfungi (aquatic hyphomycetes), with and without macroinvertebrate detritivores (a trichopteran and a gammarid amphipod).
4. The presence of microcrustaceans enhanced leaf mass loss by 62 and 22% in treatments with fungi or trichopteran alone, respectively, while no significant effect was observed for treatments with the amphipod. Microcrustaceans strongly increased the production of fine particulate organic matter, particularly in treatments with fungi alone (+637%). The leaf consumption rate by the amphipod significantly decreased ( 61%) at 13 days in the presence of microcrustaceans, likely due to predation on cladocerans.
5. Our study supports the potential role of microcrustaceans in the detrital food web of streams and rivers. Interestingly, microcrustaceans may interact with microbial and macroinvertebrate decomposers in either positive or negative ways. Therefore, microcrustaceans add complexity to detrital food webs by increasing vertical diversity and modulating biotic interactions with important consequences for carbon and energy transfers in stream ecosystems
Towards an improved understanding of biogeochemical processes across surface-groundwater interactions in intermittent rivers and ephemeral streams
Surface-groundwater interactions in intermittent rivers and ephemeral streams (IRES), waterways which do not flow year-round, are spatially and temporally dynamic because of alternations between flowing, non-flowing and dry hydrological states. Interactions between surface and groundwater often create mixing zones with distinct redox gradients, potentially driving high rates of carbon and nutrient cycling. Yet a complete understanding of how underlying biogeochemical processes across surface-groundwater flowpaths in IRES differ among various hydrological states remains elusive. Here, we present a conceptual framework relating spatial and temporal hydrological variability in surface water-groundwater interactions to biogeochemical processing hotspots in IRES. We combine a review of theIRES biogeochemistry literature with concepts of IRES hydrogeomorphology to: (i) outline common distinctions among hydrological states in IRES; (ii) use these distinctions, together with considerations of carbon, nitrogen, and phosphorus cycles within IRES, to predict the relative potential for biogeochemical processing across different reach-scale processing zones (flowing water, fragmented pools, hyporheic zones, groundwater, and emerged sediments); and (iii) explore the potential spatial and temporal variability of carbon and nutrient biogeochemical processing across entire IRES networks. Our approach estimates the greatest reach-scale potential for biogeochemical processing when IRES reaches are fragmented into isolated surface water pools, and highlights the potential of relatively understudied processing zones, such as emerged sediments. Furthermore, biogeochemical processing in fluvial networks dominated by IRES is likely more temporally than spatially variable. We conclude that biogeochemical research in IRES would benefit from focusing on interactions between different nutrient cycles, surface-groundwater interactions in non-flowing states, and consideration of fluvial network architecture. Our conceptual framework outlines opportunities to advance studies and expand understanding of biogeochemistry in IRES
Hydrodynamics Alter the Tolerance of Autotrophic Biofilm Communities Toward Herbicides
Multiple stressors pose potential risk to aquatic ecosystems and are the main reasons for failing ecological quality standards. However, mechanisms how multiple stressors act on aquatic community structure and functioning are poorly understood. This is especially true for two important stressors types, hydrodynamic alterations and toxicants. Here we perform a mesocosm experiment in hydraulic flumes connected as a bypass to a natural stream to test the interactive effects of both factors on natural (inoculated from streams water) biofilms. Biofilms, i.e., the community of autotrophic and heterotrophic microorganisms and their extracellular polymeric substances (EPS) in association with substratum, are key players in stream functioning. We hypothesized (i) that the tolerance of biofilms toward toxicants (the herbicide Prometryn) decreases with increasing hydraulic stress. As EPS is known as an absorber of chemicals, we hypothesize (ii) that the EPS to cell ratio correlates with both hydraulic stress and herbicide tolerance. Tolerance values were derived from concentration-response assays. Both, the herbicide tolerance and the biovolume of the EPS significantly correlated with the turbulent kinetic energy (TKE), while the diversity of diatoms (the dominant group within the stream biofilms) increased with flow velocity. This indicates that the positive effect of TKE on community tolerance was mediated by turbulence-induced changes in the EPS biovolume. This conclusion was supported by a second experiment, showing decreasing effects of the herbicide to a diatom biofilm (Nitzschia palea) with increasing content of artificial EPS. We conclude that increasing hydrodynamic forces in streams result in an increasing tolerance of microbial communities toward chemical pollution by changes in EPS-mediated bioavailability of toxicants
Geographically widespread C-13-depletion of grazing caddis larvae:a third way of fuelling stream food webs?
Stream ecosystems are supported by both green (i.e. based on grazing) and brown (i.e. detritus) food webs, whereas methane-derived carbon is not considered generally to be important; here, we add circumstantial evidence for this potential third way. Grazing cased-caddis (Trichoptera) larvae in the family Glossosomatidae can be very abundant in springs and headwaters and frequently have much lower stable carbon isotope ratios (i.e. they are depleted in the heavier C-13 stable isotope) than the biofilm (epilithon) on the upper surfaces of the stones on which they live, and which is their presumed diet. Evidence for similar isotopic depletion in other lotic invertebrates is currently limited, however; even for glossosomatids it has been observed so far only in some streams draining the southern English cretaceous chalk and in a few headwaters in northern California. If this phenomenon proves to be more widespread, among streams or taxa, it could imply a more general underpinning of stream food webs by isotopically light carbon derived from methane and accessed via consumers feeding on methanotrophic bacteria. Here, we sampled 58 stream sites to examine whether caddis larvae are also C-13-depleted in streams draining other geologies. We focused mainly on carboniferous limestone and sandstone, as well as on further chalk streams representative of most of the British chalk aquifer: together, these new sites covered an area of almost 90,000 km(2), around three times greater than that surveyed previously. At all 58 sites methane gas was supersaturated relative to the atmospheric equilibrium, and at 49 of them larvae were conspicuously C-13-depleted (from -17.5 parts per thousand to -3.6 parts per thousand) relative to the bulk epilithon (components of which we know can oxidise methane). Although still most pronounced on chalk, this phenomenon was geographically and geologically much more widespread than shown previously and suggests methane-derived carbon could indeed play a prominent role in stream food webs (i.e. the third way)
Effects of riparian plant diversity loss on aquatic microbial decomposers become more pronounced at longer times
We examined the potential long-term impacts of riparian plant diversity loss on diversity and activity of aquatic microbial decomposers. Microbial assemblages were obtained
in a mixed-forest stream by immersion of mesh bags contain-ing three leaf species (alder, oak and eucalyptus), commonly
found in riparian corridors of Iberian streams. Simulation of
species loss was done in microcosms by including a set of all
leaf species, retrieved from the stream, and non-colonized
leaves of three, two or one leaf species. Leaves were renewed
every month throughout six months, and microbial inoculum
was ensured by a set of colonized leaves from the previous
month. Microbial diversity, leaf mass loss and fungal biomass
were assessed at the second and sixth months after plant
species loss. Molecular diversity of fungi and bacteria, as the
total number of operational taxonomic units per leaf diversity
treatment, decreased with leaf diversity loss. Fungal biomass
tended to decrease linearly with leaf species loss on oak and
eucalyptus, suggesting more pronounced effects of leaf diver-sity on lower quality leaves. Decomposition of alder and
eucalyptus leaves was affected by leaf species identity, mainly
after longer times following diversity loss. Leaf decomposi-tion of alder decreased when mixed with eucalyptus, while
decomposition of eucalyptus decreased in mixtures with oak.
Results suggest that the effects of leaf diversity on microbial
decomposers depended on leaf species number and also on
which species were lost from the system, especially after
longer times. This may have implications for the management
of riparian forests to maintain stream ecosystem functioning.FEDER-POFC-COMPETE and the Portuguese
Foundation for Science and Technology supported this study (PEst-C/
BIA/UI4050/2011, PTDC/AAC-AMB/113746/2009 and PTDC/AAC-AMB/117068/2010), S. Duarte (SFRH/BPD/47574/2008) and I.
Fernandes (SFRH/BD/42215/2007)
Molecular and Morphological Snapshot Characterisation of the Protist Communities in Contrasting Alpine Glacier Forefields
Phagotrophic protist diversity in oligotrophic soils such as alpine glacier forefields is still poorly studied. Combining morphologic observations with molecular-based analyses, we assessed the diversity of major phagotrophic protist groups in two contrasting glacier forefields in the Swiss Alps (Tiefen glacier forefield, siliceous bedrock, and Wildstrubel glacier forefield, calcareous bedrock), at sites differing in soil development. Ciliates and heterotrophic flagellates could be detected with both approaches, while amoebae could be observed only microscopically. Soils from Tiefen and Wildstrubel glacier forefields harboured distinctly different ciliate, flagellate and amoebae communities. The ciliate clone libraries from the Tiefen glacier forefield were dominated by Oligohymenophorea-related sequences while those from the Wildstrubel glacier forefield were dominated by Spirotrichea-related sequences. Testate amoebae morphospecies of the genera Corythion, Cryptodifflugia, Euglypha and Tracheleuglypha were restricted to the Tiefen glacier forefield, while Centropyxis and Trinema to the Wildstrubel one. No ciliate sequences and only a few ciliate and testate amoebae morphospecies could be retrieved from unvegetated soils of both glacier forefields. The ciliate and testate amoebae community detected at unvegetated sites were a subset of the community developed at vegetated sites. Overall, our results suggest that alpine glacier forefields are colonised by a diverse community of phagotrophic protists which seems to be shaped by bedrock geology and vegetation cover
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