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  • 1
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    Intracellular, environmental and biotic interactions influence recruitment of benthic Microcystis (Cyanophyceae) in a shallow eutrophic lake (2016)
    Oxford University Press
    Details
    Publication Date: 2016-10-08
    Description: Microcystis is known to overwinter on sediment surfaces and provide an inoculum to support water column blooms in lakes. There is uncertainty as to whether recruitment is an active process triggered by internal changes in buoyancy, or a passive process induced by resuspension. The effect on Microcystis recruitment of ammonium, light and temperature was assessed in laboratory experiments using sediments collected in a small eutrophic lake from two habitats: near-edge (containing Microcystis and Aphanizomenon gracile ) and mid-lake (predominantly Microcystis ). In all experiments single cells, rather than colonies, accounted for the majority (〉55%) of recruited cells. Microcystis recruitment was significantly lower ( P  〈 0.001) in near-shore samples suggesting that A. gracile elicits allelopathic effects on Microcystis. In mid-lake samples, Microcystis recruitment was significantly higher at moderate ammonium concentrations (0.1, 0.2 and 0.5 mg L –1 ; P  〈 0.001), at two temperatures (16 and 25°C; P  〈 0.001) and high light intensities (50 and 100 µmol m –2 s –1 ; P  〈 0.01). Microcystis cells were isolated from sediment in spring, early and late summer and assessed using transmission electron microscopy. The percentage of cell area filled with gas vesicles increased significantly ( P  〈 0.001). These data demonstrate that allopathic interactions, ammonium, light and temperature can individually and synergistically regulate gas vesicle synthesis and Microcystis recruitment.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 2
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    Increased mud deposition reduces stromatolite complexity (2017)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2017-06-09
    Description: Microbial mat growth can produce diagnostic delicate structures in low-energy environments, but mat morphology, and thus preservation of delicate structures as morphological biosignatures, is affected by mud accumulation. In Lake Joyce, Antarctica, varying rates of siliciclastic mud deposition affected the morphology of partially calcified microbial mats. These mats were characterized along a shore-parallel transect from higher- to lower-sedimentation regions of the lake. Mats with high mud accumulation rates were predominantly flat with sparse pinnacles. At lower sedimentation rates, mats developed more pinnacles and more delicate features, including vertical webs of biofilm suspended between pinnacles. Morphological transitions suggest that mud deposition disrupts growth of delicate microbial structures like biofilm webs and inhibits pinnacle growth at higher accumulation rates. The simplification of mat morphology with increasing mud accumulation has important implications for the distribution of stromatolite types in the rock record. Stromatolites with intricate biofilm structures are rare, possibly due to the paucity of appropriate environments rather than the intrinsic properties of microbial communities. Communities capable of forming delicate microbialites likely produced morphologically simpler pinnacles and flat mat in environments with significant siliciclastic mud or micrite influx. Thus, delicate mats have narrow environmental ranges for growth, and temporal or spatial variations in siliciclastic mud or micrite sedimentation rates bias the record of microbial activity preserved in stromatolites.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 3
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    Microbial Mat Communities along an Oxygen Gradient in a Perennially Ice-Covered Antarctic Lake [Environmental Microbiology] (2016)
    The American Society for Microbiology (ASM)
    Details
    Publication Date: 2016-01-08
    Description: Lake Fryxell is a perennially ice-covered lake in the McMurdo Dry Valleys, Antarctica, with a sharp oxycline in a water column that is density stabilized by a gradient in salt concentration. Dissolved oxygen falls from 20 mg liter –1 to undetectable over one vertical meter from 8.9- to 9.9-m depth. We provide the first description of the benthic mat community that falls within this oxygen gradient on the sloping floor of the lake, using a combination of micro- and macroscopic morphological descriptions, pigment analysis, and 16S rRNA gene bacterial community analysis. Our work focused on three macroscopic mat morphologies that were associated with different parts of the oxygen gradient: (i) "cuspate pinnacles" in the upper hyperoxic zone, which displayed complex topography and were dominated by phycoerythrin-rich cyanobacteria attributable to the genus Leptolyngbya and a diverse but sparse assemblage of pennate diatoms; (ii) a less topographically complex "ridge-pit" mat located immediately above the oxic-anoxic transition containing Leptolyngbya and an increasing abundance of diatoms; and (iii) flat prostrate mats in the upper anoxic zone, dominated by a green cyanobacterium phylogenetically identified as Phormidium pseudopriestleyi and a single diatom, Diadesmis contenta . Zonation of bacteria was by lake depth and by depth into individual mats. Deeper mats had higher abundances of bacteriochlorophylls and anoxygenic phototrophs, including Chlorobi and Chloroflexi . This suggests that microbial communities form assemblages specific to niche-like locations. Mat morphologies, underpinned by cyanobacterial and diatom composition, are the result of local habitat conditions likely defined by irradiance and oxygen and sulfide concentrations.
    Print ISSN: 0099-2240
    Electronic ISSN: 1098-5336
    Topics: Biology
    Published by The American Society for Microbiology (ASM)
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  • 4
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    Antarctic microbial mats: A modern analog for Archean lacustrine oxygen oases (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-09-15
    Description: The evolution of oxygenic photosynthesis was the most important geochemical event in Earth history, causing the Great Oxidation Event (GOE) ~2.4 b.y. ago. However, evidence is mixed as to whether O 2 production occurred locally as much as 2.8 b.y. ago, creating O 2 oases, or initiated just prior to the GOE. The biogeochemical dynamics of possible O 2 oases have been poorly constrained due to the absence of modern analogs. However, cyanobacteria in microbial mats in a perennially anoxic region of Lake Fryxell, Antarctica, create a 1–2 mm O 2 -containing layer in the upper mat during summer, providing the first known modern analog for formation of benthic O 2 oases. In Lake Fryxell, benthic cyanobacteria are present below the oxycline in the lake. Mat photosynthesis rates were slow due to low photon flux rate (1–2 µmol m –2 s –1 ) under thick ice cover, but photosynthetic O 2 production was sufficient to sustain up to 50 µmol O 2 L –1 , sandwiched between anoxic overlying water and anoxic sediments. We hypothesize that Archean cyanobacteria could have similarly created O 2 oases in benthic mats prior to the GOE. Analogous mats may have been at least partly responsible for geological evidence of oxidative weathering prior to the GOE, and habitats such as Lake Fryxell provide natural laboratories where the impact of benthic O 2 oases on biogeochemical signatures can be investigated.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 5
    Electronic Resource
    Electronic Resource
    The role of photosynthesis/light relationships in determining lower depth limits of Characeae in South Island, New Zealand lakes (1996)
    Oxford BSL : Blackwell Science Ltd
    Freshwater biology 35 (1996), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The maximum depth of colonization of aquatic macrophytes (Zc) was investigated in eighteen South Island, New Zealand lakes. The downward attenuation coefficient for photosynthetically active radiation (Kd(PAR)) was calculated and the spectral characteristics of the lakes determined with a spectroradiometer.2. Characean algae dominated the deepest communities in sixteen of the study lakes.3. Zc was significantly related to Kd(PAR) by the relationship Zc = 4.5/Kd– 2.2.4. From measurements of the photosynthetic properties of Chara corallina (Kl. ex Willd., em R.D.W.) and incident radiation over the course of a year we calculated the depth at which daily net photosynthesis would be equal to zero for each day of the year. An annual average of this depth was significantly related to Zc with anr2 of 0.86.5. Correcting Kd(PAR) for spectral quality and taking into account the potential absorption spectrum of a characean meadow did not improve the relationships.6. We suggest that relationships established between Kd(PAR) and Zc of characean algae in South Island, New Zealand lakes can be explained to a great extent by light limitation of photosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1996.00481.x
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  • 6
    Electronic Resource
    Electronic Resource
    Removal of settled sediments and periphyton from macrophytes by grazing invertebrates in the littoral zone of a large oligotrophic lake (2000)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 44 (2000), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 〈list style="custom"〉1The resistance and resilience of littoral zone communities to sedimentation will depend both on the extent to which sediment deposition affects productivity, and on interactions within the communities. A series of hypotheses were set up and tested to examine interactions and feedback mechanisms among deposited sediments, periphyton, macrophytes and grazers in a large oligotrophic lake subject to fluctuating sediment loadings.2Although sediments incorporated into periphyton reduced light availability to macrophytes, periphytic algae were generally the dominant light absorbing component under natural conditions. When grazers were absent, both sediments incorporated in the periphyton and periphytic algal densities increased, and both were then important in reducing light available to macrophytes.3Grazing rate and assimilation efficiency for the dominant grazer, the prosobranch gastropod Potamopyrgus antipodarum, increased with increasing sediment content under natural lake conditions to reach a maximum at 10 mg sediment cm−2.4An increase in sediment incorporation into periphyton films resulted in an increased grazing rate and hence grooming of sediments from macrophytes.5Grazing invertebrates can play a major role in maintenance of littoral communities by continuously grooming macrophyte hosts of periphytic algae and settled sediments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2000.00563.x
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  • 7
    Electronic Resource
    Electronic Resource
    Nutrients and their effects on phytoplankton populations in lakes on Signy Island, Antarctica (1983)
    Springer
    Polar biology 2 (1983), S. 115-126 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Seasonal changes in nutrient concentrations, phytoplankton biomass and nutritional state were followed in two contrasting Antarctic lakes. Oligotrophic Sombre Lake receives little phosphate from its catchment and this limits the standing crop of phytoplankton which can develop in spring and summer. This situation appears to be typical of unenriched Maritime Antarctic lakes. Large numbers of seals and seabirds in the catchment of nearby Heywood Lake increase its phosphate loading and allow a much denser growth of phytoplankton. The N:P ratio is low and nitrogen rather than phosphate is the most limiting nutrient. Despite limitation of standing crop, photosynthetic rates in both lakes are relatively high and recycling of nutrients within the lake may be rapid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00303177
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  • 8
    Electronic Resource
    Electronic Resource
    Photosynthesis in thick cyanobacterial films: a comparison of annual and perennial antarctic mat communities (1993)
    Springer
    Hydrobiologia 252 (1993), S. 203-209 
    Details
    ISSN: 1573-5117
    Keywords: Antarctica ; cyanobacterial mats ; periphyton ; photosynthesis ; self-shading ; streams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Annual and perennial cyanobacterial mats from streams on Signy Island, Antarctica, show similar areal concentrations of chlorophyll-a and areal rates of photosynthesis. Maximum rates of photosynthesis were temperature dependant over the range 0–14 C, with a Q10 of approximately 2.5. Rates of photosynthesis per unit chlorophyll-a were comparable to other Antarctic mat communities but low compared to phytoplankton from upstream lakes. Areal rates of photosynthesis were however much higher than for phytoplankton. Low chlorophyll-specific rates of photosynthesis are interpreted as the effect of self shading within the mats. It is hypothesised that these mats rapidly attenuate incoming radiation and that photosynthesis in most of the mat is effectively light-limited. This situation is likely to occur in all thick periphyton films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00005470
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  • 9
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    Sensitivity of freshwater macrophytes to UV radiation: relationship to depth zonation in an oligotrophic New Zealand lake (2001)
    In:  EPIC3Marine And Freshwater Research, 52(7), pp. 1023-1032, ISSN: 1323-1650
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 10
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    Reduction of UV-B radiation causes an enhancement of photoinhibition in high light stressed aquatic plants from New Zealand lakes (2006)
    In:  EPIC3Journal of photochemistry and photobiology b-biology, 84(2), pp. 89-102
    Details
    Publication Date: 2019-07-17
    Description: Anthropogenic stratospheric ozone depletion causes an increase of UV-B radiation impinging on the earth surface, which is a threat to plants not adapted to higher UV-B irradiances. Investigations were undertaken with aquatic plants from New Zealand, where UV-irradiances are naturally higher due to the southern latitude, to compare with former results of polar species. The experiments reported in this study were undertaken with plants collected from different lakes of the South Island, with different UV transparencies. Photoinhibition was induced under controlled conditions using a sun simulator, which mimicked the natural underwater radiation spectrum. Photosynthetic activity during high light stress, and during recovery in dim light, was determined in vivo by measuring fluorescence changes, using a PAM fluorometer device. A comparison of different species showed that the extent to which UV causes an additional decrease of photosynthetic performance during high light stress varies according to the depth of growth and UV transparency of the water body. This observation fits with previous studies. However, a new finding was that some species were even more strongly inhibited when UV-B was filtered out of the simulated sun spectrum, indicating a supporting effect of the short UVR wavelength range against photoinhibition. These results were also confirmed by field experiments under natural radiation conditions. Thus, UV-B does not solely cause negative effects on photosynthesis, but it may even support recovery processes in aquatic plants adapted to a high UV-radiation environment. The latter is in contrast to earlier studies, in which UV-B radiation was considered causing only harmful effects on photosynthesis of aquatic plants.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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