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  • PAGEPress Publications  (3)
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  • PAGEPress Publications  (3)
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  • 1
    Online Resource
    Online Resource
    Representative monitoring of the calcifying alga 〈em〉Phacotus lenticularis〈/em〉 (Chlamydophyceae) in lentic ecosystems : Representative monitoring of calcifying algae
    PAGEPress Publications ; 2020
    In:  Journal of Limnology Vol. 79, No. 2 ( 2020-01-30)
    Details
    In: Journal of Limnology, PAGEPress Publications, Vol. 79, No. 2 ( 2020-01-30)
    Abstract: The biogenic carbonate precipitation by the freshwater alga Phacotus lenticularis may play a role in long-term carbon (C) fixation that has not yet been quantified. This is partly due to the absence of a standardised methodology to representatively sample and assess the cell density and sedimentation of P. lenticularis in lakes. The objective of the present study was to define an adequate sampling methodology taking into account the spatiotemporal variation of P. lenticularis as well as the sedimentation and dissolution of calcite shells. Simultaneous measurements in three different lake sub-basins of Lake Grosser Ostersee, Germany, showed that the spatial cell density of P. lenticularis was similar in each sub-basin. At all sites, the vertical P. lenticularis cell density maxima corresponded with the slowly downshifting thermocline from depths of 2 to 6 m. During the entire growth period, composite samples from 0 to 7 m included 89% of the total P. lenticularis population. Lake bathymetry, as well as external factors like wind exposure, did not appear to affect the abundance of these calcifying algae. Sediment traps at a depth below the thermocline (at 7 m) and 1 m above the lake bottom recorded sedimentation rates of P. lenticularis shell halves (sh) between 1.1×106 and 1.1×108 sh m−2 d−1, while mean cell concentrations in the water column were between 1.1×108 and 1.7×109 shells per m². Sinking velocity ranged between 3 and 4 m d−1. Sediment from traps installed at a depth of 7 m did not reflect mean shell concentrations in the water column above. Dissolution of carbonates reduced the number of shells in sediment traps at the lake bottom and during the storage of samples. A laboratory experiment showed that even distilled water used for dilution during microscopic analysis led to dissolution of P. lenticularis shells. In conclusion, combined sampling of P. lenticularis from open water and sediment traps close to the lake bottom delivers a most representative assessment of biogenic carbonate precipitation. Due to dissolution effects, high temporal resolution along with appropriate sample preservation are crucial, whereas spatial representativeness was already achieved with low number of sampling sites per lake.
    Type of Medium: Online Resource
    ISSN: 1723-8633 , 1129-5767
    URL: Article
    DOI: 10.4081/jlimnol.2020.1946
    Language: Unknown
    Publisher: PAGEPress Publications
    Publication Date: 2020
    detail.hit.zdb_id: 2034229-9
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Calcite production by the calcifying green alga Phacotus lenticularis
    PAGEPress Publications ; 2018
    In:  Journal of Limnology Vol. 77, No. 2 ( 2018-01-04)
    Details
    In: Journal of Limnology, PAGEPress Publications, Vol. 77, No. 2 ( 2018-01-04)
    Abstract: The importance of carbonate precipitation by phytoplankton in fresh water lakes has not been sufficiently considered in global carbon cycles and climate change scenarios. The objective of this study was to determine the influence of the calcifying bivalved phytoflagellate Phacotus lenticularis (Ehrenberg) Deising 1866 on the total calcite precipitation in five European hard-water lakes. For this purpose, an accurate mass determination of single Phacotus lenticularis shells was required. We developed a novel methodological approach to precisely determine the volume and mass of the calcified shells. Focused ion beam (FIB) techniques were employed to investigate internal structural features. Thin layer cross-sections of the shell profiles were reproduced and perforation as well as the crystalline structure of the calcite plates were monitored. 3D-shell models were computed by 360° rotation of the shell cross-sections using a CAD 3D imaging software to calculate precise volumes and estimate realistic masses. In contrast to previous estimates, we determined a 2.8-fold higher shell mass of 0.86 ng CaCO3 (standard deviation SD = 0.18) for the highly massive shells at a mean volume per individual of 334.1 µm³ (SD = 70). An initial shell porosity of less than 5% was derived from thin layer cross-section images, resulting in a presumed mean shell density of 0.0026 ng µm−3. The shell diameter was significantly influenced by the lake’s origin. The shells from each lake displayed substantial variations in diameter and shape. The pores in the shells showed two variations. Wider pore canals penetrated the whole shell wall, whereas small, elongated pores were located along the interspaces between calcite crystals with tabular habit. The approximate average dimensions of these calcite plates were 1.0 × 1.6 × 0.2 µm. The mean lateral wall thickness at the rim and centre of the shell were 1.98 µm (SD = 0.42) and 0.79 µm (SD = 0.17), respectively. The average carbonate precipitation by Phacotus lenticularis in relation to the total epilimnetic suspended calcite precipitation was 6.0% in the oligotrophic lake Großer Ostersee (Bavaria, Germany). During the growing season, Phacotus lenticularis contributed up to 21% of the particulate calcium carbonate in the epilimnion. These findings suggest that Phacotus lenticularis should be considered in the assessment of hard-water lake carbon cycling.
    Type of Medium: Online Resource
    ISSN: 1723-8633 , 1129-5767
    URL: Article
    DOI: 10.4081/jlimnol.2018.1692
    Language: Unknown
    Publisher: PAGEPress Publications
    Publication Date: 2018
    detail.hit.zdb_id: 2034229-9
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
  • 3
    Online Resource
    Online Resource
    Phacotus lenticularis content in carbonate sediments and epilimnion in four German hard water lakes : P. lenticularis content in German hard-water lakes
    PAGEPress Publications ; 2020
    In:  Journal of Limnology Vol. 79, No. 2 ( 2020-04-01)
    Details
    In: Journal of Limnology, PAGEPress Publications, Vol. 79, No. 2 ( 2020-04-01)
    Abstract: Autochthonous calcite precipitation is an important process for C-fixation in hard-water lakes, which is mainly induced by the photosynthesis of planktonic microorganisms. Among these, the widespread calcifying green alga Phacotus lenticularis (Ehrenberg) Diesing contributes to biogenic calcite precipitation in temperate regions. Its role in carbonate precipitation needs to be investigated, because there are no studies dedicated to the quantitative contribution of Phacotus shells to long term carbonate sequestration in hard-water lake sediments. In order to fill this gap, the Phacotus shell content in the sediments of four German hard-water lakes was determined and compared to the fraction of Phacotus shells in the total suspended autochthonous calcite of the euphotic zone.It was found that the Phacotus shells contributed at least 10% to the autochthonous carbonate precipitation in the upper water column in three investigated lakes. During a Phacotus mass occurrence with a cell density of 1.8 × 106 Ind L-1 in Lake Hopfensee, even 59% of the 3.6 mg L-1 total carbonate concentration consisted of Phacotus shells. In contrast to this high amount, the topmost basinal sediment contained a Phacotus shell content between 80 and 36,252 individuals per mg dry sediment, representing only 0.02% to 2.28% of the total carbonate sediment content. In a gravity core from Lake Grosser Ostersee, dating back ~150 years, the Phacotus shell content was continuously below 0.24% whereas the shell diameters remained equal to those of living individuals found in the water column proving that Phacotus shells are capable to persist in the sediment after deposition.A main reason for the large discrepancy between Phacotus shell abundance in the euphotic zone and in sediment was found to be the gross authigenic carbonate precipitation, which dilutes the sedimenting Phacotus shells that accumulate exclusively during short and intensive population peaks in summer. Additionally, dissolution of the carbonate shells during sedimentation was proven to be a relevant factor in Lake Igelsbachsee by means of reducing the number of Phacotus shells reaching the lake bottom. These facts explain that short-term high Phacotus carbonate contents of the total suspended carbonate in the water column do not mirror the contribution of Phacotus shells in the sedimentary record.
    Type of Medium: Online Resource
    ISSN: 1723-8633 , 1129-5767
    URL: Article
    DOI: 10.4081/jlimnol.2020.1945
    Language: Unknown
    Publisher: PAGEPress Publications
    Publication Date: 2020
    detail.hit.zdb_id: 2034229-9
    SSG: 12
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
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