123 research outputs found
Short-term variability in the sedimentary BIT index of Lake Challa, East Africa over the past 2200 years : validating the precipitation proxy
typifying four Ehrenberg names and a preliminary checklist of the African taxa
To comply with the new phylogeny within the Surirellales as supported by
molecular and morphological data, re-evaluations and re-combinations of taxa
from and within the genera Surirella, Cymatopleura, and Stenopterobia and with
the re-established genus Iconella are necessary. Since the African diatom
flora is rich with taxa from these genera, especially Iconella, and the
authors have studied these taxa recently, describing also new taxa, a
preliminary checklist of African Iconella and Surirella is here presented. 94
names are contained on this list. 57 taxa have been transferred to Iconella;
55 taxa were formerly ranked within Surirella and two taxa within
Stenopterobia. 10 taxa have stayed within Surirella and six taxa have been
transferred from Cymatopleura to Surirella. 20 Surirella and 1 Stenopterobia
names are listed which are either unrevised or unrevisable since morphological
data is missing. Four names and taxa described by Ehrenberg are here typified.
Two had been transferred to Iconella already: Iconella bifrons (Ehrenb.) Ruck
& Nakov and Iconella splendida (Ehrenb.) Ruck & Nakov. Two are re-transferred
from Cymatopleura to Surirella: Surirella librile (Ehrenb.) Ehrenb. and
Surirella undulata (Ehrenb.) Ehrenb.; both taxa are currently known by their
younger synonyms: Cymatopleura solea (Bréb.) W. Smith and Cymatopleura
elliptica (Bréb. ex Kützing) W. Smith. Lectotypes for Iconella bifrons, I.
splendida, Surirella librile, and S. undulata were designated
Morphology of two Mastogloia species (Bacillariophyta) from Lac de Guiers (Senegal) and comparison with the type material of M. braunii
[EN] Two Mastogloia Thwaites ex W.Sm. taxa were found during a survey of the diatom flora of Lac de Guiers, Senegal. Based on all currently available literature, one taxon could be identified as M. belaensis M.Voigt, a species formerly described from Pakistan. The second species showed some resemblance to M. braunii Grunow. Analysis of the type of M. braunii revealed, however, important morphologic differences, leading to the description of a new species from the Senegal population: M. senegalensis Van de Vijver, Fofana, Sow & Ector sp. nov. The present paper describes this new species and discusses and illustrates the morphology of M. belaensis and the type of M. braunii. All taxa are discussed with morphologically similar taxaSIThe project was financed by the Agence universitaire de la Francophonie (AUF) (project n° D-2092 RR 723
Seasonal variability in the abundance and stable carbon-isotopic composition of lipid biomarkers in suspended particulate matter from a stratified equatorial lake (Lake Chala, Kenya/Tanzania): Implications for the sedimentary record
We studied the distribution and stable carbon-isotopic (δ13C) composition of various lipid biomarkers in suspended particulate matter (SPM) from the water column of Lake Chala, a permanently stratified crater lake in equatorial East Africa, to evaluate their capacity to reflect seasonality in water-column processes and associated changes in the lake's phytoplankton community. This lake has large seasonal variation in water-column dynamics (stratified during wet seasons and mixing during dry seasons) with associated phytoplankton succession. We analyzed lipid biomarkers in SPM collected monthly at 5 depths (0–80 m) from September 2013 to January 2015. Seasonal variation in total phytoplankton biovolume is strongly reflected in the concentration of phytadienes, a derivative of the general photosynthetic pigment chlorophyll. The wax and wane of several specific biomarker lipids between June and December 2014 reflect pronounced phytoplankton succession after deep mixing, starting with a long and sustained chlorophyte bloom (reflected by C23:1, C25:1 and Cn-alkenes, and C21 and C23n-alkanes), followed by a peak in diatoms between July and October (loliolide and isololiolide), and then eustigmatophytes (C30 and C32 1,15 diols) once stratification resumes in October. Peak abundance of the C19:1n-alkene during shallow mixing of the water column in January–February 2014 can be tentatively linked to the seasonal distribution of cyanobacteria. The concentration, seasonal variability, and low δ13C values of the C28 fatty acid in the SPM suggest that this biomarker is produced in the water column of Lake Chala instead of having the typically assumed vascular plant origin. The δ13C signature of particulate carbon and all aquatic biomarkers become increasingly more negative (by up to 16‰) during mixing-induced episodes of high productivity, whereas enrichment would be expected during such blooms. This reversed fractionation may be attributed to chemically enhanced diffusion, which generates depleted HCO3− under high pH (>9) conditions, as occur in the epilimnion of Lake Chala during periods of high productivity. The influence of this process can potentially explain previously observed 13C-depleted carbon signatures in the paleorecord of Lake Chala, and should be considered prior to paleorecord interpretation of organic-matter δ13C values derived (partially) from aquatic organisms in high-pH, i.e. alkaline, lake
Amphora calumeticoides spec. nov (Bacillariophyta), an endemic diatom from Lake Tanganyika
Algologische studie van het Noordelijk bekken van het Tanganyikameer, in het bijzonder de diatomeeën van het litoraal en van oppervlaktesedimenten
Notes on Cymatopleura calcarata Hustedt (Bacillariophyceae), an endemic diatom from Lake Tanganyika.
Seasonal variations of epilithic diatom communities in the northern basin of Lake Tanganyika.
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