[show abstract][hide abstract] ABSTRACT: This paper presents an illustrated guide to the identification of non-pollen palynomorphs (NPPs) preserved in lake-sediment archives from equatorial East Africa. Modern NPPs were recovered from recently deposited surface sediment in 20 small crater lakes in western Uganda, located along environmental gradients of vegetation (moist evergreen and semi-deciduous forest, wooded and open grass savannah), land use (pastoralism, crop agriculture, plantations) and lake characteristics (basin morphometry, water chemistry and aquatic production). We analyzed 9700 NPP specimens, which could be assigned to 265 distinct morphotypes, of which 239 belong to six major taxonomic groups: spores and other remains of fungi (198 morphotypes), spores of ferns and mosses (19 morphotypes), microscopic zoological remains (14 morphotypes), colonies, coenobia or zygo-/aplanospores produced by filamentous algae (7 morphotypes) and microscopic aquatic plant remains (1 morphotype). The remaining 26 morphotypes could not be assigned to a specific taxonomic category. Using primary taxonomic and molecular phylogenetic literature, 73 (28%) of the recovered morphotypes could be identified at the species, genus or family level, thereby conferring ecological indicator value to them. This study may facilitate the use of fossil NPPs to help reconstruct past climatic and anthropogenic impacts on African ecosystems, as already broadly established in other study regions outside Africa.Research Highlights► Illustrated guide of 187 non-pollen palynomorphs from East African lake sediments. ► 28 % of the recovered 265 morphotypes are identified and ecologically classified. ► NPPs may shed light on past climatic and human impacts on African ecosystems.
Review of Palaeobotany and Palynology 01/2011; 164:143-173. · 1.93 Impact Factor
[show abstract][hide abstract] ABSTRACT: Background and aims - With a depth of at least 220 m, Lake Kyaninga is the deepest known maar crater lake in western Uganda. We studied its limnology and phytoplankton community to determine how the frequency and depth of water-column mixing influences nutrient cycling and seasonality in this aquatic ecosystem.Methods - Water-column temperature was measured continuously during a full annual cycle between August 2007 and August 2008. Other physical and chemical variables as well as diatom and other phytoplankton communities were investigated on three occasions, namely during the dry season in August of 2007 and 2008, and during the main wet season in April 2009.Key results and conclusions - The water column of Lake Kyaninga is permanently stratified (meromictic) below ∼ 100 m depth. Above this depth, mixing frequency varies from daily (down to 8-12 m depth) over at least once per year (down to 39-47 m depth), to once in several years or decades (between 39-47 and ∼ 100 m depth). Nutrient and chlorophyll concentrations as well as phytoplankton data classify the lake as low in aquatic productivity (oligotrophic). Its pelagic, open-water phytoplankton community is dominated by Cyanobacteria (blue-green algae) and Chlorophyta (green algae). Bacillariophyta (diatoms) contribute only a minor part of total phytoplankton biomass in both wet and dry seasons, and are characterized by an assemblage of small Nitzschia species. Epiphytic and epipelic diatoms are relatively few, because steep rocky crater slopes limit the littoral zone even though water-column transparency is high. The composition of recently deposited diatom assemblages preserved in offshore surface sediments gives a good, annually integrated representation of the present-day pelagic diatom community. The documented species richness of the diatom flora of Lake Kyaninga is moderate with about 150 taxa. Only ∼ 17% of these are biogeographically restricted to tropical Africa; and most of these belong to the genus Nitzschia.
Plant Ecology and Evolution 10/2010; 143(3):365-377. · 1.19 Impact Factor
[show abstract][hide abstract] ABSTRACT: Type microscope slides and material from Ghana from which Foged described nine new Surirella taxa in the 1960's were reinvestigated. Although these taxa have not been reported in the literature afterwards, the results of our study confirm the identity of six species: Surirella agonaensis, S. bonsaensis, S. esamangensis, S. nagbogensis, S. sorriensis and S. takoradiensis. They constitute an important element of the endemic diatom flora of West Africa. The study of Surirella takoradiensis var. suhinensis resulted in its proposed synonymy with the nominate variety. Surirella delicatissima var. ghanaensis is transferred to the genus Stenopterobia: Stenopterobia delicatissima var. ghanaensis (Foged) Cocquyt & Kusber comb. nov. Valves resembling Foged's drawing of Surirella dodowaensis could not be detected on the holotype slide; however, two observed frustules in girdle view are in agreement with the description of this taxon.The report of Surirella ventricosa, a diatom described from Sulawesi, in samples from Ghana could not to be justified. Valves similar in shape to S. ventricosa fall within the variability of the closely related S. nagbogensis, described from Ghana.
Nova Hedwigia 07/2010; 91(1-2):111-136. · 0.81 Impact Factor
[show abstract][hide abstract] ABSTRACT: The population of an unknown naviculoid diatom from Lake Vrana in Croatia was identified as Navicula hedinii, a species described in 1922 from a small lake in eastern Turkestan (China). This species has some similarities with Navicula pseudocrassirostris, a marine species found in European coastal waters. Based on the ultrastructure of the two species, they can no longer be included within the taxonomical concept of Navicula sensu stricto. Following a comparative morphological analysis of both species with genera bearing similar characters (Adlafia, Veigaludwigia, Kobayasiella, Cavinula, Stenoneis, Climaconeis, Berkeleya, Sellaphora, Cosmioneis), a new genus, Envekadea is proposed for the two species. The new genus is characterized by a sigmoid raphe course with golfclub-like terminal fissures deflected in opposite directions, the areolae covered by external porous hymenes and the presence of one chloroplast, H-shaped in valve view.
[show abstract][hide abstract] ABSTRACT: A nearshore core (LT03-05) from the north basin of Lake Tanganyika provides diatom, pollen, and sedimentary time series covering the last ca. 3800 yr at 15–36 yr resolution. A chronology supported by 21 AMS dates on terrestrial and lacustrine materials allows us to account for ancient carbon effects on 14C ages and to propose refinements of the region's climatic history. Conditions drier than those of today were followed after ca. 3.30 ka by an overall wetting trend. Several century-scale climate variations were superimposed upon that trend, with exceptionally rainy conditions occurring 1.70–1.40 ka, 1.15–0.90 ka, 0.70–0.55 ka, and 0.35–0.20 ka. Around 0.55–0.35 ka, during the Spörer sunspot minimum, drier conditions developed in the northern Tanganyika basin while more humid conditions were registered at Lakes Victoria and Naivasha. This indicates significant variability in the nature and distribution of near-equatorial rainfall anomalies during much of the Little Ice Age.
Quaternary Research 01/2009; 72(1):47-56. · 2.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: During a preliminary survey of the diatoms from the Peruvian hot spring of La Calera (Colca Canyon, Peru), several new species were found: Navicula cadeei sp. nov., Ulnaria colcae sp. nov., Cymbella comperei sp. nov. and Denticula thermaloides sp. nov. Based on detailed light and scanning electron microscopic analysis, it is clear that these four species can distinctly be separated from other similar taxa. The paper presents morphologic details for the four new species and discusses their taxonomic position and characteristic features.
Diatom Research - DIATOM RES. 01/2009; 24(1):209-223.
[show abstract][hide abstract] ABSTRACT: Summary1. In order to evaluate limitation of different phytoplankton groups by inorganic nutrients, multiple nutrient enrichment bioassays using the addition of iron (Fe) and the combined addition of nitrogen and phosphorus (NP) were carried out in the north and the south of Lake Tanganyika during the rainy and dry seasons in 2003 and 2004.2. Nutrient additions resulted in an increase in phytoplankton growth rate relative to control treatments in all experiments. HPLC pigment data and epifluorescence microscopy counts indicated differential stimulation of the dominant phytoplankton groups. Iron additions mainly stimulated prokaryotic picophytoplankton, while enrichments with nitrogen and phosphorus stimulated green algae and in some cases diatoms. Extended incubation (3 days) indicated co-limitation of Fe and NP, in particular for picocyanobacteria.
[show abstract][hide abstract] ABSTRACT: Surirella bifrons var. intermedia O.Müll. and Surirella fuellebornii O.Müll., including its infraspecific taxa, were re-evaluated using historical East African material collected in the early 20th century from which Otto Müller described more than 100 new diatom taxa. In addition, material from the Hustedt Diatom Collection together with material collected during the past decades in the region of the African Great Lakes was studied. The investigation of the original material of Surirella bifrons Ehrenb. in the Ehrenberg Collection allowed to elevate Surirella bifrons var.intermedia to species rank: Surirella kusberi nom. nov. The variation observed in the material studied supported the abandonment of taxonomic recognition of Surirella fuellebornii f. subconstricta O.Müll. and var. constricta O.Müll. On the other hand, var. tumida Hustedt and var.elliptica O.Müll. are here elevated to species rank: Surirella crawfordii nom. nov. and Surirella friedelhinziae nom. nov. respectively. Finally, Surirella fuellebornii var.worthingtonii H.Bachm. was found to belong within the variability of Surirella malombae O.Müll.
Systematics and Geography of Plants 11/2007; 77(2):213-228.
[show abstract][hide abstract] ABSTRACT: This study aims to evaluate the seasonal and interannual variability in the importance of the microbial food web in Lake Tanganyika. Phytoplankton, bacteria and protozoa (heterotrophic nanoflagellates and ciliates) were monitored at two contrasting pelagic sites (Kigoma and Mpulungu) during 3 consecutive years. In addition, spatial variation was studied along 3 north-south transects during contrasting seasons. The study period covered a wide range of limnological conditions, with mixing depth ranging from 13 to >100 m and euphotic depth from 14 to 65 m. The consistently high bacterial biomass (up to 62 μg C l−1 ) and the high contribution of small phytoplankton (< 5 μm) to the total phytoplankton biomass (on average 50 % in Kigoma and 84 % in Mpulungu) point to an important role of the microbial food web in the lake throughout the year. Total phytoplankton biomass increased during periods of low water column stability, with an increased biomass of small eukaryotic phytoplankton (2 to 5 μm) at both stations, together with autotrophic prokaryotic picoplankton at the southern station Mpulungu and diatoms at the northern station Kigoma. Heterotrophic bacteria, heterotrophic nanoflagellates (0.06 to 11.01 μg C l−1 ) and ciliates (up to 8.16 μg C l−1 ) did not show this seasonality. The main seasonal and spatial variability in the importance of the microbial food web seems therefore primarily linked to the contribution of small phytoplankton, which may be better adapted to lower average light intensities and higher N:P ratios during periods of deep mixing.
Fundamental and Applied Limnology / Archiv für Hydrobiologie 08/2007; 170(1):49-63. · 1.19 Impact Factor
[show abstract][hide abstract] ABSTRACT: Three Surirella taxa described by O.Müller from material collected at the beginning of the 20 th century in Lakes Malawi and Malombe were re-evaluated, and lectotypes are assigned from the original material. One infraspecific taxon, S. nyassae var. sagitta, was synonymized with the nominate variety of S. nyassae and one forma, S. malombae f. acuta, was synonymized with S. malombae. As S. malombae is very rare in the original material from Lake Malombe, an epitype was also assigned from material collected at the end of the 19th century in Lake Victoria. Light and scanning electron microscopic information is given for these two taxa; their distribution in Africa and their habitat preference is summarized from the literature. A third, closely related taxon which was regularly observed in Lake Tanganyika is here described as Surirella chepurnovii sp. nov.
Nova Hedwigia 04/2007; 84(3-4):529-548. · 0.81 Impact Factor
[show abstract][hide abstract] ABSTRACT: Otto Müller's published data and pictures of Navicula elkab were re-evaluated and compared with literature data and a Holocene sediment core material from Ounianga (Chad, Africa). A valid name under Craticula is provided and a lectotype and an epitype are selected. An unusual siliceous covering over the valves is discussed.
Diatom Research 01/2007; 22(1):117-126. · 0.75 Impact Factor
[show abstract][hide abstract] ABSTRACT: The investigation of 30 fossil diatom samples found in a 500-year sediment record from Hausburg Tarn, a glacial lake located in the Alpine zone of Mount Kenya, revealed a diatom diversity of 57 specific and infraspecific taxa. Of the eight taxa (14% of total species diversity) with a distribution restricted to the African continent, two species (3.5%) are unique to Mount Kenya. These afro-alpine diatoms are: Pinnularia coei and Surirella coei. An earlier study on other alpine lakes of Mount Kenya, undertaken in the 1960's, reported two more endemic taxa, Navicula coei and N. kenyae, which were not observed in the Hausburg Tarn samples. A number of taxa could not be attributed to known diatom species and were referred to with the qualification cf, e.g. Navicula cf. brevissima, N. cf. pseudoventralis. Some of these are probably new to science, but a more thorough investigation will be needed to properly assess morphological variability within the species. The presence of four and possibly more endemic taxa on Mt. Kenya makes its diatom flora unique.Although the most abundant taxa in Hausburg Tarn, Achnanthidium minutissimum and A. affine, and the major part of other recovered taxa have a cosmopolitan or palaeoarctic distribution, the recovered diatom flora has a distinct alpine and boreal character.Besides a brief description, each taxon is depicted on a LM photograph. For a number of taxa SEM images are presented in addition. A description of the SEM features of the external and/or internal valve is also given for one of the endemic diatoms, Pinnularia coei, and for Achnanthidium kenyae, an Afroalpine taxon also reported from the Ruwenzori Mountains. Based on these observations a new combination was made for the latter: Achnanthidium kenyae (Cholnoky) Cocquyt comb nov.; basionym: Achnanthes kenyae Cholnoky.
Diatom Research 01/2007; 22(2):255-285. · 0.75 Impact Factor
[show abstract][hide abstract] ABSTRACT: Representatives of the Trebouxiophyceae genus Eremosphaera (with the exception of E. viridis) show great variation in their morphology, and some of the described species, varieties and forms are still of uncertain taxonomic position. Recent material from the phytoplankton of the large, deep, alkaline, ancient, tropical Lake Tanganyika was compared with the formerly described taxa and was found to be peculiar by the ellipsoidal cells with lamellate cell walls, commonly equipped with polar nodules consisting of two parts, by the numerous (30-60) parietal wedge-shaped chloroplasts densely pressed to each other and arranged in (2)-3-4 circles (each chloroplast bearing 1-2 distinct pyrenoids covered by bipartite starch sheath), as well by its ecological requirements. Therefore, a new species, E. tanganyikae sp. nov., is erected.
Belgian Journal of Botany 05/2006; 139(1):3-13. · 0.63 Impact Factor
[show abstract][hide abstract] ABSTRACT: La recherche a porté sur les propriétés physique et chimique et la composition algale de 13 sources thermales situées au Burundi, en Afrique centrale, entre les altitudes 773 et 2550 m. Les eaux de ces sources sont principalement de type bicarbonaté, certaines sources étant très riches en chlorures ; leur température varie de 29°C à 57.5°C. Au total, 92 taxons appartenant aux groupes des Cyanobacteria, Chlorophyta et Bacillariophyta ont été observés dans 13 échantillons, 80 taxons appartenant à ce dernier groupe. Les espèces des sources thermales ne diffèrent pas de celles des autres eaux du Burundi déjà étudiées et peuvent être considérées comme des espèces thermo-tolérantes. Une analyse canonique des correspondances appliquée aux espèces de diatomées ainsi qu'aux variables physiques et chimiques a permis de repérer les taxons associés aux sources thermales faiblement minéralisées et ceux associés aux sources fortement minéralisées et indique que leur séparation est principalement due à la conductivité, aux bicarbonates et aux chlorures.
Belgian Journal of Botany 01/2006; 138(2):152-164. · 0.63 Impact Factor
[show abstract][hide abstract] ABSTRACT: Diatoms are frequently used as indicators of eutrophication in temperate systems, but little is known about their application
to impacted African tropical systems. Five streams located within Gombe Stream National Park and five streams supporting human
settlements draining into Lake Tanganyika, East Africa, were investigated for species composition, richness and diversity
of epilithic algae. In addition, a trophic diatom index (TDI) developed for monitoring European rivers was applied to these
tropical systems. 54 specific and infraspecific diatom taxa representing 20 genera were identified for all sites with Achnanthes s.l., Gomphonema and Navicula s.l. being the most common genera. Species richness varied between 10 and 21 in disturbed streams and 13 and 19 in undisturbed
streams. Nutrients were significantly enriched in streams draining the deforested watersheds but indices of diversity and
evenness (Shannon H, J and Simpson–Yule D, E) did not show any significant differences between streams in forested and deforested
watersheds. Significant differences were observed between pooled data for the TDI between forested and deforested watersheds.
Analysis of percent pollution tolerant diatom taxa indicates that organic pollution of streams in deforested watersheds may
be contributing to eutrophication. This study shows that African diatoms, cosmopolitan or resembling well-known North American
and European taxa, allows for trophic indices tailored to the autecological preferences of species to be applied to new regions,
although intensive studies on these African taxa will lead to more accurate results. Measures of species-richness and diversity,
historically used to describe the state of an ecosystem, may not be suitable to evaluate streams which are not grossly polluted.
[show abstract][hide abstract] ABSTRACT: East African original material from which Otto Müller had described more than 100 new diatom taxa at the beginning of the 20th century was re-evaluated. In this paper nine of his names of Surirella taxa have been assigned lectotypes. For three taxa specimens were chosen from the original samples, for six taxa Müller's drawings have to serve as type, for three of these also an epitype is designated. Three taxa are elevated to species rank (S. tumida, S. likomensis, S. africani-orientalis), for the latter two species substitute names are validated. One taxon is synonymized. The distribution of the eight accepted taxa in East Africa is summarized from literature. Although rare, all but one have been recorded after Müller's first description. In addition to the above mentioned, these are S. brevicostata, S. linearis var. elliptica, S. margaritacea, S. turbo; only S. panganensis seems to be so rare that it has never been recorded since its first description.
[show abstract][hide abstract] ABSTRACT: Vertical and latitudinal differences in bacterial community composition (BCC) in Lake Tanganyika were studied during the dry season of 2002 by means of denaturing gradient gel electrophoresis analysis of PCR-amplified 16S RNA fragments. Dominant bands were sequenced and identified as members of the Cyanobacteria, Actinobacteria, Nitrospirae, green nonsulfur bacteria, and Firmicutes divisions and the Gamma- and Deltaproteobacteria subdivisions. The BCC in the lake displayed both vertical and latitudinal variation. Vertical changes in BCC were related to the thermal water column stratification, which influences oxygen and nutrient concentrations. Latitudinal variation was related to upwelling of deep water and increased primary production in the south of the lake. The number of bands per sample increased with bacterial production in the epilimnion of the lake, suggesting a positive diversity-productivity relationship.
Applied and Environmental Microbiology 10/2005; 71(9):5029-37. · 3.68 Impact Factor