Observations on the limnology and phytoplankton community of crater Lake Kyaninga (Uganda), with special attention to its diatom flora

peer reviewedBackground 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. © 2010 National Botanic Garden of Belgium and Royal Botanical Society of Belgium

Reconstructing disappeared landscapes of wet areas. Problems and new possibilities applied to a test area in western Sealands Flanders in the Flemish coastal plain

Coastal landscapes show very specific characteristics since the sea and the water of the tidal channels mainly influenced their origins. This paper presents some preliminary results of an interdisciplinary project that focuses on the reconstruction of medieval landscapes in the coastal area of medieval Flander

Diversity and ecology of tropical African fungal spores from a 25,000-year palaeoenvironmental record in southeastern Kenya

Fossil fungal spores and other non-pollen palynomorphs (NPPs) are powerful environmental proxies in European palaeoecological and archaeological contexts. However, their application on other continents, and particularly in the tropics, is hampered by uncertain equivalence with morphologically similar taxa in Europe, and incomplete knowledge of their ecology in the new local contexts. Here we use fossil NPP assemblages in a 25,000-year sediment record from Lake Challa, a steep-sided crater lake near Mt. Kilimanjaro in southeasternKenya, to assess NPP diversity in atropical-African context and the equivalence of African taxa with their European counterparts. We recovered a total of 65 well-defined NPP types, of which 61 are fungal spores, and 42 could be linked to known taxa. We provide diagnoses and illustrations of 61 recovered taxa, 58 of which have not been documented before. Using the Challa pollen record of past regional vegetation dynamics and two independent proxies of past temperature and rainfall, we also assessed the association of individual fungal taxa with particular species and biomes of tropical-African vegetation, and with the history of regional climate change. We often found strong correspondence between the stratigraphic distribution of individual fungal spore taxa and the occurrence of specific vegetation types. Changing climate conditions appear to have had a strong impact on the ability of fungi to play a role in the decomposition of dead plants. For fungal spore assemblages, the most prominent change in regional palaeoenvironments over the past 25,000 years occurred at the start of the wet early Holocene, following Younger Dryas drought. Epicoccum purpurascens is common in the Glacial and Late-Glacial parts of the sequence, but shows a strong decline during the early Holocene. Coniochaeta cf. ligniaria occurs throughout the record but shows dramatic fluctuations that appear to relate to major changes in humidity. Correlation between fungal abundance and humidity is also observed in taxa for which the Challa region provided suitable habitat from ca. 16,500 cal. yr BP (e.g., Curvularia) or from the Late-Glacial to Holocene transition (e.g., Tetraploa aristata, Dictyoarthrinium cf. sacchari, cf. Byssothecium, types HdV-1032 and HdV-1033, cf. Alternaria, cf. Brachysporium, cf. Helminthosporium, Spegazzinia tessarthra and cf. Lasiodiplodia theobromae). Many of these taxa did not occur, or were rare, during both wet and dry phases of the Glacial period, suggesting an additional temperature effect on their occurrence in tropical African environments. A possibly dominant role of temperature is revealed in the stratigraphic distribution of Acrodictys, which appears at the onset of deglacial climate warming ca. 17,500 cal. yr BP and remains common throughout both wet and dry phases of the Holocene. Spores of the dung-inhabiting fungus Sporormiella occur throughout the 25,000-year record without notable fluctuations, suggesting little changes in the overall population density of large herbivores in the region