Inhibition of phytoplankton photosynthesis by solar ultraviolet radiation: studies in Lake Titicaca, Bolivia

1. Lake Titicaca is a large, high altitude (3810 m a.s.l.) tropical lake (16°S, 68°W) that lies on the border of Bolivia and Perú, receiving high fluxes of ultraviolet radiation (UVR) throughout the year. Our studies were conducted during September of 1997 with the main objective of studying the impact of solar UVR upon phytoplankton photosynthesis.
2. Water samples were taken daily and incubated in situ (down to 14 m depth) under three radiation treatments to study the relative responses to PAR (Photosynthetic Available Radiation, 400–700 nm), UV-A (320–400 nm), and UV-B (280–320 nm) radiation.
3. Photosynthetic inhibition by UVR in surface waters was about 80%, with UV-A accounting for 60% and UV-B for 20%; the inhibition by high levels of PAR was less than 20%. The inhibition due to UVR decreased with depth so that there were no significant differences between treatments at 8.5 m depth.
4. The amount of inhibition per unit energy received by phytoplankton indicates that even though there was a significant inhibition of photosynthesis due to UVR, species in Lake Titicaca seem to be better adapted than species in high latitude environments.
5. The cellular concentration of UV-absorbing compounds, a possible mechanism of photoadaptation, was low in phytoplanktonic species. However, they were abundant in zooplankton, suggesting a high rate of bioaccumulation through the diet.     

Late Quaternary clay mineral record in Central Lake Baikal (Academician Ridge, Siberia)

We investigated the mineralogical composition of two cores recovered on the Academician Ridge (Central Lake Baikal, Siberia). Sedimentological features show that the cores are unaffected by turbidity currents. However, hemipelagic deposition is not continuous, but intermittently disturbed by syn- or post-sediment reworking (e.g., bioturbation, slumps, faulting). Such modes of deposition are consistent with the complex uplift history of the ridge. Bulk mineralogy suggests that terrigenous sediment supplies are constant through glacial/interglacial stages, and diluted by diatom-rich intervals related to warmer interglacial stages. The core stratigraphy is based on the correlation of the diatom zonation and opal abundance with the marine oxygen isotope reference curve SPECMAP. The ∼8-m cores partly recover the last four interglacial/glacial cycles, i.e., since oxygen isotope stage 8. We test the use of clay minerals as a proxy for paleoclimatic reconstruction. The clays are more weathered during the diatom-rich intervals in agreement with warmer climate conditions. However, the mean clay composition does not change significantly through glacial/interglacial stages. This observation implies that, in the Academician Ridge sediments, a simple smectite/illite ratio (S/I) does not alone provide a reliable indicator of climatic variation. It reflects the complex clay assemblages, especially the smectite group, delivered to Central Lake Baikal. Smectites include primarily illite-smectite mixed layers, made of a mixture of montmorillonite and beidellite. According to their behavior after cation saturation, the illite-smectite mixed layers are primarily transformed smectites, with some neoformed smectites intermittently observed. In addition, Al-smectites occur in minor proportions. We conclude that the S/I ratio has a climatic significance only if it evolves in parallel with the weathering stage of the clays and is confirmed by a change in the composition of the smectites.     

Microbially influenced lacustrine carbonates: A comparison of Late Quaternary Lahontan tufa and modern thrombolite from Fayetteville Green Lake,NY

Carbonate microbialites in lakes can serve as valuable indicators of past environments, so long as the biogenicity and depositional setting of the microbialite can be accurately determined. Late Pleistocene to Early Holocene frondose draping tufa deposits from Winnemucca Dry Lake (Nevada, USA), a subbasin of pluvial Lake Lahontan, were examined in outcrop, petrographically, and geochemically to determine whether microbially induced precipitation is a dominant control on deposition. These observations were compared to modern, actively accumulating microbialites from Fayetteville Green Lake (New York, USA) using similar methods. In addition, preserved microbial DNA was extracted from the Lahontan tufa and sequenced to provide a more complete picture of the microbial communities. Tufas are texturally and geochemically similar to modern thrombolitic microbialites from Fayetteville Green Lake, and the stable isotopic composition of organic C, N, inorganic C, and O supports deposition associated with a lacustrine microbial mat environment dominated by photosynthetic processes. DNA extraction and sequencing indicate that photosynthetic microbial builders were present during tufa deposition, primarily Chloroflexi and Proteobacteria with minor abundances of Cyanobacteria and Acidobacteria. Based on the sequencing results, the depositional environment of the tufas can be constrained to the photic zone of the lake, contrasting with some previous interpretations that put tufa formation in deeper waters. Additionally, the presence of a number of mesothermophilic phyla, including Deinococcus–Thermus, indicates that thermal groundwater may have played a role in tufa deposition at sites not previously associated with groundwater influx. The interpretation of frondose tufas as microbially influenced deposits provides new context to interpretations of lake level and past environments in the Lahontan lake basins.     

Distribution and faunal associations of benthic invertebrates at Lake Turkana,Kenya

The benthic environment and fauna of Lake Turkana were studied during 1978–1979 to determine distribution patterns and associations of benthic invertebrates. Lake Turkana is a large, closed-basin, alkaline lake, located in northern Kenya.Detailed environmental information is currently only available for substrate variations throughout Lake Turkana. Water chemistry and other data are currently inadequate to evaluate their effects on the distribution of Lake Turkana benthic invertebrates. Three weak faunal-substrate associations were discovered at Turkana. A littoral, soft bottom association (large standing crop) is dominated by the corixid Micronecta sp. and the ostracod Hemicypris kliei. A littoral, rocky bottom association, also with a large standing crop, is dominated by various gastropods and insects. A profundal, muddy bottom association, with a very small standing crop, is dominated by the ostracods Hemicypris intermedia and Sclerocypris cf. clavularis and several gastropod and chironomid species.     

Late Quaternary diatoms in the sediments of Przedni Staw Lake (Polish Tatra Mountains)

The paper presents a diatom succession in the Late Glacial and Holocene sediments of the Przedni Staw lake in the Pie Stawów Polskich Valley High Tatra Mts. Ten diatom phases are distinguished and presented against a pollen diagram from the analyzed core showing continuous sedimentation from the Oldest Dryas to the Subatlantic period. The diatom flora in the Late Glacial sediments is predominantly littoral — Fragilaria, Navicula, Nitzschia, Diploneis, Pinnularia and Amphora species. The Holocene sediments enclose more abundant planktonic species such as Cyclotella quadriiuncta, Asterionella formosa and Melosira distans.     

The microanatomy of Phaeaster pascheri Scherffel (Chrysophyceae)

The morphology of this freshwater phytoflagellate (Chrysophyceae or Chrysomonadida) has been studied in detail by electron microscopy. It is unusually complex for a member of its class, having a depressed reniform shape and a second flagellum modified as a photoreceptor, and also possessing rhizopodia, scales and a stellate chloroplast with a central pyrenoid. These structures are compared with similar ones in other members of the class and possible relationships are briefly discussed.     

The evolutionary history of Late Permian Darwinulocopina Sohn, 1988 (Ostracoda) from the Russian Plate

Evolutionary trends in Late Permian Darwinulocopina are summarised with reference to extensive collections from eastern European Russia, from the White Sea in the North to the Cis-Caspian in the South. They inhabited large, shallow lakes in which the variety of habitats was favourable for high ostracod diversity. Three superfamilies are represented: the Darwinuloidea preferred lakes with terrigenous sedimentation and insignificant bicarbonate, the Suchonelloidea inhabited lakes with increased bicarbonate and could also live in low-sulphate waters, and the Darwinuloidoidea inhabited high-bicarbonate water bodies and could also survive in low-magnesium waters. Different evolutionary trends account for the different ages of the crucial stages of development of each superfamily: the beginning of the mid-Tatarian for the Darwinuloidea, the late Tatarian for the Suchonelloidea and Darwinuloidoidea.     

Analysis of trophic relationships in two shallow equatorial lakes Lake Naivasha (Kenya) and Lake Ihema (Rwanda) using a multispecifies trophic model

A multispecifies trophic model called ECOPATH II, which can be used to describe the trophic relationships in aquatic ecosystems on a quantitative basis, is briefly presented. When properly used, it can help to explain the trophic relationships in ecosystems and possible evolution of fishstocks after modifications of the environment (e.g. eutrophication, introduction of a new population and/or a significant increase of the fishing effort), and to compare the trophic structure of several ecosystems. Examples are provided on two shallow lakes: Lake Ihema and Lake Naivasha. They are compared with Lake George which was previously documented.     

Oxygen concentration profiles in sediments of two ancient lakes: Lake Baikal (Siberia,Russia) and Lake Malawi (East Africa)

Oxygen concentration profiles have been measured, by means of with microelectrodes in sediments of Lake Baikal and Lake Malawi, along transects allowing to give a survey of two major ancient Rift lakes: Lake Baikal (Eastern Siberia) and Lake Malawi (East Africa), along depth transects in the constitutive basins of the lakes and/or of relevant depths with regard to oxygen (including including the deepest point, 1680 m, in Lake Baikal). Sediment oxygen penetration depths (SOPs) display very different patterns, depending on the lake in the two lakes. In Lake Baikal, SOPs are variable, show no significant relationship with bathymetric depth and are surprisingly deep on Akademichesky ridge (> 50.0 mm), emphasizing the distinctive feature of this region in the lake. While the Selenga river is an important source of eutrophication, the similarity of SOP-values in the Selenga shallow with those of most other sites suggests either a dilution of organic material by allochthonous matter, or a strong south-to-north transport of particles. In Lake Malawi, available oxygen is restricted to a maximum of three millimetres of the sediment, and there is a negative relationship with bathymetric depth, as a result of a steady decline of oxygen concentration with depth through the water column. Amongst the few parameters known to affect SOPs, the oxygen consumption by the sediment seems the most significant in both lakes. SOP-values furthermore confirm differences in the trophic status of Baikal and Malawi, respectively. The importance of oxygen as a factor likely to create ecological segregation for benthic organisms is discussed. Lake Malawi offers possibilities of bathymetric segregation but no vertical segregation in the sediment. In contrast, no bathymetric segregation related to oxygen is possible in Lake Baikal, but vertical segregation in the sediment is very likely. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biota of Lake Cheder (Tuva,Russia)

The algal flora and invertebrate fauna of Lake Cheder, located in the Central Tuva Basin, Russia, have been studied from collections made in August 1999. Eighteen taxa belonging to diatoms, blue–green and green algae, and seven species of fauna (two crustaceans and five insects) were present.     

Waxing and waning of forests: Late Quaternary biogeography of southeast Africa

African ecosystems are at great risk. Despite their ecological and economic importance, long‐standing ideas about African forest ecology and biogeography, such as the timing of changes in forest extent and the importance of disturbance, have been unable to be tested due to a lack of sufficiently long records. Here, we present the longest continuous terrestrial record of late Quaternary vegetation from southern Africa collected to date from a drill core from Lake Malawi covering the last ~600,000 years. Pollen analysis permits us to investigate changes in vegetation structure and composition over multiple climatic transitions. We observe nine phases of forest expansion and collapse related to regional hydroclimate change. The development of desert, steppe and grassland vegetation during arid periods is likely dynamically linked to thresholds in regional hydrology associated with lake level and moisture recycling. Species composition of these dryland ecosystems varied greatly and is unlike the vegetation found at Malawi today, with assemblages suggesting strong Somali‐Masai affinities. Furthermore, nearly all semiarid assemblages contain low forest taxa abundances, suggesting that moist lowland gallery forests formed refugia along waterways during arid times. When the region was wet, forests were species‐rich and very high afromontane tree abundances suggest frequent widespread lowland colonization by modern high elevation trees. Furthermore, species composition varied little amongst forest phases until ~80 ka when disturbance tolerant tree taxa characteristic of the modern vegetation increased in abundance. The waxing and waning of forests has important implications for understanding the processes that control modern tropical vegetation biogeography as well as the environments of early humans across Africa. Finally, this work highlights the resilience of montane forests during previous warm intervals, which is relevant for future climate change; however, we point to a fundamental shift in disturbance regimes which are crucial for the structure and composition of modern East African landscapes.     

Culturable bacteriorhodopsin-producing haloarchaea of Tuz Lake (Turkey)

Abstract

Lake Tuz, the largest hypersaline lake in Turkey, has a great variety of microbial communities that adapted to its extreme environment and produce many industrially important compounds such as photosensitive bacteriorhodopsins. So far, the information about the bacteriorhodopsin-producing haloarchaea species of the lake is still limited. In the present study, archaeal bacteriorhodopsin producers were isolated from three locations of the lake. Their bacteriorhodopsin-producing capability was validated by the purification and SDS-PAGE analysis of the delipidated bacteriorhodopsin molecule. The active isolates were identified by the sequencing of partial 16S rDNA gene regions. According to the results, 11 bacteriorhodopsin-producing isolates grouped in Halobacterium salinarum (4), Halobacterium sp. (3), Haloarcula salaria (2), Haloarcula sp. (1) and Halorubrum sp. (1). Our research demonstrated that Lake Tuz is an important natural source of bacteriorhodopsin-producing haloarchaea and the isolates can be valuable for the related technological applications.     

Biological implications of a suggested Late Pleistocene desiccation of Lake Victoria

If, as recently suggested, Lake Victoria dried up completely in theLate Pleistocene and refilled c 12,400 BP, not only must therate of speciation of its flock of cichlid fishes have been extremelyrapid but, more significantly, so too must the rate of morphologicaldifferentiation. Such desiccation also implies that fishes belongingto seven other families achieved endemic status since the lakerefilled, and in one case became generically distinct, acquiredstriking morphological/physiological adaptations to life in deepwater, and split into two species. Such rapid evolution within thesefamilies appears to have no parallel in Africa. This suggests thatprudence be applied in the interpretation of what appears to beunambiguous evidence, especially as this seems to be at variance withwhat also appears to be convincing geophysical evidence of adifferent kind.     

Late Quaternary vegetation history at Stracciacappa (Rome, central Italy)

The pollen diagram from Stracciacappa (Sabatini volcanic complex, Rome) provides a record of vegetational and climatic change spanning the last 60000 years, which is the time since when volcanic activity in the crater came to an end. The chronological framework of the sediment core is set by five AMS and three conventional radiocarbon dates; the mean sedimentation rate obtained by radiocarbon measurements was used to extrapolate the age of the record beyond the reach of ¹⁴C dating. The sequence from Stracciacappa provides results of fundamental importance for the understanding of the vegetational changes which occurred during the last pleniglacial period in central Italy, and it can be considered as a reference pollen record for the regional biostratigraphic characterization of this period. The site shows a high climatic sensitivity, particularly highlighted by the development of some pleniglacial oscillations with woodland, which interrupted the succession of steppe and grassland vegetational formations typical of the glacial periods. Unfortunately, due to sedimentation problems and alteration of the top level sediments, the Holocene is only recorded in part. Only for one millennium, from ca. 8300 to 7200 uncalb.p., was a real forest expansion characterized by over 90% arboreal pollen found.     

Sex ratio in Mesocyclops leuckarti (Claus) populations in Lake Kinneret (Israel)

Sex ratio (F/M) values of adult Mesocyclops leuckarti (Claus) populations in Lake Kinneret during 1970 and 1974 showed a periodic pattern of winter (January–March) and summer (August–October) female peaks. It is suggested that water temperature governs the appearance of both peaks but through different pathways.Contribution no. 163, Israel Oceanographic & Limnological Research Ltd.     

贵州省红枫湖现生介形类新纪录

本文首次记述了采自我国贵州省红枫湖的现生介形类5属7种,分别为:近锐豆形玻璃介Fabae formiscandona subacuta(Yang,1982)、比利时舍氏玻璃介(相似种)Schellencandona cf.belgica(Klie,1937)、亮球星介Cy-clocyprisserena(Kock,1838)、克氏丽星介Cypria kraepelini(G.W.Müller,1903)、条纹薄壳介(相似种)Dolerocypris cf.fasciata(O.F.Müller,1776)、布氏土星介Ilyocypris bradyi Sars,1890、粗糙土星介I.sale-brosa Stepanaitys,1960。这些属种在红枫湖和贵州省均系首次报道,其中S.cf.belgica在我国是首次发现,文内对F.subacuta活体特征的描述在我国尚属首次。     

Distribution and summer diapause of Canthocamptus staphylinus (Jurine) (Copepoda: Harpacticoida) in Lake Ladoga

The spatial distribution of Canthocamptus staphylinus (Jurine) in Lake Ladoga was examined. C. staphylinus is one of the most numerous species of harpacticoids in the lake. It can dwell in almost all littoral biotopes. In profundal biotopes strongly exposed to anthropogenic influence (pollution and eutrophication) only this species of harpacticoid was found. A peculiarity of C. staphylinus biology is that in summer individuals are in the resting stage as cysts. In summer active individuals were found in littoral habitats at a water temperature of 20 °C, but their number was small in comparison with cold periods of the year. In the littoral zone the relative number of individuals in cysts was clearly related to water temperature. Twelve degrees temperature appears to be critical for development of littoral populations of C. staphylinus.     

Late Oligocene to Early Miocene foraminifers and ostracods from Karben (Wetterau,Hesse State,Germany): stratigraphic occurrence and palaeoecological implications

Foraminiferal and ostracod assemblages from two upper Oligocene to lower Miocene sections located in the Wetterau region (NE Frankfurt a. M.) were analysed. The lithologie units investigated encompass Cyrenenmergel, Glimmersand, Vilbeler Kies, Cerithiensand, Cerithienkalk andCorbicula-Schichten. Hemicyprideis basiliensis, H. helvetica andCypridopsis? cyclocypriformae are characteristic of Cyrenenmergel deposits, representing the last marine influence around the Rupelian/Chattian boundary. The ostracod assemblages from the Cerithiensand are characterized by variousHemicyprideis species, of whichH. rhenana is the most frequent. The microfossil assemblages of the Cerithiensand indicate normal marine conditions for the basal and upper portions of the unit and slightly brackish to normal marine conditions for the middle portion. Very low salinities are indicated for some levels close to the base (around levels of emergence above sealevel) and for the clay layer around sample 30 in the lower part of the Cerithiensand. The Cerithienkalk represents a transitional facies from normal marine to brackish/freshwater conditions as indicated by successive higher contents of stress tolerant foraminifera and freshwater ostracods. TheCorbicula-Schichten are characterized by largeEucypris-moulds and various proportions ofCypridopsis spp. (freshwater indicators). When foraminifera (Bolivina spp.) are present, the fauna indicates slightly higher but still low salinities for a few levels of theCorbicula-Schichten. Oxygenation levels were generally high (presence of large ostracods and epifaunal foraminifera) and vary from suboxic to high oxic. As in the Mainz Basin, the last occurrence ofHemicyprideis rhenana marks the upper boundary of the Cerithienschichten.Protelphidium nonioninoides can be used to identify the Cyrenenmergel when it occurs in high numbers. Cerithiensand-samples show the highest diversities and contain high portions ofUvigerinella michelsi. Overall, highest diversities and normal marine salinities are reached during deposition of the basal and upper parts of the Cerithiensand, which may correspond to global sealevel rises at the end of the Chattian.