Sample records for lake tanganyika vertical

  1. Bacterial Community Composition in Lake Tanganyika: Vertical and Horizontal Heterogeneity

    Microsoft Academic Search

    Aaike De Wever; Koenraad Muylaert; Katleen Van der Gucht; Samuel Pirlot; Christine Cocquyt; Jean-Pierre Descy; Pierre-Denis Plisnier; Wim Vyverman

    2005-01-01

    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

  2. Phytoplankton in Lake Tanganyikavertical and horizontal distribution of in vivo fluorescence

    Microsoft Academic Search

    K. Salonen; J. Sarvala; M. Järvinen; V. Langenberg; M. Nuottajärvi; K. Vuorio; D. B. R. Chitamwebwa

    1999-01-01

    Determinations of chlorophyll a and in vivo fluorescence of photosynthetic pigments were used to study vertical and horizontal distribution of phytoplankton in Lake Tanganyika (East Africa). Blue excited fluorescence (IVFb) was an approximate predictor of chlorophyll a at different depths and locations. Green excited fluorescence (IVFg), which reflects phycoerythrin in cyanobacteria, explained chlorophyll a variation equally well, and in combination

  3. Lake Tanganyika ecosystem management strategies

    Microsoft Academic Search

    Hudson H. Nkotagu

    2008-01-01

    Lake Tanganyika is a large East African rift valley system holding about 1\\/6 of the world's liquid freshwater with about 2000 species of organisms (fauna and flora), of which about 700 are endemic. The lake faces a number of threats including excess sedimentation, overfishing, pollution, habitat destruction, along with climate change. Efforts to better understand these involved an assessment of

  4. Vertical stability and the Brunt-Väisäla frequency of deep natural waters by the example of Lake Baikal, Lake Tanganyika, and the World Ocean

    NASA Astrophysics Data System (ADS)

    Sherstyankin, P. P.; Kuimova, L. N.

    2009-12-01

    Theoretical analysis, calculations, and comparison with the results of observations in Lake Baikal, Lake Tanganyika, and the World Ocean are performed for the vertical stability E and the Brunt-Väisäla frequency N in the form of N 2 with regard to all components (at the constant temperature T and the salinity S, the common adiabatic form at T, S Const). The adiabatic stability E ad and the Väisäla frequency N in the form of N {/ad 2} are always positive; at a change from the inverse to the direct temperature stratification, they have deep minimums reaching 10-16 m-1 and 10-15 s-2 and less; the minimums have the form of a special point, a reversal point of the first kind called a “cusp.” The reality of these reversal points is confirmed by the analysis of the investigation procedure, comparison with the results of previous theoretical (Sherstyankin, et al., 2007), and experimental (observations in Baikal, Shimaraev et al., 1994) works. The features of vertical profiles of E ad , E and N {/ad 2}, N 2, as well as the layers where the Brunt-Väisäla frequency is less than the inertial frequency, are studied. The analysis with regard to all components of the stability E ad and the Brunt-Väisäla frequency N makes a great contribution to understanding of mixing processes in theoretical and experimental investigations; it is valid in all reservoirs of the Earth with inverse and direct temperature stratification, including Lake Baikal, Lake Tanganyika, and the World Ocean.

  5. Ecological Consequences of a Century of Warming in Lake Tanganyika

    Microsoft Academic Search

    Piet Verburg; Robert E. Hecky; Hedy Kling

    2003-01-01

    Deep tropical lakes are excellent climate monitors because annual mixing is shallow and flushing rates are low, allowing heat to accumulate during climatic warming. We describe effects of warming on Lake Tanganyika: A sharpened density gradient has slowed vertical mixing and reduced primary production. Increased warming rates during the coming century may continue to slow mixing and further reduce productivity

  6. Tempo and Mode of Diversification of Lake Tanganyika Cichlid Fishes

    E-print Network

    Cotton, James

    Tempo and Mode of Diversification of Lake Tanganyika Cichlid Fishes Julia J. Day1,2 *, James A/Principal Findings: Here we investigate the cichlid fish radiation of Lake Tanganyika and show that per lineage. The result holds even at peak periods of diversification in Lake Tanganyika, ruling out the age of the lake

  7. Nearshore carbonate deposits in Lake Tanganyika

    Microsoft Academic Search

    Andrew S. Cohen; Catherine Thouin

    1987-01-01

    An exceptionally wide variety of carbonate fades, dominated by high-magnesian calcite, occurs along the littoral and shallow sublittoral zones (<50 m) of Lake Tanganyika in central Africa. These facies include exposed and submerged, calcite-cemented ridges of nearshore terrigenous sand, ooid sand shoals, and lithified oolite ridges, Chara meadows of bioturbated calcareous silts, gastropod shell blankets and related coquinas, and extensive

  8. Fossil and living stromatolites are abundant around the margins of Lake Tanganyika, Af-

    E-print Network

    Awramik, Stanley M.

    ABSTRACT Fossil and living stromatolites are abundant around the margins of Lake Tanganyika, Af,biologicallyme- diated Mg-calcite precipitates in the lake. Lake Tanganyika's lake levels have been re- markably stable to the most recent opening of Lake Kivu into the Lake Tanganyika basin (ca. A.D. 550) was not marked by major

  9. Origin of intraseasonal variability in Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Naithani, Jaya; Deleersnijder, Eric; Plisnier, Pierre-Denis

    2002-12-01

    Intraseasonal thermocline oscillations in Lake Tanganyika are analysed using observations near Mpulungu and simple analytical/numerical models, in order to understand their origin. The region around the lake is characterised by strong and persistent southeast winds during the four months dry season, lasting from May to August. The associated wind-stress causes the tilting of the thermocline which oscillates for the whole year. The wavelet transform spectra of temperature at 30 m depth of the lake near Mpulungu indicates the presence of various scales of motion, localised in frequency and time. The dominant modes of thermocline oscillations are intraseasonal variability with 3-4 weeks periods. Similar results are obtained from a reduced-gravity model with various wind forcing, including the observed forcing, and a simple analytical solution. In addition, the model results indicates that the dominant mode of oscillation exhibits one node only. From the study, it is inferred that the free modes of oscillations of the lake are in resonance with wind pulses.

  10. HYDROLOGICAL CHANGES IN RELATION TO BIOLOGICAL PRODUCTION IN SOUTHERN LAKE TANGANYIKA

    Microsoft Academic Search

    W. Coulter

    A rcvicw of the hydrology and an account of hydrological changes in the southeastern arm of Lake Tanganyika between July 1960 and January 1962 arc given. Thermal stratifi- cation broke down here in July 1960 and 1961, and instability and vertical mixing persisted throughout each cool season until restratification in Scptcmber. The distribution of dis- solved oxygen in this period

  11. The Geochemistry and Hydrography of Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Craig, H.

    2001-12-01

    John Edmond was a key member of the scientific group that participated in the two SIO expeditions on Lake Tanganyika, involved in both the water sampling on the lake and the operations in the potable chemical laboratory used ashore. Much of his data on the nutrient chemistry of the lake has been published in summary form (Limnol.Oceanog.1993). The present paper, which describes some of the other studies made on the lake, is dedicated to John, who was both a close personal friend and a brilliant colleague. Along the ~650 km length of the lake we occupied 18 stations and sampled the major inflowing streams. The CI concentration of the lake waters below ~150m (depth of the epilimnion) is constant (27.8ppm), so that temperature is the only hydrographic variable, and distinctive profiles occur in the two major deep basins (North & South, = NB and SB). In the NB from 100 to 1200m, T° C decreases smoothly to 400m, below which are two ~ isothermal layers extending down to a sharp discontinuity at 700m, followed by a decrease to an nderline{in-situ} minimum (23.32° C at 870m, the coldest water in Lake Tanganyika). The lower-most 300m of the profile is essentially adiabatic, with a bottom T = 23.32° C. The 700m T discontinuity is associated witha sharp cusp in methane concentration, which increases smoothly with depth from zero at the base of the mixed layer to 2.5 cc/kg at 700m, and then increases rapidly to 5.0 cc/kg at 1200m. In the SB, T decreases smoothly to 600m depth, below which is an almost isothermal layer to 1100m, followed by an ~ adiabatic gradient for 300m, to 23.40° C at 1400m. In this basin the CH4 profile is a smoothly continuous curve from 100-1200m, showing that the effective sill-depth between the two basins is at ~700m. Helium isotope profiles also show distinctive profiles in the two deep basins. In the NB, the 4He profile increases downward from atmospheric saturation to a smooth maximum at 450m (2.26 x saturation) and a 3He/4He ratio anomaly ? (3He) = -40% of atmospheric value). In the SB there is a similar though less marked He maximum at 900m. These extrema show the depths of injection of He from crustal sources, which in both basins has a 3He/4He ratio of 0.28 x atmospheric, close to the ratio in radiogenic helium. The He concentration requires a saturation T of 15° C at the present level of 773m above sealevel. If the deep water has not changed and was saturated at the present 23° C, the required lake level is ~250m below the present level. Co2 and 13C data show production of light CO2 at 220m, the depth of a ? (13C) minimum, and on the lake bottom where heavy CO2 is produced by CH4 production. Other data to be discussed as time permits include stable isotopes (D and 18O, enriched in deep water), 14C, tritium, 226Ra, 210Pb, and dissolved N2, Ne, and Ar. Our logistical work was supported by UNDP-FAO. G.W. Coulter (UNDP, Burundi), Ray Weiss (SIO), and Valerie Craig (SIO) participated in the expedition work at sea and on land.

  12. Distribution of glycerol dialkyl glycerol tetraether lipids in the water column of Lake Tanganyika

    E-print Network

    Wehrli, Bernhard

    Distribution of glycerol dialkyl glycerol tetraether lipids in the water column of Lake Tanganyika tetraethers (GDGTs) in suspended particulate matter from the water column of Lake Tanganyika (East Africa the TEX86 proxy has been applied is Lake Tanganyika (East Africa), one of the largest in the world

  13. What prevents outgassing of methane to the atmosphere in Lake Tanganyika?

    E-print Network

    Wehrli, Bernhard

    What prevents outgassing of methane to the atmosphere in Lake Tanganyika? Edith DurischKaiser,1 June 2011. [1] Tropical East African Lake Tanganyika hosts the Earth's largest anoxic freshwater body but also in the anoxic part of the water column of Lake Tanganyika. We measured CH4, 13 C of dissolved CH4

  14. HISTORICAL AND MODERN FLUCTUATIONS OF LAKES TANGANYIKA AND RUKWA AND THEIR RELATIONSHIP

    E-print Network

    Nicholson, Sharon E.

    HISTORICAL AND MODERN FLUCTUATIONS OF LAKES TANGANYIKA AND RUKWA AND THEIR RELATIONSHIP TO RAINFALL.S.A. Abstract. This paper describes the fluctuations of Lakes Tanganyika and Rukwa over the last two centuries and in the 1950s. Lake Tanganyika returned to extremely high stands in the 1960s and has continued to maintain

  15. Siderocelis irregularis (Chlorophyta, Trebouxiophyceae) in Lake Tanganyika (Africa)

    Microsoft Academic Search

    Maya P. Stoyneva; Elisabeth Ingoli?; Werner Kofler; Wim Vyverman

    2008-01-01

    Siderocelis irregularis Hindák, representing a genus Siderocelis (Naumann) Fott that is known from European temperate waters, was identified as a common phytoplankter in Lake Tanganyika.\\u000a It was found aposymbiotic as well as ingested (possibly endosymbiotic) in lake heterotrophs, mainly Strombidium sp. and Vorticella spp. The morphology and ultrastructure of the species, studied with LM, SEM and TEM, are described with

  16. Fisheries research towards resource management on Lake Tanganyika

    Microsoft Academic Search

    H. Mölsä; J. E. Reynolds; E. J. Coenen; O. V. Lindqvist

    1999-01-01

    Lake Tanganyika hosts one of the largest inland fisheries in Africa and is a significant source of food and livelihood to millions dwelling inside and outside of its basin. The lake and its environs support a wide array of subsistence and commercial activity as well as a remarkable assemblage of tropical flora and fauna, including highly diverse populations of endemic

  17. Nutrient chemistry of the water column of Lake Tanganyika

    Microsoft Academic Search

    J. M. EDMOND; R. F. STALLARD; H. CRAIG; V. CRAIG; R. F. WEISS; G. W. COULTER

    1993-01-01

    Lake Tanganyika shows pcrmancnt thermal stratification with deep-water temperatures that have been stable over the period of observation (since 1939). The lake is anoxic below - 150-m depth. In general the nutrients show Redficld behavior save in the deep waters of the northern basin where large excesses of phosphate and ammonia are prcscnt. Bacterial disproportionation of organic material probably plays

  18. Anaerobic ammonium oxidation in a tropical freshwater system (Lake Tanganyika)

    Microsoft Academic Search

    Carsten J. Schubert; Edith Durisch-Kaiser; Bernhard Wehrli; Bo Thamdrup; Phyllis Lam; Marcel M. M. Kuypers

    2006-01-01

    Summary Here we provide the first direct evidence for the anam- mox process (anaerobic ammonium oxidation) in a lacustrine system, Lake Tanganyika, the second larg- est lake in the world. Incubations with 15 N labelled nitrate showed that anammox occurred in the suboxic water layer at 100-110 m water depth. Anammox rates up to 10 nM N 2 h -

  19. Mating and Parental Care in Lake Tanganyika's Cichlids.

    PubMed

    Sefc, Kristina M

    2011-01-01

    Cichlid fishes of Lake Tanganyika display a variety of mating and parental care behaviors, including polygamous and monogamous mouthbrooding and substrate breeding, cooperative breeding, as well as various alternative reproductive tactics such as sneaking and piracy. Moreover, reproductive behaviors sometimes vary within species both in space and in time. Here, I survey reports on mating and parenting behaviors of Lake Tanganyika cichlid species and address the evolution of mating and parental care patterns and sexual dimorphism. Notes on measures of sexual selection intensity and the difficulties of defining mating systems and estimating selection intensities at species level conclude the essay. PMID:21822482

  20. Mating and Parental Care in Lake Tanganyika's Cichlids

    PubMed Central

    Sefc, Kristina M.

    2011-01-01

    Cichlid fishes of Lake Tanganyika display a variety of mating and parental care behaviors, including polygamous and monogamous mouthbrooding and substrate breeding, cooperative breeding, as well as various alternative reproductive tactics such as sneaking and piracy. Moreover, reproductive behaviors sometimes vary within species both in space and in time. Here, I survey reports on mating and parenting behaviors of Lake Tanganyika cichlid species and address the evolution of mating and parental care patterns and sexual dimorphism. Notes on measures of sexual selection intensity and the difficulties of defining mating systems and estimating selection intensities at species level conclude the essay. PMID:21822482

  1. Analysis of Wind-Induced Thermocline Oscillations of Lake Tanganyika

    Microsoft Academic Search

    Jaya Naithani; Eric Deleersnijder; Pierre-Denis Plisnier

    2003-01-01

    An analysis is presented of the wind-induced thermocline oscillations of Lake Tanganyika, East Africa. The region undergoes a four month dry season and the wet season for the rest of the year. The dry season is characterised by nearly constant high southeasterly winds, while for the rest of the year mild wind blows generally from the northeast. Observations show that

  2. Hydrothermal vents in Lake Tanganyika, East African, Rift system

    Microsoft Academic Search

    Jean-Jacques Tiercelin; Catherine Pflumio; Maryse Castrec; Jacques Boulégue; Pascal Gente; Joël Rolet; Christophe Coussement; Karl O. Stetter; Robert Huber; Sony Buku; Wafula Mifundu

    1993-01-01

    Sublacustrine hydrothermal vents with associated massive sulfides were discovered during April 1987 at Pemba and Cape Banza on the Zaire side of the northern basin of Lake Tanganyika, East African Rift system. New investigations by a team of ten scuba divers during the multinational (France, Zaire, Germany, and Burundi) TANGANYDRO expedition (August-October 1991) found hydrothermal vents down to a depth

  3. Hydrothermal vents is Lake Tanganyika, East African Rift system

    Microsoft Academic Search

    J. J. Tiercelin; C. Pflumio; M. Castrec

    1993-01-01

    Sublacustrine hydrothermal vents with associated massive sulfides were discovered during April 1987 at Pemba and Cape Banza on the Zaire side of the northern basin of Lake Tanganyika, East African Rift system. New investigations by a team of ten scuba divers during the multinational (France, Zaire, Germany, and Burundi) TANGANYDRO expedition (August-October 1991) found hydrothermal vents down to a depth

  4. Mercury biomagnification in the food web of Lake Tanganyika (Tanzania, East Africa)

    Microsoft Academic Search

    L. Campbell; Piet Verburg; D. G. Dixon; R. E. Hecky

    2008-01-01

    Lake Tanganyika is a globally important lake with high endemic biodiversity. Millions of people in the lake basin depend on several fish species for consumption. Due to the importance of fish consumption as an exposure route of mercury to humans, we sampled Lake Tanganyika in 2000 to assess total mercury concentrations and biomagnification of total mercury through the food web.

  5. Are there internal Kelvin waves in Lake Tanganyika?

    NASA Astrophysics Data System (ADS)

    Naithani, Jaya; Deleersnijder, Eric

    2004-03-01

    It is generally believed that the Earth's rotation has negligible impact on the water circulation in basins which are very narrow or located near the Equator. However, herein evidence is presented of the influence of the Earth's rotation on the hydrodynamics of Lake Tanganyika, which is both very narrow (width/length ~ 0.08) and located near the Equator. Numerical simulations exhibit small upwellings at the western shores as a result of the thermocline oscillations induced by the southeasterly winds of the dry season. These structures tend to propagate cyclonically around the lake similar to internal Kelvin waves. Numerical experiments in which f is varied concludes that internal Kelvin waves are present in Lake Tanganyika. It is also evidenced from this study that the internal Kelvin waves cannot be anticipated based on classic scaling arguments.

  6. What prevents outgassing of methane to the atmosphere in Lake Tanganyika?

    NASA Astrophysics Data System (ADS)

    Durisch-Kaiser, Edith; Schmid, Martin; Peeters, Frank; Kipfer, Rolf; Dinkel, Christian; Diem, Torsten; Schubert, Carsten J.; Wehrli, Bernhard

    2011-06-01

    Tropical East African Lake Tanganyika hosts the Earth's largest anoxic freshwater body. The entire water column holds over 23 Tg of the potent greenhouse gas methane (CH4). Methane is formed under sulphate-poor conditions via carbon dioxide reduction or fermentation from detritus and relict sediment organic matter. Permanent density stratification supports an accumulation of CH4 below the permanent oxycline. Despite CH4 significance for global climate, anaerobic microbial consumption of CH4 in freshwater is poorly understood. Here we provide evidence for intense methanotrophic activity not only in the oxic but also in the anoxic part of the water column of Lake Tanganyika. We measured CH4, 13C of dissolved CH4, dissolved oxygen (O2), sulphate (SO42-), sulphide (HS-) and the transient tracers chlorofluorocarbon-12 (CFC-12) and tritium (3H). A basic one-dimensional model, which considers vertical transport and biogeochemical fluxes and transformations, was used to interpret the vertical distribution of these substances. The results suggest that the anaerobic oxidation of CH4 is an important mechanism limiting CH4 to the anoxic zone of Lake Tanganyika. The important role of the anaerobic oxidation for CH4 concentrations is further supported by high abundances (up to ˜33% of total DAPI-stained cells) of single living archaea, identified by fluorescence in situ hybridization.

  7. Interspecific relationships of aufwuchs-eating fishes in Lake Tanganyika

    Microsoft Academic Search

    Kenzi Takamura

    1984-01-01

    On a rocky shore of Lake Tanganyika aufwuchs-eating is practiced by 18 fish species: 17 cichlids and 1 cyprinid. The majority takes mostly either filamentous or unicellular algae.Tropheus moorei and its taxonomically related species most closely resemble one another in diet among the species taking mostly filamentous algae, and thePetrochromis species do so among the species taking mostly unicellular algae.Petrochromis

  8. Ancient lakes as evolutionary reservoirs: evidence from the thalassoid gastropods of Lake Tanganyika

    Microsoft Academic Search

    Anthony B. Wilson; Matthias Glaubrecht; Axel Meyer

    2004-01-01

    Ancient lakes are often collectively viewed as evolutionary hot spots of diversification. East Africa's Lake Tanganyika has long been the subject of scientific interest owing to dramatic levels of endemism in species as diverse as cichlid fishes, paludomid gastropods, decapod and ostracod crustaceans and poriferans. It is the largest and deepest of the African rift lakes, and its endemic fauna

  9. Upwelling couples chemical and biological dynamics across the littoral and pelagic zones of Lake Tanganyika, East Africa

    E-print Network

    McIntyre, Peter

    and littoral zones of Lake Tanganyika near Kigoma, Tanzania. During the dry season of 2004, a rise occurs during most years in northern Lake Tanganyika. The observed sensitivity of littoral nutrients affect the dynamics of the spectacular nearshore ecosystem of Lake Tanganyika, as has been proposed

  10. A SNAIL'S SPACE SETS A SNAIL'S PACE: MOVEMENT RATES OF LAVIGERIA GASTROPODS IN LAKE TANGANYIKA, EAST AFRICA

    E-print Network

    McIntyre, Peter

    A SNAIL'S SPACE SETS A SNAIL'S PACE: MOVEMENT RATES OF LAVIGERIA GASTROPODS IN LAKE TANGANYIKA gastropods are diverse and common in the benthos of Lake Tanganyika. We used in situ studies of marked of three closely related species of gastropods in Lake Tanganyika. In addition to potential interspecific

  11. Climate Effect on Circulation in Lake Tanganyika: Increase of the Anoxic Hypolimnion and Loss of Productivity

    NASA Astrophysics Data System (ADS)

    Verburg, P.; Hecky, B.

    2003-12-01

    Lake Tanganyika, largest by volume of the East African Great Lakes (maximum depth 1470 m), has warmed up over the past century. Heating rates, the density depth gradient and the oxygen distributions were examined. The amount of energy absorbed by Lake Tanganyika is substantial on a global heat budget scale and is in the same order as that absorbed by the melting of Arctic sea-ice in the past century. At higher temperatures density decreases. Because the surface warmed up more than deep water the difference in density between shallow and deep water increased. The increased density gradient has slowed down vertical mixing and circulation and as a result oxygen concentrations and the maximum depth of oxygen penetration have decreased. SO4, introduced to the lake by river inflow, is now almost completely (98 %) lost from the lake by reduction at the oxic-anoxic interface. As a result the depth at which H2S is detectable has become much more shallow, from 300 m in 1938 to 120 m in 2000. At the south end where mixing is traditionally deepest in the lake, driven by south east trade winds, organisms which lived at 100-300 m a century ago are now forced into a more shallow distribution. The increase of the density gradient from deep nutrient rich to shallow nutrient poor water and the reduced mixing capacity of the lake has substantially impacted the offshore ecosystem. Primary production by phytoplankton has decreased as shown by increased silica concentrations and lower algal biomass, probably by reduced availability of essential macro and micro nutrients in epilimnetic water. The epilimnetic dissolved silica concentration tripled as diatom production and sedimentation of biogenic silica dropped in the last decades of the past century. Blooms of cyanobacteria in the stratified season may have been more common earlier in the century compared with the present and the lake is now much more transparent. Temperature is an important parameter in tropical lakes and climate warming has changed the ecosystem in Lake Tanganyika over the past century. Both reduced productivity and a reduced oxygen penetration will threaten the persistence of some of the hundreds of endemic species in Lake Tanganyika, as their habitats contract spatially and become more nutrient poor.

  12. Comment on ``Are there internal Kelvin waves in Lake Tanganyika?'' by Jaya Naithani and Eric Deleersnijder

    NASA Astrophysics Data System (ADS)

    Antenucci, Jason P.

    2005-11-01

    Recent numerical modelling efforts have demonstrated the presence of Kelvin waves in Lake Tanganyika (Naithani and Deleersnijder, 2004), however it is claimed that these waves should not appear according to classical scaling arguments. Based on existing classical scaling arguments, supported by laboratory and field investigations, I will show why they can, and apparently do, appear in Lake Tanganyika.

  13. Persistent chlorinated pesticides and polychlorinated biphenyls in selected fish species from Lake Tanganyika, Burundi, Africa

    Microsoft Academic Search

    P Manirakiza; A Covaci; L Nizigiymana; G Ntakimazi; P Schepens

    2002-01-01

    Concentrations of selected organochlorine pesticides and PCBs in seven fish species (cichlids) from the north end of the Lake Tanganyika, Burundi, Africa were determined. Results were compared to previous work on the Lake Tanganyika and other water bodies and to the European Community maximum residue levels (MRLs) in edible fat. The analytical method included a hot Soxhlet extraction with a

  14. Complete mitochondrial DNA replacement in a Lake Tanganyika cichlid fish.

    PubMed

    Nevado, B; Koblmüller, S; Sturmbauer, C; Snoeks, J; Usano-Alemany, J; Verheyen, E

    2009-10-01

    We used nuclear and mitochondrial DNA (mtDNA) sequences from specimens collected throughout Lake Tanganyika to clarify the evolutionary relationship between Lamprologus callipterus and Neolamprologus fasciatus. The nuclear data support the reciprocal monophyly of these two shell-breeding lamprologine cichlids. However, mtDNA sequences show that (i) L. callipterus includes two divergent and geographically disjunct (North-South) mtDNA lineages; and that (ii) N. fasciatus individuals cluster in a lineage sister group to the northern lineage of L. callipterus. The two mtDNA lineages of L. callipterus diverged c. 684 kya to 1.2 Ma, coinciding with a major water level low stand in Lake Tanganyika, which divided the lake into isolated sub-lakes. This suggests that the two mtDNA lineages originated as the result of the separation of L. callipterus populations in different sub-basins. The incongruent phylogenetic position of N. fasciatus can best be explained by an ancient unidirectional introgression from L. callipterus into N. fasciatus. Remarkably, our data indicate that this event resulted in the complete mtDNA replacement in N. fasciatus. Our data suggest that hybridization occurred soon after the divergence of the two L. callipterus mtDNA lineages, probably still during the water level low stand, and that subsequently the invading mtDNA lineage spread throughout the lake. PMID:19780975

  15. Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: IX. Summary of paleorecords of environmental change and catchment deforestation at Lake Tanganyika and impacts on the Lake Tanganyika ecosystem

    Microsoft Academic Search

    Andrew S. Cohen; Manuel R. Palacios-Fest; Emma S. Msaky; Simone R. Alin; Brent McKee; Catherine M. O’Reilly; David L. Dettman; Hudson Nkotagu; Kiram E. Lezzar

    2005-01-01

    Paleorecords from multiple indicators of environmental change provide evidence for the interactions between climate, human alteration of watersheds and lake ecosystem processes at Lake Tanganyika, Africa, a lake renowned for its extraordinary biodiversity, endemism and fisheries. This paper synthesizes geochronology, sedimentology, paleoecology, geochemistry and hydrology studies comparing the history of deltaic deposits from watersheds of various sizes and deforestation disturbance

  16. Evolutionary History of Lake Tanganyika's Predatory Deepwater Cichlids.

    PubMed

    Kirchberger, Paul C; Sefc, Kristina M; Sturmbauer, Christian; Koblmüller, Stephan

    2012-01-01

    Hybridization among littoral cichlid species in Lake Tanganyika was inferred in several molecular phylogenetic studies. The phenomenon is generally attributed to the lake level-induced shoreline and habitat changes. These allow for allopatric divergence of geographically fragmented populations alternating with locally restricted secondary contact and introgression between incompletely isolated taxa. In contrast, the deepwater habitat is characterized by weak geographic structure and a high potential for gene flow, which may explain the lower species richness of deepwater than littoral lineages. For the same reason, divergent deepwater lineages should have evolved strong intrinsic reproductive isolation already in the incipient stages of diversification, and, consequently, hybridization among established lineages should have been less frequent than in littoral lineages. We test this hypothesis in the endemic Lake Tanganyika deepwater cichlid tribe Bathybatini by comparing phylogenetic trees of Hemibates and Bathybates species obtained with nuclear multilocus AFLP data with a phylogeny based on mitochondrial sequences. Consistent with our hypothesis, largely congruent tree topologies and negative tests for introgression provided no evidence for introgressive hybridization between the deepwater taxa. Together, the nuclear and mitochondrial data established a well-supported phylogeny and suggested ecological segregation during speciation. PMID:22675652

  17. Low lake stands in lakes Malawi and tanganyika, East Africa, delineated with multifold seismic data.

    PubMed

    Scholz, C A; Rosendahl, B R

    1988-06-17

    Seismic data reveal that water level in Lake Malawi, East Africa, was 250 to 500 meters lower before about 25,000 years ago. Water levels in Lake Tanganyika at that time were more than 600 meters below the current lake level. A drier climate appears to have caused these low stands, but tectonic tilting may also have been a contributing factor in Lake Malawi. High-angle discordances associated with shallow sequence boundaries suggest that these low stands probably lasted many tens of thousands of years. Because of its basement topography, the Lake Tanganyika basin had three separate paleolakes, whereas the Lake Malawi basin had only one. The different geographies of these paleolakes may be responsible in part for the differences in the endemic fish populations in these lakes. PMID:17745221

  18. The Adaptive Radiation of Cichlid Fish in Lake Tanganyika: A Morphological Perspective

    PubMed Central

    Takahashi, Tetsumi; Koblmüller, Stephan

    2011-01-01

    Lake Tanganyika is the oldest of the Great Ancient Lakes in the East Africa. This lake harbours about 250 species of cichlid fish, which are highly diverse in terms of morphology, behaviour, and ecology. Lake Tanganyika's cichlid diversity has evolved through explosive speciation and is treated as a textbook example of adaptive radiation, the rapid differentiation of a single ancestor into an array of species that differ in traits used to exploit their environments and resources. To elucidate the processes and mechanisms underlying the rapid speciation and adaptive radiation of Lake Tanganyika's cichlid species assemblage it is important to integrate evidence from several lines of research. Great efforts have been, are, and certainly will be taken to solve the mystery of how so many cichlid species evolved in so little time. In the present review, we summarize morphological studies that relate to the adaptive radiation of Lake Tanganyika's cichlids and highlight their importance for understanding the process of adaptive radiation. PMID:21716857

  19. The adaptive radiation of cichlid fish in lake tanganyika: a morphological perspective.

    PubMed

    Takahashi, Tetsumi; Koblmüller, Stephan

    2011-01-01

    Lake Tanganyika is the oldest of the Great Ancient Lakes in the East Africa. This lake harbours about 250 species of cichlid fish, which are highly diverse in terms of morphology, behaviour, and ecology. Lake Tanganyika's cichlid diversity has evolved through explosive speciation and is treated as a textbook example of adaptive radiation, the rapid differentiation of a single ancestor into an array of species that differ in traits used to exploit their environments and resources. To elucidate the processes and mechanisms underlying the rapid speciation and adaptive radiation of Lake Tanganyika's cichlid species assemblage it is important to integrate evidence from several lines of research. Great efforts have been, are, and certainly will be taken to solve the mystery of how so many cichlid species evolved in so little time. In the present review, we summarize morphological studies that relate to the adaptive radiation of Lake Tanganyika's cichlids and highlight their importance for understanding the process of adaptive radiation. PMID:21716857

  20. Hydrothermal vents in Lake Tanganyika, East African, Rift system

    NASA Astrophysics Data System (ADS)

    Tiercelin, Jean-Jacques; Pflumio, Catherine; Castrec, Maryse; Boulégue, Jacques; Gente, Pascal; Rolet, Joël; Coussement, Christophe; Stetter, Karl O.; Huber, Robert; Buku, Sony; Mifundu, Wafula

    1993-06-01

    Sublacustrine hydrothermal vents with associated massive sulfides were discovered during April 1987 at Pemba and Cape Banza on the Zaire side of the northern basin of Lake Tanganyika, East African Rift system. New investigations by a team of ten scuba divers during the multinational (France, Zaire, Germany, and Burundi) TANGANYDRO expedition (August-October 1991) found hydrothermal vents down to a depth of 46 m along north-trending active faults bounding the Tanganyika rift on the western side. Temperatures from 53 to 103 °C were measured in hydrothermal fluids and sediments. Veins of massive sulfides 1-10 cm thick (pyrite and marcasite banding) were found associated with vents at the Pemba site. At Cape Banza,active vents are characterized by 1-70-cm-high aragonite chimneys, and there are microcrystalline pyrite coatings on the walls of hydrothermal pipes. Hydrothermal fluid end members show distinctive compositions at the two sites. The Pemba end member is a NaHCO3-enriched fluid similar to the NaHCO3 thermal fluids from lakes Magadi and Bogoria in the eastern branch off the rift. The Cape Banza end member is a solution enriched in NaCl. Such brines may have a deep-seated basement origin, as do the Uvinza NaCl brines on the eastern flank of the Tanganyika basin. Geothermometric calculations have yielded temperatures of fluid-rock interaction off 219 and 179 °C in the Pemba and Cape Banza systems, respectively. Abundant white or reddish-brown microbial colonies resembling Beggiatoa mats were found surrounding the active vents. Thermal fluid circulation is permitted by opening of cracks related to 130 °N normal-dextral faults that intersect the north- south major rift trend. The source of heat for such hydrothermal systems may relate to the existence of magmatic bodies under the rift, which is suggested by the isotopic composition of carbon dioxide released at Pemba and Cape Banza.

  1. Diatoms from surface sediments of the northern part of Lake Tanganyika

    Microsoft Academic Search

    A. G. Caljon; C. Z. Cocquyt

    1992-01-01

    227 Diatom taxa were observed in the surface sediments of the northern part of Lake Tanganyika, including 1 new to science: Amphora tanganyikae. The diatom community of these sediments is mainly composed of benthic organisms while planktonic diatoms are rather rare. Many brackish-water and a few marine organisms were observed. Cosmopolitan organisms (77.1%) dominate the diatom flora but tropical, tropical

  2. A late Holocene paleoclimatic history of Lake Tanganyika, East Africa

    NASA Astrophysics Data System (ADS)

    Stager, J. Curt; Cocquyt, Christine; Bonnefille, Raymonde; Weyhenmeyer, Constanze; Bowerman, Nicole

    2009-07-01

    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.

  3. Lake Tanganyika—A 'Melting Pot' of Ancient and Young Cichlid Lineages (Teleostei: Cichlidae)?

    PubMed Central

    Weiss, Juliane D.; Cotterill, Fenton P. D.; Schliewen, Ulrich K.

    2015-01-01

    A long history of research focused on the East Africa cichlid radiations (EAR) revealed discrepancies between mtDNA and nuclear phylogenies, suggesting that interspecific hybridisation may have been significant during the radiation of these fishes. The approximately 250 cichlid species of Lake Tanganyika have their roots in a monophyletic African cichlid assemblage, but controversies remain about the precise phylogenetic origin and placement of different lineages and consequently about L. Tanganyika colonization scenarios. 3312 AFLP loci and the mitochondrial ND2 gene were genotyped for 91 species representing almost all major lacustrine and riverine haplotilapiine east African cichlid lineages with a focus on L. Tanganyika endemics. Explicitly testing for the possibility of ancient hybridisation events, a comprehensive phylogenetic network hypothesis is proposed for the origin and diversification of L. Tanganyika cichlids. Inference of discordant phylogenetic signal strongly suggests that the genomes of two endemic L. Tanganyika tribes, Eretmodini and Tropheini, are composed of an ancient mixture of riverine and lacustrine lineages. For the first time a strong monophyly signal of all non-haplochromine mouthbrooding species endemic to L. Tanganyika (“ancient mouthbrooders”) was detected. Further, in the genomes of early diverging L. Tanganyika endemics Trematocarini, Bathybatini, Hemibatini and Boulengerochromis genetic components of other lineages belonging to the East African Radiation appear to be present. In combination with recent palaeo-geological results showing that tectonic activity in the L. Tanganyika region resulted in highly dynamic and heterogeneous landscape evolution over the Neogene and Pleistocene, the novel phylogenetic data render a single lacustrine basin as the geographical cradle of the endemic L. Tanganyika cichlid lineages unlikely. Instead a scenario of a pre-rift origin of several independent L. Tanganyika precursor lineages which diversified in ancient rivers and precursor lakes and then amalgamated in the extant L. Tanganyika basin is put forward as an alternative: the 'melting pot Tanganyika' hypothesis. PMID:25928886

  4. Lake tanganyika-a 'melting pot' of ancient and young cichlid lineages (teleostei: cichlidae)?

    PubMed

    Weiss, Juliane D; Cotterill, Fenton P D; Schliewen, Ulrich K

    2015-01-01

    A long history of research focused on the East Africa cichlid radiations (EAR) revealed discrepancies between mtDNA and nuclear phylogenies, suggesting that interspecific hybridisation may have been significant during the radiation of these fishes. The approximately 250 cichlid species of Lake Tanganyika have their roots in a monophyletic African cichlid assemblage, but controversies remain about the precise phylogenetic origin and placement of different lineages and consequently about L. Tanganyika colonization scenarios. 3312 AFLP loci and the mitochondrial ND2 gene were genotyped for 91 species representing almost all major lacustrine and riverine haplotilapiine east African cichlid lineages with a focus on L. Tanganyika endemics. Explicitly testing for the possibility of ancient hybridisation events, a comprehensive phylogenetic network hypothesis is proposed for the origin and diversification of L. Tanganyika cichlids. Inference of discordant phylogenetic signal strongly suggests that the genomes of two endemic L. Tanganyika tribes, Eretmodini and Tropheini, are composed of an ancient mixture of riverine and lacustrine lineages. For the first time a strong monophyly signal of all non-haplochromine mouthbrooding species endemic to L. Tanganyika ("ancient mouthbrooders") was detected. Further, in the genomes of early diverging L. Tanganyika endemics Trematocarini, Bathybatini, Hemibatini and Boulengerochromis genetic components of other lineages belonging to the East African Radiation appear to be present. In combination with recent palaeo-geological results showing that tectonic activity in the L. Tanganyika region resulted in highly dynamic and heterogeneous landscape evolution over the Neogene and Pleistocene, the novel phylogenetic data render a single lacustrine basin as the geographical cradle of the endemic L. Tanganyika cichlid lineages unlikely. Instead a scenario of a pre-rift origin of several independent L. Tanganyika precursor lineages which diversified in ancient rivers and precursor lakes and then amalgamated in the extant L. Tanganyika basin is put forward as an alternative: the 'melting pot Tanganyika' hypothesis. PMID:25928886

  5. Mn seasonal upwellings recorded in Lake Tanganyika mussels

    NASA Astrophysics Data System (ADS)

    Langlet, D.; Alleman, L. Y.; Plisnier, P.-D.; Hughes, H.; André, L.

    2006-09-01

    Biogenic productivity of Lake Tanganyika is highly dependent on seasonal upwellings of anoxic deep waters. We investigated the shell of freshwater bivalve Pleiodon spekii as a geochemical archive of these periodic hydrological changes tuned by the monsoon regime. The results of a 2-years-long geochemical survey of the coastal waters performed on the dissolved and particulate fractions were put in perspective against laser ablation ICP-MS profiles of Mn in five aragonitic shells from the same lake location. Skeletal Mn profiles in 3 shells are very similar and dominated by episodic peaks that matched the Mn increase recorded in surface waters during the 2002 upwelling, while a shell collected during 2003 dry season detect both 2002 and 2003 upwelling events. Larger shells showing an extremely reduced growth display more than 8Mn peaks suggesting at least an 8 years record of seasonal changes in water composition.

  6. Recent paleorecords document rising mercury contamination in Lake Tanganyika

    USGS Publications Warehouse

    Conaway, C.H.; Swarzenski, P.W.; Cohen, A.S.

    2012-01-01

    Recent Lake Tanganyika Hg deposition records were derived using 14C and excess 210Pb geochronometers in sediment cores collected from two contrasting depositional environments: the Kalya Platform, located mid-lake and more removed from watershed impacts, and the Nyasanga/Kahama River delta region, located close to the lake's shoreline north of Kigoma. At the Kalya Platform area, pre-industrial Hg concentrations are 23??0.2ng/g, increasing to 74ng/g in modern surface sediment, and the Hg accumulation rate has increased from 1.0 to 7.2??g/m 2/a from pre-industrial to present, which overall represents a 6-fold increase in Hg concentration and accumulation. At the Nyasanga/Kahama delta region, pre-industrial Hg concentrations are 20??3ng/g, increasing to 46ng/g in surface sediment. Mercury accumulation rate has increased from 30 to 70??g/m 2/a at this site, representing a 2-3-fold increase in Hg concentration and accumulation. There is a lack of correlation between charcoal abundance and Hg accumulation rate in the sediment cores, demonstrating that local biomass burning has little relationship with the observed Hg concentration or Hg accumulation rates. Examined using a sediment focusing-corrected mass accumulation rate approach, the cores have similar anthropogenic atmospheric Hg deposition profiles, suggesting that after accounting for background sediment concentrations the source of accumulating Hg is predominantly atmospheric in origin. In summary, the data document an increase of Hg flux to the Lake Tanganyika ecosystem that is consistent with increasing watershed sediment delivery with background-level Hg contamination, and regional as well as global increases in atmospheric Hg deposition. ?? 2011.

  7. Surface Energy Balance and The Mixed Layer at Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Verburg, P.; Hecky, R.

    2002-12-01

    Lake Tanganyika is a very large (670 by 50 km) and deep rift lake (max depth 1.5 km) in East Africa between 3.5 and 9 degree south of the equator. Mixing of the upper layers in this meromictic lake is most intense in the trade wind season (May - September). Apart from increased wind speeds, lower air temperatures and evaporative cooling of the surface layer combine to enhance mixing. Previous work indicated that correlation of evaporation and heat loss from the lake leaves room for a significant portion in the variability of heat content to be explained by other factors. The components of the energy balance which contribute to mixing were compared among seasons and between the north and south ends of the lake, over diel and annual cycles. Sensible heat and latent heat fluxes were estimated with bulk aerodynamic formulas and the heat storage change in the surface water layer was determined. Solar radiation was measured and longwave and all-wave net radiation calculated. Evaporation provided a major contribution to mixing but varied per site and over seasons. Mixing intensity was related to oxygen and nutrient cycles. Apart from evaporative cooling, sensible heat transfer and the emission of long wave radiation were important mechanisms in cooling the surface layer at night. Sensible heat transfer and outgoing longwave radiation were relatively more important at the north end of the lake, compared with the south end, in explaining nocturnal heat loss from the surface.

  8. Species-Specific Population Structure in Rock-Specialized Sympatric Cichlid Species in Lake Tanganyika, East Africa

    E-print Network

    Alvarez, Nadir

    and structure among three sympatric rock-dwelling cichlids of Lake Tanganyika, Eretmodus cyanostictus, Tropheus Great Lakes range from 9 to 12 million years (my), with 250 species, for Lake Tanganyika; 4 to 9 mySpecies-Specific Population Structure in Rock-Specialized Sympatric Cichlid Species in Lake

  9. Geochemical imprint on deep Tanganyika Lake water from hydrothermalism, groundwater or riverine sources.

    NASA Astrophysics Data System (ADS)

    Alleman, L. Y.; André, L.; Plisnier, P.-D.

    2003-04-01

    Lake Tanganyika (East Africa) is one of the oldest and largest freshwater lake in the world. The morphology of the northern basin is governed by an extensional system, limited to the east and west by two major normal fault trending N-S to NNE-SSW while the southern basin is controlled by the Tanganyika-Rukwana-Malawi transcurrent fault zone. These is no active volcanism around the lake but near surface hydrothermalism has been evidenced in the northern basin (Cape Banza). The lake presents also a permanent anoxic hypolimnion below 50-100 m in the North and below 250 m in the South due to poor mixing water masses. Trace elements along physico-chemical parameters (pH, temp., cond., D.O., alkal., nutrients) have been measured on several deep water and suspended particle profiles in the northern and southern basins during a cruise performed in July 2002. While most dissolved trace elements vertical profiles demonstrate a homogeneous water column, redox sensitive (Fe, Mn, P) and particulate reactive elements (Ca, Ba, Mg, REE) shows different comportment between the northern and southern basins. These differences are also observed on physico-chemical parameters such as pH and temperature in deep water. In the particulate phase, similar geochemical anomalies near the sediment-water interface between north and south basin are evidenced for Fe, Mg, Mn and Ba. Two main hypotheses are discussed: a deep hydrothermalism influencing the Northern basin and the potential impact of the Ruzizi river, the major tributary of the lake out-flowing from lake Kivu. Various geochemical tracers associated with physical proxies helped us to decipher between these two hypotheses, somehow complicated by the fact that Lake Kivu and the Ruzizi river present both a strong hydrothermal signature.

  10. Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: I. An introduction to the project

    Microsoft Academic Search

    Andrew S. Cohen; Manuel R. Palacios-Fest; James McGill; Peter W. Swarzenski; Dirk Verschuren; Robert Sinyinza; Tharcisse Songori; Bombi Kakagozo; Mutanga Syampila; Catherine M. O’Reilly; Simone R. Alin

    2005-01-01

    We investigated paleolimnological records from a series of river deltas around the northeastern rim of Lake Tanganyika, East Africa (Tanzania and Burundi) in order to understand the history of anthropogenic activity in the lake’s catchment over the last several centuries, and to determine the impact of these activities on the biodiversity of littoral and sublittoral lake communities. Sediment pollution caused

  11. Manganese content records seasonal upwelling in Lake Tanganyika mussels

    NASA Astrophysics Data System (ADS)

    Langlet, D.; Alleman, L. Y.; Plisnier, P.-D.; Hughes, H.; André, L.

    2007-03-01

    Biogenic productivity of Lake Tanganyika is highly dependent on seasonal upwellings of cold, oxygen-depleted, nutrient-rich deep waters. We investigated the shell of freshwater bivalve Pleiodon spekii as a geochemical archive of these periodic hydrological changes tuned by the monsoon regime. The results of a three-year-long limnological and geochemical survey of the coastal waters performed on the dissolved and particulate fractions were compared to LA-ICP-MS profiles of Mn in five aragonitic shells from the same lake location. Three shells present very similar Mn/Ca profiles dominated by a peak that matched the concomitant increase of Mn and chlorophyll a in surface waters during the 2002 upwelling, while a shell collected during 2003 dry season detect both 2002 and 2003 upwelling events. Larger shells showing an extremely reduced growth display more than 8 Mn/Ca peaks suggesting at least an 8-year-record of seasonal changes in water composition. We postulate that Mn/Ca in shells record the conjunction of an increase of biological activity with supplied of dissolved Mn and nutriments in coastal waters, resulting in an enhanced assimilation of biogenic Mn-rich particles. By combining the most recent generation of laser ablation system and the powerful High Resolution ICP-MS, the spatial resolution could be improved down to 5 to 10 µm crater size and end up in a better constrain of the relative variations of the annual Mn peaks. Such an approach on P. spekii from Lake Tanganyika has definitively a great potential to provide recent and past records on primary productivity associated with the monsoon climate system.

  12. Hydrothermal vents is Lake Tanganyika, East African Rift system

    SciTech Connect

    Tiercelin, J.J. [Universite de Bretagne Occidentale, Brest (France)] [Universite de Bretagne Occidentale, Brest (France); Pflumio, C.; Castrec, M. [Universite Paris VI, Paris (France)] [and others] [Universite Paris VI, Paris (France); and others

    1993-06-01

    Sublacustrine hydrothermal vents with associated massive sulfides were discovered during April 1987 at Pemba and Cape Banza on the Zaire side of the northern basin of Lake Tanganyika, East African Rift system. New investigations by a team of ten scuba divers during the multinational (France, Zaire, Germany, and Burundi) TANGANYDRO expedition (August-October 1991) found hydrothermal vents down to a depth of 46 m along north-trending active faults bounding the Tanganyika rift on the western side. Temperatures from 53 to 103 {degrees}C were measured in hydrothermal fluids and sediments. Veins of massive sulfides 1-10 cm thick (pyrite and marcasite banding) were found associated with vents at the Pemba site. At Cape Banza, active vents are characterized by 1-70-cm-high aragonite chimneys, and there are microcrystalline pyrite coatings on the walls of hydrothermal pipes. Hydrothermal fluid end members show distinctive compositions at the two sites. The Pemba end member is a NaHCO{sub 3}-enriched fluid similar to the NaHCO{sub 3} thermal fluids form lakes Magadi and Bogoria in the eastern branch of the rift. The Cape Banza end member is a solution enriched in NaCl. Such brines may have a deep-seated basement origin, as do the Uvinza NaCl brines on the eastern flank of the Tanganyika basin. Geothermometric calculations have yielded temperatures of fluid-rock interaction of 219 and 179 {degrees}C in the Pemba and Cape Banza systems, respectively. Abundant white or reddish-brown microbial colonies resembling Beggiatoa mats were found surrounding the active vents. Thermal fluid circulation is permitted by opening of cracks related to 130{degrees}N normal-dextral faults that intersect the north-south major rift trend. The sources of heat for such hydrothermal systems may relate to the existence of magmatic bodies under the rift, which is suggested by the isotopic composition of carbon dioxide released at Pemba and Cape Banza. 21 refs., 2 figs.

  13. km on Lake Tanganyika (Fig. 2C). Single airguns or multigun arrays in the size range of40 to 140 cubic

    E-print Network

    Richardson, David

    km on Lake Tanganyika (Fig. 2C). Single airguns or multigun arrays in the size range of40 to 140 and a few lines have been migrated to date. All Lake Tanganyika dip lines have been migrated. 2. Lake Malawi depths ofabout 200 m (3). Lake Tanganyika is about 650 by 70 km and has a maximum depth of about 1500 m

  14. Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: V. Palynological evidence for deforestation and increased erosion

    Microsoft Academic Search

    Emma S. Msaky; Daniel Livingstone; Owen K. Davis

    2005-01-01

    Pollen spectra from seven short cores taken from deltaic sites in the central and northern parts of Lake Tanganyika provide information about vegetation changes around the lake during the last 5000 years. Pollen analysis was undertaken to understand the history and timing of catchment deforestation and its causal linkage to excess sedimentation and ecosystem change in Lake Tanganyika. The spectra are

  15. Climate change decreases aquatic ecosystem productivity of Lake Tanganyika, Africa

    NASA Astrophysics Data System (ADS)

    O'Reilly, Catherine M.; Alin, Simone R.; Plisnier, Pierre-Denis; Cohen, Andrew S.; McKee, Brent A.

    2003-08-01

    Although the effects of climate warming on the chemical and physical properties of lakes have been documented, biotic and ecosystem-scale responses to climate change have been only estimated or predicted by manipulations and models. Here we present evidence that climate warming is diminishing productivity in Lake Tanganyika, East Africa. This lake has historically supported a highly productive pelagic fishery that currently provides 25-40% of the animal protein supply for the populations of the surrounding countries. In parallel with regional warming patterns since the beginning of the twentieth century, a rise in surface-water temperature has increased the stability of the water column. A regional decrease in wind velocity has contributed to reduced mixing, decreasing deep-water nutrient upwelling and entrainment into surface waters. Carbon isotope records in sediment cores suggest that primary productivity may have decreased by about 20%, implying a roughly 30% decrease in fish yields. Our study provides evidence that the impact of regional effects of global climate change on aquatic ecosystem functions and services can be larger than that of local anthropogenic activity or overfishing.

  16. Limnological annual cycle inferred from physical-chemical fluctuations at three stations of Lake Tanganyika

    Microsoft Academic Search

    P.-D. Plisnier; D. Chitamwebwa; L. Mwape; K. Tshibangu; V. Langenberg; E. Coenen

    1999-01-01

    Ten variables were measured at least twice per month at three locations of Lake Tanganyika (East Africa) over one year (1993–94). Upwelling was observed in the south of the lake during the dry, windy season from May to September. Stratification was variable in strength but always present in the north. The lake showed a marked tilting of the epilimnion during

  17. Historical and Modern Fluctuations of Lakes Tanganyika and Rukwa and Their Relationship to Rainfall Variability

    Microsoft Academic Search

    Sharon E. Nicholson

    1999-01-01

    This paper describes the fluctuations of Lakes Tanganyika and Rukwa over the last two centuries. Lake chronologies extending back to the late eighteenth century are derived from reports of European visitors, settlers and explorers and from oral accounts of the local peoples. The historical fluctuations are meshed with the modern record to provide a picture of the lakes' fluctuations until

  18. Mastacembelid eels support Lake Tanganyika as an evolutionary hotspot of diversification

    Microsoft Academic Search

    Katherine J Brown; Lukas Rüber; Roger Bills; Julia J Day

    2010-01-01

    BACKGROUND: Lake Tanganyika (LT) is the oldest of the African Rift Lakes and is one of the richest freshwater ecosystems on Earth, with high levels of faunal diversity and endemism. The endemic species flocks that occur in this lake, such as cichlid fishes, gastropods, catfish and crabs, provide unique comparative systems for the study of patterns and processes of speciation.

  19. Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500

    NASA Astrophysics Data System (ADS)

    Tierney, Jessica E.; Mayes, Marc T.; Meyer, Natacha; Johnson, Christopher; Swarzenski, Peter W.; Cohen, Andrew S.; Russell, James M.

    2010-06-01

    Instrumental observations suggest that Lake Tanganyika, the largest rift lake in East Africa, has become warmer, increasingly stratified and less productive over the past 90years (refs 1,2). These trends have been attributed to anthropogenic climate change. However, it remains unclear whether the decrease in productivity is linked to the temperature rise, and whether the twentieth-century trends are anomalous within the context of longer-term variability. Here, we use the TEX86 temperature proxy, the weight per cent of biogenic silica and charcoal abundance from Lake Tanganyika sediment cores to reconstruct lake-surface temperature, productivity and regional wildfire frequency, respectively, for the past 1,500years. We detect a negative correlation between lake-surface temperature and primary productivity, and our estimates of fire frequency, and hence humidity, preclude decreased nutrient input through runoff as a cause for observed periods of low productivity. We suggest that, throughout the past 1,500years, rising lake-surface temperatures increased the stratification of the lake water column, preventing nutrient recharge from below and limiting primary productivity. Our records indicate that changes in the temperature of Lake Tanganyika in the past few decades exceed previous natural variability. We conclude that these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming, with potentially important implications for the Lake Tanganyika fishery.

  20. Century-Long Warming Trends in the Upper Water Column of Lake Tanganyika.

    PubMed

    Kraemer, Benjamin M; Hook, Simon; Huttula, Timo; Kotilainen, Pekka; O'Reilly, Catherine M; Peltonen, Anu; Plisnier, Pierre-Denis; Sarvala, Jouko; Tamatamah, Rashid; Vadeboncoeur, Yvonne; Wehrli, Bernhard; McIntyre, Peter B

    2015-01-01

    Lake Tanganyika, the deepest and most voluminous lake in Africa, has warmed over the last century in response to climate change. Separate analyses of surface warming rates estimated from in situ instruments, satellites, and a paleolimnological temperature proxy (TEX86) disagree, leaving uncertainty about the thermal sensitivity of Lake Tanganyika to climate change. Here, we use a comprehensive database of in situ temperature data from the top 100 meters of the water column that span the lake's seasonal range and lateral extent to demonstrate that long-term temperature trends in Lake Tanganyika depend strongly on depth, season, and latitude. The observed spatiotemporal variation in surface warming rates accounts for small differences between warming rate estimates from in situ instruments and satellite data. However, after accounting for spatiotemporal variation in temperature and warming rates, the TEX86 paleolimnological proxy yields lower surface temperatures (1.46 °C lower on average) and faster warming rates (by a factor of three) than in situ measurements. Based on the ecology of Thaumarchaeota (the microbes whose biomolecules are involved with generating the TEX86 proxy), we offer a reinterpretation of the TEX86 data from Lake Tanganyika as the temperature of the low-oxygen zone, rather than of the lake surface temperature as has been suggested previously. Our analyses provide a thorough accounting of spatiotemporal variation in warming rates, offering strong evidence that thermal and ecological shifts observed in this massive tropical lake over the last century are robust and in step with global climate change. PMID:26147964

  1. Estimating the age of formation of lakes: An example from Lake Tanganyika, East African Rift system

    SciTech Connect

    Cohen, A.; Soreghan, M.J. [Univ. of Arizona, Tucson, AZ (United States)] [Univ. of Arizona, Tucson, AZ (United States); Scholz, C.A. [Duke Univ. Marine Lab., Beaufort, NC (United States)] [Duke Univ. Marine Lab., Beaufort, NC (United States)

    1993-06-01

    Age estimates for ancient lakes are important for determining their histories and their rates of biotic and tectonic evolution. In the absence of dated core material from the lake`s sedimentary basement, several techniques have been used to generate such age estimates. The most common of these, herein called the reflection seismic-radiocarbon method (RSRM), combines estimates of short-term sediment-accumulation rates derived from radiocarbon-dated cores and depth-to-basement estimates derived from reflection-seismic data at or near the same locality to estimate an age to basement. Age estimates form the RSRM suggest that the structural basins of central Lake Tanganyika began to form between 9 and 12 Ma. Estimates for the northern and southern basins are younger (7 to 8 Ma and 2 to 4 Ma, respectively). The diachroneity of estimates for different segments of the lake is equivocal, and may be due to erosional loss of record in the northern and southern structural basins or to progressive opening of the rift. The RSRM age estimates for Lake Tanganyika are considerably younger than most prior estimates and clarify the extensional history of the western branch of the East African Rift system. 31 refs., 3 figs., 1 tab.

  2. Mitochondrial Phylogeny of the Lamprologini, the Major Substrate Spawning Lineage of Cichild Fishes from Lake Tanganyika in Eastern Africa

    Microsoft Academic Search

    Christian Sturmbauer; Erik Verheyen

    Lake Tanganyika harbors the oldest, morphologically and behaviorally most diverse flock of cichlid species. While the cichlids in Lakes Malawi and Victoria breed their eggs exclusively by buccal incubation (termed \\

  3. Behavior of rare earth and trace elements in Lake Tanganyika and its three major tributaries

    NASA Astrophysics Data System (ADS)

    Sako, A.; Johnson, R.

    2004-12-01

    Water samples were collected, during the rainy and dry seasons 2003, from three major rivers and several locations of the Lake Tanganyika. They were directly filtered (0.45 im pore size) into pre-washed polyethylene bottles, and acidified at pH 2. Finnigan Element 2 high resolution (HR)-IC-MPS was used to measure trace and rare earth elements (REE) concentrations under clean laboratory conditions, and (115In) was used as an internal standard. Because of the close relationship between light rare earth element (LREE) and Fe, riverine REE of the three were used to study the process trace element scavenging by Fe oxyhydroxides in three different two sub-basins of the lake. This confirmed by the significant positive correlation between Nd and Fe. The vertical distribution of Fe and Mn oxides were also used to investigate removal and release of trace elements in the water column. The normalized lacustrine REE to their riverine counterpart showed a gradual removal of REE across the lake, which was in the order of LREE>MREE>HREE. Hence, the rivers are the sole source of the lacustrine REE abundance. Coincidence of Fe maxima with those of Ce anomalies and La indicates that trace element profiles are chiefly controlled by the coating of Fe oxyhydroxides through oxidation of Fe2+ to Fe3+ under high dissolved oxygen contents and pH and vice versa. Due to differences in hydrodynamics between the extreme ends of the lake (upwelling in the southern end during the dry season), high mixing between bottom water and surface was observed at the surface in the Southern Basin while the mixing occurred mainly between 40 m and 80 m depth in the Northern Basin. There was also a clear similarity between Ba and NO3- and PO43- profiles in the southern end of the lake, supporting the idea that deep anoxic water, rich in nutrients and trace elements, are bought the surface during this period of intensive upwelling. In conclusion, the surface water chemical compositions of Lake Tanganyika are controlled by fluvial inputs and the seasonal changes in hydrodynamics across the lake.

  4. Lake level and paleoenvironmental history of Lake Tanganyika, Africa, as inferred from late Holocene and modern stromatolites

    Microsoft Academic Search

    Andrew S. Cohen; Michael R. Talbot; David L. Dettman; Paul Abell

    1997-01-01

    Fossil and living stromatolites are abundant around the margins of Lake Tanganyika, Af- rica, and provide a wealth of paleolimnologic and paleoclimatic information for the late Holo- cene. Six lines of evidence show that stromato- lites and cements are precipitating in the lake to- day: (1) carbonate saturation state calculations, (2) documentation of living stromatolites and their depth distribution, (3)

  5. Lake-level history of Lake Tanganyika, East Africa, for the past 2500 years based on ostracode-inferred water-depth reconstruction

    Microsoft Academic Search

    Simone R. Alin; Andrew S. Cohen

    2003-01-01

    Assemblages of ostracodes from sediment cores illuminate lake-level history at decadal to centennial timescales during the late Holocene at Lake Tanganyika, East Africa. The ostracode-based lake-level curves for several cores resemble both each other and the only previously published lake-level record of comparable resolution for Lake Tanganyika during this interval, successfully reconstructing known highstands, improving the chronology of known lowstands,

  6. General nutrient distribution in the water column of Northern Lake Tanganyika

    Microsoft Academic Search

    David Nahimana; Natacha Brion; Willy Baeyens; Gaspard Ntakimazi

    2008-01-01

    A one-year's sampling programme of ammonium, nitrate and nitrite, and silica was performed at a station located in the pelagic area of northern Lake Tanganyika, about 4 km offshore in the vicinity of Bujumbura city. Sampling was generally conducted twice a month and water samples were collected at 10 m intervals between 0 and 100 m depth and analyzed spectrophotometrically

  7. Mitochondrial Phylogeny of the Endemic Mouthbrooding Lineages of Cichlid Fishes from Lake Tanganyika in Eastern Africa

    Microsoft Academic Search

    Christian Sturmbauer

    Of the three cichlid species flocks in eastern Africa, Lake Tanganyika harbors the oldest species assemblage, which is also the most diverse morphologically and be- haviorally. For 12 species (20 individuals) of 12 genera of the tribe Ectodini, 852 bp from two segments (cytochrome b and control region) of the mitochondrial genome were sequenced. In addition, orthologous sequences were obtained

  8. Population structure in two sympatric species of the Lake Tanganyika cichlid tribe Eretmodini: evidence for introgression

    Microsoft Academic Search

    Lukas Ruber; Axel Meyer; Christian Sturmbauer; Erik Verheyen

    2001-01-01

    Patterns of genetic differentiation were analysed and compared in two sympatric species of the endemic Lake Tanganyika cichlid tribe Eretmodini by means of mitochondrial DNA (mtDNA) sequences of the control region and six microsatellite DNA loci. The sample area covers a total of 138 km of mostly uninterrupted rocky shoreline in the Democratic Republic of Congo and includes the entire

  9. Distribution of the primates on the eastern shore of Lake Tanganyika

    Microsoft Academic Search

    Takayoshi Kano

    1971-01-01

    The mountainous and broken hill country in the middle part of the eastern shore of Lake Tanganyika is one of the areas which have been well studied primatologically. In particular, the chimpanzee has been studied for years by many primatologists at several sites. At least ten species of primates appear in this area. Nevertheless, the geographical range of some of

  10. Trace metal concentrations in water, sediments and fish tissue from Lake Tanganyika

    Microsoft Academic Search

    F. M. M. Chale

    2002-01-01

    Trace metal (Cu, Pb, Fe, Mn, Zn, Cd) concentrations were determined in water, sediments, various fin fish species and a bivalve (Mutelaspekei) from Lake Tanganyika using an atomic absorption spectrophotometer. Integrated water samples to depths of 10 m were collected using a pre-rinsed flexible plastic pipe. Sediment samples were collected using a ponar mud sampler. Fish samples were obtained using

  11. Ecophysiology of Aufwuchs-eating cichlids in Lake Tanganyika: niche separation by trophic specialization

    Microsoft Academic Search

    Christian Sturmbauer; Wolfgang Mark; Reinhard Dallinger

    1992-01-01

    Synopsis The Aufwuchs-eating cichlids of Lake Tanganyika show clear trophic differences that are correlated to their morphology, physiology and foraging behaviour. The species are grouped into three categories of relative intestinal length according to their feeding habits. A correlation between the intestinal length and the diet could be demonstrated, ranging from around 2.5 for species ingesting more animal food, to

  12. Geographical colour variation in cichlid fishes at the southern end of Lake Tanganyika

    Microsoft Academic Search

    Masanori Kohdal; Yasunobu Yanagisawa; Tetsu Sato; Kazuhiro Nakaya; Yasuo Niimura; Kazunori Matsumoto; Haruki Ochi

    1996-01-01

    Geographical colour variation and distribution of 48 common cichlid fish species were studied at 20 sites along an 85 km shoreline at the southern end of Lake Tanganyika, Africa. Sixteen species had two or more colour morphs and 11 species showed a limited distribution in the study area. They were all rock-dwellers. Distributional borders of the color morphs and species

  13. Effects of landscape Disturbances on Animal Communities in Lake Tanganyika, East Africa

    Microsoft Academic Search

    Simone R. Alin; Andrew S. Cohen; Roger Bills; Masta Mukwaya Gashagaza; A. E. Michel; Jean-Jacques Tiercelin; Koen Martens; P. Coeveliers; Sima Keita Mboko; Kelly West; Michael Soreghan; Sona Kimbadi; Gaspard Ntakimazi

    1999-01-01

    Watershed deforestation, road building, and other anthropogenic activities result in sediment in- undation of lacustrine habitats. In Lake Tanganyika, this threatens the survival of many rock-dwelling spe- cies by altering the structure and quality of rocky habitats. We investigated the relationship between habitat quality, as related to watershed disturbance intensity, and the biodiversity of faunal communities at three rocky littoral

  14. Replicated Evolution of Trophic Specializations in an Endemic Cichlid Fish Lineage from Lake Tanganyika

    Microsoft Academic Search

    Lukas Ruber; Erik Verheyen; Axel Meyer

    1999-01-01

    The current phylogenetic hypothesis for the endemic Lake Tanganyika cichlid fishes of the tribe Eretmodini is based solely on morphology and suggests that more complex trophic morphologies derived only once from a less specialized ancestral condition. A molecular phylogeny of eretmodine cichlids based on partial mitochondrial DNA cytochrome b and control-region sequences was used to reconstruct the evolutionary sequence of

  15. Evolutionary convergence of body shape and trophic morphology in cichlids from Lake Tanganyika

    Microsoft Academic Search

    L. RUBER; D. C. ADAMS

    2001-01-01

    A recent phylogenetic analysis of mitochondrial DNA sequences from eretmodine cichlids from Lake Tanganyika indicated independent origins of strikingly similar trophic specializations, such as dentition characters. Because genetic lineages with similar trophic morphologies were not monophyletic, but instead were grouped with lineages with different trophic phenotypes, raises the question of whether trophic morphology covaries with additional morphological characters. Here, we

  16. Evolution of the tribe Tropheini from Lake Tanganyika: synchronized explosive speciation producing multiple evolutionary parallelism

    Microsoft Academic Search

    Christian Sturmbauer; Ursula Hainz; Sanja Baric; Erik Verheyen; Walter Salzburger

    2003-01-01

    One of the most surprising outcomes of recent molecular studies on cichlid fishes of the three Great East African Lakes Victoria, Malawi and Tanganyika, was the stunning rapidity of speciation and cladogenesis at early stages of adaptive radiation. Despite their rapid pace, speciation events were so far intuitively assumed to proceed in a bifurcating and tree-like fashion, even if they

  17. An experimental test of the effects of sedimentation on Lake Tanganyika rocky shore gastropod survivorship

    Microsoft Academic Search

    Ellinor Michel

    Sediment erosion from land and transport and deposition on littoral habitats has been identified as a form of pollution threatening the biodiversity of Lake Tanganyika (Cohen et al., 1993, 1996; Alin et al. 1999; Donoghue & Irvine, 2003; McIntrye et al. submitted). This anthropogenic sediment can alter the native aquatic habitat by blocking light when it is in suspension, affecting

  18. Century-Long Warming Trends in the Upper Water Column of Lake Tanganyika

    PubMed Central

    Kraemer, Benjamin M.; Hook, Simon; Huttula, Timo; Kotilainen, Pekka; O’Reilly, Catherine M.; Peltonen, Anu; Plisnier, Pierre-Denis; Sarvala, Jouko; Tamatamah, Rashid; Vadeboncoeur, Yvonne; Wehrli, Bernhard; McIntyre, Peter B.

    2015-01-01

    Lake Tanganyika, the deepest and most voluminous lake in Africa, has warmed over the last century in response to climate change. Separate analyses of surface warming rates estimated from in situ instruments, satellites, and a paleolimnological temperature proxy (TEX86) disagree, leaving uncertainty about the thermal sensitivity of Lake Tanganyika to climate change. Here, we use a comprehensive database of in situ temperature data from the top 100 meters of the water column that span the lake’s seasonal range and lateral extent to demonstrate that long-term temperature trends in Lake Tanganyika depend strongly on depth, season, and latitude. The observed spatiotemporal variation in surface warming rates accounts for small differences between warming rate estimates from in situ instruments and satellite data. However, after accounting for spatiotemporal variation in temperature and warming rates, the TEX86 paleolimnological proxy yields lower surface temperatures (1.46 °C lower on average) and faster warming rates (by a factor of three) than in situ measurements. Based on the ecology of Thaumarchaeota (the microbes whose biomolecules are involved with generating the TEX86 proxy), we offer a reinterpretation of the TEX86 data from Lake Tanganyika as the temperature of the low-oxygen zone, rather than of the lake surface temperature as has been suggested previously. Our analyses provide a thorough accounting of spatiotemporal variation in warming rates, offering strong evidence that thermal and ecological shifts observed in this massive tropical lake over the last century are robust and in step with global climate change. PMID:26147964

  19. A Curious Ecological `Niche' among the Fishes of Lake Tanganyika

    Microsoft Academic Search

    G. Marlier; N. Leleup

    1954-01-01

    PREVIOUS studies on certain Tanganyika Cichlids1 have shown that, in species of the genus Plecodus, the stomach content is often composed of fish scales. It was not known if this was an indication of a very peculiar diet, and whether these scales had been taken from live or dead fish.

  20. New palaeogeographic and lake-level reconstructions of Lake Tanganyika: implications for tectonic, climatic and biological evolution in a rift lake

    Microsoft Academic Search

    A. S. Cohen; K.-E. Lezzar; J.-J. Tiercelin; M. Soreghan

    1997-01-01

    Palaeogeographic and lake-level reconstructions provide powerful tools for evaluating competing scenarios of biotic, climatic and geological evolution within a lake basin. Here we present new reconstructions for the northern Lake Tanganyika subbasins, based on reflection seismic, core and outcrop data. Reflection seismic radiocarbon method (RSRM) age estimates provide a chronological model for these reconstructions, against which yet to be obtained

  1. Mitochondrial Phylogeography of Rock-Dwelling Cichlid Fishes Reveals Evolutionary Influence of Historical Lake Level Fluctuations of Lake Tanganyika, Africa

    Microsoft Academic Search

    Erik Verheyen; Lukas Ruber; Jos Snoeks; Axel Meyer

    1996-01-01

    The East African Lakes Tanganyika, Malawi and Victoria each harbour hundreds of endemic invertebrate and vertebrate species. Inferences about the ecological and evolutionary processes responsible for the origin of these species flocks will only be possible when they are made within historical and comparative frameworks. Specifically, the relative importance of intrinsic characteristics and extrinsic factors may offer information about the

  2. Temporal Changes in Lead Depositions in East Africa: A Case Study of Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Odigie, K. O.; Flegal, A. R.

    2011-12-01

    Environmental changes (e.g., increasing rates of soil erosion) in East Africa have been attributed to local human activities and global climate change. However, reports on the impacts of these changes on the remobilization and transport of heavy metals, such as lead, in the environment are presently limited in literature. Therefore, this study was designed to chronicle the historic transport and deposition of lead in East Africa as recorded in the sediments of Lake Tanganyika. Sediment cores collected from regions with varying anthropogenic impacts of Lake Tanganyika were divided into sections, dated using excess lead-210, and analyzed for lead concentrations and isotopic composition. The results show that the amount of lead deposited in some regions of the lake increased recently (e.g., by more than 25% over the past two decades preceding 2000) which is consistent with regional changes in sediment accumulation rates in Lake Tanganyika. Temporal changes in the sources of that lead are being characterized by their isotopic compositions.

  3. Ecology and conservation status of endemic freshwater crabs in Lake Tanganyika, Africa

    Microsoft Academic Search

    Saskia A. E. Marijnissen; Ellinor Michel; Daniel F. R. Cleary; Peter B. McIntyre

    2009-01-01

    Sedimentation resulting from riparian deforestation has a wide range of detrimental effects on aquatic biodiversity, but predicting\\u000a the full consequences of such disturbances requires an understanding of the ecosystem’s key functional components. We investigated\\u000a the ecology and response to sedimentation of the diverse, endemic freshwater crabs of Lake Tanganyika, which may occupy important\\u000a positions in littoral foodwebs. Our surveys revealed

  4. Parental care and mating systems of cichlid fishes in Lake Tanganyika: a preliminary field survey

    Microsoft Academic Search

    Tetsuo Kuwamura

    1986-01-01

    Reproductive ecology and ethology of 52 cichlid fishes were studied along the shore of Myako, east-middle coast of Lake Tanganyika.\\u000a Seventeen species were substrate-brooders (guarders), 31 were mouthbrooders, and the remaining 4 were intermediate, performing\\u000a prolonged biparental guarding of fry after mouthbrooding. Among the substrate-brooders maternal care (and polygyny) was seen\\u000a about as frequently as biparental care. In most of

  5. The stoichiometry of particulate nutrients in Lake Tanganyika – implications for nutrient limitation of phytoplankton

    Microsoft Academic Search

    Marko Järvinen; Kalevi Salonen; Jouko Sarvala; Kristiina Vuorio; Anne Virtanen

    1999-01-01

    We studied the potential nutrient limitation of phytoplankton by means of seston nutrient stoichiometry and nutrient enrichment bioassays in the epilimnion of Lake Tanganyika. In most cases, the particulate carbon to phosphorus (C:P) ratio was high and indicated moderate P deficiency, while the respective C:N ratio mainly suggested moderate N deficiency. The N:P ratios of seston indicated rather balanced N

  6. Food habits and foraging behaviour of benthivorous cichlid fishes in Lake Tanganyika

    Microsoft Academic Search

    Masahide Yuma

    1994-01-01

    A study was made of the food habits and foraging behaviour of coexisting benthivorous cichlid fishes along the rocky northwestern coast of Lake Tanganyika. The five group-foraging species regularly found in the study area,Gnathochromis pfefferi, Lamprologus callipterus, Altolamprologus compressiceps, Lepidiolamprologus elongatus andLobochilotes labiatus, have different foraging techniques, although all eat shrimps (family Atyidae). Individuals of each species allow potential food-competitors

  7. Late Holocene linkages between decade–century scale climate variability and productivity at Lake Tanganyika, Africa

    Microsoft Academic Search

    Andrew S. Cohen; Kiram E. Lezzar; Julia Cole; David Dettman; Geoffrey S. Ellis; Meagan Eagle Gonneea; Pierre-Denis Plisnier; Victor Langenberg; Maarten Blaauw; Derrick Zilifi

    2006-01-01

    Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between ??2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little

  8. Alternative Reproductive Tactics in the Shell-Brooding Lake Tanganyika Cichlid Neolamprologus brevis.

    PubMed

    Ota, Kazutaka; Aibara, Mitsuto; Morita, Masaya; Awata, Satoshi; Hori, Michio; Kohda, Masanori

    2012-01-01

    Alternative reproductive tactics (ARTs) are found in several Lake Tanganyika shell-brooding cichlids. Field studies were conducted in the Wonzye population to examine reproductive ecology and ARTs in the Lake Tanganyika shell-brooding cichlid Neolamprologus brevis. We discovered that this fish occurred in both rocky- and sandy-bottom habitats, but in rocky habitats, brood-caring females exclusively occurred in shell-patches that another cichlid species created. All N. brevis of both sexes in the patches were sexually mature, whereas immature males and females with unripe eggs were found frequently in sandy-bottom habitats. Males in sandy-bottom habitats were smaller, but fed more frequently and were in better somatic condition than males in the patches. Similar tendency was found in females. This indicates that N. brevis uses different habitats depending on the stage of its life history, with migration from sandy-bottom habitats to the shell-patches for reproduction. Males in the patches exhibited different behavior patterns: floating above the patches and lying in the patches. The former was larger, more aggressive, and invested less in gonads (relative to body size) than the latter. These results accord with those of other shell-brooding Lake Tanganyika cichlids with ARTs, and they therefore suggest the presence of ARTs in N. brevis. PMID:22888463

  9. Alternative Reproductive Tactics in the Shell-Brooding Lake Tanganyika Cichlid Neolamprologus brevis

    PubMed Central

    Ota, Kazutaka; Aibara, Mitsuto; Morita, Masaya; Awata, Satoshi; Hori, Michio; Kohda, Masanori

    2012-01-01

    Alternative reproductive tactics (ARTs) are found in several Lake Tanganyika shell-brooding cichlids. Field studies were conducted in the Wonzye population to examine reproductive ecology and ARTs in the Lake Tanganyika shell-brooding cichlid Neolamprologus brevis. We discovered that this fish occurred in both rocky- and sandy-bottom habitats, but in rocky habitats, brood-caring females exclusively occurred in shell-patches that another cichlid species created. All N. brevis of both sexes in the patches were sexually mature, whereas immature males and females with unripe eggs were found frequently in sandy-bottom habitats. Males in sandy-bottom habitats were smaller, but fed more frequently and were in better somatic condition than males in the patches. Similar tendency was found in females. This indicates that N. brevis uses different habitats depending on the stage of its life history, with migration from sandy-bottom habitats to the shell-patches for reproduction. Males in the patches exhibited different behavior patterns: floating above the patches and lying in the patches. The former was larger, more aggressive, and invested less in gonads (relative to body size) than the latter. These results accord with those of other shell-brooding Lake Tanganyika cichlids with ARTs, and they therefore suggest the presence of ARTs in N. brevis. PMID:22888463

  10. Facies distributions within contrasting structural components of a rift lake: Lake Tanganyika, Africa

    SciTech Connect

    Soreghan, M.J.; Cohen, A.S. (Univ. of Arizona, Tucson (United States))

    1991-03-01

    Lake Tanganyika is the most widely cited modern analog for interpreting ancient rift lakes; thus, understanding controls on its facies distribution is critical for refining stratigraphic models for rifts. Four recurrent margin types occur along the alternating half-graben structure of the lake: rift axes, platforms, escarpments, and accommodation zones. Data from study sites in the northern part of the lake suggest that predictable facies differences exist between these structural margin types. The rift axis site comprises a low-gradient, clastic (wave/current)-dominated deltaic system, with strong facies asymmetry and minor carbonate accumulations on raised benches. The platform margin site comprises a series of structurally controlled benches over which long, continuous facies tracts occur. Carbonate sands, muds, and shell gravel dominate; clastics are limited to moderate-sized silty deltas and long, narrow shoreface sands. The escarpment margin site is a steep-gradient system along which small ({lt}1 km{sup 2}) fan deltas alternate with cemented talus. The accommodation zone margin sites are also dominated by rugged structural relief, generally small fan deltas, and semicontinuous shoreface sand belts ({gt}5 km) onshore and poorly sorted silts offshore. TOC from fine-grained samples reflects the contrast in margin types. TOC values for the platform and rift axis range from 0.4 - 2.1 wt. % (avg. 1.3%), whereas accommodation zone and escarpment margin values range from 0.5-5.5% (avg. 3.0%). Acid insoluble sulfur shows a similar trend. Although all data are significantly correlated with depth, the relative area of the lake margin above and below the oxicline is directly controlled by the structural style of the lake margin.

  11. Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: I. An introduction to the project

    USGS Publications Warehouse

    Cohen, A.S.; Palacios-Fest, M. R.; McGill, J.; Swarzenski, P.W.; Verschuren, D.; Sinyinza, R.; Songori, T.; Kakagozo, B.; Syampila, M.; O'Reilly, C. M.; Alin, S.R.

    2005-01-01

    We investigated paleolimnological records from a series of river deltas around the northeastern rim of Lake Tanganyika, East Africa (Tanzania and Burundi) in order to understand the history of anthropogenic activity in the lake's catchment over the last several centuries, and to determine the impact of these activities on the biodiversity of littoral and sublittoral lake communities. Sediment pollution caused by increased rates of soil erosion in deforested watersheds has caused significant changes in aquatic communities along much of the lake's shoreline. We analyzed the effects of sediment discharge on biodiversity around six deltas or delta complexes on the east coast of Lake Tanganyika: the Lubulungu River delta, Kabesi River delta, Nyasanga/Kahama River deltas, and Mwamgongo River delta in Tanzania; and the Nyamuseni River delta and Karonge/Kirasa River deltas in Burundi. Collectively, these deltas and their associated rivers were chosen to represent a spectrum of drainage-basin sizes and disturbance levels. By comparing deltas that are similar in watershed attributes (other than disturbance levels), our goal was to explore a series of historical "experiments" at the watershed scale, with which we could more clearly evaluate hypotheses of land use or other effects on nearshore ecosystems. Here we discuss these deltas, their geologic and physiographic characteristics, and the field procedures used for coring and sampling the deltas, and various indicators of anthropogenic impact. ?? Springer 2005.

  12. Mitochondrial phylogeography of rock-dwelling cichlid fishes reveals evolutionary influence of historical lake level fluctuations of Lake Tanganyika, Africa.

    PubMed

    Verheyen, E; Rüber, L; Snoeks, J; Meyer, A

    1996-06-29

    The East African Lakes Tanganyika, Malawi and Victoria each harbour hundreds of endemic invertebrate and vertebrate species. Inferences about the ecological and evolutionary processes responsible for the origin of these species flocks will only be possible when they are made within historical and comparative frameworks. Specifically, the relative importance of intrinsic characteristics and extrinsic factors may offer information about the processes that drive diversification and speciation in these species. We investigated the sequence variation of a segment of the mitochondrial DNA control region of 32 populations representing all four nominal species in the three genera of eretmodine cichlids from Lake Tanganyika. Based on a phylogenetic analysis of these data we attempted to evaluate the importance of major lake level fluctuations on patterns of intralacustrine speciation. The geography of genetic variation reveals a high degree of within-lake endemism among genetically well-separated lineages distributed along the inferred shore lines of three historically intermittent lake basins. Seismic data indicate that extreme lowering of water levels in the Pleistocene caused the single Lake Tanganyika basin to split into three isolated ones. The strong phylogeographic structure of the Eretmodini, and the observation that some closely related populations occur on opposite shores of the lake, agree with this geological scenario. The three-clade-three-basin phylogeographic pattern was repeated twice within this tribe of cichlids. The phylogeographic pattern of eretmodine cichlids suggests that major fluctuations in the level of the lake have been important in shaping their adaptive radiation and speciation. The mitochondrially defined clades are in conflict with the current taxonomy of the group and suggest that there has been convergent evolution in trophic morphology, particularly in the shapes of oral teeth, taxonomically the most diagnostic characters of the three genera. PMID:8693021

  13. Effects of land-use change on aquatic biodiversity: A view from the paleorecord at Lake Tanganyika, East Africa

    Microsoft Academic Search

    Simone R. Alin; Catherine M. O'Reilly; Andrew S. Cohen; David L. Dettman; Manuel R. Palacios-Fest; Brent A. McKee

    2002-01-01

    Population growth and watershed deforestation in northwestern Tanzania threaten the biodiversity of Lake Tanganyika through erosion and habitat degradation. We used cores collected offshore from Gombe Stream National Park and a deforested watershed to re- construct how land-use changes in the Gombe Stream area since A.D. 1750 have affected lake biodiversity. Paleoenvironmental and paleoecological data reveal substantial changes in mass

  14. Greenwoodochromini Takahashi from Lake Tanganyika is a junior synonym of Limnochromini poll (Perciformes: Cichlidae).

    PubMed

    Takahashi, T

    2014-04-01

    The infraorbitals (IOs) of four species endemic to Lake Tanganyika were examined and on the basis of this information and previous morphological and molecular studies, the tribe Greenwoodochromini is synonymized with the tribe Limnochromini and a new combination for Limnochromis abeelei and Limnochromis staneri is proposed: Greenwoodochromis abeelei and Greenwoodochromis staneri. The revised tribe Limnochromini, comprising 10 species belonging to seven genera, is characterized by IOs representing types G and I. The revised genus Greenwoodochromis, which consists of four species, is characterized by IOs representing type I. PMID:24673106

  15. Recent climate variability signals in limnology and fisheries at Lake Tanganyika.

    NASA Astrophysics Data System (ADS)

    Plisnier, P.-D.

    2003-04-01

    Global climatic change affects Lake Tanganyika area. The rate of air temperature increase (+ 0.7 to 0.9 degree C in the last 30 years) is higher since the late seventies while the winds have decreased during the same period. This trend is confirmed in Lake Tanganyika by a warming of lake waters and a reduced thermocline depth in the North probably due to a lower tilting of this layer during the dry and windy season from May to September. Nutrients rich layers below the thermocline are now closer from the photic zone in the Northern end where transparency and oxic layers are also reduced. Weaker annual upwelling seem to result also from this changing climate conditions. The long term trend in the catches per units of the industrial fisheries shows a simultaneous marked decrease of the clupeids but an increase of Lates stappersi in the South. Climate oscillations partly tied to ENSO (El Ninõ/Southern Oscillation) can be correlated to fluctuating fish catches: e.g. Stolothrissa tanganyicae catches per unit are negatively correlated to El Niño events and inversely for Lates stappersi . Hypothesis are presented. An ongoing research project (CLIMLAKE) is presently investigating the variability of this ecosystem to allow paleo-climate reconstruction and possibly fisheries forecasting.

  16. Distribution of organic facies in recent sediments in northern part of Lake Tanganyika

    SciTech Connect

    Huc, A.Y.; Vandenbroucke, M.; Bessereau, G.; Le Fournier, J.

    1987-05-01

    A better understanding of the relation between the organic facies and the depositional environments is a basic prerequisite to allow predictions of the lateral variations of source rocks and then to achieve realistic quantitative evaluation of the petroleum potential of a sedimentary basin. Lake Tanganyika is a suitable example to address the problem of organic sedimentology in an environment related to a rifting situation. More than 400 dredged samples have been used to construct detailed maps of the organic facies in the surficial sediments of the northern part of Lake Tanganyika. These maps include Bujumbura and Rumonge basins. Beyond an apparent complex pattern, the distribution of the organic facies can be explained in terms of differential preservation and sedimentological processes including pelagic sedimentation on the top of structural blocks, winnowing processes which drive the low-density organic matter from the shallow agitated waters (above the thermocline) toward depocenters in the deepest parts of the basin, and gravity transport mechanisms which dispatch sediments together with their specific organic content along sedimentary transit pathways. In this lake the main biological precursors for the sedimentary organic matter are diatoms. Organic geochemical studies including kerogen analyses and pyrolysis-GC show that the preeminent factor controlling the quality of the organic material, principally its hydrogen richness (in other words, its petroleum potential), is the extent of its degradation which is closely related to the depositional environment (oxic environment above the thermocline versus anoxic environment below the thermocline).

  17. Primary production and rates of algal growth in Lake Tanganyika

    Microsoft Academic Search

    R. E. HECKY; E. J. FEE

    1981-01-01

    Ahtract In October-November 1975 the mean rate of integral prima *y production in Lake Tangan- yika was 1.4 g C.n-2.d-1 (for cloudless weather). The rang:e of values for daily integral primary production observed at this time of year over the whclle lake could occur at a single station in the course of a day. Small-scale spatial variability WLS equally extreme.

  18. Water-level fluctuations of Lake Tanganyika in phase with oceanic changes during the last glaciation and deglaciation

    Microsoft Academic Search

    Franpoise Gasse; Vincent Lédée; Marc Massault; Jean-Charles Fontes

    1989-01-01

    THERE has been considerable controversy about the magnitude of fluctuations of the levels of Lake Tanganyika, the Earth's second deepest lake (1,470 m), following the discovery of submerged valleys extending down to 550 m below present lake levels1. These fluctuations register changes in the precipitation\\/(evaporation + evapotranspiration) ratio in a large equatorial-tropical area of catchment, south of the Equator. Here

  19. Tectonic controls of sedimentary pathways and depocenters: Canyon conveyor belts and ridge rubbish on the Luiche River Platform Margin, Lake Tanganyika

    Microsoft Academic Search

    Leah Morgan; Kiram Lezzar

    Lake Tanganyika is an expression of the western branch of the East African rift system, a series of basins formed by overlapping half-grabens (Morley 1988) extending from Uganda to Malawi. Tanganyika, with an estimated age of 9 - 12 Ma, stretches 650 km from Burundi to Zambia, has a mean width of 50 km, a maximum depth of 1470 meters,

  20. Paleolimnology of Lake Tanganyika, East Africa, over the past 100 k yr

    USGS Publications Warehouse

    Scholz, C.A.; King, J.W.; Ellis, G.S.; Swart, Peter K.; Stager, J.C.; Colman, Steven M.

    2003-01-01

    New sediment core data from a unique slow-sedimentation rate site in Lake Tanganyika contain a much longer and continuous record of limnological response to climate change than have been previously observed in equatorial regions of central Africa. The new core site was first located through an extensive seismic reflection survey over the Kavala Island Ridge (KIR), a sedimented basement high that separates the Kigoma and Kalemie Basins in Lake Tanganyika. Proxy analyses of paleoclimate response carried out on core T97-52V include paleomagnetic and index properties, TOC and isotopic analyses of organic carbon, and diatom and biogenic silica analyses. A robust age model based on 11 radiocarbon (AMS) dates indicates a linear, continuous sedimentation rate nearly an order of magnitude slower here compared to other core sites around the lake. This age model indicates continuous sedimentation over the past 79 k yr, and a basal age in excess of 100 k yr. The results of the proxy analyses for the past ??? 20 k yr are comparable to previous studies focused on that interval in Lake Tanganyika, and show that the lake was about 350 m lower than present at the Last Glacial Maximum (LGM). Repetitive peaks in TOC and corresponding drops in ??13C over the past 79 k yr indicate periods of high productivity and mixing above the T97-52V core site, probably due to cooler and perhaps windier conditions. From ??? 80 through ??? 58 k yr the ??13C values are relatively negative (-26 to -28???) suggesting predominance of algal contributions to bottom sediments at this site during this time. Following this interval there is a shift to higher values of ??13C, indicating a possible shift to C-4 pathway-dominated grassland-type vegetation in the catchment, and indicating cooler, dryer conditions from ??? 55 k yr through the LGM. Two seismic sequence boundaries are observed at shallow stratigraphic levels in the seismic reflection data, and the upper boundary correlates to a major discontinuity near the base of T97-52V. We interpret these discontinuities to reflect major, prolonged drops in lake level below the core site (393 m), with the lower boundary correlating to marine oxygen isotope Stage 6. This suggests that the previous glacial period was considerably cooler and more arid in the equatorial tropics than was the last glacial period.

  1. Toward a generic method for studying water renewal, with application to the epilimnion of Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Gourgue, Olivier; Deleersnijder, Eric; White, Laurent

    2007-09-01

    We present a method, based on the concept of age and residence time, to study the water renewal in a semi-enclosed domain. We split the water of this domain into different water types. The initial water is the water initially present in the semi-enclosed domain. The renewing water is defined as the water entering the domain of interest. Several renewing water types may be considered depending on their origin. We present the equations for computing the age and the residence time of a certain water type. These timescales are of use to understand the rate at which the water renewal takes place. Computing these timescales can be achieved at an acceptable extra computer cost. The above-mentioned method is applied to study the renewal of epilimnion (i.e. the surface layer) water in Lake Tanganyika. We have built a finite element reduced-gravity model modified to take into account the water exchange between the epilimnion and the hypolimnion (i.e. the bottom layer), the water supply from precipitation and incoming rivers, and the water loss from evaporation and the only outgoing river. With our water renewal diagnoses, we show that the only significant process in the renewal of epilimnion water in Lake Tanganyika is the water exchange between the epilimnion and the hypolimnion, other phenomena being negligible.

  2. Lake Tanganyika as an evolutionary reservoir of old lineages of East African cichlid fishes: Inferences from allozyme data

    Microsoft Academic Search

    M. Nishida; Arap Siongok

    1991-01-01

    Genetic differences between 20 species of cichlid fish, representing all the 12 tribes proposed for the cichlid fish fauna of Lake Tanganyika, were studied by allozyme electrophoresis. Most species were genetically very differentiated from each other. Phylogenetic analysis based on the allozyme data indicated that at least seven old, ancestral lineages have contributed to the present cichlid fauna of the

  3. The dynamics of endemic diversification: Molecular phylogeny suggests an explosive origin of the thiarid gastropods of Lake Tanganyika

    Microsoft Academic Search

    E. Michel

    2000-01-01

    The endemic gastropod fauna of Lake Tanganyika is remarkable not only for its great species richness, but also for its unusually ornate and heavily calcified shell morphologies that are convergent with diverse marine forms. The origin and intralacustrine radiation of these thiarid gastropods have been debated since the late nineteenth century, as they are perhaps the most dramatic lacustrine radiation

  4. Geochemical and Sedimentological Records of Late Quaternary Climate Change, Lake Tanganyika, Tropical East Africa

    NASA Astrophysics Data System (ADS)

    Felton, A. A.; Russell, J. M.; Cohen, A. S.; Baker, M. E.; McGlue, M. M.; Lezzar, K. E.

    2005-12-01

    We have analyzed piston core records from Lake Tanganyika (western Tanzania, East African Rift Valley) to investigate possible signals of tropical paleoclimate change during the Late Quaternary. Long paleoclimate records from East Africa are of importance for understanding climatic processes such as the role of solar variability in regulating tropical climates at Milankovitch time scales, and the relationship between abrupt climate changes, migration of Intertropical Convergence Zone, and regional climate variability (Nicholson, 2000). However, records of pre-Holocene climate variability from tropical African lakes (>25ka) are still quite rare. Long records from Lake Tanganyika are of particular interest given the lake's antiquity and its demonstrated potential for producing high resolution (frequently annually laminated) sedimentary records (Cohen et al., 1993). We analyzed physical properties, grain size, total organic carbon, major, minor and trace element variability, and biogenic silica data for a 7.75 m core from the Kalya slope and horst region of central Lake Tanganyika at 640m water depth. Nine 14C dates provide an age model for the core, which spans ~62 cal kyr. Elemental concentrations preserved in Lake Tanganyika sediments record variability in deposition and runoff into the lake basin. Under conditions of rapid erosion, exposure and rapid weathering of bedrock has been shown to generate high concentrations of original silicate minerals enriched in soluble cations such as sodium and potassium, elements that are also biologically conservative. Prior to 40ka cal yr. core sediments are characterized by high magnetic susceptibility, intermediate levels of organic carbon, low to intermediate levels of biogenic silica, and fine grain size, indicative of relatively high precipitation. There is a profound decrease in magnetic susceptibility, a decrease in organic carbon and an increase in grain size at 40ka cal yr, which persists until ~16ka cal yr. Seismic reflection profiles demonstrate the existence of paleodeltas at ~360m below modern lake level that may have formed during this period, although it is unclear whether this deposit represents a Late Quaternary (OIS 2) or earlier (OIS 6) event. Maximum aridity occurred at about 20-20.5ka cal yr, consist with earlier interpretations of lake lowstands (Gasse et al., 1989, Scholz et al., 1997). The late Pleistocene and earliest Holocene sediments in our record are characterized by generally rising magnetic susceptibility, declining organic carbon and biogenic silica, and finer grain size. However during this period there are marked fluctuations in magnetic susceptibility and biogenic silica at millennial time-scales. These indicate intervals of fluctuating precipitation, productivity, and possibly windiness and are particularly prominent during the Pleistocene-Holocene transition. Massive clays, rising magnetic susceptibility, low biogenic silica and low organic carbon mark the early Holocene, indicative of increased rainfall during a regionally wet interval. These sediments are capped by a laminated ooze, indicative of drier conditions and a more stratified water body.

  5. High-Resolution Reconstructions of Temperature and Precipitation During the Last Millennium from Lake Tanganyika, Africa

    NASA Astrophysics Data System (ADS)

    Mayes, M.; Tierney, J.; Huang, Y.; Russell, J.

    2008-12-01

    Though numerous syntheses of high-resolution paleoclimate data have documented temperature changes associated with the Medieval Period, the Little Ice Age, and the Industrial era in north temperate regions, few records of temperature variability exist for the Southern Hemisphere (Mann and Jones, 2003, GRL doi: 10.1029/2003GL017814). Here, we present a new, high-resolution record of terrestrial temperature and rainfall from southeast tropical Africa, based upon organic geochemical analyses of annually laminated sediment cores from Lake Tanganyika, East Africa, providing the first millennium-long, high-resolution record of temperature from the East African tropics. Extending to 700CE with decadal resolution, the record uses the TEX86 paleothermometer and hydrogen stable isotope ratios (dD) of leaf waxes, which have been shown to reflect temperature and hydrologic conditions in Tanganyika, respectively (Tierney 2008, Science). The TEX86-based temperature reconstruction shows that Tanganyika temperatures were relatively warm at 700CE, cooler from 800-1000CE, and then warmer again between approximately 1050-1300CE. The latter warm interval is coincident with periods of warmer temperatures documented in the Northern Hemisphere. Yet temperatures are highly variable within the Little Ice Age (~1450-1800CE) and do not cool substantially relative to older time periods, in contrast to north temperate regions. Pronounced warming from approximately 1850 to the present is unprecedented in comparison to patterns of temperature variability during the previous centuries. The temperature variability documented here does not seem to correspond strongly to lake level fluctuations in Tanganyika over the past millennium (Cohen et al., 2005, JoPL, doi 10.1007/s10933-005- 2422-4), suggesting that Southeast African climate variability is more complex than alternating cycles of warm/wet and cool/dry conditions. dD analyses document considerable hydrologic variability over the past millennium, with temporal patterns that may be consistent with previous precipitation reconstructions from central East Africa. Overall, our records show that climate, particularly temperature, has changed abruptly during the past thousand years in southeast tropical Africa.

  6. Trematodes indicate animal biodiversity in the chilean intertidal and Lake Tanganyika

    USGS Publications Warehouse

    Hechinger, R.F.; Lafferty, K.D.; Kuris, A.M.

    2008-01-01

    Trematode communities in populations of estuarine snails can reflect surrounding animal diversity, abundance, and trophic interactions. We know less about the potential for trematodes to serve as bioindicators in other habitats. Here, we reanalyze data from 2 published studies concerning trematodes, 1 in the Chilean rocky intertidal zone and the other from the East African rift lake, Lake Tanganyika. Our analyses indicate that trematodes are more common in protected areas and that in both habitats they are directly and positively related to surrounding host abundance. This further supports the notion that trematodes in first intermediate hosts can serve as bioindicators of the condition of free-living animal communities in diverse ecosystems. ?? American Society of Parasitologists 2008.

  7. Persistent unstable atmospheric boundary layer enhances sensible and latent heat loss in a tropical great lake: Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Verburg, Piet; Antenucci, Jason P.

    2010-06-01

    Energy fluxes across the surface of lakes regulate heat storage and affect the water balance. Sensible and latent heat fluxes are affected by atmospheric stability, especially for large lakes. We examined the effect of atmospheric stability on the heat fluxes on seasonal time scales at Lake Tanganyika, East Africa, by estimating hourly sensible and latent heat fluxes and net radiation using thermistor chains and meteorological stations. The atmosphere was almost always unstable, in contrast to the atmosphere above North American Great Lakes which is unstable in winter and stable in summer. Persistent atmospheric instability resulted in a 13% and 18% increase in the annual mean heat loss by latent and sensible heat fluxes, respectively, relative to conditions of neutral stability. The persistent unstable atmosphere is caused by a higher water surface temperature compared with air temperature, which we argue is the case in general in (sub)tropical lakes. Low humidity further enhanced the frequency of unstable conditions and enhanced the exchange of heat and vapor from the lake to the atmosphere. The estimated heat fluxes were sensitive to the temporal scale of data inputs and to the local values of parameters such as air density. To our knowledge this is the first paper that demonstrates and quantifies the effect of atmospheric stability on latent and sensible heat fluxes from a lake on an annual basis, using data collected from the lake surface.

  8. Protist herbivory: a key pathway in the pelagic food web of Lake Tanganyika.

    PubMed

    Tarbe, Anne-Laure; Unrein, Fernando; Stenuite, Stephane; Pirlot, Samuel; Sarmento, Hugo; Sinyinza, Danny; Descy, Jean-Pierre

    2011-08-01

    Herbivory and bacterivory by phagotrophic protists were estimated in the southern basin of the oligotrophic Lake Tanganyika at different seasons (in the rainy season in February-March 2007 and in the dry season in July-August 2006 and September 2007), using two independent methods: the selective inhibitor technique for assessing community grazing on picocyanobacteria (PCya) and fluorescently labelled bacteria (FLB) and Synechococcus (FLA) to estimate bacterivory and herbivory by phagotrophic nanoflagellates (NF) and ciliates. Protistan grazing impact on both heterotrophic bacteria and PCya was mainly due to NF, which contributed up to 96% of the microbial grazing. There was a clear selection of FLA by protists. PCya represented the main carbon source for both flagellates and ciliates in the mixolimnion, accounting for an average of 83% of the total carbon obtained from the ingestion of picoplanktonic organisms. Protists were the main consumers of particulate primary production (46-74% depending on season). Significant seasonal variation of grazing rates (0.011-0.041 h(-1)) was found, chiefly following variation of PCya production and biomass. Assuming a growth efficiency of 0.4, total protozoan production varied seasonally (189-313 g C m(-2) day(-1)) and was roughly half of particulate phytoplankton production. This study provides evidence that NF and PCya were tightly coupled in Lake Tanganyika and that herbivory by protists may be one of the reasons why this great lake has high productivity. Our results bring support to the idea that microbial herbivory is a major process in oligotrophic freshwater systems. PMID:21336683

  9. Chloride concentrations in Lake Tanganyika: an indicator of the hydrological budget?

    NASA Astrophysics Data System (ADS)

    Branchu, Ph.; Bergonzini, Laurent

    On a historical time scale, this paper investigates the effect of hydroclimatic variations on the surface water salinity of Lake Tanganyika, the largest African lake and an open freshwater reservoir. Through annual water and chemical budgets, based on original and bibliographic data, a tracer of the water regime is proposed. Chloride, an inert and conservative element, seems to be the best candidate although its contribution to salinity is small; its use as a tracer of the water regime is validated on seasonal and historical time scales. Seasonally, a monthly water and chloride budget, constructed for an average year has been compared with data acquired in 1973. On a historical time scale, bibliographic data of chloride concentrations, compiled since 1939 have been compared with the level variation curve. The relation between lake level and surface water chloride concentration is significant on both time scales. Hence, the surface salinity/chlorinity of this freshwater lake is sensitive to hydroclimatic variations even if level variations are very limited in comparison with its great depth. This sensitivity is due mainly to the permanent thermo-haline stratification of the lake.

  10. Trace metal enrichments in Lake Tanganyika sediments: Controls on trace metal burial in lacustrine systems

    NASA Astrophysics Data System (ADS)

    Poulson Brucker, Rebecca; McManus, James; Severmann, Silke; Owens, Jeremy; Lyons, Timothy W.

    2011-01-01

    We investigate the distributions of several key diagenetic reactants (C, S, Fe) and redox-sensitive trace metals (Mo, Cd, Re, U) in sediments from Lake Tanganyika, East Africa. This study includes modern sediments from a chemocline transect, which spans oxygenated shallow waters to sulfidic conditions at depth, as well as ancient sediments from a longer core (˜2 m) taken at ˜900 m water depth. Modern sediments from depths spanning ˜70-335 m are generally characterized by increasing enrichments of C, S, Mo, Cd, and U with increasing water depth but static Fe distributions. It appears that the sedimentary enrichments of these elements are, to varying degrees, influenced by a combination of organic carbon cycling and sulfur cycling. These modern lake characteristics contrast with a period of high total organic carbon (C org), total sulfur (S Tot), and trace metal concentrations observed in the 900 m core, a period which follows the most recent deglaciation (˜18-11 ky). This interval is followed abruptly by an interval (˜11-6 ky) that is characterized by lower C, S, U, and Mo. Consistent with other work we suspect that the low concentrations of S, Mo, and U may indicate a period of intense lake mixing, during which time the lake may have been less productive and less reducing as compared to the present. An alternative, but not mutually exclusive, hypothesis is that changes in the lake's chemical inventory, driven by significant hydrological changes, could be influencing the distribution of sedimentary trace elements through time.

  11. A tribal level phylogeny of Lake Tanganyika cichlid fishes based on a genomic multi-marker approach.

    PubMed

    Meyer, Britta S; Matschiner, Michael; Salzburger, Walter

    2015-02-01

    The species-flocks of cichlid fishes in the East African Great Lakes Victoria, Malawi and Tanganyika constitute the most diverse extant adaptive radiations in vertebrates. Lake Tanganyika, the oldest of the lakes, harbors the morphologically and genetically most diverse assemblage of cichlids and contains the highest number of endemic cichlid genera of all African lakes. Based on morphological grounds, the Tanganyikan cichlid species have been grouped into 12-16 distinct lineages, so-called tribes. While the monophyly of most of the tribes is well established, the phylogenetic relationships among the tribes remain largely elusive. Here, we present a new tribal level phylogenetic hypothesis for the cichlid fishes of Lake Tanganyika that is based on the so far largest set of nuclear markers and a total alignment length of close to 18kb. Using next-generation amplicon sequencing with the 454 pyrosequencing technology, we compiled a dataset consisting of 42 nuclear loci in 45 East African cichlid species, which we subjected to maximum likelihood and Bayesian inference phylogenetic analyses. We analyzed the entire concatenated dataset and each marker individually, and performed a Bayesian concordance analysis and gene tree discordance tests. Overall, we find strong support for a position of the Oreochromini, Boulengerochromini, Bathybatini and Trematocarini outside of a clade combining the substrate spawning Lamprologini and the mouthbrooding tribes of the 'H-lineage', which are both strongly supported to be monophyletic. The Eretmodini are firmly placed within the 'H-lineage', as sister-group to the most species-rich tribe of cichlids, the Haplochromini. The phylogenetic relationships at the base of the 'H-lineage' received less support, which is likely due to high speciation rates in the early phase of the radiation. Discordance among gene trees and marker sets further suggests the occurrence of past hybridization and/or incomplete lineage sorting in the cichlid fishes of Lake Tanganyika. PMID:25433288

  12. A tribal level phylogeny of Lake Tanganyika cichlid fishes based on a genomic multi-marker approach

    PubMed Central

    Meyer, Britta S.; Matschiner, Michael; Salzburger, Walter

    2015-01-01

    The species-flocks of cichlid fishes in the East African Great Lakes Victoria, Malawi and Tanganyika constitute the most diverse extant adaptive radiations in vertebrates. Lake Tanganyika, the oldest of the lakes, harbors the morphologically and genetically most diverse assemblage of cichlids and contains the highest number of endemic cichlid genera of all African lakes. Based on morphological grounds, the Tanganyikan cichlid species have been grouped into 12–16 distinct lineages, so-called tribes. While the monophyly of most of the tribes is well established, the phylogenetic relationships among the tribes remain largely elusive. Here, we present a new tribal level phylogenetic hypothesis for the cichlid fishes of Lake Tanganyika that is based on the so far largest set of nuclear markers and a total alignment length of close to 18 kb. Using next-generation amplicon sequencing with the 454 pyrosequencing technology, we compiled a dataset consisting of 42 nuclear loci in 45 East African cichlid species, which we subjected to maximum likelihood and Bayesian inference phylogenetic analyses. We analyzed the entire concatenated dataset and each marker individually, and performed a Bayesian concordance analysis and gene tree discordance tests. Overall, we find strong support for a position of the Oreochromini, Boulengerochromini, Bathybatini and Trematocarini outside of a clade combining the substrate spawning Lamprologini and the mouthbrooding tribes of the ‘H-lineage’, which are both strongly supported to be monophyletic. The Eretmodini are firmly placed within the ‘H-lineage’, as sister-group to the most species-rich tribe of cichlids, the Haplochromini. The phylogenetic relationships at the base of the ‘H-lineage’ received less support, which is likely due to high speciation rates in the early phase of the radiation. Discordance among gene trees and marker sets further suggests the occurrence of past hybridization and/or incomplete lineage sorting in the cichlid fishes of Lake Tanganyika. PMID:25433288

  13. Paleolimnologic Evidence for Decadal to Centurial Scale Climate & Productivity Linkages in Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Cohen, A.; Lezzar, K. E.; Cole, J. E.; Dettman, D. L.; Eagle, M. J.; Michelo, V.; Zilifi, D.; Chororoka, K.; Plisnier, P.; Ellis, G.

    2001-12-01

    An annually resolved, paleoclimate record from Lake Tanganyika, East Africa, from ~1200BC-800AD, provides evidence for strong linkages between precipitation and lacustrine productivity, on ~37-52yr, 52-90yr, and 166-250yr cycles, as well as weaker linkages on interannual and ENSO time scales. The longer periodicities are consistent with solar cycles, previously linked to paleoprecipitation variability in East Africa. Coastal platform cores from the lake consistently display cyclic bundling of laminae, with alternating clusters of thick and thin laminations. Paired light and dark laminae record the flux of dry, windy season sediments (diatom ooze), formed by productive upwelling conditions, alternating with wet, calm season terrigenous deposits, respectively. We hypothesize that the alternating bundles of thick and thin laminae record decadal to centurial scale variation in terrestrial runoff, which in turn regulates the recharging of the lake's deep-water nutrient pool. Windy-season upwelling of nutrient rich water regularly depletes the deep-water phosphorous pool, which must be resupplied by terrestrially derived P. Although the deep-water nutrient pool greatly exceeds the annual terrestrial input and sedimentary export of P, over time declining nutrient inputs will eventually reduce deep-water P concentrations and diminish primary productivity. Because fisheries productivity in Lake Tanganyika ( ~200,000 t y-1) is closely linked to the regeneration of sequestered nutrients from the metalimnion to surface waters, understanding the long term relationship between nutrient recharge and climate is important to the region's economy. On an annual cycle this production is linked to seasonal, wind-driven upwelling, but at longer time scales, precipitation and P-rich runoff may be more important. Mass balance considerations suggest that the deep-water P pool of the lake is currently out of equilibrium, increasing by ~0.1% yr-1, as a result of external P loading from both the watershed and rainfall. Understanding how the nutrient pool is recharged at longer time scales is also critical for long-term planning, as the region enters a period of significant lake warming, which, in the short term, is likely to increase water column stability, reduce deep water mixing, and counteract external P loading.

  14. Chalinochromis cyanophleps, a new species of cichlid fish (Teleostei: Cichlidae) from Lake Tanganyika.

    PubMed

    Kullander, Sven O; Karlsson, Mikael; Karlsson, Magnus; Norén, Michael

    2014-01-01

    Chalinochromis cyanophleps is described from nine specimens, the largest 129 mm SL, from Namansi. It differs from other species of Chalinochromis in plain trunk colouration, absence of black stripes on the head, relatively narrow lips, presence of tricuspid jaw teeth, and presence of five rather than four dentary lateralis foramina. The blue iridescent stripe below the eye is shared with other lamprologin cichlids, but is broader and more conspicuous in C. cyanophleps. Chalinochromis cyanophleps occurs at depths between 6 and 45 m in rocky habitats along the Tanzanian coast of Lake Tanganyika, from Mvuna Island south to Kalala Island, a stretch of about 90 km. Field observations were made of specimens up to 18 cm total length. The COI DNA barcode sequence differs by 1.8% from that of C. popelini. PMID:24869876

  15. Testing the stages model in the adaptive radiation of cichlid fishes in East African Lake Tanganyika.

    PubMed

    Muschick, Moritz; Nosil, Patrik; Roesti, Marius; Dittmann, Marie Theres; Harmon, Luke; Salzburger, Walter

    2014-11-22

    Adaptive radiation (AR) is a key process in the origin of organismal diversity. However, the evolution of trait disparity in connection with ecological specialization is still poorly understood. Available models for vertebrate ARs predict that diversification occurs in the form of temporal stages driven by different selective forces. Here, we investigate the AR of cichlid fishes in East African Lake Tanganyika and use macroevolutionary model fitting to evaluate whether diversification happened in temporal stages. Six trait complexes, for which we also provide evidence of their adaptiveness, are analysed with comparative methods: body shape, pharyngeal jaw shape, gill raker traits, gut length, brain weight and body coloration. Overall, we do not find strong evidence for the 'stages model' of AR. However, our results suggest that trophic traits diversify earlier than traits implicated in macrohabitat adaptation and that sexual communication traits (i.e. coloration) diversify late in the radiation. PMID:25274371

  16. Genetic basis of male colour dimorphism in a Lake Tanganyika cichlid fish.

    PubMed

    Takahashi, T; Sota, T; Hori, M

    2013-06-01

    Phenotypic polymorphisms can be applied to study the micro-evolutionary forces that maintain genetic variation and can mediate speciation, but it can be difficult to determine the genetic basis of polymorphisms. Recently, restriction-site-associated DNA (RAD) sequencing has become popular, which can easily produce multiple single nucleotide polymorphisms from whole genomes. Here, we combined RAD sequencing, allele-specific PCR and Sanger sequencing to determine the genetic basis underlying male colour dimorphism of a Lake Tanganyika cichlid fish, Cyprichromis leptosoma. Our analyses using both a cross-family (two parents and 12 F2 males) and 64 wild individuals do not contradict a hypothesis that two alleles of one-locus control male colour dimorphism. Also, the locus may be located on a genome region that experiences reduced levels of recombination. Although more analyses will be needed to conclude these findings, this study is the first to suggest the genetic basis of a colour polymorphism using RAD sequencing. PMID:23176589

  17. Nocturnal claroteine catfishes reveal dual colonisation but a single radiation in Lake Tanganyika.

    PubMed

    Peart, Claire R; Bills, Roger; Wilkinson, Mark; Day, Julia J

    2014-04-01

    Lake Tanganyika (LT) is a biodiversity hotspot supporting many endemic radiations that provide comparative systems in which to investigate if there are common factors leading to the build-up of its considerable diversity. Despite LT containing the highest diversity of lacustrine catfishes on Earth, the evolutionary relationships of nocturnal catfishes within the sub-family Claroteinae have not been investigated and it is unknown if its constituent genera have diversified via single or independent colonisation events. We report the first molecular phylogeny of the LT claroteine catfishes based on a multigene dataset (three nuclear markers, two mitochondrial totalling 4227 bp), including 85 samples from LT and outside of the lake basin. These data support LT claroteine monophyly, with the exclusion of the LT endemic Chrysichthys brachynema that independently colonised the lake but has not radiated. Multiple sampling localities from LT and the use of Bayesian species delimitation methods reveal additional locally restricted diversity within the LT Claroteinae clade. Fossil calibrated molecular divergence dates suggest that diversification occurred within full lake conditions as demonstrated in other LT lineages. PMID:24503480

  18. Strontium isotopes and rare-earth element geochemistry of hydrothermal carbonate deposits from Lake Tanganyika, East Africa

    Microsoft Academic Search

    J. A. Barrat; J. Boulègue; J. J. Tiercelin; M. Lesourd

    2000-01-01

    At Cape Banza (North Tanganyika Lake), fluids and aragonite chimneys have been collected many times since the discovery of this sublacustrine field in 1987. This sampling has been investigated here for the Sr isotopic compositions and the rare-earth element features of the carbonates and a few fluid samples. The 87Sr\\/86Sr ratios of the chimneys indicate that they have precipitated from

  19. Insights into the evolution of freshwater sponges (Porifera: Demospongiae: Spongillina): Barcoding and phylogenetic data from Lake Tanganyika endemics indicate multiple invasions and unsettle existing taxonomy.

    PubMed

    Erpenbeck, Dirk; Weier, Tina; de Voogd, Nicole J; Wörheide, Gert; Sutcliffe, Patricia; Todd, Jonathan A; Michel, Ellinor

    2011-10-01

    Sponges are a conspicuous element in many benthic habitats including in Africa's oldest, deepest lake, Lake Tanganyika. Despite their prevalence and pivotal ecological role as filter feeders, knowledge of the evolutionary history of sponges is in its infancy. Here, we provide the first molecular analysis targeting the evolution of sponges from Lake Tanganyika. Independent markers indicate the occurrence of several colonisation events which have shaped the current Tanganyikan lacustrine sponge biodiversity. This is in contrast to a range of previously studied organisms that have diversified within the lake from single lineages. Our tree reconstructions indicate the presence of two genera, Oncosclera and Eunapius, which are globally distributed. Therefore, we reject the hypothesis of monophyly for the sponges from Lake Tanganyika and challenge existing higher taxonomic structure for freshwater sponges. PMID:21669294

  20. A new mastacembelid species from Lake Tanganyika: a case of complex evolutionary history.

    PubMed

    Vreven, E J; Snoeks, J

    2009-10-01

    A detailed morphometric study of 123 specimens identified as Mastacembelus albomaculatus and the six syntypes of M. tanganicae was undertaken. On each specimen, 27 morphometric measurements and 12 meristics were taken. The type series of M. tanganicae contains more than one species, with four specimens attributed to a new species M. reygeli sp. nov. A redescription of M. albomaculatus and a description of the new species are provided. Both species are endemic to the northern and central part of Lake Tanganyika. They can be distinguished based on the number of caudal vertebrae [47-52 (median 49) in M. albomaculatus v. 42-46 (44) in M. reygeli sp. nov.], the total number of vertebrae [85-90 (88) v. 78-83 (81)] and the distance from the snout to the last externally visible dorsal spine (S-LDS) [61.8-67.0 (mean 64.0) v. 66.6-71.5 (68.6)% L(S)]. In addition, intermediate specimens and populations between M. albomaculatus and M. reygeli were discovered from several parts of the lake, but mainly from the southern part. The latter intermediate populations were provisionally identified as introgressed populations. PMID:20738596

  1. Effects of land-use change on aquatic biodiversity: A view from the paleorecord at Lake Tanganyika, East Africa

    NASA Astrophysics Data System (ADS)

    Alin, Simone R.; O'Reilly, Catherine M.; Cohen, Andrew S.; Dettman, David L.; Palacios-Fest, Manuel R.; McKee, Brent A.

    2002-12-01

    Population growth and watershed deforestation in northwestern Tanzania threaten the biodiversity of Lake Tanganyika through erosion and habitat degradation. We used cores collected offshore from Gombe Stream National Park and a deforested watershed to reconstruct how land-use changes in the Gombe Stream area since A.D. 1750 have affected lake biodiversity. Paleoenvironmental and paleoecological data reveal substantial changes in mass accumulation rates for sediment and organic matter, nitrogen stable isotope values, and benthic species composition offshore from the deforested watershed since 1880. Comparable changes were not observed offshore from the park.

  2. Ostracode trace metal geochemistry from Lake Tanganyika, Africa: Towards the development of a lacustrine paleothermometer

    NASA Astrophysics Data System (ADS)

    Ash, J.; Cohen, A. S.; Reiners, P. W.; Dettman, D. L.

    2011-12-01

    The development of quantitative lacustrine paleotemperature records is critical to understanding how past climate changes influenced the ecology and hydrology of lakes. Whereas paleoecological transfer functions, TEX-86 and clumped isotopes are all widely applied methods, all have their limitations. We aim to further the development of an alternative method with wider applications: ostracode trace metal geochemistry. Trace element compositions of ostracode valves reflect discriminatory element uptake that in turn reflect ambient environmental conditions and have previously shown promise for quantitative paleotemperature determination. Understanding the specific environmental controls on element concentrations and ratios is an area of active research with much attention focusing on Mg/Ca and Sr/Ca ratios and their relationships with temperature and salinity. Here, HR-ICP-MS geochemical analyses of ostracode valves are compared to an existing TEX-86 temperature record as well as gastropod stable isotopes from Lake Tanganyika, Africa. Two ostracode species (M. opaca and R. ampla) were chosen for analyses from core LT-98-58 (1759 +/- 133 AD-modern). Molar Mg/Ca ratios for M. opaca range from .04 to .16, and a trend towards increased Mg/Ca begins around 1880 AD. Molar Mg/Ca ratios for R. ampla range from .05 to .2, and no trend is discernable. Sr/Ca ratios in both species range from .003-.006 and remain relatively stable, indicating that changes in Mg/Ca are the result of temperature rather than salinity. The M. opaca Mg/Ca record closely resembles the existing TEX-86 paleotemperature record of Tierney et al. (2010) for the past ~240 yr. We intend these preliminary results to facilitate the future research and use of ostracode trace metal geochemistry in a wide range of lakes for paleotemperature reconstruction.

  3. Evolutionary Relationships in the Sand-Dwelling Cichlid Lineage of Lake Tanganyika Suggest Multiple Colonization of Rocky Habitats and Convergent Origin of Biparental Mouthbrooding

    Microsoft Academic Search

    Stephan Koblmüller; Walter Salzburger; Christian Sturmbauer

    2004-01-01

    The cichlid species flock of Lake Tanganyika is comprised of seven seeding lineages that evolved in step with changes of the lake environment. One seeding lineage diversified into at least six lineages within a short period of time. Our study focuses on the diversification of one of these lineages, the Ectodini, comprising highly specialized, sand- and rock-dwelling species. They display

  4. Phylogeny of the Lake Tanganyika Cichlid Species Flock and Its Relationship to the Central and East African Haplochromine Cichlid Fish Faunas

    Microsoft Academic Search

    Walter Salzburger; Axel Meyer; Sanja Baric; Erik Verheyen; Christian Sturmbauer

    2002-01-01

    Lake Tanganyika, the oldest of the East African Great Lakes, harbors the ecologically, mor- phologically, and behaviorally most complex of all assemblages of cichlid éshes, consisting of about 200 described species. The evolutionary old age of the cichlid assemblage, its extreme degree of mor- phological differentiation, the lack of species with intermediate morphologies, and the rapidity of lineage formation have

  5. Phenotypic integration of brain size and head morphology in Lake Tanganyika Cichlids

    PubMed Central

    2014-01-01

    Background Phenotypic integration among different anatomical parts of the head is a common phenomenon across vertebrates. Interestingly, despite centuries of research into the factors that contribute to the existing variation in brain size among vertebrates, little is known about the role of phenotypic integration in brain size diversification. Here we used geometric morphometrics on the morphologically diverse Tanganyikan cichlids to investigate phenotypic integration across key morphological aspects of the head. Then, while taking the effect of shared ancestry into account, we tested if head shape was associated with brain size while controlling for the potentially confounding effect of feeding strategy. Results The shapes of the anterior and posterior parts of the head were strongly correlated, indicating that the head represents an integrated morphological unit in Lake Tanganyika cichlids. After controlling for phylogenetic non-independence, we also found evolutionary associations between head shape, brain size and feeding ecology. Conclusions Geometric morphometrics and phylogenetic comparative analyses revealed that the anterior and posterior parts of the head are integrated, and that head morphology is associated with brain size and feeding ecology in Tanganyikan cichlid fishes. In light of previous results on mammals, our results suggest that the influence of phenotypic integration on brain diversification is a general process. PMID:24593160

  6. Reverse evolution in RH1 for adaptation of cichlids to water depth in Lake Tanganyika.

    PubMed

    Nagai, Haruka; Terai, Yohey; Sugawara, Tohru; Imai, Hiroo; Nishihara, Hidenori; Hori, Michio; Okada, Norihiro

    2011-06-01

    Reverse evolution is a widespread phenomenon in biology, but the genetic mechanism for the reversal of a genetic change for adaptation to the ancestral state is not known. Here, we report the first case of complete reverse evolution of two amino acids, serine and alanine, at a single position in RH1 opsin pigment for adaptation to water depth. We determined RH1 sequences of cichlid fishes from four tribes of Lake Tanganyika with different habitat depths. Most of the species were divided into two types: RH1 with 292A for species in shallow water or 292S for species in deep water. Both types were adapted to their ambient light environments as indicated by the absorption spectra of the RH1 pigments. Based on the RH1 locus tree and ecological data, we inferred the ancestral amino acids at position 292 and the distribution of the depth ranges (shallow or deep) of ancestral species of each tribe. According to these estimates, we identified two distinct parallel adaptive evolutions: The replacement A292S occurred at least four times for adaptation from shallow to deep water, and the opposite replacement S292A occurred three times for adaptation from deep to shallow water. The latter parallelism represents the complete reverse evolution from the derived to the ancestral state, following back adaptive mutation with reversal of the RH1 pigment function accompanied by reversal of the species habitat shift. PMID:21172834

  7. Mapping landslide processes in the North Tanganyika - Lake Kivu rift zones: towards a regional hazard assessment

    NASA Astrophysics Data System (ADS)

    Dewitte, Olivier; Monsieurs, Elise; Jacobs, Liesbet; Basimike, Joseph; Delvaux, Damien; Draida, Salah; Hamenyimana, Jean-Baptiste; Havenith, Hans-Balder; Kubwimana, Désiré; Maki Mateso, Jean-Claude; Michellier, Caroline; Nahimana, Louis; Ndayisenga, Aloys; Ngenzebuhoro, Pierre-Claver; Nkurunziza, Pascal; Nshokano, Jean-Robert; Sindayihebura, Bernard; Philippe, Trefois; Turimumahoro, Denis; Kervyn, François

    2015-04-01

    The mountainous environments of the North Tanganyika - Lake Kivu rift zones are part of the West branch of the East African Rift. In this area, natural triggering and environmental factors such as heavy rainfalls, earthquake occurrences and steep topographies favour the concentration of mass movement processes. In addition anthropogenic factors such as rapid land use changes and urban expansion increase the sensibility to slope instability. Until very recently few landslide data was available for the area. Now, through the initiation of several research projects and the setting-up of a methodology for data collection adapted to this data-poor environment, it becomes possible to draw a first regional picture of the landslide hazard. Landslides include a wide range of ground movements such as rock falls, deep failure of slopes and shallow debris flows. Landslides are possibly the most important geohazard in the region in terms of recurring impact on the populations, causing fatalities every year. Many landslides are observed each year in the whole region, and their occurrence is clearly linked to complex topographic, lithological and vegetation signatures coupled with heavy rainfall events, which is the main triggering factor. Here we present the current knowledge of the various slope processes present in these equatorial environments. A particular attention is given to urban areas such as Bukavu and Bujumbura where landslide threat is particularly acute. Results and research perspectives on landslide inventorying, monitoring, and susceptibility and hazard assessment are presented.

  8. High-Resolution Geochemical and Paleoecological Records of Climate Change Since the Late Glacial at Lake Tanganyika, East Africa

    NASA Astrophysics Data System (ADS)

    Alin, S. R.; Cohen, A. S.

    2002-12-01

    We used high-resolution geochemical and paleoecological records from shallow-water sediment cores to refine previous descriptions of climatic conditions at Lake Tanganyika, East Africa, for the period from the Late Glacial to the present. Radiocarbon and 210Pb dating were used to establish chronologies for the cores. Sedimentological changes indicate that lake level has risen approximately 50-70 m since the Late Glacial. A depositional hiatus occurred between 6.4 and 11.4 ka BP (all dates in calendar years) in several of the shallow-water cores. Elemental abundance (%C, %N) and stable isotopic (?15N, ?13C) data for one core suggest that substantial changes in primary productivity and nutrient recycling regimes have occurred since 6.4 ka BP. Carbonate and ostracode crustacean preservation were low and nil, respectively, prior to 2.4 ka BP. Generally, these data support previous interpretations of regional paleoclimate and lake conditions, with wet and warm conditions during the interval from 6.4 to 4.0 ka, and increasingly arid conditions since 2.4 ka. However, for the interval from 4.0 to 2.4 ka, paleoenvironmental indicators (?15N, reduced carbonate and ostracode preservation) suggest that the central part of Lake Tanganyika was stably stratified at a shallower depth than present as a result of diminished southerly trade winds. After 2.4 ka BP, sedimentary carbonate concentrations increase, and ?13C values become enriched, suggesting that lacustrine productivity increased with the resumption of deeper wind-driven mixing, lasting until 1 ka BP. For post-2.4 ka samples, species abundance data for ostracodes were used to generate an ostracode water depth index (OWDI). OWDI indicated that severe drought conditions were persistent or recurred at Lake Tanganyika between 1550 and 1850 A.D. Droughts resulted in marked lowstands at Lake Tanganyika at 1580+/-15 A.D., 1730+/-35 A.D., and 1800+/-30 A.D. These data contribute new information on the timing of Little Ice Age droughts and Mid-Late Holocene changes in trade wind intensity in tropical East Africa.

  9. Effects of Local Farming and Deforestation on Sediment Discharge Inferred From Sediment Accumulation Rates and Patterns in Lake Core Records From Coastal Lake Tanganyika, East Africa

    NASA Astrophysics Data System (ADS)

    Strickler, M. L.; Lezzar, K. E.; Soreghan, M.; Cohen, A. S.; Swarzenski, P. W.; Berke, M.; McHeni, M.; Gunderson, K.; Allen, K.; Palke, A.; Modesta, M.; Nkotagu, H.

    2006-12-01

    Lake Tanganyika is the oldest and largest of the East African rift lakes and vital to the economy of the surrounding villages and countries. Deforestation around the lake causes many negative effects from an increased sediment flux and has changed dramatically as a function of population. Increases in inorganic sediment flux from deforested watersheds and an associated decrease in organic sediment flux may negatively impact the viability of littoral habitats in the lake. This study examines the interrelationship between deforestation on streams that feed into Lake Tanganyika and sedimentation offshore. We mapped stream morphology of two distinct streams: Kalande (Gombe Stream National Park), and Ngelwa (deforested). An offshore core was collected from the lake bottom just offshore of the deforested Ngelwa stream at a water depth of 106m and dated using 14C and 210Pb geochronologic methods. In addition, multiple laboratory analyses were performed on the core and within the streams to help constrain sedimentation and deforestation effects. Three distinct units within the core correlate to reflect changes in sedimentation (higher rates as deforestation continues) in addition to a shift from dry, low lake level conditions to wet, high lake levels as evidenced by shifts in core lithologies, diatom taxonomy and content, magnetic susceptibility, and clastic particle size. Streambed and suspended sediment analyses reflect high levels of erosion in deforested watersheds coupled with changes in dissolved nutrients in the water (silica, orthophosphate), which may suggest an overall diminished level of ecosystem function in deforested and heavily farmed watersheds.

  10. Rapid radiation, ancient incomplete lineage sorting and ancient hybridization in the endemic Lake Tanganyika cichlid tribe Tropheini.

    PubMed

    Koblmüller, Stephan; Egger, Bernd; Sturmbauer, Christian; Sefc, Kristina M

    2010-04-01

    The evolutionary history of the endemic Lake Tanganyika cichlid tribe Tropheini, the sister group of the species flocks of Lake Malawi and the Lake Victoria region, was reconstructed from 2009 bp DNA sequence of two mitochondrial genes (ND2 and control region) and from 1293 AFLP markers. A period of rapid cladogenesis at the onset of the diversification of the Tropheini produced a multitude of specialized, predominantly rock-dwelling aufwuchs-feeders that now dominate in Lake Tanganyika's shallow habitat. Nested within the stenotopic rock-dwellers is a monophyletic group of species, which also utilize more sediment-rich habitat. Most of the extant species date back to at least 0.7 million years ago. Several instances of disagreement between AFLP and mtDNA tree topology are attributed to ancient incomplete lineage sorting, introgression and hybridization. A large degree of correspondence between AFLP clustering and trophic types indicated fewer cases of parallel evolution of trophic ecomorphology than previously inferred from mitochondrial data. PMID:19853055

  11. A 60,000-yr record of climate in Southeast Tropical Africa: Preliminary results from Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Tierney, J.; Russell, J.

    2006-12-01

    Few paleoclimate records exist that record high-frequency climate variability within tropical Africa, particularly during Marine Isotope Stage 3 (30-60,000 years BP). Thus very little is known about the potential role or response the region may have with regards to high-latitude abrupt climate change. However, climate variability in tropical East Africa is linked to large-scale changes in the convective intensity and location of the inter- tropical convergence zone (ITCZ) and the strength of the seasonal monsoonal winds from both the Atlantic and Indian Oceans. Understanding tropical African climate history may illuminate the causes and amplifying mechanisms of global climate change. We present here a multiproxy record of 60,000 years of climate variability from the sediments of Lake Tanganyika, southeast tropical Africa, which addresses outstanding questions regarding the role of East Africa in the context of abrupt climate change. Continuously accumulating hemipelagic sediments recovered from 650 m water depth from the southern half of Lake Tanganyika record hydrologic variability, terrestrial paleoenvironments, and changes in wind-driven upwelling intensity. Major element variations in Tanganyika sediments measured at 1 mm resolution by scanning XRF resolve changes in sediment geochemistry over decadal to centennial timescales, shedding light on the amplitude and frequency of short-term climate variability in this region. Additionally, records of bulk stable isotopes (?13C, ?15N), compound- specific ?D, and biogenic silica indicate rapid, dramatic changes in lake productivity, vegetation, and rainfall over millennial time-scales from Marine Isotope Stage 3 to present, including the Younger Dryas. In the case of the latter, the Younger Dryas is manifest in Lake Tanganyika as a sedimentary sequence of low diatom content, indicating reductions in southerly monsoonal windspeed and lake upwelling, and hydrogen isotope data over this interval indicate significant changes in moisture balance. These data suggest that the ITCZ occupied a more southerly position over Africa during the Younger Dryas, an interpretation consistent with previous studies conducted in this region. Older millennial-scale events exhibit similar lithological and geochemical changes, suggesting analogous shifts in the ITCZ over tropical Africa during Marine Isotope Stage 3.

  12. A molecular perspective on Late Quaternary climate and vegetation change in the Lake Tanganyika basin, East Africa

    NASA Astrophysics Data System (ADS)

    Tierney, Jessica E.; Russell, James M.; Huang, Yongsong

    2010-03-01

    Characterizing the nature of past hydrological change and its interactions with vegetation is fundamental to acquiring a better understanding of continental tropical climate dynamics. Here, we outline major shifts in the climate and ecosystem of tropical East Africa for the past 60,000 years (60 ka) by examining molecular records of hydrology, vegetation, and temperature from a sediment sequence from Lake Tanganyika. We demonstrate, via comparison with pollen spectra, that stable carbon isotopes measured on higher plant leaf waxes ( ?13C wax) are a reliable proxy for vegetation change. In addition we argue that the D/H ratio of higher plant leaf waxes ( ?D wax) is a robust and independent indicator of past changes in aridity, and is not affected by regional vegetation change directly. Our paired, compound-specific isotope data show that shifts in vegetation lead major changes in hydrology in the Tanganyika basin at several major climate transitions during the past 60,000 years, suggesting that vegetation in the Tanganyika basin is not as sensitive to aridity as previous studies have suggested and that variations in carbon dioxide, temperature, and internal ecosystem dynamics are equally, if not more, important. We hypothesize that regional vegetation change may exert a positive feedback on regional hydrology, thus partially accounting for the abrupt threshold behavior evident in our paleohydrological data. Furthermore, we find that past changes in Tanganyika basin climate and ecology are closely linked to concentrations of atmospheric trace gases, highlighting the paramount influence of global climatic shifts upon regional tropical climate over glacial/interglacial timescales.

  13. Colour-assortative mating among populations of Tropheus moorii, a cichlid fish from Lake Tanganyika, East Africa

    PubMed Central

    Salzburger, Walter; Niederstätter, Harald; Brandstätter, Anita; Berger, Burkhard; Parson, Walther; Snoeks, Jos; Sturmbauer, Christian

    2005-01-01

    The species flocks of cichlid fishes in the East African Lakes Tanganyika, Malawi and Victoria are prime examples of adaptive radiation and explosive speciation. Several hundreds of endemic species have evolved in each of the lakes over the past several thousands to a few millions years. Sexual selection via colour-assortative mating has often been proposed as a probable causal factor for initiating and maintaining reproductive isolation. Here, we report the consequences of human-mediated admixis among differentially coloured populations of the endemic cichlid fish Tropheus moorii from several localities that have accidentally been put in sympatry in a small harbour bay in the very south of Lake Tanganyika. We analysed the phenotypes (coloration) and genotypes (mitochondrial control region and five microsatellite loci) of almost 500 individuals, sampled over 3 consecutive years. Maximum-likelihood-based parenthood analyses and Bayesian inference of population structure revealed that significantly more juveniles are the product of within-colour-morph matings than could be expected under the assumption of random mating. Our results clearly indicate a marked degree of assortative mating with respect to the different colour morphs. Therefore, we postulate that sexual selection based on social interactions and female mate choice has played an important role in the formation and maintenance of the different colour morphs in Tropheus, and is probably common in other maternally mouthbrooding cichlids as well. PMID:16543167

  14. Estimating the age of formation of lakes: An example from Lake Tanganyika, East African Rift system

    Microsoft Academic Search

    A. Cohen; M. J. Soreghan; C. A. Scholz

    1993-01-01

    Age estimates for ancient lakes are important for determining their histories and their rates of biotic and tectonic evolution. In the absence of dated core material from the lake`s sedimentary basement, several techniques have been used to generate such age estimates. The most common of these, herein called the reflection seismic-radiocarbon method (RSRM), combines estimates of short-term sediment-accumulation rates derived

  15. Contrasting parasite communities among allopatric colour morphs of the Lake Tanganyika cichlid Tropheus

    PubMed Central

    2013-01-01

    Background Adaptation to different ecological environments is thought to drive ecological speciation. This phenomenon culminates in the radiations of cichlid fishes in the African Great Lakes. Multiple characteristic traits of cichlids, targeted by natural or sexual selection, are considered among the driving factors of these radiations. Parasites and pathogens have been suggested to initiate or accelerate speciation by triggering both natural and sexual selection. Three prerequisites for parasite-driven speciation can be inferred from ecological speciation theory. The first prerequisite is that different populations experience divergent infection levels. The second prerequisite is that these infection levels cause divergent selection and facilitate adaptive divergence. The third prerequisite is that parasite-driven adaptive divergence facilitates the evolution of reproductive isolation. Here we investigate the first and the second prerequisite in allopatric chromatically differentiated lineages of the rock-dwelling cichlid Tropheus spp. from southern Lake Tanganyika (Central Africa). Macroparasite communities were screened in eight populations belonging to five different colour morphs. Results Parasite communities were mainly composed of acanthocephalans, nematodes, monogeneans, copepods, branchiurans, and digeneans. In two consecutive years (2011 and 2012), we observed significant variation across populations for infection with acanthocephalans, nematodes, monogeneans of the genera Gyrodactylus and Cichlidogyrus, and the copepod Ergasilus spp. Overall, parasite community composition differed significantly between populations of different colour morphs. Differences in parasite community composition were stable in time. The genetic structure of Tropheus populations was strong and showed a significant isolation-by-distance pattern, confirming that spatial isolation is limiting host dispersal. Correlations between parasite community composition and Tropheus genetic differentiation were not significant, suggesting that host dispersal does not influence parasite community diversification. Conclusions Subject to alternating episodes of isolation and secondary contact because of lake level fluctuations, Tropheus colour morphs are believed to accumulate and maintain genetic differentiation through a combination of vicariance, philopatric behaviour and mate discrimination. Provided that the observed contrasts in parasitism facilitate adaptive divergence among populations in allopatry (which is the current situation), and promote the evolution of reproductive isolation during episodes of sympatry, parasites might facilitate speciation in this genus. PMID:23409983

  16. Evolution of body shape in sympatric versus non-sympatric Tropheus populations of Lake Tanganyika.

    PubMed

    Kerschbaumer, M; Mitteroecker, P; Sturmbauer, C

    2014-02-01

    Allopatric speciation often yields ecologically equivalent sister species, so that their secondary admixis enforces competition. The shores of Lake Tanganyika harbor about 120 distinct populations of the cichlid genus Tropheus, but only some are sympatric. When alone, Tropheus occupies a relatively broad depth zone, but in sympatry, fish segregate by depth. To assess the effects of competition, we studied the partial co-occurrence of Tropheus moorii 'Kaiser' and 'Kirschfleck' with Tropheus polli. A previous study demonstrated via standardized breeding experiments that some observed differences between Tropheus 'Kaiser' living alone and in sympatry with T. polli have a genetic basis despite large-scale phenotypic plasticity. Using geometric morphometrics and neutral genetic markers, we now investigated whether sympatric populations differ consistently in body shape from populations living alone and if the differences are adaptive. We found significant differences in mean shape between non-sympatric and sympatric populations, whereas all sympatric populations of both color morphs clustered together in shape space. Sympatric populations had a relatively smaller head, smaller eyes and a more anterior insertion of the pectoral fin than non-sympatric populations. Genetically, however, non-sympatric and sympatric 'Kaiser' populations clustered together to the exclusion of 'Kirschfleck'. Genetic distances, but not morphological distances, were correlated with geographic distances. Within- and between-population covariance matrices for T. moorii populations deviated from proportionality. It is thus likely that natural selection acts on both phenotypic plasticity and heritable traits and that both factors contribute to the observed shape differences. The consistency of the pattern in five populations suggests ecological character displacement. PMID:24065182

  17. Estimating the age of formation of lakes: An example from Lake Tanganyika, East African Rift system

    Microsoft Academic Search

    Andrew S. Cohen; Michael J. Soreghan; Christopher A. Scholz

    1993-01-01

    Age estimates for ancient lakes are important for determining their histories and their rates off biotic and tectonic evolution. In the absence of dated core material from the lake's sedimentary basement, several techniques have been used to generate such age estimates. The most common off these, herein called the reflection seismic-radiocarbon method (RSRM), combines estimates off short-term sediment-accumulation rates derived

  18. Evolutionary history of the Lake Tanganyika cichlid tribe Lamprologini (Teleostei: Perciformes) derived from mitochondrial and nuclear DNA data.

    PubMed

    Sturmbauer, Christian; Salzburger, Walter; Duftner, Nina; Schelly, Robert; Koblmüller, Stephan

    2010-10-01

    Lake Tanganyika comprises a cichlid species flock with substrate-breeding and mouthbrooding lineages. While sexual selection via mate choice on male mating color is thought to boost speciation rates in mouthbrooding cichlids, this is not the case in substrate-breeding lamprologines, which mostly form stable pairs and lack sexual dichromatism. We present a comprehensive reconstruction of the evolution of the cichlid tribe Lamprologini, based upon mtDNA sequences and multilocus nuclear DNA (AFLP) markers. Twelve mtDNA clades were identified, seven of which were corroborated by the AFLP tree. The radiation is likely to have started about 5.3 MYA, contemporarily with that of the mouthbrooding C-lineage, and probably triggered by the onset of deep-water conditions in Lake Tanganyika. Neither the Congo- nor the Malagarazi River species form the most ancestral branch. Several conflicts in the mtDNA phylogeny with taxonomic assignments based upon color, eco-morphology and behavior could be resolved and complemented by the AFLP analysis. Introgressive hybridization upon secondary contact seems to be the most likely cause for paraphyly of taxa due to mtDNA capture in species involving brood-care helpers, while accidental hybridization best explains the para- or polyphyly of several gastropod shell breeders. Taxonomic error or paraphyly due to the survival of ancestral lineages appear responsible for inconsistencies in the genera Lamprologus and Neolamprologus. PMID:20601006

  19. Evolutionary history of the Lake Tanganyika cichlid tribe Lamprologini (Teleostei: Perciformes) derived from mitochondrial and nuclear DNA data

    PubMed Central

    Sturmbauer, Christian; Salzburger, Walter; Duftner, Nina; Schelly, Robert; Koblmüller, Stephan

    2010-01-01

    Lake Tanganyika comprises a cichlid species flock with substrate-breeding and mouthbrooding lineages. While sexual selection via mate choice on male mating color is thought to boost speciation rates in mouthbrooding cichlids, this is not the case in substrate-breeding lamprologines, which mostly form stable pairs and lack sexual dichromatism. We present a comprehensive reconstruction of the evolution of the cichlid tribe Lamprologini, based upon mtDNA sequences and multilocus nuclear DNA (AFLP) markers. Twelve mtDNA clades were identified, seven of which were corroborated by the AFLP tree. The radiation is likely to have started about 5.3 MYA, contemporarily with that of the mouthbrooding C-lineage, and probably triggered by the onset of deep-water conditions in Lake Tanganyika. Neither the Congo- nor the Malagarazi River species form the most ancestral branch. Several conflicts in the mtDNA phylogeny with taxonomic assignments based upon color, eco-morphology and behavior could be resolved and complemented by the AFLP analysis. Introgressive hybridization upon secondary contact seems to be the most likely cause for paraphyly of taxa due to mtDNA capture in species involving brood-care helpers, while accidental hybridization best explains the para- or polyphyly of several gastropod shell breeders. Taxonomic error or paraphyly due to the survival of ancestral lineages appear responsible for inconsistencies in the genera Lamprologus and Neolamprologus. PMID:20601006

  20. Ancyrocephalidae (Monogenea) of Lake Tanganyika: III: Cichlidogyrus infecting the world's biggest cichlid and the non-endemic tribes Haplochromini, Oreochromini and Tylochromini (Teleostei, Cichlidae).

    PubMed

    Muterezi Bukinga, Fidel; Vanhove, Maarten P M; Van Steenberge, Maarten; Pariselle, Antoine

    2012-11-01

    Lake Tanganyika is the deepest and oldest African Great Lake and of economic importance. While the diversity of its endemic cichlid radiations yielded scientific interest, a number of cichlid tribes have few representatives in the lake. Some of those, namely Oreochromini (ex-Tilapiini), Haplochromini and Tylochromini, reach higher species numbers in riverine systems. Conversely, the phylogenetic position of the monospecific and endemic Boulengerochromini is unclear. The oreochromines Oreochromis tanganicae and Oreochromis niloticus, the haplochromine Astatotilapia burtoni, the tylochromine Tylochromis polylepis and the boulengerochromine Boulengerochromis microlepis, the largest cichlid species worldwide, were surveyed for ancyrocephalid monogenean gill parasites. Five new species are proposed. Cichlidogyrus gillardinae sp. n. is described from A. burtoni, Cichlidogyrus mbirizei sp. n. from O. tanganicae and Cichlidogyrus nshomboi sp. n. from B. microlepis. T. polylepis harbours Cichlidogyrus mulimbwai sp. n., Cichlidogyrus muzumanii sp. n. and a third, presently undescribed species. Four species known from outside the Tanganyika Basin were retrieved on the oreochromines. The host species are scientific models or important in the sectors of fisheries or ornamental fish trade. Moreover, their phylogenetic positions render them well-suited to help elucidate the historic relationships between riverine and lacustrine African cichlids. In this framework, their Cichlidogyrus fauna is compared to congeners known from African rivers and to the few Tanganyika representatives described. While the parasites of Oreochromis, A. burtoni and T. polylepis are reminiscent of those infecting related hosts throughout Africa, B. microlepis hosts a Cichlidogyrus morphotype typical of Lake Tanganyika. This supports its placement within an endemic cichlid radiation. PMID:22983218

  1. Phylogenetic Relationships and Ancient Incomplete Lineage Sorting Among Cichlid Fishes in Lake Tanganyika as Revealed by Analysis of the Insertion of Retroposons

    Microsoft Academic Search

    Kazuhiko Takahashi; Yohey Terai; Mutsumi Nishida; Norihiro Okada

    Lake Tanganyika harbors numerous endemic species of extremely diverse cichlid fish that have been classified into 12 major taxonomic groups known as tribes. Analysis of short interspersed element (SINE) insertion data has been acknowledged to be a powerful tool for the elucidation of phylogenetic relationships, and we applied this method in an attempt to clarify such relationships among these cichlids.

  2. The phytoplankton and protozooplankton of the euphotic zone of Lake Tanganyika: Species composition, biomass, chlorophyll content, and spatio-temporal distribution

    Microsoft Academic Search

    R. E. HECKY; H. J. KLING

    1981-01-01

    The seasonal cycle of phytoplankton and protozooplankton 1 iomass observed at two widely separated pelagic stations in the euphotic zone of Lake Tanganyika from February through November 1975 could be divided into three phases, based oil algal abundance and species succession and coinciding with three phases of annual thermal stratification. Phytoplankton biomass was minimal (as low as 60 mg*m-\\

  3. Genetic and Morphological Evidence Implies Existence of Two Sympatric Species in Cyathopharynx furcifer (Teleostei: Cichlidae) from Lake Tanganyika.

    PubMed

    Takahashi, Tetsumi; Hori, Michio

    2012-01-01

    Although the cichlid fishes from Lake Tanganyika are treated as a textbook example of adaptive radiation, many taxonomic problems remain unresolved. Cyathopharynx furcifer, which belongs to the currently monospecific genus Cyathopharynx, contains two colour morphs at the southern end of the lake: one has a yellow anal fin, and the other has a black anal fin. Some books for hobbyists of ornamental fish treat these morphs as different species, but taxonomic studies have neither mentioned the existence nor addressed the status of these colour morphs. In the present paper, we analysed these two colour morphs using mitochondrial, microsatellite, morphometric, and meristic data sets. Both molecular and morphological data allowed clear discrimination between these morphs, suggesting the existence of two distinct sympatric species. Three taxonomic species have been described in this genus, and only C. furcifer is currently considered valid. Observations of type specimens of these three nominal species will be needed to determine the scientific names of these colour morphs. PMID:22675655

  4. Ionospheric plasma turbulence over region of 2006 Iran, 2005 Lake Tanganyika and 2010 New Britain Region earthquakes.

    NASA Astrophysics Data System (ADS)

    Kosciesza, Malgorzata; Blecki, Jan; Wronowski, Roman; Parrot, Michel

    2013-04-01

    We report the results of the observation of ELF plasma turbulence registered by DEMETER satellite in the ionosphere over epicenter region of three earthquakes. First one took place on 2nd of February 2005 in Lake Tanganyika Region with magnitude 6.9. Second was earthquake with magnitude 6.1 in Iran on 31st March 2006. The last one took place on 4th of August 2010 in New Britain Region with magnitude 7.0. Obtained results we compare with data gathered during corresponding time and region with quiet seismic conditions. To study this turbulent processes we apply Fourier, wavelet, bispectral analysis and statistical description with use of kurtosis and skewness of the electric field fluctuations. These registrations are correlated with the plasma parameters measured onboard DEMETER satellite and with geomagnetic indices.

  5. Environmental Magnetism as an Instrument for Characterizing Paleoclimatic Variations in the Sediment Record of Lake Tanganyika, East Africa.

    NASA Astrophysics Data System (ADS)

    Wetter, L.; Verosub, K.; Acton, G.; Russell, J.

    2004-12-01

    Due to their age and their continuous record of sedimentation, the lacustrine sediments of Lake Tanganyika, East Africa, provide an excellent resource for paleoclimatic research. During an eight-day cruise in July of 2004, participants in the Nyanza Project collected four Kullenburg piston cores in the vicinity of the Kalya horst, a mid-lake topographic high located south of the Mahale Mountains. Thirty meters of core were recovered. Initial lithologic analysis of the cores revealed that they consist of massive silty clay beds alternating with laminated diatomaceous oozes. U-channel samples were collected from the cores in order to obtain a continuous record of paleomagnetic directions recorded by the sediments as well as an environmental record of changes in the composition and concentration of magnetic minerals. In conjunction with other techniques, the directional record will help to provide a chronology for the cores, which are thought to extend well into Marine Isotope Stage 3. This chronology will be used to place the evolution of the lake system and its sedimentary processes within the context of global climate variability. The environmental magnetic record will provide information about both large-scale and small-scale climatic variations. The paleomagnetic and environmental magnetic information obtained from these cores will make it possible to draw definitive conclusions about past climate variations, current atmospheric composition, and the present-day quality of the lake.

  6. Female-to-male shift of mouthbrooding in a cichlid fish, Tanganicodus irsacae , with notes on breeding habits of two related species in Lake Tanganyika

    Microsoft Academic Search

    Tetsuo Kuwamura; Makoto Nagoshi; Tetsu Sato

    1989-01-01

    Synopsis  Parental-care patterns and mating systems of three goby-like cichlids in Lake Tanganyika were investigated. In Tanganicodus irsacae females mouthbrooded eggs and small young for about two weeks and then males took over the role for about one week. Field\\u000a observations of tagged fish suggest that this species is monogamous: a male's home range largely overlapped with that of its\\u000a mate,

  7. Evidence for divergent natural selection of a Lake Tanganyika cichlid inferred from repeated radiations in body size.

    PubMed

    Takahashi, T; Watanabe, K; Munehara, H; Rüber, L; Hori, M

    2009-07-01

    Divergent natural selection is thought to play a vital role in speciation, but clear, measurable examples from nature are still few. Among the many possible sources of divergent natural selection, predation pressure may be important because predators are ubiquitous in food webs. Here, we show evidence for divergent natural selection in a Lake Tanganyika cichlid, Telmatochromis temporalis, which uses burrows under stones or empty snail shells as shelters. This species contains normal and dwarf morphs at several localities. The normal morph inhabits rocky shorelines, whereas the dwarf morph invariably inhabits shell beds, where empty snail shells densely cover the lake bottom. Genetic evidence suggested that the dwarf morph evolved independently from the normal morph at two areas, and morphological analysis and evaluation of habitat structure revealed that the body sizes of morphs closely matched the available shelter sizes in their habitats. These findings suggest that the two morphs repeatedly evolved through divergent natural selection associated with the strategy for sheltering from predators. PMID:19549109

  8. Lithogenic Sediments as a Proxy Record of Tropical Aridity and Monsoon Intensity: An Example from Lake Tanganyika, Africa

    NASA Astrophysics Data System (ADS)

    Soreghan, M. J.; Scholz, C. A.; Cohen, A. S.

    2005-12-01

    The flux and grain size of wind-blown sediment to Lake Tanganyika allows reconstruction of wind regimes in this tropical continental setting, which is important for understanding temporal changes of the Asian Monsoon. In Lake Tanganyika, Africa, a 6 m core was collected from an isolated bathymetric ridge in 393 m of water. Geomorphic and seismic evidence suggests that clastic sedimentation to this site is primarily suspension derived. A previously published sedimentation model based on 11 calibrated C-14 AMS dates of bulk sediment suggests a slow, linear sedimentation rate. Samples collected on 4-cm spacing were subjected to a multi-stage chemical treatment to remove carbonate, organic, and oxide phases. The remaining lithogenic fraction in the sampled interval ranged between 5 and 74 % (by weight) and mean grain size of the fraction ranged between 5.9 and 101 ?m. The temporal trends show significant variation: low lithogenic fraction and mean grain sizes during the Holocene (core top to ~9 kyrs BP), abruptly changed downward to very high lithogenic fraction and maximal grain size at ~11 kyrs BP, which corresponds to Younger Dryas (YD) interval. Immediately preceding the YD, lithogenic fraction and mean grain size were low, but during the Last Glacial Maximum (LGM) both variables were much higher than Holocene values. Prior to ~20 kyrs BP, the lithogenic fraction was generally lower, although broad peaks of higher lithogenic fraction occur at roughly 29, 34, 40, 46 and 53 kyrs BP. The mean grain size data prior to ~20 kyrs BP does not necessarily track the lithogenic fraction, and exhibits more abrupt peaks, particularly prior to ~42 kyrs BP. The dataset as a whole correlate well with previous data from the Indian Ocean that suggests enhanced monsoonal circulation during the Late Glacial Maximum and correspondingly enhanced dust loads. Further, the lithogenic fraction data show an inverse correlation with the ice-core methane record from Vostok, Antarctica. Trace element geochemical analysis of the lithogenic fraction suggests that the source regions for the eolian dust did not vary significantly, except possibly during the Younger Dryas. However, the geochemical analyses were performed on a coarse temporal scale and more work is needed to confirm this conclusion. Finally, the lithogenic fraction shows a strong positive covariance with previously collected carbon isotope data on the bulk organic fraction, such that higher lithogenic fractions correspond to less negative carbon isotopes in the organic fraction.

  9. Repeated parallel evolution of parental care strategies within Xenotilapia, a genus of cichlid fishes from Lake Tanganyika.

    PubMed

    Kidd, Michael R; Duftner, Nina; Koblmüller, Stephan; Sturmbauer, Christian; Hofmann, Hans A

    2012-01-01

    The factors promoting the evolution of parental care strategies have been extensively studied in experiment and theory. However, most attempts to examine parental care in an evolutionary context have evaluated broad taxonomic categories. The explosive and recent diversifications of East African cichlid fishes offer exceptional opportunities to study the evolution of various life history traits based on species-level phylogenies. The Xenotilapia lineage within the endemic Lake Tanganyika cichlid tribe Ectodini comprises species that display either biparental or maternal only brood care and hence offers a unique opportunity to study the evolution of distinct parental care strategies in a phylogenetic framework. In order to reconstruct the evolutionary relationships among 16 species of this lineage we scored 2,478 Amplified Fragment Length Polymorphisms (AFLPs) across the genome. We find that the Ectodini genus Enantiopus is embedded within the genus Xenotilapia and that during 2.5 to 3 million years of evolution within the Xenotilapia clade there have been 3-5 transitions from maternal only to biparental care. While most previous models suggest that uniparental care (maternal or paternal) arose from biparental care, we conclude from our species-level analysis that the evolution of parental care strategies is not only remarkably fast, but much more labile than previously expected. PMID:22347454

  10. Ancyrocephalidae (Monogenea) of Lake Tanganyika: II: description of the first Cichlidogyrus spp. parasites from Tropheini fish hosts (Teleostei, Cichlidae).

    PubMed

    Gillardin, Céline; Vanhove, Maarten P M; Pariselle, Antoine; Huyse, Tine; Volckaert, Filip A M

    2012-01-01

    Although Lake Tanganyika hosts the most diverse endemic cichlid fish assemblage, its monogenean parasite fauna has hardly been documented. The cichlid tribe Tropheini has generated great interest because of its systematic position within the Haplochromini s.l. and its diversity in trophic morphology, reproductive behaviour and population structure. It has the potential to host a diverse Monogenea fauna. Here, we describe the first Cichlidogyrus spp.: Cichlidogyrus steenbergei sp. n., Cichlidogyrus irenae sp. n. and Cichlidogyrus gistelincki sp. n. The three host species, Limnotilapia dardennii, Ctenochromis horei and Gnathochromis pfefferi, are all infected by a single unique Cichlidogyrus sp. The genital and haptoral structure of the new species suggests a close relationship, which might mirror the close affinities between the hosts within the Tropheini. Based on haptoral configuration, the new species belong to a morphological group within the genus containing parasites both of West African cichlids and of Haplochromini, and hence, do not represent a new organisation of the attachment organ (as has recently been described of congeners infecting the ectodine cichlid Ophthalmotilapia). PMID:21710349

  11. Social status-dependent nest choice of territorial males under reproductive parasitism in a Lake Tanganyika cichlid Telmatochromis vittatus.

    PubMed

    Ota, K; Kohda, M

    2011-03-01

    Field and laboratory studies were conducted to examine how territorial males of a Lake Tanganyika cichlid Telmatochromis vittatus balance the conflicting demands on nest choice between occupying large nests with more females and avoiding reproductive parasitism (nest piracy, which is adopted by the largest males in the population). Pirates less frequently intruded the nests farther from neighbours, perhaps due to the costs associated with travelling between nests. The field experiment showed that territorial male T. vittatus sacrificed the fitness benefits that large nests offer and instead prioritized occupying the nests farther from neighbours on which fewer pirates intruded. The field observations suggested that they adopt different strategies for nest choice according to their relative competitive ability to pirates; the large territorial males, who are size-matched to pirates and can defend their nests against them, compete for larger nests among the more-isolated nests, whereas subordinate territorial males, which are smaller than pirates and thus inferior to them, compete for the more-isolated nests among the less-isolated nests. These findings suggest that the territorial male T. vittatus chooses the more-isolated nests to avoid pirate males at the expense of occupying large nests. PMID:21366567

  12. Textural and compositional variability across littoral segments of Lake Tanganyika: The effect of asymmetric basin structure on sedimentation in large rift lakes

    SciTech Connect

    Soreghan, M.J.; Cohen, A.S. [Univ. of Arizona, Tucson, AZ (United States)

    1996-03-01

    Lake Tanganyika, part of the East African rift system, represents one of the most widely cited modern analogs for interpreting ancient rift lakes. To date, few published detailed sedimentologic studies of the modern sediments allow for comparisons to outcrop- and well-bore-scale observations within ancient strata. Four recurrent structural margin types exist along the alternating half-graben structure of the lake: hinged margins, axial margins, accommodation zone margins, and escarpment margins. The hinged margin consists of a series of structurally controlled benches over which long, continuous tracts of bioclastic lag deposits predominate; clastic sands are limited to moderate-size silty deltas and long, narrow shoreface sands. The axial margin is dominated by a wave-dominated, silt-rich delta system. Accommodation zone margins consist of bioclastic lag deposits atop structural highs, whereas carbonate and clastic mud accumulates farther offshore. Escarpment margins contain small fan-delta deposits alternating along shore with talus deposits; offshore carbonate and clastic mud is present away from active gravity-flow deposition. Total organic carbon (TOC) and pyrolysis data from fine-grained samples subtly reflect the contrasts in margin types, but these values are controlled more directly by water depth. Although facies are similar among all margin types, their spatial distribution, in particular the degree to which facies tracts trend parallel to shore, best discriminates among the different margin types. These data suggest that unique but predictable associations of reservoir, seal, and source facies exist along each of the different margin types.

  13. Abrupt Climatic Events Observed in Organic-Rich Sediments From Lake Tanganyika, Tropical East Africa, Over the Past 50 kyr

    NASA Astrophysics Data System (ADS)

    Burnett, A. P.; Weyhenmeyer, C. E.; Scholz, C. A.; Swart, P. K.

    2006-12-01

    Abrupt climate changes such as Dansgaard-Oeschger Cycles and Heinrich Events were first detected in high- latitude records, but an increasing number of studies suggest that these rapid changes are actually global events. The degree to which the tropics drive, control and/or respond to such rapid changes is still poorly understood due to a scarcity of data from low-latitude regions. A recently acquired sediment core from Lake Tanganyika, East Africa, provides a unique archive to study abrupt climate events in the tropics throughout the last glaciation. The core provides a continuous, undisturbed and high resolution climate record over the past 100 kyr. An age-depth model based on 25 new radiocarbon dates provides a solid, high-resolution chronology for the past 50 kyr. Throughout this time, several rapid changes in paleoclimate proxy data are observed along the core. Sedimentation rates remained fairly constant from the Holocene until the Last Glacial Maximum (LGM) but increased abruptly from ~80 mm/1000 yr to ~150 mm/1000 yr around 18 kyr BP. At the same time, the sediment record reveals a sudden increase in total organic carbon (TOC) from 4% to 12% indicating a rapid increase in organic matter contributions at the end of the LGM. Abrupt changes in TOC and ?13C values are also found at ~38 kyr, ~30 kyr and ~16 kyr BP, suggesting a possible link to Heinrich events 4, 3 and 1, respectively. Forthcoming very high-resolution analyses, to augment existing low-resolution data, include ?13C, ?15N, C/N ratios and TOC values. Furthermore, TEX86 measurements will be carried out to determine whether the observed changes in organic matter contributions are associated with changes in water temperatures. In combination with the solid 14C chronology, the new data will allow us to precisely determine the onset, timing and nature of abrupt changes and evaluate them in the global context.

  14. Strontium isotopes and rare-earth element geochemistry of hydrothermal carbonate deposits from Lake Tanganyika, East Africa

    NASA Astrophysics Data System (ADS)

    Barrat, J. A.; Boulègue, J.; Tiercelin, J. J.; Lesourd, M.

    2000-01-01

    At Cape Banza (North Tanganyika Lake), fluids and aragonite chimneys have been collected many times since the discovery of this sublacustrine field in 1987. This sampling has been investigated here for the Sr isotopic compositions and the rare-earth element features of the carbonates and a few fluid samples. The 87Sr/ 86Sr ratios of the chimneys indicate that they have precipitated from a mixture of lake water (more than 95%) and hydrothermal fluids. No zoning in the chimneys was detected with our Sr data. For the rare-earth elements, the situation is more complex. The external walls of the chimneys are rare-earth-element-poor (La ? 500 ppb, Yb ? 200 ppb, La/Yb = 2 to 3.4). Their shale normalised rare-earth element patterns suggest that they are in equilibrium with the inferred carbonate-depositing fluids. The rare-earth element concentrations of the internal walls of the chimneys are significantly light rare earth elements (LREE)-enriched with La contents sometimes up to 5 ppm. We suggest that they contain more vent-fluid rare-earth elements than the external wall samples, possibly adsorbed on the surface of growing crystals or simply hosted by impurities. It was not possible to constrain the nature of these phases, but the variations of the compositions of the internal wall materials of the active chimneys with time, as well as data obtained on an inactive chimney indicate that this rare-earth element excess is mobile. Partition coefficients were calculated between the external wall aragonite and carbonate-depositing fluid. The results are strikingly similar to the values obtained by Sholkovitz and Shen (1995) on coral aragonite, and suggest that there is no significant biologic effect on the incorporation of rare-earth elements into coral aragonite and that the various carbonate complexes involved Me(CO 3+) complexes are the main LREE carriers in seawater (Cantrell and Byrne, 1987) instead of Me(CO 3) 2- in Banza fluids) have the same behaviour during aragonite precipitation.

  15. Strontium isotopes and rare-earth element geochemistry of hydrothermal carbonate deposits from Lake Tanganyika, East Africa

    SciTech Connect

    Barrat, J.A.; Boulegue, J.; Tiercelin, J.J.; Lesourd, M.

    2000-01-01

    At Cape Banza (North Tanganyika Lake), fluids and aragonite chimneys have been collected many times since the discovery of this sublacustrine field in 1987. This sampling has been investigated here for the Sr isotopic compositions and the rare-earth element features of the carbonates and a few fluid samples. The {sup 87}Sr/{sup 86}Sr ratios of the chimneys indicate that they have precipitated from a mixture of lake water (more than 95%) and hydrothermal fluids. No zoning in the chimneys was detected with the Sr data. For the rare-earth elements, the situation is more complex. The external walls of the chimneys are rare-earth-element-poor (La {approx} 500 ppb, Yb {approx} 200 ppb, La/Yb = 2 to 3.4). Their shale normalized rare-earth element patterns suggest that they are in equilibrium with the inferred carbonate-depositing fluids. The rare-earth element concentrations of the internal walls of the chimneys are significantly light rare earth elements (LREE)-enriched with La contents sometimes up to 5 ppm. The authors suggest that they contain more vent-fluid rare-earth elements than the external wall samples, possibly adsorbed on the surface of growing crystals or simply hosted by impurities. It was not possible to constrain the nature of these phases, but the variations of the compositions of the internal wall materials of the active chimneys with time, as well as data obtained on an inactive chimney indicate that this rare-earth element excess is mobile. Partition coefficients were calculated between the external wall aragonite and carbonate-depositing fluid. The results are strikingly similar to the values obtained by Sholkovitz and Shen (1995) on coral aragonite, and suggest that there is no significant biologic effect on the incorporation of rare-earth elements into coral aragonite and that the various carbonate complexes involved Me(CO{sub 3}{sup +}) complexes are the main LREE carriers in seawater instead of Me(CO{sub 3}){sub 2}{sup {minus}} in Banza fluids have the same behavior during aragonite precipitation.

  16. A Novel Family of Short Interspersed Repetitive Elements (SINEs) from Cichlids: The Patterns of Insertion of SINEs at Orthologous Loci Support the Proposed Monophyly of Four Major Groups of Cichlid Fishes in Lake Tanganyika

    Microsoft Academic Search

    Kazuhiko Takahashi; Yohey Terai; Mutsumi Nishida; Norihiro Okada

    Short interspersed repetitive elements (SINEs) have been shown to be excellent markers of molecular phylogeny, since the integration of a SINE at a particular position in a genome can be considered an unambiguous derived homologous character. In the present study, we isolated a new family of SINEs from cichlids in Lake Tanganyika, whose speciation and diversification have been regarded as

  17. Social organization of a polygynous Cichlid Lamprologns furcifer in Lake Tanganyika

    Microsoft Academic Search

    Yasunobu Yanagisawa

    1987-01-01

    Lamprologus furcifer inhabited vertical or overhanging rock surfaces. Females persistently stayed at particular sites and singly guarded the offspring\\u000a there. Males also stayed at particular sites but often left them to visit females. A dominant male controlled the territories\\u000a of several breeding females at a time. Schools of young under maternal care spread horizontally on the rock surface as they

  18. Separated by sand, fused by dropping water: habitat barriers and fluctuating water levels steer the evolution of rock-dwelling cichlid populations in Lake Tanganyika.

    PubMed

    Koblmüller, Stephan; Salzburger, Walter; Obermüller, Beate; Eigner, Eva; Sturmbauer, Christian; Sefc, Kristina M

    2011-06-01

    The conditions of phenotypic and genetic population differentiation allow inferences about the evolution, preservation and loss of biological diversity. In Lake Tanganyika, water level fluctuations are assumed to have had a major impact on the evolution of stenotopic littoral species, though this hypothesis has not been specifically examined so far. The present study investigates whether subtly differentiated colour patterns of adjacent Tropheus moorii populations are maintained in isolation or in the face of continuous gene flow, and whether the presumed influence of water level fluctuations on lacustrine cichlids can be demonstrated in the small-scale population structure of the strictly stenotopic, littoral Tropheus. Distinct population differentiation was found even across short geographic distances and minor habitat barriers. Population splitting chronology and demographic histories comply with our expectation of old and rather stable populations on steeper sloping shore, and more recently established populations in a shallower region. Moreover, population expansions seem to coincide with lake level rises in the wake of Late Pleistocene megadroughts ~100 KYA. The imprint of hydrologic events on current population structure in the absence of ongoing gene flow suggests that phenotypic differentiation among proximate Tropheus populations evolves and persists in genetic isolation. Sporadic gene flow is effected by lake level fluctuations following climate changes and controlled by the persistence of habitat barriers during lake level changes. Since similar demographic patterns were previously reported for Lake Malawi cichlids, our data furthermore strengthen the hypothesis that major climatic events synchronized facets of cichlid evolution across the East African Great Lakes. PMID:21518059

  19. The Lake Tanganyika Accommodation Zone Structural Highs: Probable Archive of Continuous Miocene to Recent Paleoenvironmental and Paleoclimatic Information for East Africa

    NASA Astrophysics Data System (ADS)

    Cohen, A. S.; Lezzar, K. E.; Russell, J.; Scholz, C. A.; Tiercelin, J.; Gans, C. R.; Helfrich, L. C.

    2004-12-01

    Continental drilling of lake deposits has proven an important source of high-resolution paleoclimatic and paleoenvironmental information. The large rift lakes of East Africa react dramatically to climatic perturbations, recording responses in sedimentary records of lake level, chemistry, and biota. No continuous continental paleoclimate records covering the full period of hominid evolution, especially the critical transitions of the late Miocene through the Plio-Pleistocene, are currently available or forthcoming. However, approximately 1000 km of sparker and air gun reflection seismic profiles collected during a number of field campaigns on Lake Tanganyika demonstrate the existence of three major mid-lake isolated structural highs: from N-S the Ubwari, Kavala Island, and Kalya horsts, whose sedimentary cover may provide records of this critical interval. Several coring campaigns demonstrated sedimentation rates over the last 100 ka much slower than adjacent basinal settings, in some cases as low as 0.1 mm/year. Sequence stratigraphic analyses of sediments on the shallower (300-500 m) of these horsts (Ubwari and Kavala Island), and on other structural platforms have shown the presence of numerous unconformities related to lake level fluctuations and paleoclimatic variability. During the Last Glacial Maximum, for example, features such as prograding delta lobes and paleochannels indicate water levels may have fallen by as much as 360 meters. Erosional unconformities at depths of as much as 600 m have been noted at basinal sites adjacent to these relatively shallow horsts. The northeastern edge of the Kalya horst, however, lies at sufficient water depths (> 600 m) to have escaped these major erosional truncations. Furthermore, this site is located in a depositional environment of relative tectonic quiescence, apparently undisturbed by faulting, unlike the northern structural highs. Preliminary seismic stratigraphic analysis of the Kalya horst shows the presence of at least 300 m of continuously accumulated sediment. Cores from the region, spanning the late Pleistocene and Holocene, have shown that the sediments are partially laminated and contain a wealth of geochemical and paleoecological indicators of glacial-interglacial to millennial-scale hydroclimatic fluctuations. Given the age of Lake Tanganyika (10-12 Ma) and the highly continuous nature of sedimentation on the deep accommodation zone, the Kalya horst has the potential to provide a continuous and readily-interpretable record of paleoclimate history over much, if not all, of the critical phases of hominid evolution in East Africa.

  20. First description of monogenean parasites in Lake Tanganyika: the cichlid Simochromis diagramma (Teleostei, Cichlidae) harbours a high diversity of Gyrodactylus species (Platyhelminthes, Monogenea).

    PubMed

    Vanhove, Maarten P M; Snoeks, Jos; Volckaert, Filip A M; Huyse, Tine

    2011-03-01

    Lake Tanganyika harbours the most diverse endemic cichlid fish assemblage of Africa, but its monogenean fish parasites have not been investigated. Here we report, for the first time, on the Gyrodactylus parasites in this hotspot of fish biodiversity. Haptor morphometrics and nuclear ribosomal DNA sequences revealed 3 new species on Zambian Simochromis diagramma: Gyrodactylus sturmbaueri n. sp., G. thysi n. sp. and G. zimbae n. sp. Their distinct morphology and strong genetic differentiation suggest that they belong to distant lineages within the genus Gyrodactylus, and phylogenetic reconstructions suggest affinities with other genera of gyrodactylids. Additional U-shaped haptoral plates in G. thysi n. sp. and a second large spine-like structure in the male copulatory organ of G. zimbae seem to represent new features for the genus. Such large diversity on a single host species can probably be explained by host-switching events during the course of evolution, in agreement with the generally accepted concept that ecological transfer is an important aspect of gyrodactylid speciation. Additional parasitological surveys on other host species, covering a broader phylogenetic and geographical range, should clarify the evolutionary history of Gyrodactylidae on cichlids in the African Great Lake and other parts of Africa. PMID:20946697

  1. Genetic support for random mating between left and right-mouth morphs in the dimorphic scale-eating cichlid fish Perissodus microlepis from Lake Tanganyika.

    PubMed

    Lee, H J; Pittlik, S; Jones, J C; Salzburger, W; Barluenga, M; Meyer, A

    2010-05-01

    Population genetic analyses were conducted to investigate whether random mating occurs between left and right-mouth morphs of the dimorphic scale-eating cichlid fish Perissodus microlepis from two geographical sites in southern Lake Tanganyika. The mitochondrial and nuclear DNA markers (13 microsatellite loci) revealed no genetic differentiation between left and right morphs (i.e. widespread interbreeding). The observed lack of genetic divergence between the different morphs allowed for the exclusion of the possibility of assortative mating between same morph types. The microsatellite data showed no significant departures of heterozygosity from Hardy-Weinberg equilibrium, suggesting purely random mating between the morphs. Overall, this study indicated no genetic evidence for either assortative or disassortative mating, but it did provide support for the random mating hypothesis. Highly significant, albeit weak, spatial population structure was also found when samples of different morphs were pooled according to geographical sites. An additional analysis of two microsatellite loci that were recently suggested to be putatively linked to the genetic locus that determines the laterality of these mouth morphs did not show any such association. PMID:20557648

  2. Comparative support for the expensive tissue hypothesis: Big brains are correlated with smaller gut and greater parental investment in Lake Tanganyika cichlids.

    PubMed

    Tsuboi, Masahito; Husby, Arild; Kotrschal, Alexander; Hayward, Alexander; Buechel, Séverine D; Zidar, Josefina; Løvlie, Hanne; Kolm, Niclas

    2015-01-01

    The brain is one of the most energetically expensive organs in the vertebrate body. Consequently, the energetic requirements of encephalization are suggested to impose considerable constraints on brain size evolution. Three main hypotheses concerning how energetic constraints might affect brain evolution predict covariation between brain investment and (1) investment into other costly tissues, (2) overall metabolic rate, and (3) reproductive investment. To date, these hypotheses have mainly been tested in homeothermic animals and the existing data are inconclusive. However, there are good reasons to believe that energetic limitations might play a role in large-scale patterns of brain size evolution also in ectothermic vertebrates. Here, we test these hypotheses in a group of ectothermic vertebrates, the Lake Tanganyika cichlid fishes. After controlling for the effect of shared ancestry and confounding ecological variables, we find a negative association between brain size and gut size. Furthermore, we find that the evolution of a larger brain is accompanied by increased reproductive investment into egg size and parental care. Our results indicate that the energetic costs of encephalization may be an important general factor involved in the evolution of brain size also in ectothermic vertebrates. PMID:25346264

  3. Testing for differences in rates of speciation, extinction, and morphological evolution in four tribes of cichlids endemic to Lake Tanganyika, East Africa.

    PubMed

    Hoerner, Marie E

    2011-12-01

    Patterns of morphological disparity yield important insight into the causes of diversification and adaptive radiation in East African cichlids. However, comparisons of cichlid disparity have often failed to consider the effects that differing clade ages or stochasticity may have on disparity before making interpretations. Here, a model of branching morphological evolution allows assessment of the relative contributions of differing turnover and morphological change rates, clade ages, and stochastic variation to the observed patterns of disparity in four endemic tribes of Lake Tanganyika cichlids. Simulations compare the likelihood of generating the observed disparity of the four tribes using 200-parameter combinations and four model conditioning variations, which allows inference of evolutionary rate differences among clades. The model is generally robust to model conditioning, the approach to data analysis, and model assumptions. Disparity differences among the first three cichlid tribes, Ectodini, Lamprologini, and Tropheini, can be explained entirely by stochasticity and age, whereas the fourth tribe, Cyprichromini, has likely experienced lower rates of turnover and morphological change. This rate difference is likely related to the low dietary diversity of the Cyprichromini. These results highlight the importance of considering both clade age and stochastic variation when interpreting morphological diversity and evolutionary processes. PMID:22133214

  4. Comparative support for the expensive tissue hypothesis: Big brains are correlated with smaller gut and greater parental investment in Lake Tanganyika cichlids

    PubMed Central

    Tsuboi, Masahito; Husby, Arild; Kotrschal, Alexander; Hayward, Alexander; Buechel, Séverine D; Zidar, Josefina; Løvlie, Hanne; Kolm, Niclas

    2015-01-01

    The brain is one of the most energetically expensive organs in the vertebrate body. Consequently, the energetic requirements of encephalization are suggested to impose considerable constraints on brain size evolution. Three main hypotheses concerning how energetic constraints might affect brain evolution predict covariation between brain investment and (1) investment into other costly tissues, (2) overall metabolic rate, and (3) reproductive investment. To date, these hypotheses have mainly been tested in homeothermic animals and the existing data are inconclusive. However, there are good reasons to believe that energetic limitations might play a role in large-scale patterns of brain size evolution also in ectothermic vertebrates. Here, we test these hypotheses in a group of ectothermic vertebrates, the Lake Tanganyika cichlid fishes. After controlling for the effect of shared ancestry and confounding ecological variables, we find a negative association between brain size and gut size. Furthermore, we find that the evolution of a larger brain is accompanied by increased reproductive investment into egg size and parental care. Our results indicate that the energetic costs of encephalization may be an important general factor involved in the evolution of brain size also in ectothermic vertebrates. PMID:25346264

  5. SPECIATION IN ANCIENT LAKES Ecological correlates of species differences in the Lake

    E-print Network

    Loon, E. Emiel van

    SPECIATION IN ANCIENT LAKES Ecological correlates of species differences in the Lake Tanganyika Springer Science+Business Media B.V. 2008 Abstract The endemic crabs of Lake Tanganyika include for the maintenance of species diversity in Lake Tanganyika. Keywords Decapod Á Adaptive radiation Á Niche

  6. Vertical deformation at Lake Taupo, New Zealand, from lake levelling surveys, 1979–99

    Microsoft Academic Search

    P. M. Otway; G. H. Blick; B. J. Scott

    2002-01-01

    Lake Taupo, occupying much of the Taupo Volcanic Centre and spanning the Taupo Fault Belt, has routinely been monitored for vertical deformation since 1979 using a portable lake levelling survey technique. Regular monitoring continues to the present time. This technique is used at a number of fixed points around the lake to efficiently determine their height changes. Long?term trends and

  7. Vertical distribution of phytoplankton in a clear water lake of Colombian Amazon (Lake Boa, Middle Caquetá)

    Microsoft Academic Search

    Gabriel A. Pinilla; Jorge Tadeo

    2006-01-01

    Vertical distribution of phytoplankton is highly influenced by physical and chemical factors, but the knowledge about these\\u000a aspects remain unknown in Colombian Amazon lakes. In this work, the relations between the physico-chemical variables and the\\u000a vertical distribution of phytoplankton community of a clear water lake (Lake Boa) are analyzed. Samples were taken at every\\u000a 30 cm from surface to bottom in

  8. Zooplankton Diel Vertical Distributions in Lake Crescent, a Deep Oligotrophic Lake in Washington (USA)

    Microsoft Academic Search

    Jonathan D. Rainey; William V. Sobczak; Steven C. Fradkin

    2007-01-01

    We evaluated diel vertical migration (DVM) of major zooplankton populations in Lake Crescent, Washington, a deep oligotrophic lake where this phenomenon has not previously been studied. Duplicate daytime and nighttime samples were collected on June 27 and August 1, 2003 at ten depth intervals spanning 0–140 m. The major zooplankton taxa were the crustaceans Diaptomus tyrrelli, Daphnia rosea, Holopedium gibberum

  9. Spectral P-wave magnitudes, magnitude spectra and other source parameters for the 1990 southern Sudan and the 2005 Lake Tanganyika earthquakes

    NASA Astrophysics Data System (ADS)

    Moussa, Hesham Hussein Mohamed

    2008-10-01

    Teleseismic Broadband seismograms of P-waves from the May 1990 southern Sudan and the December, 2005 Lake Tanganyika earthquakes; the western branch of the East African Rift System at different azimuths have been investigated on the basis of magnitude spectra. The two earthquakes are the largest shocks in the East African Rift System and its extension in southern Sudan. Focal mechanism solutions along with geological evidences suggest that the first event represents a complex style of the deformation at the intersection of the northern branch of the western branch of the East African Rift and Aswa Shear Zone while the second one represents the current tensional stress on the East African Rift. The maximum average spectral magnitude for the first event is determined to be 6.79 at 4 s period compared to 6.33 at 4 s period for the second event. The other source parameters for the two earthquakes were also estimated. The first event had a seismic moment over fourth that of the second one. The two events are radiated from patches of faults having radii of 13.05 and 7.85 km, respectively. The average displacement and stress drop are estimated to be 0.56 m and 1.65 MPa for the first event and 0.43 m and 2.20 MPa for the second one. The source parameters that describe inhomogeneity of the fault are also determined from the magnitude spectra. These additional parameters are complexity, asperity radius, displacements across the asperity and ambient stress drop. Both events produce moderate rupture complexity. Compared to the second event, the first event is characterized by relatively higher complexity, a low average stress drop and a high ambient stress. A reasonable explanation for the variations in these parameters may suggest variation in the strength of the seismogenic fault which provides the relations between the different source parameters. The values of stress drops and the ambient stresses estimated for both events indicate that these earthquakes are of interplate type.

  10. Physical and biogeochemical limits to internal nutrient loading of meromictic Lake Kivu Natacha Pasche,a,b,* Christian Dinkel,a Beat Muller,a,b Martin Schmid,a Alfred Wuest,a,b and

    E-print Network

    Wehrli, Bernhard

    to be totally lost by denitrification in Lake Tanganyika. In Lake Kivu, nutrient uptake by primary production (Hecky et al. 1996). Recent studies showed that primary production in Lake Malawi and Lake Tanganyika

  11. VERTICAL DIFFUSION IN SMALL STRATIFIED LAKES: DATA AND ERROR ANALYSIS

    EPA Science Inventory

    Water temperature profiles were measured at 2-min intervals in a stratified temperate lake with a surface area of 0.06 km2 and a aximum depth of 10 m from May 7 to August 9, 1989. he data were used to calculate the vertical eddy diffusion coefficient K2 in the hypolimnion. he dep...

  12. NOAA Technical Memorandum ERL GLERL-59 CALCULATION OF VERTICAL DIFFUSIVITY IN LAKE WASHINGTON

    E-print Network

    NOAA Technical Memorandum ERL GLERL-59 CALCULATION OF VERTICAL DIFFUSIVITY IN LAKE WASHINGTON BASED-calculated diffusivities (cm2 m-l>, 1963-76. Page 1 1 3 3 7 8 10 20 20 23 iii #12;FIGURES Page 2Lake Washington and surrounding area.1. 2. Three vertical regimes of turbulent mixing in Lake Washington during stratified period

  13. Vertical gradient of nutrients in two dimictic lakes – influence of phototrophic sulfur bacteria on nutrient balance

    Microsoft Academic Search

    Uwe Selig; Thomas Hübener; Reinhard Heerkloss; Hendrik Schubert

    2004-01-01

    Vertical profiles of soluble and particulate nutrients were analyzed at the end of summer stratification in two dimictic lakes located in northeast Germany. In addition, irradiance and plankton biomass were determined. The concentrations of particulate organic carbon and phytoplankton biomass in the epilimnion were higher in Lake Tiefer than in Lake Dudinghausen, even though the apparent trophic status of Lake

  14. Infestation and Pathological Alterations by Ergasilus sarsi (Copepoda) on the Tanganyika Killifish from Africa

    PubMed Central

    Kilian, Esmari; Avenant-Oldewage, Annemariè

    2013-01-01

    A total of 204 Ergasilus sarsi, a copepod, were collected from Tanganyika Killifish Lamprichthys tanganicanus in Lake Tanganyika during March 2010. The prevalence was 86.40%, the mean intensity was 7.56, and the mean abundance was 6.38. Only 27 of the fish were infested, and the highest infestation on one fish was 29. Proliferation of mucus cells and lamellar fusion occurred. Haemorrhage due to blood vessel compression was noted. This is the first record of E. sarsi from Tanganyika Killifish. This study is also the first to provide a description of the pathological alterations caused by E. sarsi. PMID:24341764

  15. Infestation and pathological alterations by Ergasilus sarsi (Copepoda) on the Tanganyika Killifish from Africa.

    PubMed

    Kilian, Esmari; Avenant-Oldewage, Annemariè

    2013-12-01

    A total of 204 Ergasilus sarsi, a copepod, were collected from Tanganyika Killifish Lamprichthys tanganicanus in Lake Tanganyika during March 2010. The prevalence was 86.40%, the mean intensity was 7.56, and the mean abundance was 6.38. Only 27 of the fish were infested, and the highest infestation on one fish was 29. Proliferation of mucus cells and lamellar fusion occurred. Haemorrhage due to blood vessel compression was noted. This is the first record of E. sarsi from Tanganyika Killifish. This study is also the first to provide a description of the pathological alterations caused by E. sarsi. PMID:24341764

  16. The vertical distribution of zooplankton in brackish meromictic lake with deep-water chlorophyll maximum

    Microsoft Academic Search

    Yegor S. Zadereev; Alexander P. Tolomeyev

    2007-01-01

    We examined the dynamics of the vertical stratification of physical, chemical and biological factors in a brackish meromictic\\u000a lake with a deep-water chlorophyll maximum (Shira Lake, Russia, Khakasia) during the growing season and estimated how the\\u000a vertical distribution of these factors influences the vertical distribution of the zooplankton community. The vertical distribution\\u000a of zooplankton was restricted by the anoxic hypolimnion.

  17. The dominating higher order vertical modes of the internal seiche in a small lake

    Microsoft Academic Search

    BRUCE D. LAZERTE

    1980-01-01

    The internal seiche structure of a small, shallow lake (Frains Lake, Michigan) is shown to be dominated by the higher order vertical modes. The resonalit frequencies and the vertical velocity profiles of each mode were predicted from observed temperature profiles. The oh- served resonant frequencies and observed phase shifts in the velocity profiles of each mode corresponded closely to those

  18. Back to Tanganyika: a case of recent trans-species-flock dispersal in East African haplochromine cichlid fishes

    PubMed Central

    Meyer, Britta S.; Indermaur, Adrian; Ehrensperger, Xenia; Egger, Bernd; Banyankimbona, Gaspard; Snoeks, Jos; Salzburger, Walter

    2015-01-01

    The species flocks of cichlid fishes in the East African Great Lakes are the largest vertebrate adaptive radiations in the world and illustrious textbook examples of convergent evolution between independent species assemblages. Although recent studies suggest some degrees of genetic exchange between riverine taxa and the lake faunas, not a single cichlid species is known from Lakes Tanganyika, Malawi and Victoria that is derived from the radiation associated with another of these lakes. Here, we report the discovery of a haplochromine cichlid species in Lake Tanganyika, which belongs genetically to the species flock of haplochromines of the Lake Victoria region. The new species colonized Lake Tanganyika only recently, suggesting that faunal exchange across watersheds and, hence, between isolated ichthyofaunas, is more common than previously thought.

  19. Back to Tanganyika: a case of recent trans-species-flock dispersal in East African haplochromine cichlid fishes.

    PubMed

    Meyer, Britta S; Indermaur, Adrian; Ehrensperger, Xenia; Egger, Bernd; Banyankimbona, Gaspard; Snoeks, Jos; Salzburger, Walter

    2015-03-01

    The species flocks of cichlid fishes in the East African Great Lakes are the largest vertebrate adaptive radiations in the world and illustrious textbook examples of convergent evolution between independent species assemblages. Although recent studies suggest some degrees of genetic exchange between riverine taxa and the lake faunas, not a single cichlid species is known from Lakes Tanganyika, Malawi and Victoria that is derived from the radiation associated with another of these lakes. Here, we report the discovery of a haplochromine cichlid species in Lake Tanganyika, which belongs genetically to the species flock of haplochromines of the Lake Victoria region. The new species colonized Lake Tanganyika only recently, suggesting that faunal exchange across watersheds and, hence, between isolated ichthyofaunas, is more common than previously thought. PMID:26064619

  20. Changing Planet: Warming Lakes

    NSDL National Science Digital Library

    Windows to the Universe/NBC Learn

    The video addresses impact of warming temperatures on major lakes of the world with specific focus on Lake Superior and Lake Tanganyika. It discusses the science of water stratification and its impact on lake ecosystems and on human populations whose livelihoods depend on the lakes.

  1. VERTICAL DISTRIBUTION OF PROFUNDAL BENTHOS IN LAKE SUPERIOR SEDIMENTS

    EPA Science Inventory

    Layers of sediment in box cores from 10 Lake Superior open lake sites were sieved at 250 micrometers to retain benthos. The average density of benthic organisms, 3,055/sq m, was higher than has previously been reported for profundal regions of the lake, suggesting that biological...

  2. Diel vertical migration and spatial overlap between fish larvae and zooplankton in two tropical lakes, Brazil.

    PubMed

    Picapedra, Phs; Lansac-Tôha, Fa; Bialetzki, A

    2015-05-01

    The effect of fish larvae on the diel vertical migration of the zooplankton community was investigated in two tropical lakes, Finado Raimundo and Pintado lakes, Mato Grosso do Sul State, Brazil. Nocturnal and diurnal samplings were conducted in the limnetic region of each lake for 10 consecutive months from April 2008 to January 2009. The zooplankton community presented a wide range of responses to the predation pressure exerted by fish larvae in both environments, while fish larvae showed a typical pattern of normal diel vertical migration. Our results also demonstrated that the diel vertical migration is an important behaviour to avoid predation, since it reduces the spatial overlap between prey and potential predator, thus supporting the hypothesis that vertical migration is a defence mechanism against predation. PMID:26132018

  3. Vertical transport of mercury in a Wisconsin seepage lake

    SciTech Connect

    Hurley, J.P. (Univ. of Wisconsin, Madison (United States)); Watras, C.J. (Univ. of Wisconsin, Boulder Junction (United States))

    1990-01-09

    During summer stratification, dissolved and particulate mercury species reach maxima in oxygen-depleted, sulfide-rich bottom water of a Wisconsin seepage lake. Initially, it appeared that this hypolimnetic build-up was due to redox-controlled release from bottom sediments. However, Hg did not increase near the bottom sediments during winter anoxia, when lakes are sealed from atmospheric inputs and biological productivity is low. In contrast, Fe shows both a summer and winter build-up with depth. Reinterpretation of depth profiles using seston distributions and sediment trap collections suggests that hypolimnetic enrichment may result from the transport of epilimnetic Hg to deeper waters via biotic particles. Furthermore, a preliminary Hg mass balance for the ice-free season shows that atmospheric inputs are the dominant source of Hg to the lakes and that Hg inputs are removed by sedimentation. Mercury-rich biotic particles tend to accumulate in layers at depth through both settling and in situ growth. We hypothesize that recycling of Hg within these deep plankton layers has a strong influence on the distribution and speciation of Hg in these lakes.

  4. Water and gas chemistry at Lake Kivu (DRC): Geochemical evidence of vertical and horizontal heterogeneities in a multibasin structure

    Microsoft Academic Search

    F. Tassi; O. Vaselli; D. Tedesco; G. Montegrossi; T. Darrah; E. Cuoco; M. Y. Mapendano; R. Poreda; A. Delgado Huertas

    2009-01-01

    Waters and dissolved gases collected along vertical profiles in the five basins (Main, Kabuno Bay, Kalehe, Ishungu, and Bukavu) forming the 485 m deep Lake Kivu (Democratic Republic of the Congo) were analyzed to provide a geochemical conceptual model of the several processes controlling lake chemistry. The measured horizontal and vertical variations of water and gas compositions suggest that each

  5. Vertical distribution of zooplankton in subalpine and alpine lakes: Ultraviolet radiation, fish predation, and the transparency-gradient hypothesis

    Microsoft Academic Search

    Kirsten Kessler; Ryan S. Lockwood; Craig E. Williamson; Jasmine E. Saros

    2008-01-01

    The transparency-gradient hypothesis argues that ultraviolet radiation (UV) is a primary determinant of the vertical distribution of zooplankton in transparent lakes with fewer fish, while fish predation is the primary driver in less transparent lakes where fish are more abundant. We measured vertical profiles of UV, photosynthetically active radiation (PAR, essentially visible light used as a proxy for fish predation),

  6. Diel and Seasonal Patterns of Horizontal and Vertical Movements of Telemetered Cutthroat Trout in Lake Washington, Washington

    Microsoft Academic Search

    Gretchen M. Nowak; Thomas P. Quinn

    2002-01-01

    Salmonid fishes are often the top predators in cool lakes, and their movements may reflect the distribution of available prey as well as physical factors such as light and temperature. We used ultrasonic telemetry to examine the vertical and horizontal movement patterns of cutthroat trout Oncorhynchus clarki in Lake Washington, a monomictic lake in Washington State. We hypothesized that the

  7. Repeated Parallel Evolution of Parental Care Strategies within Xenotilapia, a Genus of Cichlid Fishes from Lake

    E-print Network

    Hofmann, Hans A.

    Fishes from Lake Tanganyika Michael R. Kidd1,2 *, Nina Duftner1 , Stephan Koblmu¨ ller3 , Christian within Xenotilapia, a Genus of Cichlid Fishes from Lake Tanganyika. PLoS ONE 7(2): e31236. doi:10 life history traits based on species-level phylogenies. The Xenotilapia lineage within the endemic Lake

  8. Small-scale turbulence and vertical mixing in Lake Baikal

    Microsoft Academic Search

    Thomas M. Ravens; Otti Kocsis; Alfred Wüest; N. Granin

    2000-01-01

    The water column of Lake Baikal is extremely weakly—but permanently—stratified below 250 m. Despite the thickness of this relatively stagnant water mass of more than 1000 m, the water age (time since last contact with the atmosphere) is only slightly more than a decade, indicating large-scale advective exchange. In the stratified deep water, the fate of water constituents is determined

  9. Vertically-challenged limnology; contrasts between deep and shallow lakes

    Microsoft Academic Search

    Brian Moss; Meryem Beklioglu; Laurence Carvalho; Sabri Kilinc; Suzanne McGowan; Deborah Stephen

    1997-01-01

    Previous work on a set of small lakes, of varying depth, themeresof North West England, has shown that nitrogen availabilitycontrols the summer phytoplankton populations in the deeperones(max depth>3 m) and zooplankton grazing in shallow ones. Themeres have generally high total phosphorus concentrations andthismay be a natural phenomenon dependent on the localgeochemistry.Some anthropogenic eutrophication has occurred, however, andfroma chain of three

  10. Internal seiche climatology in a small lake where transversal and second vertical modes are usually observed

    Microsoft Academic Search

    E. Roget; G. Salvude; F. Zamboni

    1997-01-01

    From the analysis of thermistor chain data recorded in a small clongatcd lake, compared with the results of numerical simulations, second vertical modes of the internal scichcs are shown to be active during more than two- thirds of the whole stratifcd period, although no rcsonancc with the wind is observed. On the other hand, due to the wind pattern, transversal

  11. Big Soda Lake (Nevada). 4. Vertical fluxes of particulate matter: Seasonality and variations across the chemocline

    Microsoft Academic Search

    JAMES E. CLOERN; BRIAN E. COLE; SALLY M. WIENKE

    1987-01-01

    Vertical fluxes of particulate organic matter were measured with sediment traps above and below the chcmocline of Big Soda Lake to dcfinc the seasonality of sinking losses from the mixolimnion and dctcrmine the effectiveness of the chcmocline (pycnocline) as a barrier to the sinking of biogenic particles. Seasonality of sedimentation rates reflected seasonal changes in the community of au- totrophs.

  12. Vertical and Seasonal Dynamics of Planktonic Ciliates in a Strongly Stratified Hypertrophic Lake

    Microsoft Academic Search

    Priit Zingel

    2005-01-01

    Seasonal population dynamics and the vertical distribution of planktonic ciliates in a hypertrophic and strongly stratified temperate lake were studied from April to October in 2000 and from April to June in 2001. In the epi- and metalimnion the ciliate abundance peaked in spring and late summer, reaching maximum values in the metalimnion (86 cells ml?1) on 7th August 2000. In the

  13. Vertical and seasonal dynamics of planktonic ciliates in a strongly stratified hypertrophic lake

    Microsoft Academic Search

    Priit Zingel

    Seasonal population dynamics and the vertical distribution of planktonic ciliates in a hypertrophic and strongly stratified\\u000a temperate lake were studied from April to October in 2000 and from April to June in 2001. In the epi- and metalimnion the\\u000a ciliate abundance peaked in spring and late summer, reaching maximum values in the metalimnion (86 cells ml?1) on 7th August 2000.

  14. Temperature sensitivity of vertical distributions of zooplankton and planktivorous fish in a stratified lake.

    PubMed

    Helland, Ingeborg Palm; Freyhof, Jörg; Kasprzak, Peter; Mehner, Thomas

    2007-03-01

    Recent studies have indicated that temporal mismatches between interacting populations may be caused by consequences of global warming, for example rising spring temperatures. However, little is known about the impact of spatial temperature gradients, their vulnerability to global warming, and their importance for interacting populations. Here, we studied the vertical distribution of two planktivorous fish species (Coregonus spp.) and their zooplankton prey in the deep, oligotrophic Lake Stechlin (Germany). The night-time vertical centre of gravity both of the fish populations and of two of their prey groups, daphnids and copepods, were significantly correlated to the seasonally varying water temperature between March and December 2005. During the warmer months, fish and zooplankton occurred closer to the surface of the lake and experienced higher temperatures. The Coregonus populations differed significantly in their centre of gravity; hence, also, the temperature experienced by the populations was different. Likewise, daphnids and copepods occurred in different water depths and hence experienced different temperatures at least during the summer months. We conclude that any changes in the vertical temperature gradient of the lake as a result of potential future global warming may impact the two fish populations differently, and may shape interaction strength and timing between fish and their zooplankton prey. PMID:17024386

  15. Vertical distribution of nitrogen-fixing phylotypes in a meromictic, hypersaline lake.

    PubMed

    Steward, G F; Zehr, J P; Jellison, R; Montoya, J P; Hollibaugh, J T

    2004-01-01

    We investigated the diversity of nitrogenase genes in the alkaline, moderately hypersaline Mono Lake, California to determine (1) whether nitrogen-fixing (diazotrophic) populations were similar to those in other aquatic environments and (2) if there was a pattern of distribution of phylotypes that reflected redox conditions, as well as (3) to identify populations that could be important in N dynamics in this nitrogen-limited lake. Mono Lake has been meromictic for almost a decade and has steep gradients in oxygen and reduced compounds that provide a wide range of aerobic and anaerobic habitats. We amplified a fragment of the nitrogenase gene (nifH) from planktonic DNA samples collected at three depths representing oxygenated surface waters, the oxycline, and anoxic, ammonium-rich deep waters. Forty-three percent of the 90 sequences grouped in nifH Cluster I. The majority of clones (57%) grouped in Cluster III, which contains many known anaerobic bacteria. Cluster I and Cluster III sequences were retrieved at every depth indicating little vertical zonation in sequence types related to the prominent gradients in oxygen and ammonia. One group in Cluster I was found most often at every depth and accounted for 29% of all the clones. These sequences formed a subcluster that contained other environmental clones, but no cultivated representatives. No significant nitrogen fixation was detected by the 15N2 method after 48 h of incubation of surface, oxycline, or deep waters, suggesting that pelagic diazotrophs were contributing little to nitrogen fluxes in the lake. The failure to measure any significant nitrogen fixation, despite the detection of diverse and novel nitrogenase genes throughout the water column, raises interesting questions about the ecological controls on diazotrophy in Mono Lake and the distribution of functional genes in the environment. PMID:15259267

  16. Vertical structure of archaeal communities and the distribution of ammonia monooxygenase A gene variants in two meromictic High Arctic lakes.

    PubMed

    Pouliot, Jérémie; Galand, Pierre E; Lovejoy, Connie; Vincent, Warwick F

    2009-03-01

    The distribution of archaeal amoA and 16S rRNA genes was evaluated in two marine-derived, meromictic lakes in the Canadian High Arctic: Lake A and Lake C1 on the northern coast of Ellesmere Island. The amoA gene was recorded in both lakes, with highest copy numbers in the oxycline. Sequence analysis showed that amoA from the two lakes shared 94% similarity, indicating at least two phylogenetically distinct clusters. Clone libraries of archaeal 16S rRNA genes from Lake A revealed strong vertical differences in archaeal community diversity and composition down the water column. The oxic layer was dominated by one group of Euryarchaeota affiliated to the Lake Dagow Sediment (LDS) cluster. This group was absent from the oxycline, which had an extremely low archaeal diversity of two phylotypes. Both belonged to the Crenarchaeota Marine Group I (MGI), the marine group that has been linked to archaeal amoA; however, there was a low ratio of amoA to MGI copy numbers, suggesting that many MGI Archaea did not carry the amoA gene. The anoxic zone contained representatives of the RC-V (Rice Cluster-V) and LDS clusters of Euryarchaeota. These results show the strong vertical differentiation of archaeal communities in polar meromictic lakes, and they suggest archaeal nitrification within the oxycline of these highly stratified waters. PMID:19207564

  17. Lakes and reservoirs as sentinels, integrators, and regulators of climate change Craig E. Williamson,a,* Jasmine E. Saros,b Warwick F. Vincent,c and John P. Smold

    E-print Network

    Vincent, Warwick F.

    that they provide (Vincent 2009; Williamson et al. 2009). Even the deepest and largest lakes in the world, from Lake Tanganyika in Africa (O'Reilly et al. 2003) to Lake Baikal in Siberia (Hampton et al. 2

  18. Water and gas chemistry at Lake Kivu (DRC): Geochemical evidence of vertical and horizontal heterogeneities in a multibasin structure

    NASA Astrophysics Data System (ADS)

    Tassi, F.; Vaselli, O.; Tedesco, D.; Montegrossi, G.; Darrah, T.; Cuoco, E.; Mapendano, M. Y.; Poreda, R.; Delgado Huertas, A.

    2009-02-01

    Waters and dissolved gases collected along vertical profiles in the five basins (Main, Kabuno Bay, Kalehe, Ishungu, and Bukavu) forming the 485 m deep Lake Kivu (Democratic Republic of the Congo) were analyzed to provide a geochemical conceptual model of the several processes controlling lake chemistry. The measured horizontal and vertical variations of water and gas compositions suggest that each basin has distinct chemical features produced by (1) different contribution from long circulating fluid system containing magmatic CO2, responsible of the huge CO2(CH4)-rich reservoir hosted within the deep lake water; (2) spatial variations of the biomass distribution and/or speciation; and (3) solutes from water-rock interactions. The Kabuno Bay basin is characterized by the highest rate of magmatic fluid input. Accordingly, this basin must be considered the most hazardous site for possible gas outburst that could be triggered by the activity of the Nyiragongo and Nyamulagira volcanoes, located a few kilometers north of the lake.

  19. Zooplankton grazing in a eutrophic lake: implications of diel vertical migration. [Scenedesmus; Eudiaptomus; Daphnia; Ceriodaphnia; Synechococcus

    SciTech Connect

    Lampert, W.; Taylor, B.E.

    1985-02-01

    During summer and fall, depth profiles of zooplankton community grazing were determined in situ during day and night in the Schoehsee, a small eutrophic lake. Labeled algae of two different sizes were mixed with the natural suspension of phytoplankton in a grazing chamber. A small blue-green alga (Synechococcus, 1 ..mu..m) was labeled with /sup 32/P; a larger green alga (Scenedesmus, 4-15 ..mu..m) was labeled with /sup 14/C. During summer, grazing in the upper 5 m was negligible during day but strong at night. Hence, algae grow relatively unimpeded by grazing during daytime but are harvested at night. Vertical and diel differences in grazing rates disappeared when the vertical migration ceased in fall. Selectivity of grazing was controlled by the zooplankton species composition. Eudiaptomus showed a strong preference for Scenedesmus. Daphnia showed a slight preference for Scenedesmus, but Ceriodaphnia preferred Synechococcus. Cyclopoid copepodites did not ingest the small blue-green. Because Daphnia and Eudiaptomus were dominant, grazing rates on larger cells were usually higher than grazing rates on the small cells. Negative electivity indices for scenedesmus occurred only when the biomass of large crustaceans was extremely low (near the surface, during day). Zooplankton biomass was the main factor controlling both vertical and seasonal variations in grazing. Highest grazing rates (65%/d) were measured during fall when zooplankton abundance was high. Because differential losses can produce substantial errors in the results, it was necessary to process the samples on the boat immediately after collection, without preservation.

  20. On the Combined Use of GRACE and Geodetic Observations for Vertical Motion in the Great Lakes Region

    Microsoft Academic Search

    E. Rangelova; G. Fotopoulos; M. G. Sideris

    2007-01-01

    As the measurements from geodetic observations become more accurate, they are implemented to not only empirically derive velocity surfaces but also to infer mantle viscosity. Accurate empirical models for vertical crustal motion are of particular interest in the Great Lakes region, where the line of zero motion (hinge line) is an important constraint for postglacial rebound modelling. With the abundance

  1. Do Daphnia use metalimnetic organic matter in a north temperate lake? An analysis of vertical migration

    USGS Publications Warehouse

    Brosseau, Chase Julian; Cline, Timothy J.; Cole, Jonathan J.; Hodgson, James R.; Pace, Michael L.; Weidel, Brian C.

    2012-01-01

    Diel vertical migration of zooplankton is influenced by a variety of factors including predation, food, and temperature. Research has recently shifted from a focus on factors influencing migration to how migration affects nutrient cycling and habitat coupling. Here we evaluate the potential for Daphnia migrations to incorporate metalimnetic productivity in a well-studied northern Wisconsin lake. We use prior studies conducted between 1985 and 1990 and current diel migration data (2008) to compare day and night Daphnia vertical distributions with the depth of the metalimnion (between the thermocline and 1% light depth). Daphnia migrate from a daytime mean residence depth of between about 1.7 and 2.5 m to a nighttime mean residence depth of between 0 and 2.0 m. These migrations are consistent between the prior period and current measurements. Daytime residence depths of Daphnia are rarely deep enough to reach the metalimnion; hence, metalimnetic primary production is unlikely to be an important resource for Daphnia in this system.

  2. Sediment infill within rift basins: Facies distribution and effects of deformation: Examples from the Kenya and Tanganyika Rifts, East Africa

    SciTech Connect

    Tiercelin, J.J.; Lezzar, K.E. (Universite de Bretagne Occidentale, Brest (France)); Richert, J.P. (Elf Aquitaine, Pau (France))

    1994-07-01

    Oil is known from lacustrine basins of the east African rift. The geology of such basins is complex and different depending on location in the eastern and western branches. The western branch has little volcanism, leading to long-lived basins, such as Lake Tanganyika, whereas a large quantity of volcanics results in the eastern branch characterized by ephemeral basins, as the Baringo-Bogoria basin in Kenya. The Baringo-Bogoria basin is a north-south half graben formed in the middle Pleistocene and presently occupied by the hypersaline Lake Bogoria and the freshwater Lake Baringo. Lake Bogoria is fed by hot springs and ephemeral streams controlled by grid faults bounding the basin to the west. The sedimentary fill is formed by cycles of organic oozes having a good petroleum potential and evaporites. On the other hand, and as a consequence of the grid faults, Lake Baringo is fed by permanent streams bringing into the basin large quantities of terrigenous sediments. Lake Tanganyika is a meromictic lake 1470 m deep and 700 km long, of middle Miocene age. It is subdivided into seven asymmetric half grabens separated by transverse ridges. The sedimentary fill is thick and formed by organic oozes having a very good petroleum potential. In contrast to Bogoria, the lateral distribution of organic matter is characterized by considerable heterogeneity due to the existence of structural blocks or to redepositional processes.

  3. Vertical stratification of bacteria and archaea in sediments of a boreal stratified humic lake

    NASA Astrophysics Data System (ADS)

    Rissanen, Antti J.; Mpamah, Promise; Peura, Sari; Taipale, Sami; Biasi, Christina; Nykänen, Hannu

    2015-04-01

    Boreal stratified humic lakes, with steep redox gradients in the water column and in the sediment, are important sources of methane (CH4) to the atmosphere. CH4 flux from these lakes is largely controlled by the balance between CH4-production (methanogenesis), which takes place in the organic rich sediment and in the deepest water layers, and CH4-consumption (methanotrophy), which takes place mainly in the water column. While there is already some published information on the activity, diversity and community structure of bacteria in the water columns of these lakes, such information on sediment microbial communities is very scarce. This study aims to characterize the vertical variation patterns in the diversity and the structure of microbial communities in sediment of a boreal stratified lake. Particular focus is on microbes with the potential to contribute to methanogenesis (fermentative bacteria and methanogenic archaea) and to methanotrophy (methanotrophic bacteria and archaea). Two sediment cores (26 cm deep), collected from the deepest point (~6 m) of a small boreal stratified lake during winter-stratification, were divided into depth sections of 1 to 2 cm for analyses. Communities were studied from DNA extracted from sediment samples by next-generation sequencing (Ion Torrent) of polymerase chain reaction (PCR) - amplified bacterial and archaeal 16S rRNA gene amplicons. The abundance of methanogenic archaea was also specifically studied by quantitative-PCR of methyl coenzyme-M reductase gene (mcrA) amplicons. Furthermore, the community structure and the abundance of bacteria were studied by phospholipid fatty acid (PLFA) analysis. Dominant potential fermentative bacteria belonged to families Syntrophaceae, Clostridiaceae and Peptostreptococcaceae. There were considerable differences in the vertical distribution among these groups. The relative abundance of Syntrophaceae started to increase from the sediment surface, peaked at depth layer from 5 to 10 cm (up to 21 % of bacterial 16S rRNA gene amplicons) and decreased gradually towards deeper layers while the relative abundances of Clostridiaceae and Peptostreptococcaceae started to increase at deeper depths, at 5 cm and 10 cm, respectively, both peaking at depth layer from 20 to 26 cm (Clostridiaceae up to 13 % and Peptostreptococcaceae up to 11 % of bacterial 16S rRNA amplicons). Methanogenic community was dominated by acetoclastic methanogens (genus Methanosaeta), which were most abundant at depth layer from sediment surface to 10 cm (up to 87 % of archaeal 16S rRNA gene amplicons) and decreased drastically until the depth of 18 cm having quite stable relative abundance from 18 to 26 cm (5 to 11 % of archaeal 16S rRNA gene amplicons). Hydrogenotrophic methanogens (Methanoregula, Methanolinea, Methanospirillum, Methanocella) (3 to 11 % of archaeal 16S rRNA gene amplicons) did not show any specific depth patterns. The proportion of methanotrophic microbes was very low and they consisted almost completely of type II methanotrophic bacteria (family Methylocystaceae), which had highest relative abundance at depth layer from 5 to 10 cm (up to 3 % of bacterial 16S rRNA gene amplicons) and were almost absent below 15 cm. Anaerobic methanotrophic archaea were not detected. These findings will be discussed with results from PLFA and q-PCR analyses.

  4. The influence of light on the diel vertical migration of young-of-the-year burbot Lota lota in Lake Constance

    Microsoft Academic Search

    W. N. Probst; R. Eckmann

    2009-01-01

    The diel vertical distribution of young-of-the-year (YOY) burbot Lota lota in the pelagic zone of Lake Constance was compared to light intensity at the surface and to the light intensity at their mean depth. Lota lota larvae inhabited the pelagic zone of Lake Constance from the beginning of May until the end of August. From early June, after the stratification

  5. Holocene Full-Vector Secular Variation from African Lakes

    NASA Astrophysics Data System (ADS)

    Lund, S.; Platzman, E. S.; Johnson, T. C.; Scholz, C. A.; Cohen, A. S.; Russell, J. M.

    2014-12-01

    We are developing a regional pattern of Holocene paleomagnetic secular variation (PSV) from four lakes in East Africa - Lake Turkana (3°N), Lake Victoria (1°S), Lake Tanganyika (5°S), and Lake Malawi (10°S). Detailed paleomagnetic and rock magnetic measurements have been made on two cores from Lake Malawi (9m meters in depth, last ~10,000 years), two cores from Lake Victoria (8 m, last ~8,000 years), 11 cores from Lake Turkana (2-9 m, last ~10,000 years), and one core from Lake Tanganyika (5 m, last ~5,000 years). Our rock magnetic studies identify significant intervals of magnetic mineral dissolution in Lakes Victoria and Tanganyika making parts of these cores unsuitable for relative paleointensity studies. On the other hand, rock magnetic variability in the Lake Malawi and Lake Turkana cores are stable and correlatable among cores. We have recovered directional secular variation records from Lakes Malawi, Victoria, and Turkana. Millennial-scale inclination and declination features can be correlated among cores at each lake and between lakes. We have also recovered relative paleointensity records from Lakes Malawi and Turkana. More than 20 radiocarbon dates and detailed seismic stratigraphy (Turkana) provide critical added information for correlating and dating the paleomagnetic records.

  6. Observations of the second vertical mode of the internal seiche in an alpine lake

    Microsoft Academic Search

    M. Miinnich; A. Wiiest; D. M. IMBODEN

    1992-01-01

    The analysis of wind and temperature data from Alpnacher See (Switzerland) shows the second vertical mode of the internal (baroclinic) seiche to dominate over the first vertical mode. Resonance with diurnal wind is responsible for the high amplitudes of the second mode. Two different models are used to calculate the periods and velocity distribution of the various modes of the

  7. Vertical gradients of PCBs and PBDEs in fish from European high mountain lakes

    NASA Astrophysics Data System (ADS)

    Grimalt, J. O.; Gallego, E.; Bartrons, M.; Catalan, J.; Camarero, L.; Stuchlik, E.; Battarbee, R.

    2006-12-01

    A first case of temperature-dependent distribution of polybromodiphenyl eters (PBDEs) in remote areas is shown. Analysis of these compounds in fish from Pyrenean lakes distributed along an altitudinal transect shows higher concentrations at lower temperatures, as predicted in the global distillation model. Conversely, no temperature-dependent distribution is observed in a similar transect in the Tatra mountains (Central Europe) nor in fish from high mountain lakes distributed throughout Europe. The fish concentrations of polychlorobiphenyls (PCBs) examined for comparison showed significant temperature correlations in all these studied lakes. In the interval of feasible temperatures for high mountain lakes, cold trapping of both PCBs and PBDEs concerned the less volatile congeners. In the Pyrenean lake transect the concentrations of PCBs and PBDEs in fish were correlated despite the distinct use of these compounds and their 40 year time-lag of emissions to the environment. Thus, temperature effects have overcome these anthropogenic differences constituting at present the main process determining their distributions. The cases of distinct PBDE and PCB behavior in high mountains can therefore be interpreted to reflect early stages in the environmental distribution of the former compounds.

  8. Comparative aspects of adaptive radiation and speciation in Lake Baikal and the great rift lakes of Africa

    Microsoft Academic Search

    Geoffrey Fryer

    1991-01-01

    Lakes Baikal, Tanganyika and Malawi have similar origins, are physiographically similar, and of similar size. The hydrological regime of Baikal is, however, very different from that which prevails in its African sisters. Apart from being much cooler, it differs fundamentally in being oxygenated to all depths while the two great African rift lakes possess only a relatively thin oxygenated surface

  9. Age-specific light preferences and vertical migration patterns of a Great Lakes invasive invertebrate, Hemimysis anomala

    USGS Publications Warehouse

    Boscarino, Brent T.; Halpin, Kathleen E.; Rudstam, Lars G.; Walsh, Maureen G.; Lantry, Brian F.

    2012-01-01

    We use a combination of spectral sensitivity analyses, laboratory behavioral observations and field distributions of a vertically migrating invertebrate, Hemimysis anomala (a recent invasive species to the Laurentian Great Lakes of North America), to determine if light preference and timing of emergence has an ontogenetic component. Juvenile Hemimysis (?3.4 and 10?2.4 mylux— a Hemimysis-specific unit of brightness derived from visual pigment analyses (wavelength of maximum absorbance = 500 nm; 1 mylux ~ 159 lx). These preferred light levels are equivalent to those present during nautical twilight on the Earth's surface and were several orders of magnitude brighter than those most preferred by adults (> 4.5 mm) in the laboratory (10?6.4 to 10?7.4 mylux). Both size classes completely avoided light levels of 10?0.4 mylux and greater, which are representative of daytime light levels at the Earth's surface. Net hauls taken at ~ 20-min intervals from sunset to the end of nautical twilight on two sampling occasions on Seneca Lake, New York (sampling depth = 2 m) revealed that juveniles emerged into the water column during civil twilight. Adult Hemimysis emerged later during nautical twilight when juveniles had already reached their maximum abundance in the water column. Laboratory-derived light preferences successfully predicted the timing of emergence and time of maximal abundance of both size classes on both sampling occasions. This study is one of the first to demonstrate that Hemimysis diel vertical migration has an ontogenetic component and to report the specific light levels likely to initiate and limit vertical movements.

  10. Functional coupling constrains craniofacial diversification in Lake Tanganyika cichlids

    PubMed Central

    Tsuboi, Masahito; Gonzalez-Voyer, Alejandro; Kolm, Niclas

    2015-01-01

    Functional coupling, where a single morphological trait performs multiple functions, is a universal feature of organismal design. Theory suggests that functional coupling may constrain the rate of phenotypic evolution, yet empirical tests of this hypothesis are rare. In fish, the evolutionary transition from guarding the eggs on a sandy/rocky substrate (i.e. substrate guarding) to mouthbrooding introduces a novel function to the craniofacial system and offers an ideal opportunity to test the functional coupling hypothesis. Using a combination of geometric morphometrics and a recently developed phylogenetic comparative method, we found that head morphology evolution was 43% faster in substrate guarding species than in mouthbrooding species. Furthermore, for species in which females were solely responsible for mouthbrooding the males had a higher rate of head morphology evolution than in those with bi-parental mouthbrooding. Our results support the hypothesis that adaptations resulting in functional coupling constrain phenotypic evolution. PMID:25948565

  11. Functional coupling constrains craniofacial diversification in Lake Tanganyika cichlids.

    PubMed

    Tsuboi, Masahito; Gonzalez-Voyer, Alejandro; Kolm, Niclas

    2015-05-01

    Functional coupling, where a single morphological trait performs multiple functions, is a universal feature of organismal design. Theory suggests that functional coupling may constrain the rate of phenotypic evolution, yet empirical tests of this hypothesis are rare. In fish, the evolutionary transition from guarding the eggs on a sandy/rocky substrate (i.e. substrate guarding) to mouthbrooding introduces a novel function to the craniofacial system and offers an ideal opportunity to test the functional coupling hypothesis. Using a combination of geometric morphometrics and a recently developed phylogenetic comparative method, we found that head morphology evolution was 43% faster in substrate guarding species than in mouthbrooding species. Furthermore, for species in which females were solely responsible for mouthbrooding the males had a higher rate of head morphology evolution than in those with bi-parental mouthbrooding. Our results support the hypothesis that adaptations resulting in functional coupling constrain phenotypic evolution. PMID:25948565

  12. Buoyancy regulation and vertical migration by Oscillatoria rubescens in Crooked Lake, Indiana

    Microsoft Academic Search

    Allan Konopka

    1982-01-01

    Filaments of Oscillatoria rubescens stratified in the metalimnion of Crooked Lake, Indiana at depths of 6–9 m, where the incident light intensity averaged 2% of the surface intensity. Buoyancy (due to gas vesicles) was regulated in response to light intensity, and increased turgor pressure generated at high light intensity could contribute to the collapse of gas vesicles. Filaments exposed to

  13. Vertical distribution and organic matter production of photosynthetic sulfur bacteria in Japanese lakes

    Microsoft Academic Search

    MASAYUKI TAKAHASHI; SHUN-EI ICHIMURA

    1968-01-01

    The role of photosynthetic sulfur bacteria as primary producers in stagnant lakes having hydrogen sulfide is described. Photosynthetic bacteria normally appear at the boundary layer of the oxidative and reductive zones, where H& is present and the light intensity is lower than 10% of the surface value. The water of this layer was milky green or pink due to dense

  14. Wildlife Conservation in Tanganyika under German Colonial Rule

    Microsoft Academic Search

    Rolf D. Baldus

    At the beginning of the new millenium the conservation of wildlife and other natural resources in Tanzania is undergoing major changes. Interestingly enough, the situation was the same in Tanganyika, German East Africa one century ago. Whereas today the new concepts are called sustainable use, involvement of rural communities and maintaining biological diversity, at the beginning of last century one

  15. Vertical profiles of primary productivity, biomass and physico-chemical properties in meromictic Big Soda Lake, Nevada, U.S.A

    Microsoft Academic Search

    J. C. Priscu; R. P. Axler; R. G. Carlton; J. E. Reuter; P. A. Arneson; C. R. Goldman

    1982-01-01

    The contribution of bacteria to total primary production was estimated in Big Soda Lake and related to vertical profiles of biomass and various physical and chemical properties. The purple sulfur bacteriaThiocapsa sp. was responsible for 25% of the total primary production. Bacteriochlorophyll (BChl) distribution and DCMU sensitivity experiments confirmed this bacterial activity. High concentrations of photosynthetically inactive phytoplankton were detected

  16. Lake Ontario zooplankton in 2003 and 2008: community changes and vertical redistribution

    USGS Publications Warehouse

    Rudstam, Lars G.; Holeck, Kristen T.; Bowen, Kelly L.; Watkins, James M.; Weidel, Brian C.; Luckey, Frederick J.

    2014-01-01

    Lake-wide zooplankton surveys are critical for documenting and understanding food web responses to ecosystem change. Surveys in 2003 and 2008 during the binational intensive field year in Lake Ontario found that offshore epilimnetic crustacean zooplankton declined by a factor of 12 (density) and factor of 5 (biomass) in the summer with smaller declines in the fall. These declines coincided with an increase in abundance of Bythotrephes and are likely the result of direct predation by, or behavioral responses to this invasive invertebrate predator. Whole water column zooplankton density also declined from 2003 to 2008 in the summer and fall (factor of 4), but biomass only declined in the fall (factor of 2). The decline in biomass was less than the decline in density because the average size of individual zooplankton increased. This was due to changes in the zooplankton community composition from a cyclopoid/bosminid dominated community in 2003 to a calanoid dominated community in 2008. The increase in calanoid copepods was primarily due to the larger species Limnocalanus macrurus and Leptodiaptomus sicilis. These coldwater species were found in and below the thermocline associated with a deep chlorophyll layer. In 2008, most of the zooplankton biomass resided in or below the thermocline during the day. Increased importance of copepods in deeper, colder water may favor cisco and rainbow smelt over alewife because these species are better adapted to cold temperatures than Alewife.

  17. Lake

    ERIC Educational Resources Information Center

    Wien, Carol Anne

    2008-01-01

    The lake is blue black and deep. It is a glaciated finger lake, clawed out of rock when ice retracted across Nova Scotia in a northerly direction during the last ice age. The lake is narrow, a little over a mile long, and deep, 90 to 190 feet in places according to local lore, off the charts in others. The author loves to swim there, with a sense…

  18. The Vertical Dynamics of Larval Chironomids on Artificial Substrates in Lake Lido (Bogor, Indonesia)

    PubMed Central

    Wardiatno, Yusli; Krisanti, Majariana

    2013-01-01

    The composition and abundance of chironomid larval communities was studied on artificial substrates in Lido Lake, located in Bogor, West Java, Indonesia. The lake is organically enriched as a result of fish farming activity. Seventy two artificial substrates were deployed at three depths (2.0, 3.5 and 5.0 m) at two sites: a cage culture site and a non-cage culture site (control). Larval chironomid larvae were collected 7, 14, 28 and 56 days after the artificial substrates were deployed. In addition, selected physical and chemical parameters of the water were simultaneously measured. Three chironomid subfamilies, the Chironominae, Tanypodinae and Orthocladiinae, were found at both sites. At the cage culture site, both diversity and total abundance were significantly higher at the 2.0 and 3.5 m depths than at the 5.0 m depth, but this was not the case at the non-cage culture site. Based on pooling of the data from all depths, a Mann-Whitney U test showed that the non-cage culture site had a significantly higher diversity and total abundance than the cage culture site. Dissolved oxygen (DO) and turbidity showed significant differences between the 2.0 m depth and the 2 greater depths at the cage culture site, whereas none of the environmental parameters showed significant differences among the three depths at the non-cage culture site. A comparison of the environmental parameters at the same depth at the two sites showed significant differences in turbidity, pH and DO. A Spearman rank correlation analysis at the cage culture site showed that abundance and DO were positively correlated, whereas abundance and turbidity were negatively correlated. However, only pH was negatively correlated with abundance at the non-cage culture site. PMID:24575246

  19. APPLICATION OF A SEDIMENT DYNAMICS MODEL FOR ESTIMATION OF VERTICAL BURIAL RATES OF PCBS IN SOUTHERN LAKE MICHIGAN

    EPA Science Inventory

    The recovery of Lake Michigan from PCB contamination depends on the rates of reduction in PCB input from external sources and removal of PCBs present in the lake system. The loading of PCBs to the Great Lakes should be decreasing. Consequently, if the PCB burden of the lake is al...

  20. Analysis of patterns of vertical and temporal distribution of phytoplankton using multifactorial analysis: Acidic Lake Caviahue, Patagonia, Argentina

    Microsoft Academic Search

    Sara G. Beamud; Mónica M. Diaz; Nora B. Baccalá; Fernando L. Pedrozo

    2010-01-01

    Most existing studies on the algal communities of acid lakes are based on environments that have been caused by anthropogenic disturbances. Such lakes have a different origin compared to the natural acidic lakes and could be expected to differ also in the mechanisms controlling phytoplankton and trophic status. Planktonic community in Lake Caviahue is somewhat diverse in spite of the

  1. Interactive effects of vertical mixing, nutrients and ultraviolet radiation: in situ photosynthetic responses of phytoplankton from high mountain lakes in Southern Europe

    NASA Astrophysics Data System (ADS)

    Helbling, E. W.; Carrillo, P.; Medina-Sánchez, J. M.; Durán, C.; Herrera, G.; Villar-Argaiz, M.; Villafañe, V. E.

    2013-02-01

    Global change, together with human activities, has resulted in increasing amounts of organic material (including nutrients) that water bodies receive. This input further attenuates the penetration of solar radiation, leading to the view that opaque lakes are more "protected" from solar ultraviolet radiation (UVR) than clear ones. Vertical mixing, however, complicates this view as cells are exposed to fluctuating radiation regimes, for which the effects have, in general, been neglected. Furthermore, the combined impacts of mixing, together with those of UVR and nutrient inputs are virtually unknown. In this study, we carried out complex in situ experiments in three high mountain lakes of Spain (Lake Enol in the National Park Picos de Europa, Asturias, and lakes Las Yeguas and La Caldera in the National Park Sierra Nevada, Granada), used as model ecosystems to evaluate the joint impact of these climate change variables. The main goal of this study was to address the question of how short-term pulses of nutrient inputs, together with vertical mixing and increased UVR fluxes modify the photosynthetic responses of phytoplankton. The experimentation consisted in all possible combinations of the following treatments: (a) solar radiation: UVR + PAR (280-700 nm) versus PAR (photosynthetically active radiation) alone (400-700 nm); (b) nutrient addition (phosphorus (P) and nitrogen (N)): ambient versus addition (P to reach to a final concentration of 30 ?g P L-1, and N to reach N:P molar ratio of 31); and (c) mixing: mixed (one rotation from surface to 3 m depth (speed of 1 m 4 min-1, total of 10 cycles)) versus static. Our findings suggest that under ambient nutrient conditions there is a synergistic effect between vertical mixing and UVR, increasing phytoplankton photosynthetic inhibition and excretion of organic carbon (EOC) from opaque lakes as compared to algae that received constant mean irradiance within the epilimnion. The opposite occurs in clear lakes where antagonistic effects were determined, with mixing partially counteracting the negative effects of UVR. Nutrient input, mimicking atmospheric pulses from Saharan dust, reversed this effect and clear lakes became more inhibited during mixing, while opaque lakes benefited from the fluctuating irradiance regime. These climate change related scenarios of nutrient input and increased mixing, would not only affect photosynthesis and production in lakes, but might also further influence the microbial loop and trophic interactions via enhanced EOC under fluctuating UVR exposure.

  2. Dominant Microbial Composition and Its Vertical Distribution in Saline Meromictic Lake Kaiike (Japan) as Revealed by Quantitative Oligonucleotide Probe Membrane Hybridization

    Microsoft Academic Search

    Yoshikazu Koizumi; Hisaya Kojima; Manabu Fukui

    2004-01-01

    Vertical distributions of dominant bacterial populations in saline meromictic Lake Kaiike were investigated throughout the water column and sediment by quantitative oligonucleotide probe membrane hybridization. Three oligonucleotide probes specific for the small-subunit (SSU) rRNA of three groups of Chlorobiaceae were newly designed. In addition, three general domain (Bacteria, Archaea, and Eukarya)-specific probes, two - Proteobacteria-specific probes, a Chlorobiaceae-specific probe, and

  3. Vertical electrical sounding (VES) and multi-electrode resistivity in environmental impact assessment studies over some selected lakes: a case study

    Microsoft Academic Search

    N. Sundararajan; S. Sankaran; T. K. Al-Hosni

    A combined geophysical investigation consisting of vertical electrical sounding (VES) and multielectrode system was carried\\u000a out to map the subsurface resistivity in all major lakes which are highly polluted by the discharge of sewage and other chemical\\u000a effluents in greater Hyderabad, India. The structural features identified in the study area play a major role in groundwater\\u000a flow and storage. The

  4. Interactive effects of vertical mixing, nutrients and ultraviolet radiation: in situ photosynthetic responses of phytoplankton from high mountain lakes of Southern Europe

    NASA Astrophysics Data System (ADS)

    Helbling, E. W.; Carrillo, P.; Medina-Sanchez, J. M.; Durán, C.; Herrera, G.; Villar-Argaiz, M.; Villafañe, V. E.

    2012-07-01

    Global change, together with human activities had resulted in increasing amounts of organic material (including nutrients) received by water bodies. This input further attenuates the penetration of solar radiation leading to the view that opaque lakes are more "protected" from solar ultraviolet radiation (UVR) than clear ones. Vertical mixing, however, complicates this view as cells are exposed to fluctuating radiation regimes, which effects have in general been neglected. Even more, the combined impacts of mixing, together with those of UVR and nutrients input are virtually unknown. In this study, we carried out in situ experiments in three high mountain lakes of Spain (Lake Enol in Asturias, and lakes Las Yeguas and La Caldera in Granada) to determine the combined effects of these three variables associated to global change on photosynthetic responses of natural phytoplankton communities. The experimentation consisted in all possible combinations of the following treatments: (a) solar radiation: UVR + PAR (280-700 nm) versus PAR alone (400-700 nm); (b) nutrient addition (phosphorus (P) and nitrogen (N)): ambient versus addition (P to reach to a final concentration of 30 ?g P l-1, and N to reach a N : P molar ratio of 31) and, (c) mixing: mixed (one rotation from surface to 3 m depth (speed of 1 m every 4 min, total of 10 cycles) versus static. Our findings suggest that under in situ nutrient conditions there is a synergistic effect between vertical mixing and UVR, increasing phytoplankton photosynthetic inhibition and EOC from opaque lakes as compared to algae that received constant mean irradiance within the epilimnion. The opposite occurs in clear lakes where antagonistic effects were determined, with mixing partially counteracting the negative effects of UVR. Nutrients input mimicking atmospheric pulses from Saharan dust, reversed this effect and clear lakes became more inhibited during mixing, while opaque lakes benefited from the fluctuating irradiance regime. These climate change-related nutrients input and increased mixing would not only affect photosynthesis and production of lakes, but might also further influence the microbial loop and trophic interactions via enhanced EOC under fluctuating UVR exposure.

  5. Horizontal and vertical distribution of PCBs (polychlorinated biphenyls) in southern Lake Michigan sediments and the effect of Waukegan Harbor as a point source

    SciTech Connect

    Swackhamer, D.L.; Armstrong, D.E.

    1988-01-01

    The spatial distribution of PCBs in southern Lake Michigan sediments was obtained from the analysis of 66 box cores and 8 grab samples. PCB concentrations in surficial sediments were closely related to the sedimentation zone and to the oxidizable organic matter content of the sediments. Average surficial sediment concentrations ranged from 81 micrograms/g in depositional zones to 7.2 micrograms/g in non-depositional zones. The vertical distribution of PCBs was determined at several sites and was used to estimate the areal burden and flux of PCBs in each of the southern sedimentation zones. The total sediment PCB burden in the southern portion of the lake was estimated to be 5,900 kg. Southern Lake Michigan has received PCBs since approximately 1930 at an average flux of 7.1 micrograms/sq m/yr. The effect of Waukegan Harbor as a point source of PCBs to Lake Michigan was evaluated by comparing the PCB distribution and Aroclor composition of harbor sediments to those of sediments of decreasing distances from the harbor. Significant differences in total PCB concentration between non-depositional zones near the harbor and those in other areas of the basin indicate that Waukegan Harbor has influenced the PCB burden of Lake Michigan.

  6. [FeFe]-Hydrogenase Abundance and Diversity along a Vertical Redox Gradient in Great Salt Lake, USA

    PubMed Central

    Boyd, Eric S.; Hamilton, Trinity L.; Swanson, Kevin D.; Howells, Alta E.; Baxter, Bonnie K.; Meuser, Jonathan E.; Posewitz, Matthew C.; Peters, John W.

    2014-01-01

    The use of [FeFe]-hydrogenase enzymes for the biotechnological production of H2 or other reduced products has been limited by their sensitivity to oxygen (O2). Here, we apply a PCR-directed approach to determine the distribution, abundance, and diversity of hydA gene fragments along co-varying salinity and O2 gradients in a vertical water column of Great Salt Lake (GSL), UT. The distribution of hydA was constrained to water column transects that had high salt and relatively low O2 concentrations. Recovered HydA deduced amino acid sequences were enriched in hydrophilic amino acids relative to HydA from less saline environments. In addition, they harbored interesting variations in the amino acid environment of the complex H-cluster metalloenzyme active site and putative gas transfer channels that may be important for both H2 transfer and O2 susceptibility. A phylogenetic framework was created to infer the accessory cluster composition and quaternary structure of recovered HydA protein sequences based on phylogenetic relationships and the gene contexts of known complete HydA sequences. Numerous recovered HydA are predicted to harbor multiple N- and C-terminal accessory iron-sulfur cluster binding domains and are likely to exist as multisubunit complexes. This study indicates an important role for [FeFe]-hydrogenases in the functioning of the GSL ecosystem and provides new target genes and variants for use in identifying O2 tolerant enzymes for biotechnological applications. PMID:25464382

  7. The rise and fall of plankton: long-term changes in the vertical distribution of algae and grazers in Lake Baikal, Siberia.

    PubMed

    Hampton, Stephanie E; Gray, Derek K; Izmest'eva, Lyubov R; Moore, Marianne V; Ozersky, Tedy

    2014-01-01

    Both surface water temperatures and the intensity of thermal stratification have increased recently in large lakes throughout the world. Such physical changes can be accompanied by shifts in plankton community structure, including changes in relative abundances and depth distributions. Here we analyzed 45 years of data from Lake Baikal, the world's oldest, deepest, and most voluminous lake, to assess long-term trends in the depth distribution of pelagic phytoplankton and zooplankton. Surface water temperatures in Lake Baikal increased steadily between 1955 and 2000, resulting in a stronger thermal gradient within the top 50 m of the water column. In conjunction with these physical changes our analyses reveal significant shifts in the daytime depth distribution of important phytoplankton and zooplankton groups. The relatively heavy diatoms, which often rely on mixing to remain suspended in the photic zone, shifted downward in the water column by 1.90 m y(-1), while the depths of other phytoplankton groups did not change significantly. Over the same time span the density-weighted average depth of most major zooplankton groups, including cladocerans, rotifers, and immature copepods, exhibited rapid shifts toward shallower positions (0.57-0.75 m y(-1)). As a result of these depth changes the vertical overlap between herbivorous copepods (Epischura baikalensis) and their algal food appears to have increased through time while that for cladocerans decreased. We hypothesize that warming surface waters and reduced mixing caused these ecological changes. Future studies should examine how changes in the vertical distribution of plankton might impact energy flow in this lake and others. PMID:24586441

  8. The influence of light on the diel vertical migration of young-of-the-year burbot Lota lota in Lake Constance.

    PubMed

    Probst, W N; Eckmann, R

    2009-01-01

    The diel vertical distribution of young-of-the-year (YOY) burbot Lota lota in the pelagic zone of Lake Constance was compared to light intensity at the surface and to the light intensity at their mean depth. Lota lota larvae inhabited the pelagic zone of Lake Constance from the beginning of May until the end of August. From early June, after the stratification of the water column, fish performed diel vertical migrations (DVM) between the hypolimnion and epilimnion. The amplitude of DVM increased constantly during the summer and reached 70 m by the end of August. Lota lota started their ascent to the surface after sunset and descended into the hypolimnion after sunrise. As the YOY fish grew from May to August, they experienced decreasing diel maximum light intensities: in May and early June L. lota spent the day at light intensities >40 W m(-2), but they never experienced light intensities >0.1 W m(-2) after the end of June. From this time, L. lota experienced the brightest light intensities during dusk and dawn, suggesting feeding opportunities at crepuscular hours. The present study implies, that YOY L. lota in the pelagic zone of Lake Constance increased their DVM amplitude during the summer to counteract a perceived predation risk related to body size and pigmentation. PMID:20735530

  9. Geomagnetic polarity epochs: new data from Olduvai Gorge, Tanganyika

    USGS Publications Warehouse

    Gromme, C.S.; Hay, R.L.

    1967-01-01

    The lower lava flow of Bed I in Olduvai Gorge, Tanganyika, carries natural remanent magnetization (NRM) having normal polarity. Thermal demagnetization experiments demonstrate the stability of this NRM. Thus the Olduvai geomagnetic polarity event, which was originally named from the upper lava flow in Bed I, is represented in its type locality by two normally magnetized lavas. These lavas have been shown to be 1.9 m.y. old, and although they are distinct from each other in composition and surface structure, their eruptions appear to have been closely spaced in time. ?? 1967.

  10. Challenges of an ecosystem approach to water monitoring and management of the African Great Lakes

    Microsoft Academic Search

    Eric O. Odada; Daniel O. Olago

    2006-01-01

    The Great Lakes Belt of Africa cuts across five major drainage basins: The Nile, Congo-Zaire, Rift Valley, Coastal and Zambezi basins. The region contains the earth's largest aggregation of tropical lakes. Three of these lakes–Victoria, Tanganyika and Malawi—hold one quarter of the earth's total surface water supply, and are home to rich and diverse assemblages of fish. Apart from the

  11. Vertical and horizontal particle transport in the coastal waters of a large lake: An assessment by sediment trap and thorium-234 measurements

    NASA Astrophysics Data System (ADS)

    Waples, James T.; Klump, J. Val

    2013-10-01

    The horizontal and vertical flux of particulate material in the nearshore of southern Lake Michigan (0-40 m) was estimated with the naturally occurring radionuclide 234Th. Horizontal fluxes of 234Th supplemented apparent vertical fluxes of 234Th in the water column (based on local 234Th/238U disequilibria) by a factor of 7-14, reinforcing the importance of lateral transport in coastal environments. Calculated onshore transport of particulate material across the 40 m isobath was as high as 1.1 × 106 kg km-1 d-1, and exceeds estimates of terrigenous (riverine and bluff erosion) loading. Estimates of onshore flux of organic carbon exceeded areal primary productivity by as much as ˜300%, and should be considered in nearshore carbon budgets. Bottom-tethered sediment traps (placed 5 m above the bottom) measured sedimentation rates that were ˜1 order of magnitude lower than 234Th derived mass fluxes from the water column and ˜2 orders of magnitude lower than 234Th derived mass fluxes to the lakebed. We ascribe this difference to under collecting by the sediment trap either because of trap hydrodynamics or flux occurring below the trap capture plane. Cross-shore fluxes showed a periodicity of ˜4 days and correlated strongly with a topographic vorticity wave that is present throughout the year in southern Lake Michigan. The impact of this wave (as a driver of bidirectional cross-shore flux) on biogeochemical cycling and both nearshore and offshore food webs has not yet been explicitly considered.

  12. Vertical and temporal variability in concentration and distribution of thaumarchaeotal tetraether lipids in Lake Superior and the implications for the application of the TEX86 temperature proxy

    NASA Astrophysics Data System (ADS)

    Woltering, Martijn; Werne, Josef P.; Kish, Jason L.; Hicks, Randall; Sinninghe Damsté, Jaap S.; Schouten, Stefan

    2012-06-01

    This study investigated the vertical and temporal distribution of Thaumarchaeota derived core isoprenoid glycerol dialkyl glycerol tetraether (GDGT) lipids through sampling and analysis of both suspended particulate matter from the water column at different times in the annual cycle and a 3 year long record of settling particles in two sediment traps at different depths at an open lake location in Lake Superior. Results from these analyses suggest that Thaumarchaeota were present throughout the water column during times of overturning, but mainly resided below the depth of the thermocline (20-40 m) during the period of thermal stratification. Fluxes of thaumarchaeotal produced GDGTs were highly periodic and mainly occurred during two periods of the annual cycle (winter and late spring/early summer). A covariance of both branched and isoprenoid GDGT fluxes with the mass accumulation flux combined with the observation that those periods of maximum fluxes were associated with increased BIT index values, however, suggest that these two periods of elevated fluxes may be related to an influx of resuspended particles transported from shallower near shore regions of Lake Superior. During all sampling periods TEX86 inferred temperatures from SPM were in good agreement with in situ water temperatures of the depths at which the SPM was sampled. The observed range of TEX86 inferred temperatures in 3 years of settling particles is relatively small and does not show significantly higher inferred temperatures during the thermally stratified period, indicating that the sedimentary TEX86 signal during the summer thermally stratified period mainly originated from depths below the relatively shallow thermocline. Additionally, TEX86 values during the winter period of increased fluxes did not capture the decrease in water temperatures observed throughout the water column during this period, and thus may be a further indication that the thaumarchaeotal lipid flux was the result of sediment focusing. Flux-weighted TEX86 inferred temperatures from both sediment traps were in good agreement with TEX86 temperatures from surface sediments from the same location in Lake Superior. Both flux weighted TEX86 temperatures from the sediment traps and average TEX86 temperatures from surface sediments were similar to averaged measured water temperatures at below ˜40 m depth within the error of the lacustrine TEX86 calibration. Based on the observed depths of Thaumarchaeota in the water column, TEX86 values in sediments of Lake Superior likely reflect a combination of mixed-season and sub-thermocline temperatures. This is effectively the same as the annual averaged water temperature observed at depths below 40 m in Lake Superior. Thus, trends in TEX86 inferred temperatures in sediment records of Lake Superior, and similar lakes, are likely to reflect subsurface temperature variability rather than that of surface temperatures.

  13. Remote sensing of freshwater aquatic macrophytes in a southeastern lake: Part 1, Analysis of 30 years of vertical aerial photography

    SciTech Connect

    Jensen, J.R. (South Carolina Univ., Columbia, SC (United States). Dept. of Geography); Mackey, H.E. Jr. (Westinghouse Savannah River Co., Aiken, SC (United States))

    1991-01-01

    This paper summarizes the alternatives for conducting aquatic macrophyte mapping using in situ and remote sensing technologies, and then focuses on estimation of historical changes in persistent and non-persistent macrophyte beds in a large cooling lake in South Carolina from 1958 to 1990. Based on analysis of the historical aerial photography, rapid growth of the persistent beds of macrophytes along the shoreline did not begin until the early to mid-1970s and essentially stabilized by the late 1970s or early 1980s. Extensive growth of the non-persistent macrophytes began a few years after the persistent beds and, likewise, stabilized by the early 1980s. Comparisons of in situ and aerial photographic measurements indicate that large-scale, aerial photography can be used to accurately monitor lacustrine wetlands. Multidate photography is required if the lake is not successionally stable and if persistent and nonpersistent macrophyte beds occur, leading to large seasonal changes.

  14. Remote sensing of freshwater aquatic macrophytes in a southeastern lake: Part 1, Analysis of 30 years of vertical aerial photography

    SciTech Connect

    Jensen, J.R. [South Carolina Univ., Columbia, SC (United States). Dept. of Geography; Mackey, H.E. Jr. [Westinghouse Savannah River Co., Aiken, SC (United States)

    1991-12-31

    This paper summarizes the alternatives for conducting aquatic macrophyte mapping using in situ and remote sensing technologies, and then focuses on estimation of historical changes in persistent and non-persistent macrophyte beds in a large cooling lake in South Carolina from 1958 to 1990. Based on analysis of the historical aerial photography, rapid growth of the persistent beds of macrophytes along the shoreline did not begin until the early to mid-1970s and essentially stabilized by the late 1970s or early 1980s. Extensive growth of the non-persistent macrophytes began a few years after the persistent beds and, likewise, stabilized by the early 1980s. Comparisons of in situ and aerial photographic measurements indicate that large-scale, aerial photography can be used to accurately monitor lacustrine wetlands. Multidate photography is required if the lake is not successionally stable and if persistent and nonpersistent macrophyte beds occur, leading to large seasonal changes.

  15. Vertical distribution of zooplankton in subalpine and alpine lakes: Ultraviolet radiation, fish predation, and the transparency-gradient hypothesis

    E-print Network

    Williamson, Craig E.

    as a proxy for fish predation), temperature, pH, conductivity, chlorophyll a (Chl a), and zooplankton of the variance in zooplankton vertical distribution than did either PAR or chlorophyll. Calanoids had high. For example, the response of Daphnia to variation in food concentrations in the water column is modified

  16. Continental lake level variations from Topex/Poseidon (1993 1996)

    NASA Astrophysics Data System (ADS)

    Ponchaut, Frédérique; Cazenave, Anny

    1998-01-01

    The water level of continental lakes fluctuates due to variations in evaporation and precipitation within their catchment basin in response to regional climatic changes. With satellite altimetry, lake level variations can now he monitored almost continuously with a precision of a few centimeters. In this note, we present water level changes of three American Great Lakes (Superior, Michigan and Huron) and three African lakes (Tanganyika. Malawi and Turkana) based on 4 years (1993-1996) of altimetry data of the Topex/Poseidon (T/P) satellite. The levels of these lakes show a dominant annual cycle highly correlated with precipitations. American Great Lakes are regulated, hence present little interannual variations. This is unlike African lakes which markedly respond to regional (possibly global) climatic changes. A large water level decrease of lakes Tanganyika and Malawi (? 20 cm.yr -1) is observed by T/P for 1993-1996. This trend is associated with recurrent droughts recorded in East and South Africa since the early 1990s, as a result of the series of recent ENSO events.

  17. A 12,000-year record of vertical deformation across the Yellowstone caldera margin: The shorelines of Yellowstone Lake

    NASA Technical Reports Server (NTRS)

    Locke, William W.; Meyer, Grant A.

    1994-01-01

    The 600 ka Yellowstone caldera exhibits several signs of unrest, the most evident of which is historic ground deformation including both uplift and subsidence. We document deformation in the area of the southern caldera across approximately 12,000 years using the postglactic shoreline terraces of Yellowstone Lake. Raised shoreline elevations were interpreted from 230 leveling profiles surveyed across flights of terraces, with an accuracy of +/- 0.5 m. Of about 11 recognizable terraces, the five most continuous raised shorelines were correlated around the lake basin to reveal deformation patterns. Net deformation over the past approximatley 3 kyr has been dominantly up within the caldera interior and slightly down along the caldera rim, relative to the extracaldera region. This uplift is roughly similar to the historic pattern and may largely represent the effects of the most recent inflation episode. Subtraction of the total estimated magnitude of inflation in this epsiode suggests that the overall trend of postglacial deformation has been subsidence. The cause of this trend is undetermined but is most likely related to the effects of regional extension and long-term cooling within the Yellowstone caldera.

  18. Lacustrine mollusc radiations in the Lake Malawi Basin: experiments in a natural laboratory for evolution

    NASA Astrophysics Data System (ADS)

    Van Damme, D.; Gautier, A.

    2013-09-01

    In terminal Pliocene-early Pleistocene times, part of the Malawi Basin was occupied by paleo-lake Chiwondo. Molluscan biostratigraphy situates this freshwater lake either in the East African wet phase between 2.7-2.4 Ma or that of 2.0-1.8 Ma. In-lake divergent evolution remained restricted to a few molluscan taxa and was very modest. The lacustrine Chiwondo fauna went extinct at the beginning of the Pleistocene. The modern Lake Malawi malacofauna is depauperate and descends from ubiquistic southeast African taxa and some Malawi basin endemics that invaded the present lake after the Late Pleistocene mega-droughts. The Pleistocene aridity crises caused dramatic changes, affecting the malacofauna of all East African lakes. All lacustrine endemic faunas that had evolved in the Pliocene rift lakes, such as paleo-lake Chiwondo, became extinct. In Lake Tanganyika, the freshwater ecosystem did not crash as in other lakes, but the environmental changes were sufficiently important to trigger a vast radiation. All African endemic lacustrine molluscan clades that are the result of in-lake divergence are hence geologically young, including the vast Lavigeria clade in Lake Tanganyika (ca. 43 species).

  19. Metamorphic and structural evidence for significant vertical displacement along the Ross Lake fault zone, a major orogen-parallel shear zone in the Cordillera of western North America

    USGS Publications Warehouse

    Baldwin, J.A.; Whitney, D.L.; Hurlow, H.A.

    1997-01-01

    Results of an investigation of the petrology and structure of the Skymo complex and adjacent terranes constrain the amount, timing, and sense of motion on a segment of the > 600-km-long Late Cretaceous - early Tertiary Ross Lake fault zone (RLFZ), a major orogen-parallel shear zone in the Cordillera of western North America. In the study area in the North Cascades, Washington state, the RLFZ accommodated significant pre-middle Eocene vertical displacement, and it juxtaposes the Skymo complex with upper amphibolite facies (650??-690??C and 6-7 kbar) Skagit Gneiss of the North Cascades crystalline core to the SW and andalusite-bearing phyllite of the Little Jack terrane (Intermontane superterrane) to the NE. The two main lithologic units of the Skymo complex, a primitive mafic intrusion and a fault-bounded block of granulite facies metasedimentary rocks, are unique in the North Cascades. Granulite facies conditions were attained during high-temperature (> 800??C), low pressure (??? 4 kbar) contact metamorphism associated with intrusion of the mafic magma. P-T estimates and reaction textures in garnet-orthopyroxene gneiss suggest that contact metamorphism followed earlier, higher pressure regional metamorphism. There is no evidence that the Skagit Gneiss experienced high-T - low-P contact metamorphism. In the Little Jack terrane, however, texturally late cordierite ?? spinel and partial replacement of andalusite by sillimanite near the terrane's fault contact with Skymo gabbro suggest that the Little Jack terrane experienced high-T (??? 600??C) - low-P (??? 4 kbar) contact metamorphism following earlier low-grade regional metamorphism. Similarities in the protoliths of metasedimentary rocks in the Skymo and Little Jack indicate that they may be part of the same terrane. Differences in pressure estimates for the Little Jack versus Skymo for regional metamorphism that preceded contact metamorphism indicate vertical displacement of ??? 10 km (west side up) on the strand of the RLFZ that now separates the two structural blocks. High-angle faults in the study area are dextral-reverse mylonitic shear zones that experienced later brittle normal slip. Vertical motion on these shear zones before intrusion of Skymo gabbro can account for metamorphic discontinuities indicated by P-T results. The terranes have also been internally deformed by nonintersecting but coeval dextral and sinistral shear zones that formed after the terranes were brought together in the RLFZ and intruded by Eocene dikes. These results show that the RLFZ has accommodated significant vertical displacement but perhaps no more than tens of kilometers of early Tertiary lateral movement. Structural evidence for earlier, large-magnitude strike-slip displacement is not preserved.

  20. Metamorphic and structural evidence for significant vertical displacement along the Ross Lake fault zone, a major orogen-parallel shear zone in the Cordillera of western North America

    NASA Astrophysics Data System (ADS)

    Baldwin, Julia A.; Whitney, Donna L.; Hurlow, Hugh A.

    1997-08-01

    Results of an investigation of the petrology and structure of the Skymo complex and adjacent terranes constrain the amount, timing, and sense of motion on a segment of the > 600-km-long Late Cretaceous - early Tertiary Ross Lake fault zone (RLFZ), a major orogen-parallel shear zone in the Cordillera of western North America. In the study area in the North Cascades, Washington state, the RLFZ accommodated significant pre-middle Eocene vertical displacement, and it juxtaposes the Skymo complex with upper amphibolite facies (650°-690°C and 6-7 kbar) Skagit Gneiss of the North Cascades crystalline core to the SW and andalusite-bearing phyllite of the Little Jack terrane (Intermontane superterrane) to the NE. The two main lithologic units of the Skymo complex, a primitive mafic intrusion and a fault-bounded block of granulite facies metasedimentary rocks, are unique in the North Cascades. Granulite facies conditions were attained during high-temperature (> 800°C), low pressure (? 4 kbar) contact metamorphism associated with intrusion of the mafic magma. P-T estimates and reaction textures in garnet-orthopyroxene gneiss suggest that contact metamorphism followed earlier, higher pressure regional metamorphism. There is no evidence that the Skagit Gneiss experienced high-T - low-P contact metamorphism. In the Little Jack terrane, however, texturally late cordierite ± spinel and partial replacement of andalusite by sillimanite near the terrane's fault contact with Skymo gabbro suggest that the Little Jack terrane experienced high-T (˜ 600°C) - low-P (? 4 kbar) contact metamorphism following earlier low-grade regional metamorphism. Similarities in the protoliths of metasedimentary rocks in the Skymo and Little Jack indicate that they may be part of the same terrane. Differences in pressure estimates for the Little Jack versus Skymo for regional metamorphism that preceded contact metamorphism indicate vertical displacement of ˜ 10 km (west side up) on the strand of the RLFZ that now separates the two structural blocks. High-angle faults in the study area are dextral-reverse mylonitic shear zones that experienced later brittle normal slip. Vertical motion on these shear zones before intrusion of Skymo gabbro can account for metamorphic discontinuities indicated by P-T results. The terranes have also been internally deformed by nonintersecting but coeval dextral and sinistral shear zones that formed after the terranes were brought together in the RLFZ and intruded by Eocene dikes, These results show that the RLFZ has accommodated significant vertical displacement but perhaps no more than tens of kilometers of early Tertiary lateral movement. Structural evidence for earlier, large-magnitude strike-slip displacement is not preserved.

  1. Vertical distribution of ammonia-oxidizing crenarchaeota and methanogens in the epipelagic waters of Lake Kivu (Rwanda-Democratic Republic of the Congo).

    PubMed

    Llirós, Marc; Gich, Frederic; Plasencia, Anna; Auguet, Jean-Christophe; Darchambeau, François; Casamayor, Emilio O; Descy, Jean-Pierre; Borrego, Carles

    2010-10-01

    Four stratified basins in Lake Kivu (Rwanda-Democratic Republic of the Congo) were sampled in March 2007 to investigate the abundance, distribution, and potential biogeochemical role of planktonic archaea. We used fluorescence in situ hybridization with catalyzed-reported deposition microscopic counts (CARD-FISH), denaturing gradient gel electrophoresis (DGGE) fingerprinting, and quantitative PCR (qPCR) of signature genes for ammonia-oxidizing archaea (16S rRNA for marine Crenarchaeota group 1.1a [MCG1] and ammonia monooxygenase subunit A [amoA]). Abundance of archaea ranged from 1 to 4.5% of total DAPI (4',6-diamidino-2-phenylindole) counts with maximal concentrations at the oxic-anoxic transition zone (?50-m depth). Phylogenetic analysis of the archaeal planktonic community revealed a higher level of richness of crenarchaeal 16S rRNA gene sequences (21 of the 28 operational taxonomic units [OTUs] identified [75%]) over euryarchaeotal ones (7 OTUs). Sequences affiliated with the kingdom Euryarchaeota were mainly recovered from the anoxic water compartment and mostly grouped into methanogenic lineages (Methanosarcinales and Methanocellales). In turn, crenarchaeal phylotypes were recovered throughout the sampled epipelagic waters (0- to 100-m depth), with clear phylogenetic segregation along the transition from oxic to anoxic water masses. Thus, whereas in the anoxic hypolimnion crenarchaeotal OTUs were mainly assigned to the miscellaneous crenarchaeotic group, the OTUs from the oxic-anoxic transition and above belonged to Crenarchaeota groups 1.1a and 1.1b, two lineages containing most of the ammonia-oxidizing representatives known so far. The concomitant vertical distribution of both nitrite and nitrate maxima and the copy numbers of both MCG1 16S rRNA and amoA genes suggest the potential implication of Crenarchaeota in nitrification processes occurring in the epilimnetic waters of the lake. PMID:20802065

  2. Climate Change Affects the East African Rift Valley Lakes

    NASA Astrophysics Data System (ADS)

    O'Reilly, C. M.; Plisnier, P.; Cohen, A. S.

    2004-12-01

    Over the last 100 years, air temperatures in eastern African have been warming consistent with the global average temperature increase. This has led to warmer water temperatures in the East African Rift Valley lakes, increasing the stability of the water column. Subsequently, there has been a reduction in the upwelling of deep nutrient-rich waters that are the primary source of nutrients for most of these lakes. There were decreases in surface water N and P and increases in the Si:P ratio over the past 70 years for Lakes Malawi, Tanganyika, Edward, and Albert. The lower nutrient concentrations in the surface waters were associated with reduced algal biomass and increased water clarity. The consistent, regional-scale changes among these lakes provide strong evidence that climate warming may be having a large negative affect on these unique tropical lakes. A decrease in primary productivity of 20% has been indicated for Lake Tanganyika, which would be associated with a 30% decrease in fisheries yields. The human implications of such subtle, but progressive, environmental changes are potentially dire in this densely populated region of the world, where these large lakes are an important nutritional and economic resource.

  3. Quantifying Wintertime Aerosol Nitrate Formation Pathways and Their Vertical Profiles in the Great Lakes Region of North America by CMAQ Process Analysis and Hourly Observations

    NASA Astrophysics Data System (ADS)

    Kim, Y.; Spak, S.; Carmichael, G. R.; Riemer, N. S.; Baek, J.; Fontaine, A.; Janssen, M.; Kenski, D. M.

    2012-12-01

    In order to better understand wintertime episodes of elevated fine particle (PM2.5) in the Great Lakes region, a modeling analysis using the CMAQ air quality model was conducted for January-March 2009, a period where special surface based observations were conducted at a pair of urban and rural sites in Wisconsin. The episodes are found to be regional and are characterized by low wind speeds, near-freezing temperatures, and elevated levels of ammonium nitrate. Integrated process rate (IPR) analysis and integrated reaction rate analysis (IRR) in 12 km regional simulations with the Community Multiscale Air Quality model (CMAQ) are employed to quantify contributions to nitrate formation from all simulated processes, most importantly local chemical production and transport. Substantial vertical profiles are found for nitric acid, nitrate, and N2O5. The maximum concentrations of aerosol nitrate occur at the surface and decrease with altitude. Nitric acid is produced most efficiently 50-200m above the surface at night. Surface concentrations of aerosol nitrate are maintained by downward transport via vertical diffusion. Aerosol nitrate is predominantly removed by dry deposition. The aerosol production rate is significantly higher during episodes, and both daytime and nighttime (N2O5) chemical pathways are important contributors to elevated concentrations. Near the surface at Milwaukee, the daytime formation pathway for nitric acid is larger than the nighttime pathways, while in rural areas, the relative magnitudes are reversed. Across the region, the importance of the nighttime pathway increases with altitude. A spatial analysis highlights regional variability at the surface layer and ~90m above surface for the period February 4 thru February 10, which includes two PM2.5 episodes. The net aerosol chemistry process rates and concentrations show the evolution of regional PM build-up of aerosol nitrate and nitric acid.

  4. Vertical distribution of trace-element concentrations and occurrence of metallurgical slag particles in accumulated bed sediments of Lake Roosevelt, Washington, September 2002

    USGS Publications Warehouse

    Cox, S.E.; Bell, P.R.; Lowther, J.S.; Van Metre, P.C.

    2005-01-01

    Sediment cores were collected from six locations in Lake Roosevelt to determine the vertical distributions of trace-element concentrations in the accumulated sediments of Lake Roosevelt. Elevated concentrations of arsenic, cadmium, copper, lead, mercury, and zinc occurred throughout much of the accumulated sediments. Concentrations varied greatly within the sediment core profiles, often covering a range of 5 to 10 fold. Trace-element concentrations typically were largest below the surficial sediments in the lower one-half of each profile, with generally decreasing concentrations from the 1964 horizon to the surface of the core. The trace-element profiles reflect changes in historical discharges of trace elements to the Columbia River by an upstream smelter. All samples analyzed exceeded clean-up guidelines adopted by the Confederated Tribes of the Colville Reservation for cadmium, lead, and zinc and more than 70 percent of the samples exceeded cleanup guidelines for mercury, arsenic, and copper. Although 100 percent of the samples exceeded sediment guidelines for cadmium, lead, and zinc, surficial concentrations of arsenic, copper, and mercury in some cores were less than the sediment-quality guidelines. With the exception of copper, the trace-element profiles of the five cores collected along the pre-reservoir Columbia River channel typically showed trends of decreasing concentrations in sediments deposited after the 1964 time horizon. The decreasing concentrations of trace elements in the upper half of cores from along the pre-reservoir Columbia River showed a pattern of decreasing concentrations similar to reductions in trace-element loading in liquid effluent from an upstream smelter. Except for arsenic, trace-element concentrations typically were smaller at downstream reservoir locations along the pre-reservoir Columbia River. Trace-element concentration in sediments from the Spokane Arm of the reservoir showed distinct differences compared to the similarities observed in cores from along the pre-reservoir Columbia River. Particles of slag, which have physical and chemical characteristics of slag discharged to the Columbia River by a lead-zinc smelter upstream of the reservoir at Trail, British Columbia, were found in sediments of Lake Roosevelt. Slag particles are more common in the upstream reaches of the reservoir. The chemical composition of the interior matrix of slag collected from Lake Roosevelt closely approximated the reported elemental concentrations of fresh smelter slag, although evidence of slag weathering was observed. Exfoliation flakes were observed on the surface of weathered slag particles isolated from the core sediments. The concentrations of zinc on the exposed surface of slag grains were smaller than concentrations on interior surfaces. Weathering rinds also were observed in the cross section of weathered slag grains, indicating that the glassy slag material was undergoing hydration and chemical weathering. Trace elements observed in accumulated sediments in the middle and lower reaches of the reservoir are more likely due to the input from liquid effluent discharges compared to slag discharges from the upstream smelter.

  5. Diel vertical movements, and effects of infection by the cestode Schistocephalus solidus on daytime proximity of three-spined sticklebacks Gasterosteus aculeatus to the surface of a large Alaskan lake.

    PubMed

    Quinn, T P; Kendall, N W; Rich, H B; Chasco, B E

    2012-01-01

    We conducted a field study in Iliamna Lake, Alaska, to test the hypothesis that proximity of three-spined sticklebacks Gasterosteus aculeatus to the lake's surface during the daytime varies with macroparasitic cestode parasite Schistocephalus solidus infection in a manner consistent with enhanced vulnerability to avian predators. Extensive sampling in the lake and likelihood-based modeling revealed that sticklebacks displayed a diel vertical migration, being closer to the surface at night than during the evening and early morning. Additional sampling, also coupled with a likelihood-based modeling approach, showed that fish caught at the surface of the lake during the day were more often parasitized (76 vs. 65%), more heavily parasitized (26.8 vs. 22.7% of their body mass), and had larger individual parasites (0.24 vs. 0.20 g) than those caught at night. Parasite infection was related, non-linearly, to fish size, which also differed between day and night sampling at the surface. We performed statistical competitions among nested hierarchies of models that accounted for this effect of length. The most likely models indicated that fish captured during the day had greater parasite prevalence, higher parasite burdens, and larger parasites than did fish captured at night. Proximity to the surface during the day in this very clear lake would likely increase the vulnerability of sticklebacks to predation from birds, enabling completion of the parasite's lifecycle. PMID:21748321

  6. An in lake comparison of the branched GDGT lacustrine paleothermometer with other temperature proxies

    NASA Astrophysics Data System (ADS)

    Loomis, S. E.; Russell, J. M.; Sinninghe Damste, J. S.

    2011-12-01

    Quantitative paleoclimate reconstructions are essential for testing the efficacy of climate models, yet there are very few proxies that can reconstruct temperature over much of the terrestrial landscape. A novel group of bacterial membrane lipids known as branched glycerol dialkyl glycerol tetraethers (GDGTs) have strong potential to be used as a paleotemperature proxy given their ubiquity in peats, soils, lacustrine sediments, and near shore ocean sediments. There are nine known branched GDGTs, and the degree of methylation and cyclisation of these compounds has been shown to relate to the mean annual air temperature (MAAT) of their environment. Several different calibrations have been put forth relating branched GDGT distribution to MAAT, but up to now, there has been limited success applying these calibrations lake cores to reconstruct paleotemperatures. We have now developed a branched GDGT temperature calibration based upon 109 lake surface sediments in tropical Africa. Here we test the applicability of branched GDGT lacustrine paleothermometer on three different tropical lakes, including Lake Tanganyika, Lake Malawi, and Lake Peten Itza. These lakes were chosen because they have paleotemperature reconstructions derived from proxies independent of branched GDGTs, including TEX86, fossil pollen (Tanganyika and Malawi) and biogenic carbonate isotopes (Peten Itza) to reconstruct past lake water temperatures, allowing us to directly compare our reconstructions to those derived from other proxies. We apply both published and unpublished calibrations to our lake core data in an attempt to deduce the most accurate calibrations to reconstruct temperatures from lacustrine sediments.

  7. Stable isotope composition of Earth's large lakes

    NASA Astrophysics Data System (ADS)

    Jasechko, S.; Gibson, J. J.; YI, Y.; Birks, S. J.; Sharp, Z. D.

    2011-12-01

    Lakes cover about three percent of Earth's continental area. Large lakes can significantly influence lake shore and regional climates by increasing specific humidity during evaporation and by moderating air temperatures. Stable isotopes of oxygen and hydrogen can be used to quantify lake evaporation, providing a supplementary and often cost-advantageous alternative to conventional hydrologic approaches that require over lake monitoring. Further, stable isotopes in lake sediments are an established tool in paleolimnology; however, interpreting changes to a lake's past isotope composition requires a comprehensive understanding of contemporary controls. Here, ?18O and ?2H values of water in modern lakes exceeding roughly five hundred square kilometres are compiled (n > 35). Voluminous and seasonally mixed lakes - such as the North American Great Lakes - have the most homogenous stable isotope compositions, while perennially-stratified and shallow lakes show greater variability. A rudimentary stable isotope mass balance is used to assess evaporation fluxes from large lakes on Earth. The approach taken simultaneously constrains evaporation outputs for both oxygen and hydrogen stable isotopes by accounting for lake effects on the overlying atmosphere. Model development highlights important considerations such as isotopic stratification (Tanganyika), disequilibrium isotopic mass balances (Baikal), and non-steady hydrologic balances. Further, the isotope composition of Earth's continental surface water reservoir is calculated. This value - weighted to volume - is ?18O = -7.5±1.7 per mille relative to standard mean ocean water. The compiled data may be a useful tracer of continental evaporate in global atmospheric water cycle studies and could be coupled to climate models capable of incorporating oxygen-18 and deuterium tracers to improve or validate calculations of lake effects on regional water cycling.

  8. High prevalence of non-synonymous substitutions in mtDNA of cichlid fishes from Lake Victoria.

    PubMed

    Shirai, Kazumasa; Inomata, Nobuyuki; Mizoiri, Shinji; Aibara, Mitsuto; Terai, Yohey; Okada, Norihiro; Tachida, Hidenori

    2014-12-01

    When a population size is reduced, genetic drift may fix slightly deleterious mutations, and an increase in nonsynonymous substitution is expected. It has been suggested that past aridity has seriously affected and decreased the populations of cichlid fishes in Lake Victoria, while geographical studies have shown that the water levels in Lake Tanganyika and Lake Malawi have remained fairly constant. The comparably stable environments in the latter two lakes might have kept the populations of cichlid fishes large enough to remove slightly deleterious mutations. The difference in the stability of cichlid fish population sizes between Lake Victoria and the Lakes Tanganyika and Malawi is expected to have caused differences in the nonsynonymous/synonymous ratio, ? (=dN/dS), of the evolutionary rate. Here, we estimated ? and compared it between the cichlids of the three lakes for 13 mitochondrial protein-coding genes using maximum likelihood methods. We found that the lineages of the cichlids in Lake Victoria had a significantly higher ? for several mitochondrial loci. Moreover, positive selection was indicated for several codons in the mtDNA of the Lake Victoria cichlid lineage. Our results indicate that both adaptive and slightly deleterious molecular evolution has taken place in the Lake Victoria cichlids' mtDNA genes, whose nonsynonymous sites are generally conserved. PMID:25241383

  9. Levels and patterns of persistent organic pollutants (POPs) in tilapia (Oreochromis sp.) from four different lakes in Tanzania: geographical differences and implications for human health.

    PubMed

    Polder, A; Müller, M B; Lyche, J L; Mdegela, R H; Nonga, H E; Mabiki, F P; Mbise, T J; Skaare, J U; Sandvik, M; Skjerve, E; Lie, E

    2014-08-01

    In Tanzania fish is one of the most important protein sources for the rapidly increasing population. Wild fish is threatened by overfishing and pollution from agriculture, industries, mining, household effluents and vector control. To monitor possible implications for public health, the geographical differences of the occurrence and levels of persistent organic pollutants (POPs) in tilapia fish (Oreochromis sp.) from four different Tanzanian lakes were investigated in 2011. Concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyls (PBDEs) and hexabromocyclododecane (HBCDD) were determined in pooled samples of tilapia muscle from Lake (L) Victoria, L. Tanganyika, L. Nyasa (also called L. Malawi) and L. Babati in Tanzania in 2011. Levels of ?-DDTs (274 ng/g lipid weight (lw)) and sum of 7 indicator PCBs (?-7PCBs) (17 ng/g lw) were significantly higher in tilapia from L. Tanganyika compared to the other lakes. The highest levels of ?-endosulfan (94 ng/g lw) were detected in tilapia from L. Victoria. Toxaphenes were detected in low levels in fish from L. Tanganyika and L. Babati. Results revealed a geographic difference in the use of DDT and endosulfan between L. Victoria and L. Tanganyika. Low ratios of DDE/DDT in tilapia from L. Tanganyika indicated an on-going use of DDT in the area. Median levels of ?BDEs, including BDE-209, were highest in L. Victoria (19.4 ng/g lw) and BDE-209 was present in 68% of the samples from this lake. The presence of BDE-209 indicates increasing influence of imported products from heavy industrialized countries. The measured POP levels in the studied tilapia were all below MRLs of EU or were lower than recommended levels, and thus the fish is considered as safe for human consumption. They may, however, pose a risk to the fish species and threaten biodiversity. PMID:24836134

  10. Nutrient recycling by Tropheus brichardi across a littoral productivity gradient in Lake Tanganyika

    Microsoft Academic Search

    Tana Hintz; Peter McIntyre

    Nutrient recycling occurs when nutrients are released into the environment by animals or microbial consumers. Fish-mediated nutrient recycling is an important source of nutrients for primary producers in many aquatic ecosystems, sometimes even exceeding external loading rates (Attayde and Hansson 2001). Consumers release non-assimilated nutrients as liquid waste that is available to primary producers or as feces that is available

  11. Reproductive biology of Eretmodus cyanostictus , a cichlid fish from Lake Tanganyika

    Microsoft Academic Search

    Josephine Isabelle Morley; Sigal Balshine

    2003-01-01

    One of the most widely accepted explanations for monogamy is the need for biparental care. However, the occurrence of monogamy combined with biparental care is extremely rare in oral incubating (mouthbrooding) cichlid fishes. Few studies have been performed on cichlid species that exhibit this behaviour, and therefore the ecological factors that favour monogamy in these cases remain obscure. Here we

  12. Relationships between pre-rift structure and rift architecture in Lakes Tanganyika and Malawi, East Africa

    Microsoft Academic Search

    J. Versfelt; B. R. Rosendahl

    1989-01-01

    Continental rift systems are rips in plates caused by focusing of extensional stresses along some zone. In the same way that tensile cracks in the side of a brick building generally follow the mortar between bricks, rifts initially follow the weakest pathways in the pre-rift materials. There has even been a suggestion that the occurrence of rifts is controlled by

  13. A brood parasitic catfish of mouthbrooding cichlid fishes in Lake Tanganyika

    Microsoft Academic Search

    Tetsu Sato

    1986-01-01

    Brood parasitism, where a brood of the parasitic species is fostered by the parents of another species, is well known among birds1. In most cases, such offspring show a complete reliance upon their host parents for food, protection and warmth until their independence. In other vertebrate groups, however, such total dependence upon a host species is unknown. I report here

  14. Lateralized kinematics of predation behavior in a Lake Tanganyika scale-eating cichlid fish.

    PubMed

    Takeuchi, Yuichi; Hori, Michio; Oda, Yoichi

    2012-01-01

    Behavioral lateralization has been documented in many vertebrates. The scale-eating cichlid fish Perissodus microlepis is well known for exhibiting lateral dimorphism in its mouth morphology and lateralized behavior in robbing scales from prey fish. A previous field study indicated that this mouth asymmetry closely correlates with the side on which prey is attacked, but details of this species' predation behavior have not been previously analyzed because of the rapidity of the movements. Here, we studied scale-eating behavior in cichlids in a tank through high-speed video monitoring and quantitative assessment of behavioral laterality and kinematics. The fish observed showed a clear bias toward striking on one side, which closely correlated with their asymmetric mouth morphologies. Furthermore, the maximum angular velocity and amplitude of body flexion were significantly larger during attacks on the preferred side compared to those on the nonpreferred side, permitting increased predation success. In contrast, no such lateral difference in movement elements was observed in acoustically evoked flexion during the escape response, which is similar to flexion during scale eating and suggests that they share a common motor control pathway. Thus the neuronal circuits controlling body flexion during scale eating may be functionally lateralized upstream of this common motor pathway. PMID:22238598

  15. Phylogeny of a gastropod species flock: Exploring speciation in Lake Tanganyika in a molecular framework

    Microsoft Academic Search

    E. Michel

    2000-01-01

    A phylogenetic tree based on mitochondrial DNA (mtDNA) sequence data is presented that provides a basic framework for elucidating relationships of the endemic Tanganyikan freshwater gastropod genera Lavigeria and “Nov. gen.” (yet to be formally described). Analyses indicate that these two genera are sister taxa, yet their diversification patterns contrast markedly. Each contains definable species-level clades. The two species in

  16. Overlapping territories of Pseudosimochromis curvifrons males and other herbivorous cichlid fishes in Lake Tanganyika

    Microsoft Academic Search

    Tetsuo Kuwamura

    1992-01-01

    Males of the herbivorous cichlid fishPseudosimochromis curvifrons established mating territories 3–10 m in diameter, which included both spawning and feeding sites. Territorial males attacked\\u000a conspecific males and also other species. Only conspecific males were chased out of the territories. Territorial males attacked\\u000a other species at the spawning sites while courting or waiting for females and at other sites in their

  17. Lateralized Kinematics of Predation Behavior in a Lake Tanganyika Scale-Eating Cichlid Fish

    PubMed Central

    Takeuchi, Yuichi; Hori, Michio; Oda, Yoichi

    2012-01-01

    Behavioral lateralization has been documented in many vertebrates. The scale-eating cichlid fish Perissodus microlepis is well known for exhibiting lateral dimorphism in its mouth morphology and lateralized behavior in robbing scales from prey fish. A previous field study indicated that this mouth asymmetry closely correlates with the side on which prey is attacked, but details of this species' predation behavior have not been previously analyzed because of the rapidity of the movements. Here, we studied scale-eating behavior in cichlids in a tank through high-speed video monitoring and quantitative assessment of behavioral laterality and kinematics. The fish observed showed a clear bias toward striking on one side, which closely correlated with their asymmetric mouth morphologies. Furthermore, the maximum angular velocity and amplitude of body flexion were significantly larger during attacks on the preferred side compared to those on the nonpreferred side, permitting increased predation success. In contrast, no such lateral difference in movement elements was observed in acoustically evoked flexion during the escape response, which is similar to flexion during scale eating and suggests that they share a common motor control pathway. Thus the neuronal circuits controlling body flexion during scale eating may be functionally lateralized upstream of this common motor pathway. PMID:22238598

  18. Using Carbon and Nitrogen Isotopes in Lake Sediments to Detect Land Use Change

    NASA Astrophysics Data System (ADS)

    O'Reilly, C. M.; Dettman, D. L.; Cohen, A. S.

    2001-05-01

    Stable isotopes in lakes sediments are often used to reconstruct past environmental conditions. Carbon and nitrogen isotopes can provide information about both internal processes and terrestrial inputs to a lake. As such, they offer a powerful approach to detecting human impacts on aquatic systems. We investigated the potential of stable isotopes to trace anthropogenic land use changes by comparing stable isotopic composition of sedimentary organic matter at several river deltas in Lake Tanganyika, East Africa. Lake Tanganyika is a large rift valley lake draining watersheds that differ greatly in size, with land use patterns that vary from low-impact, protected areas (such as Gombe Steam National Park) to deforested and intensely cultivated regions. We found that carbon isotopes were related to both watershed disturbance and size, while nitrogen isotopes were related only to watershed disturbance. The direct relationship between 13C and C:N ratios across all watersheds suggests that differences in ? 13C may be attributed to terrestrial inputs rather than internal changes in the lake, such as increased productivity. Stable isotope analyses of cores taken at two sites were consistent with patterns seen in surface sediments. Our results suggest that nitrogen isotopes may be a better indicator of land use than carbon isotopes and that watershed size can be a confounding factor in the interpretation of geochemical signals in lake sediments.

  19. The influence of water quality and sediment geochemistry on the horizontal and vertical distribution of phosphorus and nitrogen in sediments of a large, shallow lake

    Microsoft Academic Search

    Dennis Trolle; Guangwei Zhu; David Hamilton; Liancong Luo; Chris McBride; Lu Zhang

    2009-01-01

    Distinct horizontal water column concentration gradients of nutrients and chlorophyll a (Chl a) occur within large, shallow, eutrophic Lake Taihu, China. Concentrations are high in the north, where some of the major\\u000a polluted tributaries enter the lake, and relatively low in the south, where macrophytes generally are abundant. It is not\\u000a clear, however, whether these water column concentration gradients are

  20. Gyres and Seiches in a Large and Shallow Lake

    Microsoft Academic Search

    Zhen-Gang Ji; Kang-Ren Jin

    2006-01-01

    Gyres and seiches are two prominent features of lakes. Gyres largely transport sediments, nutrients, and algae in the horizontal direction. Seiches, on the other hand, can contribute to the vertical mixing in lakes. Theoretical analysis, statistical methods, and numerical models are used to investigate gyres and seiches in Lake Okeechobee, the largest subtropical\\/tropical lake in North America. The lake has

  1. In situ methane production in a small, hypereutrophic, hard-water lake: Loss of methane from sediments by vertical diffusion and ebullition

    Microsoft Academic Search

    RICHARD F. STRAYER; JAMES M. TIEDJE

    1978-01-01

    The rate and quantity of methane produced by sediments of Wintergreen Lake were esti- mated by separately measuring methane lost by ebullition using bubble traps and by esti- mating methane lost to the water column by diffusion. The maximum rates of methane loss by ebullition occurred in late summer and were 35 mmol. rnw2. d-i in 1972 and 37 in

  2. The impact of the African Great Lakes on the regional climate in a dynamically downscaled CORDEX simulation (COSMO-CLM)

    NASA Astrophysics Data System (ADS)

    Thiery, W.; Panitz, H.; van Lipzig, N.

    2013-12-01

    Owing to the strong contrast in albedo, roughness and heat capacity between land and water, lakes significantly influence the exchange of moisture, heat and momentum between the surface and the boundary layer. To investigate this two-way interaction, a correct representation of lakes within regional climate models is essential. To this end, the one-dimensional lake parameterisation scheme FLake was recently coupled to the regional climate model COSMO-CLM (CCLM). One region where lakes constitute a key component of the climate system is the African Great Lakes region. In this study, the CCLM CORDEX-Africa evaluation simulation is dynamically downscaled from 0.44° (50 km) to 0.0625° (7 km) over East-Africa. The performance of two lake modules within CCLM are compared for the period 1999-2008: the default FLake scheme and the alternative Community Land Model. Model results are evaluated in a three-step procedure. First, the atmospheric state variables near-surface temperature, precipitation, surface energy fluxes, fractional cloud cover and column precipitable water are evaluated using in-situ based and satellite-derived products. Second, a comprehensive set of in-situ water temperature profile observations serves to evaluate the temporal evolution of water temperatures at three sites: Lake Kivu (Ishungu), Lake Tanganyika's northern basin (Kigoma) and southern basin (Mpulungu). Finally, spatial variability of surface temperatures in Lake Kivu and Lake Tanganyika are evaluated on the basis of satellite-derived lake surface temperatures. Subsequently, the preferred model configuration is used to quantify and understand effects by lakes reported for other regions in the world, such as a dampened diurnal temperature range, enhanced evaporation, modified surface layer stability, increased downwind precipitation, stronger winds, and the formation of local circulation patterns. This is achieved through comparison to a model integration excluding lake effects.

  3. Horizontal and vertical distribution of PCBs (polychlorinated biphenyls) in southern Lake Michigan sediments and the effect of Waukegan Harbor as a point source

    Microsoft Academic Search

    D. L. Swackhamer; D. E. Armstrong

    1988-01-01

    The spatial distribution of PCBs in southern Lake Michigan sediments was obtained from the analysis of 66 box cores and 8 grab samples. PCB concentrations in surficial sediments were closely related to the sedimentation zone and to the oxidizable organic matter content of the sediments. Average surficial sediment concentrations ranged from 81 micrograms\\/g in depositional zones to 7.2 micrograms\\/g in

  4. Understanding the performance of the FLake model over the East-African Great Lakes

    NASA Astrophysics Data System (ADS)

    Thiery, Wim; Martynov, Andrey; Darchambeau, François; Plisnier, Pierre-Denis; Descy, Jean-Pierre; van Lipzig, Nicole

    2013-04-01

    As a one-dimensional lake parameterisation scheme, FLake has already been coupled to a large number of numerical weather prediction systems, regional climate models and general circulation models. However, even though FLake has therewith become a vital tool to investigate and predict climate change impacts on lacustrine ecosystems, it has never been thoroughly tested for tropical conditions. In this study, the ability of FLake to represent tropical mixolimnion temperatures is investigated for three locations in East-Africa: Lake Kivu, Lake Tanganyika's northern and southern basins. Meteorological observations from surrounding automatic weather stations are corrected and subsequently used to drive FLake, whereas a comprehensive set of water temperature profiles serves to evaluate the model at each site. Careful input data correction and model configuration allows to reproduce the observed mixed layer seasonality at Lake Kivu and Lake Tanganyika (northern and southern basins), with correct representation of both the mixed layer depth and temperature structure. In contrast, when FLake is forced with uncorrected meteorological observations or with ERA-Interim reanalysis data, a correct mixing cycle is predicted only for Lake Tanganyika's southern basin: this is mainly due to an underestimation of wind velocities. At Lake Kivu, an extensive sensitivity study reveals that FLake's water column temperatures are sensitive both to minimal variations in the external parameters (lake depth and water transparency) and to small changes in the meteorological driving data, in particular wind velocity. In each case, small modifications may already lead to a regime switch from the correctly represented seasonal mixolimnion deepening to either completely mixed or permanently stratified conditions. Near-surface water temperatures are however more robust, with acceptable predictions even when the seasonal mixing regime is not reproduced. Furthermore, a study of different initial conditions shows that for lakes lacking reliable initial data, a fully mixed, artificially warm initialisation is to be preferred, but only if the model is allowed to spin up until convergence is reached. Finally, FLake is used to attribute the seasonal cycle at Lake Kivu to variations in the near-surface meteorological conditions. It is found that the annual mixing down to 60 m during the main dry season is primarily due to enhanced lake evaporation and secondarily due to the incoming long wave radiation deficit, both causing a significant heat loss from the lake surface and associated mixolimnion cooling.

  5. Understanding the performance of the FLake model over two African Great Lakes

    NASA Astrophysics Data System (ADS)

    Thiery, W.; Martynov, A.; Darchambeau, F.; Descy, J.-P.; Plisnier, P.-D.; Sushama, L.; van Lipzig, N. P. M.

    2014-02-01

    The ability of the one-dimensional lake model FLake to represent the mixolimnion temperatures for tropical conditions was tested for three locations in East Africa: Lake Kivu and Lake Tanganyika's northern and southern basins. Meteorological observations from surrounding automatic weather stations were corrected and used to drive FLake, whereas a comprehensive set of water temperature profiles served to evaluate the model at each site. Careful forcing data correction and model configuration made it possible to reproduce the observed mixed layer seasonality at Lake Kivu and Lake Tanganyika (northern and southern basins), with correct representation of both the mixed layer depth and water temperatures. At Lake Kivu, mixolimnion temperatures predicted by FLake were found to be sensitive both to minimal variations in the external parameters and to small changes in the meteorological driving data, in particular wind velocity. In each case, small modifications may lead to a regime switch, from the correctly represented seasonal mixed layer deepening to either completely mixed or permanently stratified conditions from ? 10 m downwards. In contrast, model temperatures were found to be robust close to the surface, with acceptable predictions of near-surface water temperatures even when the seasonal mixing regime is not reproduced. FLake can thus be a suitable tool to parameterise tropical lake water surface temperatures within atmospheric prediction models. Finally , FLake was used to attribute the seasonal mixing cycle at Lake Kivu to variations in the near-surface meteorological conditions. It was found that the annual mixing down to 60 m during the main dry season is primarily due to enhanced lake evaporation and secondarily to the decreased incoming long wave radiation, both causing a significant heat loss from the lake surface and associated mixolimnion cooling.

  6. Vertical distributions of bound saturated fatty acids and compound-specific stable carbon isotope compositions in sediments of two lakes in China: implication for the influence of eutrophication.

    PubMed

    Wang, Lifang; Xiong, Yongqiang; Wu, Fengchang; Li, Qiuhua; Lin, Tian; Giesy, John P

    2014-11-01

    Lakes Dianchi (DC) and Bosten (BST) were determined to be at different stages of eutrophication, by use of total organic carbon content, bulk carbon isotopic composition, bulk nitrogen isotopic composition, and bound saturated fatty acid (BSFA) concentrations in sediment cores. A rapid increase in the supply of organic matter (OM) to DC began after the 1950s, while the environment and trophic status of BST remained constant as indicated by characteristics of OM input to sediments. The BSFA ratios of nC14?+?nC16?+?nC18/nC24?+?nC26?+?nC28 increase upward from 7 to 13 in the DC core, which are significantly greater than those from BST (2 to 3). This result is consistent with algae or bacteria being the dominant contribution of the OM increase induced by eutrophication in DC. The positive shift of nC16 compound-specific ? (13)C in the upper section might be an indicator of excess algal productivity, which was observed in the two lakes. The positive shifts of compound-specific ? (13)C of other BSFAs were also observed in the upper section of the core only from DC. The observed trends of compound-specific ?(13)C of BSFA originated from different sources became more consistent, which reflected the intensified eutrophication had profoundly affected production and preservation of OM in DC. The results observed for BST indicated that accumulation of algae did not affect the entire aquatic ecosystem until now. PMID:24996939

  7. Recent results of monitoring of the vertical component of the electrical field in Lake Baikal on the surface-bed baseline

    NASA Astrophysics Data System (ADS)

    Korotaev, S. M.; Budnev, N. M.; Serdyuk, V. O.; Zurbanov, V. L.; Mirgazov, R. R.; Shneer, V. S.; Machinin, V. A.; Kiktenko, E. O.; Buzin, V. B.; Panfilov, A. I.

    2015-05-01

    The vertical component of the electrical field was monitored on the surface-bed baseline in the region of the Baikal Deep Underwater Neutrino Observatory from 2003 to 2010. This monitoring allowed us to obtain data on internal and external field sources. However, the insufficient accuracy and reliability of the measurement setup slowed the progress in interpreting the measurements. A novel setup, which was the first to provide the means to control the base potentials of electrodes, was designed in order to overcome these constraints. The setup in its final configuration started taking measurements in 2013. Analysis of the measurement results obtained in 2013 and 2014 does, on the one hand, confirm the conclusions drawn previously on the nature of variations of the vertical component of the electrical field, but, on the other hand, it raises new questions. The field induced by flows was compared to direct velocity measurements. The conclusion regarding the correlation between long-period current variations in the hydrosphere region of the global electric circuit and the solar activity variations was confirmed, but the considerable lag observed in this correlation stands in need of explanation. A nonlocal response of the electrode base potentials that preceded an impending earthquake by up to 12 days was revealed.

  8. Lake Life.

    ERIC Educational Resources Information Center

    Ohrn, Deborah Gore, Ed.

    1993-01-01

    This quarterly publication of the State Historical Society of Iowa features articles and activities for elementary school students. This summer issue focuses on the topic of lake life. The issue includes the following features: (1) "Where the Lakes Are Map"; (2) "Letter from the Lake"; (3) "Lake People"; (4) "Spirit Lake"; (5) "Lake Manawa"; (6)…

  9. Use of Paleomagnetic Secular Variation, Excursion, and Reversal Records to Correlate African Lake Climate Records

    NASA Astrophysics Data System (ADS)

    King, J.; Heil, C.; Peck, J.; Scholz, C.; Shanahan, T.; Overpeck, J.

    2005-12-01

    Geomagnetic secular variation, excursions, and reversal records can provide an excellent means for high resolution correlation of sedimentary climate records. Recent drilling projects on Lake Bosumtwi, Ghana, and Lake Malawi, Malawi, have provided the opportunity to study long African climate records (<1 Ma). Magnetic studies of these sedimentary archives indicate that high quality SV records are preserved through most of the sequence despite the fact that anoxia is the usual condition of bottom waters in both lakes. We compare the magnetic records of Lake Bosumtwi and Lake Malawi to test our ability to correlate between West African and East African lakes. In addition, we compare the magnetic record of Lake Malawi to records from Lake Tanganyika in East Africa and the Indian Ocean region, and the record of Lake Bosumtwi to that of Lake Barombi Mbo in West Africa. Correlations within regions are straightforward and highly useful for intrasite correlation. Correlation between East and West Africa is also possible, although the resolution of the correlation is more limited.

  10. Lake Malawi sediment and pore water chemistry: Proposition of a conceptual model for stratification intensification since the end of the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Branchu, Philippe; Bergonzini, Laurent; Pons-branchu, Edwige; Violier, Eric; Dittrich, Maria; Massault, Marc; Ghaleb, Bassam

    2010-07-01

    Sedimentary records of salinity indicators are largely used to reconstruct past climatic changes in lacustrine systems where chemistry is sensitive to hydroclimatic conditions. In large fresh lakes of the East African Rift such as Lakes Tanganyika and Malawi, salinity is often considered constant and other paleoclimatological proxy data are used. However, a relation between lake surface chloride concentration and hydroclimatic regime was previously demonstrated at the century scale in Lake Tanganyika. This relation is transposed to Lake Malawi on the base of similarity between hydrochemical budgets of both lakes that are computed for the whole lake and epilimnion. Whereas numerous physico-chemical difficulties make generally debatable use of lake pore water chemistry, as illustrated here by diffusion modelling, the dissolved chloride concentration profile from a core sampled in northern Lake Malawi is considered as a potential indicator of limnological-hydroclimatic condition changes for the last 200 years. A decrease in pore water chloride concentration between 1840 AD and present situation is directly associated to a metalimnetic water salinity decrease. The chronology of this event is synchronous with diatom productivity change demonstrated by Johnson et al. (2001) at the end of the Little Ice Age (LIA). A conceptual model of Lake Malawi, based on salinity, organic carbon and its "dead" watershed contribution, lake-level and productivity changes since the mid 19th century is presented. A new scenario is proposed, based on thermal stratification reinforcement at the end of the LIA. Lake productivity and chemistry depend on stratification strength, water column mixing rate and on climatic variability. During the LIA, nutrient distribution profiles were more homogeneous with depth due to the climatically (colder and drier climatic conditions than today) induced destabilisation of the mixing barrier. The productive system is then auto-supplied and does not require external silicon supply while chloride concentration is higher due to closure of the basin. Stratification has become more stable since the end of the LIA, as in nearby Lake Tanganyika where it is linked to air temperature global increase. Results demonstrated that chloride is a suitable indicator of the present and past hydroclimatic and hydrodynamic regimes. This work shows that in Lake Malawi, assessment of "dead" carbon (or old "refractive watershed carbon") contribution to the TOC is a key parameter to set chronological frame from 14C ages.

  11. LAKE-WIDE SEASONAL CHANGES IN LIMNOLOGICAL CONDITIONS IN LAKE MICHIGAN IN 1976

    EPA Science Inventory

    Data collected on lake-wide cruises in 1976 were used to study seasonal and vertical variations in water temperature, transparency, chlorophyll a, and nutrients in Lake Michigan. Data were analyzed according to subsets corresponding to the northern and southern open lake. Compari...

  12. Male reproductive suppression in the cooperatively breeding fish Neolamprologus

    E-print Network

    Montgomerie, Bob

    in Lake Tanganyika. Gonadal investment followed patterns consistent with reproductive suppression, Lake Tanganyika, reproductive physiology, social status, sperm competition. [Behav Ecol 17:25­33 (2006

  13. Molecular phylogenetic investigations of the Viviparidae (Gastropoda: Caenogastropoda) in the lakes of the Rift Valley area of Africa.

    PubMed

    Sengupta, Mita E; Kristensen, Thomas K; Madsen, Henry; Jørgensen, Aslak

    2009-09-01

    The freshwater gastropod family Viviparidae is nearly cosmopolitan, but absent from South America. On the African continent, two genera are recognized; the widespread Bellamya and the monotypic Neothauma, which is confined to Lake Tanganyika. Most of the African Bellamya species are confined to the major lakes of the Rift Valley area in Africa, i.e. Lake Albert, Lake Malawi, Lake Mweru, and Lake Victoria. The phylogenetic analyses of mitochondrial (COI and 16S) and nuclear (H3, 18S and 28S) DNA inferred three major lake-clades; i.e. Lake Victoria/Kyoga/Albert, Lake Malawi and Lake Mweru/Bangweulu. The endemic B. rubicunda from Lake Albert and B. unicolor from Lake Kyoga were inferred to be part of the Lake Victoria clade. Bellamya capillata as identified by shell characters was polyphyletic in gene trees. The monophyletic Bellamya species radiation in Lake Malawi was most nearly related to the Lake Victoria/Kyoga/Albert-clade. Taxa from the Zambian lakes, Mweru and Bangweulu, were inferred together and placed ancestral to the other lakes. Neothauma tanganyicense was inferred as the sister-group to the Zambian Bellamya. Within the lake-clades the endemic radiations show very low genetic diversities (0-4.1% in COI), suggesting much faster morphological divergence than molecular divergence. Alternatively, Bellamya in Africa constitutes only a few species with several sub-species or eco-phenotypic morphs. The African viviparids were inferred to be the sister-group to a clade comprising Asian species, and the relatively low genetic diversity between the clades (12.6-15.5% in COI) makes a recent Miocene dispersal event from Asia to Africa much more likely than an ancient Gondwana vicarience distribution. PMID:19435609

  14. Understanding the performance of the FLake model over the African Great Lakes

    NASA Astrophysics Data System (ADS)

    Thiery, W.; Martynov, A.; Darchambeau, F.; Descy, J.-P.; Plisnier, P.-D.; Sushama, L.; van Lipzig, N. P. M.

    2013-10-01

    The ability of the one-dimensional lake model FLake to represent the mixolimnion temperatures for tropical conditions was tested for three locations in East Africa: Lake Kivu, Lake Tanganyika's northern and southern basins. Meteorological observations from surrounding Automatic Weather Stations were corrected and used to drive FLake, whereas a comprehensive set of water temperature profiles served to evaluate the model at each site. Careful forcing data correction and model configuration allowed to reproduce the observed mixed layer seasonality at Lake Kivu and Lake Tanganyika (northern and southern basins), with correct representation of both the mixed layer depth and temperature structure. At Lake Kivu, mixolimnion temperatures predicted by FLake were found sensitive both to minimal variations in the external parameters (lake depth and water transparency) as to small changes in the meteorological driving data, in particular wind velocity. In each case, small modifications may already lead to a regime switch from the correctly represented seasonal mixed layer deepening to either completely mixed (down to the model lake bottom) or permanently stratified (from ~10 m downwards) conditions. In contrast, model temperatures are found robust close to the surface, with acceptable predictions of near-surface water temperatures even when the seasonal mixing regime is not reproduced. FLake can thus be a suitable tool to parameterize tropical lake water surface temperatures within atmospheric prediction models, but may be less appropriate, in its current form, to study complex limnological processes within tropical lakes. Furthermore, a study of different initial conditions showed that for tropical lakes lacking reliable initial data, a fully mixed, artificially warm initialisation is to be preferred, but only if the model is allowed to spin up until convergence is reached. Finally, FLake was used to attribute the seasonal mixing cycle at Lake Kivu to variations in the near-surface meteorological conditions. It was found that the annual mixing down to 60 m during the main dry season is primarily due to enhanced lake evaporation and secondarily due to the decreased incoming long wave radiation, both causing a significant heat loss from the lake surface and associated mixolimnion cooling.

  15. Pleistocene desiccation in East Africa bottlenecked but did not extirpate the adaptive radiation of Lake Victoria haplochromine cichlid fishes.

    PubMed

    Elmer, Kathryn R; Reggio, Chiara; Wirth, Thierry; Verheyen, Erik; Salzburger, Walter; Meyer, Axel

    2009-08-11

    The Great Lakes region of East Africa, including Lake Victoria, is the center of diversity of the mega-diverse cichlid fishes (Perciformes: Teleostei). Paleolimnological evidence indicates dramatic desiccation of this lake ca. 18,000-15,000 years ago. Consequently, the hundreds of extant endemic haplochromine species in the lake must have either evolved since then or refugia must have existed, within that lake basin or elsewhere, from which Lake Victoria was recolonized. We studied the population history of the Lake Victoria region superflock (LVRS) of haplochromine cichlids based on nuclear genetic analysis (12 microsatellite loci from 400 haplochomines) of populations from Lake Kivu, Lake Victoria, and the connected and surrounding rivers and lakes. Population genetic analyses confirmed that Lake Kivu haplochromines colonized Lake Victoria. Coalescent analyses show a 30- to 50-fold decline in the haplochromine populations of Lake Victoria, Lake Kivu, and the region ca. 18,000-15,000 years ago. We suggest that this coincides with drastic climatic and geological changes in the late Pleistocene. The most recent common ancestor of the Lake Victoria region haplochromines was estimated to have existed about 4.5 million years ago, which corresponds to the first radiation of cichlids in Lake Tanganyika and the origin of the tribe Haplochrominii. This relatively old evolutionary origin may explain the high levels of polymorphism still found in modern haplochromines. This degree of polymorphism might have acted as a "genetic reservoir" that permitted the explosive radiation of hundreds of haplochromines and their array of contemporary adaptive morphologies. PMID:19651614

  16. The impact of the African Great Lakes on the regional climate in a dynamically downscaled CORDEX simulation

    NASA Astrophysics Data System (ADS)

    Thiery, Wim; Panitz, Hans-Jürgen; Davin, Edouard; van Lipzig, Nicole

    2014-05-01

    Owing to the strong contrast in albedo, roughness and heat capacity between land and water, lakes significantly influence the exchange of moisture, heat and momentum between the surface and the boundary layer. To investigate this two-way interaction, a correct representation of lakes within regional climate models is essential. To this end, the one-dimensional lake parameterisation scheme FLake was recently coupled to the regional climate model COSMO-CLM (CCLM). One region where lakes constitute a key component of the climate system is the African Great Lakes region. In this study, the CCLM CORDEX-Africa evaluation simulation is dynamically downscaled from 0.44° (50 km) to 0.0625° (7 km) over East-Africa, an unprecedented resolution for this region. The performance of different CCLM configurations are compared for the period 1999-2008: in particular, CCLM is tested for its sensitivity to the choice of the lake surface temperature description (SST, FLake, an improved version of FLake and Hostetler) and the land surface model (Terra and Community Land Model). Model results are evaluated in a three-step procedure. First, the atmospheric state variables near-surface temperature, precipitation, surface energy fluxes, fractional cloud cover and column precipitable water are evaluated using in-situ based and satellite-derived products. Second, a comprehensive set of in-situ water temperature profile observations serves to evaluate the temporal evolution of water temperatures at three sites: Lake Kivu (Ishungu), Lake Tanganyika's northern basin (Kigoma) and southern basin (Mpulungu). Finally, spatial variability of surface temperatures in Lake Kivu and Lake Tanganyika are evaluated on the basis of satellite-derived lake surface temperatures. Subsequently, the preferred model configuration is used to quantify and understand effects by lakes reported for other regions in the world, such as a dampened diurnal temperature range, enhanced evaporation, modified surface layer stability, increased downwind precipitation, stronger winds, and the formation of local circulation patterns. Particular attention is payed to the impact of lakes on extreme night-time convection over Lake Victoria. This is achieved through comparison to a model integration excluding lake effects.

  17. CHRIS D. JIGGINS here are more than 2,000 species of

    E-print Network

    Cai, Long

    of the genomic changes that underlie the astounding cichlid diversity seen today. Lake Malawi Lake Tanganyika-dwelling planktivore Lobe-lipped insect eater River dwellers Lake Malawi Lake Tanganyika Lake Victoria Pelagic in the three African lakes with the highest cichlid diversity -- Lake Malawi, Lake Tanganyika and Lake Victoria

  18. 13C/Palynological evidence of differential residence times of organic carbon prior to its sedimentation in East African Rift Lakes and peat bogs

    NASA Astrophysics Data System (ADS)

    Hillaire-Marcel, Claude; Aucour, Anne-Marie; Bonnefille, Raymonde; Riollet, Guy; Vincens, Annie; Williamson, David

    Most terrestrial plants producing large amounts of organic matter in the East African Rift follow the Calvin (C3) photosynthetic pathway. Their end products have ?13C values of ca. -27 ± 2‰ (vs. PDB). On the contrary, most Cyperaceae (notably Cyperus papyrus and C. latifolius) are characterized by higher 13C contents ° 13C = -10.5 ± 1‰ ) in relation to their Hatch and Slack (C4) photosynthetic cycle. In consequence, ?13C values in total organic matter (TOM) from peat bog or lake cores essentially responded to the proportion of detritus from C4-Cyperaceae. Immediate evidence of the development or disappearance of Cyperaceae around lake margins or in peat bogs can be found in pollen assemblages. Lag times between pollen signals and correlative ° 13C shifts in TOM from cores are therefore indicative of the residence time of organic matter prior to its sedimentation. Delayed sedimentation of TOM will result in 14C anomalies which depend on several parameters, most of them being site specific as shown by examples from a peat bog in Burundi and from southern Lake Tanganyika. An independent assessment of the chronology by high resolution paleomagnetic correlations indicates a ca. 1.5 ka apparent 14C age of TOM in Lake Tanganyika at the Pleistocene-Holocene transition.

  19. Lake Temperatures

    NSDL National Science Digital Library

    NBC Learn

    2010-10-07

    Scientists studying large lakes in northern and tropical latitudes are finding that rising water temperatures are affecting the ecosystems of these lakes. "Changing Planet " is produced in partnership with the National Science Foundation.

  20. Vertical Farm

    NSDL National Science Digital Library

    2004-01-01

    With the continued growth of the human population of the Earth, there is increasing concern with the planet's ability to provide sustenance for all of its inhabitants. This compelling website by Dickson Despommier and his colleagues at Columbia University provides a worthy alternative to other forms of agriculture: the vertical farm. As Dr. Despommier notes on the site, "..they offer the promise of urban renewal, sustainable production of a safe and varied food supply (year-round crop production), and the eventual repair of ecosystems that have been sacrificed for horizontal farming." The site offers a great deal of information about these vertical farms, a detailed essay on the importance of such farms, a number of potential designs, and a discussion forum. Finally, there are a number of plans that indicate how this type of farm might be effectively created and sustained.

  1. CONNECTICUT LAKES

    EPA Science Inventory

    This is a 1:24,000-scale datalayer of named lakes in Connecticut. It is a polygon Shapefile that includes all lakes that are named on the U.S. Geologicial Survey (USGS) 7½ minute topographic quadrangle maps that cover the State of Connecticut, plus other officially named lakes i...

  2. Out of Tanganyika: Genesis, explosive speciation, key-innovations and phylogeography of the haplochromine cichlid fishes

    Microsoft Academic Search

    Walter Salzburger; Tanja Mack; Erik Verheyen; Axel Meyer

    2005-01-01

    BACKGROUND: The adaptive radiations of cichlid fishes in East Africa are well known for their spectacular diversity and their astonishingly fast rates of speciation. About 80% of all 2,500 cichlid species in East Africa, and virtually all cichlid species from Lakes Victoria (~500 species) and Malawi (~1,000 species) are haplochromines. Here, we present the most extensive phylogenetic and phylogeographic analysis

  3. Evolution of predator-prey interactions in ancient lakes: implications for coevolution in marine environments

    SciTech Connect

    Cohen, A.

    1985-01-01

    Highly generalized predator-prey interrelationships are a hallmark of most lacustrine ecosystems where accommodation to the physical environment plays the major role in determining organismal distributions. Since the vast majority of lakes are ephemeral on a geological and evolutionary times scale, dispersal, rather than organism interaction, appears to be the dominant selective theme in lacustrine species evolution. In a few, very long lasting lakes, notably modern Lakes Tanganyika (Africa) and Baikal (USSR) and ancient lakes of the Brazilian Rift (Cretaceous) and Snake River Plain (Tertiary), invertebrates and fish occur which demonstrate the development of intense biological accommodation in coevolving predator-prey interactions. Shell crushing experiments on 2 endemic Tanganyikan gastropods, Lavigeria nassa and Spekia zonata show them to be comparable to warm temperature marine species in terms of grow load strength: 1-2 orders of magnitude stronger than confamilial cosmopolitan species from more ephemeral lakes in the same region of Africa. Shell repair is commonly observed in these and other Tanganyikan endemic snails although it is exceedingly rare inmost other lakes. The study of these early stages of evolutionary processes and rates in coevolving predator-prey systems in isolated lacustrine microcosms has important implications for those paleontologists concerned with marine invertebrates. It may shed considerable light on the interpretation of such events as the marine Mesozoic Revolution.

  4. CALCULATED CONTRIBUTION OF SURFACE MICROLAYER PCB TO CONTAMINATION OF LAKE MICHIGAN LAKE TROUT

    EPA Science Inventory

    The possible significance of PCB concentration in the surface microlayer of Lake Michigan to contamination of lake trout was examined using a modification of a previously developed food chain model. Vertically migrating zooplankton were assumed to spend a fraction of each day exp...

  5. In Goldman, C. R., M. Kumagai, and R. D. Robarts. In press. Effects of Global Warming on Freshwater Ecosystems of the World: what can be done to reduce negative impacts?

    E-print Network

    California at Santa Barbara, University of

    of the African Great Lakes requires examining controls on mixing dynamics. Lake Tanganyika is the largest, 706 m deep ), Lake Tanganyika (670 km, 1 470 m deep), Lake Kivu (90 km long, 480 m deep), Lake Edward and lower water columns in the shallower lakes are only a degree or two whereas in Lake Tanganyika

  6. Water quality of selected lakes in Mount Rainier National Park, Washington, with respect to lake acidification

    SciTech Connect

    Turney, G.L.; Dion, N.P.; Sumioka, S.S.

    1986-01-01

    Thirteen lakes in Mount Rainier National park were evaluated for general chemical characteristics, sensitivity to acidification by acidic precipitation, and degree of existing acidification. The lakes studies were Allen, one of the Chenuis group, Crescent, Crystal, Eleanor, Fan, one of the Golfen group, Marsh, Mowich, Mystic, Shriner, and two unnamed lakes. The lakes were sampled in August 1983. The major cations were calcium and sodium, and the major anion was bicarbonate. Alkalinity concentrations ranged from 2.1 to 9.0 mg/L in 12 of the lakes. Allen Lake was the exception, having an alkalinity concentration of 27 mg/L. The pH values for all of the lakes ranged from 5.8 to 6.5. In most of the lakes, vertical profiles of temperature, dissolved oxygen, pH, and specific conductance were relatively uniform. Exceptions to general water quality patterns were observed in three lakes. Allen Lake had a specific conductance value of 58 Microsiemens/cm. The lake of the Golfen group was anaerobic at the bottom and had relatively high concentrations of dissolved organic carbon and dissolved metals, and a lower light transmission than the other lakes studied. One of the unnamed lakes had relatively high concentrations of phytoplankton and dissolved organic carbon and relatively low levels of light transmission. Comparisons of lake data to acid-sensitivity thresholds for specific conductance and alkalinity indicated that all of the lakes except Allen would be sensitive to acidic precipitation. The small sizes of the lakes, and their locations in basins of high precipitation and weathering-resistant rock types, enhance their sensitivity. None of the lakes in this study appeared to be presently acidified.

  7. Speciation and Radiation in African Haplochromine Jacques J.M. van Alphen, Ole Seehausen, and Frietson Galis

    E-print Network

    that it is the combination of a number of factors. Of the three African great lakes, Lake Tanganyika is the oldest and its 500 and 1000 each) than the old Lake Tanganyika, with about 250 species. In particular, the Lake

  8. Indian Ocean Climate event brings floods to East Africa's lakes and the Sudd Marsh

    NASA Astrophysics Data System (ADS)

    Birkett, Charon; Murtugudde, Ragu; Allan, Tony

    During an El Niño, the expected rainfall increase over most of the Lake Victoria catchment area is ˜15-25%. However, due to anomalous warming of the western equatorial Indian Ocean during 1997, strong convection developed over parts of the Horn and eastern Africa. This resulted in a much larger 20-160% precipitation excess during the “short rainy” season. Satellite radar altimetry data reveals that not only did Lake Victoria rise by ˜1.7 m, but that the rainfall event similarly affected lakes Tanganyika, Malawi and Turkana. In addition, the seasonal level minima of the Sudd marshes and Lakes T'ana and Nasser continue to increase. Such a rainfall event will have severe, long-term consequences for the natural surface flows and storages along the White Nile. Based on the hydrological impacts of the historic 1961 East Africa event, we can expect the current high levels of Lake Victoria to be maintained for the remainder of this decade. In addition, we anticipate a major expansion of the permanent swamp regions of the Sudd marshes over the forthcoming seasons. Blue Nile flows, further enhanced by the above-average 1998 rainfall season, can also be expected to remain high, at least until early 1999.

  9. Tropical Lake Levels and Their Relationship to Rainfall

    NASA Astrophysics Data System (ADS)

    Ricko, M.; Carton, J.; Birkett, C. M.

    2009-12-01

    The availability of satellite altimeters and improvements in satellite estimates of river and lake levels are offering an exciting monitoring alternative to currently limited prediction systems using current climate models. Aware of existing limitations in data retrievals, we have developed a simple linear model for estimating lake level as a function of freshwater flux into the catchment basin for 12 tropical lakes and reservoirs: 8 in Africa, 3 in Central and South America, and 1 in Southeast Asia. In our model three parameters, effective catchment basin, time delay, and drainage timescale are determined from linear regression based on the simultaneous availability of remotely sensed lake level and rainfall. We present results of estimates of net surface freshwater flux and lake levels during a 16-year period (1992-2007). Comparison between two different altimeter satellite-based lake level datasets shows very good agreement for most lakes. For net freshwater flux (i.e., rainfall minus evaporation), we use three different rainfall products: the European Centre for Medium Range Weather Forecasts (ECMWF) ERA-Interim reanalysis, the Global Precipitation Climatology Project (GPCP) rainfall, and the Tropical Rainfall Measurement Mission (TRMM) 3B42 precipitation index rainfall. ERA-Interim evaporation is combined with each of the three rainfall products to form three estimates of net surface freshwater flux. Results from models are denominated as Model-I, Model-G, Model-T, respectively. A comparison of rainfall products shows differences, and as a result the best model for a given lake varies. The median correlation between the observed LEGOS and Model-G lake levels is significantly higher than for Model-I, with the median RMS difference between observation and model slightly lower for Model-G than for Model-I. For many tropical lakes the best results are obtained using one of the observation-based products, GPCP or TRMM. All three model results show that all lakes, except Lake Turkana, have pronounced seasonal cycles, with the largest seasonal cycles occurring for the lakes in high rainfall regions: Kainji in Africa, Balbina in South America, and Lake Tonle Sap in Southeast Asia. With the seasonal cycle removed, the east African rift valley lakes (Turkana, Tanganyika, Mweru) show pronounced rises in 1997-8 in response to the combined effects of El Niño and the Indian Ocean dipole. In contrast, the Central and South American lakes (Nicaragua and Balbina) show significant level decrease for the same time period. There is also evidence of rapid increases in lake level in response to tropical cyclones (Nicaragua and Malawi). At short intraseasonal periods, Lake Tonle Sap shows evidence of a 30-60 day fluctuation driven by rainfall fluctuations partly associated with the Madden-Julian Oscillation. These results show noticeable climate impacts on tropical lake levels.

  10. Physical drivers of lake evaporation across a gradient of climate and lake types

    NASA Astrophysics Data System (ADS)

    Lenters, J. D.; Blanken, P.; Healey, N. C.; Hinkel, K. M.; Ong, J.; Peake, C.; Potter, B. L.; Riveros-Iregui, D. A.; Spence, C.; Van Cleave, K.; Zlotnik, V. A.

    2014-12-01

    Inland waters exchange sensible and latent heat with the overlying atmosphere in ways that are very different from the surrounding terrestrial landscape. Depending on the regional climate and lake characteristics, open-water evaporation from lakes can vary out of phase with terrestrial evapotranspiration within the watershed, and key atmospheric drivers are often different as well. Lake evaporation is a complex process that interacts with many aspects of a lake ecosystem, including water temperature, vertical mixing, lake chemistry, stratification, ice cover, and water levels. Although driven primarily by vapor pressure gradient and wind speed, evaporation is also an energy-consuming process. This leads not only to significant roles from net radiation, sensible heat flux, and other components of the surface energy budget, but it also results in important feedbacks on lake temperature, ice cover, and other evaporation-mediating processes. As such, defining the climatic variables that "drive" lake evaporation is far from straightforward and often depends on timescale, lake depth, and characteristics of the regional climate. In this study, we provide some insight into the problem by examining the energy budget of a variety of lakes across a range of climatic gradients and lake types. This includes shallow Arctic lakes, deep temperate lakes, and a hypersaline lake in a semi-arid climate. Our results reveal a wide range of evaporative response to climatic forcing, including some lakes that show counterintuitive effects or even opposite responses to those of other lakes. Although process-based, mechanistic models should be able to account for such complexities, these findings highlight the need for caution when interpreting climatic drivers of lake evaporation. It is not likely, for example, that models of a solely empirical or statistical nature would be sufficient to fully capture the physics and dynamics of evaporation, particularly in an ever-changing climate.

  11. LAKE FORK

    EPA Science Inventory

    The Lake Fork of the Arkansas River Watershed has been adversely affected through mining, water diversion and storage projects, grazing, logging, and other human influences over the past 120 years. It is the goals of the LFWWG to improve the health of Lake fork by addressing th...

  12. Lake Powell

    Atmospheric Science Data Center

    2014-05-15

    ... with the construction of the Glen Canyon Dam in 1963, on the Colorado River in Page, Arizona and is the second largest man-made lake in the ... side canyons and holds approximately 8.5 trillion gallons of water. The lake's coast line of approximately 1960 miles is greater than the ...

  13. Characterization of Lake Michigan coastal lakes using zooplankton assemblages

    USGS Publications Warehouse

    Whitman, Richard L.; Nevers, Meredith B.; Goodrich, Maria L.; Murphy, Paul C.; Davis, Bruce M.

    2004-01-01

    Zooplankton assemblages and water quality were examined bi-weekly from 17 April to 19 October 1998 in 11 northeastern Lake Michigan coastal lakes of similar origin but varied in trophic status and limnological condition. All lakes were within or adjacent to Sleeping Bear Dunes National Lakeshore, Michigan. Zooplankton (principally microcrustaceans and rotifers) from triplicate Wisconsin net (80 I?m) vertical tows taken at each lake's deepest location were analyzed. Oxygen-temperature-pH-specific conductivity profiles and surface water quality were concurrently measured. Bray-Curtis similarity analysis showed small variations among sample replicates but large temporal differences. The potential use of zooplankton communities for environmental lake comparisons was evaluated by means of BIOENV (Primer 5.1) and principal component analyses. Zooplankton analyzed at the lowest identified taxonomic level yielded greatest sensitivity to limnological variation. Taxonomic and ecological aggregations of zooplankton data performed comparably, but less well than the finest taxonomic analysis. Secchi depth, chlorophyll a, and sulfate concentrations combined to give the best correlation with patterns of variation in the zooplankton data set. Principal component analysis of these variables revealed trophic status as the most influential major limnological gradient among the study lakes. Overall, zooplankton abundance was an excellent indicator of variation in trophic status.

  14. Potential Effects of Climate Warming on Fish Habitats in Temperate Zone Lakes with Special Reference to Lake 239 of the Experimental Lakes Area (ELA), North-Western Ontario

    Microsoft Academic Search

    Wolfgang Jansen; Raymond H. Hesslein

    2004-01-01

    We used simple statistics (e.g. mean temperature, degree days, cumulative volume days) to describe present thermal habitats for cool water (yellow perch, Perca flavescens) and cold water (lake trout, Salvelinus namaycush) fish of a small boreal lake. We then modelled changes in the vertical and temporal extent of these habitats under various scenarios of climatic change that included increases in

  15. Integrative Zoology 2009; 4: 75-86 doi: 10.1111/j.1749-4877.2008.00137.x Cichlid fish visual systems: mechanisms of spectral tuning

    E-print Network

    Carleton, Karen L.

    flocks have arisen independently in each of the three African Great Lakes: Tanganyika, Ma- © 2009 ISZS and diversity. Lake Tanganyika is the oldest lake (8­10 mY), with 200­250 species (Poll 1986; Konings 1998; Salz. These African lakes differ in photic environment. Lakes Tanganyika and Malawi are deep rift lakes (up to 700 m

  16. Holocene TEX86 temperature reconstructions from Lake Turkana, East Africa

    NASA Astrophysics Data System (ADS)

    Berke, M. A.; Johnson, T. C.; Werne, J. P.; Schouten, S.; Sinninghe Damsté, J. S.

    2009-12-01

    We present new high resolution Holocene lake surface temperature records from Lake Turkana, East Africa. These two TEX86 reconstructions, from the northern and southern basins of the lake, capture ~90 year resolution of climate patterns seen in this closed-basin system, as well as the thermal water dynamics between the two basins. The modern lake experiences surface temperatures in the northern basin ~1-3 °C warmer than the southern basin, due to upwelling in the southern basin induced by the predominant southerly winds. The paleotemperature records show parallel trends to this modern basinal temperature gradient, averaging ~1.5 °C warmer in the northern basin than the southern during the ~2000 years of record overlap (~450-2500 ybp). Some temperature intervals with coverage in both basins show strong agreement (i.e. ~2600-2000 Cal ybp), whereas increased wind-generated upwelling events may be responsible for periods that appear strongly antiphased (i.e. 2000-1600 Cal ybp) between basins. There does not appear to be any evidence of warming into the Medieval Warm Period (MWP, ~800-1200AD) or cooling at the start of the Little Ice Age (LIA, ~600 ybp). The southern basin temperature record indicates a substantial ~5 °C warming culminating in a thermal maximum ~5ka, immediately followed by ~3 °C cooling. This supports previous observations of an anomalously warm interval ~5ka documented in lake surface temperature records from Lakes Malawi and Tanganyika. A similar Holocene thermal maximum ~5ka has also been described from the Indian Ocean off the coast of Somalia (3°11’N, 50°26’E) (Bard et al., 1997). The abundance of these records now point to this being the warmest or one of the warmest intervals in the Holocene in tropical East Africa and indicates this may be a widespread regional climate response. Although these temperature trends appear reasonable, overall TEX86 temperatures for Lake Turkana are considerably lower than modern surface water temperatures. Present surface temperatures in Lake Turkana have a seasonal range from ~25.5-31 °C while TEX86 paleotemperatures are ~20-27 °C. An explanation for this difference is not yet known; it may be due to ecological characteristics of the Lake Turkana Crenarchaeota population that are not yet understood.

  17. Lake morphometry and wind exposure may shape the plankton community structure in acidic mining lakes

    PubMed Central

    Weithoff, Guntram; Moser, Michael; Kamjunke, Norbert; Gaedke, Ursula; Weisse, Thomas

    2011-01-01

    Acidic mining lakes (pH <3) are specific habitats exhibiting particular chemical and biological characteristics. The species richness is low and mixotrophy and omnivory are common features of the plankton food web in such lakes. The plankton community structure of mining lakes of different morphometry and mixing type but similar chemical characteristics (Lake 130, Germany and Lake Langau, Austria) was investigated. The focus was laid on the species composition, the trophic relationship between the phago-mixotrophic flagellate Ochromonas sp. and bacteria and the formation of a deep chlorophyll maximum along a vertical pH-gradient. The shallow wind-exposed Lake 130 exhibited a higher species richness than Lake Langau. This increase in species richness was made up mainly by mero-planktic species, suggesting a strong benthic/littoral – pelagic coupling. Based on the field data from both lakes, a nonlinear, negative relation between bacteria and Ochromonas biomass was found, suggesting that at an Ochromonas biomass below 50 ?g C L?1, the grazing pressure on bacteria is low and with increasing Ochromonas biomass bacteria decline. Furthermore, in Lake Langau, a prominent deep chlorophyll maximum was found with chlorophyll concentrations ca. 50 times higher than in the epilimnion which was build up by the euglenophyte Lepocinclis sp. We conclude that lake morphometry, and specific abiotic characteristics such as mixing behaviour influence the community structure in these mining lakes. PMID:23225914

  18. Lake morphometry and wind exposure may shape the plankton community structure in acidic mining lakes.

    PubMed

    Weithoff, Guntram; Moser, Michael; Kamjunke, Norbert; Gaedke, Ursula; Weisse, Thomas

    2010-05-01

    Acidic mining lakes (pH <3) are specific habitats exhibiting particular chemical and biological characteristics. The species richness is low and mixotrophy and omnivory are common features of the plankton food web in such lakes. The plankton community structure of mining lakes of different morphometry and mixing type but similar chemical characteristics (Lake 130, Germany and Lake Langau, Austria) was investigated. The focus was laid on the species composition, the trophic relationship between the phago-mixotrophic flagellate Ochromonas sp. and bacteria and the formation of a deep chlorophyll maximum along a vertical pH-gradient. The shallow wind-exposed Lake 130 exhibited a higher species richness than Lake Langau. This increase in species richness was made up mainly by mero-planktic species, suggesting a strong benthic/littoral - pelagic coupling. Based on the field data from both lakes, a nonlinear, negative relation between bacteria and Ochromonas biomass was found, suggesting that at an Ochromonas biomass below 50 ?g C L(-1), the grazing pressure on bacteria is low and with increasing Ochromonas biomass bacteria decline. Furthermore, in Lake Langau, a prominent deep chlorophyll maximum was found with chlorophyll concentrations ca. 50 times higher than in the epilimnion which was build up by the euglenophyte Lepocinclis sp. We conclude that lake morphometry, and specific abiotic characteristics such as mixing behaviour influence the community structure in these mining lakes. PMID:23225914

  19. Lake level change and total water discharge in East Africa Rift Valley from satellite-based observations

    NASA Astrophysics Data System (ADS)

    Hassan, Ayman A.; Jin, Shuanggen

    2014-06-01

    The measurement of total basin water discharge is important for understanding the hydrological and climatologic issues related to the water and energy cycles. Climatic extreme events are normal climatic occurrences in Africa. For example, extensive droughts are regular features in the last few decades in parts of East Africa, which suffers from a lack of in situ observations as well as a lack of regional hydrological models. In this study, multi-disciplinary different types of space-borne observations and global hydrological models are used to study total water discharge in the Great Rift Valley of East Africa (i.e. Lakes Victoria, Tanganyika, and Malawi) from January 2003 to December 2012. The data include the following: (1) total water storage (TWS) variations from Gravity Recovery and Climate Experiment (GRACE), (2) the lake level variations from Satellite Alimetric data, (3) rainfall from Tropical Rainfall Measurement Mission (TRMM) products, (4) soil moisture from WaterGAP Global Hydrology Model (WGHM), and (5) water fluxes from Global Land Data Assimilation System (GLDAS). Results show that a significant decline in the average lake level is found for all of the three lakes between 2003 and 2006. GRACE TWS variations of the whole basin area show the same pattern of variation as the average lake level variations estimated from Altimetric data. The TWS in the basin area of Lakes Victoria and Malawi is governed by the surface water stored in each lake itself, while for Lake Tanganyika, it is governed by both surface water and the soil moisture content in the basin area. Furthermore, the effect of rainfall on TWS is also studied. A phase lag of ~ 2 months is found between TRMM rainfall and GRACE TWS (generally, rainfall precedes the GRACE TWS) for the three lakes. In addition, the regional evapotranspiration ET is estimated from the water balance equation using GRACE land-water solutions, rainfall data from TRMM and runoff values obtained as a fraction of rainfall. It is found that the computed ET represents approximately 90% of the rainfall over the study region.

  20. Lake Restoration: Medical Lake, Washington

    Microsoft Academic Search

    Raymond A. Soltero; Donald G. Nichols; Anthony F. Gasperino; Michael A. Beckwith

    1981-01-01

    For several decades the thick algal scums and offensive odors of Medical Lake have limited its use. High phosphorus levels, resulting from internal cycling of the nutrient, were responsible for the excessive algal growth. Disruption of the cycle was achieved by whole-lake applications of aluminum sulfate. The treatment significantly reduced phosphorus levels, eliminated nuisance blooms and enhanced water clarity.

  1. Study of dissolved chlorofluorocarbons in Lake Washington

    Microsoft Academic Search

    Lijun Han; John L. Bullister; David P. Wisegarver

    2003-01-01

    Measurements of three chlorofluorocarbons (CFCs): trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12) and trichlorotrifluoroethane (CFC-113), along with methyl chloroform (CH3CCl3) and carbon tetrachloride (CCl4) were made in water samples from Lake Washington, using Electron Capture-Gas Chromatography (EC-GC). The samples were collected in mid-autumn, a period when the lake's upper layer undergoes rapid cooling. At the time of sampling, a strong vertical temperature gradient

  2. Characteristics of true lake breezes along the eastern shore of Lake Michigan

    NASA Astrophysics Data System (ADS)

    Ryznar, Edward; Touma, Jawad S.

    Measurements of temperature, humidity and wind velocity made from 1973 to 1978 at several special stations near Lake Michigan are analyzed to determine true lake breeze occurrences, movement inland and effects of cloudiness and wind speed on lake breeze behavior. A total of 187 true lake breezes occurred in the 6 year period, with July and August having the most frequent occurrences. Nearly half of these moved inland as far as 19 km. Fifty retreated lakeward after having moved inland. The formation and behavior of true lake breezes are discussed in relation to the strength of the offshore wind and cloudiness. Vertical temperature differences associated with the passage, duration and retreat of true lake breezes are presented and discussed.

  3. Hydrogeochemical features of Lake Ngozi (SW Tanzania)

    NASA Astrophysics Data System (ADS)

    Delalande-Le Mouëllic, Manuëlla; Gherardi, Fabrizio; Williamson, David; Kajula, Stephen; Kraml, Michael; Noret, Aurélie; Abdallah, Issah; Mwandapile, Ezekiel; Massault, Marc; Majule, Amos; Bergonzini, Laurent

    2015-03-01

    Located on the triple rift junction hosting the Karonga-Usungu depression in Tanzania, Lake Ngozi is the second largest crater lake of the East African Rift. The lake has a number of peculiar features: it has a near constant water level, no permanent surface inlets and outlets, it is vertically well-mixed, with homogeneous distribution of temperature and chemical composition, and it is characterised by near neutral to slightly acid Na-Cl waters of comparatively high salinity and high P-CO2. Based on the different chemical signature of surface and ground waters (low-Cl type) from lake waters, mass balance methods have been applied to investigate lake dynamics. Water enters the lake mainly by precipitation and groundwater inflow, and leaves by groundwater outflow and evaporation. A large groundwater outflow of 2.4 m yr-1 has been estimated. The high salinity, Na-Cl signature of Lake Ngozi waters, together with 3He/4He ratios measured on dissolved gases (between 7 and 8.3 Ra) and high-PCO2 values estimated all along the water vertical column indicate the inflow of deep-seated fluids, likely magmatic in origin, into the lake. The existence of a hydrothermal system possibly at 250 °C in the root of the volcanic edifice is also hypothesised on the basis of solute geothermometry. Despite the current lack of vertical stratification, the lake is suspected to act as condenser for CO2 and other gases of deep magmatic origin, and should be then further monitored for the risk of limnic eruptions as well as for environmental and climatic concerns.

  4. Lake Nipigon

    NSDL National Science Digital Library

    2001-01-01

    These recent postings from the Canada Centre for Remote Sensing's (CCRS) "Images of Canada" series provide an interesting introduction to remote sensing techniques and the history of landforms, both natural and human-made. The Landsat image of Ontario's Lake Nipigon, a name meaning "deep, clear lake," is viewable in two sizes and is accompanied by text and other remote images on the structural geology, rock types, recent forest fires, and forestry research around the lake. The CCRS was last mentioned in the May 24, 2000 Scout Report for Science and engineering.

  5. Temperature gradients, not food resource gradients, affect growth rate of migrating Daphnia mendotae in Lake Michigan

    Microsoft Academic Search

    Kevin L. Pangle; Scott D. Peacor

    2010-01-01

    Zooplankton production plays a critical role in the Great Lakes ecosystem, and vertical migration, which is exhibited by many zooplankton species, could affect production. We examined the effects of water temperature and food resource gradients on the growth rate of zooplankton undergoing vertical migration in Lake Michigan. In three laboratory experiments, juvenile Daphnia mendotae, native herbivorous cladocerans, were incubated for

  6. SIMULATION OF DISSOLVED OXYGEN PROFILES IN A TRANSPARENT, DIMICTIC LAKE

    EPA Science Inventory

    Thrush Lake is a small, highly transparent lake in northeastern Minnesota. rom 1986 to 1991, vertical profiles of water temperature, dissolved oxygen, chlorophyll a concentration, underwater light irradiance, and Secchi depths were measured at monthly intervals during the ice-fre...

  7. Microbial communities of the stratified soda Lake Doroninskoe (Transbaikal region)

    Microsoft Academic Search

    V. M. Gorlenko; S. P. Buryukhaev; E. B. Matyugina; S. V. Borzenko; Z. B. Namsaraev; I. A. Bryantseva; E. N. Boldareva; D. Yu. Sorokin; B. B. Namsaraev

    2010-01-01

    The physicochemical properties, species composition, and vertical distribution of microorganisms in the water column, shoreline\\u000a microbial mat, and small shoreline mud volcanoes of the stratified soda Lake Doroninskoe were investigated in September 2007.\\u000a The lake is located in the Transbaikal region, in the permafrost zone (51°25?N; 112°28?E). The maximal depth of the contemporary\\u000a lake is about 6 m, the pH

  8. Causal mechanisms of the deep chlorophyll maximum in Lake Superior: A numerical modeling investigation

    E-print Network

    Matsumoto, Katsumi

    Superior. In a survey of summertime vertical chlorophyll distribution at 19 offshore sites in Lake SuperiorCausal mechanisms of the deep chlorophyll maximum in Lake Superior: A numerical modeling Keywords: Lake superior Deep chlorophyll maximum Numerical modeling The deep chlorophyll maximum (DCM

  9. Pigment and lipid compositions of algal and bacterial communities in Ace Lake, Vestfold Hills, Antarctica

    Microsoft Academic Search

    J. K. Volkmanl; H. R. Burton; D. A. Everitt; D. I. Allen

    1988-01-01

    The compositions of carotenoids, chlorophylls and lipids at four depths in Ace Lake have been determined as a means of studying the vertical zonation of species in the lake and for comparison with the lipids found in the bottom sediments. The four major species of phytoplankton found in the lake were identified by electron microscopy. The most abundant phytoplankter was

  10. Pyramid Lake

    USGS Multimedia Gallery

    Pyramid Lake, Nevada, not only holds deep cultural connections for the Paiute Tribe and tribal member Dan Mosely (pictured), but also supports a tribal economy centered on fishing and recreational activities. ...

  11. Katherine A. Allen contact Department of Earth & Environmental Sciences, Columbia University office: 845-365-8668

    E-print Network

    -2012 Tropical lake sediment: field collection and geochemistry Lake Tanganyika, Tanzania June-July 2006/Ca) Encyclopedia of Quaternary Science, 2nd edition. Allen, K., 2008. Geochemistry of Lake Tanganyika Sediment

  12. New evidence for the role of heterochrony in the repeated evolution of cichlid opsin expression

    E-print Network

    Carleton, Karen L.

    -wavelength-sensitive profiles among unrelated cichlids in Lake Tanganyika (LT). To address these questions, we surveyed opsin the three East African Great Lakes: Lakes Tanganyika (LT), Malawi (LM), and Victoria (LV). Cichlids from

  13. Thermal, Chemical and Physical Investigations into Lake Deepening Processes on Spillway Lake, Ngozumpa Glacier, Nepal

    NASA Astrophysics Data System (ADS)

    Horodyskyj, U. N.

    2014-12-01

    The Ngozumpa glacier is one of Nepal's largest and longest glaciers, fed by catchments on the slopes of Cho Oyu, the 6th highest peak in the world. Supraglacial lakes abound along its ~18-km-long ablation zone, but these are dwarfed in area and volume by Spillway lake, a terminal supraglacial lake that is currently expanding and deepening in the lowest kilometer of the glacier. This lake poses a potential future downstream flooding threat, hence there is a perceived need for continuous monitoring and for quantifying factors that lead to growth, deepening and potential instability. Point-interpolated depth surveys (2010/2012) by Thompson and others have revealed deepening hotspots in multiple locations within the lake. The current study reports University of Colorado surveys in 2013 and 2014 that quantify a) vertical water temperature variations in areas of deepening and shallowing; b) physical and chemical characteristics of dredged sediment samples from the lake floor; c) lake water chemistry; d) lake floor bathymetry imaged using high-resolution side-scan sonar and e) lake bottom hardness and roughness. These parameters are analyzed with a view to assessing their role in controlling lake floor deepening and growth.

  14. Functional convergence among pelagic sculpins of Lake Baikal and deepwater ciscoes of the Great Lakes

    USGS Publications Warehouse

    Eshenroder, Randy L.; Sideleva, Valentina G.; Todd, Thomas N.

    1999-01-01

    The vast, well-oxygenated hypolimnia of Lake Baikal and the Great Lakes were both dominated by endemic planktivorous fishes. These dominants, two species of sculpins (Comephorus,Comephoridae) in Lake Baikal and six species of deepwater ciscoes (Coregonus, Salmonidae) in the Great Lakes, although distant taxonomically, have morphologies suggesting a surprising degree of functional convergence. Here it is proposed that the same two buoyancy-regulation strategies observed in Baikal sculpins also arose in the deepwater ciscoes of the Great Lakes. One strategy favors hydrostatic lift (generated by low specific gravity) and is characterized by fatter, larger-bodied fish with smaller paired fins; the second strategy favors hydrodynamic lift (generated by swimming) and is characterized by leaner, smaller-bodied fish with larger paired fins. Both types likely evolved to feed on a single species of ecologically analogous, vertically migrating macrozooplankter: Macrohectopus branickii in Lake Baikal and Mysis relicta in the Great Lakes. It is suggested that Coregonus did not diversify and proliferate in Lake Baikal as they did in the Great Lakes because by the time Coregonus colonized Lake Baikal, pelagic sculpins were already dominant.

  15. Principles of lake sedimentology

    SciTech Connect

    Janasson, L.

    1983-01-01

    This book presents a comprehensive outline on the basic sedimentological principles for lakes, and focuses on environmental aspects and matters related to lake management and control-on lake ecology rather than lake geology. This is a guide for those who plan, perform and evaluate lake sedimentological investigations. Contents abridged: Lake types and sediment types. Sedimentation in lakes and water dynamics. Lake bottom dynamics. Sediment dynamics and sediment age. Sediments in aquatic pollution control programmes. Subject index.

  16. Numerical simulation analysis of the interaction of lakes and ground water

    USGS Publications Warehouse

    Winter, Thomas C.

    1976-01-01

    Numerical-model simulations were run to evaluate the factors that control the interaction of lakes and grounder water. The study is concerned only with lakes encircled by water-table mounds that are at a higher altitude than lake level. Simulations of one-lake and multiple-lake systems in vertical sections show that for many hydrogeologic settings, the line (divide) separating local from regional ground-water flow systems is continuous beneath individual lakes. If the divide is continuous, there exists a point along it at which the head is a minimum compared to all other points along the divide. This point of minimum head is always greater than the head represented by lake level, therefore in such a setting there can be no movement of lake water through the lake bed to the ground-water system. In a setting where the divide is not continuous, the lake loses water through part of its bed, but rarely in the littoral zone of the lake. Factors that strongly influence the position, shape and continuity of the flow-system divide beneath lakes are height of the water table on the downslope side of the lake relative to lake level, position and hydraulic conductivity of quifers within the ground-water reservoir, ratio of horizontal to vertical hydraulic conductivity of the ground-water system, and lake depth. (Woodard-USGS)

  17. The role of upstream lakes in determining downstream severe lake-effect snowstorms

    NASA Astrophysics Data System (ADS)

    Rose, Bruce L., Jr.

    2001-06-01

    A severe lake-effect snowstorm on 25-26 December 1993 was successfully modeled using the Penn State/NCAR MM5 model at 7 km grid resolution. Another simulation performed with Lake Michigan removed from the domain resulted in a two-thirds reduction in snowfall maxima, reduced vertical ascent (50% smaller maxima), and cloud depth (50-100 mb in vertical depth) upwind and over Lake Erie. The downstream snowband shifted northward and eastward as a consequence of stronger background flow and weaker shoreline convergence in the removed case. An idealized model of two-lake interaction was devised using an alternative set of MM5 preprocesses, allowing the definition of simple boundary conditions subject to a single thermal profile applied across the domain. Fixed background winds, temperature, and humidity were then allowed to interact with a surface boundary composed of flat land and elliptical lakes. In the absence of orography and synoptic-scale transients, model responses could be attributed directly to mesoscale forcing via the thermal and frictional disparity between land and water. Results showed that multi-lake interaction did occur once heat and moisture advected from the upstream to downstream lakes (12-18 hours under 10 m s-1 background flow). When background conditions known to produce strong lake-effect snowband development are imposed, the heat and moisture plume from the upstream lake warmed the CIBL between the two lakes by 4- 6°C, and elevated cloud liquid water by amounts exceeding 0.20 g kg-1. The dynamical adjustment resulting from the upstream surface-forcing lowered pressure by 1.5-2.0 mb downwind of the upstream lake; produced a mesoscale low pressure with flow reversal along the northern one-third of the upstream lake; and accelerated flow downwind of the lower one- third of this lake. Removal of turbulent heat fluxes from the upstream lake demonstrated that sensible heating is directly responsible for the establishment and maintenance of the upstream local pressure perturbation through dynamic adjustment or thermal troughing. Suppression of moisture availability or latent heat flux from the upstream lake greatly reduces precipitation amounts and areal extents over the downstream lake, much more so than removal of both latent and sensible heat fluxes, or removal of the lake itself.

  18. Adaptive divergence between lake and stream populations of an East African cichlid fish.

    PubMed

    Theis, Anya; Ronco, Fabrizia; Indermaur, Adrian; Salzburger, Walter; Egger, Bernd

    2014-11-01

    Divergent natural selection acting in different habitats may build up barriers to gene flow and initiate speciation. This speciation continuum can range from weak or no divergence to strong genetic differentiation between populations. Here, we focus on the early phases of adaptive divergence in the East African cichlid fish Astatotilapia burtoni, which occurs in both Lake Tanganyika (LT) and inflowing rivers. We first assessed the population structure and morphological differences in A. burtoni from southern LT. We then focused on four lake-stream systems and quantified body shape, ecologically relevant traits (gill raker and lower pharyngeal jaw) as well as stomach contents. Our study revealed the presence of several divergent lake-stream populations that rest at different stages of the speciation continuum, but show the same morphological and ecological trajectories along the lake-stream gradient. Lake fish have higher bodies, a more superior mouth position, longer gill rakers and more slender pharyngeal jaws, and they show a plant/algae and zooplankton-biased diet, whereas stream fish feed more on snails, insects and plant seeds. A test for reproductive isolation between closely related lake and stream populations did not detect population-assortative mating. Analyses of F1 offspring reared under common garden conditions indicate that the detected differences in body shape and gill raker length do not constitute pure plastic responses to different environmental conditions, but also have a genetic basis. Taken together, the A. burtoni lake-stream system constitutes a new model to study the factors that enhance and constrain progress towards speciation in cichlid fishes. PMID:25256664

  19. Primary production in a tropical large lake: the role of phytoplankton composition.

    PubMed

    Darchambeau, F; Sarmento, H; Descy, J-P

    2014-03-01

    Phytoplankton biomass and primary production in tropical large lakes vary at different time scales, from seasons to centuries. We provide a dataset made of 7 consecutive years of phytoplankton biomass and production in Lake Kivu (Eastern Africa). From 2002 to 2008, bi-weekly samplings were performed in a pelagic site in order to quantify phytoplankton composition and biomass, using marker pigments determined by HPLC. Primary production rates were estimated by 96 in situ (14)C incubations. A principal component analysis showed that the main environmental gradient was linked to a seasonal variation of the phytoplankton assemblage, with a clear separation between diatoms during the dry season and cyanobacteria during the rainy season. A rather wide range of the maximum specific photosynthetic rate (PBm) was found, ranging between 1.15 and 7.21 g carbong(-1)chlorophyll ah(-1), and was best predicted by a regression model using phytoplankton composition as an explanatory variable. The irradiance at the onset of light saturation (Ik) ranged between 91 and 752 ?E m(-2)s(-1) and was linearly correlated with the mean irradiance in the mixed layer. The inter-annual variability of phytoplankton biomass and production was high, ranging from 53 to 100 mg chlorophyll am(-2) (annual mean) and from 143 to 278 g carbon m(-2)y(-1), respectively. The degree of seasonal mixing determined annual production, demonstrating the sensitivity of tropical lakes to climate variability. A review of primary production of other African great lakes allows situating Lake Kivu productivity in the same range as that of lakes Tanganyika and Malawi, even if mean phytoplankton biomass was higher in Lake Kivu. PMID:24370692

  20. Vertical dynamics Spiral structure

    E-print Network

    Kruit, Piet van der

    Outline Vertical dynamics Spiral structure The Hubble type of the Galaxy STRUCTURE OF GALAXIES 7;Outline Vertical dynamics Spiral structure The Hubble type of the Galaxy Outline Vertical dynamics van der Kruit, Kapteyn Astronomical Institute Structure of galaxy disks #12;Outline Vertical dynamics

  1. ARTICLE OPEN doi:10.1038/nature13726

    E-print Network

    Cai, Long

    : Neolamprologus brichardi/pulcher (older radiation, Lake Tanganyika), Metriaclima zebra(recentradiation,LakeMalawi),Pundamilianyererei (veryrecentradiation,LakeVictoria),andAstatotilapiaburtoni (riverine species around Lake Tanganyika). We foundVictoria and less than 5 million years for Malawi3­5 , but 10­12 million years for Lake Tanganyika6 . The radiations

  2. Orbital- versus glacial-mode forcing of tropical African climate: Results of scientific drilling in Lake Malawi, East Africa

    NASA Astrophysics Data System (ADS)

    Scholz, C. A.; Cohen, A. S.; Johnson, T. C.; King, J. W.; Brown, E. T.; Lyons, R. P.; Stone, J. R.; Beuning, K. R.

    2007-12-01

    Lake Malawi extends from 9-14 degrees S within the East African Rift Valley, and at 700 m deep, contains more than 20 percent of the surface water on the African continent. In 2005 the Lake Malawi Scientific Drilling Project drilled 7 holes at two sites in the lake, recovering a continuous sediment record that samples much of the Quaternary. Detailed studies completed to date on sediments deposited during the past 145 ka indicate periods of severe aridity at precessional frequency between 135 and 75 ka, when the lake's water volume was periodically reduced by at least 95 percent. These dramatic drops in lake level (more than 550 m), signifying markedly arid conditions in the catchment, are documented in sediment lithology (decreased organic carbon content and increased authigenic carbonate content during severe lowstands), aquatic microfossils (appearance of a littoral ostracode fauna, and saline/alkaline lake diatom flora during extreme low lake stages), as well as in dramatic reductions in catchment pollen production. These intervals of pronounced tropical African aridity in the early late-Pleistocene were much more severe than the Last Glacial Maximum, and are consistent with sediment records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa). In all three lakes a major rise in water levels and a shift to more humid conditions is observed after ~70 ka. The transition to wetter, more stable conditions coincides with the relaxation of orbital eccentricity and a reduction in the amplitude of precession. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa, but these new drill cores provide evidence for dramatically drier conditions prior to 70 ka that have not as yet been detected in marine sediment records. Such climate change may have stimulated the expansion and migrations of early modern human populations.

  3. Hydro?isostatic deflection and tectonic tilting in the central Andes: Initial results of a GPS survey of Lake Minchin shorelines

    Microsoft Academic Search

    Shanaka L. de Silva; Donald R. Currey; Robert S. Emengefi; Karl D. Lillquist; Andrea Donnellan; Bruce Worden

    1994-01-01

    Stilciently large lake loads provide a means of probing theological stratification of the crust and upper mantle. Lake Minchin was the largest of the late ~leistocene pluvial lakes in the central Andes. Prominent shorelines, which formed during tempora~ still-stands in the climatically driven lake level history, preserve records of lateral variations in subsequent net vertical motions. At its maximum extent

  4. Hydro-isostatic deflection and tectonic tilting in the central Andes: Initial results of a GPS survey of Lake Minchin shorelines

    Microsoft Academic Search

    Bruce G. Bills; Shanaka L. de Silva; Donald R. Currey; Robert S. Emenger; Karl D. Lillquist; Andrea Donnellan; Bruce Worden

    1994-01-01

    Sufficiently large lake loads provide a means of probing rheological stratification of the crust and upper mantle. Lake Minchin was the largest of the late Pleistocene pluvial lakes in the central Andes. Prominent shorelines, which formed during temporary still-stands in the climatically driven lake level history, preserve records of lateral variations in subsequent net vertical motions. At its maximum extent

  5. Recent warming of lake Kivu.

    PubMed

    Katsev, Sergei; Aaberg, Arthur A; Crowe, Sean A; Hecky, Robert E

    2014-01-01

    Lake Kivu in East Africa has gained notoriety for its prodigious amounts of dissolved methane and dangers of limnic eruption. Being meromictic, it is also expected to accumulate heat due to rising regional air temperatures. To investigate the warming trend and distinguish between atmospheric and geothermal heating sources, we compiled historical temperature data, performed measurements with logging instruments, and simulated heat propagation. We also performed isotopic analyses of water from the lake's main basin and isolated Kabuno Bay. The results reveal that the lake surface is warming at the rate of 0.12°C per decade, which matches the warming rates in other East African lakes. Temperatures increase throughout the entire water column. Though warming is strongest near the surface, warming rates in the deep waters cannot be accounted for solely by propagation of atmospheric heat at presently assumed rates of vertical mixing. Unless the transport rates are significantly higher than presently believed, this indicates significant contributions from subterranean heat sources. Temperature time series in the deep monimolimnion suggest evidence of convection. The progressive deepening of the depth of temperature minimum in the water column is expected to accelerate the warming in deeper waters. The warming trend, however, is unlikely to strongly affect the physical stability of the lake, which depends primarily on salinity gradient. PMID:25295730

  6. Recent Warming of Lake Kivu

    PubMed Central

    Katsev, Sergei; Aaberg, Arthur A.; Crowe, Sean A.; Hecky, Robert E.

    2014-01-01

    Lake Kivu in East Africa has gained notoriety for its prodigious amounts of dissolved methane and dangers of limnic eruption. Being meromictic, it is also expected to accumulate heat due to rising regional air temperatures. To investigate the warming trend and distinguish between atmospheric and geothermal heating sources, we compiled historical temperature data, performed measurements with logging instruments, and simulated heat propagation. We also performed isotopic analyses of water from the lake's main basin and isolated Kabuno Bay. The results reveal that the lake surface is warming at the rate of 0.12°C per decade, which matches the warming rates in other East African lakes. Temperatures increase throughout the entire water column. Though warming is strongest near the surface, warming rates in the deep waters cannot be accounted for solely by propagation of atmospheric heat at presently assumed rates of vertical mixing. Unless the transport rates are significantly higher than presently believed, this indicates significant contributions from subterranean heat sources. Temperature time series in the deep monimolimnion suggest evidence of convection. The progressive deepening of the depth of temperature minimum in the water column is expected to accelerate the warming in deeper waters. The warming trend, however, is unlikely to strongly affect the physical stability of the lake, which depends primarily on salinity gradient. PMID:25295730

  7. The biogeochemistry of tropical lakes: A case study from Lake Matano, Indonesia

    E-print Network

    Crowe, S.A.; O'Neill, A.H.; Katsev, S.; Hehanussa, P.; Haffner, G. Douglas; Sundby, Bjorn; Mucci, Alfonso; Fowle, David A.

    2008-01-16

    (wind, density flows, seiches, etc.). The stability frequency characterizes the first part of this balance. We calculated the stability frequency for Lake Matano from the vertical density variation. Despite the variety of driving forces, in environments... to an isopleth along the lake bottom can also redistribute Fe and drive fluxes of Fe(II) into the hypolimnion (Shaffer 1986; Katsev et al. 2006). Short-term (several hours) fluctuations could result from seiching, whereas longer term fluctuations could...

  8. Temperature profiles and bathymetry of some high mountain lakes.

    PubMed

    Leopold, L B

    2000-06-01

    The ice cover in high mountain lakes breaks up and disappears in about an hour, in part because it has been divided into fragile vertical spindles, which are individual crystals. Contributing to this process are vertical holes in the ice remaining after particles of dust melt downward as they are warmed by the sun. Temperature profiles of lakes in the Wind River Mountains of Wyoming include those of five lakes in the high wilderness. All are isothermal at or near 5 degrees C below a depth of 20 to 30 m, regardless of elevation or lake depth. Large lakes have a deeper mixed layer than do small ones because of longer fetch and thus more effective wind shear. PMID:10841531

  9. Temperature profiles and bathymetry of some high mountain lakes

    PubMed Central

    Leopold, Luna B.

    2000-01-01

    The ice cover in high mountain lakes breaks up and disappears in about an hour, in part because it has been divided into fragile vertical spindles, which are individual crystals. Contributing to this process are vertical holes in the ice remaining after particles of dust melt downward as they are warmed by the sun. Temperature profiles of lakes in the Wind River Mountains of Wyoming include those of five lakes in the high wilderness. All are isothermal at or near 5°C below a depth of 20 to 30 m, regardless of elevation or lake depth. Large lakes have a deeper mixed layer than do small ones because of longer fetch and thus more effective wind shear. PMID:10841531

  10. The photobehaviour of Daphnia spp. as a model to explain diel vertical migration in zooplankton

    Microsoft Academic Search

    J. Ringelberg

    1999-01-01

    Many pelagic animal species in the marine environment and in lakes migrate to deeper water layers before sunrise and return around sunset. The amplitude of these diel vertical migrations (DVM) varies from several hundreds of metres in the oceans to approx. 5-20 m in lakes. DVM can be studied from a proximate and an ultimate point of view. A proximate

  11. Large-scale variability of wind erosion mass flux rates at Owens Lake 1. Vertical profiles of horizontal mass fluxes of wind-eroded particles with diameter greater than 50 ?m

    USGS Publications Warehouse

    Gillette, Dale A.; Fryrear, D.W.; Xiao, Jing Bing; Stockton, Paul; Ono, Duane; Helm, Paula J.; Gill, Thomas E; Ley, Trevor

    1997-01-01

    A field experiment at Owens (dry) Lake, California, tested whether and how the relative profiles of airborne horizontal mass fluxes for >50-?m wind-eroded particles changed with friction velocity. The horizontal mass flux at almost all measured heights increased proportionally to the cube of friction velocity above an apparent threshold friction velocity for all sediment tested and increased with height except at one coarse-sand site where the relative horizontal mass flux profile did not change with friction velocity. Size distributions for long-time-averaged horizontal mass flux samples showed a saltation layer from the surface to a height between 30 and 50 cm, above which suspended particles dominate. Measurements from a large dust source area on a line parallel to the wind showed that even though the saltation flux reached equilibrium ?650 m downwind of the starting point of erosion, weakly suspended particles were still input into the atmosphere 1567 m downwind of the starting point; thus the saltating fraction of the total mass flux decreased after 650 m. The scale length difference and ratio of 70/30 suspended mass flux to saltation mass flux at the farthest down wind sampling site confirm that suspended particles are very important for mass budgets in large source areas and that saltation mass flux can be a variable fraction of total horizontal mass flux for soils with a substantial fraction of <100-?m particles.

  12. Lake Victoria

    NSDL National Science Digital Library

    This online article, from "The Biodiversity Crisis: Losing What Counts", provides insight into how human behavior has put one of the world's largest ecosystems close to death. It covers the astonishingly diverse cichlid species that live only in Lake Victoria and changes to the ecosystem brought about by the introduction of a non-native species.

  13. Mating system variability in a mouthbrooding cichlid fish from a tropical lake.

    PubMed

    Sefc, K M; Hermann, C M; Koblmüller, S

    2009-08-01

    Intraspecific variability in mating behaviour and disparities between social and reproductive behaviour add complexity to the description of animal mating systems. A previously published field study on a population of the maternally mouthbrooding cichlid fish Ctenochromis horei in the north of Lake Tanganyika suggested mate monopolization by the most dominant male. In the present study, genetic reconstructions of paternity in a population in the south of the lake provided no evidence for male mate monopolization, as none of the inferred sires had offspring in more than one brood. The ability to reconstruct sire genotypes from offspring alleles was confirmed by computer simulations. Multiple paternity occurred in several broods and was significantly more frequent in the sample taken in the rainy season than in the dry season sample (100% of broods vs. 14%, respectively; P = 0.005). The data suggest geographical and temporal variation in the mating behaviour of C. horei despite its continuous year-round reproduction, invariable brood care behaviour and habitat-specific distribution in the relatively constant and confined environment of a tropical lake. Moreover, our data show that inferences on the distribution of male reproductive success, if based on each geographical or temporal data set alone, would fail to describe the potential for sexual selection in this species. PMID:19659476

  14. Great Lakes Information Network

    NSDL National Science Digital Library

    The Great Lakes Information Network (GLIN) is a partnership that has compiled information relating to the binational Great Lakes-St. Lawrence region of North America. Sections of the site include an overview of the Great Lakes, the environment of the Great Lakes, the economy of the Great Lakes, education, maps and Geographic Information Systems (GIS), and tourism.

  15. Vertical Map Storage.

    ERIC Educational Resources Information Center

    Perry, Joanne M.

    1982-01-01

    Discusses the superiority of vertical filing of maps in compressor-style vertical units over horizontal filing in drawers, emphasizing such factors as physical protection of the collection, ease of filing and retrieval, and efficient use of space. Disadvantages of vertical filing are also reviewed. (Author/JL)

  16. Recent speciation between sympatric Tanganyikan cichlid colour morphs

    E-print Network

    Woods Road, Ithaca, NY 14850, USA Abstract Lake Tanganyika, Africa's oldest lake, harbours an impressive initially rapid, cichlids from Lake Tanganyika show little evidence for ongoing speciation. In contrast an unusual example of active diversification in Lake Tanganyika's generally ancient cichlid fauna and enable

  17. SHORT REVIEW Genetic and developmental basis of cichlid trophic

    E-print Network

    Kocher, Thomas D.

    history of cichlid evolution The ancestors of most East African cichlids can be traced to Lake Tanganyika. At 8­10 million years old, Lake Tanganyika is the oldest of the rift valley lakes. Several lines of evidence suggest that Lake Tanganyika acted as an

  18. BioMed Central Page 1 of 16

    E-print Network

    Alvarez, Nadir

    lineages are endemic to Lake Tanganyika (plus one non-endemic representative), and these are the only two diversified rapidly into at least six lineages that inhabit lakes and rivers in East Africa. Lake Tanganyika that almost 1,800 cichlid species inhabit Lakes Tanganyika, Published: 19 June 2006 BMC Evolutionary Biology

  19. Construction of chromosome markers from the Lake Victoria cichlid Paralabidochromis chilotes and their application to comparative mapping.

    PubMed

    Kuroiwa, A; Terai, Y; Kobayashi, N; Yoshida, K; Suzuki, M; Nakanishi, A; Matsuda, Y; Watanabe, M; Okada, N

    2014-01-01

    Cichlid fishes in the African Great Lakes are known as a spectacular example of adaptive radiation in vertebrates. Four linkage maps have been constructed to identify the genes responsible for adaptation and speciation, and the genetic linkages of those genes are assumed to play an important role during adaptive evolution. However, it is difficult to analyze such linkages because the linkage groups of one species do not match well with those of the other species. Chromosome markers are a powerful tool for the direct identification of linkage homology between different species. We used information about the linkage map of the Lake Malawi cichlid (Labeotropheus fuelleborni/Metriaclima zebra) to isolate bacterial artificial chromosome (BAC) clones from the BAC library of Paralabidochromis chilotes, Lake Victoria. We identified 18 of 22 P. chilotes chromosomes by single- and multi-color BAC fluorescence in situ hybridization using 19 BAC clones. Comparative mapping with the chromosome markers of P. chilotes in Astatotilapia burtoni (2n = 40) from Lake Tanganyika revealed the chromosome rearrangements that have occurred in this lineage. These chromosome markers will be useful for delineating the process of genome and chromosome evolution in African species. PMID:24217467

  20. The large lake ecosystems of northern Canada

    Microsoft Academic Search

    M. S Evans

    2000-01-01

    The Great Lakes of northern Canada are relatively understudied ecosystems in comparison to the better-investigated Laurentian Great Lakes. This chain of lakes extends north from Lake Winnipeg (a shallow prairie lake) to Wollaston Lake and Lake Athabasca (moderately deep arboreal lakes) to Great Slave Lake (a deep subarctic lake) to Great Bear Lake (a deep lake located in the Arctic

  1. Bathymetry of Bonnie Doone Lake, Kornbow Lake, Mintz Pond, and Glenville Lake, Cumberland County, North Carolina, 1996-98

    USGS Publications Warehouse

    Giorgino, M.J.; Strain, R.E.

    1999-01-01

    Bathymetric surveys were conducted at four water-supply impoundments of Little Cross Creek in Cumberland County, North Carolina. The surveys were conducted in April 1996 at Mintz Pond and Glenville Lake, and in January 1998 at Bonnie Doone Lake and Kornbow Lake. The resulting bathymetric maps are the first to cover the entire range in depth for these reservoirs and provide a framework for future evaluations of bathymetry and storage capacity. Bathymetric maps were constructed from depth and position data collected at each reservoir. A boat-mounted, research-grade fathometer was used to record water depths with a vertical accuracy of 0.1 foot. At Mintz Pond and Glenville Lake, position was measured by using a wide-band laser tracking system interfaced with a total station survey instrument. This positioning method required multiple land-based control points to be established and was hampered by line-of-sight restrictions between the control points and the boat. At Bonnie Doone Lake and Kornbow Lake, a global positioning system was used to collect differentially corrected location data. This positioning method enabled more rapid data collection, eliminated the need for land-based control points, and provided improved data coverage. Spillway elevations range from 172.8 feet above mean sea level at Bonnie Doone Lake to 113.1 feet at Glenville Lake. Surface area and storage volume were computed for each reservoir and were related to water-surface elevations at 1-foot intervals. The combined surface acreage of the four Little Cross Creek reservoirs at their full-pool elevations is 120.97 acres, consisting of 21.20 acres at Bonnie Doone Lake, 47.09 acres at Kornbow Lake, 15.56 acres at Mintz Pond, and 37.12 acres at Glenville Lake. The four reservoirs have a combined usable storage capacity of 674.91 acre-feet, which is the sum of 127.93 acre-feet in Bonnie Doone Lake, 320.62 acre-feet in Kornbow Lake, 53.25 acre-feet in Mintz Pond, and 173.11 acre-feet in Glenville Lake.

  2. Spatial heterogeneity of daphniid parasitism within lakes.

    PubMed

    Hall, Spencer R; Duffy, Meghan A; Tessier, Alan J; Cáceres, Carla E

    2005-05-01

    Spatially explicit models show that local interactions of hosts and parasites can strongly influence invasion and persistence of parasites and can create lasting spatial patchiness of parasite distributions. These predictions have been supported by experiments conducted in two-dimensional landscapes. Yet, three-dimensional systems, such as lakes, ponds, and oceans, have received comparatively little attention from epidemiologists. Freshwater zooplankton hosts often aggregate horizontally and vertically in lakes, potentially leading to local host-parasite interactions in one-, two-, or three-dimensions. To evaluate the potential spatial component of daphniid parasitism driven by these local interactions (patchiness), we surveyed vertical and horizontal heterogeneity of pelagic Daphnia infected with multiple microparasites in several north temperate lakes. These surveys uncovered little evidence for persistent vertical patchiness of parasitism, since the prevalence of two parasites showed little consistent trend with depth in four lakes (but more heterogeneity during day than at night). On a horizontal scale of tens of meters, we found little systematic evidence of strong aggregation and spatial patterning of daphniid hosts and parasites. Yet, we observed broad-scale, basin-wide patterns of parasite prevalence. These patterns suggest that nearshore offshore gradients, rather than local-scale interactions, could play a role in governing epidemiology of this open water host-parasite system. PMID:15909131

  3. Mono Lake, California

    NSDL National Science Digital Library

    Sierra WebPage

    This Sierra Webpage is dedicated to Mono Lake, CA. It offers a brief description of Mono Lake, including photos and sightseeing tips, and features numerous writings by Mono Lake Park Ranger David Carle. Subjects include the Mono Lake environment, visiting the lake, and the water issue. An entry of particular interest is Strange Water- Mono Lake Gourmet: An Unusual Recipe. It includes 'Mock Mono Lake Soup' and 'Tufa Porridge Extraordinaire'- two recipes designed to illustrate the composition of Mono Lake and the chemical processes involved in tufa formation.

  4. Behavioral Ecology doi:10.1093/beheco/arn031

    E-print Network

    Neff, Bryan D.

    with regard to relatedness. Key words: cichlidae, inbreeding avoidance, Lake Tanganyika, mate choice of this study was to determine whether Neolamprologus pulcher, a cichlid fish endemic to Lake Tanganyika, avoids

  5. ORIGINAL ARTICLE Evolution of body shape in sympatric versus non-sympatric

    E-print Network

    Richner, Heinz

    populations of Lake Tanganyika M Kerschbaumer1, P Mitteroecker2 and C Sturmbauer1 Allopatric speciation often. The shores of Lake Tanganyika harbor about 120 distinct populations of the cichlid genus Tropheus, but only

  6. TEACH Great Lakes

    NSDL National Science Digital Library

    The Education And Curriculum Home site (TEACH) is a new component of the Great Lakes Information Network, with a focus on advancing Great Lakes-related educational materials for the broad audience of educators and students in the Great Lakes region and beyond. TEACH features mini-lessons on Great Lakes topics: environment, history and culture, geography, pollution, careers, and business. Geared for elementary through high school students, the modules are continually expanded and updated and include links to a glossary to help explain scientific terms and acronyms. Also included is a section for questions and answers, and education links. Specific topics within the site include: Great Lakes native flora, water levels on the Great Lakes, native peoples of the Great Lakes region, Great Lakes law and policy, introduction to the Great Lakes, how the lakes were formed, Great Lakes shoreline geology, non-native species, and urban sprawl.

  7. Study of dissolved chlorofluorocarbons in Lake Washington

    Microsoft Academic Search

    Han Lijun; John L. Bullister; David P. Wisegarver

    2003-01-01

    Measurements of three chlorofluorocarbons (CFCs): trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12) and trichlorotrifluoroethane\\u000a (CFC-113), along with methyl chloroform (CH3CCl3) and carbon tetrachloride (CCl4) were made in water samples from Lake Washington, using Electron Capture-Gas Chromatography (EC-GC). The samples were collected\\u000a in mid-autumn, a period when the lake's upper layer undergoes rapid cooling. At the time of sampling, a strong vertical temperature\\u000a gradient

  8. Great Lakes and Lake Effect Snow

    NSDL National Science Digital Library

    Lori Perkins

    1999-12-03

    Great Lakes and Lake Effect Snow. This animation is a dissolve between 2 different SeaWiFS images taken in 1999. One image is taken in the spring,April, and the second image is taken in the winter, December. The December 1999 image shows a traditional lake effect snow storm. This animation shows the difference between the seasons in the Great Lakes region.

  9. Lake Effects: The Lake Superior Curriculum Guide.

    ERIC Educational Resources Information Center

    Beery, Tom; And Others

    This curriculum guide was launched in response to a need for Lake Superior-specific educational materials and contains lessons and activities that can be used to teach about Lake Superior. The lessons in this book are divided into four sections. Each of the first three sections has a background section that provides basic information about Lake

  10. Lake Trout Rehabilitation in Lake Huron

    Microsoft Academic Search

    Randy L. Eshenroder; N. Robert Payne; James E. Johnson; Charles Bowen II; Mark P. Ebener

    1995-01-01

    Efforts to restore lake trout (Salvelinus namaycush) in Lake Huron after their collapse in the 1940s were underway in the early 1970s with completion of the first round oflampricide applications in tributary streams and the stocking of several genotypes. We assess results of rehabilitation and establish a historical basis for comparison by quantifying the catch of spawning lake trout from

  11. Hydrogeologic setting of the Glacial Lake Agassiz Peatlands, northern Minnesota

    USGS Publications Warehouse

    Siegel, Donald I.

    1981-01-01

    Seven test holes drilled in the Glacial Lake Agassiz Peatlands indicate that the thickness of surficial materials along a north-south traverse parallel to Minnesota Highway 72 ranges from 163 feet near Blackduck, Minn., to 57 feet about 3 miles south of Upper Red Lake. Lenses of sand and gravel occur immediately above bedrock on the Itasca moraine and are interbedded with lake clay and till under the peatlands. Vertical head gradients measured in a piezometer nest near Blackduck on the moraine are downward, indicative of recharge to the regional ground-water-flow system. Vertical head gradients are upward in a piezometer nest on a sand beach ridge in the peatlands 12 miles north of Upper Red Lake. Numerical sectional models indicate that this discharge probably comes from local flow systems recharged from ground-water mounds located under large raised bogs. (USGS)

  12. Great Lakes RESTORATION

    E-print Network

    Great Lakes RESTORATION NATIONALOCEAN IC AND ATMOSPHERIC ADMINISTRATION U.S. D EPARTMENT OF COMM E R CE Great Lakes Restoration Initiative Recognizing the importance of the Great Lakes to our nation, President Obama made restoration a national priority. The resulting Great Lakes Restoration Initiative (GLRI

  13. Great Lakes RESTORATION

    E-print Network

    Great Lakes RESTORATION NATIONALOCEAN IC AND ATMOSPHERIC ADMINISTRATION U.S. D EPARTMENT OF COMM E R CE The Great Lakes Restoration Initiative Recognizing the importance of the Great Lakes to our nation, President Obama made their restoration a national priority. The resulting Great Lakes Restoration

  14. Great Lakes RESTORATION

    E-print Network

    Great Lakes RESTORATION NATIONALOCEAN IC AND ATMOSPHERIC ADMINISTRATION U.S. D EPARTMENT OF COMM E R CE Great Lakes Restoration Initiative Recognizing the importance of the Great Lakes to our nation, President Obama made their restoration a national priority. The resulting Great Lakes Restoration Initiative

  15. Hydrogen peroxide distribution, production, and decay in boreal lakes

    Microsoft Academic Search

    Petri J. Häkkinen; Alexandre M. Anesio; Wilhelm Granéli

    2004-01-01

    The distribution, production, and decay of hydrogen peroxide (H2O2) were studied in 10 boreal lakes of dif- fering physical-chemical characteristics. Diurnal and vertical fluctuations in H2O2 concentration were followed in the lakes by sampling at six depths three times per day. In addition, incubations of water filtered through 0.2-µm mesh were made under artificial irradiation to study the abiotic production

  16. Modeling basin-scale internal waves in a stratified lake

    Microsoft Academic Search

    Ben R. Hodges; Jörg Imberger; Angelo Saggio; K. B. Winters

    2000-01-01

    Basin-scale internal waves provide the driving forces for vertical and horizontal fluxes in a stratified lake below the wind-mixed layer. Thus, correct modeling of lake mixing and transport requires accurate modeling of basin- scale internal waves: examining this capability with a hydrostatic, z-coordinate three-dimensional (3D) numerical model at coarse grid resolutions is the focus of this paper. It is demonstrated

  17. Vertical electromagnetic profiling (VEMP)

    Microsoft Academic Search

    Lytle

    1984-01-01

    Vertical seismic profiling (VSP) is based upon reception measurements performed in a borehole with a source near the ground surface. This technology has seen a surge in application and development in the last decade. The analogous concept of vertical electromagnetic profiling (VEMP) consists of reception measurements performed in a borehole with a source near the ground surface. Although the electromagnetic

  18. Early observations on an emerging Great Lakes invader Hemimysis anomala in Lake Ontario

    USGS Publications Warehouse

    Walsh, Maureen G.; Lantry, Brian F.; Boscarino, Brent; Bowen, Kelly; Gerlofsma, Jocelyn; Schaner, Ted; Back, Richard; Questel, Jennifer; Smythe, A. Garry; Cap, Roberta; Goehle, Michael; Young, Bryan; Chalupnicki, Marc; Johnson, James H.; McKenna, James E.

    2010-01-01

    Hemimysis anomala, a Ponto-Caspian littoral mysid, is an emerging Great Lakes invader that was discovered in Lakes Michigan and Ontario in 2006. Similar to the native mysid Mysis diluviana, Hemimysis exhibits a diel vertical migration pattern but generally inhabits shallower and warmer waters than M. diluviana. Because basic information on the distribution, habitat use, and biology of Hemimysis in the Great Lakes is scarce, the potential for food web disruption by Hemimysis cannot easily be predicted. Preliminary observations indicate widespread invasion of Hemimysis in Lake Ontario. In this study, we confirm the presence of Hemimysis at sites spanning the northern and southern shores of Lake Ontario and the presence of the individuals during winter months. In one horizontal tow in November 2007, over 26,000 individuals were collected with a length range of 4.4 to 9.0. mm and an average caloric density of 611. cal/g wet weight. The most effective methods for sampling Hemimysis were horizontal tows with either a zooplankton net in the water column or a benthic sled near the lake bottom. Although more quantitative data on the life history and distribution of this species is necessary, our preliminary observations support the prediction that the potential for Hemimysis to impact the nearshore food web in Lake Ontario appears high.

  19. The Great Lakes Atlas

    NSDL National Science Digital Library

    Lee Botts

    This is an online version of the text, The Great Lakes: An Environmental Atlas and Resource Book. Taking an ecosystem approach, the Atlas helps readers understand the Great Lakes and other natural resources in the Great Lakes region as an interdependent system across an international border. Its purpose is to demonstrate how the Great Lakes are affected by use and to increase public appreciation for the importance of these lakes as a North American and global resource. A French version is available.

  20. Biodivers Conserv (2009) 18:15551573 DOI 10.1007/s10531-008-9543-9

    E-print Network

    McIntyre, Peter

    2009-01-01

    and conservation status of endemic freshwater crabs in Lake Tanganyika, Africa Saskia A. E. Marijnissen · Ellinor freshwater crabs of Lake Tanganyika, which may occupy important positions in littoral foodwebs. Our surveys Aquatic invertebrates · Benthos · Littoral ecosystem · Freshwater conservation · Lake Tanganyika · Stable

  1. Biogeosciences, 4, 195203, 2007 www.biogeosciences.net/4/195/2007/

    E-print Network

    Paris-Sud XI, Université de

    in Lake Tanganyika mussels D. Langlet, L. Y. Alleman, P.-D. Plisnier, H. Hughes, and L. Andr´e Section de productivity of Lake Tanganyika is highly dependent on seasonal upwellings of cold, oxygen- depleted, nutrient. spekii from Lake Tanganyika has definitively a great potential to provide recent and past records

  2. TWO NEW SPECIES OF PLATYTHELPHUSA A. MILNE-EDWARDS, 1887 (DECAPODA, POTAMOIDEA, PLATYTHELPHUSIDAE) AND COMMENTS

    E-print Network

    Cumberlidge, Neil

    ) AND COMMENTS ON THE TAXONOMIC POSITION OF P. DENTICULATA CAPART, 1952 FROM LAKE TANGANYIKA, EAST AFRICA (Decapoda, Potamoidea, Platythelphusidae), are described from Lake Tanganyika. P. immaculata sp. nov. and P with P. conculcata. This brings the number of platythelphusid species reported from Lake Tanganyika

  3. 3, 14531471, 2006 Upwellings recorded

    E-print Network

    Paris-Sud XI, Université de

    BGD 3, 1453­1471, 2006 Upwellings recorded in Lake Tanganyika mussels D. Langlet et al. Title Page Mn seasonal upwellings recorded in Lake Tanganyika mussels D. Langlet, L. Y. Alleman, P.-D. Plisnier­1471, 2006 Upwellings recorded in Lake Tanganyika mussels D. Langlet et al. Title Page Abstract Introduction

  4. BioMed Central Page 1 of 15

    E-print Network

    Alvarez, Nadir

    Lake Tanganyika endemics. We find that the three most ancestral lineages of the haplochromines sensu diverse and specialized endemics from Lake Tanganyika. A reconstruction of life-history traits revealed individuals evolved. Conclusion: We conclude that Lake Tanganyika is the geographic and genetic cradle of all

  5. Lake Süßer See as a natural sink for heavy metals from copper mining

    Microsoft Academic Search

    Andreas Becker; Wolfgang Klöck; Kurt Friese; Peter Schreck; Hanns-Christian Treutler; Bernhard Spettel; Martine C Duff; W. EISENACHER

    2001-01-01

    Lake Süßer See, west of Halle, Germany, is a natural sink for heavy metals, which are abundant in the streams crossing the Mansfeld copper shale mining and smelting district in Central Germany. The lake and its environment serve as a recreational area for the local residents. We investigated the vertical distribution of key metals such as Cu, Pb and Zn

  6. GEOCHEMICAL FEATURES OF WATER-ROCK INTERACTIONS AT THE SULPHUR BANK MERCURY MINE, LAKE COUNTY, CALIFORNIA

    EPA Science Inventory

    The Sulphur Bank Mercury Mine on the eastern shore of Clear Lake is the source of poor quality acid mine drainage seeping into Clear Lake. Lateral and vertical geochemical trends in ground water composition point to a number of redox reactions taking place as a function of subsu...

  7. Physiological modifications by seston in response to physicochemical gradients within Lake Superior

    EPA Science Inventory

    Lake Superior is a non-steady state and phosphorus (P) depleted ecosystem. In September 2011, the vertical distribution and composition of dissolved and particulate P-pools throughout the Lake were examined. Differences in seston P content were evident with depth, as average sest...

  8. The role of olivine in the crystallization of the prehistoric Makaopuhi tholeiitic lava lake, Hawaii

    Microsoft Academic Search

    James G. Moore; Bernard W. Evans

    1967-01-01

    On eruption, the tholeiitic basalt lava of the prehistoric Makaopuhi lake contained nearly seven percent euhedral olivine phenocrysts of approximately Fa14 composition. In the center of the 225 foot vertical section of the lake, the lava became more than 90 percent solid at 1000° C after about 30 years. At the surface the lava was quenched to air temperature, whereas,

  9. Mixotrophic ciliates in an Andean lake: dependence on light and prey of an Ophrydium naumanni population

    Microsoft Academic Search

    Beatriz E. Modenutti; Esteban G. Balseiro

    2002-01-01

    SUMMARY 1. Planktonic ciliates were examined during a spring-summer period (November 1998- April 1999) in the ultraoligotrophic Lake Moreno Oeste (41?5¢ S and 71?33¢ W, 758 m a.s.l), which belongs to the Nahuel Huapi System (Patagonia, Argentina). The lake is deep (Zmaxà 90 m) and warm monomictic. 2. Sampling was performed at a mid-lake station, where vertical profiles of temperature

  10. A theoretical analysis of vertical flow equilibrium

    SciTech Connect

    Yortsos, Y.C.

    1992-01-01

    The assumption of Vertical Flow Equilibrium (VFE) and of parallel flow conditions, in general, is often applied to the modeling of flow and displacement in natural porous media. However, the methodology for the development of the various models is rather intuitive, and no rigorous method is currently available. In this paper, we develop an asymptotic theory using as parameter the variable R{sub L} = (L/H){radical}(k{sub V})/(k{sub H}). It is rigorously shown that present models represent the leading order term of an asymptotic expansion with respect to 1/R{sub L}{sup 2}. Although this was numerically suspected, it is the first time that is is theoretically proved. Based on the general formulation, a series of models are subsequently obtained. In the absence of strong gravity effects, they generalize previous works by Zapata and Lake (1981), Yokoyama and Lake (1981) and Lake and Hirasaki (1981), on immiscible and miscible displacements. In the limit of gravity-segregated flow, we prove conditions for the fluids to be segregated and derive the Dupuit and Dietz (1953) approximations. Finally, we also discuss effects of capillarity and transverse dispersion.

  11. Vertical electromagnetic profiling (VEMP)

    SciTech Connect

    Lytle, R.J.

    1984-08-01

    Vertical seismic profiling (VSP) is based upon reception measurements performed in a borehole with a source near the ground surface. This technology has seen a surge in application and development in the last decade. The analogous concept of vertical electromagnetic profiling (VEMP) consists of reception measurements performed in a borehole with a source near the ground surface. Although the electromagnetic concept has seen some application, this technology has not been as systematically developed and applied as VSP. Vertical electromagnetic profiling provides distinct and complementary data due to sensing different physical parameters than seismic profiling. Certain of the advantages of VEMP are presented. 28 references, 7 figures.

  12. Vertical axis wind turbine

    SciTech Connect

    Kutcher, H.R.

    1984-05-15

    A Darrieus-type vertical axis wind turbine is disclosed which includes a vertically extending rotor tube mounted on a support structure with two or three rotor blades of troposkein configuration on the rotor tube for rotating the tube in response to wind energy and thereby drive a generator to produce electrical power. The turbine includes an erection hinge which permits assembly of the rotor tube and blades at close to ground level followed by upward hinging of the rotor assembly to a vertical position. It also includes a system for automatically lubricating the top bearing upon erection and a system for visually tensioning the guy cables.

  13. Vertical Line Test

    NSDL National Science Digital Library

    2010-01-01

    In this activity, students try to connect given points on a graph in a way that they will pass the vertical line test. If the points can't be made to pass the vertical line test, the student must adjust the points so they will pass the test. This activity allows students to explore the vertical line test for functions. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

  14. Life history of lake herring of Green Bay, Lake Michigan

    USGS Publications Warehouse

    Smith, Stanford H.

    1956-01-01

    Although the lake herring has been an important contributor to the commercial fish production of Green Bay, little has been known about it. This study is based on field observations and data from about 6,500 lake herring collected over the period 1948 to 1952. Relatively nonselective commercial pound nets were a primary source of material for the study of age and growth. Commercial and experimental gill nets were used to obtain data on gear selectivity and vertical distribution. Scales were employed to investigate age and growth. Age group IV normally dominated commercial catches during the first half of the calendar year and age group III the last half. At these ages the fish averaged about 10.5 inches in length. The season's growth started in May, was most rapid in July, and terminated near the end of October. The sexes grew at the same rate. Selectivity of fishing gear was found to influence the estimation of growth. Geographical and annual differences in growth are shown. Factors that might contribute to discrepancies in calculated growth are evaluated. Possible real and apparent causes of growth compensation are given. The relation between length and weight is shown to vary with sex, season, year, and method of capture. Females were relatively more plentiful in commercial catches in February than in May through December. The percentage of females decreased with increase in age in pound-net catches but increased with age in gill-net samples. Within a year class the percentage of females decreased with increase in age. Most Green Bay lake herring mature during their second or third year of life. They are pelagic spawners with most intensive spawning over shallow areas. Spawning takes place between mid-November and mid-December, and eggs hatch in April and May. Lake herring ovaries contained from 3,500 to 11,200 eggs (averaged 6,375). Progress of spawning by age, sex, and length is given. Lake herring were distributed at all depths in Green Bay in early May, were concentrated within 30 feet of the surface in late May, moved to deeper water in June, and were restricted to depths greater than 30 feet in July when temperatures in shallower water became unfavorably high (greater than 18A?C.). In October, lake herring were again at all depths but were most abundant near the surface.

  15. Vertical neck lifting.

    PubMed

    Jacono, Andrew A; Talei, Benjamin

    2014-05-01

    The authors' vertical neck lifting procedure is an extended deep plane facelift, which elevates the skin and SMAS-platysma complex as a composite unit. The goal is to redrape cervicomental laxity vertically onto the face rather than laterally and postauricularly. The authors consider this an extended technique because it lengthens the deep plane flap from the angle of the mandible into the neck to release the cervical retaining ligaments that limit platysmal redraping. This technique does not routinely use midline platysmal surgery because it counteracts the extent of vertical redraping. A majority of aging face patients are good candidates for this procedure in isolation, but indications for combining vertical neck lifting with submental surgery are elucidated. PMID:24745389

  16. Vertical sleeve gastrectomy

    MedlinePLUS

    ... smaller stomach is about the size of a banana. It limits the amount of food you can ... staples. This creates a long vertical tube or banana-shaped stomach. The surgery does not involve cutting ...

  17. Micromachined electrostatic vertical actuator

    DOEpatents

    Lee, Abraham P. (Walnut Creek, CA); Sommargren, Gary E. (Santa Cruz, CA); McConaghy, Charles F. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

    1999-10-19

    A micromachined vertical actuator utilizing a levitational force, such as in electrostatic comb drives, provides vertical actuation that is relatively linear in actuation for control, and can be readily combined with parallel plate capacitive position sensing for position control. The micromachined electrostatic vertical actuator provides accurate movement in the sub-micron to micron ranges which is desirable in the phase modulation instrument, such as optical phase shifting. For example, compact, inexpensive, and position controllable micromirrors utilizing an electrostatic vertical actuator can replace the large, expensive, and difficult-to-maintain piezoelectric actuators. A thirty pound piezoelectric actuator with corner cube reflectors, as utilized in a phase shifting diffraction interferometer can be replaced with a micromirror and a lens. For any very precise and small amplitudes of motion` micromachined electrostatic actuation may be used because it is the most compact in size, with low power consumption and has more straightforward sensing and control options.

  18. Lake Trout Movements in Northwestern Lake Michigan

    Microsoft Academic Search

    Patrick J. Schmalz; Michael J. Hansen; Mark E. Holey; Patrick C. McKee; Michael L. Toneys

    2002-01-01

    We quantified the distance that lake troutSalvelinus namaycushmoved in northwestern Lake Michigan and examined (1) the directional preference and (2) the effect of population density on movement. Lake trout were captured in spring and fall 1983-1996, tagged with Floy anchor tags, and recaptured during subsequent agency sampling and by commercial fishers and anglers during 1983-1997. Angler recaptures were used to

  19. Hydrodynamic modelling of small upland lakes under strong wind forcing

    NASA Astrophysics Data System (ADS)

    Morales, L.; French, J.; Burningham, H.

    2012-04-01

    Small lakes (Area < 1 km2) represent 46.3% of the total lake surface globally and constitute an important source of water supply. Lakes also provide an important sedimentary archive of environmental and climate changes and ecosystem function. Hydrodynamic controls on the transport and distribution of lake sediments, and also seasonal variations in thermal structure due to solar radiation, precipitation, evaporation and mixing and the complex vertical and horizontal circulation patterns induced by the action of wind are not very well understood. The work presented here analyses hydrodynamic motions present in small upland lakes due to circulation and internal scale waves, and their linkages with the distribution of bottom sediment accumulation in the lake. For purpose, a 3D hydrodynamic is calibrated and implemented for Llyn Conwy, a small oligotrophic upland lake in North Wales, UK. The model, based around the FVCOM open source community model code, resolves the Navier-Stokes equations using a 3D unstructured mesh and a finite volume scheme. The model is forced by meteorological boundary conditions. Improvements made to the FVCOM code include a new graphical user interface to pre- and post process the model input and results respectively, and a JONSWAT wave model to include the effects of wind-wave induced bottom stresses on lake sediment dynamics. Modelled internal scale waves are validated against summer temperature measurements acquired from a thermistor chain deployed at the deepest part of the lake. Seiche motions were validated using data recorded by high-frequency level sensors around the lake margins, and the velocity field and the circulation patterns were validated using the data recorded by an ADCP and GPS drifters. The model is shown to reproduce the lake hydrodynamics and reveals well-developed seiches at different frequencies superimposed on wind-driven circulation patterns that appear to control the distribution of bottom sediments in this small upland lake.

  20. Measurements of supraglacial lake drainage and surface streams over West Greenland and effects on ice dynamics

    NASA Astrophysics Data System (ADS)

    Tedesco, M.; Willis, I. C.; Alexander, P. M.; Banwell, A. F.

    2011-12-01

    During the summer of 2011 we measured the filling and draining of two surface lakes in the Paakitsoq region of the West Greenland Ice Sheet (49.79 W, 69.57 N), together with the level of streams flowing into the basins feeding the lakes. We also used GPS to record the horizontal and vertical movement of the ice sheet surface at five locations surrounding the lakes for a two week period (overlapping the draining of the two lakes). In this talk we report results concerning the processes of lake filling and draining between the two lakes. 'Lake Half Moon', with a smaller catchment area, filled slowly at a steady rate over several days, then drained gradually over a 24 hour period as an existing moulin located outside the bottom of the lake became active; the lake level continued to drop very slowly over the remaining week as the surface stream leading from the lake to the moulin incised. 'Lake Ponting', with the larger catchment area, filled more rapidly and at an accelerating rate as depressions upstream of the lake filled with water, overflowed and delivered increasing volumes of water to the lake. Lake Ponting drained by hydrofracture following a particularly rapid rise in water level, generating a new ~ 800m long extensional crevasse on the ice sheet surface. The entire ~ 3 x 106 m3 lake drained within a few hours. For the Lake Pointing, we show, for the first time, a movie of the lake draining, showing many features that we observed right after its drainage. The rate of lake level lowering during the drainage varied; initially moderately rapid while the fractures formed and accommodated the water, then exceptionally rapid as the fractures reached the bed allowing the lake to drain completely. The analysis of the GPS data suggest that the different styles of lake draining affect the vertical and horizontal movement of the ice sheet in different ways. We also anticipate that the effect of the draining of Lake Ponting was affecting the GPS sensors in a different manner, hence providing information on how ice sheet dynamics (at which distance and direction) are impacted by the drainage of surface lakes.

  1. Modern lacustrine stromatolites, Walker Lake, Nevada

    NASA Astrophysics Data System (ADS)

    Osborne, Robert H.; Licari, Gerald R.; Link, Martin H.

    1982-05-01

    The Walker River drainage basin occupies about 10,000 km 2 in western Nevada and parts of California and is essentially a closed hydrologic system which drains from the crest of the Sierra Nevada in California and terminates in Walker Lake, Nevada. Walker Lake trends north and is about 27.4 km long and 8 km wide with water depths exceeding 30.5 m. The lake is situated in an asymmetric basin with steep alluvial fans flanking the western shoreline (Wassuk Range) and more gentle but areally more extensive alluvial fans flanking the eastern shoreline (Gillis Range). Exposed lake terraces and the present shoreline of Walker Lake record a sequence of Pleistocene and Holocene stromatolitic and tufaceous carbonate deposits. Small generalized and columnar stromatolites, frequently encrusted on exposed coarse-grained clasts or bedrock, are present along parts of the nearshore margin of Walker Lake and at elevated lake stands. Columnar stromatolites as much as 4 cm high are subcylindrical to club shaped discrete, and laterally linked at the base with local branching. These digitate stromatolites start as wavy, generalized stromatolites which are vertically transitional to small, laterally linked cabbage heads with laminae which thicken over the crests. Although algal structures are not well preserved in the older stromatolites, recent precipitation of low magnesium calcite occurs as smooth encrustations and as tiny mounds which are consistently associated with a diverse, seasonally variable, green and blue-green algal community including Cladophora glomerata, Ulothrix (cf. aequalis), Gongrosira, Schizothrix, Amphithrix janthina, Calothrix, Homeothrix, Spirulina, Anabaena, Lyngbya, and Entophysalis. Cladophora glomerata and a species of Ulothrix, which are the two most abundant algae within the Walker Lake stromatolite community, are known to condition semi-alkaline lake water by the removal of CO 2 from bicarbonate during photosynthesis. Such conditioning results in the precipitation of calcium carbonate, which is trapped and bound by an understory of green and blue-green algae. The occurrence of stromatolites in highly siliciclastic lakes seems to be restricted to shoreline and nearshore environments, and can be used to locate ancient lake margins.

  2. Lake Nasser and Toshka Lakes, Egypt

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Lake Nasser (center) and the Toshka Lakes (center left) glow emerald green and black in this MODIS true-color image acquired March 8, 2002. Located on and near the border of Egypt and Norther Sudan, these lakes are an oasis of water in between the Nubian (lower right) and Libyan Deserts (upper left). Also visible are the Red Sea (in the upper right) and the Nile River (running north from Lake Nasser). Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  3. The 5 Great Lakes: HOMES

    NSDL National Science Digital Library

    2012-04-21

    You will review these five websites and complete a flow chart for each of the five Great Lakes. Project Organizer: Flow Chart First, you will learn about Lake Huron. Go to Lake Huron to learn more about this great lake.Complete a Flow Chart Flow Chart for Lake Huron. Write "Lake Huron" under Topic and include five supporting details you learned ...

  4. Simulation Study about the Influence of Macrophytes on Hydrodynamics in an extreme shallow Water Lake - Lake Federsee

    NASA Astrophysics Data System (ADS)

    Wolf, T.; Barchmann, M.

    2012-04-01

    Lake Federsee is formed primarily by ice age processes and was subjected to strong siltation processes in post-glacial times, while in the last two centuries anthropogenic impact due to amelioration projects became more important. It has a maximum length of 2.4 km with a maximum width of 1.1 km and an area of 1.4 km2. Lake Federsee is the third largest lake in the federal state of Baden-Wuerttemberg situated in the south of Germany. It is characterized by its very flat bathymetry with a maximum depth of about 3.15 m and an average depth of about 1 m. In recent years Lake Federsee has undergone a strong reduction of the nutrient content, thus developing from hypertrophic states in the years 1980ies to eutrophic conditions in the years 2000ies. Since 2005 this development is accompanied by a change of the general habitus of the lake converting from a lake dominated by algae to a lake dominated by macrophytes. Changing successions of aquatic plants have been observed in the lake with strong seasonal variations in the composition and density of the vegetation cover, however forming often an almost complete coverage of the lake. In the present study the implementation of the hydrodynamic, three-dimensional model FLOW3D for this extreme shallow water lake will be presented. The impact of some numerical parameters will be investigated in a sensitivity study, which is aiming to set up the hydrodynamic model in an optimal way. The influence of the macrophyte population on general circulation processes and the vertical mixing processes in the lake will be discussed. It is shown by numerical simulations studies that both - circulation pattern and mixing processes - are influenced severely by macrophytes in the lake.

  5. Utah: Salt Lake Region

    Atmospheric Science Data Center

    2014-05-15

    article title:  Winter and Summer Views of the Salt Lake Region     View Larger Image Magnificent views of the region surrounding Salt Lake City, Utah are captured in these winter and summer images from the ...

  6. Quebec: Lake Manicouagan

    Atmospheric Science Data Center

    2013-04-17

    ... lake is bounded by erosion-resistant metamorphic and igneous rocks, and shock metamorphic effects are abundant in the target rocks of the crater floor. Today Lake Manicouagan serves as a reservoir and is ...

  7. Lake Ice phenology of small lakes: Impacts of climate variability in the Great Lakes region

    Microsoft Academic Search

    Vimal Mishra; Keith A. Cherkauer; Laura C. Bowling; Matthew Huber

    2011-01-01

    Formation of lake ice is common in lakes located in mid and high latitudes. Lake ice plays a vital role in heat storage, controlling lake water temperature, survival of aquatic ecosystems, and maintaining the bio diversity of lakes. Significant warming in air temperature during the cold season (October–May) may lead to reduced ice cover of lakes and eventually disturb the

  8. Lake trout rehabilitation in Lake Ontario

    USGS Publications Warehouse

    Elrod, Joseph H.; O'Gorman, Robert; Schneider, Clifford P.; Eckert, Thomas H.; Schaner, Ted; Bowlby, James N.; Schleen, Larry P.

    1995-01-01

    Attempts to maintain the native lake trout (Salvelinus namaycush) population in Lake Ontario by stocking fry failed and the species was extirpated by the 1950s. Hatchery fish stocked in the 1960s did not live to maturity because of sea lamprey (Petromyzon marinus) predation and incidental commercial harvest. Suppression of sea lampreys began with larvicide treatments of Lake Ontario tributaries in 1971 and was enhanced when the tributaries of Oneida Lake and Lake Erie were treated in the 1980s. Annual stocking of hatchery fish was resumed with the 1972 year class and peaked at about 1.8 million yearlings and 0.3 million fingerlings from the 1985-1990 year classes. Survival of stocked yearlings declined over 50% in the 1980s and was negatively correlated with the abundance of lake trout > 550 mm long (r = -0.91, P < 0.01, N = 12). A slot length limit imposed by the state of New York for the 1988 fishing season reduced angler harvest. Angler harvest in Canadian waters was 3 times higher in eastern Lake Ontario than in western Lake Ontario. For the 1977-1984 year classes, mean annual survival rate of lake trout age 6 and older was 0.45 (range: 0.35-0.56). In U.S. waters during 1985-1992, the total number of lake trout harvested by anglers was about 2.4 Times greater than that killed by sea lampreys. The number of unmarked lake trout < 250 mm long in trawl catches in 1978-1992 was not different from that expected due to loss of marks and failure to apply marks at the hatchery, and suggested that recruitment of naturally-produced fish was nil. However, many of the obstacles which may have impeded lake trout rehabilitation in Lake Ontario during the 1980s are slowly being removed, and there are signs of a general ecosystem recovery. Significant recruitment of naturally produced lake trout by the year 2000, one interim objective of the rehabilitation plan for the lake, may be achieved.

  9. Lake-Effect Snowfall over Lake Michigan.

    NASA Astrophysics Data System (ADS)

    Braham, Roscoe R., Jr.; Dungey, Maureen J.

    1995-05-01

    Aircraft measurements of snow particle size spectra from 36 flights on 26 snowy days are used to estimate snow precipitation rates over Lake Michigan. Results show that average rates during 14 wind-parallel-type lake-effect storms increased from the upwind shore to about midlake and then were essentially uniform (1.5 2 mm day1, liquid water equivalent) to the downwind shore. Snow from midlake bands and shoreline bands maximized over the lake. The position of the maximum during these types of lake-effect storms depends on meteorological conditions. In any given case it may be near either shore or anywhere between them. This study combines 12 cases of midlake and shoreline bands. The resulting cross-lake snow profile shows a broad maximum reaching over 4 mm day1 near midlake. The single sample maximum snow precipitation rate encountered in this study was 77.7 mm day1. The average cross-lake profile from combining 26 cases of lake-effect storms shows that snowfall into the lake is considerably greater than one would expect from a linear interpolation between values measured along either shore.An attempt is made to estimate the average increase in snow over lake Michigan resulting from combined lake-effect and large-scale cyclonic storms. The result is interesting but not considered very reliable because it depends upon the relative frequencies of different types of lake-effect storms as well as overtake snow rates from large-scale cyclonic storms; neither is well known.

  10. Great Minds? Great Lakes!

    ERIC Educational Resources Information Center

    Environmental Protection Agency, Chicago, IL. Great Lakes National Program Office.

    This book contains lesson plans that provide an integrated approach to incorporating Great Lakes environmental issues into elementary subjects. The book is divided into three subject areas: (1) History, which includes the origins of the Great Lakes, Great Lakes people, and shipwrecks; (2) Social Studies, which covers government, acid rain as a…

  11. Great Lakes NATIONALOCEAN

    E-print Network

    Great Lakes NATIONALOCEAN IC AND ATMOSPHERIC ADMINISTRATION U.S. D EPARTMENT OF COMM E R CE CoastWatch is a nationwide NOAA program in which the Great Lakes Environmental Research Laboratory (GLERL) functions as the Great Lakes regional node. GLERL obtains, produces, and delivers environmental data and products

  12. Great Lakes: Chemical Monitoring

    ERIC Educational Resources Information Center

    Delfino, Joseph J.

    1976-01-01

    The Tenth Great Lakes Regional Meeting of the American Chemical Society met to assess current Chemical Research activity in the Great Lakes Basin, and addressed to the various aspects of the theme, Chemistry of the Great Lakes. Research areas reviewed included watershed studies, atmospheric and aquatic studies, and sediment studies. (BT)

  13. Exploding Lakes in Cameroon

    USGS Multimedia Gallery

    In 1986, Lake Nyos, in the volcanic region of Cameroon, released a cloud of CO2 into the atmosphere, killing 1,700 people and 3,500 livestock in nearby towns and villages. Since then, engineers have been artificially removing the gas from the lake through piping. This photo shows the Lake Nyos pipe ...

  14. Exploding Lakes in Cameroon

    USGS Multimedia Gallery

    In 1986, Lake Nyos, in the volcanic region of Cameroon, released a cloud of CO2 into the atmosphere, killing 1,700 people and 3,500 livestock in nearby towns and villages. Since then, engineers have been artificially removing the gas from the lake through piping. A small CO2 cloud from Lake Monoun k...

  15. LAKE COLUSA SAN JOAQUIN

    E-print Network

    Marysville Nevada City Downieville Auburn Coloma Placerville Soda Springs Tahoe Vista South Lake Tahoe DEL NORTE SISKIYOU MODOC LASSEN BUTTE PLUMAS GLENN LAKE COLUSA SUTTER YUBA NEVADA SIERRA PLACER EL LAKE COLUSA SUTTER YUBA NEVADA SIERRA PLACER EL DORADO AMADOR SONOMA NAPA YOLO CALAVERAS SAN JOAQUIN

  16. Lake Survey DETROIT, MICH.

    E-print Network

    ; · Lake Survey Center DETROIT, MICH. NOAA TM NOS LSC 06 NOAA Technical Memorandum NOS LSC 06 U. S Winter 1971_72 R. A. Ass.,i Lake Survey Center National Ocean Survey, NOAA Detroit, Michigan I ABSTRACT. Thirty-fi ve ice charts were produced from data collected on 23 Lake SUrvey Center ice reconnai5sance fli

  17. Limnology and fish ecology of sockeye salmon nursery lakes of the world

    USGS Publications Warehouse

    Hartman, Wilbur L.; Burgner, R.L.

    1972-01-01

    Many important, recently glaciated oligotrophic lakes that lie in coastal regions around the northern rim of the Pacific Ocean produce anadromous populations of sockeye salmon, Oncorhynchus nerka. This paper describes the limnology and fish ecology of two such lakes in British Columbia, five in Alaska, and one in Kamchatka. Then we discuss the following general topics: the biogenic eutrophication of nursery lakes from the nutrients released from salmon carcasses wherein during years of highest numbers of spawners, lake phosphate balances in Lakes Babine, Iliamna, and Dalnee are significantly affected; the use of nursery lakes by young sockeye that reveals five patterns related to size and configuration of lake basins and the distribution of spawning areas; the interactions between various life history stages of sockeye salmon and such resident predators, competitors, and prey as Arctic char, lake trout, Dolly Varden, cutthroat trout, lake whitefish, pygmy whitefish, pond smelt, sticklebacks, and sculpins; the self-regulation of sockeye salmon abundance in these nursery lakes as controlled by density-dependent processes; the interrelations between young sockeye salmon biomass and growth rates, and zooplankton abundance in Babine Lake; and finally, the diel, vertical, pelagial migratory behavior of young sockeye in Babine Lake and the new hypothesis dealing with bioenergetic conservation.

  18. THE FERTILIZATION OF GREAT CENTRAL LAKE II. ZOOPLANKTON STANDING STOCK

    E-print Network

    THE FERTILIZATION OF GREAT CENTRAL LAKE II. ZOOPLANKTON STANDING STOCK R. J. LEBRASSEUR AND O. D. KENNEDY' ABSTRACT The regional, vertical, and seasonal abundance of the dominant zooplankton species were, and Diap- tomus oregonensis were the most numerically abundant zooplankton species. The introduction

  19. Autotrophic processes in meromictic Big Soda Lake, Nevada

    Microsoft Academic Search

    JAMES E. CLOERN; BRIAN E. COLE; RONALD S. OREMLAND

    1983-01-01

    Daily rates of oxygenic photosynthesis (OP) by phytoplankton, anoxygenic photosynthesis (AP) by purple sulfur bacteria, and chemoautotrophic productivity (CP = dark CO, assimila- tion) were measured once each season in saline, meromictic Big Soda Lake. Total daily pro- ductivity and the relative importance of each autotrophic process varied with seasonal changes in vertical mixing, light availability, and the biomass of

  20. EARLY DIAGENESIS AND CHEMICAL MASS TRANSFER IN LAKE ERIE SEDIMENTS

    EPA Science Inventory

    Vertical profiles of pore water and sediment solids chemistry were obtained from two sites in Lake Erie. Samples were collected using both gravity coring and pore water 'peeper' techniques. In general, concentrations of nutrients and toxic metals in sediment solids decreased with...

  1. Population dynamics of Nitzschia gracilis (Bacillariaceae) in a hypertrophic lake

    Microsoft Academic Search

    M. Alvarez Cobelas; C. Rojo García-Morato

    1990-01-01

    A population of Nitzschia gracilis was studied with weekly sampling over 8 months in a hypertrophic gravel pit lake near Madrid, Spain. Sedimentation losses were measured and net growth rates were calculated. Physical factors (incoming solar radiation, vertical attenuation coefficient, water temperature, Zeu:Zm ratio and the Brunt-Väisäla frequency), chemical factors (inorganic nitrogen, soluble reactive phosphorus, silica and both dissolved atomic

  2. Responses of subepilimnetic primary producers to experimental lake acidification

    SciTech Connect

    Moffett, M.F.

    1991-01-01

    Subepilimnetic phytoplankton communities were found to increase in abundance during experimental acidification with sulfuric acid of two Canadian Shield lakes, Lake 223 and Lake 302S, at the Experimental Lakes Area (ELA) in northwestern Ontario. As epilimnetic pH declined in Lake 223, small, edible species of phytoplankton increased more than larger, less edible taxa. Species diversity ultimately decreased when epilimnetic acidity reached the target pH 5.0. In Lake 302S algal populations, Chrysochromulina spp. and Chlamydomonas sp., reached [open quotes]bloom[close quotes] conditions below the epilimnion in the third and fourth summers, respectively, of sulfuric acid additions as pH declined from above pH 6 to pH 5.6 and 5.4. Meta- and hypolimnetic waters of these lakes did not experience similar declines in pH. All responses in Lake 223 and Lake 302S were in contrast to communities in 5-10 ELA lakes not undergoing acidification. Vertical depth profiles of chlorophyll fluorescence were used to follow trends in subepilimnetic communities during the first four years of sulfuric acid additions to Lake 302S. Fluorescence was found to reliably predict chlorophyll a concentrations (r[sup 2] = 0.80-0.94). Characteristics of subepilimnetic communities and the habitats in which they were located were studied at the ELA. Many were mixed with photosynthetic bacteria. Fluorometric techniques with DCMU (3-(3,4-dichlorophenyl-1,1-dimethyl urea)) were used to determine which fluorescence maxima contained viable algal populations. In situ inorganic carbon uptake rates for the algal-dominated communities below the epilimnion were similar to rates by epilimnetic communities. Enclosure experiments demonstrated that growth and inorganic carbon uptake rates of subepilimnetic algal populations were light-limited.

  3. Unusual bacterioplankton community structure in ultra-oligotrophic Crater Lake

    USGS Publications Warehouse

    Urbach, Ena; Vergin, Kevin L.; Morse, Ariel

    2001-01-01

    The bacterioplankton assemblage in Crater Lake, Oregon (U.S.A.), is different from communities found in other oxygenated lakes, as demonstrated by four small subunit ribosomal ribonucleic acid (SSU rRNA) gene clone libraries and oligonucleotide probe hybridization to RNA from lake water. Populations in the euphotic zone of this deep (589 m), oligotrophic caldera lake are dominated by two phylogenetic clusters of currently uncultivated bacteria: CL120-10, a newly identified cluster in the verrucomicrobiales, and ACK4 actinomycetes, known as a minor constituent of bacterioplankton in other lakes. Deep-water populations at 300 and 500 m are dominated by a different pair of uncultivated taxa: CL500-11, a novel cluster in the green nonsulfur bacteria, and group I marine crenarchaeota. b-Proteobacteria, dominant in most other freshwater environments, are relatively rare in Crater Lake (<=16% of nonchloroplast bacterial rRNA at all depths). Other taxa identified in Crater Lake libraries include a newly identified candidate bacterial division, ABY1, and a newly identified subcluster, CL0-1, within candidate division OP10. Probe analyses confirmed vertical stratification of several microbial groups, similar to patterns observed in open-ocean systems. Additional similarities between Crater Lake and ocean microbial populations include aphotic zone dominance of group I marine crenarchaeota and green nonsulfur bacteria. Comparison of Crater Lake to other lakes studied by rRNA methods suggests that selective factors structuring Crater Lake bacterioplankton populations may include low concentrations of available trace metals and dissolved organic matter, chemistry of infiltrating hydrothermal waters, and irradiation by high levels of ultraviolet light.

  4. Vertical emitting aperture nanoantennas.

    PubMed

    Yaacobi, Ami; Timurdogan, Erman; Watts, Michael R

    2012-05-01

    Herein we propose, theoretically investigate, and numerically demonstrate a compact design for a vertical emitter at a wavelength of 1.5 ?m based on nanophotonic aperture antennas coupled to a dielectric waveguide. The structure utilizes a plasmonic antenna placed above a Si3N4 waveguide with a ground plane for breaking the up-down symmetry and increasing the emission efficiency. Three-dimensional (3-D) finite-difference time-domain (FDTD) simulations reveal that up to 60% vertical emission efficiency is possible in a structure only four wavelengths long with a 3 dB bandwidth of over 300 nm. PMID:22555702

  5. Mono Lake Web Site

    NSDL National Science Digital Library

    Greg Reis

    Mono Lake Web Site is the homepage of the Mono Lake Committee and offers helpful information regarding the unique hypersaline and alkaline environment. Visitors will find information about the Mono Lake Committee, natural and political histories of the area, related water policies, a photo gallery with image descriptions, and links to related sites- including a clearinghouse. Those interested in Mono Basin birds will find sightings, counts, bird walks, and other related information. An additional feature, Mono Lake Live, offers up-to-the-minute data on road conditions, satellite images, weather, lake level, bird sightings, snow pack, and earthquakes.

  6. An event-driven phytoplankton bloom in southern Lake Michigan observed by satellite

    NASA Astrophysics Data System (ADS)

    Lesht, B. M.; Stroud, J. R.; McCormick, M. J.; Fahnenstiel, G. L.; Stein, M. L.; Welty, L. J.; Leshkevich, G. A.

    2002-04-01

    Sea-viewing Wide Field-of-View Sensor (SeaWiFS) images from June 1998 show a surprising early summer phytoplankton bloom in southern Lake Michigan that accounted for approximately 25% of the lake's annual gross offshore algal primary production. By combining the satellite imagery with in situ measurements of water temperature and wind velocity we show that the bloom was triggered by a brief wind event that was sufficient to cause substantial vertical mixing even though the lake was already stratified. We conclude that episodic events can have significant effects on the biological state of large lakes and should be included in biogeochemical process models.

  7. Food of lake trout in Lake Superior

    USGS Publications Warehouse

    Dryer, William R.; Erkkila, Leo F.; Tetzloff, Clifford L.

    1965-01-01

    Stomachs were examined from 1,492 lake trout and 83 siscowets collected from Lake Superior. Data are given on the food of lake trout of legal size (17 inches or longer) by year, season, and depth of water, and on the relation between food and size among smaller lake trout. Fish contributed 96.7 to 99.9 per cent of the total volume of food in the annual samples. Ciscoes (Coregonus spp.) were most common (52.2 to 87.5 per cent of the volume) in 1950 to 1953 and American smelt ranked first (65.6 per cent of the volume) in 1963. Cottids were in 8.9 to 12.3 per cent of the stomachs in 1950 to 1953 but in only 4.3 per cent in 1963. Insects ranked second to fish in occurrence (9.6 per cent for the combined samples) and crustaceans followed at 3.9 per cent. The greatest seasonal changes in the food of lake trout were among fish caught at 35 fathoms and shallower. The occurrence of Coregonus increased from 34.6 per cent in February-March to 71.1 per cent in October-December. Smelt were in 76.9 per cent of the stomachs in February-March but in only 2.2 per cent in October-December. Cottids, Mysis relicta, and insects were most common in the July-September collections. Lake trout taken at depths greater than 35 fathoms had eaten a higher percentage of Cottidae and Coregonus than had those captured in shallower water. Smelt, ninespine sticklebacks, Mysis, and insects were more frequent in stomachs of lake trout from less than 35 fathoms. Crustaceans comprised more than 70 per cent of the total volume of food for 4.0- to 7.9-inch lake trout but their importance decreased as the lake trout grew larger. Pontoporeia affinis was the most common in the stomachs of 4.0- to 6.9-inch lake trout and Mysis held first rank at 7.0 to 12.9 inches. Ostracods were important only to 4.0- to 4.9-inch lake trout. As the lake trout became larger, the importance of fish grew from 4.4-per cent occurrence at 5.0 to 5.9 inches to 93.9 per cent at 16.0 to 16.9 inches. Smelt were most commonly eaten by undersize (less than 17 inches) lake trout.

  8. Surface heat flux variability of a large lake: Lake Geneva, Switzerland

    NASA Astrophysics Data System (ADS)

    Irani Rahaghi, A.; Lemmin, U.; Bouffard, D.; Riffler, M.; Wunderle, S.; Barry, D. A.

    2014-12-01

    The heat budget of a lake is a fundamental component of physical limnology, and is strongly dependent on the surface heat flux. However, the surface energy exchange depends on several factors, making it difficult to estimate. In this study we employed several bulk formulas to estimate Lake Geneva's surface heat flux. Combination of different surface heat flux terms leads to a surface heat exchange model which requires various data. Different data sources were used in the heat flux estimates. Meteorological data were taken from an operational numerical weather prediction model, namely COSMO-2 (run by the Swiss meteorological service), while satellite imagery was used for the lake surface water temperature (LSWT). In order to find the best combination of the bulk formulas and to calibrate the model, the temporal evolution of the heat budget was estimated using long-term time series of vertical temperature profiles. Vertical temperature profiles at two points (one in the Lake Geneva's large basin and one in its small basin) were used. A sensitivity analysis was performed to find the key parameters, and more significantly the optimal combination of different heat flux terms. Finally, the spatio-temporal surface heat flux variation was calculated according to the proposed model. In addition, the relationship between variability of the surface heat flux and meteorological forcing was assessed. The different models, which are of differing complexity, gave reasonably consistent results, with differences attributed to simplifications inherent in them. The modeling results revealed that the LSWT and wind forcing are dominant factors underlying Lake Geneva surface heat flux spatial variation, while its temporal variability is mainly due to the global radiation and air temperature changes. In conclusion, the bulk heat balance approach is a useful tool to estimate various heat flux terms as well as their monthly or seasonally contributions. But, in large lakes where the LSWT is highly variable, the variable surface heat flux would be unavoidable.

  9. Vertical shaft windmill

    NASA Technical Reports Server (NTRS)

    Grana, D. C.; Inge, S. V., Jr. (inventors)

    1983-01-01

    A vertical shaft has several equally spaced blades mounted. Each blade consists of an inboard section and an outboard section skew hinged to the inboard section. The inboard sections automatically adjust their positions with respect to the fixed inboard sections with changes in velocity of the wind. This windmill design automatically governs the maximum rotational speed of shaft.

  10. Lake trout rehabilitation in Lake Huron

    USGS Publications Warehouse

    Eshenroder, Randy L.; Payne, N. Robert; Johnson, James E.; Bowen, Charles, II; Ebener, Mark P.

    1995-01-01

    Efforts to restore lake trout (Salvelinus namaycush) in Lake Huron after their collapse in the 1940s were underway in the early 1970s with completion of the first round of lampricide applications in tributary streams and the stocking of several genotypes. We assess results of rehabilitation and establish a historical basis for comparison by quantifying the catch of spawning lake trout from Michigan waters in 1929-1932. Sixty-eight percent of this catch occurred in northern waters (MH-1) and most of the rest (15%) was from remote reefs in the middle of the main basin. Sea lampreys (Petromyzon marinus) increased in the early 1980s in the main basin and depressed spawning populations of lake trout. This increase was especially severe in northern waters and appeared to be associated with untreated populations in the St. Marys River. Excessive commercial fishing stemming from unresolved treaty rights also contributed to loss of spawning fish in northern Michigan waters. Seneca-strain lake trout did not appear to be attacked by sea lampreys until they reached a size > 532 mm. At sizes > 632 mm, Seneca trout were 40-fold more abundant than the Marquette strain in matched-planting experiments. Natural reproduction past the fry stage has occurred in Thunder Bay and South Bay, but prospects for self-sustaining populations of lake trout in the main basin are poor because sea lampreys are too abundant, only one side of the basin is stocked, and stocking is deferred to allow commercial gillnetting in areas where most of the spawning occurred historically. Backcross lake trout, a lake trout x splake (s. Fontinalis x s. Namaycush) hybrid, did not reproduce in Georgian Bay, but this genotype is being replaced with pure-strain lake trout, whose early performance appears promising.

  11. On the cyclonic mean circulation of large lakes

    PubMed Central

    Csanady, G. T.

    1977-01-01

    In large lakes, during the heating season, the combination of surface wind drift and solar heating results in the horizontal transport of some of the absorbed heat into the coastal zone. Large-scale vertical movements associated with alternating upwellings and downwellings distribute the heat over a deeper water mass than at mid-lake. As a result, the mean shape of isotherm surfaces is “domed” and, correspondingly, the lake surface is slightly raised near shore and depressed over the center thermocline dome. The mean circulation in geostrophic equilibrium with this surface elevation field is a cyclonic gyre. In Lake Ontario, the amplitude of the mean surface velocity associated with this gyre is of the order of 3 cm sec-1. PMID:16592399

  12. Origin and deformation of Holocene shoreline terraces, Yellowstone Lake, Wyoming

    SciTech Connect

    Meyer, G.A.; Locke, W.W.

    1986-08-01

    Geodetic surveys within the Yellowstone caldera have documented active uplift that is most likely caused by magmatic processes in the upper crust. Along the northeast shore of Yellowstone Lake, maximum relative uplift rates are 10 mm/yr for the period 1923-1975. However, information on deformation prior to historic instrumental records has been lacking. In this study, closely spaced data on elevations of postglacial shoreline terraces around the north end of Yellowstone Lake reveal complex tilting. Though most Holocene deformation is probably magma related, the pattern of shoreline tilting deviates significantly from the historic pattern of roughly symmetric inflation of the caldera. Along the northeast shore, where tilt directions of historic and shoreline deformation are similar, differential uplift of a > 2500-yr-old terrace is roughly 10 m; this gives a maximum uplift rate of 4 mm/yr. These unique Holocene terraces may exist due to episodic deformation because vertical movements affecting the lake outlet directly control lake level.

  13. Evidence of deep circulation in two perennially ice-covered Antarctic lakes

    USGS Publications Warehouse

    Tyler, S.W.; Cook, P.G.; Butt, A.Z.; Thomas, J.M.; Doran, P.T.; Lyons, W.B.

    1998-01-01

    The perennial ice covers found on many of the lakes in the McMurdo Dry Valley region of the Antarctic have been postulated to severely limit mixing and convective turnover of these unique lakes. In this work, we utilize chlorofluorocarbon (CFC) concentration profiles from Lakes Hoare and Fryxell in the McMurdo Dry Valley to determine the extent of deep vertical mixing occurring over the last 50 years. Near the ice-water interface, CFC concentrations in both lakes were well above saturation, in accordance with atmospheric gas supersaturations resulting from freezing under the perennial ice covers. Evidence of mixing throughout the water column at Lake Hoare was confirmed by the presence of CFCs throughout the water column and suggests vertical mixing times of 20-30 years. In Lake Fryxell, CFC-11, CFC-12, and CFC-113 were found in the upper water column; however, degradation of CFC-11 and CFC-12 in the anoxic bottom waters appears to be occurring with CFC-113 only present in these bottom waters. The presence of CFC-113 in the bottom waters, in conjunction with previous work detecting tritium in these waters, strongly argues for the presence of convective mixing in Lake Fryxell. The evidence for deep mixing in these lakes may be an important, yet overlooked, phenomenon in the limnology of perennially ice-covered lakes.

  14. Thermal stratification, nutrient dynamics, and phytoplankton productivity during the onset of spring phytoplankton growth in Lake Baikal, Russia

    Microsoft Academic Search

    Charles R. Goldman; James J. Elser; Robert C. Richards; John E. Reuters; John C. Priscu; A. L. Levin

    1996-01-01

    Lake Baikal, Russian Siberia, was sampled in July 1990 during the period of spring mixing and initiation of thermal stratification. Vertical profiles of temperature, dissolved nutrients (nitrate and soluble reactive phosphorus), phytoplankton biomass, and primary productivity were determined in an eleven-station transect encompassing the entire 636 km length of the lake. Pronounced horizontal variability in hydrodynamic conditions was observed, with

  15. 9. GRANT LAKE AND MONO LAKE IN DISTANCE, LOOKING NORTHEAST ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    9. GRANT LAKE AND MONO LAKE IN DISTANCE, LOOKING NORTHEAST - Los Angeles Aqueduct, From Lee Vining Intake (Mammoth Lakes) to Van Norman Reservoir Complex (San Fernando Valley), Los Angeles, Los Angeles County, CA

  16. Climatic change and evaporative processes in the development of Common Era hypersaline lakes, East Antarctica: A study of Lake Suribati

    NASA Astrophysics Data System (ADS)

    Nakashima, H.; Seto, K.; Katsuki, K.; Kaneko, H.; yamada, K.; Imura, S.; Dettman, D. L.

    2011-12-01

    The Antarctic continent was uplifted by glacioisostatic rebound due to the regression of ice sheets after the last glacial period. Today's saline lakes were formed in shallow basins originally below sea level. Antarctic hypersaline lakes are formed by concentration of isolated seawater bodies as affected by recent climate change. Many saline lakes are found in the ice-free area of the Soya coast, East Antarctica. Lake Suribati is located in Sukarvsnes on the Soya coast. It is a hypersaline lake with maximum salinity ~200 psu, and an observable stable halocline at 7~12m depth. This study uses Lake Suribati sediment core Sr4C-01, collected by the 46th Japanese Antarctica Research Expedition, to examine the relationship of climatic change to evaporative processes and solute concentration in Lake Suribati in the Common Era. Sr4C-01 core was collected at 9.53m water depth in Lake Suribati in 2005 (core length is 63cm). This core primarily consists of black mud and laminated black organic mud. In the interval from 10 to 24cm below the sediment surface evaporite crystals occur. The age of the Sr4C-01 core bottom is estimated to be ~3,500 cal yrs BP, based on AMS carbon-14 dating at 6 core horizons. The evaporite crystals were indentified as aragonite based on XRD. Total inorganic carbon (TIC) content is low, around 0.5%, throughout the Sr4C-01 core, with higher values, approximately 1~4%, in two intervals, 57~52cm and 29~10cm core depth. Variation in CaO content tracks TIC content. We suggest that synchronous change in CaO and TIC contents indicate the vertical change in the amount of aragonite. Two intervals of evaporite precipition imply two intervals of evaporation and concentration of lake water. Hypersaline lake conditions did not occur soon after the isolation from the sea, rather these occurred under repeated concentration and dilution of lake water. Dilution of saline lake water could occur through the inflow of melt water from local snow or ice, indicating a warm climate interval. During cool periods, local snow and ice sheet may have remained frozen. In this case, lake water volume would decrease by sublimation from the frozen lake surface, leading to salt concentration. Based on MgO and Na2O content data, we suggest that other Mg and Na evaporites occur in the core. If such evaporates can be identified, a detailed solute concentration process can be described. Analysis of evaporites in sediment core from Antarctic hypersaline lakes have great potential as proxy indicators for the study of climate change in Antarctica.

  17. Convective Structures in a Cold Air Outbreak over Lake Michigan during Lake-ICE.

    NASA Astrophysics Data System (ADS)

    Zurn-Birkhimer, Suzanne M.; Agee, Ernest M.; Sorbjan, Zbigniew

    2005-07-01

    The Lake-Induced Convection Experiment provided special field data during a westerly flow cold air outbreak (CAO) on 13 January 1998, which has afforded the opportunity to examine in detail an evolving convective boundary layer. Vertical cross sections prepared from these data, extending from upstream over Wisconsin out across Lake Michigan, show the modifying effects of land-water contrast on boundary layer mixing, entrainment, heating, and moisture flux. Through this analysis, an interesting case of lake-effect airmass modification was discovered. The data show atypical differing heights in vertical mixing of heat and moisture, as well as offshore downwelling and subsidence effects in the atmosphere. Analysis shows evidence of a new observational feature, the moisture internal boundary layer (MIBL) that accords well with the often recognized thermal internal boundary layer (TIBL). The “interfacial” layer over the lake is also found to be unusually thick and moist, due in part to the upstream conditions over Wisconsin as well as the effectiveness of vertical mixing of moist plumes over the lake (also seen in the aircraft datasets presented). Results show that the atmosphere can be much more effective in the vertical mixing of moisture than heat or momentum (which mixed the same), and thus represents a significant departure from the classical bottom-up and top-down mixing formulation.Four scales of coherent structures (CSs) with differing spatial and temporal dimensions have been identified. The CSs grow in a building block fashion with buoyancy as the dominating physical mechanism for organizing the convection (even in the presence of substantial wind shear). Characteristic turbulence statistics from aircraft measurements show evidence of these multiple scales of CSs, ranging from the smallest (microscale) in the cloud-free path region near the Wisconsin shore, to the largest (mesoscale) in the snow-filled boundary layer near the Michigan shore.A large eddy simulation (LES) model has also been employed to study the effects of buoyancy and shear on the convective structures in lake-effect boundary layers. The model simulation results have been divided into two parts: 1) the general relationship of surface heat flux versus wind shear, which shows the interplay and dominance of these two competing forcing mechanisms for establishing convection patterns and geometry (i.e., rolls versus cells), and 2) a case study simulation of convection analogous to the CSs seen in the CFP region for the 13 January 1998 CAO event. Model simulations also show, under proper conditions of surface heating and wind shear, the simultaneous occurrence of differing scales of CSs and at different heights, including both cells and rolls and their coexisting patterns (based on the interplay between the effects of buoyancy and shear).

  18. Recent sediment geochemistry of an alkaline lake: Lake Acigöl (Denizli), SW Anatolia Turkey

    NASA Astrophysics Data System (ADS)

    Budakoglu, M.; Karaman, M.; Karabel, S. B.; Geredeli, S. G.; Bulbul, A.; Kurt, H.; Uzasci, S.; Kan, A.; Akay, A. K.; Yilmaz, F. R.; Gumus, L.; Civas, M.; Sevis, C.; Kumral, M.

    2012-04-01

    Lake Ac?göl (Denizli) is one of the largest alkaline lake in Turkey. Surface, and shallow core samples was studied to determine the effects of riverine and aeolian processes on sediment physical properties and sediment geochemistry. Total organic carbon, total nitrogen content and major and minor element geochemistry of Lake Ac?göl sediments were investigated. Major (Si, Ti, Al, Fe, Mg, Ca, K, Na, P, S) and trace elements (Mn, As, V, Cr, Ni, Cu, Zn, Sr, Y, Zr, Ba, Pb) showed significant differences in bulk chemical composition between the surface and shallow core samples. Sediment properties were examined by water content, loss-on-ignition (LOI). While most of core samples characteristic with relative LOI increase from bottom towards sediment surface, limited core samples that were taken from eastern shore of the lake show increase of LOI values from sediment surface towards bottom, suggesting shallow water levels, aeolian and dentritic riverine inputs on a regional scale. The Fe/Mn ratio was calculated to study changes in the redox potential. Distribution of Fe, Mn, and S concentration were related to redox condition of lake sediment and are due to mobilization of these elements in the pore waters. Calculated two particulate ratios (C:N and N:P) indicate predominantly lacustrine origin. Vertical changes of heavy metals occur in the all shallow downcore profiles, although the concentrations keep to ppm levels. Principal components analysis (PCA) was also used to examine all studied parameters and intercorrelations among the variables.

  19. The Nyanza Project: Interdisciplinary Research Training In Tropical Lakes

    NASA Astrophysics Data System (ADS)

    Cohen, A. S.; Lezzar, K. E.; Michel, E.; O'Reilly, C. M.; Russell, J. M.; Nkotagu, H.; Kimirei, I.

    2005-12-01

    The Nyanza Project is a research training program for American and African students, run annually at Lake Tanganyika (LT), Tanzania. The Project`s objective is to provide undergraduates, graduate students and secondary school teachers with the skills to plan and conduct interdisciplinary research on various aspects of tropical lake studiees. At a time of rapid global change there is a pressing need for young scientists trained to investigate environmental processes in an interdisciplinary framework. Training students to understand long-term changes in water availability, water quality and the relationship of aquatic ecosystems to rapid climate change represents a critical element of this societal need. Waterbodies in the tropics are particularly useful proving grounds for training future researchers on the impacts of global change on natural waters, as they are very sensitive to environmental and climatic change. Moreover, they are likely to provide instructive bellwethers of changes to come in U.S. inland waters. Each year 17-22 undergraduates, 3-4 graduate students and one secondary school teacher are selected for the program from the US and Africa. To date (1998-2005), 89 undergraduate students, 24 graduate students, and 8 secondary school teachers from the US have participated through the Project`s NSF support and 58 African students (from Tanzania, Burundi, Zambia, Congo, Kenya, and Burkina Faso) have been funded to participate in the Nyanza Project through supporting grants from our non-NSF funding sources. The 7-week program comprises an initial two week intensive short course on all aspects of the LT system and project preparation period, followed by 5 weeks of directed research, written report preparation, and scientific meeting-styled presentations. Focal topics for Nyanza Project research include: 1) investigating East African paleoclimates using sediment cores and reflection seismic profiling, 2) mapping & interpreting the geologic structure and depositional processes on the lake`s floor and watersheds 3) studying the extremely diverse and largely endemic fish and invertebrate fauna found in the littoral zone of LT to understand species interactions, environmental controls on species distribution, and factors regulating species diversification, 4) understanding the linkages between short-term climate variability, internal circulation in the lake, nutrient availability, and productivity in the open water (pelagic) portion of LT, and 5) investigating the impacts of deforestation and soil erosion in the LT basin on lake and stream ecosystems. Given that the Nyanza Project primarily serves undergraduates it has been extremely productive in terms of research output, with 27 articles published/in press in peer reviewed journals/edited volumes, 73 presentations given at national or international scientific meetings (59% by student first authors) and 16 theses based on Nyanza work. Extended abstracts for all 100 student projects from 1998-2004 are available at our website. Alumni surveys indicate that the Nyanza Project has significantly changed past student`s approach to science and/or career directions.

  20. Great Lakes Shoreline Geology

    NSDL National Science Digital Library

    This resource describes the shorelines of the Grate Lakes from the wetlands along the Lake Ontario shore, to the sand dunes along Lake Michigan, to the rocky shore of Lake Superior, which abounds in diversity. Students will discover that millions of years of glacial formation, wind, lava flows, and changing lake levels have sculpted a unique and ever changing shoreline. The first section describes the work of the glaciers while the second explains the formation, composition, and importance of beaches and continues to the third which describes sand dunes. The next section contains detailed information about the wetlands associated with the Great Lakes. The glaciated rocky shore of Isle Royale is the next topic and the site ends with a statement regarding human impact on the shoreline. Each section contains links to sites for more information.

  1. The Living Lakes

    NSDL National Science Digital Library

    Living Lakes Partnership, a nonprofit organization has a goal to "create and support a network within which local lake organizations can find critical kinds of assistance for promoting sustainable development in lake areas." Their award winning site highlights nearly twenty lakes around the world, describing their individual, watershed, and biological characteristics as well as the geologic and human history of the area. The Living With Lakes section discusses lake management and conservation issues dealing with agriculture and urban areas (such as pollution and habitat loss). Other links include a photo gallery, news and events section, discussion groups, and much more. Visitors will enjoy the rich content and visuals that make up this site and will find themselves exploring it for some time and learning along the way.

  2. Vertical ionospheric sounding measurements

    Microsoft Academic Search

    W. F. Utlaut; T. N. Gautier

    1964-01-01

    This report presents data on the ionospheric perturbations resulting from the five 1962 high-altitude nuclear detonations, Star Fish, Check Mate, Blue Gill, King Fish, and Tight Rope, as obtained with sweep-frequency vertical-incidence ionosondes operated at the Islands of Maui, Tern (French Frigate Shoals), Midway, Wake (Star Fish only), Canton, Tutuila (American Samoa), and Tongatapu. The ionosondes at Midway and Tongataupu

  3. To Brunswick Folsom Lake

    E-print Network

    ANGELS FROGTOWN MERIDIAN MINERALS RACETRACK STANISLAUS CALAVERAS ALPINE Markleeville EARLY INTAKE NEW Lake Mc Clure NEW MELONES PEORIA EXCHEQUER MERCED FALLS OAKHURST COARSEGOLD YANKE (NORTH FORK) LUNAR

  4. Great Lakes Fieldscope

    NSDL National Science Digital Library

    This highly interactive mapping tool features rivers and streams, watershed boundaries, water depth, political boundaries, elevation and land cover of the Great Lakes region. Students, volunteers and others can upload quantitative measurements and field notes, and share this with others around the globe. This type of learning provides a rich geographic context that allows participants to gain a better understanding of how they are connected to the Great Lakes. National Geographic partnered with Michigan Sea Grant to develop Great Lakes FieldScope to encourage the exploration and investigation of Great Lakes science and education.

  5. A Killer Lake

    NSDL National Science Digital Library

    Thomas Horvath

    2005-10-01

    In 1986, Lake Nyos, a volcanic lake in Cameroon, released a huge amount of carbon dioxide gas, killing over 1,700 people in the surrounding area. This case study, developed for use in a limnology or aquatic biology course, explores that event, introducing students to concepts relating to lake formation, thermal stratification, and dissolved gases. Students interpret graphs showing temperature, dissolved oxygen, pH, and conductivity measurements for the lake, and then synthesize these different types of limnological data to solve the problem.

  6. Texas' Natural Lake 

    E-print Network

    Wythe, Kathy

    2006-01-01

    . Unique because it is one of only 19 wetlands ?of unique importance? in the United States. Unique because of its bald cypress and tupelo trees that are Caddo?s Lake signature. This unique lake and its ecosystem, however, are being threatened... to distribute their seeds and dry spells that lower lake levels and allow seeds to germinate. Flooding in the past also helped sweep sediment from the lake and inhibited plant growth. Invasive aquatic plants, introduced by man, are choking off water bodies...

  7. Great Lakes Literacy Principles

    NASA Astrophysics Data System (ADS)

    Fortner, Rosanne W.; Manzo, Lyndsey

    2011-03-01

    Lakes Superior, Huron, Michigan, Ontario, and Erie together form North America's Great Lakes, a region that contains 20% of the world's fresh surface water and is home to roughly one quarter of the U.S. population (Figure 1). Supporting a $4 billion sport fishing industry, plus $16 billion annually in boating, 1.5 million U.S. jobs, and $62 billion in annual wages directly, the Great Lakes form the backbone of a regional economy that is vital to the United States as a whole (see http://www.miseagrant.umich.edu/downloads/economy/11-708-Great-Lakes-Jobs.pdf). Yet the grandeur and importance of this freshwater resource are little understood, not only by people in the rest of the country but also by many in the region itself. To help address this lack of knowledge, the Centers for Ocean Sciences Education Excellence (COSEE) Great Lakes, supported by the U.S. National Science Foundation and the National Oceanic and Atmospheric Administration, developed literacy principles for the Great Lakes to serve as a guide for education of students and the public. These “Great Lakes Literacy Principles” represent an understanding of the Great Lakes' influences on society and society's influences on the Great Lakes.

  8. A Killer Lake

    NSDL National Science Digital Library

    Thomas Horvath

    2005-01-01

    In 1986, Lake Nyos, a volcanic lake located in Cameroon, Africa, released a huge amount of carbon dioxide gas, killing over 1,700 people and countless livestock and other animals in the area. This case, intended for use in a limnology or an aquatic biology course, explores that event, introducing students to concepts related to lake formation, thermal stratification, and dissolved gases. Students interpret graphs containing temperature, dissolved oxygen, pH, and conductivity data for the lake, and then synthesize these different types of limnological data to understand what happened.

  9. Grays Lake Ecosystem

    NSDL National Science Digital Library

    This case study looks at the marsh ecosystem of Grays Lake in southeast Idaho, and is hosted by the Northern Prairie Wildlife Research Center (NPWRC). Grays Lake has been the focus of numerous research studies to understand factors affecting breeding water birds, habitat management practices, populations, and geological factors. This report gives general information about the Grays Lake ecosystem, including climate, habitats, plant communities, wildlife, water, and geology. More specific details are given through flora and fauna lists, historical and cultural overviews, details about the Grays Lake National Wildlife Refuge, and research information on management of wetlands.

  10. Lake Tahoe Data Clearinghouse

    NSDL National Science Digital Library

    Hoong, Connie

    The Lake Tahoe Data Clearinghouse Web site is part of the US Geological Survey's Lake Tahoe Initiative. The agency's goal for the site is to facilitate the coordination of research, monitoring, and environmental-management activities in the Lake Tahoe Basin and to ensure the widest possible access to data and information resulting from such activities. Products available include Digital Elevation Models, Digital Orthophoto Quadrangles, Digital Line Graphs, Digital Raster Graphics, maps and soil information of the area, and much more. The downloads include clear descriptions and examples for those unsure of the particular data types, making their use a snap for researchers, professionals, or anyone interested in the Lake Tahoe region. [JAB

  11. Vertical distribution of Chlamydomonas changes in response to grazer and predator kairomones

    E-print Network

    Pfrender, Michael

    freshwater lakes also varies in response to the resident zooplankton community (Arvola et al. 1992 migration patterns in response to kairomones produced by zooplankton (Daphnia) and planktivores (fish). Our the amplitude of diurnal vertical migrations (De Meester 1993). Kairomones produced by zooplankton

  12. Testing the spatial and temporal framework of speciation in an ancient lake species flock: the leech genus Dina (Hirudinea: Erpobdellidae) in Lake Ohrid

    NASA Astrophysics Data System (ADS)

    Trajanovski, S.; Albrecht, C.; Schreiber, K.; Schultheiß, R.; Stadler, T.; Benke, M.; Wilke, T.

    2010-07-01

    Ancient Lake Ohrid on the Balkan Peninsula is considered to be the oldest ancient lake in Europe with a suggested Plio-Pleistocene age. Its exact geological age, however, remains unknown. Therefore, molecular clock data of Lake Ohrid biota may serve as an independent constraint of available geological data, and may thus also help to refine age estimates. Such evolutionary data may also help unravel potential biotic and abiotic factors that promote speciation events. Here, mitochondrial sequencing data of one of the largest groups of endemic taxa in Lake Ohrid, the leech genus Dina, is used to test whether it represents an ancient lake species flock, to study the role of horizontal and vertical barriers in Lake Ohrid for evolutionary events, to estimate the onset of intralacustrine diversification in this group based on molecular clock analyses, and to compare this data with data from other endemic species for providing an approximate time frame for the origin of Lake Ohrid. Based on the criteria speciosity, monophyly and endemicity, it can be concluded that Lake Ohrid Dina, indeed, represents an ancient lake species flock. Lineage sorting of its species, however, does not seem to be complete. Analyses of population structures of Dina spp. in the Ohrid watershed indicate a horizontal zonation of haplotypes from spring and lake populations, corroborating the role of lake-side springs, particularly the southern feeder springs, for evolutionary processes in endemic Ohrid taxa. Vertical differentiation of lake taxa, however, appears to be limited, though differences between populations from the littoral and the profundal are apparent. Molecular clock analyses indicate that the most recent common ancestor of extant species of this flock is approximately 1.99±0.83 Ma old, whereas the split of the Lake Ohrid Dina flock from a potential sister taxon outside the lake is estimated at 8.30±3.60 Ma. Comparisons with other groups of endemic Ohrid species indicated that in all cases, intralacustrine diversification started ?2 Ma ago. Thus, this estimate may provide information on a minimum age for the origin of Lake Ohrid. Maximum ages are less consistent and generally less reliable. But cautiously, a maximum age of 3 Ma is suggested. Interestingly, this time frame of approximately 2-3 Ma for the origin of Lake Ohrid, generated based solely on evolutionary data, well fits the time frame most often used in the literature by geologists. Future studies must show whether this concurrence holds true.

  13. Crater Lake revealed

    USGS Publications Warehouse

    Ramsey, David W.; Dartnell, Peter; Bacon, Charles R.; Robinson, Joel E.; Gardner, James V.

    2003-01-01

    Around 500,000 people each year visit Crater Lake National Park in the Cascade Range of southern Oregon. Volcanic peaks, evergreen forests, and Crater Lake’s incredibly blue water are the park’s main attractions. Crater Lake partially fills the caldera that formed approximately 7,700 years ago by the eruption and subsequent collapse of a 12,000-foot volcano called Mount Mazama. The caldera-forming or climactic eruption of Mount Mazama drastically changed the landscape all around the volcano and spread a blanket of volcanic ash at least as far away as southern Canada. Prior to the climactic event, Mount Mazama had a 400,000 year history of cone building activity like that of other Cascade volcanoes such as Mount Shasta. Since the climactic eruption, there have been several less violent, smaller postcaldera eruptions within the caldera itself. However, relatively little was known about the specifics of these eruptions because their products were obscured beneath Crater Lake’s surface. As the Crater Lake region is still potentially volcanically active, understanding past eruptive events is important to understanding future eruptions, which could threaten facilities and people at Crater Lake National Park and the major transportation corridor east of the Cascades. Recently, the lake bottom was mapped with a high-resolution multibeam echo sounder. The new bathymetric survey provides a 2m/pixel view of the lake floor from its deepest basins virtually to the shoreline. Using Geographic Information Systems (GIS) applications, the bathymetry data can be visualized and analyzed to shed light on the geology, geomorphology, and geologic history of Crater Lake.

  14. Local response of a glacier to annual filling and drainage of an ice-marginal lake

    USGS Publications Warehouse

    Walder, J.S.; Trabant, D.C.; Cunico, M.; Fountain, A.G.; Anderson, S.P.; Anderson, R. Scott; Malm, A.

    2006-01-01

    Ice-marginal Hidden Creek Lake, Alaska, USA, outbursts annually over the course of 2-3 days. As the lake fills, survey targets on the surface of the 'ice dam' (the glacier adjacent to the lake) move obliquely to the ice margin and rise substantially. As the lake drains, ice motion speeds up, becomes nearly perpendicular to the face of the ice dam, and the ice surface drops. Vertical movement of the ice dam probably reflects growth and decay of a wedge of water beneath the ice dam, in line with established ideas about jo??kulhlaup mechanics. However, the distribution of vertical ice movement, with a narrow (50-100 m wide) zone where the uplift rate decreases by 90%, cannot be explained by invoking flexure of the ice dam in a fashion analogous to tidal flexure of a floating glacier tongue or ice shelf. Rather, the zone of large uplift-rate gradient is a fault zone: ice-dam deformation is dominated by movement along high-angle faults that cut the ice dam through its entire thickness, with the sense of fault slip reversing as the lake drains. Survey targets spanning the zone of steep uplift gradient move relative to one another in a nearly reversible fashion as the lake fills and drains. The horizontal strain rate also undergoes a reversal across this zone, being compressional as the lake fills, but extensional as the lake drains. Frictional resistance to fault-block motion probably accounts for the fact that lake level falls measurably before the onset of accelerated horizontal motion and vertical downdrop. As the overall fault pattern is the same from year to year, even though ice is lost by calving, the faults must be regularly regenerated, probably by linkage of surface and bottom crevasses as ice is advected toward the lake basin.

  15. Hydrology and water quality of East Lake Tohopekaliga, Osceola County, Florida

    USGS Publications Warehouse

    Schiffer, Donna M.

    1987-01-01

    East Lake Tohopekaliga, one of the major lakes in central Florida, is located in the upper Kissimmee River basin in north-east Osceola County. It is one of numerous lakes in the upper basin used for flood control, in addition to recreation and some irrigation of surrounding pasture. This report is the fourth in a series of lake reconnaissance studies in the Kissimmee River basin prepared in cooperation with the South Florida Water Management District. The purpose of the report is to provide government agencies and the public with a brief summary of the lake 's hydrology and water quality. Site information is given and includes map number, site name, location, and type of data available (specific conductivity, pH, alkalinity, turbidity, color, dissolved oxygen, hardness, dissolved chlorides, dissolved sodium, dissolved calcium, dissolved magnesium, dissolved potassium, nitrogen, ammonia, nitrates, carbon and phosphorus). The U.S. Geological Survey (USGS) maintained a lake stage gaging station on East Lake Tohopekaliga from 1942 to 1968. The South Florida Water Management District has recorded lake stage since 1963. Periodic water quality samples have been collected from the lake by the South Florida Water Management District and USGS. Water quality and discharge data have been collected for one major tributary to the lake, Boggy Creek. Although few groundwater data are available for the study area, results of previous studies of the groundwater resources of Osceola County are included in this report. To supplement the water quality data for East Lake Tohopekaliga, water samples were collected at selected sites in November 1982 (dry season) and in August 1983 (rainy season). Samples were taken at inflow points, and in the lake, and vertical profiles of dissolved oxygen and temperature were measured in the lake. A water budget from an EPA report on the lake is also included. (Lantz-PTT)

  16. Vertical Motion Simulator

    NSDL National Science Digital Library

    The Vertical Motion Simulator (VMS), at the NASA Ames Research Center, is an advanced flight simulation facility. This Web site provides thorough descriptions of all of the VMS systems. The VMS is a full immersion environment, complete with customizable cockpit, controls, and instrumentation to give the appearance of any aerospace vehicle. One of its most intriguing characteristics is "out-the-window graphics." This allows the pilot to see computer generated imagery of real locations, so virtually everything is identical to the actual flying experience. Even aircraft that are still in the design stage can be simulated on the VMS.

  17. Polar lake circulation during ice break-up

    NASA Astrophysics Data System (ADS)

    Kirillin, Georgiy; Forrest, Alexander; Graves, Kelly; Laval, Bernard

    2014-05-01

    An extensive dataset on lake physical properties has been collected during the final stage of the ice-covered period in May-June 2013 in polar Lake Kilpisjärvi, Finland. The data reveal several important features of lake dynamics, which shed new light on the mechanism of ice cover break-up and ice melting in lakes and marginal seas. CTD transects with high spatial resolution showed up a 300m-wide upwelling zone in the center of the lake, driven by downslope converging flow of warm waters from open-water 'moat' along the lake shoreline. The resulting radial density gradient, balanced by the Coriolis force, created a lake-wide anti-cyclonically rotating gyre with a measured peak azimuthal velocity of 0.05 m/s. Appreciable marginal heating is driven in polar enclosed basins by high amount of solar radiation and by surface inflow of meltwater. Hence, quasi-geostrophic anticyclonic circulation is suggested to be a general feature of polar lakes, redistributing heat within a water body and potentially accelerating ice melting. In addition, high-resolution records of pressure, current velocities and water temperature revealed under-ice seiches with periods of 10 to 25 min. The ice breakup was associated with 10 times increase of seiche amplitudes under ice. The seiches decayed within 10-15 hours; during this short period, the previously ice-covered lake became ice-free. We suggest that seiche-driven vertical motions of the soft ice sheet contribute significantly to breaking and melting of seasonal ice in enclosed reservoirs.

  18. Investigating groundwater-lake interactions by hydraulic heads and a water balance.

    PubMed

    Rudnick, Sebastian; Lewandowski, Jörg; Nützmann, Gunnar

    2015-01-01

    Discharge of groundwater into lakes (lacustrine groundwater discharge, LGD) can play a major role in water balances of lakes. Unfortunately, studies often neglect this input path because of methodological difficulties in its determination. Direct measurements of LGD are labor-consuming and prone to error. The present study uses both spatially variable hydraulic-head data and meteorological data to estimate groundwater input by LGD and lake water output through infiltration. The study sites are two shallow, groundwater-fed lakes without any surface inflows or outflows. Horizontally interpolated groundwater heads were combined with lake water levels to obtain vertical hydraulic gradients between the aquifer and the lake, which are separated by a thick layer of lake bed sediment which has a much lower hydraulic conductivity than the underlying aquifer. By fitting the hydraulic gradient to the results of a simple mass balance and considering the process of clogging, we were able to estimate the hydraulic conductivity of the lake bed sediments. We calculated groundwater inputs by LGD and lake water outputs by infiltration on an annual basis. Although our method requires several assumptions, the results are reasonable and provide useful information about the exchange between the aquifer and the lake, which can, for example, be used for the calculation of nutrient mass balances. PMID:24854019

  19. Great Lakes: Great Gardening.

    ERIC Educational Resources Information Center

    New York Sea Grant Inst., Albany, NY.

    This folder contains 12 fact sheets designed to improve the quality of gardens near the Great Lakes. The titles are: (1) "Your Garden and the Great Lakes"; (2) "Organic Gardening"; (3) "Fruit and Vegetable Gardening"; (4) "Composting Yard Wastes"; (5) "Herbicides and Water Quality"; (6) "Watering"; (7) "Soil Erosion by Water"; (8) "Soil…

  20. The Great Lakes.

    ERIC Educational Resources Information Center

    Seasons, 1987

    1987-01-01

    The Great Lakes are one of the world's greatest reserviors of fresh water, the foundation of Ontario's economic development, a primary force in ecological systems, and a base for pleasure and recreation. These lakes and their relationship with people of Canada and the United States can be useful as a subject for teaching the impact of human…

  1. Lake Darling Comparison

    USGS Multimedia Gallery

    The photo on the left was taken on April 18, 1997 by a USGS Personnel, of the new gates at Lake Darling. The photo to the right was taken on June 13, 2011 by Nathan A. Stroh (USGS), of Lake Darling....

  2. Exploding Lakes in Cameroon

    USGS Multimedia Gallery

    In 1986, Lake Nyos, in the volcanic region of Cameroon, released a cloud of CO2 into the atmosphere, killing 1,700 people and 3,500 livestock in nearby towns and villages. Since then, engineers have been artificially removing the gas from the lake through piping. The gas burst in 1986 from the 200-m...

  3. Exploding Lakes in Cameroon

    USGS Multimedia Gallery

    In 1986, Lake Nyos, in the volcanic region of Cameroon, released a cloud of CO2 into the atmosphere, killing 1,700 people and 3,500 livestock in nearby towns and villages. Since then, engineers have been artificially removing the gas from the lake through piping. This photo shows a pipe top and raft...

  4. Lake Wobegon Dice

    ERIC Educational Resources Information Center

    Moraleda, Jorge; Stork, David G.

    2012-01-01

    We introduce Lake Wobegon dice, where each die is "better than the set average." Specifically, these dice have the paradoxical property that on every roll, each die is more likely to roll greater than the set average on the roll, than less than this set average. We also show how to construct minimal optimal Lake Wobegon sets for all "n" [greater…

  5. Archeology Around Yellowstone Lake

    NSDL National Science Digital Library

    Ann M. Johnson

    This 9-page PDF examines the importance of Yellowstone Lake to humans in prehistoric times. The shorelines around the lake have been eroding and exposing artifacts that remain hidden elsewhere in the Park. The archeological sites expose artifacts, mostly rock chips, which point to seasonal occupations such as stone procurement, tool manufacture and repair.

  6. Lessons from a Lake.

    ERIC Educational Resources Information Center

    Goethals, Susan

    1997-01-01

    Describes a study that included classroom lessons on hydroelectric power, the history and construction of a nearby lake, data recording, the use of field guides, and methods of counting natural populations. The study culminated in a field trip to the lake. (JRH)

  7. Lake Michigan VANDERBURGH

    E-print Network

    Polly, David

    Lake Michigan LAKE JAY ALLEN KNOX VIGO WHITE CASS PIKE JASPER RUSH CLAY PARKE VERMILLION LAPORTE WHITLEY WASHINGTON JENNINGS TIPTON DELAWARE LAGRANGE HENDRICKS MONTGOMERY STEUBEN JOHNSON HOWARD HANCOCK 50 60 Kilometers Map of Indiana Counties Indiana Geological Survey · 611 North Walnut Grove Ave

  8. Great Lakes Beach Health

    USGS Multimedia Gallery

    As schools close for the year and summer weather beckons, many recreationalists head to the Great Lakes' public beaches. However, these coastal areas can become contaminated with disease-causing bacteria that threaten public health, disrupt water recreation, and pay a toll on the Great Lakes economi...

  9. Hydrography and circulation of ice-marginal lakes at Bering Glacier, Alaska, U.S.A.

    USGS Publications Warehouse

    Josberger, E.G.; Shuchman, R.A.; Meadows, G.A.; Savage, S.; Payne, J.

    2006-01-01

    An extensive suite of physical oceanographic, remotely sensed, and water quality measurements, collected from 2001 through 2004 in two ice-marginal lakes at Bering Glacier, Alaska-Berg Lake and Vitus Lake-show that each has a unique circulation controlled by their specific physical forcing within the glacial system. Conductivity profiles from Berg Lake, perched 135 m a.s.l., show no salt in the lake, but the temperature profiles indicate an apparently unstable situation, the 4??C density maximum is located at 10 m depth, not at the bottom of the lake (90 m depth). Subglacial discharge from the Steller Glacier into the bottom of the lake must inject a suspended sediment load sufficient to marginally stabilize the water column throughout the lake. In Vitus Lake, terminus positions derived from satellite imagery show that the glacier terminus rapidly retreated from 1995 to the present resulting in a substantial expansion of the volume of Vitus Lake. Conductivity and temperature profiles from the tidally influenced Vitus Lake show a complex four-layer system with diluted (???50%) seawater in the bottom of the lake. This lake has a complex vertical structure that is the result of convection generated by ice melting in salt water, stratification within the lake, and freshwater entering the lake from beneath the glacier and surface runoff. Four consecutive years, from 2001 to 2004, of these observations in Vitus Lake show little change in the deep temperature and salinity conditions, indicating limited deep water renewal. The combination of the lake level measurements with discharge measurements, through a tidal cycle, by an acoustic Doppler Current Profiler (ADCP) deployed in the Seal River, which drains the entire Bering system, showed a strong tidal influence but no seawater entry into Vitus Lake. The ADCP measurements combined with lake level measurements established a relationship between lake level and discharge, which when integrated over a tidal cycle, gives a tidally averaged discharge ranging from 1310 to 1510 m3 s-1. ?? 2006 Regents of the University of Colorado.

  10. Eastern lake survey: regional estimates of lake chemistry (journal version)

    Microsoft Academic Search

    D. H. Landers; W. S. Overton; R. A. Linthurst; D. F. Brakke

    1988-01-01

    The Eastern Lake Survey was conducted by the US EPA in the fall of 1984. Lakes were selected at random, based on a rigorous statistical design that permits estimates of the chemical and physical status of lake populations in specified regions of the survey. Complete chemical characterization was performed on water samples from each lake and a detailed-quality assurance and

  11. Anaglyph, Salt Lake City, Utah

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The 2002 Winter Olympics are hosted by Salt Lake City at several venues within the city, in nearby cities, and within the adjacent Wasatch Mountains. This anaglyph image provides a stereoscopic map view of north central Utah that includes all of these Olympic sites. In the south, next to Utah Lake, Provo hosts the ice hockey competition. In the north, northeast of the Great Salt Lake, Ogden hosts curling and the nearby Snowbasin ski area hosts the downhill events. In between, southeast of the Great Salt Lake, Salt Lake City hosts the Olympic Village and the various skating events. Further east, across the Wasatch Mountains, the Park City ski resort hosts the bobsled, ski jumping, and snowboarding events. The Winter Olympics are always hosted in mountainous terrain. This view shows the dramatic landscape that makes the Salt Lake City region a world-class center for winter sports.

    The stereoscopic effect of this anaglyph was created by first draping a Landsat satellite image over a Shuttle Radar Topography Mission digital elevation model and then generating two differing perspectives, one for each eye. When viewed through special glasses, the result is a vertically exaggerated view of Earth's surface in its full three dimensions. Anaglyph glasses cover the left eye with a red filter and cover the right eye with a blue filter.

    Landsat has been providing visible and infrared views of the Earth since 1972. SRTM elevation data matches the 30-meter (98-foot) resolution of most Landsat images and will substantially help in analyzing the large and growing Landsat image archive, managed by the U.S. Geological Survey (USGS).

    Elevation data used in this image was acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on Feb. 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect 3-D measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter(approximately 200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between NASA, the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Earth Science Enterprise, Washington, D.C.

    Size: 222 x 93.8 kilometers (138 x 58.2 miles) Location: 40.0 to 42.0 deg. North lat., 111.25 to 112.25.0 deg. West lon.(exactly) Orientation: North at top Image Data: Landsat Bands 3, 2, 1 as panchromatic grey. Original Data Resolution: SRTM 1 arcsecond (30 meters or 98 feet), Thematic Mapper 30 meters (98 feet) Date Acquired: February 2000 (SRTM), 1990s (Landsat 5 image mosaic)

  12. Vertical wind turbine

    SciTech Connect

    Danson, D.P.

    1988-08-16

    This patent describes a wind driven turbine of the vertical axis type comprising: (a) a support base; (b) a generally vertical column rotatably mounted to the support base; (c) upper and lower support means respectively mounted on the column for rotation therewith; wind driven blades connected between the upper and lower support means for rotation about the column and each blade being individually rotatable about a blade axis extending longitudinally through the blade to vary a blade angle of attach thereof relative to wind velocity during rotation about the column; and (e) control means for variably adjusting angles of attack of each blade to incident wind, the control means including a connecting rod means having drive means for rotating each blade about the associated blade axis in response to radial movement of the connecting rod means and control shaft pivotally mounted within the column and having a first shaft portion connected to the connecting rod means and a second shaft portion radially offset from the first shaft portion and pivotally connected to radially displace the first portion and thereby the connecting rod means to vary the blade angles of attack during rotation about the column.

  13. Evidence of offshore lake trout reproduction in Lake Huron

    USGS Publications Warehouse

    DeSorcie, Timothy J.; Bowen, Charles A., II

    2003-01-01

    Six Fathom Bank-Yankee Reef, an offshore reef complex, was an historically important spawning area believed to represent some of the best habitat for the rehabilitation of lake trout Salvelinus namaycush in Lake Huron. Since 1986, lake trout have been stocked on these offshore reefs to reestablish self-sustaining populations. We sampled with beam trawls to determine the abundance of naturally reproduced age-0 lake trout on these offshore reefs during May-July in 1994-1998 and 2000-2002. In total, 123 naturally reproduced lake trout fry were caught at Six Fathom Bank, and 2 naturally reproduced lake trout fry were caught at nearby Yankee Reef. Our findings suggest that this region of Lake Huron contains suitable habitat for lake trout spawning and offers hope that lake trout rehabilitation can be achieved in the main basin of Lake Huron.

  14. Establishment of a vertical control network along the St. Croix River in New Brunswick and Maine

    USGS Publications Warehouse

    Lombard, Pamela J.

    2013-01-01

    Consistent elevations at stable benchmarks, referenced to a common datum, are important for measuring and comparing water levels and for computing flows throughout a watershed. Elevations are presented for 38 control points within the St. Croix River watershed, mostly along the main stem of the St. Croix River. Vertical control points are located at 7 dams, 3 Environment Canada (EC) lake monitoring gages, 1 EC streamflow monitoring gage, 2 U.S. Geological Survey (USGS) lake monitoring gages, and 4 USGS streamgages. At least one point at each location was determined through High Precision Global Positioning System observation. Elevations of remaining points were determined through differential leveling. Elevations are referenced to the North American Vertical Datum of 1988, Geoid 09 and to the National Geodetic Vertical Datum of 1929.

  15. Lake whitefish and lake herring population structure and niche in ten south-central Ontario lakes

    USGS Publications Warehouse

    Carl, Leon M.; McGuiness, Fiona

    2006-01-01

    This study compares simple fish communities of ten oligotrophic lakes in south-central Ontario. Species densities and population size structure vary significantly among these lake communities depending on fish species present beyond the littoral zone. Lake whitefish are fewer and larger in the presence of lake herring than in their absence. Diet analysis indicates that lake whitefish shift from feeding on both plankton and benthic prey when lake herring are absent to a primarily benthic feeding niche in the presence of lake herring. When benthic round whitefish are present, lake whitefish size and density decline and they move lower in the lake compared to round whitefish. Burbot are also fewer and larger in lakes with lake herring than in lakes without herring. Burbot, in turn, appear to influence the population structure of benthic coregonine species. Lower densities of benthic lake whitefish and round whitefish are found in lakes containing large benthic burbot than in lakes with either small burbot or where burbot are absent. Predation on the pelagic larvae of burbot and lake whitefish by planktivorous lake herring alters the size and age structure of these populations. As life history theory predicts, those species with poor larval survival appear to adopt a bet-hedging life history strategy of long-lived individuals as a reproductive reserve.

  16. Study of environmental isotope distribution in the Aswan High Dam Lake (Egypt) for estimation of evaporation of lake water and its recharge to adjacent groundwater.

    PubMed

    Aly, A I; Froehlich, K; Nada, A; Awad, M; Hamza, M; Salem, W M

    1993-03-01

    Oxygen-18 ((18)0) and deuterium isotopes were used to estimate the evaporation from the Aswan High Dam Lake and to investigate the inter-relation between the lake water and adjacent groundwater.According to stable isotopic analysis of samples taken in 1988 and 1989, the lake can be divided into two sections. In the first section extending between Abu Simbel and a point between EI-Alaki and Krosko, a remarkable vertical gradient of (18)0 and deuterium isotopic composition was observed. The second northern sector extending to the High Dam is characterised by a lower vertical isotopic gradient. In this sector in general, higher values of (18)O and deuterium contents were found at the top and lower values at the bottom. Also a strong horizontal increase of the heavy isotope content was observed. Thus, in the northern section evaporation is of dominating influence on the isotopic composition of the lake water.With the help of an evaporation pan experiment it was possible to calibrate the evaporative isotope enrichment in the lake and to facilitate a preliminary estimate of evaporative losses of lake water. The evaporation from the lake was estimated to be about 19% of the input water flow rate.The groundwater around the lake was investigated and samples from production wells and piezometers were subjected to isotopic analysis. The results indicate that recent recharge to the groundwater aquifer is limited to wells near to the lake and up to a maximum distance of about 10 km. The contribution of recent Nile water to the groundwater in these wells was estimated to range between 23 and 70%. Beyond this distance, palaeowater was observed with highly depleted deuterium and (18)0 contents, which was also confirmed by 14c dating. The age of palaeo groundwater in this area can reach values of more than 26,000 years.Recommendations are given for efficient water management of the lake water. PMID:24198080

  17. Silver Lake Limnological Survey, 2004

    Microsoft Academic Search

    Joseph C. Makarewicz; Theodore W. Lewis; William Guenther

    2005-01-01

    During the spring, summer and fall of 2004, a limnological survey of Silver Lake was conducted. The purpose of the survey was to update the status of Silver Lake. Some of the questions being asked were as follows. Was the lake highly productive? Were the bottom layers of the lake devoid of oxygen? Was phosphorus being released from the sediments

  18. Lake level observations to detect crustal tilt: San Andreas Lake, California, 1979-1989

    SciTech Connect

    Mueller, R.J.; Johnston, M.J.S.; Myren, G.D. (Geological Survey, Menlo Park, CA (USA)); Murray, T. (Cascades Volcano Observatory, Vancouver, WA (USA))

    1989-07-01

    A pair precision lake level gauging stations, installed in 1978, have been monitoring differential crustal uplift (crustal tilt) at San Andreas lake, California, near the suspected epicenter on the San Andreas fault of the M = 8.3, 1906 San Francisco earthquake. The stations are installed in the lake with a 4.2 km station separation parallel to the San Andreas fault. The gauging stations use quartz pressure transducers that are capable of detecting intermediate to long-term vertical displacements greater than 0.4 mm relative to a fluid surface. Differencing data from the two sites reduces the noise contributed by atmospheric pressure, temperature, and density changes, and isolates the relative elevation changes between the ends of the lake. At periods less than 20 minutes, the differenced data are dominated by lake seiches which have a fundamental mode at a period of 13 {plus minus} 0.3 minutes. These seiche harmonics can be filtered or predicted and removed from the data. Wind shear, typically lasting several days, can generate apparent short term tilt of the lake and large seiche amplitudes. The tilt noise power spectrum obtained from these data decreases by about 15 dB/decade of frequency. Monthly averages of the data between 1979-1989 indicate a tilt rate of 0.02 {plus minus} 0.08 microradians/yr (down S34{degree}E). No measurable horizontal tilt has apparently occurred in this region of the San Andreas fault during the last decade, however, measurements of trilateration networks show this region to be undergoing a horizontal strain of 0.6 {plus minus} 0.2 {mu}strain/yr.

  19. Measurement of ultralow vertical emittance using a calibrated vertical undulator

    NASA Astrophysics Data System (ADS)

    Wootton, K. P.; Boland, M. J.; Rassool, R. P.

    2014-11-01

    Very few experimental techniques are useful for the direct observation of ultralow vertical emittance in electron storage rings. In this work, quantitative measurements of ultralow (pm rad) electron beam vertical emittance using a vertical undulator are presented. An undulator radiation model was developed using the measured magnetic field of the APPLE-II type undulator. Using calibrated experimental apparatus, a geometric vertical emittance of ?y=0.9 ±0.3 pm rad has been observed. These measurements could also inform modeling of the angular distribution of undulator radiation at high harmonics, for proposed diffraction-limited storage ring light sources.

  20. Greenland supraglacial lake drainages triggered by hydrologically induced basal slip.

    PubMed

    Stevens, Laura A; Behn, Mark D; McGuire, Jeffrey J; Das, Sarah B; Joughin, Ian; Herring, Thomas; Shean, David E; King, Matt A

    2015-06-01

    Water-driven fracture propagation beneath supraglacial lakes rapidly transports large volumes of surface meltwater to the base of the Greenland Ice Sheet. These drainage events drive transient ice-sheet acceleration and establish conduits for additional surface-to-bed meltwater transport for the remainder of the melt season. Although it is well established that cracks must remain water-filled to propagate to the bed, the precise mechanisms that initiate hydro-fracture events beneath lakes are unknown. Here we show that, for a lake on the western Greenland Ice Sheet, drainage events are preceded by a 6-12 hour period of ice-sheet uplift and/or enhanced basal slip. Our observations from a dense Global Positioning System (GPS) network allow us to determine the distribution of meltwater at the ice-sheet bed before, during, and after three rapid drainages in 2011-2013, each of which generates tensile stresses that promote hydro-fracture beneath the lake. We hypothesize that these precursors are associated with the introduction of meltwater to the bed through neighbouring moulin systems (vertical conduits connecting the surface and base of the ice sheet). Our results imply that as lakes form in less crevassed, interior regions of the ice sheet, where water at the bed is currently less pervasive, the creation of new surface-to-bed conduits caused by lake-draining hydro-fractures may be limited. PMID:26040890

  1. Introduction to the Great Lakes

    NSDL National Science Digital Library

    As part of The Great Lakes Information Network, The Education And Curriculum Homesite (TEACH) "focuses on advancing Great Lakes-related educational materials for the broad audience of educators and students in the Great Lakes region and beyond." The Introduction to the Great Lakes pages contain an overview of the watershed, including maps, photographs, and descriptions; other sections take a more detailed look at the five individual lakes. Additional links for further information are also provided -- such as Great Lake geography, history and culture, pollution, and more -- giving kids or anyone interested a well-designed introduction to the lakes.

  2. Seiche-induced resuspension in Lake Kinneret: A fluorescent tracer experiment

    Microsoft Academic Search

    B. Shteinman; W. Eckert; S. Kaganowsky; T. Zohary

    1997-01-01

    In warm-monomictic Lake Kinneret, wind-induced internal waves with amplitudes of up to 10 meters are common during April –\\u000a October. This study was aimed to follow the horizontal and vertical transport of resuspended particles due to internal wave\\u000a activity using fluorescently-dyed sediment particles (lake sediments and lyophilized algal cells) as tracers. Color-coded\\u000a (5 colors) tracers were deployed along a transact

  3. A comparison of lakes in the Kolyma River region that receive inputs of Holocene and Pleistocene origin

    NASA Astrophysics Data System (ADS)

    Henriksen, E. H.; Vonk, J. E.; Schade, J. D.; Mann, P. J.; Bulygina, E. B.; Sobczak, W. V.; Zimov, S. A.; Holmes, R. M.

    2011-12-01

    The Siberian Arctic contains vast amounts of carbon stored in permafrost soils. Throughout this region there are many lakes and rivers that receive input of organic matter from terrestrial sources. Previous research suggests that these freshwater ecosystems are actively processing carbon, rather than functioning only as passive transporters. Ongoing climate warming in this vulnerable region is expected to cause increasing permafrost thaw and a likely increase of the inflow of permafrost-derived carbon to freshwater ecosystems. We aim to improve our understanding of how these freshwater ecosystems are processing carbon to increase our ability to predict how climate change will affect this region. This study was performed in July 2011 as part of the Polaris Project (www.polarisproject.org). We focused upon lakes in the Kolyma River watershed, the world's largest river underlain by continuous permafrost. These lakes receive inputs of allochthonous material from either Holocene (floodplain lakes) or Pleistocene (yedoma lakes) soils. We sampled a range of lakes (floodplain n=3; yedoma n=3) for DOC concentration and lability, by means of biological oxygen demand assays, in combination with N and P measurements and water column profiles (oxygen concentrations, pH, specific conductivity and temperature). Chlorophyll a concentrations were measured as a comparison of autochthonous production between lakes. Our findings indicate that yedoma lakes are generally stratified but also display a high variability in their vertical structure over relatively short time scales (the fieldwork took place over three weeks). Furthermore, floodplain lakes had more than twice the concentration of chlorophyll a in the surface water as yedoma lakes, suggesting more autotrophic production. Yedoma lakes contained approximately 40% more DOC than floodplain lakes in surface waters. However, the lability of yedoma lake DOC was half that of floodplain lakes. The higher concentrations of DOC within yedoma lakes may therefore be driven by the more refractory nature of the organic matter pool within these lakes.

  4. Yellowstone Lake Nanoarchaeota

    PubMed Central

    Clingenpeel, Scott; Kan, Jinjun; Macur, Richard E.; Woyke, Tanja; Lovalvo, Dave; Varley, John; Inskeep, William P.; Nealson, Kenneth; McDermott, Timothy R.

    2013-01-01

    Considerable Nanoarchaeota novelty and diversity were encountered in Yellowstone Lake, Yellowstone National Park (YNP), where sampling targeted lake floor hydrothermal vent fluids, streamers and sediments associated with these vents, and in planktonic photic zones in three different regions of the lake. Significant homonucleotide repeats (HR) were observed in pyrosequence reads and in near full-length Sanger sequences, averaging 112 HR per 1349 bp clone and could confound diversity estimates derived from pyrosequencing, resulting in false nucleotide insertions or deletions (indels). However, Sanger sequencing of two different sets of PCR clones (110 bp, 1349 bp) demonstrated that at least some of these indels are real. The majority of the Nanoarchaeota PCR amplicons were vent associated; however, curiously, one relatively small Nanoarchaeota OTU (71 pyrosequencing reads) was only found in photic zone water samples obtained from a region of the lake furthest removed from the hydrothermal regions of the lake. Extensive pyrosequencing failed to demonstrate the presence of an Ignicoccus lineage in this lake, suggesting the Nanoarchaeota in this environment are associated with novel Archaea hosts. Defined phylogroups based on near full-length PCR clones document the significant Nanoarchaeota 16S rRNA gene diversity in this lake and firmly establish a terrestrial clade distinct from the marine Nanoarcheota as well as from other geographical locations. PMID:24062731

  5. Whiting in Lake Michigan

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Satellites provide a view from space of changes on the Earth's surface. This series of images from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) aboard the Orbview-2 satellite shows the dramatic change in the color of Lake Michigan during the summer. The bright color that appears in late summer is probably caused by calcium carbonate-chalk-in the water. Lake Michigan always has a lot of calcium carbonate in it because the floor of the lake is limestone. During most of the year the calcium carbonate remains dissolved in the cold water, but at the end of summer the lake warms up, lowering the solubility of calcium carbonate. As a result, the calcium carbonate precipitates out of the water, forming clouds of very small solid particles that appear as bright swirls from above. The phenomenon is appropriately called a whiting event. A similar event occured in 1999, but appears to have started later and subsided earlier. It is also possible that a bloom of the algae Microcystis is responsible for the color change, but unlikely because of Lake Michigan's depth and size. Microcystis blooms have occured in other lakes in the region, however. On the shore of the lake it is possible to see the cities of Chicago, Illinois, and Milwaukee, Wisconsin. Both appear as clusters of gray-brown pixels. Image courtesy the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  6. Topographically controlled circulation and mixing in a lake

    NASA Astrophysics Data System (ADS)

    Bowyer, Peter A.

    2001-04-01

    It is well known that the wind-driven circulation in a wide lake may be controlled by its topography. Wind stress acting on the smaller mass of the water column in the shallows results in downwind flow there and return flow in the deeper water. In lakes with large areas of shallow water this circulation may cause rapid mixing in weakly stratified conditions. In more strongly stratified conditions, topographically induced horizontal wind driven circulation may influence the vertical stratification of the lake. Lough Mask is about 10 km long and has a maximum width of about 8 km. The lake may be divided into shallow eastern and deeper western portions with mean depths of 10 and 35 m respectively. In late Autumn, water at depth in the deep part of the lake moves upwind at speeds of up to 50 cm s-1 in response to axial winds of up to 15 m s-1. At the same location a weaker upwind flow is observed in the near surface water. This return flow is topographically driven. Temperature differences between near surface and near bottom meters were small (<0.5°C) and inversely correlated with the deep current. In a cool, windy summer, temperature time series in the deep part of the lake indicate a deep (>20 m) surface mixed layer and a cooler layer at depth whose temperature fluctuates in response to wind stress along the axis of the lake. Modelling results, supported by drogue measurements, indicate that the return flow associated with axial winds in these summer conditions is confined to the surface mixed layer. If this layer is thin, shear between the surface layer and the underlying water can be sufficient to cause mixing and a thickening of the surface layer until the Richardson number is ˜1. Thus the vertical temperature structure of the deep part of the lake can be influenced by flows driven by the lake topography. In the shallow part of the lake, there is evidence of thermally driven motion in periods of calm weather in summer.

  7. An overview of circulation during episodic events great lakes experiment in lake michigan

    NASA Astrophysics Data System (ADS)

    Rao, Y.; Murthy, R.; McCormick, M.

    2003-04-01

    Satellite images have revealed episodic late winter-spring sediment plumes coinciding with northerly storms in southern Lake Michigan. National Science Foundation (NSF) and National Oceanic and Atmospheric Administration (NOAA) to study the importance of these episodic events on the cross-margin transport and subsequent ecological consequences initiated a major inter-disciplinary observational program (Episodic Events Great Lakes Experiment, EEGLE). As a part of EEGLE program Eulerian and Lagrangian currents were measured during the winter-spring periods of 1998-2000 in southern Lake Michigan. Both current meter and drifter data were analyzed to provide the kinematics description of the coastal flow and cross-shore exchange characteristics in southern Lake Michigan. The data shows current reversals coupled with changes in surface wind stress. The observations show the signature of forced two-gyre circulation in the southern basin. The low pass filtered currents for the winter season shows significantly higher alongshore currents compared to cross-shore flow. However, during the northerly storm events cross-shore flow increased at a few stations. These storm episodes depict slightly higher horizontal turbulent exchanges and increased vertical current shear in comparison to the overall winter conditions.

  8. Understanding Sediment Dynamics in a Shallow, Hypereutrophic Lake within the Middle St. Johns River: Lake Jesup, FL

    NASA Astrophysics Data System (ADS)

    Nielsen, S.; Anderson, W. T.; Corbett, D. R.; Fugate, D. C.; Scinto, L. J.; Thomas, S.; Brandt-Williams, S.

    2011-12-01

    Improved knowledge of sediment dynamics within a lake system is important for understanding lake water quality. This research was focused on an assessment of the vertical sediment flux in Lake Jesup, a shallow (1.3 m average depth) hypereutrophic lake of central Florida. Sediment dynamics were assessed at varying time scales (daily to weekly) to understand the transport of sediments from external forces; wind, waves, precipitation and/or runoff. Four stations were selected within the lake based on water depth and the thicknesses of unconsolidated (floc) and consolidated sediments. At each of these stations, a 10:1 high aspect ratio trap (STHA) was deployed to collect particulate matter for a one to two week period. The water and sediment samples were collected and analyzed for total carbon (TC), total phosphorus (TP) and total nitrogen (TN). Mass accumulation rates (MAR) collected by the traps varied from 77 to 418 g m-2 d-1 over seven deployments. TN, TP and TC sediment concentrations collected by the traps were consistently higher than the sediments collected by coring the lake bottom and is most likely associated with water column biomass.

  9. Lake Granbury and Lake Whitney Assessment Initiative 

    E-print Network

    Harris, B.L.; Roelke, Daniel; Grover, James; Brooks, Bryan

    2010-01-01

    A team of Texas AgriLife Research, Baylor University and University of Texas at Arlington researchers studied the biology and ecology of Prymnesium parvum (golden algae) in Texas lakes using a three-fold approach that involved system-wide monitoring...

  10. LAKE RESTORATION BY DILUTION: MOSES LAKE, WASHINGTON

    EPA Science Inventory

    Dilution water, low in macronutrients, was added to Moses Lake on three occasions in 1977 and once in 1978 during the spring-summer period. The addition resulted in reducing the annual average inflow concentration of phosphorus from about 130-140 micrograms/l to 100 micrograms/l....

  11. Coupled resonator vertical cavity laser

    SciTech Connect

    Choquette, K.D.; Chow, W.W.; Hou, H.Q.; Geib, K.M.; Hammons, B.E.

    1998-01-01

    The monolithic integration of coupled resonators within a vertical cavity laser opens up new possibilities due to the unique ability to tailor the interaction between the cavities. The authors report the first electrically injected coupled resonator vertical-cavity laser diode and demonstrate novel characteristics arising from the cavity coupling, including methods for external modulation of the laser. A coupled mode theory is used model the output modulation of the coupled resonator vertical cavity laser.

  12. Dynamics of geckos running vertically

    Microsoft Academic Search

    K. Autumn; S. T. Hsieh; D. M. Dudek; J. Chen; C. Chitaphan; R. J. Full

    2006-01-01

    Geckos with adhesive toe pads rapidly climb even smooth vertical surfaces. We challenged geckos (Hemidactylus garnotii) to climb up a smooth vertical track that contained a force platform. Geckos climbed vertically at up to 77·cm·s -1 with a stride frequency of 15·Hz using a trotting gait. During each step, whole body fore-aft, lateral and normal forces all decreased to zero

  13. Vertical Cable Seismic Survey for Hydrothermal Deposit

    NASA Astrophysics Data System (ADS)

    Asakawa, E.; Murakami, F.; Sekino, Y.; Okamoto, T.; Ishikawa, K.; Tsukahara, H.; Shimura, T.

    2012-04-01

    The vertical cable seismic is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by surface, deep-towed or ocean bottom sources. Analyzing the reflections from the sub-seabed, we could look into the subsurface structure. This type of survey is generally called VCS (Vertical Cable Seismic). Because VCS is an efficient high-resolution 3D seismic survey method for a spatially-bounded area, we proposed the method for the hydrothermal deposit survey tool development program that the Ministry of Education, Culture, Sports, Science and Technology (MEXT) started in 2009. We are now developing a VCS system, including not only data acquisition hardware but data processing and analysis technique. Our first experiment of VCS surveys has been carried out in Lake Biwa, JAPAN in November 2009 for a feasibility study. Prestack depth migration is applied to the 3D VCS data to obtain a high quality 3D depth volume. Based on the results from the feasibility study, we have developed two autonomous recording VCS systems. After we carried out a trial experiment in the actual ocean at a water depth of about 400m and we carried out the second VCS survey at Iheya Knoll with a deep-towed source. In this survey, we could establish the procedures for the deployment/recovery of the system and could examine the locations and the fluctuations of the vertical cables at a water depth of around 1000m. The acquired VCS data clearly shows the reflections from the sub-seafloor. Through the experiment, we could confirm that our VCS system works well even in the severe circumstances around the locations of seafloor hydrothermal deposits. We have, however, also confirmed that the uncertainty in the locations of the source and of the hydrophones could lower the quality of subsurface image. It is, therefore, strongly necessary to develop a total survey system that assures a accurate positioning and a deployment techniques. We have carried out two field surveys in FY2011. One is a 3D survey with a boomer for a high-resolution surface source and the other one for an actual field survey in the Izena Cauldron an active hydrothermal area in the Okinawa Trough. Through these surveys, the VCS will become a practical exploration tool for the exploration of seafloor hydrothermal deposits.

  14. Bathymetry of Crater Lake

    NSDL National Science Digital Library

    The bathymetry survey of Crater Lake by scientists from the USGS, University of New Hampshire's Center for Coastal and Ocean Mapping, and the National Park Service, began on July 28, 2000. This site houses the first images gained from the high-resolution multi-beam technology survey. Various digital data such as digital raster graphics and digital line graphs may be viewed as .jpeg and .gif images or downloaded as .zip files. Besides the bathymetric data, the site features information on the geology, ecology, and history of Crater Lake, and beautiful .gif images of the lake and surrounding areas.

  15. Vertical landing on an asteroid

    NASA Technical Reports Server (NTRS)

    Harel, D.; Geulman, M.

    1992-01-01

    This work is concerned with the final approach phase and vertical landing on an asteroid with a power-limited, electrically propelled spacecraft. With gravitational effects taken into account, a new solution to the fuel optimal vertical landing on an asteroid was obtained. In this solution, the spacecraft commanded acceleration is explicitly expressed as a function of vehicle velocity and time to go. Based on qualitative methods of analysis, the guidance strategy and the resulting trajectories were studied. It is shown that these fuel-optimal trajectories effectively assure a vertical soft landing on the asteroid. Results of numerical simulations for the vertical landing, starting from an elliptical orbit are presented.

  16. Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover

    NASA Technical Reports Server (NTRS)

    Squyres, S. W.; Andersen, D. W.; Nedell, S. S.; Wharton, R. A. Jr; Wharton RA, J. r. (Principal Investigator)

    1991-01-01

    Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites.

  17. Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover.

    PubMed

    Squyres, S W; Andersen, D W; Nedell, S S; Wharton, R A

    1991-01-01

    Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites. PMID:11538650

  18. Sensitivity of a Sediment transport Model for Lake Michigan

    NASA Astrophysics Data System (ADS)

    Hawley, N.; Lesht, B. M.; Harris, C. K.

    2008-12-01

    A two dimensional (vertical and cross-shore) sediment transport model was used to examine its sensitivity to variations in the input parameters (waves, currents, initial bottom sediment size distribution, settling velocity, and bottom stress required for erosion). The model was applied to several transects in southern Lake Michigan using observations of waves and currents recorded during the spring of 2000. Conditions during this period included several storms that are among the largest observed in the lake. The results show that changing the physical forcing (waves and currents) or the initial bottom sediment size distribution affected the results more than varying the particle properties or the size classes used to describe the size distribution. The results indicate that a relatively simple sediment transport model should produce reasonably accurate simulations of suspended transport in the lake, and that further improvements in specifying the input parameters are more likely to increase the accuracy than including other sediment processes, such as flocculation and bed consolidation.

  19. Modelling the relative importance of internal and external nutrient loads on water column nutrient concentrations and phytoplankton biomass in a shallow polymictic lake

    Microsoft Academic Search

    David F. Burger; David P. Hamilton; Conrad A. Pilditch

    2008-01-01

    Lake Rotorua is a large (area 79km2), shallow (mean depth 10.8m), polymictic lake in central North Island, New Zealand. The lake is eutrophic, with a mean external aerial load of 18.5mgm?2d?1 for total nitrogen and 1.2mgm?2d?1 for total phosphorus. Blooms of cyanobacteria and occasional anoxia of bottom waters occur during summer (December–March). We used a vertically resolved water quality model,

  20. The Tintah-Campbell gap and implications for glacial Lake Agassiz drainage during the Younger Dryas cold interval

    NASA Astrophysics Data System (ADS)

    Breckenridge, Andy

    2015-06-01

    Reconstructions of glacial Lake Agassiz paleogeography and drainage have been an important contribution to formulating a hypothesis in which glacial Lake Agassiz drainage to the Atlantic Ocean initiated the Younger Dryas cold interval. This study evaluates the lake level and outlet history of Lake Agassiz as recorded by strandlines visible on lidar digital elevation models from North Dakota and Minnesota. The former lake levels are warped due to glacial isostatic adjustment. Older levels have experienced more uplift and therefore have more curvature. The strandline data establish that the Moorhead lowstand of Lake Agassiz was bracketed by the strongly diverging Campbell and Tintah lake levels, which creates a vertical gap between the former lake levels. This gap exists due to a lake level drop of ?90 m when the Laurentide Ice Sheet retreat opened a lower outlet, which must have been a northwest outlet to the Arctic Ocean. By applying an exponential decay rebound model, this event dates to 12,180 ± 480 cal yr BP, post-dating the beginning of the Younger Dryas at 12,900 cal yr BP. Eastern drainage outlets to the Atlantic Ocean through the Laurentian Great Lakes that were contemporaneous with the onset of the Younger Dryas cannot be ruled out, but if these outlets existed, their duration of occupation was short-lived and not characterized by significant drawdown events within glacial Lake Agassiz.

  1. TEACH Great Lakes

    NSDL National Science Digital Library

    1969-12-31

    The TEACH Great Lakes Web site is provided by the Great Lakes Information Network (last mentioned in the September 15, 1995 Scout Report). The site features online lessons specific to Great Lakes subjects such as the environment, geography, and pollution. Students can begin with the Introduction to the Great Lakes module and then move on to learn about water levels, shoreline geology, water pollution, and even explore the history and culture or careers and business areas as well. Geared for elementary through high school students, the activities present easily read material along with good photographs and other interesting graphics. Overall, the site provides good information on interesting topics with which students will enjoy becoming familiar as part of their science related curriculum.

  2. Identification and Characterization of Dynamic Alpine Subglacial Lakes Using InSAR, Radio- Echo Sounding, and Crevasse Interpretation

    NASA Astrophysics Data System (ADS)

    Capps, D. L.; Rabus, B. T.; Clague, J. J.

    2007-12-01

    We use interferometric synthetic aperture radar (InSAR), radio-echo sounding (RES), and crevasse interpretation to identify and characterize two dynamic alpine subglacial lakes in Glacier Bay National Park, Alaska. Although significant literature exists on large subglacial lakes in Antarctica, little research has been done on alpine subglacial lakes. Subglacial and subaerial glacier-dammed lakes and the catastrophic floods (jokulhlaups) that release are a hazard in glacierized mountain regions around the world. Many glacier-dammed lakes form subglacially during periods of glacier retreat and downwasting, but are not identified until they become subaerially exposed or release a jokulhlaup. The two lakes discussed here are dammed by Brady Glacier in southeast Alaska, 120 km west of Juneau. Initially, a conspicuous, 3-km-long crevasse in the glacier drew our attention to Hinge Lake, so named because of its hinge-like appearance. For the InSAR analysis, we utilized 20 ascending and descending ERS-1 and -2 tandem radar images provided by the European Space Agency. We obtained a DEM from Glacier Bay National Park that was based on data from the SRTM mission, with gaps filled using photogrammetry data. We co-registered and processed raw SAR signal data into complex, single-look images, created interferograms, and unwrapped the phase. To simplify the analysis, we assumed zero horizontal glacier movement. This assumption is valid because ice is flowing into a closed depression and all interferograms analyzed in this study show very little or zero horizontal motion. To further characterize the lakes, we conducted a RES survey to determine ice depths and substrate. We deduced principle stresses by interpreting crevasses patterns in combination with vertical displacement data derived from interferograms. A time series of interferograms shows vertical motion over large areas of the two lakes. A hydraulic connection between the two lakes is inferred from contemporaneous vertical displacement of the overlying ice. The RES survey provided minimum depths of floating ice. We explain crevasse patterns using a two-fold stress field caused by simple downslope ice movement and vertical displacement of the overlying ice due to filling and draining of the lakes. This study demonstrates that a combination of InSAR, RES, and glaciological interpretation can effectively identify and characterize alpine subglacial lakes. Knowledge of these lakes is important for understanding glacier motion, outburst flood potential and routing, and glacier mass balance. This research is a component of a dissertation that seeks to identify and characterize the glacier-dammed lakes of Glacier Bay, Denali, and Wrangell - St. Elias National Parks using ground-truthed radar and optical remote sensing techniques. It is our aim to eventually apply these techniques to glacier-dammed lakes worldwide.

  3. Trace Metal Associations in an Anoxic Lake: the Relative Roles of Organic Carbon and Reduced Sulfur

    NASA Astrophysics Data System (ADS)

    Poulson Brucker, R.; McManus, J.; Severmann, S.; Owens, J.; Lyons, T.

    2008-12-01

    We investigate the geochemistry of the trace elements Mo, U, and Re in sediments from a transect through the chemocline of Lake Tanganyika, East Africa. In addition to these relatively shallow cores (70 to 330m), we present data from a longer core representing ~30,000 years of lake history, which was taken within the sulfidic waters that lie well below the chemocline (~900m water depth). Our goal is to establish a framework for trace metal deposition within the context of organic carbon and sulfur burial - two important carrier phases for these metals. Sediment organic carbon contents are high, generally between 5 and 10 wt% at the shallow sites, and up to 16 wt% in the deep basin. Despite the very low sulfate (~35 ?M) and sulfide (~30 ?M) concentrations in the lake water, sediment reduced sulfur contents are up to 1.5 wt% in the shallow sites and as high as 5 wt% in the deepest sediments. Sediment C:S ratios for all study sites are consistent with these sediments generally being sulfur limited. Sediment C:S ratios decrease from ~22, which agree well with previously published freshwater values, to ~6 with increasing site depth. The lower C:S ratios are more comparable to the marine value (2.8), and suggest that a considerable amount of organic carbon must be decomposing via sulfate reduction. C:S ratios in the deepest site are highly variable, with some even lower than the marine threshold. In light of the sedimentary organic carbon and sulfur data, trace metal distributions imply that U deposition is closely associated with organic carbon deposition and is independent of sulfur cycling. In contrast, Mo behavior suggests both an association with organic carbon as well as sulfur, but is subject to poor preservation where the sediment C:S ratios are highest. Rhenium accumulation only appears significant at the deepest most sulfur-rich site, and there is a close correspondence between Mo and Re distributions. These latter observations suggest that sulfur burial is particularly important for the authigenic accumulation of Mo and Re in this lacustrine system, in contrast to marine anoxic sediments which show a much tighter coupling between Mo and organic carbon. Despite our expectation of sulfur limitation in this system, there is evidence of substantial reduced sulfur accumulation and corresponding metal enrichment within the lake sediments.

  4. Is Lake Tahoe Terminal?

    NASA Astrophysics Data System (ADS)

    Coats, R. N.; Reuter, J.; Heyvaert, A.; Lewis, J.; Sahoo, G. B.; Schladow, G.; Thorne, J. H.

    2014-12-01

    Lake Tahoe, an iconic ultra-oligotrophic lake in the central Sierra Nevada, has been studied intensively since 1968, with the goal of understanding and ultimately controlling its eutrophication and loss of clarity. Research on the lake has included a) periodic profiles of primary productivity, nutrients, temperature, and plankton; b) Secchi depth; c) nutrient limitation experiments; d) analysis of sediment cores; e) radiocarbon dating of underwater in-place tree stumps; g) analysis of long-term temperature trends. Work in its watershed has included a) monitoring of stream discharge, sediment and nutrients at up to 20 stream gaging stations; b) monitoring of urban runoff water quality at selected sites; c) development of a GIS data base, including soils, vegetation, and land use. Based on these studies, we know that a) primary productivity in the lake is limited by phosphorus, and continues to increase; b) the loss of clarity continues, but at a declining rate; c) the lake has been warming since 1970, and its resistance to deep mixing is increasing; d) historically the lake level drops below the outlet elevation about one year in seven; e) 6300 to 4300 yrs BP lake level was below the present outlet elevation long enough for large trees to grow; f) the date of the peak snowmelt runoff is shifting toward earlier dates; g) after accounting for annual runoff, loads of nutrients and suspended sediment have declined significantly in some basin streams since 1980. Downscaled outputs from GCM climatic models have recently been used to drive hydrologic models and a lake clarity model, projecting future trends in the lake and watersheds. Results show a) the temperature and thermal stability will likely continue to increase, with deep mixing shutting down in the latter half of this century; b) the lake may drop below the outlet for an extended period beginning about 2085; c) the annual snowpack will continue to decline, with earlier snowmelt and shift from snowfall to rain; d) the climatic water deficit will increase, especially at high elevations that will be most affected by the loss of snow, with likely consequences for existing vegetation and fire frequency. Hydrologically, Lake Tahoe is intermittently terminal; in a medical sense it is not yet terminal, but its condition—especially its valued clarity and deep blue color--is serious.

  5. Exotic species in large lakes of the world

    Microsoft Academic Search

    S. R Hall; E. L Mills

    2000-01-01

    Many of the large lakes of the world have been exposed to the introduction of exotic species. We have reviewed here the introduction of aquatic species in 18 large lakes on five continents (Laurentian Great Lakes, African Great Lakes, several Canadian lakes, Lake Titicaca, Lake Baikal, Lake Ladoga, Gatun Lake, and Lake Biwa). We found that human activities, social preferences,

  6. Lake Baikal Homepage

    NSDL National Science Digital Library

    One of the deepest and most ancient lakes in the world, Lake Baikal is situated in the south of Eastern Siberia. Its age and complicated evolutionary history make it home to a wide variety of plants and animals. This site describes ecological problems, climatic conditions, geology, and cultural aspects of the region, and includes detailed maps and photographs. Portions of the site are translated into French and German.

  7. Lake Superior, Duluth, MN

    NASA Technical Reports Server (NTRS)

    1973-01-01

    This view shows the west end of Lake Superior and Duluth, MN (47.0N, 91.0W). Portions of Minnesota, Michigan and Ontario, Canada are in the scene. The Duluth metropolitan area is at the west end of the lake. The discoloration plume in the water at Duluth is the result of tailings from the iron ore smelters that process the iron ore from the nearby open pit mines seen near the upper left corner of the photo.

  8. Latitude and longitude vertical disparities.

    PubMed

    Read, Jenny C A; Phillipson, Graeme P; Glennerster, Andrew

    2009-01-01

    The literature on vertical disparity is complicated by the fact that several different definitions of the term "vertical disparity" are in common use, often without a clear statement about which is intended or a widespread appreciation of the properties of the different definitions. Here, we examine two definitions of retinal vertical disparity: elevation-latitude and elevation-longitude disparities. Near the fixation point, these definitions become equivalent, but in general, they have quite different dependences on object distance and binocular eye posture, which have not previously been spelt out. We present analytical approximations for each type of vertical disparity, valid for more general conditions than previous derivations in the literature: we do not restrict ourselves to objects near the fixation point or near the plane of regard, and we allow for non-zero torsion, cyclovergence, and vertical misalignments of the eyes. We use these expressions to derive estimates of the latitude and longitude vertical disparities expected at each point in the visual field, averaged over all natural viewing. Finally, we present analytical expressions showing how binocular eye position-gaze direction, convergence, torsion, cyclovergence, and vertical misalignment-can be derived from the vertical disparity field and its derivatives at the fovea. PMID:20055544

  9. Functions and Vertical Line Test

    NSDL National Science Digital Library

    2010-01-01

    This lesson is designed to introduce students to the vertical line test for functions as well as practice plotting points and drawing simple functions. The lesson provides links to discussions and activities related to the vertical line test and functions as well as suggested ways to integrate them into the lesson.

  10. Measuring Growth with Vertical Scales

    ERIC Educational Resources Information Center

    Briggs, Derek C.

    2013-01-01

    A vertical score scale is needed to measure growth across multiple tests in terms of absolute changes in magnitude. Since the warrant for subsequent growth interpretations depends upon the assumption that the scale has interval properties, the validation of a vertical scale would seem to require methods for distinguishing interval scales from…

  11. A Killer Lake

    NSDL National Science Digital Library

    Thomas Horvath

    These are the teaching notes for a case study in which students are presented with data on a particular lake that they must synthesize in order to determine the cause of an event that occurred in 1986 in Cameroon, Africa. The case centers on Cameroon's Lake Nyos, a volcanic lake which released a large quantity of carbon dioxide gas, killing over 1700 people, livestock, and wildlife in the area. The case can be used in a limnology or an aquatic biology course and was intended to introduce and reinforce the concepts of thermal stratification and use students' curiosity about this event to get them to think about how layers of water develop. The case could also be extended to cover or review other concepts such as lake formation (in this case, volcanism as a lake-forming process) or gas solution (in this case, carbon dioxide solution). The case could also be used throughout a limnology course because it deals with many aspects of the subject: lake origins, thermal stratification, gases, water movements, and applied limnology (remediation of problems). Instructors can introduce the case early in a course and refer back to it when each new topic comes up. The case also allows students to synthesize different types of limnological data to solve a serious problem.

  12. Lake bottom magnetotellurics

    NASA Astrophysics Data System (ADS)

    Schultz, Adam; Booker, John; Larsen, Jim

    1987-09-01

    The study of the electrical conductivity structure of the lower crust and the upper mantle and midmantle promises to place important constraints on the thermobaric and compositional state of the earth's interior. Such work, particularly for depths above approximately 400 km, is best attempted by magnetotelluric sounding, an effort frustrated by the almost complete absence of stable long-period electric field measurements. In this paper, we propose that proven techniques developed for seafloor magnetotellurics be applied also to deep freshwater lakes. The establishment of such long-period electric and magnetic observatories in the thermally stable, low-noise lake bottom environment will yield new insights on the deep electrical structure beneath the continents. A lake bottom long-span electric field array was deployed in a deep freshwater lake adjacent to Seattle, Washington. A vector flux gate magnetometer was buried on the shore of the lake, and magnetotelluric data of high quality were collected. The analysis of the data described in this work clearly demonstrates the feasibility of establishing such lake bottom continental magnetotelluric observatories. Inversion of the data provides a view of structure beneath the site consistent with regional seismic and tectonic models.

  13. Clear Lake Annotated Bibliography October 2, 2009

    E-print Network

    Thompson, Lisa C.

    : Newspaper Article Record Number: 256 Year: 1859 Title: Another California Curiosity-Borax Lake Newspaper Curiosity-Borax Lake Abstract: need abstract Notes: clear lake; pollution; html ONLINE -borax lake -sulphur

  14. Importance of light, temperature, zooplankton, and fish in predicting the nighttime vertical distribution of Mysis diluviana

    USGS Publications Warehouse

    Murphy, Marilyn K.; Robert O'Gorman; Boscarino, Brent T.; Rudstam, Lars G.; Eillenberger, June L.

    2009-01-01

    The opossum shrimp Mysis diluviana (formerly M. relicta) performs large amplitude diel vertical migrations in Lake Ontario and its nighttime distribution is in?uenced by temperature, light and the distribution of its predators and prey. At one location in southeastern Lake Ontario, we measured the vertical distribution of mysids, mysid predators (i.e. planktivorous ?shes) and mysid prey (i.e. zooplankton), in addition to light and temperature, on 8 occasions from May to September, 2004 and 2005. We use these data to test 3 different predictive models of mysid habitat selection, based on: (1) laboratoryderived responses of mysids to different light and temperature gradients in the absence of predator or prey cues; (2) growth rate of mysids, as estimated with a mysid bioenergetics model, given known prey densities and temperatures at different depths in the water column; (3) ratio of growth rates (g) and mortality risk (?) associated with the distribution of predatory ?shes. The model based on light and temperature preferences was a better predictor of mysid vertical distribution than the models based on growth rate and g:?on all 8 occasions. Although mysid temperature and light preferences probably evolved as mechanisms to reduce predation while increasing foraging intake, the response to temperature and light alone predicts mysid vertical distribution across seasons in Lake Ontario.

  15. Importance of light, temperature, zooplankton and fish in predicting the nighttime vertical distribution of Mysis diluviana

    USGS Publications Warehouse

    Boscarino, B.T.; Rusdtam, L.G.; Eillenberger, J.L.; O'Gorman, R.

    2009-01-01

    The opossum shrimp Mysis diluviana (formerly M. relicta) performs large amplitude diel vertical migrations in Lake Ontario and its nighttime distribution is influenced by temperature, light and the distribution of its predators and prey. At one location in southeastern Lake Ontario, we measured the vertical distribution of mysids, mysid predators (i.e. planktivorous fishes) and mysid prey (i.e. zooplankton), in addition to light and temperature, on 8 occasions from May to September, 2004 and 2005. We use these data to test 3 different predictive models of mysid habitat selection, based on: (1) laboratory-derived responses of mysids to different light and temperature gradients in the absence of predator or prey cues; (2) growth rate of mysids, as estimated with a mysid bioenergetics model, given known prey densities and temperatures at different depths in the water column; (3) ratio of growth rates (g) and mortality risk (??) associated with the distribution of predatory fishes. The model based on light and temperature preferences was a better predictor of mysid vertical distribution than the models based on growth rate and g:?? on all 8 occasions. Although mysid temperature and light preferences probably evolved as mechanisms to reduce predation while increasing foraging intake, the response to temperature and light alone predicts mysid vertical distribution across seasons in Lake Ontario. ?? Inter-Research 2009.

  16. Availability of lake trout reproductive habitat in the Great Lakes

    USGS Publications Warehouse

    Edsall, Thomas A.; Kennedy, Gregory W.

    1995-01-01

    A decades-long program to reestablish self-sustaining stocks of lake trout (Salvelinus namaycush) in the four lower Great Lakes produced excellent fisheries supported by stocked fish. These fish spawned widely and small numbers of their offspring were collected intermittently from Lakes Michigan, Huron, and Ontario, but no self-sustaining stocks were established. Irt this paper we address habitat sufficiency as a factor in the failure of stocked lake trout to established self-sustaining populations in the four lower Great Lakes. We present the previously unpublished results of lake trout spawning habitat surveys conducted at seven sites in the Great Lakes since 1987 and we compare them with the published results of similar surveys conducted at 24 other sites in the four lower lakes since 1981. Our evaluation indicates all but two of these sites can support the production of viable fry from spawnings by the shallow-water strains of lake trout that are stocked in the Great Lakes. However, some of the best spawning, egg, and fry habitat in the lower Great Lakes seems to be at deeper offshore sites that may be unattractive to these shallow-water strains. Thus, we suggest also stocking the lower four lakes with strains from Lake Superior that might more fully exploit the best spawning habitat at these deeper, offshore sites.

  17. Tropical high-altitude Andean lakes located above the tree line attenuate UV-A radiation more strongly than typical temperate alpine lakes.

    PubMed

    Aguilera, Ximena; Lazzaro, Xavier; Coronel, Jorge S

    2013-09-01

    Tropical high-altitude Andean lakes are physically harsh ecosystems. Located above the treeline (?4000 m a.s.l.), they share common features with temperate alpine lakes, which impose extreme conditions on their aquatic organisms: e.g., strong winds, broad diel variations in water temperature, and intense solar ultraviolet radiation (UVR). However, because of their latitude, they differ in two major ecological characteristics: they lack ice cover during the winter and they do not present summer water column stratification. We sampled 26 tropical high-altitude Andean lakes from three regions of the Bolivian Eastern Andes Cordillera during the wet period (austral summer). We performed an ordination to better describe the typology of Andean lakes in relation to the environmental variables, and we assessed the relationships among them, focussing on the UV-A transparency (360 nm) throughout the water column. We found a positive correlation between UV-A transparency calculated as Z(1%) (the depth which reaches 1% of the surface UV-A), the lake maximum depth and Secchi transparency (r = 0.61). Z(1%) of UV-A was smaller in shallow lakes than in deep lakes, indicating that shallow lakes are less transparent to UV-A than deep lakes. We hypothesize that, compared to shallow lakes, deep lakes (maximum depth > 10 m) may have lower dissolved organic carbon (DOC) concentrations (that absorb UV radiation) due to lower temperature and reduced macrophyte cover. Based on our data, tropical high-altitude Andean lakes are less transparent to UV-A (K(d) range = 1.4-11.0 m(-1); Z(1%) depth range = 0.4-3.2 m) than typical temperate alpine lakes (1-6 m(-1), 3-45 m, respectively). Moreover, they differ in vertical profiles of UV-A, chlorophyll-a, and temperature, suggesting that they may have a distinct ecological functioning. Such peculiarities justify treating tropical high-altitude Andean lakes as a separate category of alpine lakes. Tropical high-altitude Andean lakes have been poorly studied. Thus they deserve more in-depth studies in the face of global changes regarding the use of their UV transparency as a sentinel proxy of climate changes, particularly global warming. PMID:23722356

  18. Contaminants in American alligator eggs from Lake Apopka, Lake Griffin, and Lake Okeechobee, Florida

    USGS Publications Warehouse

    Heinz, G.H.; Percival, H.F.; Jennings, M.L.

    1991-01-01

    Residues of organochlorine pesticides, polychlorinated biphenyls (PCBs), and 16 elements were measured in American alligator (Alligator mississippiensis) eggs collected in 1984 from Lakes Apopka, Griffin, and Okeechobee in central and south Florida. Organochlorine pesticides were highest in eggs from Lake Apopka. None of the elements appeared to be present at harmful concentrations in eggs from any of the lakes. A larger sample of eggs was collected in 1985, but only from Lakes Griffin, a lake where eggs were relatively clean, and Apopka, where eggs were most contaminated. In 1985, hatching success of artificially incubated eggs was lower for Lake Apopka, and several organochlorine pesticides were higher than in eggs from Lake Griffin. However, within Lake Apopka, higher levels of pesticides in chemically analyzed eggs were not associated with reduced hatching success of the remaining eggs in the clutch. Therefore, it did not appear that any of the pesticides we measured were responsible for the reduced hatching of Lake Apopka eggs.

  19. COSEE Great Lakes Lake Superior Exploration Workshop

    NSDL National Science Digital Library

    Teachers of grades 4-10 or informal settings and scientists from universities, federal agencies, state agencies, and not-for-profit organizations are invited to take part in innovative and cutting edge science education. Participants will experience the Lake Superior ecosystem firsthand with experts through: field and classroom activities, classroom activity idea sharing, learning how to use cutting edge research, data, and technology with their students, and making peer connections.

  20. A vertical microfluidic probe.

    PubMed

    Kaigala, G V; Lovchik, R D; Drechsler, U; Delamarche, E

    2011-05-01

    Performing localized chemical events on surfaces is critical for numerous applications. We earlier invented the microfluidic probe (MFP), which circumvented the need to process samples in closed microchannels by hydrodynamically confining liquids that performed chemistries on surfaces (Juncker et al. Nat. Mater. 2005, 4, 622-628). Here we present a new and versatile probe, the vertical MFP (vMFP), which operates in the scanning mode while overcoming earlier challenges that limited the practical implementation of the MFP technology. The key component of the vMFP is the head, a microfluidic device (?1 cm(2) in area) consisting of glass and Si and having microfluidic features fabricated in-plane in the Si layer. The base configuration of the head has two micrometer-size channels that inject/aspirate liquids and terminate at the apex which is ?1 mm(2). In scanning mode, the head is oriented vertically with the apex parallel to the surface with typical spacing of 1-30 ?m. Such length scales and using flow rates from nanoliters/second to microliters/second allow chemical events to be performed on surfaces with tens of picoliter quantities of reagents. Before scanning, the head is clipped on a holder for leak-free, low dead volume interface assembly, providing a simple world-to-chip interface. Surfaces are scanned by mounting the holder on a computer-controlled stage having ?0.1 ?m resolution in positioning. We present detailed steps to fabricate vMFP heads having channels with dimensions from 1 ?m × 1 ?m to 50 ?m × 50 ?m for liquid localization over areas of 10-10,000 ?m(2). Additionally, advanced design strategies are described to achieve high yield in fabrication and to support a broad range of applications. These include particulate filters, redundant aperture architectures, inclined flow-paths that service apertures, and multiple channels to enable symmetric flow confinement. We also present a method to characterize flow confinement and estimate the distance between the head and the surface by monitoring the evolution of a solution of fluorescently labeled antibody on an activated glass surface. This flow characterization reveals regimes of operation suitable for different surface topographies. We further integrate the dispensing of immersion liquid to the vMFP head for processing surfaces for extended periods of time (?60 min). The versatility of the vMFP is exemplified by patterning fluorescently labeled proteins, inactivation of cells using sodium hypochlorite, and staining living NIH fibroblasts with Cellomics. These applications are enabled by the compact design of the head, which provides easy access to the surface, simplifies alignment, and enables processing surfaces having dimensions from the micrometer to the centimeter scale and with large topographical variations. We therefore believe that ease-of-operation, reconfigurability, and conservative use of chemicals by the vMFP will lead to its widespread use by microtechnologists and the chemical and biomedical communities. PMID:21476506