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1

Phytoplankton in Lake Tanganyika – vertical and horizontal distribution of in vivo fluorescence  

Microsoft Academic Search

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

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

1999-01-01

2

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)

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.

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

2009-12-01

3

Ecological Consequences of a Century of Warming in Lake Tanganyika  

Microsoft Academic Search

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

Piet Verburg; Robert E. Hecky; Hedy Kling

2003-01-01

4

Tempo and Mode of Diversification of Lake Tanganyika Cichlid Fishes  

E-print Network

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

Cotton, James

5

Nearshore carbonate deposits in Lake Tanganyika  

Microsoft Academic Search

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

Andrew S. Cohen; Catherine Thouin

1987-01-01

6

Gastritis in Lake Tanganyika cichlids (Tropheus duboisii)  

Microsoft Academic Search

Necrotic and granulomatous gastritis is described in Lake Tanganyika cichlids. Clostridium hastiforme and flagellated protozoa were both associated with the reaction but the significance of either is unknown. Nevertheless, treatment of surviving fish with ampicillin was carried out and mortalities ceased. The possible involvement of an unsuitable diet as a predisposing factor is discussed.

HW Ferguson; S Rosendal; S Groom

1985-01-01

7

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

E-print Network

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

Awramik, Stanley M.

8

Origin of intraseasonal variability in Lake Tanganyika  

NASA Astrophysics Data System (ADS)

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.

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

2002-12-01

9

HYDROLOGICAL CHANGES IN RELATION TO BIOLOGICAL PRODUCTION IN SOUTHERN LAKE TANGANYIKA  

Microsoft Academic Search

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

W. Coulter

10

The Geochemistry and Hydrography of Lake Tanganyika  

NASA Astrophysics Data System (ADS)

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.

Craig, H.

2001-12-01

11

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

E-print Network

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

Wehrli, Bernhard

12

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

E-print Network

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

Wehrli, Bernhard

13

Nutrient chemistry of the water column of Lake Tanganyika  

Microsoft Academic Search

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

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

1993-01-01

14

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

Microsoft Academic Search

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 -

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

2006-01-01

15

Fisheries research towards resource management on Lake Tanganyika  

Microsoft Academic Search

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

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

1999-01-01

16

Mating and Parental Care in Lake Tanganyika's Cichlids.  

PubMed

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

Sefc, Kristina M

2011-01-01

17

Hydrothermal vents in Lake Tanganyika, East African, Rift system  

Microsoft Academic Search

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

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

18

Analysis of Wind-Induced Thermocline Oscillations of Lake Tanganyika  

Microsoft Academic Search

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

Jaya Naithani; Eric Deleersnijder; Pierre-Denis Plisnier

2003-01-01

19

Are there internal Kelvin waves in Lake Tanganyika?  

NASA Astrophysics Data System (ADS)

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.

Naithani, Jaya; Deleersnijder, Eric

2004-03-01

20

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

NASA Astrophysics Data System (ADS)

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.

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

2011-06-01

21

Interspecific relationships of aufwuchs-eating fishes in Lake Tanganyika  

Microsoft Academic Search

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

Kenzi Takamura

1984-01-01

22

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

E-print Network

; Nicholson 1995). Though Lake Victoria's rise was the most dramatic, Lake Tanganyika rose over two meters Africa. With a surface area of 32,600 km2 , it is less than half the size of Lake Victoria, but drains

Nicholson, Sharon E.

23

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

Microsoft Academic Search

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

Anthony B. Wilson; Matthias Glaubrecht; Axel Meyer

2004-01-01

24

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

E-print Network

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

McIntyre, Peter

25

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

E-print Network

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

McIntyre, Peter

26

Facies relationships and sedimentation in large rift lakes and implications for hydrocarbon exploration: Examples from lakes Turkana and Tanganyika  

Microsoft Academic Search

Cohen, A. S., 1989. Facies relationships and sedimentation in large rift lakes and implications for hydrocarbon exploration: examples from lakes Turkana and Tanganyika. Palaeogeogr., Palaeoclimatol., Palaeoecol., 70: 65-80. Two African lakes, Turkana and Tanganyika, illustrate a spectrum of sediments and facies architectures which can occur in large rift lacustrine basins. They demonstrate contrasts between sediments deposited in a semi-arid, moderately

Andrew S. Cohen

1989-01-01

27

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

NASA Astrophysics Data System (ADS)

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.

Verburg, P.; Hecky, B.

2003-12-01

28

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

NASA Astrophysics Data System (ADS)

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.

Antenucci, Jason P.

2005-11-01

29

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

Microsoft Academic Search

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

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

2002-01-01

30

Complete mitochondrial DNA replacement in a Lake Tanganyika cichlid fish.  

PubMed

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

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

2009-10-01

31

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

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

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

32

Evolutionary History of Lake Tanganyika's Predatory Deepwater Cichlids.  

PubMed

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

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

2012-01-01

33

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

PubMed

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

Takahashi, Tetsumi; Koblmüller, Stephan

2011-01-01

34

Diatoms from surface sediments of the northern part of Lake Tanganyika  

Microsoft Academic Search

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

A. G. Caljon; C. Z. Cocquyt

1992-01-01

35

A late Holocene paleoclimatic history of Lake Tanganyika, East Africa  

NASA Astrophysics Data System (ADS)

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.

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

2009-07-01

36

Mn seasonal upwellings recorded in Lake Tanganyika mussels  

NASA Astrophysics Data System (ADS)

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.

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

2006-09-01

37

Recent paleorecords document rising mercury contamination in Lake Tanganyika  

USGS Publications Warehouse

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.

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

2012-01-01

38

Surface Energy Balance and The Mixed Layer at Lake Tanganyika  

NASA Astrophysics Data System (ADS)

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.

Verburg, P.; Hecky, R.

2002-12-01

39

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

E-print Network

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

Alvarez, Nadir

40

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

NASA Astrophysics Data System (ADS)

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.

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

2003-04-01

41

Manganese content records seasonal upwelling in Lake Tanganyika mussels  

NASA Astrophysics Data System (ADS)

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.

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

2007-03-01

42

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

Microsoft Academic Search

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

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

43

Hydrothermal vents is Lake Tanganyika, East African Rift system  

SciTech Connect

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.

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

44

Climate change decreases aquatic ecosystem productivity of Lake Tanganyika, Africa  

NASA Astrophysics Data System (ADS)

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.

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

2003-08-01

45

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

Microsoft Academic Search

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

Sharon E. Nicholson

1999-01-01

46

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

Microsoft Academic Search

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

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

1999-01-01

47

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

NASA Astrophysics Data System (ADS)

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.

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

2010-06-01

48

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

SciTech Connect

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.

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

49

The Lake Tanganyika cichlid species assemblage: recent advances in molecular phylogenetics  

Microsoft Academic Search

Lake Tanganyika is not the most species-rich of the Great East African Lakes, but comprises the greatest diversity of cichlid\\u000a fishes in terms of morphology, ecology, and breeding styles. The lake contains a polyphyletic assemblage of cichlid lineages,\\u000a which evolved from several ancient species that colonized the emerging lake some 9–12 million years ago. Based on morphological\\u000a characteristics, the Tanganyikan cichlids

Stephan Koblmüller; Kristina M. Sefc; Christian Sturmbauer

2008-01-01

50

Marine Incursion: The Freshwater Herring of Lake Tanganyika Are the Product of a Marine Invasion into West Africa  

PubMed Central

The spectacular marine-like diversity of the endemic fauna of Lake Tanganyika, the oldest of the African Great Lakes, led early researchers to suggest that the lake must have once been connected to the ocean. Recent geophysical reconstructions clearly indicate that Lake Tanganyika formed by rifting in the African subcontinent and was never directly linked to the sea. Although the Lake has a high proportion of specialized endemics, the absence of close relatives outside Tanganyika has complicated phylogeographic reconstructions of the timing of lake colonization and intralacustrine diversification. The freshwater herring of Lake Tanganyika are members of a large group of pellonuline herring found in western and southern Africa, offering one of the best opportunities to trace the evolutionary history of members of Tanganyika's biota. Molecular phylogenetic reconstructions indicate that herring colonized West Africa 25–50MYA, at the end of a major marine incursion in the region. Pellonuline herring subsequently experienced an evolutionary radiation in West Africa, spreading across the continent and reaching East Africa's Lake Tanganyika during its early formation. While Lake Tanganyika has never been directly connected with the sea, the endemic freshwater herring of the lake are the descendents of an ancient marine incursion, a scenario which may also explain the origin of other Tanganyikan endemics. PMID:18431469

Wilson, Anthony B.; Teugels, Guy G.; Meyer, Axel

2008-01-01

51

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

NASA Astrophysics Data System (ADS)

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.

Sako, A.; Johnson, R.

2004-12-01

52

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

Microsoft Academic Search

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 \\

Christian Sturmbauer; Erik Verheyen

53

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

NASA Astrophysics Data System (ADS)

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 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 from 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 off estimates for different segments of the lake. is equivocal, and may be due to erosional loss off 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.

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

1993-06-01

54

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

Microsoft Academic Search

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)

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

1997-01-01

55

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

Microsoft Academic Search

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,

Simone R. Alin; Andrew S. Cohen

2003-01-01

56

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

Microsoft Academic Search

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

Lukas Ruber; Axel Meyer; Christian Sturmbauer; Erik Verheyen

2001-01-01

57

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

Microsoft Academic Search

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

Christian Sturmbauer; Wolfgang Mark; Reinhard Dallinger

1992-01-01

58

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

Microsoft Academic Search

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

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

59

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

Microsoft Academic Search

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

F. M. M. Chale

2002-01-01

60

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

Microsoft Academic Search

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

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

2003-01-01

61

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

Microsoft Academic Search

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

Christian Sturmbauer

62

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

Microsoft Academic Search

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

L. RUBER; D. C. ADAMS

2001-01-01

63

Distribution of the primates on the eastern shore of Lake Tanganyika  

Microsoft Academic Search

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

Takayoshi Kano

1971-01-01

64

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

Microsoft Academic Search

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

Lukas Ruber; Erik Verheyen; Axel Meyer

1999-01-01

65

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

Microsoft Academic Search

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

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

1996-01-01

66

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

Microsoft Academic Search

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.

G. Marlier; N. Leleup

1954-01-01

67

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

Microsoft Academic Search

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

Erik Verheyen; Lukas Ruber; Jos Snoeks; Axel Meyer

1996-01-01

68

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

Microsoft Academic Search

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

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

1997-01-01

69

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

70

Protist Herbivory: a Key Pathway in the Pelagic Food Web of Lake Tanganyika  

Microsoft Academic Search

Herbivory and bacterivory by phagotrophic protists were estimated in the southern basin of the oligotrophic Lake Tanganyika\\u000a at different seasons (in the rainy season in February–March 2007 and in the dry season in July–August 2006 and September 2007),\\u000a using two independent methods: the selective inhibitor technique for assessing community grazing on picocyanobacteria (PCya)\\u000a and fluorescently labelled bacteria (FLB) and Synechococcus

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

71

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

Microsoft Academic Search

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

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

72

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

Microsoft Academic Search

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

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

1999-01-01

73

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

Microsoft Academic Search

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

Tetsuo Kuwamura

1986-01-01

74

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

Microsoft Academic Search

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

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

2009-01-01

75

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

PubMed

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

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

2012-01-01

76

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

SciTech Connect

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.

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

1991-03-01

77

Ancestry to an endemic radiation in Lake Tanganyika? Evolution of the viviparous gastropod Potadomoides Leloup, 1953 in the Congo River system (Caenogastropoda, Cerithioidea, Paludomidae)  

Microsoft Academic Search

Providing another spectacular model for understanding speciation and radiation, the origin of the gastropod species flock in Lake Tanganyika (with an estimated age of approximately 12 Myr) remained enigmatic to date. Although, for a long time, an in situ radiation was assumed, Lake Tanganyika could have functioned as a reservoir for ancient African lineages, implying that the now lacustrine taxa

MATTHIAS GLAUBRECHT; ELLEN E. STRONG

78

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

USGS Publications Warehouse

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.

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

79

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

Microsoft Academic Search

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

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

2002-01-01

80

Primary production and rates of algal growth in Lake Tanganyika  

Microsoft Academic Search

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.

R. E. HECKY; E. J. FEE

1981-01-01

81

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

PubMed

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

Takahashi, T

2014-04-01

82

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

NASA Astrophysics Data System (ADS)

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.

Plisnier, P.-D.

2003-04-01

83

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

SciTech Connect

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).

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

1987-05-01

84

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

Microsoft Academic Search

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

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

1989-01-01

85

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

USGS Publications Warehouse

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.

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

2003-01-01

86

Thermophilic Sulfate Reduction in Hydrothermal Sediment of Lake Tanganyika, East Africa  

PubMed Central

In environments with temperatures above 60°C, thermophilic prokaryotes are the only metabolically active life-forms. By using the 35SO42- tracer technique, we studied the activity of sulfate-reducing microorganisms (SRM) in hot sediment from a hydrothermal vent site in the northern part of freshwater Lake Tanganyika (East Africa). Incubation of slurry samples at 8 to 90°C demonstrated meso- and thermophilic sulfate reduction with optimum temperatures of 34 to 45°C and 56 to 65°C, respectively, and with an upper temperature limit of 80°C. Sulfate reduction was stimulated at all temperatures by the addition of short-chain fatty acids and benzoate or complex substrates (yeast extract and peptone). A time course experiment showed that linear thermophilic sulfate consumption occurred after a lag phase (12 h) and indicated the presence of a large population of SRM in the hydrothermal sediment. Thermophilic sulfate reduction had a pH optimum of about 7 and was completely inhibited at pH 8.8 to 9.2. SRM could be enriched from hydrothermal chimney and sediment samples at 60 and 75°C. In lactate-grown enrichments, sulfide production occurred at up to 70 and 75°C, with optima at 63 and 71°C, respectively. Several sporulating thermophilic enrichments were morphologically similar to Desulfotomaculum spp. Dissimilatory sulfate reduction in the studied hydrothermal area of Lake Tanganyika apparently has an upper temperature limit of 80°C. PMID:16349249

Elsgaard, Lars; Prieur, Daniel; Mukwaya, Gashagaza M.; Jørgensen, Bo B.

1994-01-01

87

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

NASA Astrophysics Data System (ADS)

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.

Gourgue, Olivier; Deleersnijder, Eric; White, Laurent

2007-09-01

88

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

NASA Astrophysics Data System (ADS)

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.

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

2005-12-01

89

Evolutionary history of the endemic Lake Tanganyika cichlid fish Tylochromis polylepis: a recent intruder to a mature adaptive radiation  

Microsoft Academic Search

With an age of 9-12 million years (Myr) Lake Tanganyika holds the oldest and most complex species flock of cichlid fishes. It is believed to be of polyphyletic origin and rooted in nine ancient African lineages, six of which underwent diversification, while three remained monotypic. Here, the evolutionary history, route and timing of colonization were analyzed, as well as intraspecific

M. Koch; S. Koblmüller; K. M. Sefc; N. Duftner; C. Katongo; C. Sturmbauer

2007-01-01

90

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

Microsoft Academic Search

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

E. Michel

2000-01-01

91

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

Microsoft Academic Search

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

M. Nishida; Arap Siongok

1991-01-01

92

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

NASA Astrophysics Data System (ADS)

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.

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

2008-12-01

93

Trematodes indicate animal biodiversity in the chilean intertidal and Lake Tanganyika  

USGS Publications Warehouse

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.

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

2008-01-01

94

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

NASA Astrophysics Data System (ADS)

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.

Verburg, Piet; Antenucci, Jason P.

2010-06-01

95

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

PubMed

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

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

2011-08-01

96

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

NASA Astrophysics Data System (ADS)

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.

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

2011-01-01

97

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

NASA Astrophysics Data System (ADS)

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.

Branchu, Ph.; Bergonzini, Laurent

98

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

NASA Astrophysics Data System (ADS)

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.

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

99

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

PubMed

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

Takahashi, T; Sota, T; Hori, M

2013-06-01

100

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

PubMed

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

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

2014-01-01

101

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

PubMed

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

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

2015-02-01

102

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

PubMed

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

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

2014-04-01

103

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

Microsoft Academic Search

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

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

2000-01-01

104

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

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

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

2011-10-01

105

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

PubMed

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

Vreven, E J; Snoeks, J

2009-10-01

106

Observations on the transmission of Schistosoma haematobium and Schistosoma bovis in the Lake Region of Tanganyika  

PubMed Central

Previous investigations have shown that in the Lake Region of Sukumaland, Tanganyika, where Schistosoma haematobium is highly endemic, Bulinus (Physopsis) nasutus is responsible for the transmission of that schistosome in small, temporary rain pools. This area is one of low rainfall, and large artificial reservoirs are the chief source of water in the dry season. The role of these reservoirs in S. haematobium transmission was studied over a period of about a year. Previous work in South Africa had indicated the potential danger of bovine schistosomes to man. S. bovis is a very common parasite in cattle in the Lake Region, and a search for its intermediate host or hosts, previously unidentified, was therefore also made. The results of this double investigation suggest that large bodies of water are relatively unimportant in the transmission of both S. haematobium and S. bovis. Bulinus (Physopsis) africanus is shown to be a second intermediate of S. haematobium and a vector of S. bovis as well. Transmission of these parasites by this snail takes place principally in streams. PMID:14277260

Kinoti, George

1964-01-01

107

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

NASA Astrophysics Data System (ADS)

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.

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

2002-12-01

108

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

109

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

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

Stephan Koblmüller; Walter Salzburger; Christian Sturmbauer

2004-01-01

110

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

Microsoft Academic Search

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

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

2002-01-01

111

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

PubMed Central

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

2014-01-01

112

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

PubMed

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

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

2011-06-01

113

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

NASA Astrophysics Data System (ADS)

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.

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

2002-12-01

114

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

PubMed

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

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

2010-04-01

115

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)

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.

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

116

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

NASA Astrophysics Data System (ADS)

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.

Tierney, J.; Russell, J.

2006-12-01

117

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

NASA Astrophysics Data System (ADS)

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.

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

2010-03-01

118

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

PubMed Central

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

2013-01-01

119

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

PubMed Central

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

Kerschbaumer, M; Mitteroecker, P; Sturmbauer, C

2014-01-01

120

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

PubMed

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

Kerschbaumer, M; Mitteroecker, P; Sturmbauer, C

2014-02-01

121

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

PubMed

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

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

2010-10-01

122

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

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

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

2012-11-01

123

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

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.

Kazuhiko Takahashi; Yohey Terai; Mutsumi Nishida; Norihiro Okada

124

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

Microsoft Academic Search

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-\\

R. E. HECKY; H. J. KLING

1981-01-01

125

Evolution of a unique predatory feeding apparatus: functional anatomy, development and a genetic locus for jaw laterality in Lake Tanganyika scale-eating cichlids  

Microsoft Academic Search

BACKGROUND: While bilaterality is a defining characteristic of triploblastic animals, several assemblages have managed to break this symmetry in order to exploit the adaptive peaks garnered through the lateralization of behaviour or morphology. One striking example of an evolved asymmetry in vertebrates comes from a group of scale-eating cichlid fishes from Lake Tanganyika. Members of the Perissodini tribe of cichlid

Thomas A Stewart; R Craig Albertson

2010-01-01

126

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

PubMed

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

Takahashi, Tetsumi; Hori, Michio

2012-01-01

127

Pollen-Derived Rainfall and Temperature Estimates from Lake Tanganyika and Their Implication for Late Pleistocene Water Levels  

NASA Astrophysics Data System (ADS)

Palaeoclimatic estimates of mean annual temperature and rainfall in the southern Tanganyika basin between 25,000 and 9000 yr B.P. have been established from two pollen sequences based on the best-analogue method. The results give evidence of a mean temperature decrease of about 4.2°C during the last glaciation, a value consistent with that previously obtained in the catchment area on the Burundi Highlands. This cooling was synchronous with a decrease of mean annual precipitation of about 180 mm/yr. Postglacial climatic conditions were established by 12,700 yr B.P., with warming and wetness continuing to increase from this date onward. These new palaeoclimatic data will be useful for hydrological reconstructions of Lake Tanganyika, particularly during the last glacial age for which the magnitude of water-level fall has been a controversial issue; our rainfall estimates are more consistent with low values (-250 to -300 m fall) than with high ones (-600 m) previously proposed.

Vincens, Annie; Chalié, Françoise; Bonnefille, Raymonde; Guiot, Joel; Tiercelin, Jean-Jacques

1993-11-01

128

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

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

129

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

NASA Astrophysics Data System (ADS)

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.

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

2004-12-01

130

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

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,

Tetsuo Kuwamura; Makoto Nagoshi; Tetsu Sato

1989-01-01

131

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

PubMed

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

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

2009-07-01

132

Reticulate phylogeny of gastropod-shell-breeding cichlids from Lake Tanganyika – the result of repeated introgressive hybridization  

PubMed Central

Background The tribe Lamprologini is the major substrate breeding lineage of Lake Tanganyika's cichlid species flock. Among several different life history strategies found in lamprologines, the adaptation to live and breed in empty gastropod shells is probably the most peculiar. Although shell-breeding arose several times in the evolutionary history of the lamprologines, all obligatory and most facultative shell-breeders belong to the so called "ossified group", a monophyletic lineage within the lamprologine cichlids. Since their distinctive life style enables these species to live and breed in closest vicinity, we hypothesized that these cichlids might be particularly prone to accidental hybridization, and that introgression might have affected the evolutionary history of this cichlid lineage. Results Our analyses revealed discrepancies between phylogenetic hypotheses based on mitochondrial and nuclear (AFLP) data. While the nuclear phylogeny was congruent with morphological, behavioral and ecological characteristics, several species – usually highly specialized shell-breeders – were placed at contradicting positions in the mitochondrial phylogeny. The discordant phylogenies strongly suggest repeated incidents of introgressive hybridization between several distantly related shell-breeding species, which reticulated the phylogeny of this group of cichlids. Long interior branches and high bootstrap support for many interior nodes in the mitochondrial phylogeny argue against a major effect of ancient incomplete lineage sorting on the phylogenetic reconstruction. Moreover, we provide morphological and genetic (mtDNA and microsatellites) evidence for ongoing hybridization among distantly related shell-breeders. In these cases, the territorial males of the inferred paternal species are too large to enter the shells of their mate, such that they have to release their sperm over the entrance of the shell to fertilize the eggs. With sperm dispersal by water currents and wave action, trans-specific fertilization of clutches in neighboring shells seem inevitable, when post-zygotic isolation is incomplete. Conclusion From the direct observation of hybrids we conclude that hybridization between distantly related gastropod-shell-breeding cichlids of Lake Tanganyika follows inevitably from their ecological specialization. Moreover, the observed incongruence between mtDNA and nuclear multilocus phylogeny suggests that repeated hybridization events among quite distantly related taxa affected the diversification of this group, and introduced reticulation into their phylogeny. PMID:17254340

Koblmüller, Stephan; Duftner, Nina; Sefc, Kristina M; Aibara, Mitsuto; Stipacek, Martina; Blanc, Michel; Egger, Bernd; Sturmbauer, Christian

2007-01-01

133

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

NASA Astrophysics Data System (ADS)

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.

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

2005-12-01

134

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

PubMed

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

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

2012-01-01

135

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

PubMed

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

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

2012-01-01

136

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

PubMed

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

Ota, K; Kohda, M

2011-03-01

137

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

SciTech Connect

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.

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

1996-03-01

138

Diet disparity among sympatric herbivorous cichlids in the same ecomorphs in Lake Tanganyika: amplicon pyrosequences on algal farms and stomach contents.  

PubMed

BackgroundLake Tanganyika, an ancient lake in the Great Rift Valley, is famous for the adaptive radiation of cichlids. Five tribes of the Cichlidae family have acquired herbivory, with five ecomorphs: grazers, browsers, scrapers, biters, and scoopers. Sixteen species of the herbivorous cichlids coexist on a rocky littoral slope in the lake. Seven of them individually defend feeding territories against intruding herbivores to establish algal farms. We collected epiphyton from these territories at various depths and also gathered fish specimens. Algal and cyanobacteria community structures were analysed using the amplicon-metagenomic method.ResultsBased on 454-pyrosequencing of SSU rRNA gene sequences, we identified 300 phototrophic taxa, including 197 cyanobacteria, 57 bacillariophytes, and 31 chlorophytes. Algal farms differed significantly in their composition among cichlid species, even in the same ecomorph, due in part to their habitat-depth segregation. The algal species composition of the stomach contents and algal farms of each species differed, suggesting that cichlids selectively harvest their farms. The stomach contents were highly diverse, even between species in the same tribe, in the same feeding ecomorph.ConclusionsIn this study, the amplicon-metagenomic approach revealed food niche separation based on habitat-depth segregation among coexisting herbivorous cichlids in the same ecomorphs in Lake Tanganyika. PMID:25359595

Hata, Hiroki; Tanabe, Akifumi S; Yamamoto, Satoshi; Toju, Hirokazu; Kohda, Masanori; Hori, Michio

2014-10-29

139

Possible effects of global climate change on the ecosystem of Lake Tanganyika  

Microsoft Academic Search

Any change in the air temperature, wind speed, precipitation, and incoming solar radiation induced by increasing greenhouse\\u000a gasses and climate change will directly influence lakes and other water bodies. The influence can cause changes in the physical\\u000a (water temperature, stratification, transparency), chemical (nutrient loading, oxygen) and biological (structure and functioning\\u000a of the ecosystem) components of the Lake. In this work

Jaya Naithani; Pierre-Denis Plisnier; Eric Deleersnijder

2011-01-01

140

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

NASA Astrophysics Data System (ADS)

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.

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

2006-12-01

141

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

NASA Astrophysics Data System (ADS)

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.

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

2000-01-01

142

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

SciTech Connect

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.

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

2000-01-01

143

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

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

Kazuhiko Takahashi; Yohey Terai; Mutsumi Nishida; Norihiro Okada

144

Social organization of a polygynous Cichlid Lamprologns furcifer in Lake Tanganyika  

Microsoft Academic Search

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

Yasunobu Yanagisawa

1987-01-01

145

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

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

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

2011-06-01

146

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)

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.

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

2004-12-01

147

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

PubMed

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

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

2011-03-01

148

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

PubMed Central

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

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

2015-01-01

149

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

PubMed

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

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

2010-05-01

150

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

PubMed

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

Hoerner, Marie E

2011-12-01

151

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

PubMed

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

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

2015-01-01

152

VERTICAL MIXING OF LAKE SEDIMENTS BY TUBIFICID OLIGOCHAETES  

EPA Science Inventory

Vertical mixing of lake sediments by tubificid oligochaetes was studied in laboratory experiments by using a radioactive (cesium 137 labeled sediment) marker horizon. Results from these experiments were used to develop and test a mathematical model describing tubificid sediment m...

153

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

E-print Network

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

Loon, E. Emiel van

154

Vertical distribution in and isolation of bacteria from Lake Vanda: an Antarctic lake  

Microsoft Academic Search

Vertical distribution of bacteria in Lake Vanda, an Antarctic meromictic lake, was examined by the acridine orange epifluorescence direct count method. Total bacteria were 104–105 cells · ml-1 in the water at 55 m depth and above, and increased drastically to 107 cells · ml-1 in the bottom water. Filamentous or long rodshaped bacteria occurred at a high frequency in

Susumu Takiil; Toshifumi Kondal; Akira Hiraishi; Genki I. Matsumoto; Tamio Kawano; Tetsuya Torii

1986-01-01

155

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)

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.

Moussa, Hesham Hussein Mohamed

2008-10-01

156

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

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

Wehrli, Bernhard

157

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

PubMed Central

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

Kilian, Esmari; Avenant-Oldewage, Annemariè

2013-01-01

158

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

PubMed

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

Kilian, Esmari; Avenant-Oldewage, Annemariè

2013-12-01

159

Dynamics of vertical mixing in a shallow lake with submersed macrophytes  

Microsoft Academic Search

A model for vertical turbulent diffusion and stratification in a shallow lake with submersed macrophytes is formulated on the basis of a one-dimensional equation for production, transport, and dissipation of turbulent kinetic energy, coupled with a vertical heat transfer equation. Numerical solutions of the coupled equations allow simulation of the hourly variation of water temperature profiles in a shallow lake

William R. Herb; Heinz G. Stefan

2005-01-01

160

Changing Planet: Warming Lakes  

NSDL National Science Digital Library

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.

Windows to the Universe/NBC Learn

161

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...

162

A Hydrodynamical Model for Calculating the Vertical Temperature Profile in Lakes During Cooling  

Microsoft Academic Search

A one-dimensional hydrodynamical model is used for simulating the vertical temperature profile in a lake during cooling conditions. The vertical mixing rate is calculated by solving the equations for turbulent kinetic energy, k, and dissipation of energy, E. The heat exchange between the water and atmos- phere consists of the radiation fluxes, sensible and latent heat flux. Tempera- ture measurements

Jorgen Sahlberg

1983-01-01

163

Vertical deformation and shallow seismicity around Lake Taupo, New Zealand, 1985–90  

Microsoft Academic Search

Vertical deformation and shallow seismicity around Lake Taupo, which occupies much of the Taupo Volcanic Centre, displayed two regionally distinct patterns during the 1985–90 study period. In the Taupo Fault Belt, north of the lake, there was aseismic sag. A high rate of relative subsidence of 10 ± 1 mm\\/yr resulted in inward tilt exceeding 1.0 ± 0.1 |?rad\\/yr, but

Peter M. Otway; Steven Sherburn

1994-01-01

164

Vertical distribution of larval fish in pelagic waters of southwest Lake Michigan: Implications for growth, survival, and dispersal  

Microsoft Academic Search

Due to variability in biotic and abiotic conditions along a vertical gradient within aquatic systems, the vertical distribution of larval fish can profoundly affect their growth and survival. In large systems such as the Great Lakes, vertical distribution patterns also can influence dispersal and ultimately settlement events. The objective was to describe the diel vertical distribution of the larval fish

Benjamin T. Martin; Sergiusz J. Czesny; David H. Wahl

2011-01-01

165

Vertically-challenged limnology; contrasts between deep and shallow lakes  

Microsoft Academic Search

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

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

1997-01-01

166

Horizontal and Vertical Structure of the Lake Turkana Jet  

Microsoft Academic Search

An observational study was undertaken at selected sites in north Kenya (Turkana channel) in February 1983 and in June-July 1984 to investigate the horizontal and vertical extent of the Turkana low-level jet. Observations indicate that strong winds exist throughout the channel but speeds decreased where the channel became wider. Two distinct jet streams, detached from each other, exist throughout the

Joseph Hiri Kinuthia

1992-01-01

167

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

E-print Network

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

Hofmann, Hans A.

168

Horizontal and Vertical Structure of the Lake Turkana Jet.  

NASA Astrophysics Data System (ADS)

An observational study was undertaken at selected sites in north Kenya (Turkana channel) in February 1983 and in June-July 1984 to investigate the horizontal and vertical extent of the Turkana low-level jet. Observations indicate that strong winds exist throughout the channel but speeds decreased where the channel became wider. Two distinct jet streams, detached from each other, exist throughout the channel except in Marsabit where they seem to have combined into a single, very high wind jet. Computations show that divergence is a predominant feature throughout the day but was more pronounced in the morning in both seasons. Anticyclonic and cyclonic vorticity existed in both seasons in the northern half and southern half of the channel, respectively, at lower levels. Finally, it is speculated that the Turkana jet could likely affect the easterly low-level jet in West Africa.

Kinuthia, Joseph Hiri

1992-11-01

169

Vertical distribution of a deep-water moss and associated epiphytes in Crater Lake, Oregon  

USGS Publications Warehouse

A one-person submersible was used to examine the vertical distribution of the deep-water moss Drepanocladus aduncus (Hedw.) Warnst in Crater Lake (Oregon). Living specimens were found attached to sediment and rocks at depths between 25 m and 140 m. Dense beds of the moss were observed at depths between 30 m and 80 m, a region that corresponded roughly to the zone of maximum primary production by phytoplankton. The moss population supported a diverse assemblage of epiphytic algae, of which the most abundant genera included Cladophora,Oedogonium, Rhizoclonium, Tribonema, Vaucheria, and the diatoms Cocconeis, Cymbella, Epithemia, Fragilaria, Gomphonema, Melosira, Navicula, and Synedra. Chemical and physical data supported the hypothesis that the lower limit of distribution of the moss is determined by light limitation, whereas the upper limit is related to the availability of nutrients, particularly nitrate-nitrogen and trace elements. Deep-water videotapes of the moss population indicated that D. aduncus with its epiphytic algae was abundant enough in regions associated with the metalimnion and upper hypolimnion to have a potential influence on the nutrient dynamics of the Crater Lake ecosystem. Although the maximum depth at which living bryophytes occur in Crater Lake is similar to that found for Lake Tahoe, conditions in Lake Tahoe allow the growth and survival of a much more diverse assemblage of bryophytes and charophytes than is present in Crater Lake.

McIntire, C.D.; Phinney, H.K.; Larson, Gary L.; Buktenica, M.W.

1994-01-01

170

Tracer experiment with sulfur hexafluoride to quantify the vertical transport in a meromictic pit lake  

Microsoft Academic Search

This paper describes a tracer experiment with sulfurhexafluoride (SF6) in the monimolimnion of the meromictic mining lake Merseburg-Ost 1b. In October 1998, 1.1 mmol (~ 160 mg) of the conservative gas SF6 was released at the site of greatest depth 3.5 m above the sediment to observe its vertical spreading. An easy-to-use system to collect ~0.5 L water samples using

Christoph von Rohden; Johann Ilmberger

2001-01-01

171

Vertical segregation and phylogenetic characterization of ammonia-oxidizing Archaea in a deep oligotrophic lake  

PubMed Central

Freshwater habitats have been identified as one of the largest reservoirs of archaeal genetic diversity, with specific lineages of ammonia-oxidizing archaea (AOA) populations different from soils and seas. The ecology and biology of lacustrine AOA is, however, poorly known. In the present study, vertical changes in archaeal abundance by CARD-FISH, quantitative PCR (qPCR) analyses and identity by clone libraries were correlated with environmental parameters in the deep glacial high-altitude Lake Redon. The lake is located in the central Spanish Pyrenees where atmospheric depositions are the main source of reactive nitrogen. Strong correlations were found between abundance of thaumarchaeotal 16S rRNA gene, archaeal amoA gene and nitrite concentrations, indicating an ammonium oxidation potential by these microorganisms. The bacterial amoA gene was not detected. Three depths with potential ammonia-oxidation activity were unveiled along the vertical gradient, (i) on the top of the lake in winter–spring (that is, the 0?oC slush layers above the ice-covered sheet), (ii) at the thermocline and (iii) the bottom waters in summer—autumn. Overall, up to 90% of the 16S rRNA gene sequences matched Thaumarchaeota, mostly from both the Marine Group (MG) 1.1a (Nitrosoarchaeum-like) and the sister clade SAGMGC?1 (Nitrosotalea-like). Clone-libraries analysis showed the two clades changed their relative abundances with water depth being higher in surface and lower in depth for SAGMGC?1 than for MG 1.1a, reflecting a vertical phylogenetic segregation. Overall, the relative abundance and recurrent appearance of SAGMGC?1 suggests a significant environmental role of this clade in alpine lakes. These results expand the set of ecological and thermal conditions where Thaumarchaeota are distributed, unveiling vertical positioning in the water column as a key factor to understand the ecology of different thaumarchaeotal clades in lacustrine environments. PMID:22495069

Auguet, Jean-Christophe; Triadó-Margarit, Xavier; Nomokonova, Natalya; Camarero, Lluís; Casamayor, Emilio O

2012-01-01

172

Vertical segregation and phylogenetic characterization of ammonia-oxidizing Archaea in a deep oligotrophic lake.  

PubMed

Freshwater habitats have been identified as one of the largest reservoirs of archaeal genetic diversity, with specific lineages of ammonia-oxidizing archaea (AOA) populations different from soils and seas. The ecology and biology of lacustrine AOA is, however, poorly known. In the present study, vertical changes in archaeal abundance by CARD-FISH, quantitative PCR (qPCR) analyses and identity by clone libraries were correlated with environmental parameters in the deep glacial high-altitude Lake Redon. The lake is located in the central Spanish Pyrenees where atmospheric depositions are the main source of reactive nitrogen. Strong correlations were found between abundance of thaumarchaeotal 16S rRNA gene, archaeal amoA gene and nitrite concentrations, indicating an ammonium oxidation potential by these microorganisms. The bacterial amoA gene was not detected. Three depths with potential ammonia-oxidation activity were unveiled along the vertical gradient, (i) on the top of the lake in winter-spring (that is, the 0?(o)C slush layers above the ice-covered sheet), (ii) at the thermocline and (iii) the bottom waters in summer-autumn. Overall, up to 90% of the 16S rRNA gene sequences matched Thaumarchaeota, mostly from both the Marine Group (MG) 1.1a (Nitrosoarchaeum-like) and the sister clade SAGMGC-1 (Nitrosotalea-like). Clone-libraries analysis showed the two clades changed their relative abundances with water depth being higher in surface and lower in depth for SAGMGC-1 than for MG 1.1a, reflecting a vertical phylogenetic segregation. Overall, the relative abundance and recurrent appearance of SAGMGC-1 suggests a significant environmental role of this clade in alpine lakes. These results expand the set of ecological and thermal conditions where Thaumarchaeota are distributed, unveiling vertical positioning in the water column as a key factor to understand the ecology of different thaumarchaeotal clades in lacustrine environments. PMID:22495069

Auguet, Jean-Christophe; Triadó-Margarit, Xavier; Nomokonova, Natalya; Camarero, Lluís; Casamayor, Emilio O

2012-09-01

173

[Vertical distribution of PBDEs and DL-PCBs in sediments of Taihu Lake].  

PubMed

Sediment core samples collected from the Zhushan Bay, Meiliang Bay, South Taihu of Taihu Lake were analyzed for 8 polybrominated diphenylethers (PBDEs) and 12 dioxin-like PCBs (DL-PCBs). The results revealed that the PBDEs levels were highest in the Zhushan Bay, followed by Meiliang Bay and South Taihu; and the DL-PCB levels were highest in the Meiliang Bay, followed Zhushan Bay and South Taihu. The vertical distribution of PBDEs level showed an exponential growth trend in Taihu Lake sediments, BDE-209 was the most abundant PBDEs congeners; and the vertical distribution of the DL-PCBs level in the sediments revealed that the contamination caused by DL-PCBs continued to increase in recent years, indicating that there were PCBs sources in the Taihu Lake region. There was significant difference in the composition of PBDEs congeners at different depths in the sediments of Meiliang Bay, however, the detailed causes remain to be investigated in further studies. The vertical distribution pattern of PCBs congeners revealed that PCB-77, -118, -105 levels significantly decreased with increasing depth in 0-15 cm upper sediments and there chang in the lower sediments. PMID:23745425

Ma, Zhao-Hui; Jin, Jun; Qi, Xue-Kui; Wang, Ying; Jiang, Xia; He, Song-Jie; Li, Ming-Yuan

2013-03-01

174

Seasonally Dynamic Diel Vertical Migrations of Mysis diluviana, Coregonine Fishes, and Siscowet Lake Trout in the Pelagia of Western Lake Superior  

Microsoft Academic Search

Diel vertical migrations are common among many aquatic species and are often associated with changing light levels. The underlying mechanisms are generally attributed to optimizing foraging efficiency or growth rates and avoiding predation risk (?). The objectives of this study were to (1) assess seasonal and interannual changes in vertical migration patterns of three trophic levels in the Lake Superior

Tyler D. Ahrenstorff; Thomas R. Hrabik; Jason D. Stockwell; Daniel L. Yule; Greg G. Sass

2011-01-01

175

Removal of nutrients from combined sewer overflows and lake water in a vertical-flow constructed wetland system  

Microsoft Academic Search

Lake Utterslev is situated in a densely built-up area of Copenhagen, and is heavily eutrophicated from combined sewer overflows. At the same time the lake suffers from lack of water. Therefore, a 5,000 m2 vertical flow wetland system was constructed in 1998 to reduce the phosphorus discharge from combined sewer overflows without reducing the water supply to the lake. During

L. Gervin; H. Brix

176

Vertical distribution of major sulfate-reducing bacteria in a shallow eutrophic meromictic lake.  

PubMed

The vertical distribution of sulfate-reducing bacteria was investigated in a shallow, eutrophic, meromictic lake, Lake Harutori, located in a residential area of Kushiro, Japan. A steep chemocline, characterized by gradients of oxygen, sulfide and salinity, was found at a depth of 3.5-4.0 m. The sulfide concentration at the bottom of the lake was high (up to a concentration of 10.7 mM). Clone libraries were constructed using the aprA gene, which encodes adenosine-5'-phosphosulfate reductase subunit A, in order to monitor sulfate-reducing bacteria. In the aprA clone libraries, the most abundant sequences were those from the Desulfosarcina-Desulfococcus (DSS) group. A primer set for a DSS group-specific 16S rRNA gene was used to construct another clone library, analysis of which revealed that the uncultured group of sulfate-reducing bacteria, SEEP SRB-1, accounted for nearly half of the obtained sequences. Quantification of the major bacterial groups by catalyzed reporter deposition-fluorescence in situ hybridization demonstrated that the DSS group accounted for 3.2-4.8% of the total bacterial community below the chemocline. The results suggested that the DSS group was one of the major groups of sulfate-reducing bacteria and that these presumably metabolically versatile bacteria might play an important role in sulfur cycling in Lake Harutori. PMID:25034383

Kubo, Kyoko; Kojima, Hisaya; Fukui, Manabu

2014-10-01

177

Vertical distribution of microbial communities in a perennially stratified Arctic lake with saline, anoxic bottom waters  

PubMed Central

Meromictic lakes are useful biogeochemical models because of their stratified chemical gradients and separation of redox reactions down the water column. Perennially ice-covered meromictic lakes are particularly stable, with long term constancy in their density profiles. Here we sampled Lake A, a deep meromictic lake at latitude 83°N in High Arctic Canada. Sampling was before (May) and after (August) an unusual ice-out event during the warm 2008 summer. We determined the bacterial and archaeal community composition by high-throughput 16S rRNA gene tag-pyrosequencing. Both prokaryote communities were stratified by depth and the Bacteria differed between dates, indicating locally driven selection processes. We matched taxa to known taxon-specific biogeochemical functions and found a close correspondence between the depth of functional specialists and chemical gradients. These results indicate a rich microbial diversity despite the extreme location, with pronounced vertical structure in taxonomic and potential functional composition, and with community shifts during ice-out. PMID:22930670

Comeau, André M.; Harding, Tommy; Galand, Pierre E.; Vincent, Warwick F.; Lovejoy, Connie

2012-01-01

178

Comparison of the Tanganyika, Malawi, Rukwa and Turkana Rift zones from analyses of seismic reflection data  

NASA Astrophysics Data System (ADS)

Northwest-southeast extension has opened the East African Rift System along two main branches, the Western and Eastern Branches. Rift zones along the Western Branch are marked by narrow lakes floored by thick piles of fluvial clastic and 'pelagic' sediment. Magmatism is restricted to a few small areas in the 'arches' between the lakes. In contrast, rift zones along the Eastern Branch are largely filled with volcanic and volcaniclastic materials and magmatism is generally perceived to be an integral part of the rifting process. In an attempt to sort out the significance and meaning of these and other differences, we have compared multifold seismic data from three Western Branch rift zones (Tanganyika, Rukwa and Malawi) and one Eastern Branch zone (Turkana). The Tanganyika and Malawi Rift Zones are composed of half-graben basins linked in complex ways by accommodation zones which generally trend oblique to the rift axes, and sometimes oblique to the extension direction. Half-grabens alternate basinal polarities where the rift crosses Proterozoic dislocation zones. Complex fault geometries are associated with some accommodation zones; elsewhere faults are almost exclusively planar. Sedimentary fill reaches at least 4-5 km and the section is mostly Cenozoic in age. Patches of Permo-Triassic sedimentary rocks are believed to occur within both rift zones. The Rukwa Rift is a pull-apart zone that connects the northern (Livingstone) basin of Lake Malawi to the Kalemie Basin in central Lake Tanganyika. The entire pull-apart system may be a series of down-to-the-east half-grabens. An accommodation zone develops along a short stretch of the Rukwa Rift, but no full polarity reversal occurs. The break-away faults of the Livingstone, Rukwa and Kalemie basins are essentially coincident with the Proterozoic Rukwa dislocation zone, which sub-parallels the inferred extension direction. Fault geometries in the Rukwa Rift are markedly listric, especially in the pre-Cenozoic section. Sedimentary fill ranges in age from pre-Karroo through Cenozoic and locally exceeds 10 km in thickness. The Turkana Rift is composed of short, linear, NNE-trending normal fault segments that are offset in a left-lateral sense by numerous, NW-SE trending transfer faults, linking facing border fault segments together. The overall trend of the rift zone is oblique to the opening direction, like the Tanganyika and Malawi cases, but the border fault segments are sub-perpendicular. Fault geometries are highly variable, but flower structures associated with transfer faults predominate. Igneous activity is ubiquitous and appears to be localized along the transfer faults. Basin fill reaches 4-5 km in thickness and is dominated by fluvial clastic, volcaniclastic and volcanic materials. The structural differences within the Tanganyika-Rukwa-Malawi system stem mainly from the modifying effects of pre-rift anistropies on strain expressions. Fundamentally, this system is a NW-SE trending series of single-polarity pull-apart basins. At the two ends of the pull-apart zone, the rift is deflected into more N-S trending basins which have a high tendency to alternate polarities along strike. This explanation does not account for the differences in fault forms between the Tanganyika-Malawi (planar) and Rukwa (listric) Rifts. For the time being, we presume these differences arise from systematic differences between Tanganyika-Malawi and Rukwa in the age ranges of the fill and/or the maximum depths of seismic imaging. Rifting in Turkana is profoundly different than in the Tanganyika-Rukwa-Malawi sub-branch and seems to involve a softer, more ductile, more organized style of extension which may be closer to the ideal case. In a thermal sense, rifting has progressed further in Turkana than along the Western Branch zones. This does not preclude original, fundamental difference in the thermal states of two branches.

Rosendahl, Bruce R.; Kilembe, Elias; Kaczmarick, Kurt

1992-10-01

179

Carbonatitic volcanic ashes in Northern Tanganyika  

Microsoft Academic Search

In the Neogene volcanic province of Northern Tanganyika are surface limestones which cover large areas, despite variation and unsuitability of the bedrock. Field mapping has proved the existence of bedded carbonate tuffs dipping off Recent vents, and the field relationships and the trace element analyses prove the tuffs to be carbonatitic. Trace element analyses of some of the «surface limestones»

J. B. Dawson

1964-01-01

180

Carbonatitic volcanic ashes in Northern Tanganyika  

Microsoft Academic Search

In the Neogene volcanic province of Northern Tanganyika are surface limestones which cover large areas, despite variation\\u000a and unsuitability of the bedrock. Field mapping has proved the existence of bedded carbonate tuffs dipping off Recent vents,\\u000a and the field relationships and the trace element analyses prove the tuffs to be carbonatitic. Trace element analyses of some\\u000a of the «surface limestones»

J. B. Dawson

1964-01-01

181

Algorithmic identification of limnological features in vertical profiles from the Great Lakes  

NASA Astrophysics Data System (ADS)

High volume collection of environmental data in digital format presents a range of challenges for the researcher, from quality control and data management to efficient interpretation of the signal and the development of requisite information technology skills. These challenges have been termed the "data deluge". To aid in efficient data interpretation, we describe several algorithmic approaches for feature identification in signal streams, including gradient estimation, spectral analysis, and the hidden Markov model. These approaches are calibrated and evaluated over vertical temperature profiles from the Great Lakes obtained through the U.S. Environmental Protection Agency. To demonstrate the value of this data science approach, we describe how the algorithms can be integrated with the historical sampling record to yield an expert system that assists field technicians with adaptive sampling.

Wietsma, T.; Collingsworth, P.; Minsker, B. S.

2013-12-01

182

Empirical evaluation of predator-driven diel vertical migration in Lake Superior  

USGS Publications Warehouse

Recent studies on Lake Superior suggest that diel vertical migration (DVM) of prey (generalized Coregonus spp.) may be influenced by the density of predatory siscowet (Salvelinus namaycush). We empirically evaluated this hypothesis using data from acoustic, midwater trawl, and bottom trawl sampling at eight Lake Superior sites during three seasons in 2005 and a subset of sites in 2006. We expected the larger-bodied cisco (Coregonus artedi) to exhibit a shallower DVM compared with the smaller-bodied kiyi (Coregonus kiyi). Although DVM of kiyi and cisco were consistent with expectations of DVM as a size-dependent, predator-mediated process, we found no relationship between siscowet density and the magnitude of DVM of either coregonid. Cisco appear to have a size refuge from siscowet predation. Kiyi and siscowet co-occur in demersal habitat > 150 m during the day, where visual predation is unlikely, suggesting predator avoidance is not a factor in the daytime distribution of kiyi. Seasonal patterns of kiyi DVM were consistent with reported DVM of their primary prey Mysis relicta. Our results suggest that consideration of nonvisual foraging, rather than lightbased foraging theory (i.e., the antipredation window), is necessary to understand the processes driving DVM in deepwater systems.

Stockwell, J.D.; Hrabik, T.R.; Jensen, O.P.; Yule, D.L.; Balge, M.

2010-01-01

183

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

USGS Publications Warehouse

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.

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

2012-01-01

184

Analyses of the vertical and temporal distribution of sulfate-reducing bacteria in Lake Aha (China)  

NASA Astrophysics Data System (ADS)

In April and September of 2005, two sediment cores were collected from Lake Aha, which is polluted by the acid mine drainage of the mining industries. Sulfate-reducing bacteria (SRB) groups and their quantity were analyzed by using PCR and FISH (fluorescence in situ hybridization), respectively. The results showed that four SRB groups ( Desulfotomaculum, Desulfobulbus, Desulfococcus Desulfonema Desulfosarcina and Desulfovibrio Desulfomicrobium) were detected in September, while only three SRB groups ( Desulfotomaculum, Desulfobulbus and Desulfococcus Desulfonema Desulfosarcina) were detected in April. Desulfovibrio Desulfomicrobium was not detected and was expected to exist inactively, in April. Meanwhile, the distribution of every SRB group was wider in September than in April. The results indicated that different SRB groups had different vertical and temporal distribution. The vertical and temporal distribution of SRB was mainly in the upper sediments, and the number of SRB groups and quantity were larger in September than in April. It suggested that the environmental conditions of sediments in September were more suitable for SRB.

Wang, M. Y.; Liang, X. B.; Yuan, X. Y.; Zhang, W.; Zeng, J.

2008-03-01

185

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

SciTech Connect

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.

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

1994-07-01

186

Mesoscale Patterns of Rainfall, Cloudiness and Evaporation over the Great Lakes of East Africa  

Microsoft Academic Search

By employing remote sensing techniques, the characteristics of rainfall, cloudiness and evaporation over Lakes Victoria, Tanganyika and Malawi are studied. There exist diurnal cycles induced by the interaction between lake\\/land breeze and the lower level southeasterlies over each lake, particularly Lake Victoria. Generally, maximum convection\\/rainfall is in the night to early morning on the west side of the lake while

SHARON E. NICHOLSON; Xungang Yin

187

Fish communities in the African Great Lakes  

Microsoft Academic Search

Ecological conditions in tropical lacustrine systems are considered by focusing on the evolution, maintenance, exploitation and vulnerability of fish communities in the African Great Lakes. The exceptionally high biodiversities in the littoral\\/sublittoral zones of the very ancient, deep, clear, permanently stratified rift lakes Tanganyika and Malawi, are contrasted with the simpler systems in their pelagic zones, also with biodiversity in

Rosemary Lowe-McConnell

1996-01-01

188

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

Microsoft Academic Search

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

W. N. Probst; R. Eckmann

2009-01-01

189

Vertical physico-chemical gradients with distinct microbial communities in the hypersaline and heliothermal Lake Ursu (Sovata, Romania).  

PubMed

The effect of vertical physico-chemical stratification on the planktonic microbial community composition of the deep, hypersaline and heliothermal Lake Ursu (Sovata, Romania) was examined in this study. On site and laboratory measurements were performed to determine the physical and chemical variables of the lake water, and culture-based and cultivation-independent techniques were applied to identify the members of microbial communities. The surface of the lake was characterized by a low salinity water layer while the deepest region was extremely saline (up to 300 g/L salinity). Many parameters (e.g. photosynthetically active radiation, dissolved oxygen concentration, pH, redox potential) changed dramatically from 2 to 4 m below the water surface in conjunction with the increasing salinity values. The water temperature reached a maximum at this depth. At around 3 m depth, there was a water layer with high (bacterio) chlorophyll content dominated by Prosthecochloris vibrioformis, a phototrophic green sulfur bacterium. Characteristic microbial communities with various prokaryotic taxa were identified along the different environmental parameters present in the different water layers. Some of these bacteria were known to be heterotrophic and therefore may be involved in the decomposition of lake organic material (e.g. Halomonas, Idiomarina and Pseudoalteromonas) while others in the transformation of sulfur compounds (e.g. Prosthecochloris). Eukaryotic microorganisms identified by molecular methods in the lake water belonged to genera of green algae (Mantionella and Picochlorum), and were restricted mainly to the upper layers. PMID:24531691

Máthé, István; Borsodi, Andrea K; Tóth, Erika M; Felföldi, Tamás; Jurecska, Laura; Krett, Gergely; Kelemen, Zsolt; Elekes, Erzsébet; Barkács, Katalin; Márialigeti, Károly

2014-05-01

190

Densities and Diel Vertical Migration of Mysis relicta in Lake Superior: A Comparison of Optical Plankton Encounter and Net-based Approaches  

EPA Science Inventory

In this study, we used data from an OPC, and LOPC, and vertical net tows to estimate densities and describe the day/night vertical distribution of Mysis at a series of stations distributed throughout Lake Superior, and to evaluate the efficacy of using (L)OPC for examining DVM of...

191

Vertical diversity of sediment bacterial communities in two different trophic states of the eutrophic Lake Taihu, China.  

PubMed

Vertical diversity of sediment bacterial communities in 2 different trophic states (macrophyte-dominated and algae-dominated) of the large shallow eutrophic Lake Taihu, China, were investigated using denaturing gradient gel electrophoresis (DGGE) and 16S rRNA sequence analysis. Clustering analysis of DGGE profiles showed that different clusters were recognized in different depths of sediment cores in the 2 lake trophic states. Analyses of the bacterial diversity, as estimated by the Shannon index (H'), showed that different sediment layers of the macrophyte-dominated state had higher diversity than the algae-dominated state. In addition, bacterial diversity of the sediment in the macrophyte-dominated state changed abruptly throughout the layers, but bacterial diversity of the algae-dominated state decreased gradually with sediment depth. Phylogenetic analysis showed that Proteobacteria was the most abundant phylum in the middle sediment of the 2 lake trophic states. In the macrophyte-dominated state, clone sequences related to Betaproteobacteria (50.0%) were the most abundant, followed by Epsilonproteobacteria (21.1%), Acidobacteria (7.9%), Deltaproteobacteria (7.9%), Chloroflexi (7.9%), and Bacteroidetes (5.3%); whereas in the algae-dominated state, sequences affiliated with Betaproteobacteria (84.4%) were predominant, followed by Deltaproteobacteria (12.5%) and Acidobacteria (3.1%). Canonical correspondence analysis showed that organic matter and pH play key roles in driving the vertical changes of bacterial community composition. PMID:24191609

Shao, Keqiang; Gao, Guang; Wang, Yongping; Tang, Xiangming; Qin, Boqiang

2013-06-01

192

Model simulations of the influence of synoptic conditions on vertical motions in the Salt Lake City region  

SciTech Connect

The Salt Lake City basin is one of a number of broad valleys in northern Utah. It was the location of the Vertical Transport and Mixing (VTMX) program field experiment in October of 2000, and it is an area that has experienced urban air quality problems within the basin. During this experiment, flow through the Jordan Narrows, the gap in the Traverse Range that divides the Salt Lake basin from the Utah basin to the south, was found to be significant, in addition to the known night time drainage from canyons that enter the valley from the east. In earlier studies, similar flow through a gap has been found to exist between the Tooele and Rush Valleys, just to the west. The earlier studies also indicated flows, through passes, between the Rush Valley and the valleys to its east. This paper will present the results of numerical simulations of the Salt Lake City Basin and the surrounding region, including the Utah, Tooele, and Rush Valleys. The discussion will focus on how the circulations within the Salt Lake City basin are influenced by flows that enter or exit the basin from nearby canyons and basins. We will also investigate the role of synoptic weather conditions in this exchange.

Costigan, K. R. (Keeley R.)

2002-01-01

193

The vertical variation of nutrients in a sediment core of Delong Lake reveals the anthropogenic effect.  

PubMed

Phosphorus content and its species were studied for the core sediments of Delong Lake, using the SMT sequential extraction method, and then were correlated to the contents of total nitrogen and organic matter. According to (210)Pb and (137)Cs dating, the historical profiles of 33 cm core sediments were generated. The objective of this study was to understand how nutrients of lake sediments evolved in order to get insights into the effect of human activities on their sedimentary history. The nutrients contents in the core sediments slowly increased after 1957, showing the human activity influence the natural deposition of the lake sediment. From 1978 to 1985, various nutrients in the lake sediment rapid increased, showing that the human activities strengthened. From 2003 to now, most of nutrients in the sediment rapidly increased and significantly modified the natural deposition of the lake sediment. PMID:24468926

Guan, Ying; Zang, Shuying; Xiao, Haifeng

2014-05-01

194

Stratification of Archaea in the Deep Sediments of a Freshwater Meromictic Lake: Vertical Shift from Methanogenic to Uncultured Archaeal Lineages  

PubMed Central

As for lineages of known methanogens, several lineages of uncultured archaea were recurrently retrieved in freshwater sediments. However, knowledge is missing about how these lineages might be affected and structured according to depth. In the present study, the vertical changes of archaeal communities were characterized in the deep sediment of the freshwater meromictic Lake Pavin. For that purpose, an integrated molecular approach was performed to gain information on the structure, composition, abundance and vertical stratification of archaeal communities thriving in anoxic freshwater sediments along a gradient of sediments encompassing 130 years of sedimentation. Huge changes occurred in the structure and composition of archaeal assemblages along the sediment core. Methanogenic taxa (i.e. Methanosaeta and Methanomicrobiales) were progressively replaced by uncultured archaeal lineages (i.e. Marine Benthic Group-D (MBG-D) and Miscellaneous Crenarchaeal Group (MCG)) which are suspected to be involved in the methane cycle. PMID:22927959

Borrel, Guillaume; Lehours, Anne-Catherine; Crouzet, Olivier; Jézéquel, Didier; Rockne, Karl; Kulczak, Amélie; Duffaud, Emilie; Joblin, Keith; Fonty, Gérard

2012-01-01

195

Estimate of the vertical plankton biomass profile on the basis of measurements of fluorescent characteristics in pelagial of Lake Baikal  

NASA Astrophysics Data System (ADS)

We study the effect of physical, chemical and biological processes on gas exchange of CO2 in the air-water system in Lake Baikal. Photosynthesis of aquatic biota is known to play a crucial role in changing the concentration of carbon dioxide in the water. Fluorescent methods are considered to be of high performance in problems of determining quantitative characteristics of biomass, however they require preliminary calibration directly for a specific type of plankton. In the pelagic zone of Lake Baikal the species composition, quantitative and spatial distribution of phytoplankton are characterized by strong spatial and temporal variability. Therefore, the fluorescent devices calibration on a single reference does not provide acceptable accuracy of quantitative assessment of the biomass. The results discussed in the paper were obtained by shipboard measurements during the Baikal campaign of 2010-2011. Correlation between the biomass in 25-meter water layer and the integral value of the fluorescent signal in this layer was obtained for calibration. The report discusses the advantages and disadvantages of the chosen methods and the results of retrieval of the vertical profiles of the biomass for stations in the pelagic zone of Lake Baikal in spring for the 2010-2011 biennium.

Panchenko, Mikhail V.; Sakirko, Maria V.; Usoltseva, Marina V.; Popovskaya, Galina I.; Domysheva, Valentina M.; Shimaraev, Mikhail N.; Zavoruev, Valerii V.; Pestunov, Dmitrii A.

2014-11-01

196

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

NASA Astrophysics Data System (ADS)

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.

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

2006-12-01

197

two stream reaches on the Northeastern Shore of Lake Tanganyika  

E-print Network

Water provides invaluable services to humanity including drinking water, waste dilution, fisheries, irrigation, and power generation (Wetzel 2001). However the exponential growth of human population puts a severe strain on this finite resource. Agricultural, pastoral, building, and industrial activities tend to

unknown authors

198

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

Microsoft Academic Search

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

MASAYUKI TAKAHASHI; SHUN-EI ICHIMURA

1968-01-01

199

The invasive predator Bythotrephes induces changes in the vertical distribution of native copepods in Lake Michigan  

Microsoft Academic Search

Invasive predators can have large negative effects on native prey populations. The susceptibility of native prey to invasive\\u000a predators may depend on their ability to respond behaviorally to the presence of these non-native predators. In a field survey\\u000a conducted in Lake Michigan over several years, we found that high densities of the invasive predatory cladoceran Bythotrephes were correlated with lower

Paul E. Bourdeau; Kevin L. Pangle; Scott D. Peacor

200

Damaging UV radiation and invertebrate predation: conflicting selective pressures for zooplankton vertical distribution in the water column of low DOC lakes  

Microsoft Academic Search

In nature most organisms have to manage conflicting demands of food gathering, predator avoidance, and finding a favorable abiotic environment (oxygen, temperature, etc.) in order to maximize their fitness. In the vertical water column of lakes with high solar ultraviolet radiation (UV) and invertebrate predators, zooplankton face two particularly strong and conflicting selective pressures. During daylight hours invertebrate predators often

Wiebke J. Boeing; Dina M. Leech; Craig E. Williamson; Sandra Cooke; Lisette Torres

2004-01-01

201

Effects of oxygen, temperature and light gradients on the vertical distribution of rainbow trout, Oncorhynchus mykiss, in two North Island, New Zealand, lakes differing in trophic status  

Microsoft Academic Search

Vertical distributions of adult rainbow trout (> 25 cm fork length, FL) were determined with a SIMRAD ES470 split?beam echosounder in two 80–90 m deep lakes differing in water quality. Between November 1993 and February 1994, most trout (> 80%) were between 10 and 40 m, within or close to the thermocline. However, a small group of fish occupied colder

D. K. Rowe; B. L. Chisnall

1995-01-01

202

Vertical Distribution of Fish Biomass in Lake Superior: Implications for Day Bottom Trawl Surveys  

Microsoft Academic Search

Evaluation of the biases in sampling methodology is essential for understanding the limitations of abundance and biomass estimates of fish populations. Estimates from surveys that rely solely on bottom trawls may be particularly vulnerable to bias if pelagic fish are numerous. We evaluated the variability in the vertical distribution of fish biomass during the U.S. Geological Survey's annual spring bottom

Jason D. Stockwell; Daniel L. Yule; Thomas R. Hrabik; Jean V. Adams; Owen T. Gorman; Beth V. Holbrook

2007-01-01

203

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

PubMed Central

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

Wardiatno, Yusli; Krisanti, Majariana

2013-01-01

204

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...

205

Mercury methylation along a lake-forest transect in the Tapajós river floodplain, Brazilian Amazon: seasonal and vertical variations.  

PubMed

The seasonal and spatial variations of net methylmercury production in sediments, soils and other sites were evaluated by assays with 203Hg at different depths and locations along a lake-forest transect at lake Enseada Grande, Tapajós river. Soil and sediment samples were taken at the surface and at different depths up to 9 cm. Fresh samples and acidified controls (1-3 g dry wt.) were slurried with local water and incubated in the dark at 25-28 degrees C for 3 days with 0.5-1.6 microg Hg g(-1) (dry wt.) added as 203HgCl2. CH3 203Hg was extracted and measured in scintillation cocktail after acid leaching. Methylmercury production varied by orders of magnitude among sites and among sediment or soil layers. Seasonal variations were smaller than those with sample depth and location. In both seasons, MeHg formation in sediment and soil or flooded soil decreased with depth and was, in the top layers, one order of magnitude higher in the C-rich littoral macrophyte zone (2.3-8.9%) and flooded forest (3.2-4.5%) than in the center of the lake (0.2-0.56%). Similar MeHg production was found in slurried dry soils (dry season) and in soils already flooded for months. In the macrophyte zone soil (dry season), methylation was mainly associated with the thin Paspalum sp. rootlet layer. In the forest site, vertical variation in methylation was less pronounced in flooded than in dry soils and during the inundation the higher methylation rate was found in the flocculent sediment settled over the litter layer. The roots of floating Paspalum sp. were an important Hg methylation site, particularly those heavily colonized with periphyton (3.4-5.4%). Methylation in surface or near-bottom water was undetectable (< 3 x 10(-2)%) at all sites. Flooded forests and macrophyte mats are specific features of the Amazon and are important links between Hg inputs from natural and manmade sources and MeHg exposure of local populations through fish intake. PMID:11036980

Guimarães, J R; Roulet, M; Lucotte, M; Mergler, D

2000-10-16

206

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)

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.

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

2013-02-01

207

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)

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.

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

2012-07-01

208

The vertical and seasonal distribution of chlorophyll in lakes of the Experimental Lakes Area, northwestern Ontario: Implications for primary production estimates  

Microsoft Academic Search

An in vivo flow-through fluorometer system revealed narrow bands of very high chloro- phyll concentrations in the meta- or hypolimnia of all clear, stratified ELA lakes. In two experimentally fertilized lakes chlorophyll concentrations in the hypolimnion exceeded 366 ,ug liter-l while epilimnetic chlorophyll was only 3 pg liter-'. The hypolimnetic bloom rep- resented the major response to enhanced nutrient loading.

EVERETT J. FEE

1976-01-01

209

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

PubMed Central

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

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

210

Geomagnetic polarity epochs: new data from Olduvai Gorge, Tanganyika  

USGS Publications Warehouse

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.

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

1967-01-01

211

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

PubMed

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

Probst, W N; Eckmann, R

2009-01-01

212

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

Microsoft Academic Search

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

Eric O. Odada; Daniel O. Olago

2006-01-01

213

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

NASA Astrophysics Data System (ADS)

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.

Ponchaut, Frédérique; Cazenave, Anny

1998-01-01

214

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

NASA Astrophysics Data System (ADS)

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).

Van Damme, D.; Gautier, A.

2013-09-01

215

Lidar vertical profiling of water vapor and aerosols in the Great Lakes Region: A tool for understanding lower atmospheric dynamics  

NASA Astrophysics Data System (ADS)

Results of a recently developed water vapor Raman lidar instrument at Environment Canada's Center for Atmospheric Research Experiments (CARE) are shown for selected days of summer and winter seasons. The basic components of the Raman water vapor lidar consist of a 30 Hz, Q-switched Nd:YAG high-powered laser utilizing the third harmonic (355 nm), beam steering optics, a 0.76 m Cassegrain telescope and three detection channels to simultaneously observe the vertical profiles of aerosols, water vapor, and nitrogen from near ground up to 9.5 km. By manipulating the inelastic backscattering lidar signals from the Raman nitrogen channel (386.7 nm) and Raman water vapor channel (407.5 nm), vertical profiles of water vapor mixing ratio (WVMR) are deduced, calibrated, and compared against WVMR profiles obtained from coincident and collocated radiosonde profiles. The average standard deviation, in the water vapor mixing ratio, is estimated to be less than 10% between the sonde and lidar measurements. In addition, comparisons between simultaneous WVMR profiles and aerosol profiles obtained from a simple aerosol backscatter lidar, also located at the CARE facility, provide insight into the complex dynamic mixing of the lower atmosphere and their subsequent impact on climate and air quality.

Al-Basheer, Watheq; Strawbridge, Kevin B.

2015-02-01

216

Evolution in ancient lakes: radiation of Tanganyikan atyid prawns and speciation of pelagic cichlid fishes in Lake Malawi  

Microsoft Academic Search

Atyid prawns from Lake Tanganyika are still poorly understood. There are at least 11 species sharing an exceptionally small\\u000a size and a reduction in the number of branchiae. The majority are benthic although some are pelagic. This is reflected in\\u000a different morphologies of the body and walking legs. Morphological adaptions of the denticles on the chelipeds are adaptive\\u000a as they

Geoffrey Fryer

2006-01-01

217

Q&A with Tanganyika Wilder, 2009-2010 Porter Physiology Development Fellow  

NSDL National Science Digital Library

A biography written by Tanganyika Wilder, a graduate student in the Department of Physiology and Biophysics at the University of Illinois at Chicago. This Q&A-style biosketch describes Ms. WilderÃÂs interest in science and what led her to a career in physiology.

2011-12-02

218

Climate Change Affects the East African Rift Valley Lakes  

NASA Astrophysics Data System (ADS)

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.

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

2004-12-01

219

Ph. Branchu and Laurent Bergonzini Hydrology and Earth System Sciences, 8(2), 256265 (2004) EGU  

E-print Network

) © EGU Chloride concentrations in Lake Tanganyika: an indicator of the hydrological budget? Philippe the effect of hydroclimatic variations on the surface water salinity of Lake Tanganyika, the largest African budget, hydrochemical budget, Lake Tanganyika, limnology, salinity Introduction Lake Tanganyika

Boyer, Edmond

220

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

221

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

Microsoft Academic Search

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

J. Versfelt; B. R. Rosendahl

1989-01-01

222

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

PubMed Central

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

Takeuchi, Yuichi; Hori, Michio; Oda, Yoichi

2012-01-01

223

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

PubMed

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

Takeuchi, Yuichi; Hori, Michio; Oda, Yoichi

2012-01-01

224

A brood parasitic catfish of mouthbrooding cichlid fishes in Lake Tanganyika  

Microsoft Academic Search

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

Tetsu Sato

1986-01-01

225

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

Microsoft Academic Search

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

E. Michel

2000-01-01

226

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

Microsoft Academic Search

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

Tetsuo Kuwamura

1992-01-01

227

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

PubMed

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

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

2014-12-01

228

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

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

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

229

Rapid dispersal and establishment of a benthic Ponto-Caspian goby in Lake Erie: diel vertical migration of early juvenile round goby  

Microsoft Academic Search

The round goby, Apollonia melanostoma, a molluscivore specialist, was introduced to the Great Lakes in the early 1990s and rapidly expanded its distribution, especially\\u000a in Lake Erie. Adult round goby morphology suggests low dispersal and migration potential due to the lack of a swim bladder\\u000a and benthic life style. Given that the larval stage occurs inside the benthic egg, and

Todd A. Hayden; Jeffrey G. Miner

2009-01-01

230

Discovery of sublacustrine hydrothermal activity and associated massive sulfides and hydrocarbons in the north Tanganyika trough, East African Rift  

NASA Astrophysics Data System (ADS)

Massive sulfides and carbonate mineral deposits associated with sublacustrine thermal springs were recently discovered along the Zaire side of the north Tanganyika trough, western branch of the East African Rift. This hydrothermal activity, investigated by scuba diving at a maximum depth of 20 m, is located at the intersection of major north-south normal faults and northwest-southeast faults belonging to the Tanganyika-Rukwa-Malawi (TRM) strike-slip fault zone. The preliminary results presented here come from analyses of sulfide deposits, hydrothermal fluids, and associated hydrocarbons that result from geothermal activity in this part of the East African Rift filled by a thick pile of sediment, the north Tanganyika trough.

Tiercelin, Jean-Jacques; Thouin, Catherine; Kalala, Tchibangu; Mondeguer, André

1989-11-01

231

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

NASA Astrophysics Data System (ADS)

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.

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

2001-05-01

232

Water Resources, Adaptation to Climate Change and Social Action in East Africa  

E-print Network

Mt Kenya Mt ElgonMt Elgon Indian O cean Rufiji Tan a Rufiji Tan a Lake Albert Lake Albert Lake Turkana Lake Turkana Lake Victoria Lake Victoria Lake Tanganyika Lake Tanganyika Lake Rukwa Lake Rukwa BURUNDI MALAWI

Richner, Heinz

233

Parallel life history evolution in mouthbrooding cichlids from the African Great Lakes  

PubMed Central

The existence of ancient deep-water lakes provides an opportunity to study the independent adaptation of aquatic organisms to pelagic, benthic, and rocky shore habitats. With improving resolution of their phylogenetic relationships, the many cichlid fish species endemic to the African Great Lakes Malawi, Tanganyika, and Victoria provide a significant resource for the comparative study of such evolutionary processes. Here, we show that cichlid lineages colonizing rocky shores and pelagic habitats in the different lakes have independently evolved larger eggs and lower fecundities than benthic lineages, suggesting parallel adaptive life-history evolution. By contrast, other pelagic teleost fishes in both marine and freshwater habitats, including African lakes, typically produce large numbers of very small eggs. Our results also suggest that decreased fecundity and increased egg size not only occurred independently in each lake but occurred independently in the colonization of rocky and pelagic habitats. PMID:18824688

Duponchelle, Fabrice; Paradis, Emmanuel; Ribbink, Anthony J.; Turner, George F.

2008-01-01

234

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

235

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

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

236

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

NASA Astrophysics Data System (ADS)

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.

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

2014-02-01

237

The development of irrigation and its influence on the transmission of bilharziasis in Tanganyika*  

PubMed Central

Schistosoma mansoni and Schistosoma haematobium are widely distributed throughout East Africa, each being transmitted by several intermediate hosts. It is feared that the increased use of irrigation, which is proposed in Tanganyika to expand agricultural productivity, will also increase the incidence and intensity of schistosomal infection. Nine newly developed irrigation schemes have been examined to provide base-line data against which any future observations on the build-up of bilharziasis can be compared. A description is given in tabular form of each scheme together with the results of snail and parasite surveys conducted on and around it. These results are discussed in relation to the type of scheme and in the light of existing knowledge of bilharziasis in East Africa. The necessity and suitability of certain control measures are discussed. PMID:14310910

Sturrock, R. F.

1965-01-01

238

ARE LAKES GETTING WARMER? REMOTE SENSING OF LARGE LAKE TEMPERATURES  

EPA Science Inventory

Recent studies (Levitus et al., 2000) suggest a warning of the world ocean over the past 50 years. Freshwater lakes could also be getting warmer but thermal measurements to determine this are lacking. Large lake temperatures are vertically and horizontally heterogeneous and vary ...

239

STRATIFICATION OF LAKES Bertram Boehrer1  

E-print Network

STRATIFICATION OF LAKES Bertram Boehrer1 and Martin Schultze1 Received 10 July 2006; revised 26 September 2007; accepted 4 January 2008; published 30 May 2008. [1] Many lakes show vertical stratification an evolution of chemical differences with many consequences for living organisms in lakes. Temperature

Jellinek, Mark

240

Persistence of neutral polymorphisms in Lake Victoria cichlid fish  

PubMed Central

Phylogenetic trees for groups of closely related species often have different topologies, depending on the genes used. One explanation for the discordant topologies is the persistence of polymorphisms through the speciation phase, followed by differential fixation of alleles in the resulting species. The existence of transspecies polymorphisms has been documented for alleles maintained by balancing selection but not for neutral alleles. In the present study, transspecific persistence of neutral polymorphisms was tested in the endemic haplochromine species flock of Lake Victoria cichlid fish. Putative noncoding region polymorphisms were identified at four randomly selected nuclear loci and tested on a collection of 12 Lake Victoria species and their putative riverine ancestors. At all loci, the same polymorphism was found to be present in nearly all the tested species, both lacustrine and riverine. Different polymorphisms at these loci were found in cichlids of other East African lakes (Malawi and Tanganyika). The Lake Victoria polymorphisms must have therefore arisen after the flocks now inhabiting the three great lakes diverged from one another, but before the riverine ancestors of the Lake Victoria flock colonized the Lake. Calculations based on the mtDNA clock suggest that the polymorphisms have persisted for about 1.4 million years. To maintain neutral polymorphisms for such a long time, the population size must have remained large throughout the entire period. PMID:9826684

Nagl, Sandra; Tichy, Herbert; Mayer, Werner E.; Takahata, Naoyuki; Klein, Jan

1998-01-01

241

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

NASA Astrophysics Data System (ADS)

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.

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

2005-12-01

242

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)

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.

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

2010-07-01

243

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

PubMed

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

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

2009-09-01

244

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

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

245

Male reproductive suppression in the cooperatively breeding fish Neolamprologus  

E-print Network

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

Montgomerie, Bob

246

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

PubMed

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

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

2009-08-11

247

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

248

Laurance LakeLaurance Lake Lost LakeLost Lake  

E-print Network

Lost Lake gler2frnh2hm owerdle2hm Hood River Subbasin 1:200,000 Bull Trout Rainbow Cutthroat BarrierHood River Odell Parkdale Laurance LakeLaurance Lake Lost LakeLost Lake gler2frnh2hm owerdle2hm HoodRiver NealCreek DogRive r Evans Creek TonyCreek Eagle Creek LaddCreek W e st Fork H ood River La ke

249

STABLE ISOTOPE RECORDS FROM MOUNT LOGAN, ECLIPSE ICE CORES AND NEARBY JELLYBEAN LAKE. WATER CYCLE OF THE NORTH PACIFIC OVER 2000 YEARS AND OVER FIVE VERTICAL KILOMETRES: SUDDEN SHIFTS AND TROPICAL CONNECTIONS  

Microsoft Academic Search

Three ice cores recovered on or near Mount Logan, together with a nearby lake record (Jellybean Lake), cover variously 500 to 30 000 years. This suite of records offers a unique view of the lapse rate in stable isotopes from the lower to upper troposphere. The region is climatologically important, being beside the Cordilleran pin- ning-point of the Rossby Wave

D. A. FISHER; C. WAKE; K. KREUTZ; K. YALCIN; E. STEIG; P. MAYEWSKI; L. ANDERSON; J. ZHENG; S. RUPPER; C. ZDANOWICZ; M. DEMUTH; M. WASZKIEWICZ; D. DAHL-JENSEN; K. GOTO-AZUMA; J. B. BOURGEOIS; R. M. KOERNER; M. B. ABBOTT; B. P. FINNEY; S. J. BURNS; Juliane Maries Vej

250

The Thermal History of the East African Rift Lakes Region Since the Last Glacial Maximum Using TEX86 Paleothermometry  

NASA Astrophysics Data System (ADS)

We present preliminary results from a study using the TEX86 temperature proxy from sediments of East African Rift Lakes (including Lakes Turkana, Albert, and Malawi) to reconstruct the thermal history of tropical Africa for the last ~ 20,000 years at a subcentennial to multicentennial resolution. The TEX86 proxy, based on tetraether membrane lipids produced by lacustrine Crenarchaeota, has been shown to be successful at recording lake surface temperatures of some large lakes, including Lakes Malawi and Tanganyika, while providing unreasonable surface temperatures for lakes that receive a large input of soil material. The East African Rift Lakes are climatically sensitive, with the majority of water loss due to evaporation rather than outflow. Thus, they are useful for paleoclimate studies, being sensitive to even small changes in aridity. Temperature records from the northern and central basins of Lake Malawi agree well and fall within modern surface lake temperatures. A 2.5°C cooling is evident during the Younger Dryas in the northern basin record, with no response seen in the central basin. We are currently investigating mechanisms to explain why both records show a gradual cooling of 3°C during the late Holocene. Lake Albert shows an intriguing two-step cooling during the Younger Dryas, reaching temperatures 2.5°C lower than temperatures preceding or following this interval. The temperature record of Lake Turkana shows an interesting ~ 500 year cyclicity of low temperatures punctuated by abrupt warming events. Lakes Turkana and Albert show TEX86 paleotemperatures considerably lower (8°C cooler in Lake Albert and ~ 4°C cooler in Lake Turkana) than modern surface water temperatures. Although these records appear to fall in the range of temporal variability, these temperature discrepancies may indicate varying Crenarcheotal populations between lakes or other influencing factors.

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

2008-12-01

251

Circulation and mixing of lake water  

Microsoft Academic Search

The results of the research on the circulation and the mixing of lake water were organized, and the perspective of the research was considered. The flow of lake water is divided into a horizontal flow and a vertical flow. A horizontal flow is chiefly caused by the wind shear stress. As for the research of the flow caused by the

Yoshinori Sato

2009-01-01

252

A Revised Holocene History of Lake Kivu, East Africa  

NASA Astrophysics Data System (ADS)

The great lakes of the East African Rift valley are a vast chain of lakes formed in a region of active tectonics. These large, deep lakes are relatively old and many (e.g. Tanganyika, Malawi, and Turkana) have greatly influenced our understanding of terrestrial, tropical East African paleoclimate. Lake Kivu (max depth, 485m) sits at the heart of these rift lakes, north of Lake Tanganyika between the Democratic Republic of the Congo and Rwanda (roughly 250 km west of Lake Victoria). At over 1,400 meters in elevation, this 2,060 km2 mesotrophic lake has a complex stratification regime imposed by hydrothermal springs and deep waters supersaturated at STP in CO2 and CH4 gasses. The active Virunga Volcanoes to the north of the lake supply heated, high-salinity waters below 280 meters water depth maintaining the modern crenogenic meromixis. Based on detailed studies of diatom assemblages and bulk sedimentology, previous workers have suggested this hydrothermal activity began roughly 5,000 years BP. Unfortunately, dating and stratigraphic correlations of these original cores from the 1970 Woods Hole Oceanographic Institution's expedition have been problematic. Here we offer an improved chronology and new carbonate analyses from cores recovered in 2012 and 2013. Our AMS radiocarbon ages come from six terrigeneous macrofossils spanning the last 9,100 years (cal BP). These ages suggest a rather high sedimentation rate on the order of 70cm/kyr, and hence, our 8 m-long core provides us with a high-resolution lake history for the past 10,000 years. Most notable over the past 5,000 years in the lake history is the repeated onset and cessation of carbonate deposition, punctuated by organic-rich intervals. Earlier studies of the Woods Hole cores placed the onset of carbonate deposition at ca. 11,000 years BP suggesting changes in lake hydrology (i.e. closed to open), while the abrupt cessation of carbonate was dated at ca. 5,000 years BP and attributed to the beginning of significant hydrothermal activity in the lake. However our new chronology places these events much younger with the first major onset of carbonate deposition occurring around 4,300 years BP and ceasing ca. 2,700 years BP. Indeed much of central and northern Africa began to dry out at this time, following the African Humid Period ca. 15,000 to 5,000 years BP. Arid conditions could certainly favor carbonate precipitation and hence our revised ages of deposition agree well with regional paleoclimate studies. This new age model opens up the carbonate record of Lake Kivu for reinterpretation. We are investigating the extent to which the carbonate signal is influenced by internal changes and hydrothermal activity or by climate.

Votava, J. E.; Johnson, T. C.; Hecky, R. E.

2013-12-01

253

HIGH RESOLUTION MODELLING OF PCB CONGENERS IN LAKE MICHIGAN USING THE LAKE MICHIGAN (LM3) CONTAMINANT MODEL  

EPA Science Inventory

The Lake Michigan Level 3 (LM3) Model is a numerical model of Lake Michigan used to predict the fate and transport of 54 PCB congeners. The LM3 model segments Lake Michigan horizontally with a 5 x 5 km grid and vertically with 19 sigma layers for a total of 44,042 water column se...

254

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

Microsoft Academic Search

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

Walter Salzburger; Tanja Mack; Erik Verheyen; Axel Meyer

2005-01-01

255

Lake Powell  

Atmospheric Science Data Center

article title:  Lake Powell     View Larger Image ... (14.42 mb)   This true-color image over Lake Powell was acquired by Multi-angle Imaging SpectroRadiometer (MISR) in late March 2000. Lake Powell was formed with the construction of the Glen Canyon Dam in 1963, on the ...

2014-05-15

256

Lake Eyre  

Atmospheric Science Data Center

...   View Larger Image Lake Eyre is a large salt lake situated between two deserts in one of Australia's driest regions. ... the effect of sunglint at the nadir camera view angle. Dry, salt encrusted parts of the lake appear bright white or gray. Purple areas have ...

2013-04-16

257

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...

258

Transient Tsunamis in Lakes  

NASA Astrophysics Data System (ADS)

A large number of lakes are surrounded by steep and unstable mountains with slopes prone to failure. As a result, landslides are likely to occur and impact water sitting in closed reservoirs. These rare geological phenomena pose serious threats to dam reservoirs and nearshore facilities because they can generate unexpectedly large tsunami waves. In fact, the tallest wave experienced by contemporary humans occurred because of a landslide in the narrow bay of Lituya in 1958, and five years later, a deadly landslide tsunami overtopped Lake Vajont's dam, flooding and damaging villages along the lakefront and in the Piave valley. If unstable slopes and potential slides are detected ahead of time, inundation maps can be drawn to help people know the risks, and mitigate the destructive power of the ensuing waves. These maps give the maximum wave runup height along the lake's vertical and sloping boundaries, and can be obtained by numerical simulations. Keeping track of the moving shorelines along beaches is challenging in classical Eulerian formulations because the horizontal extent of the fluid domain can change over time. As a result, assuming a solid slide and nonbreaking waves, here we develop a nonlinear shallow-water model equation in the Lagrangian framework to address the problem of transient landslide-tsunamis. In this manner, the shorelines' three-dimensional motion is part of the solution. The model equation is hyperbolic and can be solved numerically by finite differences. Here, a 4th order Runge-Kutta method and a compact finite-difference scheme are implemented to integrate in time and spatially discretize the forced shallow-water equation in Lagrangian coordinates. The formulation is applied to different lake and slide geometries to better understand the effects of the lake's finite lengths and slide's forcing mechanism on the generated wavefield. Specifically, for a slide moving down a plane beach, we show that edge-waves trapped by the shoreline and free-waves moving away from it coexist. On an open coast, these two types of waves would never interact, but because of the lake's finite dimensions, here we show that local inundation height maxima are due to wave superposition on the shoreline. These interactions can be dramatic near the lake's corners. For instance, in a rectangular lake delimited by two opposite and plane beaches and two vertical walls, we find that a landslide tsunami results in an inundation height at a corner 50% larger than anywhere else. The nonlinear and linear models produce different inundation maps, and here we show that maximum wave runups can be increased by up to 56% when nonlinear terms are included.

Couston, L.; Mei, C.; Alam, M.

2013-12-01

259

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...

260

MATHEMATICAL MODELING OF PHYTOPLANKTON IN LAKE ONTARIO. PART 2. SIMULATIONS USING LAKE 1 MODEL  

EPA Science Inventory

The results of a series of simulations of the response of the open lake region of Lake Ontario to various levels of nutrient input are described. The simulations use a simplified dynamic model of phytoplankton - nutrient interactions in a vertically segmented structure. The analy...

261

Offline test of the CLM4-VRLS lake model at Lake Taihu  

NASA Astrophysics Data System (ADS)

Lakes are an important surface type for atmospheric research. With the deployment of Taihu Eddy Flux Mesonet since 2010, Lake Taihu, a large shallow lake located in eastern China (~2500 km2 and 2 m deep), provides a unique testbed for models of lake-atmosphere interactions. In this study, we evaluated CLM4-VRLS, a state-of-the-art lake model developed by NCAR, against the observations made at Lake Taihu. CLM4-VRLS is an improved version of the earlier NCAR CLM4 lake model, and includes realistic representations of roughness length, vertical mixing and sediment layer. So far evaluation of the performance of CLM4-VRLS and other models of lake-atmosphere interactions has been restricted mostly to annual cycles of water temperature. In shallow lakes such as Lake Taihu, lake temperature also experiences strong diurnal variations, and it is not known if the model can adequately predict these variations. Furthermore, we are not aware of any studies that evaluate model-predicted surface fluxes of heat, water vapor and momentum against field observations. Accurate prediction of these fluxes is important for a number of reasons, one of which is that these fluxes serve as the lower boundary conditions for models of regional climate and weather prediction. Evaluating CLM4-VRLS at Lake Taihu provides novel insights on its performance, and lays the groundwork for our future study of the feedback between regional climate and Lake Taihu. Results show that CLM4-VRLS yields good estimations of the seasonal variations of the lake surface temperature (LST) at Lake Taihu. However, in terms of the diurnal variations of LST, which are important for the boundary layer processes, CLM4-VRLS does not perform well without the adoption of lake-specific parameters. Compared with the default values in CLM4-VRLS, Lake Taihu is characterized by smaller roughness lengths for heat and water vapor, and larger light extinction coefficient due to high turbidity. In addition, the eddy diffusivity was found to be two orders smaller than that of CLM4-VRLS. Adopting these lake-specific parameters can improve the performance of CLM4-VRLS, notably for the amplitude of the diurnal variations of LST. During nighttime when the lake water is vertically unstable and the passage of cold fronts, CLM4-VRLS with the lake-specific parameters tends to overestimate the LST. We suspect that the nighttime overestimation is attributed to the fact that instability enhances vertical mixing to a lesser extent than that predicted by CLM4-VRLS, while the overestimation during a front scenario is due to synoptic advection.

Deng, B.; Lee, X.; Xiao, W.; Liu, S.; Shen, S.

2011-12-01

262

Sediment Control of Convection in Glacier Dammed Lakes  

NASA Astrophysics Data System (ADS)

During August, 2001, measurements of bathymetry, temperature, and conductivity from Berg Lake, a freshwater lake dammed by Steller Glacier, and Vitus Lake, a tidally influenced lake at the terminus of Bering Glacier, Alaska, show intense vertical convection that is controlled by suspended sediment in the former lake and salt in the latter lake. The temperature profiles from Berg Lake show a vertical structure that consists of a 10 m thick surface layer where the temperature drops from near 9 C to approximately 4 C, the temperature of maximum density for fresh water. Below this depth the temperature decreases to 0 C in the deepest portions of the lake, approximately 75 m. Superimposed on this general unstable temperature profile are spatially variable fine structure details that include vertical steps and temperature inversions. While the temperature profiles indicate a highly unstable situation, the sub-glacial discharge has a suspended sediment load sufficient to marginally stabilize the density structure in the lake. This sediment laden water flows out from below the glacier and spreads horizontally throughout Berg Lake. As the suspended sediment settles, vertical thermal convection occurs that yields the observed fine structure in the temperature profiles. In contrast, Vitus Lake is connected to the Gulf of Alaska via the 8 m deep, 7.3 km long Seal River. Measurements in this lake show strong saline stratification in the deeper portions of the lake. Thermal diffusion across the pycnocline may produce frazil ice growth, while melting of the glacier terminus produces convection at the margin of the lake, not the interior, as was observed in Berg Lake.

Josberger, E. G.; Meadows, G. A.; Shuchman, R. A.; Payne, J.

2001-12-01

263

VERTEBRATES OF FISH LAKE  

E-print Network

VERTEBRATES OF FISH LAKE CAUTION! FISH LAKE SCAVANGER HUNT RED HEADED is another majestic bird of Fish Lake. These birds can be seen perched at Fish Lake. CLUB-TAIL DRAGONFLY INSECTS OF FISH LAKE There are A LOT

Minnesota, University of

264

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

265

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

NASA Astrophysics Data System (ADS)

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.

Birkett, Charon; Murtugudde, Ragu; Allan, Tony

266

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...

267

Tropical Lake Levels and Their Relationship to Rainfall  

NASA Astrophysics Data System (ADS)

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.

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

2009-12-01

268

Holocene TEX86 temperature reconstructions from Lake Turkana, East Africa  

NASA Astrophysics Data System (ADS)

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.

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

2009-12-01

269

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

NASA Astrophysics Data System (ADS)

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.

Hassan, Ayman A.; Jin, Shuanggen

2014-06-01

270

Lake Nipigon  

NSDL National Science Digital Library

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.

2001-01-01

271

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

Microsoft Academic Search

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

Kevin L. Pangle; Scott D. Peacor

2010-01-01

272

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...

273

Numerical studies of the 4-day oscillation in Lake Champlain  

Microsoft Academic Search

The summer thermocline of Lake Champlain, which is found at depths of 20-30 m, oscillates with typical vertical amplitudes of 20-40 m and periods of ~4 days. Fluctuations at the ends of the lake are opposite in phase and accompanied in the central lake by strong shears across the thermocline. These are basin-wide baroclinic disturbances which are forced by wind.

Kenneth Hunkins; Thomas O. Manley; Patricia Manley; James Saylor

1998-01-01

274

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

Microsoft Academic Search

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

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

1988-01-01

275

Principles of lake sedimentology  

SciTech Connect

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.

Janasson, L.

1983-01-01

276

The Morphometry of Lake Palmas, a Deep Natural Lake in Brazil  

PubMed Central

Lake Palmas (A?=?10.3km2) is located in the Lower Doce River Valley (LDRV), on the southeastern coast of Brazil. The Lake District of the LDRV includes 90 lakes, whose basic geomorphology is associated with the alluvial valleys of the Barreiras Formation (Cenozoic, Neogene) and with the Holocene coastal plain. This study aimed to investigate the relationship of morphometry and thermal pattern of a LDRV deep lake, Lake Palmas. A bathymetric survey carried out in 2011 and the analysis of hydrographic and wind data with a geographic information system allowed the calculation of several metrics of lake morphometry. The vertical profiling of physical and chemical variables in the water column during the wet/warm and dry/mild cold seasons of 2011 to 2013 has furnished a better understanding of the influence of the lake morphometry on its structure and function. The overdeepened basin has a subrectangular elongated shape and is aligned in a NW-SE direction in an alluvial valley with a maximum depth (Zmax) of 50.7m, a volume of 2.2×108 m3 (0.22km3) and a mean depth (Zmv) of 21.4m. These metrics suggest Lake Palmas as the deepest natural lake in Brazil. Water column profiling has indicated strong physical and chemical stratification during the wet/warm season, with a hypoxic/anoxic layer occupying one-half of the lake volume. The warm monomictic pattern of Lake Palmas, which is in an accordance to deep tropical lakes, is determined by water column mixing during the dry and mild cold season, especially under the influence of a high effective fetch associated with the incidence of cold fronts. Lake Palmas has a very long theoretical retention time, with a mean of 19.4 years. The changes observed in the hydrological flows of the tributary rivers may disturb the ecological resilience of Lake Palmas. PMID:25406062

Barroso, Gilberto F.; Gonçalves, Monica A.; Garcia, Fábio da C.

2014-01-01

277

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

USGS Publications Warehouse

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.

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

1999-01-01

278

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

279

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

NASA Astrophysics Data System (ADS)

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.

Rose, Bruce L., Jr.

2001-06-01

280

Numerical simulation analysis of the interaction of lakes and ground water  

USGS Publications Warehouse

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)

Winter, Thomas C.

1976-01-01

281

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

PubMed

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

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

2014-11-01

282

Lake Powell  

NASA Technical Reports Server (NTRS)

The white ring around Lake Powell tells the story. The surface is down 98 feet. This is critical, because Powell, Lake Mead, and other lakes along the Colorado River provide water for millions of people in five states. We are in the eighth year of a drought on the Colorado River. This year was the driest year ever reported in Southern California, and there is a severe drought in Northern California, down to less than 30-percent of snow pack. This ASTER image of part of Lake Powell was acquired in 2001. The gray area depicts the shrunken, reduced 2007 lake extent compared to the extended, larger black area in 2001.

The image covers an area of 24 x 30 km, and is centered near 37.1 degrees north latitude, 111.3 degrees west longitude.

The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

2007-01-01

283

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

NASA Astrophysics Data System (ADS)

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.

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

284

Recent Warming of Lake Kivu  

PubMed Central

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

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

2014-01-01

285

Recent warming of lake Kivu.  

PubMed

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

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

2014-01-01

286

LONG-TERM RECOVERY OF PCB-CONTAMINATED SEDIMENTS AT THE LAKE HARTWELL SUPERFUND SITE: PCB DECHLORINATION. 2. RATES AND EXTENT  

EPA Science Inventory

This paper reports on extensive polychlorinated biphenyl (PCB) dechlorination measured in Lake Hartwell (Pickens County, SC) sediments. Vertical sediment cores were collected from 18 locations in Lake Hartwell (Pickens County, SC) and analyzed in 5-cm increments for PCB congeners...

287

Iceberg Lake  

USGS Multimedia Gallery

On Iceberg Lake in Glacier National Park, ice from the glacier is breaking up and melting at a rapid rate.  Cold, glacier fed waters provide crucial habitat for native aquatic species such as trout, and as the ice is disappearing, so are the ideal habitats to sustain native ecosystems.  ...

288

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.

289

Flow rate and vertical position influence ingestion rates of colonial zebra mussels (Dreissena polymorpha)  

E-print Network

-populated zebra mussels in the Western basin of Lake Erie possessed the potential to filter 132 000 L of water per% of individuals in Western Lake Erie, could theoretically pump between 39 and 96% of the water column daily. MostFlow rate and vertical position influence ingestion rates of colonial zebra mussels (Dreissena

Kelly, John J.

290

Vertical axis wind turbines  

Microsoft Academic Search

A vertical wind turbine having vertical blades, each blade being connected intermediate its ends by a hinge to a support arm having a hub that enables the blades to rotate around a vertical axis, a tie wire connected to the blade at positions spaced along the blade from the hinge, said tie wire engaging a spring-loaded pulley disposed inwardly of

P. E. Delgado; B. A. Holmes

1981-01-01

291

Vertical Map Storage.  

ERIC Educational Resources Information Center

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)

Perry, Joanne M.

1982-01-01

292

Evaluating the Relative Variability of Lake and Wetland Storage in the Global Water Balance  

NASA Astrophysics Data System (ADS)

Hydrologic investigations commonly stem from the analysis of observed or simulated river discharge which integrates processes upstream including snowpack and soil moisture storage. An understanding of the global water cycle, and in particular the land surface branch; however, requires consideration of all terms in the water budget, including storage in lakes, reservoirs and wetlands, which often is not represented in hydrologic models. Furthermore, direct observations of changes in these storage terms are scarce, especially at the global scale. Satellite observations provide an opportunity to incorporate information about fresh water surface storage into analyses of the water cycle at continental to global scales. We use a combination of direct measurements and modeling to evaluate the mean seasonal and interannual variability in fresh water surface storage over Africa. Satellite radar altimetry from Topex/POSEIDON for five major lakes in Africa (Nyasa, Tana, Tanganyika, Turkana and Victoria) over the period 1992-1999 is used to estimate the mean seasonal and interannual variability of large lake storage. We extend these observations to smaller water bodies using a lakes and wetland algorithm designed for use in the Variable Infiltration Capacity (VIC) land surface model, and perform a 21-year simulation (1979-1999) over Africa. JERS synthetic aperture radar observations over western Africa, in combination with a global data set of reservoirs, wetlands and lakes, provide a basis for the generation of lake geometry profiles. As a point of comparison, we evaluate the mean seasonal and interannual variability for other major terms in the surface water balance as represented by a 21-year VIC global simulation at one-half degree spatial resolution. In particular, we calculate the variability of precipitation, evaporation, runoff, and storage change in the subsurface and in snow and glaciers across a variety of spatial scales from continental to grid cell. The analysis suggests that surface water storage plays an important role in the water cycle in comparison with other terms, such as soil moisture and snow that have received considerably more attention.

Clark, E. A.; Sridhar, V. R.; Lettenmaier, D. P.; Birkett, C. M.; McDonald, K. C.; Bowling, L. C.

2004-05-01

293

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.

2007-10-26

294

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.

295

Field measurement of small ozone fluxes to snow, wet bare soil, and lake water  

Microsoft Academic Search

Eddy-correlation measurements over snow, wet bare soil, and lake water indicate very small vertical ozone fluxes. Adjustments to the small vertical fluxes are needed to take into account the effect of mean Stefan flow associated with evaporation at the surface and the effects of correlation between density variations and vertical wind fluctuations. For snow, the residual resistance calculated for the

M. L. Wesely; D. R. Cook; R. M. Williams

1981-01-01

296

Mating system variability in a mouthbrooding cichlid fish from a tropical lake.  

PubMed

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

Sefc, K M; Hermann, C M; Koblmüller, S

2009-08-01

297

Vertical axis wind turbines  

DOEpatents

A vertical axis wind turbine is described. The wind turbine can include a top ring, a middle ring and a lower ring, wherein a plurality of vertical airfoils are disposed between the rings. For example, three vertical airfoils can be attached between the upper ring and the middle ring. In addition, three more vertical airfoils can be attached between the lower ring and the middle ring. When wind contacts the vertically arranged airfoils the rings begin to spin. By connecting the rings to a center pole which spins an alternator, electricity can be generated from wind.

Krivcov, Vladimir (Miass, RU); Krivospitski, Vladimir (Miass, RU); Maksimov, Vasili (Miass, RU); Halstead, Richard (Rohnert Park, CA); Grahov, Jurij (Miass, RU)

2011-03-08

298

Aircraft measurement of HONO vertical profiles over a forested region  

Microsoft Academic Search

Here we present the first HONO vertical profiles in the atmospheric boundary layer (BL) and the lower free troposphere (FT) over a forested region in northern Michigan and the neighboring Great Lakes, measured from a small aircraft in summer of 2007. The HONO mixing ratios ranged from 4 to 17 pptv in the FT and from 8 to 74 pptv

Ning Zhang; Xianliang Zhou; Paul B. Shepson; Honglian Gao; Marjan Alaghmand; Brian Stirm

2009-01-01

299

11. Detail of portion of west wall and vertical and ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

11. Detail of portion of west wall and vertical and horizontal supports inside machine shop section of roundhouse. View to northwest. - Duluth & Iron Range Rail Road Company Shops, Roundhouse, Southwest of downtown Two Harbors, northwest of Agate Bay, Two Harbors, Lake County, MN

300

The Role of the Predaceous Copepod Parabroteas Sarsi in the Pelagic Food Web of a Large Deep Andean Lake  

Microsoft Academic Search

Parabroteas sarsi is a predaceous calanoid copepod that inhabits both shallow temporary fishless ponds and deep fish lakes of Patagonia and Antarctica. The aim of this study was to analyse the effect of P. sarsi on the plankton structure of a deep Andean lake (>100 m depth) and the zooplankton vertical distribution in order to asses a possible vertical refuge

Mariana Reissig; Beatriz Modenutti; Esteban Balseiro; Claudia Queimaliños

2004-01-01

301

Phytoplankton Dynamics and Hypoxia in Lake Erie: A Hypothesis Concerning Benthic-pelagic Coupling in the Central Basin  

Microsoft Academic Search

Recent changes in the Lake Erie ecosystem suggest that reductions in phosphorus loads and invasion by dreissenid mussels, have enhanced light penetration, and altered phytoplankton distribution patterns in the lake. In this paper, we evaluate possible links between phytoplankton dynamics in Lake Erie, and seasonal development of hypoxia in the central basin by studying seasonal pattern of the vertical distribution

Hunter J. Carrick; Jessica B. Moon; Barrett F. Gaylord

2005-01-01

302

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

E-print Network

, The Inland Watens of Tropical Afica (Longman, London, ed. 2, 1981). 6. B. R. Rosendahl, Annu. Rev. Earth Planet. Sci. 15, 445 (1987); C. J. Ebinger, B. R. Rosendahl, D. J. Reynolds, Tectonophysics 141, 215 (1987). 7. T. Specht and B. R. Rosendahl,J. Afr. Earth Sci., in press; J. Flannery, thesis, Duke

Richardson, David

303

Construction of chromosome markers from the Lake Victoria cichlid Paralabidochromis chilotes and their application to comparative mapping.  

PubMed

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

Kuroiwa, A; Terai, Y; Kobayashi, N; Yoshida, K; Suzuki, M; Nakanishi, A; Matsuda, Y; Watanabe, M; Okada, N

2014-01-01

304

The large lake ecosystems of northern Canada  

Microsoft Academic Search

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

M. S Evans

2000-01-01

305

SHORT REVIEW Genetic and developmental basis of cichlid trophic  

E-print Network

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

Kocher, Thomas D.

306

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

307

BioMed Central Page 1 of 16  

E-print Network

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

Alvarez, Nadir

308

VERTICAL DISTRIBUTION PATTERNS OF GOLDEYE, HIODON ALOSOIDES, IN FORT PECK RESERVOIR, MONTANA  

E-print Network

VERTICAL DISTRIBUTION PATTERNS OF GOLDEYE, HIODON ALOSOIDES, IN FORT PECK RESERVOIR, MONTANA JAMES/des (Rafinesque), in Fort Peck Reservoir, Mont., exhibited seasonal vertical distribution patterns, which seemed. Fort Peck Reservoir is basically a deep, clear body of water in contrast to the lakes generally

309

Mono Lake, California  

NSDL National Science Digital Library

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.

Sierra WebPage

310

Food of Lake Trout in Lake Superior  

Microsoft Academic Search

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

William R. Dryer; Leo F. Erkkila; Clifford L. Tetzloff

1965-01-01

311

Lake Trout Rehabilitation in Lake Huron  

Microsoft Academic Search

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

Randy L. Eshenroder; N. Robert Payne; James E. Johnson; Charles Bowen II; Mark P. Ebener

1995-01-01

312

Lake Trout Reproduction in Lake Champlain  

Microsoft Academic Search

Native lake trout Salvelinus namaycush were driven to extirpation in Lake Champlain in the early 1900s. Possible causes include overharvest, predation on adults by sea lamprey Petromyzon marinus, and predation on fry by rainbow smelt Osmerus mordax. Efforts to restore a lake trout fishery began in 1972 when a coordinated stocking program was initiated. Attempts to control sea lamprey populations

Brian J. Ellrott; J. Ellen Marsden

2004-01-01

313

Lake Trout Rehabilitation in Lake Ontario  

Microsoft Academic Search

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

Joseph H. Elrod; Robert O’Gorman; Clifford P. Schneider; Thomas H. Eckert; Ted Schaner; James N. Bowlby; Larry P. Schleen

1995-01-01

314

Journal of Fish Biology (1998) 53 (Supplement A), 430447 Article No. jb980833  

E-print Network

differentiation in populations of Tropheus demonstrate a drop in water level of Lake Tanganyika in the very recent populations of the genus Tropheus from different localities of Lake Tanganyika. Populations from opposite

315

ORIGINAL ARTICLE Evolution of body shape in sympatric versus non-sympatric  

E-print Network

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

Richner, Heinz

316

Behavioral Ecology doi:10.1093/beheco/arn031  

E-print Network

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

Neff, Bryan D.

317

Vertical axis wind turbines  

Microsoft Academic Search

A vertical axis wind turbine comprises one or more aerofoil section blades attached to a support structure. The blade has at least one part thereof which is acted on by centrifugal forces as the blade rotates with the support structure and thereby caused to increase its angle of inclination to the vertical axis when the speed of rotation increases beyond

Musgrove

1978-01-01

318

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

319

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

320

Lake Erie airport study  

Microsoft Academic Search

In a series of investigations to determine the best possible site for an airport in the area surrounding Lake Erie and the feasibility of an offshore airport on the Lake itself, the weather, noise levels, air and water quality impacts, airspace\\/air traffic control considerations, obstruction clearances, effects on lake currents and lake navigation routes, and aesthetic considerations are evaluated. The

1977-01-01

321

Longevity of Lake Superior lake trout  

USGS Publications Warehouse

The age structure of mature lake trout Salvelinus namaycush from the Wisconsin waters of Lake Superior increased following a population recovery that has taken place since the 1960s. As the population aged, it became apparent that scales were unreliable aging structures. Beginning in 1986, we examined both scale and sagittal otolith ages from tagged fish with a known period at liberty. We found large discrepancies in scale and sagittal otolith ages of mature fish, such that scale ages were biased low. We estimated lake trout living up to 42 years, which is greater than previously reported from Lake Superior. Investigators studying lake trout population dynamics in the Great Lakes should be aware that lake trout can live longer than previously thought.

Schram, Stephen T.; Fabrizio, Mary C.

1998-01-01

322

The Great Lakes Atlas  

NSDL National Science Digital Library

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.

Botts, Lee; Krushelnicki, Bruce

323

International Lake Environment Committee  

NSDL National Science Digital Library

The International Lake Environment Committee (ILEC) works to advance international cooperation for sustainable management of the world's lakes and reservoirs through the collection and provision of environmental data, the promotion of scientific research, and the promotion of interchange with government agencies and research institutes. The World Lake Database is particularly interesting and gives the user the ability to navigate to lakes around the world providing facts about each lake.

324

Modeling basin-scale internal waves in a stratified lake  

Microsoft Academic Search

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

Ben R. Hodges; Jörg Imberger; Angelo Saggio; K. B. Winters

2000-01-01

325

Early observations on an emerging Great Lakes invader Hemimysis anomala in Lake Ontario  

USGS Publications Warehouse

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.

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

326

3, 14531471, 2006 Upwellings recorded  

E-print Network

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

Paris-Sud XI, Université de

327

TWO NEW SPECIES OF PLATYTHELPHUSA A. MILNE-EDWARDS, 1887 (DECAPODA, POTAMOIDEA, PLATYTHELPHUSIDAE) AND COMMENTS  

E-print Network

) 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

Cumberlidge, Neil

328

Biogeosciences, 4, 195203, 2007 www.biogeosciences.net/4/195/2007/  

E-print Network

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

Paris-Sud XI, Université de

329

BioMed Central Page 1 of 15  

E-print Network

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

Alvarez, Nadir

330

A theoretical analysis of vertical flow equilibrium  

SciTech Connect

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.

Yortsos, Y.C.

1992-01-01

331

Micromachined electrostatic vertical actuator  

DOEpatents

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.

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

332

Vertical comb array microactuators  

Microsoft Academic Search

A vertical actuator fabricated using a trench-refilled-with-polysilicon (TRiPs) process technology and employing an array of vertical oriented comb electrodes is presented. This actuator structure provides a linear drive to deflection characteristic and a large throw capability which are key features in many sensors, actuators and micromechanisms. The actuation principle and relevant theory is developed, including FastCap simulations for theoretical verification.

Arjun Selvakumar; Khalil Najafi

2003-01-01

333

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...

334

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...

335

Distribution of dissolved organic carbon in lakes of different trophic types  

Microsoft Academic Search

The distributions of dissolved organic carbon (DOC) in the warm season were elucidated in ten lakes of different trophic types in Japan, Russia, and China. DOC showed similar vertical distributions in all the lakes in summer when thermal stratification occurred. DOC in the epilimnion was higher than the value of 0.8?mg?C?l ?1 found in the hypolimnion. In three Japanese lakes,

Yuko Sugiyama; Aya Anegawa; Tetsu Kumagai; Yu-nosuke Harita; Toshitaka Hori; Masahito Sugiyama

2004-01-01

336

Life history of lake herring of Green Bay, Lake Michigan  

USGS Publications Warehouse

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.

Smith, Stanford H.

1956-01-01

337

Modern lacustrine stromatolites, Walker Lake, Nevada  

NASA Astrophysics Data System (ADS)

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.

Osborne, Robert H.; Licari, Gerald R.; Link, Martin H.

1982-05-01

338

The 5 Great Lakes: HOMES  

NSDL National Science Digital Library

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 ...

2012-04-21

339

Vertical axis wind turbines  

SciTech Connect

A vertical wind turbine having vertical blades, each blade being connected intermediate its ends by a hinge to a support arm having a hub that enables the blades to rotate around a vertical axis, a tie wire connected to the blade at positions spaced along the blade from the hinge, said tie wire engaging a spring-loaded pulley disposed inwardly of the blades, the arrangement being such that when the angle of inclination of the blades to the vertical axis alters under the action of centrifugal force the tie wire exerts a force on the pulley opposing the spring force whereby as the turbine speeds up the blades will remain at a predetermined angle of inclination until the force exerted by the wire exceeds the force of the spring. One end of the tie wire can be connected to a position on one blade and connected to another position on another blade so that all of the blades adopt the same angle of inclination to the vertical axis.

Delgado, P.E.; Holmes, B.A.

1981-06-23

340

Lake Michigan Sand Waves  

USGS Multimedia Gallery

Calm Lake Michigan morning while sampling dead and dying fish for viral hemorrhagic septicemia virus (VHSV). This virus has recently emerged in the Great Lakes and caused severe epidemics in many fish species....

2009-12-11

341

Lakes Ecosystem Services Online  

EPA Science Inventory

Northeastern lakes provide valuable ecosystem services that benefit residents and visitors and are increasingly important for provisioning of recreational opportunities and amenities. Concurrently, however, population growth threatens lakes by, for instance, increasing nutrient ...

342

Cladophora Along Lake Michigan  

USGS Multimedia Gallery

Large patches of Cladophora, a green algae, lining the shore of Lake Michigan. Accumulation of Cladophora in shoreline waters is believed to be linked to avian botulism outbreaks, which have recently increased in the Great Lakes. ...

343

Utah: Salt Lake Region  

Atmospheric Science Data Center

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 ...

2014-05-15

344

Lake-Effect Snowfall over Lake Michigan.  

NASA Astrophysics Data System (ADS)

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.

Braham, Roscoe R., Jr.; Dungey, Maureen J.

1995-05-01

345

Great Lakes: Chemical Monitoring  

ERIC Educational Resources Information Center

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)

Delfino, Joseph J.

1976-01-01

346

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

347

Great Minds? Great Lakes!  

ERIC Educational Resources Information Center

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…

Environmental Protection Agency, Chicago, IL. Great Lakes National Program Office.

348

Lake Layers: Stratification.  

ERIC Educational Resources Information Center

This teacher guide and student workbook set contains two learning activities, designed for fifth through ninth grade students, that concentrate on lake stratification and water quality. In the activities students model the seasonal temperature changes that occur in temperate lakes and observe the resulting stratification of lake waters. Students…

Brothers, Chris; And Others

349

A Killer Lake  

ERIC Educational Resources Information Center

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.…

Horvath, Thomas

2005-01-01

350

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 ...

351

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...

352

Vertical emitting aperture nanoantennas.  

PubMed

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

Yaacobi, Ami; Timurdogan, Erman; Watts, Michael R

2012-05-01

353

Water balance of selected floodplain lake basins in the Middle Bug River valley  

NASA Astrophysics Data System (ADS)

This study is the first attempt in the literature on the subject of comparing water balance equations for floodplain lake basins depending on the type of connection the lake has to its parent river. Where confluent lakes (upstream connections) were concerned, it was only possible to apply a classic water balance equation. When dealing with contrafluent lakes (downstream connections) as well as lakes with a complex recharge type (contrafluent-confluent) modified equations were created. The hydrological type of a lake is decided by high water flow conditions and, consequently, the duration of potamophase (connection with a river) and limnophase (the isolation of the lake), which determine the values of particular components and the proportion of the vertical to horizontal water exchange rate. Confluent lakes are characterised by the highest proportion of horizontal components (the inflow and runoff of river water) to the vertical ones (precipitation and evaporation). The smallest differences occur with respect to a contrafluent lake. In the case of confluent lakes, the relationship between water balance components resulted from the consequent water flow through the basin, consistent with the slope of the river channel and valley. The supplying channels of contrafluent lakes had an obsequent character, which is why the flow rate was lower. Lakes with a complex, contrafluent-confluent recharge type showed intermediate features. After a period of slow contrafluent recharge, the inflow of water through a downstream crevasse from the area of the headwater of the river was activated; this caused a radical change of flow conditions into confluent ones. The conditions of water retention in lake basins were also varied. Apart from hydrological recharge, also the orographic features of the catchment areas of the lakes played an important role here, for example, the distance from the river channel, the altitude at which a given catchment was located within the floodplain and the complexity of the channels of fluvial-water inflow.

Dawidek, J.; Ferencz, B.

2013-08-01

354

Limnology and fish ecology of sockeye salmon nursery lakes of the world  

USGS Publications Warehouse

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.

Hartman, Wilbur L.; Burgner, R.L.

1972-01-01

355

Behavioral response of Lake Michigan Daphnia mendotae to Mysis relicta  

Microsoft Academic Search

We performed laboratory experiments to determine if Mysis relicta induce changes in the behavior of Daphnia mendotae collected from Lake Michigan. Laboratory results indicate that Daphnia perceived Mysis kairomones and responded by changing their vertical position in cylinders. Experiments using different resource levels, and two procedures to examine the potential effects of the chemical cues from Mysis or from particulate

Scott D. Peacor; Kevin L. Pangle; Henry A. Vanderploeg

2005-01-01

356

Depth-Related Gradients of Viral Activity in Lake Pavin  

PubMed Central

High-resolution vertical sampling and determination of viral and prokaryotic parameters in a deep volcanic lake shows that in the absence of thermal stratification but within light, oxygen, and chlorophyll gradients, host availability empirically is prevalent over the physical and chemical environments and favors lytic over lysogenic “viral life cycles.” PMID:16751565

Colombet, J.; Sime-Ngando, T.; Cauchie, H. M.; Fonty, G.; Hoffmann, L.; Demeure, G.

2006-01-01

357

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...

358

Mono Lake Web Site  

NSDL National Science Digital Library

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.

Reis, Greg; Committee, Mono L.

359

Aiding Vertical Guidance Understanding  

NASA Technical Reports Server (NTRS)

A two-part study was conducted to evaluate modern flight deck automation and interfaces. In the first part, a survey was performed to validate the existence of automation surprises with current pilots. Results indicated that pilots were often surprised by the behavior of the automation. There were several surprises that were reported more frequently than others. An experimental study was then performed to evaluate (1) the reduction of automation surprises through training specifically for the vertical guidance logic, and (2) a new display that describes the flight guidance in terms of aircraft behaviors instead of control modes. The study was performed in a simulator that was used to run a complete flight with actual airline pilots. Three groups were used to evaluate the guidance display and training. In the training, condition, participants went through a training program for vertical guidance before flying the simulation. In the display condition, participants ran through the same training program and then flew the experimental scenario with the new Guidance-Flight Mode Annunciator (G-FMA). Results showed improved pilot performance when given training specifically for the vertical guidance logic and greater improvements when given the training and the new G-FMA. Using actual behavior of the avionics to design pilot training and FMA is feasible, and when the automated vertical guidance mode of the Flight Management System is engaged, the display of the guidance mode and targets yields improved pilot performance.

Feary, Michael; McCrobie, Daniel; Alkin, Martin; Sherry, Lance; Polson, Peter; Palmer, Everett; McQuinn, Noreen

1998-01-01

360

Construction & Therapy Vertical Integration  

E-print Network

Construction & Therapy Vertical Integration Pilot Project Collaboration Partners Department to work with a local population to realize direct construction. Titled Construction & Therapy the studio will be documented and developed as a therapeutic exercise. The production of the welcome building will be delivered

Strathclyde, University of

361

A 14?000-year record of paleoenvironmental change in the western basin of China's third largest lake, Lake Taihu  

Microsoft Academic Search

The longest vertical profile from the western basin of Taihu Lake ever taken was nearly 4 m (396 cm) in length and represented a time period of over 14?000 years. The core was analyzed for the following proxies, magnetic susceptibility, organic carbon isotope, total organic carbon, total nitrogen, total pigments, saturated hydrocarbons, carbon 14, thermolytic hydrogen (the hydrogen index, HI)

Wenchuan Qu; Bin Xue; M. D. Dickman; Sumin Wang; Chengxin Fan; Ruijin Wu; Pingzhong Zhang; Jianfa Chen; Yanhong Wu

2000-01-01

362

COREGONID FISHES OF THE GREAT LAKES By WALTER KOELZ, Ph. D.  

E-print Network

_ Coregonus clupeaformis _ Lake Michigan _ Lake Huron _ Lake Superior _ Lake Nipigon _ Lake Erie _ Lake Superior _ Lake Nipigon _ artedi and artedi albus of Lake Ontario _ Leucichthys nipigon _ Genus Coregonus

363

Predation on emergent lake trout fry in Lake Champlain  

Microsoft Academic Search

The rehabilitation of extirpated lake trout (Salvelinus namaycush) in the Great Lakes and Lake Champlain has been hindered by various biological and physiological impediments. Efforts to restore a lake trout fishery to Lake Champlain include hatchery stocking and sea lamprey control. Despite these management actions, there is little evidence of recruitment of naturally-produced fish in annual fall assessments. Spawning occurs

Jacob W. Riley; J. Ellen Marsden

2009-01-01

364

Small lakes dominate a random sample of regional lake characteristics  

Microsoft Academic Search

SUMMARY 1. Lakes are a prominent feature of the Northern Highland Lake District (NHLD) of Wisconsin, covering 13% of the landscape. Summarising the physical, chemical, or biological nature of NHLD lakes at a regional scale requires a representative sample of the full size distributions of lakes. In this study, we selected at random 168 lakes from the full size distribution

PAUL C. HANSON; STEPHEN R. CARPENTER; JEFFREY A. CARDILLE; MICHAEL T. COE; LUKE A. WINSLOW

2007-01-01

365

Lake Trout Discovered in Yellowstone Lake Threaten Native Cutthroat Trout  

Microsoft Academic Search

On 30 July 1994, lake trout (Salvelinus namaycush) were discovered in Yellowstone Lake in Yellowstone National Park, Wyoming, the core of the remaining undisturbed natural habitat for native Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri). Data from this and other lake trout subsequently caught by anglers and the U.S. Fish and Wildlife Service suggest lake trout have reproduced in Yellowstone Lake

Lynn R. Kaeding; Glenn D. Boltz; Daniel G. Carty

1996-01-01

366

Lake trout rehabilitation in Lake Huron  

USGS Publications Warehouse

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.

Eshenroder, Randy L.; Payne, N. Robert; Johnson, James E.; Bowen, Charles, II; Ebener, Mark P.

1995-01-01

367

A high-resolution geochemical record from Lake Edward, Uganda Congo and the timing and causes of tropical African drought during the late Holocene  

NASA Astrophysics Data System (ADS)

High-resolution analyses of the elemental composition of calcite and biogenic silica (BSi) content in piston cores from Lake Edward, equatorial Africa, document complex interactions between climate variability and lacustrine geochemistry over the past 5400 years. Correlation of these records from Lake Edward to other climatically-forced geochemical and lake level records from Lakes Naivasha, Tanganyika, and Turkana allows us to develop a chronology of drought events in equatorial East Africa during the late Holocene. Major drought events of at least century-scale duration are recorded in lacustrine records at about 850, 1500, ˜2000, and 4100 cal year BP. Of these, the most severe event occurred between about 2050 and 1850 cal year BP, during which time Lake Edward stood about 15 m below its present level. Numerous additional droughts of less intensity and/or duration are present in the Lake Edward record, some of which may be correlated to other lacustrine climate records from equatorial East Africa. These events are superimposed on a long-term trend of increasingly arid conditions from 5400 to about 2000 cal year BP, followed by a shift toward wetter climates that may have resulted from an intensification of the winter Indian monsoon. Although the causes of decade- to century-scale climate variability in the East African tropics remain obscure, time-series spectral analysis suggests no direct linkage between solar output and regional rainfall. Rather, significant periods of ˜725, ˜125, 63-72, 31-25, and 19-16 years suggest a tight linkage between the Indian Ocean and African rainfall, and could result from coupled ocean-atmosphere variability inherent to the tropical monsoon system.

Russell, James M.; Johnson, Thomas C.

2005-07-01

368

Generation and degeneration of long internal waves in lakes  

NASA Astrophysics Data System (ADS)

The nonlinear evolution, generation and degeneration of wind-driven, basin-scale internal waves in lakes are investigated employing weakly-nonlinear, weakly-dispersive evolution models. The models studied are based on rational, asymptotic approximations of the hydrodynamic equations of motion, and include a two-layer model, a multi-modal model, and a large-lake model with the effect of earth's rotation. It is found that nonlinearity, in conjunction with the dispersive nature of the fluid medium, plays a principle role in (i) the early stage of degeneration of basin-scale waves through nonlinear steepening and subsequent generation of oscillatory waves; and (ii) the transfer of energy among multiple vertical modes in the internal field. Strong dependence of these nonlinear processes on the background stratification, the lake geometry, the horizontal extent of a lake, and the spatio-temporal wind stress function are demonstrated and quantified through a series of numerical simulations of the different models.

Sakai, Takahiro

2008-12-01

369

Lake-Effect Snowfall over Lake Michigan  

Microsoft Academic Search

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

Roscoe R. Braham Jr.; Maureen J. Dungey

1995-01-01

370

The long, the short and the stalled: on the attributes of phytoplankton selected by physical mixing in lakes and rivers  

Microsoft Academic Search

Paradoxically, although turbulence characterises the open water environments of planktonic organisms in lakes, rivers and seas, most species of phytoplankton are smaller than the size of the smallest eddies dissipating the energy and, so, must function in an immediate medium which is inherently viscous. Intensively mixed systems, such as wind-stirred shallow lakes, rivers and estuaries, however, constantly readjust the vertical

C. S. Reynolds; J. Padisdk

1994-01-01

371

Convective Structures in a Cold Air Outbreak over Lake Michigan during Lake-ICE.  

NASA Astrophysics Data System (ADS)

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).

Zurn-Birkhimer, Suzanne M.; Agee, Ernest M.; Sorbjan, Zbigniew

2005-07-01

372

Growth and reproduction of migrating and non-migrating Daphnia species under simulated food and temperature conditions of diurnal vertical migration  

Microsoft Academic Search

(1)The growth response of two Daphnia species coexisting in Lake Constance to constant and fluctuating conditions of temperature and food was tested in a flowthrough system.(2)In the lake D. hyalina exhibits a pronounced diurnal pattern of vertical migration, whereas D. galeata stays near the surface. The experiments were designed to measure growth and reproductive success of the species under the

H.-B. Stich; W. Lampert

1984-01-01

373

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)

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.

Nakashima, H.; Seto, K.; Katsuki, K.; Kaneko, H.; yamada, K.; Imura, S.; Dettman, D. L.

2011-12-01

374

Groundwater-Surface Water Interactions along a Lake Shore: Spatial Patterns and Temporal Dynamics  

NASA Astrophysics Data System (ADS)

In this study the spatial and temporal variability of groundwater-surface water interactions along a lake shore is investigated by combining different experimental methods. Study area is Lake Hinnensee, situated in the lake district north of Berlin in Germany. The lake is a seepage lake with no surface inflows or outflows. To investigate the spatial patterns of groundwater surface water interactions as well as their temporal dynamics we applied a number of different techniques: snapshots of spatial patterns were determined by gridded measurements of temperature profiles in the lake sediment as well as with distributed temperature sensing (DTS), using a fiber optic cable placed at the sediment surface. The spatial resolution of measurements adequate for pattern detection was determined by comparing experimental designs at various spatial scales and resolutions. Continuous time series of water levels and temperature time series in piezometer transects at different locations along the lake shore give insight into both spatial variability and temporal dynamics of vertical hydraulic gradients and heat transport. Exfiltration rates of groundwater into the lake were estimated with 3 different approaches. The experimental methodologies were evaluated in a "cost-benefit" analysis, comparing effort with scientific benefit. The results show that groundwater exfiltration into the lake is to some extent variable in time and is highly variable in space: there is a strong gradient perpendicular to the lake shore as well as high heterogeneity along the lake shore.

Blume, T.; Tecklenburg, C.; Krause, S.; Lewandowski, J.

2012-12-01

375

Winter and Summer Views of the Salt Lake Region  

NASA Technical Reports Server (NTRS)

Magnificent views of the region surrounding Salt Lake City, Utah are captured in these winter and summer images from the Multi-angle Imaging SpectroRadiometer's vertical-viewing (nadir) camera. Salt Lake City, situated near the southeastern shore of the Great Salt Lake, is host to the 2002 Winter Olympic Games, which open Friday, February 8. Venues for five of the scheduled events are at city (indoor) locations, and five in mountain (outdoor) facilities. All ten can be found within the area contained in these images. Some of the outdoor events take place at Ogden, situated north of Salt Lake City and at Park City, located to the east. Salt Lake City is surrounded by mountains including the Wasatch Range to the east, and the temperature difference between the Great Salt Lake and the overlying atmosphere enhances the moisture content of winter storms. These factors, in combination with natural cloud seeding by salt crystals from the lake, are believed to result in greater snowfall in neighboring areas compared to more distant locales. In addition to the obvious difference in snow cover between the winter and summer views, water color changes in parts of the Great Salt Lake are apparent in these images. The distinctly different coloration between the northern and southern arms of the Great Salt Lake is the result of a rock-filled causeway built in 1953 to support a permanent railroad. The causeway has resulted in decreased circulation between the two arms and higher salinity on the northern side. The southern part of the lake includes the large Antelope Island, and at full resolution a bridge connecting it to the mainland can be discerned. These images are natural color views acquired on February 8, 2001 and June 16, 2001, respectively. Each image represents an area of about 220 kilometers x 285 kilometers. Image courtesy NASA/GSFC/LaRC/JPL, MISR Team.

2002-01-01

376

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.

377

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.

378

The Nyanza Project: Interdisciplinary Research Training In Tropical Lakes  

NASA Astrophysics Data System (ADS)

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.

Cohen, A. S.; Lezzar, K. E.; Michel, E.; O'Reilly, C. M.; Russell, J. M.; Nkotagu, H.; Kimirei, I.

2005-12-01

379

A Killer Lake  

NSDL National Science Digital Library

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.

Horvath, Thomas

2005-10-01

380

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.

381

Texas' Natural Lake  

E-print Network

of Engineers built Lake O? the Pines on Big Cypress Creek upstream of Caddo, the area no longer flooded as much. The regulated water flows from the dam stabilized lake levels, reducing regeneration of bald cypress forests. The cypress trees must have floods... 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...

Wythe, Kathy

2006-01-01

382

A Killer Lake  

NSDL National Science Digital Library

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.

Thomas Horvath

2005-01-01

383

Lake Tahoe Data Clearinghouse  

NSDL National Science Digital Library

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

Hoong, Connie

384

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.

385

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.

386

'Endurance' Untouched (vertical)  

NASA Technical Reports Server (NTRS)

This navigation camera mosaic, created from images taken by NASA's Mars Exploration Rover Opportunity on sols 115 and 116 (May 21 and 22, 2004) provides a dramatic view of 'Endurance Crater.' The rover engineering team carefully plotted the safest path into the football field-sized crater, eventually easing the rover down the slopes around sol 130 (June 12, 2004). To the upper left of the crater sits the rover's protective heatshield, which sheltered Opportunity as it passed through the martian atmosphere. The 360-degree view is presented in a vertical projection, with geometric and radiometric seam correction.

2004-01-01

387

Vertical slender jets  

NASA Technical Reports Server (NTRS)

The shape of a vertical slender jet of fluid falling steadily under the force of gravity is studied. The problem is formulated as a nonlinear free boundary-value problem for the potential. Surface tension effects are neglected. The use of perturbation expansions results in a system of equations that can be solved by an efficient numerical procedure. Computations were made for jets issuing from orifices in various shapes including an ellipse, a rectangle, and an equilateral triangle. Computational results are presented illustrating the propagation of discontinuities and the formation of thin sheets of fluid.

Geer, J. F.; Strikwerda, J. C.

1980-01-01

388

Crater Lake revealed  

USGS Publications Warehouse

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.

Ramsey, David W.; Dartnell, Peter; Bacon, Charles R.; Robinson, Joel E.; Gardner, James V.

2003-01-01

389

The origin of oriented lakes: Evidence from the Bolivian Amazon  

NASA Astrophysics Data System (ADS)

The presence of hundreds of rectangular and oriented lakes is one of the most striking characteristics of the Llanos de Moxos (LM) landscape in the Bolivian Amazon. Oriented lakes also occur in the Arctic coastal plains of Russia, Alaska and Canada and along the Atlantic Coastal Plain from northeast Florida to southeast New Jersey and along the coast of northeast Brazil. Many different mechanisms have been proposed for their formation. In the LM, Plafker's (1964) tectonic model, in which subsidence results from the propagation of bedrock faults through the foreland sediments, is the most accepted. However, this model has not been verified. Here, we present new results from stratigraphic transects across the borders of three rectangular and oriented lakes in the LM. A paleosol buried under mid-Holocene sediments is used as a stratigraphic marker to assess the vertical displacement of sediments on both sides of the alleged faults. Our results show that there is no vertical displacement and, therefore, that Plafker's model can be ruled out. We suggest that, among all the proposed mechanisms behind lake formation, the combined action of wind and waves is the most likely. The evidence from the LM provides new hints for the formation of oriented lakes worldwide.

Lombardo, Umberto; Veit, Heinz

2014-01-01

390

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)

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.

Trajanovski, S.; Albrecht, C.; Schreiber, K.; Schultheiß, R.; Stadler, T.; Benke, M.; Wilke, T.

2010-07-01

391

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...

392

Lake Effect Clouds  

NASA Technical Reports Server (NTRS)

The lake effect is particularly clear in this Sea-viewing Wide field-of-view Sensor (SeaWiFS) true-color image of the North American Great Lakes region, acquired December 5, 2000. Lakes Nipigon, Superior, and Michigan show striking contrasts between clear and cloudy air as the wind blows from the northwest across the lakes. As it flows across the relatively warm lakes, the cold dry air gathers heat and moisture from the surface. The warm moist air rises into the atmosphere and mixes vigorously with the cold dry air above. The layer of warm moist air deepens as it travels across the lake. Some of the evaporated water from the lake condenses into streamers of fog rising from the surface, while much of the moisture condenses to form a stratocumulus cloud in the upper half of the mixed layer. The cloud-forming water droplets may freeze into ice crystals and, due to accumulated water deposition over time, grow into snowflakes. This process can generate snowstorms that produce significant amounts of snowfall downwind. It is not uncommon for lake effect snowstorms to produce as much as two feet of snow within a 24-hour period in northwestern parts of New York and Pennsylvania. Image provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

2002-01-01

393

The lakes of Titan  

USGS Publications Warehouse

The surface of Saturn's haze-shrouded moon Titan has long been proposed to have oceans or lakes, on the basis of the stability of liquid methane at the surface. Initial visible and radar imaging failed to find any evidence of an ocean, although abundant evidence was found that flowing liquids have existed on the surface. Here we provide definitive evidence for the presence of lakes on the surface of Titan, obtained during the Cassini Radar flyby of Titan on 22 July 2006 (T16). The radar imaging polewards of 70?? north shows more than 75 circular to irregular radar-dark patches, in a region where liquid methane and ethane are expected to be abundant and stable on the surface. The radar-dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes, including associated channels and location in topographic depressions. Some of the lakes do not completely fill the depressions in which they lie, and apparently dry depressions are present. We interpret this to indicate that lakes are present in a number of states, including partly dry and liquid-filled. These northern-hemisphere lakes constitute the strongest evidence yet that a condensable-liquid hydrological cycle is active in Titan's surface and atmosphere, in which the lakes are filled through rainfall and/or intersection with the subsurface 'liquid methane' table. ??2007 Nature Publishing Group.

Stofan, E.R.; Elachi, C.; Lunine, J.I.; Lorenz, R.D.; Stiles, B.; Mitchell, K.L.; Ostro, S.; Soderblom, L.; Wood, C.; Zebker, H.; Wall, S.; Janssen, M.; Kirk, R.; Lopes, R.; Paganelli, F.; Radebaugh, J.; Wye, L.; Anderson, Y.; Allison, M.; Boehmer, R.; Callahan, P.; Encrenaz, P.; Flamini, E.; Francescetti, G.; Gim, Y.; Hamilton, G.; Hensley, S.; Johnson, W.T.K.; Kelleher, K.; Muhleman, D.; Paillou, P.; Picardi, G.; Posa, F.; Roth, L.; Seu, R.; Shaffer, S.; Vetrella, S.; West, R.

2007-01-01

394

Lake Wobegon Dice  

ERIC Educational Resources Information Center

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…

Moraleda, Jorge; Stork, David G.

2012-01-01

395

Archeology Around Yellowstone Lake  

NSDL National Science Digital Library

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.

Ann M. Johnson

396

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...

397

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...

398

Lessons from a Lake.  

ERIC Educational Resources Information Center

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)

Goethals, Susan

1997-01-01

399

Utah: Salt Lake City  

Atmospheric Science Data Center

... for the 2002 Winter Olympics, to be held in Salt Lake City, Utah. The mountains surrounding Salt Lake City are renowned for the dry, ... view. The Uinta Mountains contain the highest peaks in Utah and are notable as the most prominent east-west trending range in the ...

2014-05-15

400

Local response of a glacier to annual filling and drainage of an ice-marginal lake  

USGS Publications Warehouse

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.

Walder, J.S.; Trabant, D.C.; Cunico, M.; Fountain, A.G.; Anderson, S.P.; Anderson, R. Scott; Malm, A.

2006-01-01

401

Methane metabolism in a stratified boreal lake  

NASA Astrophysics Data System (ADS)

Stratified lakes, typical of the boreal zone, are naturally anoxic from their bottoms. In these lakes methanogenesis can account for up to half of organic matter degradation. However, a major part of the methane (CH4) is oxidized in the water column before reaching the atmosphere. Since methanotrophs use CH4 as their sole carbon and energy source, much CH4-derived carbon is incorporated into their biomass. Microbially produced CH4 has strongly negative ?13C compared to other carbon forms in ecosystems, making it possible to follow its route in food webs. However, only a few studies have estimated the amount of this microbial biomass or its carbon stable isotopic composition due to difficulties in separating it from other biomass or from other carbon forms in the water column. We estimated methanotrophic biomass from measured CH4 oxidation, and ?13C of the biomass from measured ?13C values of CH4, DIC, POM and DOC. An estimate of the fraction of methanotrophs in total microbial biomass is derived from bacterial community composition measurements. The study was made in, Alinen Mustajärvi, a small (area 0.75 ha, maximum depth 6.5 m, mean depth 4.2 m,), oligotrophic, mesohumic headwater lake located in boreal coniferous forest in southern Finland. CH4 and DIC concentrations and their ?13C were measured over the deepest point of the lake at 1 m intervals. 13C of DOM and POM were analyzed from composite samples from epi-, meta-, and hypolimnion. Evasion of CH4 and carbon dioxide from the lake surface to the atmosphere was estimated with boundary layer diffusion equations. CH4oxidation was estimated by comparing differences between observed concentrations and CH4potentially transported by turbulent diffusion between different vertical layers in the lake and also by actual methanotrophy measurements and from vertical differences in ?13C-CH4. The estimate of CH4 production was based on the sum of oxidized and released CH4. Molecular microbiology methods were used to evaluate which bacteria might be participating in these processes. A substantial part of the CH4 produced was oxidized in the anoxic water column. Our results further show that production and oxidation of CH4 was important in microbial biomass production and also affected the ?13C of biota in the water column.

Nykänen, Hannu; Peura, Sari; Kankaala, Paula; Jones, Roger

2013-04-01

402

Lake Trout Rehabilitation in Lake Erie: A Case History  

Microsoft Academic Search

Native lake trout (Salvelinus namaycush) once thrived in the deep waters of eastern Lake Erie. The impact of nearly 70 years of unregulated exploitation and over 100 years of progressively severe cultural eutrophication resulted in the elimination of lake trout stocks by 1950. Early attempts to restore lake trout by stocking were unsuccessful in establishing a self-sustaining population. In the

Floyd C. Cornelius; Kenneth M. Muth; Roger Kenyon

1995-01-01

403

Relationships between lake macrophyte cover and lake and landscape features  

Microsoft Academic Search

We examined the ability of lake and landscape features to predict a variety of macrophyte cover metrics using 54 north temperate lakes. We quantified submersed cover, emergent cover, floating leaf cover, Eurasian watermilfoil cover and total macrophyte cover. Measured lake features included lake physio-chemical and morphometric variables and landscape features included hydrologic, catchment and land use\\/cover variables. Univariate regression analyses

Kendra Spence Cheruvelil; Patricia A. Soranno

2008-01-01

404

Mono Lake endangered  

NASA Astrophysics Data System (ADS)

Can Mono Lake survive Los Angeles' need for water? An environmental impact study of the Mono Basin in eastern California predicts severe ecological consequences if the city of Los Angeles continues to divert water in large amounts from streams feeding the lake. Mono Lake and its basin were designated a National Forest Scenic Area in 1984.The National Research Council (NRC) report indicates that continued diversions would lower the lake level as much as 30 feet (˜9m). Salinity of the remaining water could double and lead to drastic changes in the physical appearance and ecological balance of the basin. In a recently published economic analysis, a University of California, Davis, environmental scientist reports that the lake is far more valuable to Californians than the cost of replacing water currently drawn for Los Angeles from the Mono Basin.

Maggs, William Ward

405

Polar lake circulation during ice break-up  

NASA Astrophysics Data System (ADS)

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.

Kirillin, Georgiy; Forrest, Alexander; Graves, Kelly; Laval, Bernard

2014-05-01

406

Anaglyph, Salt Lake City, Utah  

NASA Technical Reports Server (NTRS)

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)

2002-01-01

407

Isotopic and Chemical Balance of Large Lakes Beneath the East Antarctic Ice Sheet  

NASA Astrophysics Data System (ADS)

What we know of large deeply-buried subglacial lakes, such as lakes Vostok and Concordia in East Antarctica, is based on geophysical surveys, satellite remote sensing, ice core drilling, and modeling studies. Together, these data provide information on the geometry, patterns of melting and freezing, and internal processes of the lakes. Slow circulation is driven by lateral variations in water density which are associated with the effects of overburden pressure on the solidus temperature of ice. Evidence for circulation is provided by the pattern of melting and freezing over the ice ceiling and has been confirmed for lakes Vostok and Concordia. The mass, momentum, and energy balance of these lakes have been examined from modeling and observational perspectives but equally fascinating questions concerning the balance of water isotopes and chemical species remain largely unexplored. Applying a steady-state, vertically-integrated model of lake dynamics and thermodynamics, we extend previous work to predict the areal variation of ?D, ?18O, and dissolved impurities. If pronounced spatial variations are present in Lake Vostok these might be expressed as vertical variations in the chemical and isotopic content of accreted ice in the Vostok ice core. The magnitude of such variations would differ from species to species and depend on the ice flow trajectory and patterns of melting and freezing at the lake ceiling.

Clarke, G. K.; Bell, R. E.; Studinger, M.

2005-12-01

408

Differences in UV transparency and thermal structure between alpine and subalpine lakes: implications for organisms†  

PubMed Central

Ultraviolet (UV) radiation is a globally important abiotic factor influencing ecosystem structure and function in multiple ways. While UV radiation can be damaging to most organisms, several factors act to reduce UV exposure of organisms in aquatic ecosystems, the most important of which is dissolved organic carbon (DOC). In alpine lakes, very low concentrations of DOC and a thinner atmosphere lead to unusually high UV exposure levels. These high UV levels combine with low temperatures to provide a fundamentally different vertical structure to alpine lake ecosystems in comparison to most lowland lakes. Here, we discuss the importance of water temperature and UV transparency in structuring alpine lake ecosystems and the consequences for aquatic organisms that inhabit them. We present transparency data on a global data set of alpine lakes and nearby analogous subalpine lakes for comparison. We also present seasonal transparency data on a suite of alpine and subalpine lakes that demonstrate important differences in UV and photosynthetically active radiation (PAR, 400–700 nm) transparency patterns even within a single region. These data are used to explore factors regulating transparency in alpine lakes, to discuss implications of future environmental change on the structure and function of alpine lakes, and ways in which the UV transparency of these lakes can be used as a sentinel of environmental change. PMID:19707613

Rose, Kevin C.; Williamson, Craig E.; Saros, Jasmine E.; Sommaruga, Ruben; Fischer, Janet M.

2010-01-01

409

Evidence of offshore lake trout reproduction in Lake Huron  

USGS Publications Warehouse

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.

DeSorcie, Timothy J.; Bowen, Charles A., II

2003-01-01

410

Establishment of a vertical control network along the St. Croix River in New Brunswick and Maine  

USGS Publications Warehouse

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.

Lombard, Pamela J.

2013-01-01

411

ON-LINE TOOLS FOR PROPER VERTICAL POSITIONING OF VERTICAL SAMPLING INTERVALS DURING SITE ASSESSMENT  

EPA Science Inventory

This presentation presents on-line tools for proper vertical positioning of vertical sampling intervals during site assessment. Proper vertical sample interval selection is critical for generate data on the vertical distribution of contamination. Without vertical delineation, th...

412

Crater Lake Blue Through Time  

E-print Network

) is low. The blueness of water is greatest when densities of particles and algae are low. Deepest lake) Average height from Crater Lake's surface to caldera rim About 1,000 feet (305 m) Lake surface area 21 1800s,William Gladstone Steel recognized the importance of Crater Lake for scientific understanding. He

Torgersen, Christian

413

Bottom sediments of Lake Rotoma  

Microsoft Academic Search

Lake Rotoma is a deep (70–80 m), oligotrophic, warm monomictic lake of volcanic origin with insignificant stream inflow and no clearly defined outflow. For at least 60 years up to 1972 the lake level fluctuated markedly about an overall rising trend of some 6–10 m. Nearshore profiles are related to the prevailing wave climate superimposed upon the overall rising lake

Campbell S. Nelson

1983-01-01

414

Viruses in Lake Ladoga Plankton  

Microsoft Academic Search

Lake Ladoga is the largest lake in Europe. The ecological state of Lake Ladoga has a significant impact on water quality in the Neva River, the Gulf of Finland, and the Baltic Sea. The anthropogenic pollution during recent decades considerably modified the trophicity of Lake Ladoga. Presently, this level is regarded as mesotrophic [1]. Microbial loop is a new term

A. K. Sirotkin; O. V. Gavrilova; L. N. Voloshko; B. V. Gromov

2001-01-01

415

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.

2000-01-01

416

Vertical allometry: fact or fiction?  

PubMed

In pharmacokinetics, vertical allometry is referred to the clearance of a drug when the predicted human clearance is substantially higher than the observed human clearance. Vertical allometry was initially reported for diazepam based on a 33-fold higher human predicted clearance than the observed human clearance. In recent years, it has been found that many other drugs besides diazepam, can be classified as drugs which exhibit vertical allometry. Over the years, many questions regarding vertical allometry have been raised. For example, (1) How to define and identify the vertical allometry? (2) How much difference should be between predicted and observed human clearance values before a drug could be declared 'a drug which follows vertical allometry'? (3) If somehow one can identify vertical allometry from animal data, how this information can be used for reasonably accurate prediction of clearance in humans? This report attempts to answer the aforementioned questions. The concept of vertical allometry at this time remains complex and obscure but with more extensive works one can have better understanding of 'vertical allometry'. PMID:24534003

Mahmood, Iftekhar; Boxenbaum, Harold

2014-04-01

417

Whiting in Lake Michigan  

NASA Technical Reports Server (NTRS)

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

2002-01-01

418

Yellowstone Lake Nanoarchaeota  

PubMed Central

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

Clingenpeel, Scott; Kan, Jinjun; Macur, Richard E.; Woyke, Tanja; Lovalvo, Dave; Varley, John; Inskeep, William P.; Nealson, Kenneth; McDermott, Timothy R.

2013-01-01

419

Numerical studies of the 4-day oscillation in Lake Champlain  

NASA Astrophysics Data System (ADS)

The summer thermocline of Lake Champlain, which is found at depths of 20-30 m, oscillates with typical vertical amplitudes of 20-40 m and periods of ˜4 days. Fluctuations at the ends of the lake are opposite in phase and accompanied in the central lake by strong shears across the thermocline. These are basin-wide baroclinic disturbances which are forced by wind. A numerical, one-dimensional, two-layer, shallow-water model incorporating nonlinear and frictional effects in a rectangular basin forced by wind was first tested with idealized wind impulses. The results do not resemble the observed thermocline motion. However, when this simple model is forced with wind data from a nearby shore site, there is reasonable agreement between the model results and observed long-period thermocline motions in Lake Champlain. Dispersion effects appear to be negligible here. This contrasts with other long, narrow lakes where dispersion effects are important and internal surges are followed by wave trains resembling the soliton solutions of the Korteweg-deVries equation. A possible explanation for the different regime in Lake Champlain may be found in its unique bathymetry with sloping bottom at the ends and numerous embayments on the sides that provide traps to collect wind-driven warm water and then release it slowly during recovery of equilibrium, preventing the formation of steep fronts and soliton wave trains.

Hunkins, Kenneth; Manley, Thomas O.; Manley, Patricia; Saylor, James

1998-08-01

420

Depth and Differentiation of the Orientale Melt Lake  

NASA Technical Reports Server (NTRS)

Impact melt emplacement and evolution in lunar multi-ring basins is poorly understood since impact melt deposits in basins are generally buried by mare basalt fill and obscured by subsequent impact cratering. The relatively young Orientale basin, which is only partially flooded with mare basalt, opens a rare window into basin-scale impact melts. We describe the geology of impact melt-related facies in Orientale and suggest that the central depression of Orientale may represent a solidified impact melt lake that vertically subsided shortly after basin formation due to solidification and cooling. We use Lunar Orbiter Laser Altimeter (LOLA) data to measure the depth (approx. 1.75 km) and diameter (approx 350 km) of this central depression. If all the observed subsidence of the central depression is due to solidification and cooling, the melt lake should be approx 12.5-16 km deep, far more voluminous (approx 106 km3) than the largest known differentiated igneous intrusions on Earth. We investigate the possibility that the Orientale melt lake has differentiated and model 1) the bulk composition of the melt lake, 2) the operation of melt mixing in the melt lake, and 3) the chemical evolution of the resulting liquids on the An-Fo-Qz ternary in order to predict the lithologies that might be present in the solidified Orientale melt lake. Finally, we consider the possible significance of these lithologies.

Vaughan, W. M.; Head, J. W.; Hess, P. C.; Wilson, L.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2012-01-01

421

Glacial Lake Chicago Early Lake Michigan  

E-print Network

= 640 feet above sea level Shoreline was uneven with several inlets, peninsulas and offshore islands #12 of Glenwood Phase Two-Creeks Phase 12.2-11.8 kya Lake level was low Determined in 1905 when submerged spruce was older than the Calumet shoreline Water level was lower than Calumet Stage 1982 ­ another submerged

Cochran-Stafira, D. Liane

422

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....

423

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.

424

LAKE COLUSA SAN JOAQUIN  

E-print Network

Half Moon Bay Redwood City Mountain View San Jose Scotts Valley Morgan Hill Hollister Salinas Los Banos §¨¦80 QR99 §¨¦5 §¨¦40 §¨¦15 §¨¦10 §¨¦8 QR99 §¨¦505 QR1 £¤97 £¤101 £¤395 Lake Oroville Trinity Lake QR65 ^_ £¤101 §¨¦680 QR99 §¨¦5 QR12 QR4 QR26 QR16 QR49 £¤395 Mono Lake Camanche Reservoir New Hogan

425

Understanding Sediment Dynamics in a Shallow, Hypereutrophic Lake within the Middle St. Johns River: Lake Jesup, FL  

NASA Astrophysics Data System (ADS)

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.

Nielsen, S.; Anderson, W. T.; Corbett, D. R.; Fugate, D. C.; Scinto, L. J.; Thomas, S.; Brandt-Williams, S.

2011-12-01

426

Vertically reciprocating auger  

NASA Technical Reports Server (NTRS)

The mathematical model and test results developed for the Vertically Reciprocating Auger (VRA) are summarized. The VRA is a device capable of transporting cuttings that result from below surface drilling. It was developed chiefly for the lunar surface, where conventional fluid flushing while drilling would not be practical. The VRA uses only reciprocating motion and transports material through reflections with the surface above. Particles are reflected forward and land ahead of radially placed fences, which prevent the particles from rolling back down the auger. Three input wave forms are considered to drive the auger. A modified sawtooth wave form was chosen for testing, over a modified square wave or sine wave, due to its simplicity and effectiveness. The three-dimensional mathematical model predicted a sand throughput rate of 0.2667 pounds/stroke, while the actual test setup transported 0.075 pounds/stroke. Based on this result, a correction factor of 0.281 is suggested for a modified sawtooth input.

Etheridge, Mark; Morgan, Scott; Fain, Robert; Pearson, Jonathan; Weldi, Kevin; Woodrough, Stephen B., Jr.

1988-01-01

427

The Gains from Vertical Scaling  

ERIC Educational Resources Information Center

It is often assumed that a vertical scale is necessary when value-added models depend upon the gain scores of students across two or more points in time. This article examines the conditions under which the scale transformations associated with the vertical scaling process would be expected to have a significant impact on normative interpretations…

Briggs, Derek C.; Domingue, Ben

2013-01-01

428

Measuring Growth with Vertical Scales  

ERIC Educational Resources Information Center

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…

Briggs, Derek C.

2013-01-01

429

Vertical axis wind turbine motor  

Microsoft Academic Search

A wind power conversion turbine motor has a body supported to rotate about a vertical axis and carrying a plurality of substantially upright vanes substantially spaced from the vertical axis and circumferentially spaced from one another so that wind thrusting propulsively against outer sides of the vanes can move across the space circumscribed by the vanes and thrust propulsively against

Rumsey

1977-01-01

430

Modeling Verticality Estimation During Locomotion  

E-print Network

for gravitational vertical estimation is introduced including an inclinometer combined with an imu, as proposed´eal, Qc, Canada 3 Laboratoire de Physiologie de la Perception et de l'Action, Coll`ege de France, Paris, France Abstract Estimation of the gravitational vertical is a fundamental problem faced by locomoting

Hayward, Vincent

431

Quebec: Lake Manicouagan  

Atmospheric Science Data Center

article title:  Manicouagan Impact Structure, Quebec     View ... in this image represents the remnants of one of the largest impact craters still preserved on the surface of the Earth. Lake Manicouagan in ...

2013-04-17

432

TEACH Great Lakes  

NSDL National Science Digital Library

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.

1969-12-31

433

Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover  

NASA Technical Reports Server (NTRS)

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.

Squyres, S. W.; Andersen, D. W.; Nedell, S. S.; Wharton, R. A. Jr; Wharton RA, J. r. (Principal Investigator)

1991-01-01

434

Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover.  

PubMed

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

Squyres, S W; Andersen, D W; Nedell, S S; Wharton, R A

1991-01-01

435

Lake Superior, Duluth, MN  

NASA Technical Reports Server (NTRS)

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.

1973-01-01

436

Lake Chad, Chad, Africa  

NASA Technical Reports Server (NTRS)

Hydrologic and ecologic changes in the Lake Chad Basin are shown in this Oct 1992 photograph. In space photo documentation, Lake Chad was at its greatest area extent (25,000 sq. km.) during Gemini 9 in June 1966 (see S66-38444). Its reduction during the severe droughts from 1968 to 1974 was first noted during Skylab (1973-1974). After the drought began again in 1982, the lake reached its minimum extent (1,450 sq. km.) in Space Shuttle photographs taken in 1984 and 1985. In this STS-52 photograph, Lake Chad has begun to recover. The area of the open water and interdunal impoundments in the southern basin (the Chari River Basin) is estimated to be 1,900 to 2100 sq. km. Note the green vegetation in the valley of the K'Yobe flow has wetted the northern lake basin for the first time in several years. There is evidence of biomass burning south of the K'Yobe Delta and in the vegetated interdunal areas near the dike in the center of the lake. Also note the dark 'Green Line' of the Sahel (the g

1992-01-01

437

A Killer Lake  

NSDL National Science Digital Library

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.

Horvath, Thomas

438

Trace Metal Associations in an Anoxic Lake: the Relative Roles of Organic Carbon and Reduced Sulfur  

NASA Astrophysics Data System (ADS)

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.

Poulson Brucker, R.; McManus, J.; Severmann, S.; Owens, J.; Lyons, T.

2008-12-01

439

The Role of Groundwater for Lake-Water Quality and Quantification of N Seepage.  

PubMed

The heterogeneous nature of both groundwater discharge to a lake (inflow) and nitrate concentrations in groundwater can lead to significant errors in calculations of nutrient loading. Therefore, an integrated approach, combining groundwater flow and transport modelling with observed nitrate and ammonium groundwater concentrations, was used to estimate nitrate loading from a catchment via groundwater to an oligotrophic flow-through lake (Lake Hampen, Denmark). The transport model was calibrated against three vertical nitrate profiles from multi-level wells and 17 shallow wells bordering a crop field near the lake. Nitrate concentrations in groundwater discharging to the lake from the crop field were on average 70 times higher than in groundwater from forested areas. The crop field was responsible for 96% of the total nitrate loading (16.2 t NO3 /year) to the lake even though the field only covered 4.5% of the catchment area. Consequently, a small change in land use in the catchment will have a large effect on the lake nutrient balance and possible lake restoration. The study is the first known attempt to estimate the decrease of nitrate loading via groundwater to a seepage lake when an identified catchment source (a crop field) is removed. PMID:25324021

Kidmose, Jacob; Engesgaard, Peter; Ommen, Daniela A Oliveira; Nilsson, Bertel; Flindt, Mogens R; Andersen, Frede Ø

2014-10-16

440

Exotic species in large lakes of the world  

Microsoft Academic Search

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,

S. R Hall; E. L Mills

2000-01-01

441

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

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,

David F. Burger; David P. Hamilton; Conrad A. Pilditch

2008-01-01

442