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1

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

2

Hydrothermal vents in Lake Tanganyika, East African, Rift system  

NASA Astrophysics Data System (ADS)

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

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

1993-06-01

3

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

4

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

5

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

6

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

7

Fate of heterotrophic bacteria in Lake Tanganyika (East Africa).  

PubMed

Bacterial mortality was studied using two complementary methods between 2002 and 2004 in the two main basins (north and south) of Lake Tanganyika. The disappearance of radioactivity from the DNA of natural assemblages of bacteria previously labeled with tritiated thymidine was used to estimate the mortality due to grazing by predators (72%) and due to the cell lysis (28%). Measurements of ingestion rate of bacteria by protozoa using fluorescent micro-particles yielded protozoan grazing rates similar to those provided by the thymidine method, and showed that heterotrophic nano-flagellates were responsible for most of the grazing pressure on the bacterial community of the pelagic zone (92-99%). Bacterial cell lysis was the second process involved in bacterial mortality, ranking before ciliate grazing. Overall, bacterial mortality was balanced with bacterial production. With regard to the assessment of the trophic role of bacteria, it was estimated that c. 5-8% of the organic carbon taken up by bacteria was converted into protozoan biomass and was thus available for metazoans. PMID:17983442

Pirlot, Samuel; Unrein, Fernando; Descy, Jean-Pierre; Servais, Pierre

2007-12-01

8

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

9

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

10

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

Microsoft Academic Search

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

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

2008-01-01

11

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

12

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

13

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

14

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

PubMed

Lake Tanganyika is a globally important lake with high endemic biodiversity. Millions of people in the lake basin depend on several fish species for consumption. Due to the importance of fish consumption as an exposure route of mercury to humans, we sampled Lake Tanganyika in 2000 to assess total mercury concentrations and biomagnification of total mercury through the food web. Stable nitrogen and carbon isotope analyses of food web structure indicate a complex food web with overlapping omnivory with some specialist fish species. Stable nitrogen isotope analyses further confirm that mercury is biomagnifying through the Tanganyika food web at rates similar to those seen in Lakes Malawi and Victoria, the other two African Great Lakes. Most collected fish species and all invertebrate species had mercury concentrations below 0.2 microg Hg/g wet weight. However, several fish species, Ctenochromis horei (average 0.15 microg/g ww), Neolamprologus boulengeri (0.2 microg/g ww) , Bathybates spp.spp. (0.21 microg/g ww), Mastacembelus cunningtoni (0.22 microg/g ww) and Clarias theodorae (0.22 microg/g ww) approached or slightly exceeded the World Health Organization (WHO)'s recommended guideline of 0.2 microg Hg/g for vulnerable populations with high rates of fish consumption. Two individuals of the piscivorous fish species Lates microlepis (0.54, 0.78 microg/g ww) and a Polypterus congicus (1.3 microg/g ww) exceeded the international marketing limit value of 0.5 microg/g ww. Because C. theodorae and L. microlepis are also important market fish species, there is a need to monitor mercury concentrations in internationally marketed fish from Lake Tanganikya to ensure that those fish do not present a risk to human consumers. PMID:18559282

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

2008-09-01

15

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

16

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

17

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, P. K.; Stager, J. C.; Colman, S. M.

2003-01-01

18

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

19

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

20

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

21

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

22

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

23

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

24

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

25

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

26

Hydrology and Acoustic Measurements of Lake Tanganyika.  

National Technical Information Service (NTIS)

Lake Tanganyika was selected as an experimental site for the investigation of low-frequency sound attenuation because of its high ambient temperature and low dissolved salt content. Hydrological measurements obtained in support of the acoustic program exa...

E. N. Jones J. M. Gorman W. H. Thorp D. G. Browning

1973-01-01

27

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

28

East Coast Fever in Cattle between Lakes Victoria and Tanganyika (Tanzania).  

National Technical Information Service (NTIS)

The work gives a review on etiology, pathogenesis and epizootilogy of this animal disease of much economic importance for East Africa. Prophylaxis, combat, control and eradication of the effective combat of the vector tick Rhipicephalus appendiculatus. Re...

L. Hussel C. Hassan B. Al-Janabi S. Kalif R. Wiessner H. Strickrodt

1989-01-01

29

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

30

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

31

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

32

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

PubMed Central

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.

Takahashi, Tetsumi; Koblmuller, Stephan

2011-01-01

33

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

34

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

35

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

36

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

37

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

38

Trematodes Indicate Animal Biodiversity in the Chilean Intertidal and Lake Tanganyika  

Microsoft Academic Search

Trematode communities in populations of estuarine snails can reflect surrounding animal diversity, abundance, and trophic inter- actions. 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.

Ryan F. Hechinger; Kevin D. Lafferty; Armand M. Kuris

2008-01-01

39

Marine incursion: the freshwater herring of Lake Tanganyika are the product of a marine invasion into west Africa.  

PubMed

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

40

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

41

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

42

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

43

Project Bold Venture: Lake Tanganyika Sound Attenuation Experiment.  

National Technical Information Service (NTIS)

In order to determine the cause of the low-frequency sound attenuation anomaly in seawater, comparative measurements are being made in freshwater. The Lake Tanganyika experiment was conducted to determine the temperature dependency of the anomaly and to o...

D. G. Browning J. M. Gorman E. N. Jones W. H. Thorp R. H. Mellen

1972-01-01

44

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

45

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

46

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

47

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

48

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

49

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

50

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

51

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

52

Relationship Between Primary Production and Fish Production in Lake Tanganyika  

Microsoft Academic Search

Primary production in Lake Tanganyika, 0.8 g C?m?day, is not high by comparison with other tropical lakes yet the fisheries of the lake maintain annual yields of 125 kg hectare (1.3 g C?m?year). The efficiency of carbon transfer to the fishery from primary production is anomalously high among the lakes of the world and approximates the efficiencies of the most

R. E. Hecky; E. J. Fee; H. J. Kling; J. W. M. Rudd

1981-01-01

53

Comparison of fish yields from prediction models between Lakes Tanganyika and Kariba  

Microsoft Academic Search

Fish yield from catch data and from prediction models in Lake Kariba is compared to that in Lake Tanganyika. Fish yields from catch data in L. Tanganyika are above expectation from the rates of algal production, and this disparity is not experienced in L. Kariba. Of the two hypotheses that have been forwarded to explain the situation in L. Tanganyika

C. Machenal; P. Fair

1986-01-01

54

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

55

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

56

Mating and Parental Care in Lake Tanganyika's Cichlids  

PubMed Central

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.

Sefc, Kristina M.

2011-01-01

57

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

58

Evolutionary history of Lake Tanganyika's scale-eating cichlid fishes.  

PubMed

Although Lake Tanganyika is not the most species-rich of the Great East African Lakes it comprises by far the greatest diversity of cichlid fishes in terms of morphology, ecology, and breeding styles. Our study focuses on the Tanganyikan cichlid tribe Perissodini, which exhibits one of the most peculiar feeding strategies found in cichlids-scale-eating. Their evolutionary history was reconstructed from 1416 bp DNA sequence of two mitochondrial genes (ND2 and partial control region) and from 612 AFLP markers. We confirm the inclusion of the zooplanktivorous genus Haplotaxodon in the tribe Perissodini, and species status of Haplotaxodon trifasciatus. Within the Perissodini, the major lineages emerged within a short period roughly 1.5-2 MYA, which makes their radiation slightly younger than that of other Tanganyikan cichlid tribes. Most scale-eaters evolved in deep-water habitat, perhaps associated with the previously documented radiations of other deep-water dwelling cichlid lineages, and colonized the shallow habitat only recently. PMID:17383901

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

2007-09-01

59

Report on Experiment Conducted on Lake Tanganyika, April 1969.  

National Technical Information Service (NTIS)

A series of hydrological and biological tests were conducted on Lake Tanganyika to examine the effects of 1.8 pound TNT explosive sound signals on the commercial fishery found there. The evaluation of the explosive effects was a preliminary requirement fo...

E. N. Jones A. L. Brooks

1969-01-01

60

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

61

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

62

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

63

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

64

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

65

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

66

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

67

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

68

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

69

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

70

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

71

Attenuation Research: A Case for Lake Tanganyika.  

National Technical Information Service (NTIS)

The results of the recent Lake Superior experiment indicate that the anomalous low frequency attenuation observed in sea water also exists in freshwater. Although this would tend to eliminate some possible explanations such as dissolved salts, it does not...

D. G. Browning E. N. Jones R. H. Mellen W. H. Thorp

1968-01-01

72

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

73

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

74

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

75

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

76

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

77

Trematodes indicate animal biodiversity in the Chilean intertidal and Lake Tanganyika.  

PubMed

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. PMID:18576749

Hechinger, Ryan F; Lafferty, Kevin D; Kuris, Armand M

2008-08-01

78

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

79

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

80

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

81

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

Microsoft Academic Search

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

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

2005-01-01

82

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

83

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

84

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

85

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

86

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

87

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

88

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

89

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

90

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

91

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

92

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

93

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

94

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

95

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

96

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

97

General nutrient distribution in the water column of Northern Lake Tanganyika  

Microsoft Academic Search

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

David Nahimana; Natacha Brion; Willy Baeyens; Gaspard Ntakimazi

2008-01-01

98

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

99

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

100

Geologic hypotheses of Lake Tanganyika region, Zaire, drawn from ERTS imagery  

NASA Technical Reports Server (NTRS)

Based on initial work in the Lake Tanganyika area of eastern Zaire, it has been concluded that ERTS imagery is extremely useful for reconnaissance level geologic mapping and analysis in this region of the humid tropics. In particular, ERTS imagery has proven useful for recognizing and mapping regional structural units, for recognizing major structural features, and for arriving at some preliminary hypotheses about the mineral potential of the area. Results so far indicate that ERTS imagery can make a major contribution to the development of the mineral resources of the country. Research has concentrated on applications of ERTS imagery in the field of cartography, geology, forestry, hydrology and agriculture. For the work in geology, a test site was chosen in eastern Zaire on the shore of Lake Tanganyika in the vicinity of the Lukuga River. This area was selected because of its varied geology and the existence of two frames of cloud-free ERTS imagery.

Wolyce, U.; Ilunga, S.

1974-01-01

101

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

102

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

103

Spatial and temporal changes in copepod zooplankton communities of Lake Tanganyika  

Microsoft Academic Search

Pelagic Copepoda zooplankton in Lake Tanganyika were sampled over two years at three localities. When the data from both years were pooled, post-naupliar cyclopoids formed 76% of the pelagic post-naupliar Copepoda off Bujumbura, 83% off Kigoma and 62% off Mpulungu. During both sampling years, dry weight biomass of post-naupliar copepod stages decreased at sampling sites in the order Bujumbura >

H. Kurki; I. Vuorinen; E. Bosma; D. Bwebwa

1999-01-01

104

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

105

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

106

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

107

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

PubMed Central

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.

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

2012-01-01

108

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

109

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

SciTech Connect

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, J.J.; Mondeguer, A. (Universite de Bretagne Occidentale, Brest (France)); Thouin, C. (Centre Universitaire Regional de Toliara (Madagascar)); Kalala, T. (Centre de Recherche en Sciences Naturelles, Sud-Kivu (Zaire))

1989-11-01

110

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

111

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

112

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

113

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

114

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

115

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

116

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

117

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

Microsoft Academic Search

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

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

2007-01-01

118

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

119

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

120

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

PubMed

Trace metal (Cu, Pb, Fe, Mn, Zn, Cd) concentrations were determined in water, sediments, various fin fish species and a bivalve (Mutela spekei) 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 a variety of fishing techniques. No differences in trace metal concentrations were observed in both inshore and offshore waters. Levels in inshore sediments were much higher than for the offshore ones. Sediment input through run-off may have been the cause for the differences. However, the levels were much lower than those reported for Lake Malawi sediments. The concentrations in the fish tissue were within ranges reported elsewhere for Lake Tanganyika fish species. The centrapomid Lates stappersii and the clupeids Limnothrissa miodon and Stolothrissa tanganicae are the most important commercial species in the lake followed by Lates marie. Lead and cadmium are of concern to human health. The mean concentrations of the two metals in the commercial fish species were as follows: L. stappersii (5.03 microg Pb/g, 0.28 microg Cd/g); L. marie (4.96 microg Pb/g, 0.25 microg Cd/g); L. miodon (4.64 microg Pb, 0.38 microg Cd); and S. tanganicae (4.96 microg Pb/g, 0.39 microg Cd/g). Levels of lead and iron in the bivalve species were exceptionally very high, being 11.08 and 6.54 mg/g, respectively. PMID:12462578

Chale, F M M

2002-11-01

121

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

122

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

123

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

124

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

125

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

126

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

127

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

128

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

129

Genetic population structure as indirect measure of dispersal ability in a Lake Tanganyika cichlid.  

PubMed

Diversification and speciation processes are influenced by intrinsic (ecological specialization, dispersal) and extrinsic (habitat structure and instability) factors, but the effect of ecological characteristics on dispersal is difficult to assess. This study uses mitochondrial control region sequences to investigate the population structure and demographic history of the endemic Lake Tanganyika cichlid Neolamprologus caudopunctatus with a preference for the rock-sand interface along two stretches of continuous, rocky shoreline, and across a sandy bay representing a potential dispersal barrier. Populations along uninterrupted habitat were not differentiated; whereas, the sandy bay separated two reciprocally monophyletic clades. The split between the two clades between 170,000 and 260,000 years BP coincides with a period of rising water level following a major lowstand, and indicates that clades remained isolated throughout subsequent lake level fluctuations. Low long-term effective population sizes were inferred from modest genetic diversity estimates, and may be due to recent population expansions starting from small population sizes 45,000-60,000 years BP. Comparisons with available data from specialized rock-dwelling species of the same area suggest that habitat structure and lake level fluctuations determine phylogeographic patterns on large scales, while fine-scale population structure and demography are modulated by species-specific ecologies. PMID:16897454

Koblmüller, Stephan; Sefc, Kristina Maria; Duftner, Nina; Warum, Marko; Sturmbauer, Christian

2007-06-01

130

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

131

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

132

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.

Kinoti, George

1964-01-01

133

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

134

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

135

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

136

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.

2014-01-01

137

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

138

The transmission of Schistosoma haematobium in an area of Lake Province, Tanganyika  

PubMed Central

This paper records the results of detailed studies carried out over a two-year period on the transmission of Schistosoma haematobium in an area of Lake Province, Tanganyika. The ecology of a variety of snail habitats is described; and data on the biology of the principal molluscan host (Bulinus (Physopsis) nasutus productus), on seasonal fluctuations in its population density and associated cercarial infection rates, on its response to desiccation and on other aspects of population dynamics are presented and discussed. Taking into consideration the seasonal fluctuation in snail numbers which occurs in the area and the snails' capacity to survive desiccation, it is considered that a substantial reduction in transmission of S. haematobium might be effected by application of a molluscicide timed so as to lower the population density before aestivation begins, followed by a second treatment when the habitats have been refilled by rainfall to reduce yet further the population that has survived the first treatment and subsequent desiccation. It is also suggested that a combination of methods directed against two stages in the schistosome life-cycle—the snail and the miracidium—by application of molluscicides and treatment of infected persons might be more efficacious than an attempt merely to reduce snail density and alter the population structure.

Webbe, G.

1962-01-01

139

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

140

Report on the International Conference on the Conservation and Biodiversity of Lake Tanganyika (1st). Held in Bujumbura (Burundi) on March 11-13, 1991 (Compte Rendu de la Conference Internationale sur la Conservation et la Biodiversite du Lac Tanganyika (Premiere)).  

National Technical Information Service (NTIS)

Lake Tanganyika, the largest of the African rift lakes, is also one of the most unusual biotic resources on the planet. It harbors over 500 species of endemic animals, most of which have evolved in situ within the lake basin during the lake's long and com...

A. S. Cohen

1991-01-01

141

Phylogenetic relationships of the Lake Tanganyika cichlid tribe Lamprologini: the story from mitochondrial DNA.  

PubMed

The Lamprologini are the most species-rich and diverse tribe of Lake Tanganyika cichlids, comprising around 90 described species. We reconstruct the most complete ( approximately 70 species) mtDNA phylogeny to date for this tribe, based on NADH dehydrogenase subunit 2 (ND2 approximately 1047 bp) and the non-coding control region ( approximately 874 bp) and examine the degree to which mtDNA trees are good proxies for species trees. Phylogenetic relationships are assessed using Bayesian inference, maximum likelihood and maximum parsimony to determine the robustness of relationships. The resulting topologies are largely congruent and only the tree produced by an unpartitioned BI analysis is rejected using the non-parametric likelihood-based AU test. The trees are remarkably balanced, with two major clades consistently recovered in all analyses and with reasonable support. A smaller clade of deep-water species is also recovered. Overall support is good, when compared to some groups that have undergone adaptive radiation and rapid lineage formation. The much-expanded phylogeny of the group helps resolve the placement of some previously problematic taxa, such as Neolamprologus moori, highlighting the importance of greater taxonomic sampling. The results include a number of divergent placements of closely related species, and the following genera Neolamprologus, Lamprologus, Julidiochromis, Telmatochromis are not monophyletic, with alternative hypotheses consistent with traditional taxonomy providing a significantly worse fit to the data. We find several examples of divergent mtDNA taxa sequences of presumed closely related species. This could be due to incorrect taxonomy or to the failure of the mtDNA to reflect species relationships and may support the hypothesis that speciation within this group has been facilitated by introgressive hybridisation. PMID:17416538

Day, Julia J; Santini, Simona; Garcia-Moreno, Jaime

2007-11-01

142

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

143

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.

Kerschbaumer, M; Mitteroecker, P; Sturmbauer, C

2014-01-01

144

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

145

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

146

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

147

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

148

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

149

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

150

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

151

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

152

7. View southwest, east facade of Lake Forest (original Forest ...  

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

7. View southwest, east facade of Lake Forest (original Forest Cottage structure incorporated into renamed structure) - Lake Placid Club, Forest Wing, East side of Mirror Lake Drive, North of State Route 86 & Main, North Elba, Essex County, NY

153

5. View north, south and east facade of Lake Forest ...  

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

5. View north, south and east facade of Lake Forest (original Forest Cottage structure incorporated into renamed structure) - Lake Placid Club, Forest Wing, East side of Mirror Lake Drive, North of State Route 86 & Main, North Elba, Essex County, NY

154

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

155

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

156

INTERSECTION OF 445 NORTH & 1040 EAST, SALT LAKE CITY, ...  

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

INTERSECTION OF 445 NORTH & 1040 EAST, SALT LAKE CITY, UT. VIEW LOOKING SOUTH. REPHOTOGRAPH OF HISTORIC SHIPLER PHOTO # 18272, UTAH STATE HISTORICAL SOCIETY COLLECTION. - Salt Lake City Cemetery, 200 N Street, Salt Lake City, Salt Lake County, UT

157

200 MAIN STREET, SALT LAKE CITY, UT. VIEW LOOKING EAST ...  

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

200 MAIN STREET, SALT LAKE CITY, UT. VIEW LOOKING EAST OF "MAIN' STREET. REPHOTOGRAPH OF HISTORIC SHIPLER PHOTO # 18273, UTAH STATE HISTORICAL SOCIETY COLLECTION. - Salt Lake City Cemetery, 200 N Street, Salt Lake City, Salt Lake County, UT

158

PLAT X41601 EAST (SALT LAKE CITY CEMETERY LOCATER), SALT LAKE ...  

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

PLAT X-4-160-1 EAST (SALT LAKE CITY CEMETERY LOCATER), SALT LAKE CITY, UT. VIEW LOOKING SOUTH AT CEMETERY BETWEEN OLIVE STREET (1020 EAST) AND 1000 EAST STREET, REPHOTOGRAPH OF HISTORIC SHIPLER PHOTO # 12049, UTAH STATE HISTORICAL SOCIETY COLLECTION. - Salt Lake City Cemetery, 200 N Street, Salt Lake City, Salt Lake County, UT

159

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

160

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

161

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

162

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

163

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

164

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

165

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

166

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

167

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

168

Sensitivity of the East African rift lakes to climate variability  

Microsoft Academic Search

Lakes in the East African Rift have provided excellent proxies to reconstruct past climate changes in the low latitudes. The lakes occupy volcano-tectonic depressions with highly variable climate and hydrological setting, that present a good opportunity to study the climatic and hydrogeological influences on the lake water budget. Previous studies have used lake floor sediments to establish the sensitivity of

L. Olaka; M. H. Trauth

2009-01-01

169

SEXTON'S HOUSE. 200 NORTH N STREET (895 EAST), SALT LAKE ...  

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

SEXTON'S HOUSE. 200 NORTH N STREET (895 EAST), SALT LAKE CITY, UT. VIEW OF THE NORTHEAST. REPHOTOGRAPH OF HISTORIC SHIPLER PHOTO # 18996, UTAH STATE HISTORICAL SOCIETY COLLECTION. - Salt Lake City Cemetery, 200 N Street, Salt Lake City, Salt Lake County, UT

170

44. GATES FOR REPLENISHING OWENS LAKE VIEW EAST Los ...  

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

44. GATES FOR REPLENISHING OWENS LAKE VIEW EAST - Los Angeles Aqueduct, From Lee Vining Intake (Mammoth Lakes) to Van Norman Reservoir Complex (San Fernando Valley), Los Angeles, Los Angeles County, CA

171

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

172

Radiocarbon dating of East african lake levels.  

PubMed

The fluctuations of the key East African lakes discussed are summarized in Fig. 4 which also includes the available evidence from Lake Rukwa (42) and Lake Chad (43) Exceot for Lake Victoria, all of these now lack surface outlets and are situated in much drier climates than the major lakes of the Western Rift Valley, which remain filled to their overflow levels. The apparent differendes among the fluctuations of the lakes are partly due to differendes in the nature of the evidence or the intensity of research or both, although there must also have been important local differences in the histories of the lakes Yet the consistencies are far more striking, most notably the coincidence of early Holocene high stands. Between 10,000 and 8,000 years ago, it seems that lakes in many parts of tropical Africa were greatly enlarged. Where evidence for the previous span of time is well resolved, it appears that transgressions leading to this high stand began about 12,000 years ago, and evidende from three basins (Victoria, Nakuru, and Chad) indicates a pause or minor recession just at or before 10,000 years ago. Wherever information is available for the period preceding 12,000 years ago, it can consistentlybe shown that lakes were much small-er . Several basins (Rudolf, Nakuru, and Chad) also show traces of much earlier phases of lake expansion. which are not yet well dated but which all occurred more then 20,000 years ago. The Holocene record subsequent to the maximum of 10,00 to 8,000 years ago is more complex. Three basins (Rudolf, Nakuru, and Chad) show an apparently concordant, positive oscillation at some point between 6000 and 4000 years ago, but it is uncertain how widely this episode is represented. Although many of these lakes that are now closed filled to overflowing at least once during the late Quaternary, it is evident from Fig. 4 that the periods of expansion were short-lived compared with phases of contraction to levels near those of today. This pattern may be in accord with fragmentary evidence from lower and middle Pleistocene formations, such as those of Olduvai(44)and Paninj (45), within which some relatively short-term lake expansions can be documented, but which lack evidence for any marked long-term departure from a balance of evaporation and precipitation similar to the present one Further, this pattern of brief moist pulsations, with a duration of perhaps 2000 to 5000 years, is also suggested by other late Pleistocene and Holocene sequences (based primarily on geomorphological and palynological evidence) from the Saharan area, Angola, and South Africa (46). In default of radiometric dating, such complex successions of relatively brief moist intervals provide few stratigraphic markers of broad applicability. This, together with the fact that vegetation, weathering processes, montane glaciers, lake size, lake salinity, and so forth are all likely to reflect the diverse aspects of Climatic change differently, underscores the strictures of Cooke (2) and Flint (3) against the use of pluvials and intrlvasas a basis for subdividing Quaternary time in Africa. Positive correlations between high-latitude glacial advances or maxima and intervals of high lake levels have been demonstrated or suggested for many areas of mid-latitude North America and Eurasia (47), and similar patterns have often been regarded as probable for tropical Africa as well. However, the evidence summarized above shows a notable lack of such correlations for the tropical lakes considered here. If glaciation and tropical lake levels were connected at all, then a far more complex-delayed, multiplefactor, or inverse-relationship must be sought for the late Quaternary (48). This renders the introduction of new climato-stratigraphic terms such as hypothermal and interstadial (49) of questionable value in East Africa. Further, whereas the so-called pluvial lakes of higher latitudes were probably due primarily to reduced evaporation (50), our computations for the early Holocene lakes Nakuru and Naivasha, as well as for the oscillations of Lake Rudolf and

Butzer, K W; Isaac, G L; Richardson, J L; Washbourn-Kamau, C

1972-03-10

173

Geophysical investigations of subglacial lakes Vostok and Concordia, East Antarctica  

Microsoft Academic Search

The subjects for this study are two subglacial lakes---Vostok and Concordia---located in East Antarctica. Lake Vostok is the largest known subglacial lake on Earth. Melting and freezing at the ice-water contact are known to occur in both lakes. These internal processes are important subjects for numerical modeling. The precise knowledge of the lake's bathymetry and the distribution of unconsolidated sediments

Irina Filina

2007-01-01

174

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

175

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

176

Influx of meltwater to subglacial Lake Concordia, East Antarctica  

Microsoft Academic Search

We present evidence for melting at the base of the ice that overlies Lake Concordia, an 800 km2 subglacial lake near Dome Concordia, East Antarctica, via a combination of glaciohydraulic melting (associated with the tilted ice ceiling and its influence on lake circulation\\/melting temperature) and melting by extreme strain heating (where the ice sheet is grounded). An influx of water

Anahita A. Tikku; Robin E. Bell; Michael Studinger; Garry K. C. Clarke; Ignazio Tabacco; Fausto Ferraccioli

2005-01-01

177

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

NASA Astrophysics Data System (ADS)

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

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

178

Colour-assortative mating among populations of Tropheus moorii, a cichlid fish from Lake  

Microsoft Academic Search

The species flocks of cichlid fishes in the East African Lakes Tanganyika, Malawi and Victoria are prime examples of adaptive radiation and explosive speciation. Several hundreds of endemic species have evolved in each of the lakes over the past several thousands to a few millions years. Sexual selection via colour- assortative mating has often been proposed as a probable causal

Harald Niederstatter; Anita Brandstatter; Burkhard Berger; Walther Parson; Jos Snoeks; Christian Sturmbauer

179

Does water hyacinth on East African lakes promote cholera outbreaks?  

PubMed

Cholera outbreaks continue to occur regularly in Africa. Cholera has been associated with proximity to lakes in East Africa, and Vibrio cholerae has been found experimentally to concentrate on the floating aquatic plant, water hyacinth, which is periodically widespread in East African lakes since the late 1980s. From 1994 to 2008, Nyanza Province, which is the Kenyan province bordering Lake Victoria, accounted for a larger proportion of cholera cases than expected by its population size (38.7% of cholera cases versus 15.3% of national population). Yearly water-hyacinth coverage on the Kenyan section of Lake Victoria was positively associated with the number of cholera cases reported in Nyanza Province (r = 0.83; P = 0.0010). Water hyacinth on freshwater lakes might play a role in initiating cholera outbreaks and causing sporadic disease in East Africa. PMID:20682884

Feikin, Daniel R; Tabu, Collins W; Gichuki, John

2010-08-01

180

Sensitivity of the East African rift lakes to climate variability  

NASA Astrophysics Data System (ADS)

Lakes in the East African Rift have provided excellent proxies to reconstruct past climate changes in the low latitudes. The lakes occupy volcano-tectonic depressions with highly variable climate and hydrological setting, that present a good opportunity to study the climatic and hydrogeological influences on the lake water budget. Previous studies have used lake floor sediments to establish the sensitivity of the East African rift lakes. This study focuses on geomorphology and climate to offer additional or alternative record of lake history that are key to quantifying sensitivity of these lakes as archives to external and internal climatic forcings. By using the published Holocene lake areas and levels, we analyze twelve lakes on the eastern arm of the East African rift; Ziway, Awassa, Turkana, Suguta, Baringo, Nakuru, Elmenteita, Naivasha, Natron, Manyara and compare with Lake Victoria, that occupies the plateau between the east and the western arms of the rift. Using the SRTM data, Hypsometric (area-altitude) analysis has been used to compare the lake basins between latitude 80 North and 30 South. The mean elevation for the lakes, is between 524 and 2262 meters above sea level, the lakes' hypsometric integrals (HI), a measure of landmass volume above the reference plane, vary from 0.31 to 0.76. The aridity index (Ai), defined as Precipitation/ Evapotranspiration, quantifies the water available to a lake, it encompasses land cover and climatic effects. It is lowest (arid) in the basin between the Ethiopian rift and the Kenyan rift and at the southern termination of the Kenyan Rift in the catchments of lake Turkana, Suguta, Baringo and Manyara with values of 0.55, 0.43, 0.43 and 0.5 respectively. And it is highest (wet) in the catchments of, Ziway, Awassa, Nakuru and Naivasha as 1.33,1.03 and 1.2 respectively, which occupy the highest points of the rift. Lake Victoria has an index of 1.42 the highest of these lakes and receives a high precipitation. We use a simple model written on a Matlab code to illustrate the lake volume and area response to climate of surficialy closed, graben shaped and panshaped lake basins. From preliminary results, lake basins that are sensitive to climate variability have a high HI and high aridity index, which will be presented in this conference

Olaka, L.; Trauth, M. H.

2009-04-01

181

The sensitivity of East African rift lakes to climate fluctuations  

Microsoft Academic Search

Sequences of paleo-shorelines and the deposits of rift lakes are used to reconstruct past climate changes in East Africa.\\u000a These recorders of hydrological changes in the Rift Valley indicate extreme lake-level variations on the order of tens to\\u000a hundreds of meters during the last 20,000 years. Lake-balance and climate modeling results, on the other hand, suggest relatively\\u000a moderate changes in

Lydia A. OlakaEric; Eric O. Odada; Martin H. Trauth; Daniel O. Olago

2010-01-01

182

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

183

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

184

STS-55 Earth observation of Lake Natron, Tanzania, East Africa  

NASA Technical Reports Server (NTRS)

STS-55 Earth observation taken aboard Columbia, Orbiter Vehicle (OV) 102, shows Lake Natron in Tansania, in the 35-mile-wide East African Rift Valley. This lake is surrounded by sodium carbonate volcanoes. Through erosion, these salts of volcanic origin are transported into the rift valley lakes. The various shades of bright red reflecting from the lake result from the water chemistry and biotic blooms. The white spots in the lakebed are drying soda salts. The depth and circulation of the water in the southern end of the lake cause it to appear dark blue rather than bright red. In the repeated photographs of this lake from orbit, we have seen the extent and intensity of its colors fluctuate seasonally. In this photograph, the biotic activity appears to be at a peak. Such a large extent of red-colored water was not present in the photos taken from STS-56, just a few days before (04-10-93).

1993-01-01

185

The diatom flora and limnology of lakes in the Amery Oasis, East Antarctica  

Microsoft Academic Search

The diatom flora of three lakes in the ice-free Amery Oasis, East Antarctica, was studied. Two of the lakes are meltwater reservoirs, Terrasovoje Lake (31 m depth) and Radok Lake (362 m depth), while Beaver Lake (>435 m depth) is an epishelf lake. The lakes can be characterized as cold, ultra-oligotrophic and alkaline, displaying moderate (Radok and Terrasovoje lakes) to high (Beaver Lake)

Holger Cremer; Damian Gore; Nadja Hultzsch; Martin Melles; Bernd Wagner

2004-01-01

186

The atmospheric deposition of phosphorus in Lake Victoria (East Africa)  

Microsoft Academic Search

Wet and dry atmospheric fluxes of total phosphorus (TP) and soluble reactive phosphorus (SRP) measured at four sites over a 12-month period were used to estimate lake-wide atmospheric phosphorus (P) deposition to Lake Victoria, East Africa. Atmospheric samples were collected in plastic buckets with top diameter of 25.5 cm by 30 cm deep. The highest P loading rates of 2.7 (TP) and

Rashid A. Tamatamah; Robert E. Hecky; Hamish C. Duthie

2005-01-01

187

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

188

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

189

330 NORTH & CENTER STREET (990 EAST) (8E1684E, SALT LAKE ...  

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

330 NORTH & CENTER STREET (990 EAST) (8-E-16-8-4E, SALT LAKE CITY CEMETERY LOCATER), SALT LAKE CITY, UT. VIEW LOOKING SOUTHWEST OVER THE CEMETERY. - Salt Lake City Cemetery, 200 N Street, Salt Lake City, Salt Lake County, UT

190

Bulinus coulboisi of Lake Tanganyika: assessment of its taxonomic position and role as intermediate host for S. haematobium  

Microsoft Academic Search

The freshwater snail Bulinus coulboisi (Bourguignat) has been reported by previous authors to occur in a large area of central and eastern Africa, and to be a potential intermediate host for Schistosoma haematobium. In order to establish the taxonomic position of B. coulboisi, the present authors made observations on preserved specimens from the type-locality on the western shore of Lake

D. S. Brown; D. B. Matovu; D. Rollinson

1982-01-01

191

Parallel evolution of facial stripe patterns in the Neolamprologus brichardi/pulcher species complex endemic to Lake Tanganyika.  

PubMed

Colour pattern diversity can be due to random processes or to natural or sexual selection. Consequently, similarities in colour patterns are not always correlated with common ancestry, but may result from convergent evolution under shared selection pressures or drift. Neolamprologus brichardi and Neolamprologus pulcher have been described as two distinct species based on differences in the arrangement of two dark bars on the operculum. Our study uses DNA sequences of the mitochondrial control region to show that relatedness of haplotypes disagrees with species assignment based on head colour pattern. This suggests repeated parallel evolution of particular stripe patterns. The complete lack of shared haplotypes between populations of the same or different phenotypes reflects strong philopatric behaviour, possibly induced by the cooperative breeding mode in which offspring remain in their natal territory and serve as helpers until they disperse to nearby territories or take over a breeding position. Concordant phylogeographic patterns between N. brichardi/N. pulcher populations and other rock-dwelling cichlids suggest that the same colonization routes have been taken by sympatric species and that these routes were affected by lake level fluctuations in the past. PMID:17881250

Duftner, Nina; Sefc, Kristina M; Koblmüller, Stephan; Salzburger, Walter; Taborsky, Michael; Sturmbauer, Christian

2007-11-01

192

Evaluating COSMO's lake module (FLake) for an East-African lake using a comprehensive set of lake temperature profiles  

NASA Astrophysics Data System (ADS)

The African great lakes are of utmost importance for the local economy (fishing), as well as being essential to the survival of the local people. During last decades, these lakes have been changing rapidly and their evolution is a major concern. Hence, it is important to correctly represent them in regional climate models for simulations over tropical Africa. However, so far lake models have been developed and tested primarily for boreal conditions. In this study, for the first time the freshwater lake model FLake is evaluated over East-Africa, more specifically over lake Kivu. Meteorological observations from January 2003 to December 2008 from an automatic weather station in Bukavu, DRC, are used to drive the standalone version of FLake. For the evaluation, a unique dataset is used which contains over 200 temperature profiles recorded since 2002. Results show that FLake in its default configuration is very successful at reproducing both the timing and magnitude of the seasonal cycle at 5 m depth. Flake captures that this seasonality is regulated by the water vapour pressure, which constrains evaporation except during summer (JJA). A positive bias of ~1 K is attributed to the driving data, which are collected in the city and are therefore expected to mirror higher temperatures and lower wind speeds compared to the lake surface. The evaluation also showed that driving FLake with Era-Interim from the nearest pixel does only slightly deteriorate the model performance. Using forcing fields from the Canadian Regional Climate Model, version 5 (CRCM5) simulation output gives similar performance as Era-Interim. Furthermore, a drawback of FLake is that it does not account for salinity and its effect upon lake stratification, and therefore requires artificial initial conditions for both lake depth and bottom temperature in order to reproduce the correct mixing regime in lake Kivu. Further research will therefore aim at improving FLake's representation of tropical lakes.

Thiery, W.; Martynov, A.; Darchambeau, F.; Demuzere, M.; van Lipzig, N.

2012-04-01

193

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

194

Ice cover, landscape setting, and geological framework of Lake Vostok, East Antarctica  

USGS Publications Warehouse

Lake Vostok, located beneath more than 4 km of ice in the middle of East Antarctica, is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment. Melting and freezing at the base of the ice sheet, which slowly flows across the lake, controls the flux of water, biota and sediment particles through the lake. The influx of thermal energy, however, is limited to contributions from below. Thus the geological origin of Lake Vostok is a critical boundary condition for the subglacial ecosystem. We present the first comprehensive maps of ice surface, ice thickness and subglacial topography around Lake Vostok. The ice flow across the lake and the landscape setting are closely linked to the geological origin of Lake Vostok. Our data show that Lake Vostok is located along a major geological boundary. Magnetic and gravity data are distinct east and west of the lake, as is the roughness of the subglacial topography. The physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake's circulation. Lake Vostok is a tectonically controlled subglacial lake. The tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small, but significant amounts of thermal energy into the lake. ?? 2002 Elsevier Science B.V. All rights reserved.

Studinger, M.; Bell, R. E.; Karner, G. D.; Tikku, A. A.; Holt, J. W.; Morse, D. L. , David, L.; Richter, T. G.; Kempf, S. D.; Peters, M. E.; Blankenship, D. D.; Sweeney, R. E.; Rystrom, V. L.

2003-01-01

195

Hydrology and water quality of East Lake Tohopekaliga, Osceola County, Florida  

USGS Publications Warehouse

East Lake Tohopekaliga, one of the major lakes in central Florida, is located in the upper Kissimmee River basin in north-east Osceola County. It is one of numerous lakes in the upper basin used for flood control, in addition to recreation and some irrigation of surrounding pasture. This report is the fourth in a series of lake reconnaissance studies in the Kissimmee River basin prepared in cooperation with the South Florida Water Management District. The purpose of the report is to provide government agencies and the public with a brief summary of the lake 's hydrology and water quality. Site information is given and includes map number, site name, location, and type of data available (specific conductivity, pH, alkalinity, turbidity, color, dissolved oxygen, hardness, dissolved chlorides, dissolved sodium, dissolved calcium, dissolved magnesium, dissolved potassium, nitrogen, ammonia, nitrates, carbon and phosphorus). The U.S. Geological Survey (USGS) maintained a lake stage gaging station on East Lake Tohopekaliga from 1942 to 1968. The South Florida Water Management District has recorded lake stage since 1963. Periodic water quality samples have been collected from the lake by the South Florida Water Management District and USGS. Water quality and discharge data have been collected for one major tributary to the lake, Boggy Creek. Although few groundwater data are available for the study area, results of previous studies of the groundwater resources of Osceola County are included in this report. To supplement the water quality data for East Lake Tohopekaliga, water samples were collected at selected sites in November 1982 (dry season) and in August 1983 (rainy season). Samples were taken at inflow points, and in the lake, and vertical profiles of dissolved oxygen and temperature were measured in the lake. A water budget from an EPA report on the lake is also included. (Lantz-PTT)

Schiffer, Donna M.

1987-01-01

196

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

197

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.

Kilian, Esmari; Avenant-Oldewage, Annemarie

2013-01-01

198

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.

Learn, Windows T.; National Earth Science Teachers Association (NESTA)

199

Holocene climate history of Geographical Society Ø, East Greenland — evidence from lake sediments  

Microsoft Academic Search

Sediment cores from two lakes in the outer coastal region of East Greenland were investigated for chronology, lithology, palynology, and biogeochemistry. A 10m long sequence recovered in Basaltsø comprises the entire lake history following the last glaciation of the area, probably during the Preboreal oscillation. This is indicated by a succession from glacial via glaciolimnic to limnic sediments. Deglaciation of

Bernd Wagner; Martin Melles; Jürgen Hahne; Frank Niessen; Hans-W. Hubberten

2000-01-01

200

Origin of the Superflock of Cichlid Fishes from Lake Victoria, East Africa  

Microsoft Academic Search

Lake Victoria harbors a unique species-rich flock of more than 500 endemic haplochromine cichlid fishes. The origin, age, and mechanism of diversification of this extraordinary radiation are still debated. Geological evidence suggests that the lake dried out completely about 14,700 years ago. On the basis of phylogenetic analyses of almost 300 DNA sequences of the mitochondrial control region of East

Erik Verheyen; Walter Salzburger; Jos Snoeks; Axel Meyer

2003-01-01

201

Natural Pollution Caused by the Extremely Acid Crater Lake Kawah Ijen, East Java, Indonesia (7 pp)  

Microsoft Academic Search

Background, Aims and Scope. Lakes developing in volcano craters can become highly acidic through the influx of volcanic gases, yielding one of the chemically most extreme natural environments on earth. The Kawah Ijen crater lake in East Java (Indonesia) has a pH < 0.3. It is the source of the extremely acidic and metal-polluted river Banyupahit (45 km). The lake

Ansje J. Löhr; Thom A. Bogaard; Alex Heikens; Martin R. Hendriks; Sri Sumarti; Manfred J. Van Bergen; Kees C. A. M. van Gestel; Nico van Straalen; Pieter Vroon; Budi Widianarko

2005-01-01

202

Monitoring the water balance of Lake Victoria, East Africa, from space  

NASA Astrophysics Data System (ADS)

SummaryUsing satellite gravimetric and altimetric data, we examine trends in water storage and lake levels of multiple lakes in the Great Rift Valley region of East Africa for the years 2003-2008. GRACE total water storage estimates reveal that water storage declined in much of East Africa, by as much as 60 {mm}/{year}, while altimetric data show that lake levels in some large lakes dropped by as much as 1-2 m. The largest declines occurred in Lake Victoria, the Earth's second largest freshwater body. Because the discharge from the outlet of Lake Victoria is used to generate hydroelectric power, the role of human management in the lake's decline has been questioned. By comparing catchment water storage trends to lake level trends, we confirm that climatic forcing explains only about 50decline. This analysis provides an independent means of assessing the relative impacts of climate and human management on the water balance of Lake Victoria that does not depend on observations of dam discharge, which may not be publically available. In the second part of the study, the individual components of the lake water balance are estimated. Satellite estimates of changes in lake level, precipitation, and evaporation are used with observed lake discharge to develop a parameterization for estimating subsurface inflows due to changes in groundwater storage estimated from satellite gravimetry. At seasonal timescales, this approach provides closure to Lake Victoria's water balance to within 17 {mm}/{month}. The third part of this study uses the water balance of a downstream water body, Lake Kyoga, to estimate the outflow from Lake Victoria remotely. Because Lake Kyoga is roughly 20 times smaller in area than Lake Victoria, its water balance is strongly influenced by inflow from Lake Victoria. Lake Kyoga has been shown to act as a linear reservoir, where its outflow is proportional to the height of the lake. This model can be used with satellite altimetric lake levels to estimate a time series of Lake Victoria discharge with an rms error of about 134 {m}/{s}.

Swenson, Sean; Wahr, John

2009-05-01

203

Lake Qinghai Drilling Project: Evolution History of Lake Qinghai and East Asian Monsoon Changes since the Late Miocene  

NASA Astrophysics Data System (ADS)

As a closed continental lake on the north-east margin of the Tibetan Plateau, Lake Qinghai is sensitive to climate variations as well as the environmental effects of Plateau growth/uplift. Supported by Chinese funding agencies and ICDP, onshore and offshore lake cores were drilled in 2005. We compare our preliminary chronostratigraphic, sedimentologic, and geochemical results with climatic records from the Loess Plateau, South China Sea, Arctic and global oceans, and we discuss the evolution of Lake Qinghai at different time scales since the late Miocene. Lake Qinghai is shown to have intimate linkages with the warm/moist East Asian summer monsoon, the cold/dry East Asian winter monsoon, and the growth/uplift of the Tibetan Plateau. Magnetostratigraphic studies of the onshore drill cores indicate that thick greenish clays were deposited during Late Miocene, suggesting the initial formation of the Qinghai Lake basin. Consistent with proxies from the Loess Plateau and the South China Sea, they imply summer-monsoon strengthening and inland intrusion. These changes may be related to a growth event of the Tibetan Plateau at 10-8 Ma, which led to the uplift of Qinghai Nanshan, formation of faulted lake basins, and enhanced summer monsoon circulation. From 6 to 4.6Ma eolian red clays in the core indicate lake basin dessication, as Loess Plateau dust flux increased with the strengthening of the winter monsoon and coincident with intense Arctic ice rafting at 6-5 Ma. From 4.6 to 3.5 Ma thick greenish clays were deposited as modern Lake Qinghai formed. Significantly increased fluxes of TOC, C/N and total sediment might be related to uplift of Qinghai Nanshan and basin subsidence at that time, and they are coeval with the increasing strength of East Asian monsoon during early Pliocene. At 3.5-2.6 Ma, continued strengthening of the East Asian summer monsoon, inland aridification, and increases in global ice volume suggest another growth event of the Tibetan Plateau. Shallow-water silty clays were deposited in the lake basin at this time. Since 2.6 Ma, deposition in the basin was characterized by shallow-water silty clays, intercalated with layers of loess- like material, eolian sand, gravel, and sand, indicating multiple lake expansion/dessication cycles, presumably at orbital frequencies, reflecting multiple migrations of the East Asian summer monsoon front driven by solar radiation and global ice volume changes over this region. Several previous studies of cores as much as 7m long from the depositional basins of Lake Qinghai have documented monsoon climate and environmental changes at the lake from the deglacial period through the Holocene, which are generally consistent with northern Hemisphere summer insolation and its seasonality changes. A wide variety of proxies have been used, and some cores have been studied at very high temporal resolution, especially for the last several hundred years. Results suggest that solar activity influences decadal regional temperatures, and that it is the East Asian summer monsoon as opposed to the Indian summer monsoon that acts as the dominate moisture source at the decadal scale within the local region. Offshore GLAD800 drill cores obtained in 2005 sampled fine-grained sediments before encountering thick units of sand. The fine-grained sections are 2-3 times longer than previous cores from similar sites. Paleolimnological proxy studies are underway on these cores to extend the young part of the paleoenvironmental record back to significantly before the last glacial maximum.

An, Z.; Colman, S.

2007-12-01

204

Large subglacial lakes in East Antarctica at the onset of fast-flowing ice streams.  

PubMed

Water plays a crucial role in ice-sheet stability and the onset of ice streams. Subglacial lake water moves between lakes and rapidly drains, causing catastrophic floods. The exact mechanisms by which subglacial lakes influence ice-sheet dynamics are unknown, however, and large subglacial lakes have not been closely associated with rapidly flowing ice streams. Here we use satellite imagery and ice-surface elevations to identify a region of subglacial lakes, similar in total area to Lake Vostok, at the onset region of the Recovery Glacier ice stream in East Antarctica and predicted by ice-sheet models. We define four lakes through extensive, flat, featureless regions of ice surface bounded by upstream troughs and downstream ridges. Using ice velocities determined using interferometric synthetic aperture radar (InSAR), we find the onset of rapid flow (moving at 20 to 30 m yr(-1)) of the tributaries to the Recovery Glacier ice stream in a 280-km-wide segment at the downslope margins of these four subglacial lakes. We conclude that the subglacial lakes initiate and maintain rapid ice flow through either active modification of the basal thermal regime of the ice sheet by lake accretion or through scouring bedrock channels in periodic drainage events. We suggest that the role of subglacial lakes needs to be considered in ice-sheet mass balance assessments. PMID:17314977

Bell, Robin E; Studinger, Michael; Shuman, Christopher A; Fahnestock, Mark A; Joughin, Ian

2007-02-22

205

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

206

Concentrations, distributions, sources, and risk assessment of organochlorine pesticides in surface water of the East Lake, China.  

PubMed

East Lake resides in the urban area of Wuhan City and is the largest urban lake in China. The concentrations of 16 organochlorine pesticides (OCPs) were analyzed in 108 surface water samples collected from the East Lake. The total concentrations of OCPs ranged from not detected to 120 ng L(-1) with predominance of ?-HCH, heptachlor, and ?-HCH. The mean values of HCHs and DDTs were 7.40 and 5.70 ng L(-1), respectively, accounting for 40 and 31 % of the total OCPs. For the five lakelets in East Lake, Houhu Lake exhibited the highest concentrations of HCHs, DDTs, and total OCPs, which has been used actively for fisheries and surrounded by suburban rural areas and farmlands. Historical lindane or technical HCH input was probably the source of HCH, while technical DDTs might be the source of DDT in the East Lake. The ratio between heptachlor and its metabolic products indicated recent input of heptachlor. Although the combining ecological risks for all aquatic species in the East Lake calculated by species sensitivity distribution reached approximately 10(-5), the OCPs in the East Lake had slight effects on aquatic organisms. The carcinogenic risks and non-carcinogenic hazard indices of DDTs and HCHs indicated that water in the East Lake was not suitable as water sources for human. However, the results indicated the water quality was safe for people to swim in the urban lake. PMID:24177859

Yang, Yuyi; Yun, Xiaoyan; Liu, Minxia; Jiang, Ying; Li, Qing X; Wang, Jun

2014-02-01

207

Sedimentation in arctic proglacial lakes: Mittivakkat Glacier, south-east Greenland  

Microsoft Academic Search

Several sediment cores were collected from two proglacial lakes in the vicinity of Mittivakkat Glacier, south-east Greenland, in order to determine sedimentation rates, estimate sediment yields and identify the dominant sources of the lacustrine sediment. The presence of varves in the ice-dammed Icefall Lake enabled sedimentation rates to be estimated using a combination of X-ray photography and down-core variations in

Bent Hasholt; Desmond E. Walling; Philip N. Owens

2000-01-01

208

Depositional environments of Late Triassic lake, east-central New Mexico  

SciTech Connect

The Redonda Member of the Chinle Formation represents deposition in a large, polymictic lake during the Late Triassic (Norian) in east-central New Mexico. This study documents and defines an extensive lacustrine system situated in western Pangaea which was influenced by both tectonic and climatic events. Areal extent of the lake may have been as much as 5,000 km{sup 2}.

Hester, P.M. (Bureau of Land Management, Albuquerque, NM (USA))

1989-09-01

209

18O 16O ratios in cherts associated with the saline lake deposits of East Africa  

USGS Publications Warehouse

The cherts formed from sodium silicate precursors in East African saline, alkaline lakes have ??18O values ranging from 31.1 to 44.1. The ??18O values correlate in general with lake salinities as inferred from geologic evidence, indicating that most chert was formed from its precursor in contact with lake water trapped at the time of deposition. A few of the analyzed cherts probably formed in contact with dilute meteoric water. From the widely varying ??18O values we conclude that precursors were transformed to chert in fluids of widely varying salinity and aNa+/aH+ ratio. ?? 1973.

O'Neil, J. R.; Hay, R. L.

1973-01-01

210

Rainfall Conditions in Equatorial East Africa during the Nineteenth Century as Inferred from the Record of Lake Victoria  

Microsoft Academic Search

The East African lakes have exhibited dramaticfluctuations on both historical and paleo-climatictime scales. Levels of these lakes, and otherhistorical indicators in Africa, suggested thatenvironmental conditions in the nineteenth centurywere much more extreme than anything evident in themodern record. In this study, a water balance modelis used to estimate the rainfall associated with theseconditions, based on the Lake Victoria record. Theresults

Sharon E. Nicholson; Xungang Yin

2001-01-01

211

A Review Of Mercury in Lake Victoria, East Africa: Implications for Human and Ecosystem Health  

Microsoft Academic Search

Lake Victoria, East Africa, has been the site of many recent studies measuring mercury (Hg) concentrations in water, fish, sediment, soil, and humans. Most of these studies were motivated by concerns about Hg contamination from processing of gold ore on the southern shores. Total Hg (THg) concentrations in fish were usually below permissible World Health Organization (WHO) concentrations and international

Linda M. Campbell; D. G. Dixon; R. E. Hecky

2003-01-01

212

Possibility of deep gabbroic rocks, east of Tuz Lake, central Turkey, interpreted from aeromagnetic data  

Microsoft Academic Search

In the east of Tuz lake, gabbroic rocks are observed as small outcrops from the surface geology. Regional aeromagnetic data measured by the Canadian Aero Service (CAS) show strong anomalies in the region. Gabbroic rocks are the only magnetized rocks in the region. However, surface exposures of the gabbroic rocks do not seem to have adequate size and extension to

Abdullah Ates

1999-01-01

213

Sunspots, El Niño, and the levels of Lake Victoria, East Africa  

Microsoft Academic Search

An association of high sunspot numbers with rises in the level of Lake Victoria, East Africa, has been the focus of many investigations and vigorous debate during the last century. In this paper, we show that peaks in the ?11-year sunspot cycle were accompanied by Victoria level maxima throughout the 20th century, due to the occurrence of positive rainfall anomalies

J. Curt Stager; Alexander Ruzmaikin; Declan Conway; Piet Verburg; Peter J. Mason

2007-01-01

214

Development of coarse-grained facies in lacustrine rift basins: Examples from East Africa  

NASA Astrophysics Data System (ADS)

Detailed studies of high-resolution and multifold seismic reflection data from the two largest East African rift lakes, Malawi and Tanganyika, reveal a complex suite of coarse-grained depositional facies. These facies occur within specific regions of the controlling half grabens that compose the rift lakes. Sand-prone environments include subaqueous channels and small drowned fluvial complexes. Channel systems range from large erosional canyons to deep-water turbidite channel-levee systems. Lowstand and highstand deltas of axial and shoaling-side rivers are volumetrically important coarse-grained facies. Fan deltas develop along the base of major border faults during lake lowstands; subaqueous talus fan deposits occur along the base of the border faults during lake highstands. Lowstand deltas are the best-preserved progradational facies in these rift lakes. In addition to simple tectonic control, drastic tectonically or climatically induced lake-level change significantly regulates the production of coarse-grained lacustrine synrift deposits.

Scholz, Christopher A.; Rosendahl, Bruce R.; Scott, Deborah L.

1990-02-01

215

STS-55 Earth observation of Lake Natron, Tanzania, East Africa  

NASA Technical Reports Server (NTRS)

STS-55 Earth observation taken aboard Columbia, Orbiter Vehicle (OV) 102, shows Lake Natron. Taken with color infrared (CIR) film, the typical red-colored water appears greenish. The drying soda salts in the lakebed are seen in greater detail in this CIR view. From the signatures seen in this photograph, the lake appears to be highly saline and to contain aquatic biota with little or no chlorophyll. The biomass over the rift valley escarpment is clearly defined by the reddish color in this CIR photo. Refer to STS055-93-037 for a comparative view photographed in regular color.

1993-01-01

216

Calibration and application of the branched GDGT temperature proxy on East African lake sediments  

NASA Astrophysics Data System (ADS)

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are a novel proxy for mean annual air temperature (MAAT) and have the potential to be broadly applicable to climate reconstruction using lacustrine sediments. Several calibrations have been put forth relating brGDGT distributions to MAAT using a variety of linear regressions, including the methylation (MBT) and cyclization (CBT) indices of brGDGTs, the relative abundances of the major, non-cyclized brGDGTs (MbrGDGTs), and best subsets regression (BSR) of the fractional abundances of the nine most common brGDGTs. However, these calibrations have rarely been applied to lake sediment cores to reconstruct temperatures and test the applicability of this proxy as a paleothermometer. We present an expanded East African lakes surface sediment brGDGT dataset based upon 111 lakes and examine three methods of calibrating brGDGTs to MAAT. These methods include recalculations of the East African lake MBT/CBT calibration and MbrGDGTs calibrations, as well as a new stepwise forward selection (SFS) calibration that uses the four combined brGDGTs that explain the most variance in temperature in our calibration set. We apply these new calibrations as well as five previously published lacustrine brGDGT calibrations to the brGDGT distributions of our surface sediment dataset and a 48 kyr sediment core from Sacred Lake, Mt. Kenya, producing the first brGDGT temperature reconstruction available from a small tropical lake. We compare the reconstructed temperatures to previously published paleotemperature records from East Africa to help us assess the performance of the brGDGT calibrations. We find that the SFS calibration has a consistently low root mean squared error of prediction (RMSEP) over the entire range of MAAT, while the MBT/CBT and MbrGDGT calibrations have relatively large RMSEPs, particularly between lakes with similar temperatures but variable pH. This suggests that these techniques do not properly deconvolve the temperature and pH signals recorded in the distributions of the brGDGTs. We further find that only the SFS calibration produces a credible reconstructed temperature history from Sacred Lake when compared to other last glacial maximum paleotemperature estimates from East Africa. Thus, we advocate for the use of the SFS calibration when reconstructing paleotemperatures from brGDGTs in East Africa.

Loomis, Shannon E.; Russell, James M.; Ladd, Bethany; Street-Perrott, F. Alayne; Sinninghe Damsté, Jaap S.

2012-12-01

217

Exposure and effects of perfluoroalkyl compounds on tree swallows nesting at Lake Johanna in east central Minnesota, USA  

USGS Publications Warehouse

Tree swallow (Tachycineta bicolor) samples were collected at a reference lake and a nearby lake (Lake Johanna) in east central Minnesota, USA contaminated with perfluorinated carboxylic and sulfonic acids. Tissues were analyzed for a suite of 13 perfluoroalkyl compounds (PFCs) to quantify exposure and to determine if there was an association between egg concentrations of PFCs and reproductive success of tree swallows. Concentrations of perfluoroocatane sulfonate (PFOS) were elevated in all tree swallow tissues from Lake Johanna compared to tissues collected at the reference lake. Other PFCs, except for two, were elevated in blood plasma at Lake Johanna compared to the reference lake. PFOS was the dominant PFC (>75%) at Lake Johanna, but accounted for <50% of total PFCs at the reference lake. There was a negative association between concentrations of PFOS in eggs and hatching success. Reduced hatching success was associated with PFOS levels as low as 150 ng/g wet weight.

Custer, Christine M.; Custer, Thomas W.; Schoenfuss, Heiko L.; Poganski, Beth H.; Solem, Laura

2012-01-01

218

Exposure and effects of perfluoroalkyl compounds on tree swallows nesting at Lake Johanna in east central Minnesota, USA.  

PubMed

Tree swallow (Tachycineta bicolor) samples were collected at a reference lake and a nearby lake (Lake Johanna) in east central Minnesota, USA contaminated with perfluorinated carboxylic and sulfonic acids. Tissues were analyzed for a suite of 13 perfluoroalkyl compounds (PFCs) to quantify exposure and to determine if there was an association between egg concentrations of PFCs and reproductive success of tree swallows. Concentrations of perfluoroocatane sulfonate (PFOS) were elevated in all tree swallow tissues from Lake Johanna compared to tissues collected at the reference lake. Other PFCs, except for two, were elevated in blood plasma at Lake Johanna compared to the reference lake. PFOS was the dominant PFC (>75%) at Lake Johanna, but accounted for <50% of total PFCs at the reference lake. There was a negative association between concentrations of PFOS in eggs and hatching success. Reduced hatching success was associated with PFOS levels as low as 150ng/g wet weight. PMID:21296656

Custer, Christine M; Custer, Thomas W; Schoenfuss, Heiko L; Poganski, Beth H; Solem, Laura

2012-07-01

219

Distribution and ecological assessment of heavy metals in surface sediments of the East Lake, China.  

PubMed

Concentrations and risk assessment of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), lead (Pb), cadmium (Cd) and mercury (Hg) were investigated in 106 samples of surface sediments from the East Lake, China in this study. The mean concentration of Zn was highest among the eight heavy metals (225 mg kg(-1)), followed by As (191 mg kg(-1)), Cr (145 mg kg(-1)), Cu (55 mg kg(-1)), Ni (27.1 mg kg(-1)), Pb (7.93 mg kg(-1)), Cd (0.94 mg kg(-1)) and Hg (0.21 mg kg(-1)). Niuchao Hu was less polluted by heavy metals compare to the other four lakelets of the East Lake. The correlations among these heavy metals and the results of principal component analysis indicated that the distribution of Cd, Pb and Hg was related to anthropogenic activities, whereas Cu, As and Cr were affected by the parent rocks. Zinc and Ni were influenced both by anthropogenic activities and parent rocks. Based on the Sediment Quality Guidelines, the results of toxicity assessment indicated that adverse effects caused by Cr and As would be expected frequently. Nickel, Zn, Cd and Hg may cause adverse effects occasionally and Cu and Pb may cause toxicity infrequently. Arsenic was found to have the highest acute toxicity by toxic units (TUs), followed by Cr, Ni, Zn, Hg, Cu, Cd and Pb. The potential ecological risk index analysis indicated that As, Cd and Hg had considerable or high ecological risk, whereas Cr, Ni, Cu, Zn and Pb had low ecological risk. The potential ecological risk index (RI) of the heavy metals in the surface sediments of East Lake was 483, indicating considerable ecological risk. Close attention should be paid to pollution of the heavy metals in East Lake, China. PMID:24258532

Liu, Minxia; Yang, Yuyi; Yun, Xiaoyan; Zhang, Miaomiao; Li, Qing X; Wang, Jun

2014-01-01

220

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

221

Reinvestigating Three Paleo Lake Records in the Middle East using new Model Results  

NASA Astrophysics Data System (ADS)

Here we present a reinterpretation of three oxygen isotope records from three Middle Eastern Lakes (Zeribar, Van and Eski Acigo). These lake isotope records were interpreted previously to document changes in the precipitation-to-evaporation ratio (Eski and Van) and varying seasonality of precipitation over the lake (Zeribar). These differing interpretations are a consequence of inadequate constraints on atmospheric dynamics that influence isotopic variability in the water cycle of the Middle East. We present new isotope-enabled atmospheric model results that provide a more comprehensive view of each of the potential influences that affected these lake records. Currently the Middle East exhibits a highly seasonal precipitation cycle with the bulk of the rainfall occurring during the winter months. The yearly isotopic composition of rainfall exhibits a seasonal cycle as well with decreased values during the winter and higher isotopic values in both fall and spring. We conducted two model simulations with the Isotope-incorporated Global Spectral Model (IsoGSM): 1) with present-day conditions and 2) with mid-Holocene conditions. For the mid-Holocene simulations changes were made to the surface forcing, orbital parameters and greenhouse gas concentrations. These results show that the annual averaged oxygen isotopes in precipitation 6000 years ago were depleted on the order of 1 to 3‰ compared to present day. The model results are consistent with the published lake core records. However, the shift in isotopic composition of precipitation results from the combined influences of orbital changes, the changes in green house gases and surface forcings. We have evaluated the relative contribution of each of the forcings and present a re-interpretation of the Middle Eastern lake records.

Reuter, J. M.; Stott, L. D.; Buenning, N. H.; Yoshimura, K.

2013-12-01

222

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

223

Egg banks in hypersaline lakes of the South-East Europe.  

PubMed

The cyst banks of 6 coastal hypersaline lakes of South-East Europe have been investigated. The study concerned the bottom sediments of Khersonesskoe and Koyashskoe lakes in the Crimea (Ukraine), Nartë saltworks (Albania), Vecchia Salina at Torre Colimena (Apulia, Italy), Pantano Grande and Pantano Roveto at Vendicari (Sicily, Italy). A total of 19 cyst types were recognised. The cyst banks of lakes were found to be well separated in the representation derived from a statistical multivariate data analysis. For all the lakes examined a comparison was possible between the resting community in sediments (cyst bank) and the active one in the water. The cyst banks contained more species than those recorded over a multi-year sampling effort in the water column. The study of cyst hatching, performed on 5 cyst types under lab conditions, demonstrated that cysts do not hatch under the same conditions. Furthermore, each cyst type shows a wide range of preferential hatching conditions, which allow us to confirm the ecological generalism of salt lake species. PMID:19292906

Moscatello, Salvatore; Belmonte, Genuario

2009-01-01

224

A novel primer set for multilocus phylogenetic inference in East African cichlid fishes.  

PubMed

The cichlid fishes in the East African Great Lakes are a prime model system for the study of adaptive radiation. Therefore, the availability of an elaborate phylogenetic framework is an important prerequisite. Previous phylogenetic hypotheses on East African cichlids are mainly based on mitochondrial and/or fragment-based markers, and, to date, no taxon-rich phylogeny exists that is based on multilocus DNA sequence data. Here, we present the design of an extensive new primer set (24 nuclear makers) for East African cichlids that will be used for multilocus phylogenetic analyses in the future. The primers are designed to work for both Sanger sequencing and next-generation sequencing with the 454 technology. As a proof of principle, we validate these primers in a phylogenetically representative set of 16 cichlid species from Lake Tanganyika and main river systems in the area and provide a basic evaluation of the markers with respect to marker length and diversity indices. PMID:22816488

Meyer, Britta S; Salzburger, Walter

2012-11-01

225

The impact of the geologic history and paleoclimate on the diversification of East african cichlids.  

PubMed

The cichlid fishes of the East African Great Lakes are the largest extant vertebrate radiation identified to date. These lakes and their surrounding waters support over 2,000 species of cichlid fish, many of which are descended from a single common ancestor within the past 10?Ma. The extraordinary East African cichlid diversity is intricately linked to the highly variable geologic and paleoclimatic history of this region. Greater than 10?Ma, the western arm of the East African rift system began to separate, thereby creating a series of rift basins that would come to contain several water bodies, including the extremely deep Lakes Tanganyika and Malawi. Uplifting associated with this rifting backponded many rivers and created the extremely large, but shallow Lake Victoria. Since their creation, the size, shape, and existence of these lakes have changed dramatically which has, in turn, significantly influenced the evolutionary history of the lakes' cichlids. This paper reviews the geologic history and paleoclimate of the East African Great Lakes and the impact of these forces on the region's endemic cichlid flocks. PMID:22888465

Danley, Patrick D; Husemann, Martin; Ding, Baoqing; Dipietro, Lyndsay M; Beverly, Emily J; Peppe, Daniel J

2012-01-01

226

Sunspots, El Niño, and the levels of Lake Victoria, East Africa  

NASA Astrophysics Data System (ADS)

An association of high sunspot numbers with rises in the level of Lake Victoria, East Africa, has been the focus of many investigations and vigorous debate during the last century. In this paper, we show that peaks in the ~11-year sunspot cycle were accompanied by Victoria level maxima throughout the 20th century, due to the occurrence of positive rainfall anomalies ~1 year before solar maxima. Similar patterns also occurred in at least five other East African lakes, which indicates that these sunspot-rainfall relationships were broadly regional in scale. Although irradiance fluctuations associated with the sunspot cycle are weak, their effects on tropical rainfall could be amplified through interactions with sea surface temperatures and atmospheric circulation systems, including ENSO. If this Sun-rainfall relationship persists in the future, then sunspot cycles can be used for long-term prediction of precipitation anomalies and associated outbreaks of insect-borne disease in much of East Africa. In that case, unusually wet rainy seasons and Rift Valley Fever epidemics should occur a year or so before the next solar maximum, which is expected to occur in 2011-2012 AD.

Stager, J. Curt; Ruzmaikin, Alexander; Conway, Declan; Verburg, Piet; Mason, Peter J.

2007-08-01

227

Effects of artificial destratification on water quality at East Sidney Lake, New York. Final report  

SciTech Connect

Artificial destratification has been applied at East Sidney Lake to enhance water quality of the reservoir and tailwater. Operation of the destratification system during the growing season maintained near-isothermal temperatures in the reservoir, thereby maintaining oxygenated conditions in the bottom waters via atmospheric exchange during mixing. Maintenance of aerobic bottom waters decreased solubilization of sedimentary metals, decreased internal loading of sedimentary phosphorus, increased available habitat for aquatic organisms, and improved discharge quality. Populations of algal species excessive levels in late summer, even with decreased internal phosphorus loading and disruption of thermal gradients. Consequently, improvements in water clarity were not observed. Algal control, Internal loading, Artificial destratification, Reservoirs, Eutrophication, Water quality enhancement.

Ashby, S.L.; Kennedy, R.H.

1993-09-01

228

Sedimentology and geochemistry of a perennially ice-covered epishelf lake in Bunger Hills Oasis, East Antarctica.  

PubMed

A process-oriented study was carried out in White Smoke lake, Bunger Hills, East Antarctica, a perennially ice-covered (1.8 to 2.8 m thick) epishelf (tidally-forced) lake. The lake water has a low conductivity and is relatively well mixed. Sediments are transferred from the adjacent glacier to the lake when glacier ice surrounding the sediment is sublimated at the surface and replaced by accumulating ice from below. The lake bottom at the west end of the lake is mostly rocky with a scant sediment cover. The east end contains a thick sediment profile. Grain size and delta 13C increase with sediment depth, indicating a more proximal glacier in the past. Sedimentary 210Pb and 137Cs signals are exceptionally strong, probably a result of the focusing effect of the large glacial catchment area. The post-bomb and pre-bomb radiocarbon reservoirs are c. 725 14C yr and c. 1950 14C yr, respectively. Radiocarbon dating indicates that the east end of the lake is >3 ka BP, while photographic evidence and the absence of sediment cover indicate that the west end has formed only over the last century. Our results indicate that the southern ice edge of Bunger Hills has been relatively stable with only minor fluctuations (on the scale of hundreds of metres) over the last 3000 years. PMID:11543521

Doran, P T; Wharton, R A; Lyons, W B; Des Marais, D J; Andersen, D T

2000-01-01

229

Sedimentology and geochemistry of a perennially ice-covered epishelf lake in Bunger Hills Oasis, East Antarctica  

NASA Technical Reports Server (NTRS)

A process-oriented study was carried out in White Smoke lake, Bunger Hills, East Antarctica, a perennially ice-covered (1.8 to 2.8 m thick) epishelf (tidally-forced) lake. The lake water has a low conductivity and is relatively well mixed. Sediments are transferred from the adjacent glacier to the lake when glacier ice surrounding the sediment is sublimated at the surface and replaced by accumulating ice from below. The lake bottom at the west end of the lake is mostly rocky with a scant sediment cover. The east end contains a thick sediment profile. Grain size and delta 13C increase with sediment depth, indicating a more proximal glacier in the past. Sedimentary 210Pb and 137Cs signals are exceptionally strong, probably a result of the focusing effect of the large glacial catchment area. The post-bomb and pre-bomb radiocarbon reservoirs are c. 725 14C yr and c. 1950 14C yr, respectively. Radiocarbon dating indicates that the east end of the lake is >3 ka BP, while photographic evidence and the absence of sediment cover indicate that the west end has formed only over the last century. Our results indicate that the southern ice edge of Bunger Hills has been relatively stable with only minor fluctuations (on the scale of hundreds of metres) over the last 3000 years.

Doran, P. T.; Wharton, R. A. Jr; Lyons, W. B.; Des Marais, D. J.; Andersen, D. T.; Wharton RA, J. r. (Principal Investigator)

2000-01-01

230

The disappearing of the largest lake in the Middle East: Geochemical clues for human impact on Urmia salt lake NW Iran  

NASA Astrophysics Data System (ADS)

The water level in Lake Urmia, the third largest saline lake on earth and the largest continental lake in the Middle East, has dropped by more than 9 m over the last two decades, with no signs of improvement in recent years. Urmia is a hypersaline shallow lake (average salinity ~200 ‰) located in a closed continental drainage basin in northwestern Iran, and is surrounded by a variety of rock formations, ranging in age from Precambrian metamorphic complexes to Holocene mud deposits. Lake sediments are composed of two major components; chemical-biochemical and clastic fractions. Based on grain size analysis of samples from 24 push-cores, silt-size particles dominate the lake's sediments with clay-bearing materials mostly present near the center of the lake. Sand-size particles are dominant in the northwest, where felsic to intermediate plutonic and metamorphic rocks are located in the proximity of the lake. The water of the Urmia Lake can be classified as Na-K-Cl-Mg-SO4 brine. Based on chemical analysis of conservative lithogenic elements (e.g., Ti, Si, Al, Ca) as well as redox-sensitive elements (e.g., Fe, K, Rb, Sr) in the clastic fraction of the lake's sediment, elemental distributions are reflective of regional geology. The main sources of ions to the lake are evaporite formations with minor contribution from igneous rocks. Ion concentrations in the northern part of the lake are nearly constant throughout the year while south-southeastern parts of the lake show variable annual ion concentration due to major fresh water inflows. Chemical analysis of the surface sediment samples for heavy metals (Ni, Cr, V and Hg) indicate moderate to high degrees of contamination in the affected areas, where Hg is the most abundant heavy metal. The highest concentrations of Hg (Normalized Enrichment Factor =6) are observed in the middle part of the lake, where intensive dredging and construction activities have taken place. In contrast, the lowest concentrations of Hg in undisturbed areas of the lake reveal that the heavy metals have been introduced to the lake environment in recent years. Excessive damming (28 operational and 15 under construction) on the tributaries that supply water to the lake, poor water management in their catchment basins, and construction of Kalantari Highway across the lake (started in 1980) have significantly disturbed natural water and sediment circulation, resulting in enhanced differential evaporation in the northern and southern "sub-basins" of the lake.

Sharifi, O.; Haeri-Ardakani, O.; Pourmand, A.

2012-12-01

231

Physical and Chemical Properties of Lake Tanganyika.  

National Technical Information Service (NTIS)

Environmental measurements are an important part of any acoustic propagation exercise. They are necessary in designing and interpreting acoustic experiments. Of particular importance is the physical and chemical characterization of the sound medium in bod...

C. Greene E. N. Jones

1970-01-01

232

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

233

The Late Pleistocene - Holocene palaeolimnology of Lake Victoria, East Africa, based upon elemental and isotopic analyses of sedimentary organic matter  

Microsoft Academic Search

Three piston cores from Lake Victoria (East Africa) have been analysed for organic carbon (TOC) and nitrogen (TN) content, stable isotopes (d13C and d15N), and Hydrogen Index (HI). These data are combined with published biogenic silica and water content analyses to produce a detailed palaeolimnological history of the lake over the past ca. 17.5 ka. Late Pleistocene desiccation produced a

Michael R. Talbot; Tine Lærdal

2000-01-01

234

Preliminary TEX86 temperatures and a lake level record of tropical climate extremes derived from sediment cores and seismic stratigraphy from Lake Turkana, East Africa  

NASA Astrophysics Data System (ADS)

Lake Turkana is the largest lake in the Eastern Branch of the East African Rift System and records hydrologic conditions of a region spanning nearly 2.5 degrees of latitude (~2.0 - 4.5 degrees N) in the African tropics. New data suggest the Turkana region likely experienced much wetter and cooler climate over several intervals since the latest Pleistocene. Lake level was extremely low twice during the latest Pleistocene, evidenced by depositional hiatuses in high-resolution CHIRP seismic reflection data that correlate with sediments that have low water-content, abundant sand, and low total organic carbon (TOC as low as <0.7%). Lake Turkana, like many lakes in northern tropical Africa, had a wetter climate during the African Humid Period. Intervals of high lake levels (up to ~440 m amsl) are indicated by flat-lying, laterally continuous, low-amplitude reflections that correlate in sediment cores to dark, fine-grained, laminated sediment with high TOC (up to ~6%). Calcium carbonate accumulation during this time period is nearly 0%, and combined with evidence of laminated, unbioturbated sediment suggests a fresh, stratified lake with anoxic bottom waters. During the early mid-Holocene, lake level began to fall to close to present levels (~365 m amsl). Sediments deposited during this time period have low but variable organic carbon content (~0.5 - ~2%) and are much higher in inorganic carbon (from fine-grained calcite precipitation). A moderate lowstand during the late Holocene is indicated by an erosional unconformity seen down to ~40 m below the current lake surface in several seismic profiles. This record of lake level extremes suggests highly variable rainfall patterns, forced by migration of the Intertropical Convergence Zone) across tropical East Africa over the last 20,000 years. More than 50 sediment samples from 3 piston cores represent a continuous record of TEX86 temperature from ~20,000 years ago to modern. The generally low (<0.25) BIT index for the samples indicates a signal derived mainly from organic matter of aquatic origin and limited input from soil-derived OM, thus representing lake surface temperature. The range of paleotemperatures within this preliminary record is ~5-7° C, depending upon the TEX86 calibration used. The highest temperatures are from sediments from the late Pleistocene during times of low lake level, and the lowest temperatures are from the early Holocene during a time of high lake level. Preliminary observations indicate that times of increased or reduced lake level are synchronous with changes in average temperature.

Morrissey, A. J.; Scholz, C. A.; Russell, J. M.

2012-12-01

235

Holocene precipitation and thermal coherence at Lakes Albert and Victoria, East Africa  

NASA Astrophysics Data System (ADS)

New molecular proxy records of temperature and rainfall from lacustrine sedimentary archives are helping to constrain the tropical response to global climate change and elucidate possible forcing mechanisms during the latest Pleistocene and Holocene in East Africa. It is often noted that tropical ecosystems are more sensitive to perturbations in rainfall than in temperature, due to the limited thermal range of tropical climate, however coincident shifts would likely enhance climate response to regional variability. Furthermore, on shorter time scales, patterns of moisture balance and temperature are often linked in East Africa. Here we present new records of rainfall from Lakes Albert and Victoria, using compound specific ?D from terrestrial leaf waxes, and compare these trends to TEX86 paleotemperature records in order to assess the coherence between tropical precipitation and temperature. Our results indicate generally synchronous shifts at these sites, roughly in-phase with regional climate behavior during this interval. A high resolution climate history at Lake Albert highlights a significant multi-stage cool and arid excursion characteristic of the last deglaciation, beginning ~13.8 ka and ending rapidly at ~11.5 ka and marked by a ~55% D-enrichment and 3°C cooling, linking this tropical region to high latitude climate events. The molecular perspective on the climate surrounding Lake Victoria indicates a warm, humid interval peaking at 10-9 ka, and subsequent gradual cooling and drying over the remainder of the Holocene, exhibiting shifts of ~40% in ?D and ~5°C, and thus showing a strong correlation to summer insolation. Palynological and ?13C biomarker evidence from these sites indicate significant, but not coinciding, shifts in aspects of the terrestrial vegetation ecosystem that are not well understood. Both regions support a linkage between high latitude and equatorial African climate systems, with likely teleconnections to the Indian monsoon system.

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

2011-12-01

236

Deltas of the Lake Malawi rift, east Africa: Seismic expression and exploration implications  

SciTech Connect

High-resolution, air-gun-sourced seismic reflection surveys over the offshore regions of five river deltas in Lake Malawi in the East African rift system reveal considerable variability in acoustic facies and stratigraphic architecture. This variability can largely be attributed to the influences of different structural settings, and to a lesser degree to high-amplitude (100-400 m) and high-frequency (1000 to 100,000 yr) fluctuations in lake level. Deltas on flexural and axial margins in the rift lake show well-developed progradational geometries. In contrast, a delta on a steep, accommodation zone margin distributes coarse sediments over a broad depositional apron, rather than concentrating sediment in discrete progradational lobes as on the other deltas. A large border fault margin river delta displays the most complex tectonic and stratigraphic architecture of all the deltas studied. It contains several delta-associated facies, including prograding clinoform packages, fan deltas stacked against a boundary fault, and extensive subaqueous fans. Flexural margin lowstand deltas may be the most prospective for hydrocarbon exploration due to their large, internally well-organized, progradational lobes and their close proximity to deep-water, high total organic carbon lacustrine source facies.

Scholz, C.A. [Univ. of Miami, FL (United States)

1995-11-01

237

Principal Facts for 463 Gravity Stations in the Vicinity of Tangle Lakes, East-Central Alaska  

USGS Publications Warehouse

During the summer of 2001, a gravity survey was conducted in the vicinity of Tangle Lakes, east-central Alaska. Measurements of 87 gravity stations were made. The Tangle Lakes area is located about 25 km west of Paxson and north of the Denali Highway. The gravity survey is located on the southwest corner of the Mt. Hayes and the northwest corner of the Gulkana 1:250,000 scale USGS topographic maps. The boundaries of the study area are 62 deg 30' to 63 deg 30' N. latitude and 145 deg 30' to 147 deg 00' W. longitude. A map showing the location of the study area is shown in figure 1. One gravity base station was used for control for this survey. This base station, TLIN is located at the Tangle Lakes Inn. The observed gravity of this station was calculated based on multiple ties to base stations ANCU in Anchorage, PALH in Palmer, BD27 in Gulkana, and base stations D42, and D57 along the Denali Highway.

Morin, Robert L.; Glen, Jonathan M. G.

2002-01-01

238

Comparison of the Microbial Diversity and Abundance Between the Freshwater Land-Locked Lakes of Schirmacher Oasis and the Perennially Ice-Covered Lake Untersee in East Antarctica  

NASA Technical Reports Server (NTRS)

Extreme conditions such as low temperature, dryness, and constant UV-radiation in terrestrial Antarctica are limiting factors of the survival of microbial populations. The objective of this study was to investigate the microbial diversity and enumeration between the open water lakes of Schirmacher Oasis and the permanently ice-covered Lake Untersee. The lakes in Schirmacher Oasis possessed abundant and diverse group of microorganisms compared to the Lake Untersee. Furthermore, the microbial diversity between two lakes in Schirmacher Oasis (Lake L27C and L47) was compared by culture-based molecular approach. It was determined that L27Chad a richer microbial diversity representing 5 different phyla and 7 different genera. In contrast L47 consisted of 4 different phyla and 6 different genera. The difference in microbial community could be due to the wide range of pH between L27C (pH 9.1) and L47 (pH 5.7). Most of the microbes isolated from these lakes consisted of adaptive biological pigmentation. Characterization of the microbial community found in the freshwater lakes of East Antarctica is important because it gives a further glimpse into the adaptation and survival strategies found in extreme conditions.

Huang, Jonathan; Hoover, Richard B.; Swain, Ashit; Murdock, Chris; Bej, Asim K.

2010-01-01

239

Methanotrophy and chemoautotrophy within the redox gradient of a large and deep tropical lake (Lake Kivu, East Africa)  

NASA Astrophysics Data System (ADS)

Lake Kivu (East Africa) is a large (2370 km2) and deep (maximum depth of 485 m) meromictic lake. Its vertical structure consists of an oxic and nutrient-poor mixed layer down to 70 m maximum, and a permanently anoxic monimolimnion rich in dissolved gases (methane and carbon dioxide) and inorganic nutrients. Seasonal variation of the vertical position of the oxic-anoxic interface is driven by contrasting precipitation and wind speed regimes between rainy (October-May) and dry (June-September) season, the latter being characterized by a deepening of the oxic zone, and an increased input of dissolved gases and inorganic nutrients. Our work aimed at quantifying methanotrophic and chemoautotrophic production within the redox gradient of Lake Kivu and identifying the micro-organisms involved in these processes using phospholipid-derived fatty acid markers and their carbon stable isotope composition. Our approach combined both natural stable isotope abundance analysis and 13C-labelling (13C-DIC ; 13C-CH4) experiments. Sampling was carried out at two stations in Lake Kivu during rainy (February 2012) and dry (September 2012) season conditions. Methanotrophic bacterial production rates were highly variable (from 0.1 to 7.0 ?mol C L-1 d-1), but maximum values were always observed at the oxic-anoxic interface when the CH4:O2 ratio varied between 0.1 and 10, suggesting that the majority of methane was oxidized aerobically. Furthermore, strong stable isotope labelling of monounsaturated C16 fatty acids indicate that active methane oxidizers were related to the group of type I aerobic methanotrophs (gammaproteobacteria). Despite the dominance of aerobic methane oxidation, significant methanotrophic bacterial production rates were found below the oxic-anoxic interface during the rainy season, indicating that at least a fraction of the upcoming methane may be oxidized anaerobically. This observation was further confirmed by the strong labelling at these depths of the 10Me16:0 fatty acid, biomarker for sulphate-reducing bacteria, the syntrophic partners of anaerobic methane-oxidizing archaea. The methanotrophic bacterial growth efficiency (MBGE) was variable (2-50%), and inversely related to methane concentration. Maximum chemoautotrophic bacterial production rates were recorded well below the oxycline, in sulfidic waters. However, during the rainy season, significant dark C fixation rates were measured near the oxic-anoxic interface, in a nitracline where sulphide was absent, suggesting that another energy source was involved. Incorporation of labelled carbon in the 16:1?9c ; 16:1?7c and 18:1?7 fatty acids suggest that the active chemoautotrophic organisms belong to the phylum proteobacteria. Together, the vertically integrated methanotrophic and chemoautotrophic production rates were 31 mmol m-2 d-1 and 41 mmol-2 d-1 during the rainy and dry season, respectively. These values are comparable to the net phytoplanktonic production rates in Lake Kivu ranging between 12 and 160 mmol m-2 d-1 (on average 52 mmol m-2 d-1). Our results indicate that methanotrophs and chemoautotrophs contribute substantially to the carbon cycle in Lake Kivu.

Morana, Cedric; Borges, Alberto V.; Darchambeau, François; Roland, Fleur; Montante, Laetitia; Descy, Jean-Pierre; Bouillon, Steven

2014-05-01

240

Late pleistocene and holocene history of the lakes in the Kola Peninsula, Karelia and the North-Western part of the East European plain  

Microsoft Academic Search

The paper reviews the work on paleolimnology in parts of the FSU over the last 40 years. It presents a short review of The History of the Lakes of the East European Plain, one of the books of the series The History of Lakes published by the Institute of Lake Research of the Russian Academy of Sciences. It describes the

N. Davydova; S. Servant-Vildary

1996-01-01

241

Spatial Distribution, Sources, and Age of Sedimentary Carbon in Lake Malawi, East Africa  

NASA Astrophysics Data System (ADS)

Currently, the source of organic matter to surface sediments of Lake Malawi (East Africa) is unclear; studies of offshore north-basin cores (363 m to 403 m water depth) have produced conflicting results regarding the proportion of aquatic versus terrestrial organic carbon (OC) contained in these sediments. To address this question, ten multi-cores were recovered from the north basin of Lake Malawi along a transect that follows a major river delta into the lake's deep basin, from 82 m to 386 m water depth. Bulk surface sediment data indicate that while the C/N ratio of organic matter decreases with distance from shore (ranging from 9.8 to 8.3, R2 = 0.58), and stable carbon isotope values become increasingly 13C-depleted (ranging from -21.65 to -25.25, R2 = 0.80), the concentration of OC (wt %) generally increases (ranging from 1.9% to 4.5%, R2 = 0.77). These combined trends suggest substantial carbon contribution from aquatic sources, particularly in the deeper-water, open-lake sites. This trend is supported by preliminary biomarker results. N-alcohols from surface sediments were isolated and grouped into aquatically sourced (C20, C22, and C24) and terrestrially sourced (C28 and C30) fractions for quantification as well as radiocarbon dating. N-alcohol abundance results indicate consistent contribution of terrestrial n-alcohols to surface sediments as distance from shore increases, while aquatic n-alcohol input appears to increase. Preliminary results from compound class specific radiocarbon dating indicate that aquatically sourced n-alcohols isolated from surface sediments may be significantly aged relative to bulk surface sediment.

Kruger, B. R.; Minor, E. C.; Werne, J. P.; Johnson, T. C.

2011-12-01

242

Drying out the Nile? Regional Climate Change and Water Resources in East Africa with a focus on Lake Victoria and Lake Tana  

NASA Astrophysics Data System (ADS)

The East African lakes Victoria and Tana are important local water resources for agriculture, fisheries and hydropower; they are also the main sources of the Nile. In this study we focus on the evaporative and evapotranspirative regimes of the hydrological basins for Lakes Tana and Victoria to determine how regional climate change under the A1B scenario is likely to affect the local and regional hydrology. We show results from a very high resolution (10km) simulation, where the state-of-the-art regional climate model (RCM) HIRHAM5 was driven by the global circulation model (GCM) ECHAM5 under the A1B scenario. Three time-slices have been investigated for present day (1980-1999), mid-century (2046-2065) and end of the 21st century (2080-2099) periods. Our analysis includes a comparison with a coarser 0.44o (~50 km) resolution run which demonstrates the importance of using high resolution (10km or higher) in RCM studies of this type to correctly simulate the seasonal and geographical characteristics of the present day east African monsoon system. The projections also indicate that climate change under the intermediate SRES A1B scenario is expected to cause more frequent failures of the East African rains with important consequences for the region and for the hydrology of the East African Lakes. This work introduces the proposed DACEA (Drivers of Aridity Change in East Africa) project which aims to investigate regional and global teleconnections that affect aridity in East Africa. Future work will combine climate palaeoproxies from Lake Tana and Lake Victoria with model experiments carried out with the EC-Earth coupled Ocean-Atmosphere General Circulation Model and downscaled to very high resolution with the RCM HIRHAM5 to determine regional and global scale influences on the African monsoon system. The HIRHAM5 simulations will be dynamically coupled to a regional hydrological model based on MIKE SHE, to evaluate the consequences and the feedback from the regional hydrology of the lake basins in terms of the East African rains.

Mottram, Ruth; Fox Maule, Cathrine; Thejll, Peter; Stendel, Martin; Drews, Martin; Davies, Sarah; Lamb, Henry

2014-05-01

243

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

244

Lake Ecosystem Critical to East African Food Supply is Threatened by Climate Change  

NSF Publications Database

... fish and algae populations in a major lake. The lake holds 18 percent of the world's liquid ... in lake warming in the tropics, recorded by instruments, and declining productivity of the lake's ...

245

Persistent fault controlled basin formation since the Proterozoic along the Western Branch of the East African Rift  

NASA Astrophysics Data System (ADS)

The Western Branch of the East African Rift System is outlined by elongate sedimentary basins, frequently occupied by Cenozoic rift lakes. The role of the inheritance of the leading rift faults from pre-existing basement structures has often been invoked. Recent studies in western Tanzania confirm the extent of the northwest orientated Palaeoproterozoic Ubende Belt contribution to the Phanerozoic Rift. Attention is drawn here on the occurrence of different Meso- and Neoproterozoic sedimentary basins that developed along the ductile shear belt as a result of repeated sinistral wrench fault reactivation. These basins partly overlap each other and typically bear shallow and weakly evolved sediments. North of the Ubende Belt, the Mesoproterozoic Kibara Belt is inferred to have originated as a basin controlled by the complex termination of the Ubende wrench fault. Phanerozoic rift basins also develop along the northwest orientated Ubende Belt structure. They display the same elongate shape as the Proterozoic basins. In Late Palaeozoic-Early Mesozoic the Karoo rift basins formed from a dextral lateral shear reactivation of the inherited Proterozoic shear faults. During the first phase of development the Lake Tanganyika Basin is belived to bear the same characteristics as all previous basins along the Ubende Shear Belt, mainly controlled by strike-slip movements along pre-existing shear faults. The present Lake Tanganyika Basin is subdivided in two sub-basins, separated by the transverse Mahali Shoal, which is an active structure located on the Ubende Shear. The deep lake basin mainly developed outside the Ubende Belt. The northern sub-basin appears to be structurally controlled by the reactivation of the Mesoproterozoic sinistral wrench fault termination of the Ubende shear faults. Structural control of the Palaeoproterozoic basement is however unclear for the southern sub-basin of Lake Tanganyika: this part of the rift segment is flanked by Palaeoproterozoic basement which has not been affected by the Ubende Shear.

Klerkx, J.; Theunissen, K.; Delvaux, D.

1998-04-01

246

Temperature and hydrologic variability of Lake Victoria, East Africa since the Late Pleistocene  

NASA Astrophysics Data System (ADS)

Recent organic geochemical advances have facilitated the comparison between continental temperature change and hydrologic variability. TEX86, a proxy based on the lipids of aquatic Crenarchaeota that show a positive correlation with growth temperature, was used to reconstruct surface water temperatures from Lake Victoria, East Africa during the latest Pleistocene-Holocene. Hydrologic conditions were interpreted using paleoecological implications of shifting pollen and diatom assemblages found in the lake (Kendall, 1969; Stager et al., 2003) and will be compared with future compound specific ?13C data from terrestrial biomarkers in order to determine the patterns of rainfall and aridity in this region. Initial comparisons of climatic changes seen in temperature and hydrologic records appear to show consistency between warm/wet intervals and cool/dry intervals that is often assumed, but more rarely shown, in tropical Africa. Lake Victoria temperatures show a steady warming beginning 16 cal ka, with a pause around the Younger Dryas, dominated by arid conditions and strong savannah grassland development during this interval. There is continued warming to a sustained thermal maximum for this portion of the record at ~10.5-8.5 ka, which generally coincides with the beginning of the Holocene Hypsithermal, an interval of elevated temperatures and precipitation throughout much of tropical Africa. This thermal maximum occurs during the most humid interval of this record (~9.5-8.3 ka), shown by an increase of humid forest pollen and high diatom abundance (due to increased water column mixing and nutrient runoff). Temperatures abruptly cool ~1.5°C in <800 years while precipitation becomes somewhat more seasonally restricted, coinciding with an abrupt drop in inferred P:E ratio and reduction in wind-driven mixing. The record then shows a general cooling, reaching a Holocene thermal minimum of ~18.4°C at ~4.5 ka, contrary to other East African continental and marine paleoclimate records that exhibit a Holocene thermal maximum ~5 ka. These coolest Holocene temperatures correspond to the driest interval in the surrounding region (~5.8-2.7 ka), with an increase in grassland abundance and decrease in humid forest pollen. Though a 5 ka thermal maximum is not seen in Lake Victoria, this portion of the record shows a temperature inflection and variable hydrologic signals, potentially marking a response to the end of the Holocene Hypsithermal, where temperatures begin to rise ~3°C over the remainder of the record.

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

2010-12-01

247

Occurrence, distribution and seasonal variations of polychlorinated biphenyls and polybrominated diphenyl ethers in surface waters of the East Lake, China.  

PubMed

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the surface water of the East Lake, China were investigated in winter (2012) and summer (2013). A hundred and eight samples were collected from 36 sampling sites and analyzed for the 31 PCB and 10 PBDE congeners. Concentrations of both PCBs and PBDEs showed obvious seasonal variations. The average PCB concentrations in the East Lake ranged from 3.17 to 6.09 ng L(-1) in winter and 0.19 to 0.99 ng L(-1) in summer. CB-44, 105, 118 and 179 were dominant in both winter and summer. The average PBDE concentrations in the East Lake ranged from 2.92 to 5.54 ng L(-1) in winter and 0.67 to 1.51 ng L(-1) in summer. BDE-47 was predominant in both winter and summer, which accounted for more than 37% of the total PBDEs concentration from all sampling sites. Independent-Samples t-test showed statistical significance of ?PCBs and ?PBDEs between winter and summer samples. The analysis of distribution, pattern and seasonal variations indicated the different potential sources of PCBs and PBDEs in the East Lake. The potential eco-toxicological risk was also discussed in the study. PMID:24387912

Ge, Jing; Liu, Mingxia; Yun, Xiaoyan; Yang, Yuyi; Zhang, Miaomiao; Li, Qing X; Wang, Jun

2014-05-01

248

Inland fisheries of North East Nigeria including the Upper River Benue, Lake Chad and the Nguru–Gashua wetlands  

Microsoft Academic Search

Planning and management of inland fisheries in North East Nigeria are constrained by a lack of multi-disciplinary information. To address this problem, a survey of 1316 fishing households was undertaken within the major fisheries, including the Upper River Benue, Lake Chad and the Nguru–Gashua wetlands. The resultant profile included: fisheries resources, fishing units, economic and social organisation, fishing patterns, catch

A. E Neiland; S Jaffry; B. M. B Ladu; M. T Sarch; S. P Madakan

2000-01-01

249

Sedimentary record of hydrophobic organic compounds in relation to regional economic development: A study of Taihu Lake, East China  

Microsoft Academic Search

Sediment cores taken from Taihu Lake, East China were analyzed for polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and polybrominated biphenyl ethers (PBDEs). The results showed a general sharp increase of HCH, DDT, PAH and PBDE concentrations in the surface layers, corresponding to a sedimentation time of 1980 and 1990 onward in the Meiliang Bay and Xukou Bay, respectively. The

Guoqing Liu; Gan Zhang; Zhangdong Jin; Jun Li

2009-01-01

250

Ecosystem responses during Late Glacial period recorded in the sediments of Lake ?ukie (East Poland)  

NASA Astrophysics Data System (ADS)

The main objectives of this study was to reconstruct climate impact on the functioning of Lake ?ukie and its catchment (??czna W?odawa Lake District, East European Plain) during Late Glacial period. In order to reconstruct climatic fluctuations and corresponding ecosystem responses, we analysed lake sediments for pollen, subfossil Cladocera, plant macrofossils and chemical composition of the sediment. Of these, plant macrofossils and Cladocera were used to infer minimum and mean July temperatures and ordination analysis was used to examine biotic community shifts. Multiproxy analyses of late-glacial sediments of Lake ?ukie clearly show that the main driver of aquatic and terrestrial ecosystems as well as geomorphological processes in the catchment was climate variation. The history of the lake initiated during the Older Dryas. In that period, ??czna W?odawa Lake District was covered by open habitats dominated by grasses (Poaceae), humid sites were occupied by tundra plant communities with less clubmoss (Selaginella selaginoides), dry sites by dominated by steppe-like vegetation with light-demanding species such as Helianthemum, Artemisia, Chenopodiaceae, and juniper bushes (Juniperus). Cold climate limited the growth and development of organisms in the lake, Cladocera community species composition was poor, with only few species present there all the time. During this time period, permafrost was still present in the ground limiting infiltration of rainwater and causing high erosion in the catchment area. Surface runoff is confirmed by the presence of sclerotia of Cenococcum geophilum and high terrigenous silica content. The warming of the early Allerød caused a remarkable change in the natural environment of this area. This is in accordance with the temperature rise reconstructed with the use of plant macrofossils though the Cladocera reconstruction did not recorded the rise than. This temperature increase resulted in turnover of vegetation in the catchment of Lake ?ukie, pioneer birch-pine forests dominated, later replaced by pine-birch forests. Consequently this limited the erosion. The results of all proxy suggest the water-lever rise in lake ?ukie. The Younger Dryas cooling in the region began about 12 630 14C years BP and recorded in significant drop in temperature reconstructed with plant macrofossils and Cladocera. The cooling resulted in a decline of forest communities and development of open habitats with grasses (Poaceae), Artemisia, and Chenopodiaceae), as well as juniper thickets (Juniperus) At the end of the Younger Dryas, plant communities changed, the non-arborescent pollen declined, while pollen of trees (especially Pinus) became more abundant. This change was more abruptly reflected in Cladocera and aquatic pollen results and is probably related to gradual climate warming. This study is a contribution to the Virtual Institute ICLEA (Integrated Climate and Landscape Evolution Analysis) funded by the Helmholtz Association, projects UMO-2011/01/B/ST10/07367 and N N306 036436 founded by National Science Center, Poland.

Zawiska, Izabela; S?owi?ski, Micha?; Correa-Metrio, Alex; Obremska, Milena; Luoto, Tomi; Nevalainen, Liisa; Woszczyk, Micha?; Milecka, Krystyna

2014-05-01

251

Unique qualities and special problems of the African Great Lakes  

Microsoft Academic Search

The African Great Lakes consist of large, deep rift valley lakes (e.g. Malawi & Tanganyika) and shallower lakes between the Eastern and Western Rifts (e.g. Victoria). They are a group comparable in size to the North American Great Lakes, but are old. Most are seasonally thermally stratified, and wind is the decisive factor that determines the annual cycle of cooling

George W. Coulter; Brian R. Allanson; Michael N. Bruton; P. Humphry Greenwood; Robert C. Hart; Peter B. N. Jackson; Anthony J. Ribbink

1986-01-01

252

Bathymetric and geochemical investigation of Kawah Ijen Crater Lake, East Java, Indonesia  

Microsoft Academic Search

A bathymetric survey of Kawah Ijen crater lake was conducted by acoustic sounding in 1996 to compare the lake morphology with those measured in 1922, 1925 and 1938, and to calculate the present lake volume. Even though the lake experienced several hydrothermal eruptions, the maximum depth became shallower (182 m) than before (200 m), resulting in a reduced lake volume

B. Takano; K. Suzuki; K. Sugimori; T. Ohba; S. M. Fazlullin; A. Bernard; S. Sumarti; R. Sukhyar; M. Hirabayashi

2004-01-01

253

Bacterial diversity of the rock-water interface in an East Antarctic freshwater ecosystem, Lake Tawani(P)†  

PubMed Central

Schirmacher Oasis is one of the few ice-free plateaus in East Antarctica that maintains a unique distribution of over 120 microbial-rich, dynamic freshwater lakes, most of which are unexplored. In this study, we describe the bacterial diversity of the rock-water interface in Lake Tawani(P) using culture-independent Bacterial Tag Encoded FLX Amplicon Pyrosequencing (bTEFAP), clone library construction, and culture-based analysis targeting the eubacterial 16S rRNA gene. Lake Tawani(P)was formed in a fossil valley by the accumulation of snow and glacial melt through surface channels into a low-catchment depression. Overall this lake exhibited thirteen bacterial phyla and one-hundred and twelve genera. The Qiime bioinformatics analysis on the bTEFAP alone exhibited higher coverage of the bacterial composition in Lake Tawani(P) than the clone library construction or culture-based methodology. Particularly due to the higher sensitivity of the bTEFAP approach, we detected and differentiated members of the phyla: Chloroflexi, Gemmatimonadetes, Planctomycetes, Nitrospira, and Candidate Division TM7 that other methods were unable to reveal. Nevertheless we found that the use of multiple approaches identified a more complete bacterial community than by using any single approach. Investigating the bacterial diversity of the Schirmacher Oasis lakes, especially those connected through surface channels and encompassed by valleys, will help unravel the dynamic nature of these unique seasonal, freshwater lakes, which potentially harbors highly adapted bacterial taxa with defined ecological functions.

2013-01-01

254

Reconstructing Late Holocene Climate Variability in North East China From Varved Maar Lake Sediments  

NASA Astrophysics Data System (ADS)

Reconstructing climatic variability over the past c. 2 ka years is recognised as a key PAGES timeframe (focus 2). However few high-resolution records exist from the climate sensitive region of N) China which receives the majority of its precipitation from the east Asian summer monsoon (EASM). Interactions between the EASM and the global climate system have great resonance. Such examples include how the EASM responded to changes in climate over the documented e.g. "Medieval Warm Period" (c. AD 900 - 1300), "Little Ice Age" (c. AD 1350-1850) and recent warming. At present, literature remains contradictory to such environmental changes in NE China over this time-frame due to poor chronological control, low resolution of existing studies and even due to the inexact terminology of these climatic periods. Xiaolongwan Lake (XLW) is a small, closed, maar lake located in the Long Gang Volcanic Field, NE China (42°18'N; 126°19'E). It is at an elevation of 655 m a.s.l. with a maximum depth of 15 m. A varve chronology has been created for a 143 cm composite core (2 cores collected in 2006), and here we present diatoms and organic geochemistry (?13C, TOC, C/N) evidence for environmental change over the past c. 2 ka years. Results show a gradual change in diatom species, moving from a composition where opportunistic species (e.g. Achnanthidium minutissimum) dominate (between c. 100 BC to 500 years AD) at the beginning of the record to one comprised of benthic/epiphytic species (e.g. Staurosira construens var venter, Punctastriata discoidea, Gomphonema parvulum). The introduction after c. 1850 years AD of the planktonic diatom species, Discotella woltereckii, not previously seen in the record, coincides with recent warming. This may be a response to changing limnological conditions, such as decreasing duration of lake ice-cover. Bulk organic ?13C results conducted on a short core collected from XLW in summer 2007, show that over the past c. 350 years there is a distinct decreasing trend in lake macrophytes. At the same time, trends in decreasing mean annual precipitation and an increasing trend in mean annual temperatures for the region are documented from meteorological records. It is possible that reduced EASM intensity may be affecting the limnology and therefore biology of XLW as seen in more recent years. Quantitative techniques (siZer) will later provide a method of assessing periodicities of EASM from this high-resolution record in order to compare with other independent palaeorecords.

Panizzo, V. N.; Mackay, A. W.; Rioual, P.; Chu, G.; Leng, M. J.

2008-12-01

255

East African mid-Holocene wet-dry transition recorded in palaeo-shorelines of Lake Turkana, northern Kenya Rift  

NASA Astrophysics Data System (ADS)

The 'wet' early to mid-Holocene of tropical Africa, with its enhanced monsoon, ended with an abrupt shift toward drier conditions and was ultimately replaced by a drier climate that has persisted until the present day. The forcing mechanisms, the timing, and the spatial extent of this major climatic transition are not well understood and remain the subject of ongoing research. We have used a detailed palaeo-shoreline record from Lake Turkana (Kenya) to decipher and characterise this marked climatic transition in East Africa. We present a high-precision survey of well-preserved palaeo-shorelines, new radiocarbon ages from shoreline deposits, and oxygen-isotope measurements on freshwater mollusk shells to elucidate the Holocene moisture history from former lake water-levels in this climatically sensitive region. In combination with previously published data our study shows that during the early Holocene the water-level in Lake Turkana was high and the lake overflowed temporarily into the White Nile drainage system. During the mid-Holocene (~ 5270 ± 300 cal. yr BP), however, the lake water-level fell by ~ 50 m, coeval with major episodes of aridity on the African continent. A comparison between palaeo-hydrological and archaeological data from the Turkana Basin suggests that the mid-Holocene climatic transition was associated with fundamental changes in prehistoric cultures, highlighting the significance of natural climate variability and associated periods of protracted drought as major environmental stress factors affecting human occupation in the East African Rift System.

Garcin, Yannick; Melnick, Daniel; Strecker, Manfred R.; Olago, Daniel; Tiercelin, Jean-Jacques

2012-05-01

256

Estimating areal rainfall in the Lake Victoria basin in East Africa using ground based and satellite data  

NASA Astrophysics Data System (ADS)

The goal of this study was to improve the understanding of the variability of rainfall in the Lake Victoria basin. The main objective was to use the available rain gauge data in the basin to derive a spatially detailed gridded rainfall dataset for the lake and its basin using geostatistical techniques. Such a dataset is very useful for water balance and other studies. A monthly rainfall dataset with 360 stations was used. Universal Kriging was used for the study and comparisons made with Inverse Distance Weighting. The size of the regular grids was 2000m with a discretisation of 100 points per block giving a support size of 200m. A key question that had to be addressed was related to the representation of lake rainfall given the lack of reliable long term measurements on the lake surface. We approached this by considering 3 different satellite products namely PERSIANN, TRMM and CMORPH, which have been shown to produce acceptable estimates for the region, and using the derived correlations with our dataset to adjust the lake rainfall estimates. Finally, we produced time series of areal mean rainfall for the main tributaries into the Lake Victoria basin including their uncertainty estimates. The results showed an enhancement of rainfall over the lake surface. The rainfall gradient falls sharply as one moves away from the lake shore before rising again in the highland areas to the east and west of the basin. Apart from the north-eastern part of the basin, there are no significant correlations between annual rainfall and either elevation or distance from the lake shore.

Kizza, Michael; Westerberg, Ida; Rodhe, Allan

2010-05-01

257

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

258

Basaltic lava domes, lava lakes, and volcanic segmentation on the southern East Pacific Rise  

NASA Astrophysics Data System (ADS)

Meter-scale DSL-120 sonar mapping and coregistered Argo II photographic observations reveal changes in eruptive style that closely follow the third-order structural segmentation of the ridge axis on the southern East Pacific Rise, 17°11'-18°37'S. Near segment ends we observe abundant basaltic lava domes which average 20 m in height and 200 m in basal diameter and have pillow lava as the dominant lava morphology. The ubiquity of pillow lava suggests low effusion rate eruptions. The abundance of lava domes suggests that the fissure eruptions were of sufficient duration to focus and produce a line of volcanic edifices. Near segment centers we observe fewer but larger lava domes, voluminous drained and collapsed lava lakes, and smooth lobate and sheet lava flows with very little pillow lava. The abundance of sheet flows suggests that high effusion rate eruptions are common. Fewer lava domes and large lava lakes suggest that fissure eruptions do not focus to point sources. This pattern was observed on eight third-order ridge segments suggesting that a fundamental volcanic segmentation of the ridge occurs on this scale. The third-order segment boundaries also correlate with local maxima in the seismic axial magma chamber reflector depth throughout the study area and decreased across-axis width of the region of seismic layer 2A thickening along the one segment where sufficient cross-axis seismic lines exist. The geochemically defined magmatic segment boundaries in the study area match the locations of our volcanic segment boundaries, although rock sampling density is not adequate to constrain the variation across all the third-order volcanic segments that we identify. These observations suggest that variation in the processes of crustal accretion along axis occurs at a length scale of tens of kilometers on superfast spreading (>140 km/Myr full rate) mid-ocean ridges.

White, Scott M.; MacDonald, Ken C.; Haymon, Rachel M.

2000-10-01

259

Cloning and expression of an endocellulase gene from a novel streptomycete isolated from an East African soda lake  

Microsoft Academic Search

Alkaline cellulase-producing actinomycete strains were isolated from mud samples collected from East African soda lakes. The strains were identified as novel Streptomyces spp. by 16S rDNA sequence analysis. A cellulase gene (cel12A) from Streptomyces sp. strain 11AG8 was cloned by expression screening of a genomic DNA library in Escherichia coli. From the nucleotide sequence of a 1.5-kb DNA fragment, an

Pieter Solingen; Daan Meijer; Wilhelmus A. Kleij; Christopher Barnett; Robertus Bolle; Scott D. Power; Brian E. Jones

2001-01-01

260

Dietzia natronolimnaios sp. nov., a new member of the genus Dietzia isolated from an East African soda lake  

Microsoft Academic Search

Two novel alkaliphilic aerobic organotrophic bacteria have been isolated from a moderately saline and alkaline East African\\u000a soda lake. The new isolates grow at pH values between 6 and 10, with a pH optimum for growth of 9.0, and at a salt concentration\\u000a between 0% and 10% (w\\/v). Phylogenetic analysis based on 16S rDNA sequence shows that these isolates are

Andrew W. Duckworth; Susan Grant; William D. Grant; Brian E. Jones; Daan Meijer

1998-01-01

261

Saccharospirillum impatiens gen. nov., sp. nov., a novel c-Proteobacterium isolated from hypersaline Ekho Lake (East Antarctica)  

Microsoft Academic Search

Five Gram-negative, motile, aerobic to microaerophilic spirilla were isolated from various depths of the hypersaline, heliothermal and meromictic Ekho Lake (East Antarctica). The strains are oxidase- and catalase-positive, metabolize a variety of sugars and carboxylic acids and have an absolute requirement for sodium ions. The predominant fatty acids of the organisms are C16 : 1v7c ,C 16 : 0 and

Matthias Labrenz; Paul A. Lawson; Brian J. Tindall; Matthew D. Collins; Peter Hirsch

262

Holocene climate variations from Zhuyeze terminal lake records in East Asian monsoon margin in arid northern China  

NASA Astrophysics Data System (ADS)

Zhuyeze palaeolake is a terminal lake situated in the arid northern China in the East Asian monsoon margin. In order to examine the Holocene palaeoclimatic change in the East Asian monsoon margin, Qingtu Lake section (QTL) from Zhuyeze palaeolake is sampled in high resolution. Palaeoclimatic proxies such as grain size, carbonate, TOC, C/N and ?13C of organic matter, were analyzed; eleven 14C samples and six optically stimulated luminescence (OSL) samples were dated to provide chronological control. We also investigated the geomorphic features of lake shorelines in this area. The results show that the climate was warm and dry in early-Holocene (9.5-7.0 cal ka BP), cool and humid in mid-Holocene (7.0-4.8 cal ka BP), and increasingly drier in late-Holocene (since 4.8 cal ka BP). Comparisons of our records with other records in adjacent areas, as well as with the records in the Asian monsoon areas, suggested that changes in effective moisture was synchronous in East Asian monsoon marginal zone (i.e. the pattern of dry early-Holocene, humid mid-Holocene, and aridity-increasing late-Holocene), and that the moisture optimum during the Holocene was out-of-phase between Asian monsoon margin and Asian monsoonal dominated region, possibly due to the high temperature at that time.

Long, Hao; Lai, ZhongPing; Wang, NaiAng; Li, Yu

2010-07-01

263

Assessment of metals distribution and microbial contamination at selected lake waters in and around Miri City, East Malaysia.  

PubMed

A baseline study was carried out to assess the metal concentrations and microbial contamination at selected Lake waters in and around Miri City, East Malaysia. Sixteen surface water samples were collected at specific Lakes in the environs of major settlement areas and recreational centers in Miri City. The Physico-chemical parameters [pH, Electrical Conductivity (EC) and Dissolved Oxygen (DO)], metals (Fe, Mn, Cu, Cd, Ni and Zn) and Escherichia coli (E. coli) were analysed. The concentrations of Fe, Mn and Ni have been found to be above the permissible limits of drinking water quality standards. The metals data have also been used for the calculation of heavy metal pollution index. Higher values of E. coli indicate microbial contamination in the Lake waters. PMID:22684361

Prasanna, M V; Nagarajan, R; Chidambaram, S; Elayaraja, A

2012-09-01

264

Temporal trends of pollution Pb and other metals in east-central Baffin Island inferred from lake sediment geochemistry.  

PubMed

Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify temporal patterns of anthropogenic Pb pollution in the Clyde River region of Baffin Island, Arctic Canada. Surface sediments from eight lakes on eastern Baffin Island and one from northern-most Greenland, spanning a gradient of 20 degrees latitude, showed great variability with respect to Pb concentration and stable isotopic Pb ratios, with little apparent latitudinal trend. To constrain the temporal evolution of regional Pb pollution, a well-dated core from one of the sites, Lake CF8 on east-central Baffin Island, was analyzed geochemically at high stratigraphic resolution. A pronounced decrease in the (206)Pb/(207)Pb ratio occurs in sediments deposited between 1923 and the mid-1970s, likely reflecting alkyl-Pb additives derived from the combustion of fossil fuels at a global scale. A two-component mixing model indicates that 17-26% of the Pb in the labile fraction of sediments deposited in Lake CF8 between 2001 and 2005 is from anthropogenic input. A Pb-Pb co-isotopic plot ((206)Pb/(207)Pb vs.(208)Pb/(206)Pb ratios) of the Lake CF8 time series data indicates multiple possible sources of industrial Pb pollution. Despite widespread reductions in industrial Pb emissions since the 1970s, there is no evidence for attendant reductions of pollution Pb at Lake CF8. Enhanced scavenging from increased primary production as well as changing precipitation rates as climate warms may represent important factors that modulate Pb deposition to Lake CF8, and Arctic lakes elsewhere. PMID:19665172

Michelutti, Neal; Simonetti, Antonio; Briner, Jason P; Funder, Svend; Creaser, Robert A; Wolfe, Alexander P

2009-10-15

265

Field Work Carried out in Tanganyika.  

National Technical Information Service (NTIS)

The field work in Tanganyika had two objectives: to study the coastal topography between Dar-es-Salaam and the Kenya border, and to investigate certain elements of the cultural geography in the same area. The marine and stream terraces between Dar-es-Sala...

C. S. Alexander

1966-01-01

266

Study of the Microbial Diversity of a Newly Discovered East Antarctic Freshwater Lake, L27C, and of a Perennially Ice-Covered Lake Untersee  

NASA Technical Reports Server (NTRS)

The microbial communities that reside within freshwater lakes of Schirmacher and Untersee Oases in East Antarctica must cope with extreme conditions that may include cold temperature, annual freeze-thaw cycles, exposure to UV radiation, especially during the austral summer months, low light beneath thick ice-cover, followed by seasonal darkness. The objective of this study was to assess the microbial biodiversity and distribution from samples taken from two freshwater lakes (L27C and Lake Untersee) that were collected during the Tawani 2008 International Antarctic Expedition that conducted research in this region of Antarctica. L27C is a small, previously unreported lake residing 2 km WNW of Maitri Station at Schirmacher Oasis. Biodiversity and distribution of microorganisms within the lake were studied using both culture-independent and culture-dependent methodologies based upon the analysis of eubacterial 16S rRNA gene sequences. Lake Untersee, a perennially ice-covered, ultra-oligotrophic, lake in the Otto-von-Gruber-Gebirge (Gruber Mountains) of central Dronning Maud Land was also sampled and the microbial diversity was analyzed by eubacterial 16S rRNA gene sequences derived from pure cultures. Direct culturing of water samples from each lake on separate R2A growth medium exhibited a variety of microorganisms including: Janthinobacterium, Hymenobacter, Sphingamonas, Subtercola, Deinococcus, Arthrobacter, Flavobacterium, Polaromonas, Rhodoferax and Duganella. The evaluation of samples from L27C through culture-independent methodology identified a rich microbial diversity consisting of six different phyla of bacteria. The culture-independent analysis also displayed the majority of bacteria (56%) belonged to the Class gamma-proteobacteria within the phylum Proteobacteria. Within the Class gamma-proteobacteria, Acinetobacter dominated (48%) the total microbial load. Overall, L27C exhibited 7 different phyla of bacteria and 20 different genera. Statistical analysis (Shannon-Weaver Diversity Index and Simpson Diversity Index) of the biodiversity of L27C displayed a moderately rich and diverse community. Investigations of the biodiversity and distribution of microorganisms in these lakes will help further our understanding of how the physical environment impact the structure and function within these microbially dominated ecosystems.

Huang, Jonathan P.; Hoover, Richard B.; Andersen, Dale; Bej, Asim K.

2010-01-01

267

The geochemistry, age, and origin of groundwater in a mafic pluton, East Bull Lake, Ontario, Canada  

NASA Astrophysics Data System (ADS)

The geochemistry of groundwater in the East Bull Lake gabbro-anorthosite pluton near Elliot Lake, Ontario, Canada, has been investigated. Three chemical types of groundwater are present to depths of about 650 m, and are controlled by the nature of the groundwater flow systems and the water/rock interactions in the fractures. Ca/HCO 3 water is present in the recharge area of the local flow system and evolves rapidly along the direction of groundwater flow to a high-pH, Na/HCO 3 water primarily by cation exchange reactions. Saline Na/Cl water is present below a depth of about 350 m. On the basis of its chemistry and hydraulic head measurements, the Na/Cl water is believed to be part of a deep regional groundwater flow system. Carbon-14 measurements of the Na/HCO 3 water suggest that this water was recharged shortly after the last Pleistocene deglaciation. This is supported by ? 18O values that are as much as 6%. lighter than shallow modern groundwater. Despite the high Mg content of the enclosing rocks, Mg 2+ concentrations in the groundwater of this unit are <1.0 mg L -1, and may be controlled by present-day serpentinization or formation of talc. Laumontite is thermodynamically stable in the Na/HCO 3 and Na/Cl waters and hence could still be forming under the present low-temperature conditions (<25°C). The stable isotope composition of the Na/Cl water suggests that this water type is not a geochemically evolved product of the overlying waters, although present-day albitization of the anorthosite could be responsible for the increased Ca/Na ratio in the Na/Cl water compared to the other water types. The salinity of this water appears to have been derived outside the pluton, possibly as an ancient infiltration into crystalline basement rocks of saline formation waters present in Paleozoic sedimentary rocks, which formerly overlay the pluton, or from nearby Proterozoic formations. This hypothesis is supported by Br/Cl ratios that are similar to sea water and many present-day formation waters, and the isotopic composition of the dissolved sulphate. The He "age" of the saline water is of the order of 10 8 years. Therefore both the saline water and many of its solutes appear to have ancient origins.

Bottomley, D. J.; Gascoyne, M.; Kamineni, D. C.

1990-04-01

268

Fish-community composition in Ouleout Creek, in the vicinity of East Sidney Lake, Delaware County, New York, 2000  

USGS Publications Warehouse

The U.S. Army Corps of Engineers, Baltimore District, has been conducting biological surveys of the inflow and outflow streams of East Sidney Lake since the early 1980?s. These surveys are made to identify possible detrimental effects as well as benefits of the lake and to better understand the aquatic communities in the vicinity of the lake at the present and over time. The U.S. Army Corps of Engineers and the U.S. Geological Survey jointly conducted a survey of the fish communities upstream and downstream of the reservoir in Ouleout Creek in September 2000. The fish communities upstream and downstream were compared and any differences or similarities seen in the fish communities were noted. This study found the fish communities upstream and downstream of East Sidney Lake to be in good condition, with Index of Biotic Integrity (IBI) scores 4.5 upstream and 4.3 downstream. The habitat conditions of both reaches were of optimal quality, with a score of 18 upstream and 17 downstream as determined by use of the U.S. Environmental Protection Agency?s Rapid Bioassessment Protocols, and are capable of supporting fish communities. The Shannon Index was 2.95 upstream and 2.61 downstream of the lake, indicating that both reaches are slightly impacted by species richness and individual evenness among the species. Downstream, the dominant taxa was twice that of the co-dominant taxa. The Jaccards Coefficient and the Index of Similarity statistically shows these communities are similar, with scores of 0.76 and 0.86, respectively. Of the 19 species captured downstream, 16 of those also were captured upstream.

Brightbill, R. A.; Bilger, M. D.

2001-01-01

269

Genesis and Paleo-ecological Interpretation of Swamp Ore Deposits at Sahara Paleo-lakes of East Niger  

NASA Astrophysics Data System (ADS)

In formerly vegetated flat lake-shore areas of Pleistocene and Holocene paleo-lake depressions in the Sahara of East Niger (Ténéré, Tchigai mountains and in the Erg of Bilma), ancient dune sands are covered by rampart-like or flat beds of individual or networked rhizoconcretions. The massive goethite accumulation, which partly includes an outer fringe of lepidocrocite, impregnated the ancient dune sands. Apart from Fe, P, Ca, and Mg, other heavy metals were also concentrated. The formation and morphological differentiation of these swamp ores were generally bound at vegetated shallow water areas of paleo-lakes in ancient dune fields. Accordingly, the swamp ores of the Ténéré, which has flat to undulating relief, display a large dissemination. In contrast, in the Erg of Bilma the high altitude and steep slopes of ancient dune ridges led to steeper shore areas of the paleo-lakes, at which beds of rhizoconcretions were unable to develop. The oxides were formed by oxidation of Fe2 + -ions from the lake water and concentrated around the roots in the upper root zone of the swamp vegetation. The lack of oxygen in the warm lake water of the shore region, as well as the decomposition of vegetation residues, excluded high redox potentials within the deeper water near the subhydric soil surface. Hence, the formation of rhizoconcretions can only be explained by the specific physiological characteristics of the swamp vegetation, which was able to supply oxygen to the roots through an aerenchyma. The release of surplus oxygen from such roots obviously caused high redox potentials at the root surface and in the neighbouring root environment. As a result precipitation of Fe and Mn oxides occurred, which adsorbed nutrients and heavy metals from the soil solution. The redistribution of the ions from the reduced sediments of the lake basin into the root zone of the shore area resulted from diffusion and mass flow. Paleo-climatically, the swamp ore deposits denote humid periods accompanied by a stable lake water-table over a long period of time. The sequence of several swamp ore beds along the former shore, at different elevations above the lake floor, is evidence of decreasing paleo-lake water levels within a period of increasing aridity.

Felix-Henningsen, Peter

270

Coastal wetlands: Proceedings of First Great Lakes Wetlands Colloquium, November 1984, East Lansing, Michigan  

SciTech Connect

This book explores the wetlands of the Great Lakes. Topics considered include the effects of water level fluctuations on Great Lakes coastal marshes; environmental influences on the distribution and composition of wetlands in the Great Lakes Basin; vegetation dynamics, buried seeds, and water level fluctuations on the shoreline of the Great Lakes; preliminary observations on the flux of carbon, nitrogen, and phosphorous in a Great Lakes coastal marsh; nutrient cycling by wetlands and possible effects of water levels; and avian wetland habitat functions affected by water level fluctuations.

Prince, H.H.; D'Itri, F.M.

1986-01-01

271

Atmospheric concentrations of polycyclic aromatic hydrocarbons in the watershed of Lake Victoria, East Africa.  

PubMed

In the first study of its kind in Africa, PAHs were measured in high volume (24 h) air samples collected from two sampling stations, at Kakira and Entebbe (KAK and EBB, respectively) within the Lake Victoria watershed in Uganda, to assess source contributions and generate a baseline reference data set for future studies in the East African region. Sampling was conducted over two periods [2000-2004 (KAK and EBB1) and 2008-2010 (EBB2)]. The samples were extracted by accelerated solvent extraction and analyzed for 30 PAHs by GC-MS. The mean total PAH concentrations (ng/m(3)) were found to be 74.3 (range; 19.3-311, N = 39) for KAK, 56.8 (range; 13.3-126, N = 22) for EBB1 and 33.1 (range; 4.91-108, N = 56) for EBB2. The 3-ringed PAHs were the most predominant group with mean concentrations of 35.9 ng/m(3)(EBB1), 30.5 ng/m(3)(KAK) and 23.2 ng/m(3)(EBB2). Naphthalene had an exceptionally high mean concentration (21.9 ng/m(3)) for KAK compared to 0.44 and 0.39 ng/m(3) in EBB1 and EBB2 respectively, likely due to intensive agricultural operations nearby KAK. Principal component and diagnostic ratio analyses showed that the measured levels of PAHs were associated with mixed sources, combustion of petroleum, and biomass being the major sources. PMID:23020709

Arinaitwe, Kenneth; Kiremire, Bernard T; Muir, Derek C G; Fellin, Phil; Li, Henrik; Teixeira, Camilla; Mubiru, Drake N

2012-11-01

272

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

273

Biology of the African clupeid Limnothrissa miodon with reference to its small size in artificial lakes  

Microsoft Academic Search

Summary Limnothrissa miodon is a clupeid from Lake Tanganyika which has been introduced to Lakes Kivu and Kariba and which invaded Lake Cahora Bassa. These lakes differ considerably from one another but the biology of Limnothrissa is similar in many respects in all of them. Similarities include its feeding and breeding biology, whilst its populations fluctuate, on both an annual

B. E. Marshall

1993-01-01

274

Water quality, nutrient budget, and pollutant loads in Chinese mitten crab ( Eriocheir sinensis) farms around East Taihu Lake  

NASA Astrophysics Data System (ADS)

To understand the factors causing frequent outbreaks of harmful algae blooms in the Taihu Lake, China, we studied water quality and nutrient budget in Chinese mitten crab ( Eriocheir sinensis) farm ponds in the eastern part of the lake from November 2007 to December 2009. We estimated the nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) loads. Materials input and output ponds, water exchange, and applied management practices of 838.5-hm2 crab ponds were surveyed using questionnaires. Water quality of 12 ponds, which were located no more than 2 km from East Taihu Lake, were monitored. The results show that water quality in the crab ponds was better than reference data. Feeds, including corn seed, commercial feed, trash fish, and gastropod, were the major sources of N and P input in the crab ponds, contributing 88.7% and 94.9%, respectively. In total, 60.5% of N and 37.3% of P were sequestered by macrophytes, and only 15.7% and 8.5% of them were discharged as effluent. The net loads of N and P in effluent were 16.43 kg/hm2/cycle and 2.16 kg/hm2/cycle, respectively, while the COD load was -17.88 kg/hm2/cycle. This indicated that crab farming caused minor negative impact on the trophic status of the lake area, which was attenuated by macrophytes. However, wastewater purification is still necessary in crab faming.

Cai, Chunfang; Gu, Xiaohong; Huang, Hezhong; Dai, Xiuying; Ye, Yuantu; Shi, Chenjiang

2012-01-01

275

Recent heavy metal accumulation in Dongjiu and Xijiu lakes, East China  

Microsoft Academic Search

Taihu Lake has been recognized as a seriously contaminated waterbody with regard to Cd, Cu, Pb and Zn over the last two decades.\\u000a The input of pollutants has increased due to economic and social development and population increase. Seventy percent of the\\u000a pollutants in Taihu Lake comes from rivers, with the Yili River being a major source of pollutants. Lakes

Yanhong Wu; Enfeng Liu; Shuchun Yao; Yuxin Zhu; Weilan Xia

2010-01-01

276

Late pleistocene and holocene history of the lakes in the Kola Peninsula, Karelia and the North-Western part of the East European plain  

NASA Astrophysics Data System (ADS)

The paper reviews the work on paleolimnology in parts of the FSU over the last 40 years. It presents a short review of The History of the Lakes of the East European Plain, one of the books of the series The History of Lakes published by the Institute of Lake Research of the Russian Academy of Sciences. It describes the Late Pleistocene and Holocene history of these lakes based mainly on the study of lacustrine sediments. Amongst the samples Lake Nero near Moscow which is located near the marginal zone of the last glaciation, and includes records that go back as early as 190,000 BP. The main elements of lake evolution are shown in different territories: Byelorussia; Baltic countries; Karelia; and the Kola Peninsula. Special attention is given to palaeolimnological data because its use for Holocene and Late Pleistocene palaeoclimate reconstructions.

Davydova, N.; Servant-Vildary, S.

277

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

278

Focal mechanisms from regional earthquakes in East Africa and refinements in stress patterns  

NASA Astrophysics Data System (ADS)

Accurate event locations for eleven events with magnitude greater than 3.5 in Tanzania, East Africa have been obtained using data from the Tanzania Broadband Seismic Experiment. Focal mechanisms for most of these events have been determined by modeling P and SH polarities and amplitude ratios in a grid search method. Epicenters have been constrained by using P and S arrival times. Focal depths have been constrained by waveform modeling of regional and local depth phases. Most of the earthquakes occur in two areas along the western or eastern branch of the East African Rift. The first area is located between southern Lake Tanganyika and Lake Rukwa in the western branch, and the mechanisms in this region are characterized by strike-slip or oblique extension with nodal planes striking E-W to NW-SE. These events confirm that this part of the western rift is under transtension, as compared to the Lake Tanganyika and Rukwa rifts, where the stress field appears to be almost purely extensional. The second area for which we have obtained several new focal mechanisms is near the southern end of the eastern branch where the rift impinges on the eastern margin of the Tanzania craton. The focal mechanisms from this part of the rift have strike slip or normal motions but the orientations of the nodal planes are complex, consistent with the complicated orientation of the block faults. The focal depths for the events in the first area vary from 7 to 36 km, and in the second area, they vary from 11 to 34 km.

Brazier, R. A.; Nyblade, A.

2004-12-01

279

Structural control of sedimentation patterns and implication for the economic potential of the East African Rift basins  

NASA Astrophysics Data System (ADS)

Continental rifts contain a significant proportion of world oil reserves. The Cenozoic rifts of Africa are no exception. In addition, the Africa rifts offer a potential for the accumulation of strata-bound economic resources which have not been fully investigated. Predicting the distribution of significant accumulations of metallic and non-metallic ores requires the development of depositional models that are related to basin-controlling variables such as crustal thickness, rates and degree of extension etc. Such model development relies upon observations made in areas of recent rifting, notably in East Africa. This paper offers a set of models for a spectrum of basin types that has been identified in the East African rift. They have been developed in the light of recent advances in our understanding of rift structure and development. Basins range in character from deep, narrow, structurally simple and volcanic-poor, e.g. the Tanganyika basin, through a less confined, volcanic but still simple Turkana-type basin, to the broad, shallow, volcanic-rich and structurally complex rift found in the region around Lake Baringo. Oil source rocks are accumulated in Tanganyika-type but the best reservoir rocks and seals are a product of Turkana-type settings. Turkana-type basins may also favour the accumulation of heavy minerals around lake shores and contain potentially exploitable sands and gravels. In contrast, the volcanic rocks and shallow lakes of Baringo-type rift basins encourage precipitation of economically useful evaporites (e.g. Lake Magadi) but have no oil potential.

Frostick, L. E.; Reid, I.

280

Petrophysical characterization of the lacustrine sediment succession drilled in Lake El'gygytgyn, Far East Russian Arctic  

NASA Astrophysics Data System (ADS)

Seismic profiles of Far East Russian Lake El'gygytgyn which was formed by a meteorite impact some 3.6 million years ago show a stratified sediment succession that can be separated into Subunits Ia and Ib at approximately 167 m below lake floor (= ∼ 3.17 Ma). The former is well-stratified, while the latter is acoustically more massive. The sediments are intercalated with frequent mass movement deposits mainly in the proximal parts, while the distal part is almost free of such deposits at least in the upper part. In spring 2009, a long core drilled in the lake center within the framework of the International Continental Scientific Drilling Program (ICDP) penetrated the entire lacustrine sediment succession down to ~ 320 m below lake floor and about 200 m further into the meteorite-impact related bedrock. Downhole logging data down to 390 m below lake floor show that the bedrock and the lacustrine part of the core differ largely in their petrophysical characteristics. The contact between the bedrock and the lacustrine sediments is not abrupt, but rather transitional with a mixture of impact-altered bedrock clasts in a lacustrine matrix with varying percentages. Physical and chemical proxies measured on the cores can be used to divide the lacustrine part into five different clusters. These can be plotted in a redox-condition vs. input type diagram with total organic carbon content and magnetic susceptibility values indicating anoxic or oxic conditions and with the Si/Ti ratio representing more clastic or more biogenic input. Plotting the clusters in this diagram allows identifying clusters that represent glacial phases (Cluster I), super interglacials (Cluster II), and interglacial phases (Clusters III and IV).

Gebhardt, A. C.; Francke, A.; Kück, J.; Sauerbrey, M.; Niessen, F.; Wennrich, V.; Melles, M.

2013-01-01

281

Petrophysical characterization of the lacustrine sediment succession drilled in Lake El'gygytgyn, Far East Russian Arctic  

NASA Astrophysics Data System (ADS)

Seismic profiles of Far East Russian Lake El'gygytgyn, formed by a meteorite impact some 3.6 million years ago, show a stratified sediment succession that can be separated into subunits Ia and Ib at approximately 167 m below lake floor (=~3.17 Ma). The upper (Ia) is well-stratified, while the lower is acoustically more massive and discontinuous. The sediments are intercalated with frequent mass movement deposits mainly in the proximal areas, while the distal region is almost free of such deposits at least in the upper part. In spring 2009, a long core drilled in the lake center within the framework of the International Continental Scientific Drilling Program (ICDP) penetrated the entire lacustrine sediment succession down to ~320 m below lake floor and about 200 m farther into the meteorite-impact-related bedrock. Downhole logging data down to 390 m below lake floor show that the bedrock and the lacustrine part differ significantly in their petrophysical characteristics. The contact between the bedrock and the lacustrine sediments is not abrupt, but rather transitional with a variable mixture of impact-altered bedrock clasts in a lacustrine matrix. Physical and chemical proxies measured on the cores can be used to divide the lacustrine part into five different statistical clusters. These can be plotted in a redox-condition vs. input-type diagram, with total organic carbon content and magnetic susceptibility values indicating anoxic or oxic conditions and with the Si / Ti ratio representing more clastic or more biogenic input. Plotting the clusters in this diagram allows identifying clusters that represent glacial phases (cluster I), super interglacials (cluster II), and interglacial phases (clusters III and IV).

Gebhardt, A. C.; Francke, A.; Kück, J.; Sauerbrey, M.; Niessen, F.; Wennrich, V.; Melles, M.

2013-08-01

282

Analogy between natural gas found in lakes of rift valley system of east Africa and its allied gas in Japan  

SciTech Connect

The Afar triangle in northeastern Ethiopia is where the Red Sea rift, the Carlsberg Ridge of the Indian Ocean, and the Rift Valley system of east Africa meet. In 1979, J. Welhan and H. Craig reported that hydrothermal vents at 21/sup 0/N, on the East Pacific Rise, are discharging turbid waters. Mixtures of the plumes with ambient seawater contain significant amounts of dissolved H/sub 2/ and CH/sub 4/ as well as mantel-derived /sup 3/He-rich helium. The /sup 3/He//sup 4/He ratios of rock samples obtained earlier by J. Lupton and H. Craig from the Mid-Oceanic Ridge, including the Mid-Atlantic Ridge and the east Pacific Rise, are extremely high at an almost constant value of (1.3 +/- 0.2) x 10/sup -5/, which they defined as the MOR-type helium. However, the deep brines of the Red Sea contain about 1,000 times more methane than normal seawater does, according to Gold and Soter in 1980. Much evidence leads us to believe that large amounts of /sup 3/He-rich helium-bearing natural gas have been gushing out in many places of the Rift Valley of east Africa for a long time. In 1980, Gold and Soter stated that Lake Kivu, which occupies part of the East African rift valley, contains 50 million tons of dissolved methane for which there is no adequate microbial source. The Japanese Islands began to separate from the Asian continent during the early Miocene. The early Miocene was characterized by intensive volcanic activity that produced large amounts of pyroclastics and other volcanic rocks, generally called green tuff in Japan. It has been suggested that oil and gas in green tuff is derived from the upper mantle.

Fukuta, O.

1984-09-01

283

Initial Results of Scientific Drilling on Lake Malawi, East African Rift  

NASA Astrophysics Data System (ADS)

Lake Malawi is one of the largest and oldest lakes in the southern hemisphere and in the tropical latitudes, measuring more than 580 km in length, with a maximum depth of 700 m, and with an estimated age of more than 7 Ma. The lake water column is anoxic below 200 m, thus preserving an extensive record of laminated (varved) sediments. The lake's hydrologic budget is hypersensitive to minor changes in precipitation:evaporation, and signals of lake level and limnologic change respond markedly to regional climate variations. During February-March 2005 a scientific drilling program was conducted on the deep, open waters of Lake Malawi, using a converted local fuel barge outfitted with a deep-water-capable geotechnical drilling rig, a portable dynamic positioning system, and a suite of sampling tools designed for deep lake coring. A total of 623 m of core was recovered in seven holes at two sites on the lake. The high-resolution North Basin site (water depth 359 m) was triple-cored, providing redundant sampling of the sedimentary section representing the past ~75-100 kyr; the Central Basin deep site (592 m water depth) was double cored over the period of the past ~200 kyr, and single-cored to 380 m, covering perhaps 1.5 million years. The North Basin high-resolution site targeted a hemipelagic sequence, which in core samples consists of alternating zones of laminated and homogenous silty mud. At the base of these cores we observe well-sorted medium-grained shoreface sand deposits, that we interpret to be a transgressive surface deposited following a severe (500 m) lake lowstand. Density, magnetic susceptibility, TOC, and C/N profiles closely follow lithologic changes, and correspond to periods of enhanced or diminished productivity and dramatically varying lake level. Initial dating of the North Basin site (total core length 38 m) is underway using a combination of Radiocarbon, Tephra Ar-Ar, and Optically-Stimulated Luminescence methods, and initial results indicate a near-linear sedimentation rate in the uppermost sediments of 0.35-0.5 mm/yr. The deep Central Basin site also shows pronounced cyclical signals in lithostratigraphy and physical properties, and dating is underway on the deep 380 m-long core using OSL, paleomagnetics, and Be-10. Ostracode assemblages, along with other paleoenvironmental indicators, suggest highly variable lake conditions, with some intervals of considerably higher salinities and alkalinities, and much lower lake levels than present.

Scholz, C. A.; Johnson, T. C.; King, J.; Cohen, A. S.; Lyons, R. P.; Kalindekafe, L.; Forman, S. L.; McHargue, L. R.; Singer, B. S.

2005-12-01

284

Molecular records of climate variability and vegetation response since the Late Pleistocene in the Lake Victoria basin, East Africa  

NASA Astrophysics Data System (ADS)

New molecular proxies of temperature and hydrology are helping to constrain tropical climate change and elucidate possible forcing mechanisms during the Holocene. Here, we examine a ˜14,000 year record of climate variability from Lake Victoria, East Africa, the world's second largest freshwater lake by surface area. We determined variations in local hydroclimate using compound specific ?D of terrestrial leaf waxes, and compared these results to a new record of temperature utilizing the TEX86 paleotemperature proxy, based on aquatic Thaumarchaeotal membrane lipids. In order to assess the impact of changing climate on the terrestrial environment, we generated a record of compound specific ?13C from terrestrial leaf waxes, a proxy for ecosystem-level C3/C4 plant abundances, and compared the results to previously published pollen-inferred regional vegetation shifts. We observe a general coherence between temperature and rainfall, with a warm, wet interval peaking ˜10-9 ka and subsequent gradual cooling and drying over the remainder of the Holocene. These results, particularly those of rainfall, are in general agreement with other tropical African climate records, indicating a somewhat consistent view of climate over a wide region of tropical East Africa. The ?13C record from Lake Victoria leaf waxes does not appear to reflect changes in regional climate or vegetation. However, palynological analyses document an abrupt shift from a Poaceae (grasses)-dominated ecosystem during the cooler, arid late Pleistocene to a Moraceae-dominated (trees/shrubs) landscape during the warm, wet early Holocene. We theorize that these proxies are reflecting vegetation in different locations around Lake Victoria. Our results suggest a predominantly insolation-forced climate, with warm, wet conditions peaking at the maximum interhemispheric seasonal insolation contrast, likely intensifying monsoonal precipitation, while maximum aridity coincides with the rainy season insolation and the interhemispheric contrast gradient minima. We interpret a shift in conditions at the Younger Dryas to indicate a limited switch in insolation-dominated control on climate of the Lake Victoria region, to remote teleconnections with the coupled Atlantic and Pacific climate system.

Berke, Melissa A.; Johnson, Thomas C.; Werne, Josef P.; Grice, Kliti; Schouten, Stefan; Sinninghe Damsté, Jaap S.

2012-11-01

285

A 250 ka oxygen isotope record from diatoms at Lake El'gygytgyn, far east Russian Arctic  

NASA Astrophysics Data System (ADS)

In 2003 sediment core Lz1024 was drilled at Lake El'gygytgyn, far east Russian Arctic, in an area of the Northern Hemisphere which has not been glaciated for the last 3.6 Ma. Biogenic silica was used for analysing the oxygen isotope composition (?18Odiatom) in the upper 13 m long section dating back about 250 ka with samples dominated by one taxa in the <10 ?m fraction (Cyclotella ocellata). Downcore variations in ?18O values show that glacial-interglacial cycles are present throughout the core and ?18Odiatom-values are mainly controlled by ?18Oprecipitation. Changes reflect the Holocene Thermal Maximum, the Last Glacial Maximum (LGM) and the interglacial periods corresponding to MIS 5.5 and MIS 7 with a peak-to-peak amplitude between LGM and MIS 5.5 of ?18O = 5.3‰. This corresponds to a mean annual air temperature difference of about 9 °C. Our record is the first continuous ?18Odiatom record from an Arctic lake sediment core directly responding to precipitation and dating back more than 250 ka and correlates well with the stacked marine ?18O LR04 (r = 0.58) and ?D EPICA Dome-C record (r = 0.69). With ?18O results indicating strong links to both marine and ice-core records, records from Lake El'gygytgyn can be used to further investigate the sensitivity of the Arctic climate to both past and future global climatic changes.

Chapligin, B.; Meyer, H.; Swann, G. E. A.; Meyer-Jacob, C.; Hubberten, H.-W.

2012-10-01

286

A High-Resolution 11,400Yr Diatom Record from Lake Victoria, East Africa  

Microsoft Academic Search

Fine-interval (?30–45 yr) sampling of a core from Lake Victoria's Damba Channel shows that numerous abrupt changes in the lake's diatom assemblages have occurred in response to climatic fluctuations over the past 11,40014C yr. Four distinct climatic phases bounded by sudden transitions are inferred: (1) variably dry ?11,400–10,000 yr B.P., (2) humid ?10,000–7200 yr B.P., (3) more seasonal ?7200–2200 yr

J. Curt Stager; Brian Cumming; Loren Meeker

1997-01-01

287

The decline of the native fishes of lakes Victoria and Kyoga (East Africa) and the impact of introduced species, especially the Nile perch, Lates niloticus , and the Nile tilapia, Oreochromis niloticus  

Microsoft Academic Search

There has been a decline, and in some cases an almost total disappearance, of many of the native fish species of lakes Victoria and Kyoga in East Africa since the development of the fisheries of these lakes was initiated at the beginning of this century. The Nile perch, Lates niloticus, a large, voracious predator which was introduced into these lakes

Richard Ogutu-Ohwayo

1990-01-01

288

High-latitude environmental change during MIS 8-12: biogeochemical evidence from Lake El'gygytgyn, Far East Russia  

NASA Astrophysics Data System (ADS)

Marine Isotope Stages (MIS) 11 has been proposed as an analog for the present interglacial; however, terrestrial records of this time period are rare. Sediments from Lake El'gygytgyn (67°30´ N, 172°5´ E) in Far East Russia contain a 3.56 Ma record of climate variability from the Arctic. Here, we present an organic geochemical reconstruction of environmental and climatic changes from MIS 8 through 12 (289 to 460 ka). Terrestrial vegetation changes, as revealed by plant leaf wax (n-alkane) indices and concentrations of arborinol (a biomarker for trees), show increased tree cover around the lake during interglacial periods, with higher concentrations observed during MIS 11 as compared to MIS 9. A similar pattern is also observed in records of aquatic productivity revealed by molecular indicators from dinoflagellates (dinosterol), eustigmatophyte algae (long-chain (C28-C32) 1,15 n-alkyl diols) in addition to short-chain nalkanes, where aquatic productivity is highest during MIS 11. Changes recorded in these molecular proxies track relative temperature variability as recorded by the MBT/CBT paleothermometer, based on branched glycerol dialkyl glycerol tetraethers (GDGTs). Additionally, relative MBT/CBT temperature changes generally track pollen and diatom ?18O temperature estimates, compiled by other studies, which suggest glacial-interglacial temperature changes of ~ 9-12 °C. These records of environmental and climatic change indicate Arctic sensitivity to external forcings such as orbital variability and atmospheric greenhouse gas concentrations. Overall, this study indicates that organic geochemical analyses of the Lake El'gygytgyn sediment archive can provide critical insight into the response of lake ecosystems and their sensitivity in high latitude regions.

D'Anjou, R. M.; Wei, J. H.; Castañeda, I. S.; Brigham-Grette, J.; Petsch, S. T.; Finkelstein, D. B.

2012-09-01

289

Occurrence of and Trends in Selected Sediment-Associated Contaminants in Caddo Lake, East Texas, 1940-2002  

USGS Publications Warehouse

Bottom-sediment cores were collected from four sites in Caddo Lake in East Texas during May 2002 for analyses of radionuclides (for age dating), organochlorine pesticides, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and major and trace elements, and to describe the occurrence and trends of these sediment-associated contaminants. The Goose Prairie Creek and Harrison Bayou sites receive drainage from an area that includes parts of the now-closed Longhorn Army Ammunitions Plant. The mid-lake site is relatively close to dense oil and gas operations in the lake. The Carter Lake site receives minimal discharge from developed areas. Sediment age (deposition) dates represented in the cores ranged from 1940 to 2002. The only organochlorine compounds detected in all core samples were the DDT degradation products DDE or DDD, and PCB Aroclors 1242, 1254, and 1260 were detected only at the Goose Prairie Creek site. One or more of the DDE concentrations at all sites exceeded a consensus-based threshold effect concentration (on benthic biota), but none exceeded a consensus-based probable effect concentration. The Goose Prairie Creek site had significant downward trends in concentrations of organochlorine compounds, except for no trend in DDE concentrations. The Ammunitions Plant is a possible historical source of the few organochlorine compounds detected at the Goose Prairie Creek and Harrison Bayou sites. PAH concentrations at all sites were below respective threshold effect concentrations. Highest PAH concentrations at all four sites were of C2-alkylated naphthalenes. Nearly all statistically significant PAH trends in the cores were downward. On the basis of PAH source-indicator ratios, the majority of PAH compounds appear to have originated from uncombusted sources such as leaks or spills from oil and gas operations or vehicles (automobiles, boats, aircraft) in the Caddo Lake area. Concentrations of several of the eight trace elements with threshold effect concentrations and probable effect concentrations (among 26 analyzed) were above the respective threshold effect concentrations, but all, except one lead concentration at the Goose Prairie Creek site (deposited about 1961), were below respective probable effect concentrations. Among trace element concentrations at the four sites, lead and mercury were consistently relatively high at the Goose Prairie Creek site. Again the Ammunitions Plant, because of its proximity and history of industrial activities, is the suspected primary source. Statistically significant trends in trace element concentrations were mixed, but more were downward than upward. Computations to indicate the dominant source (atmospheric fallout or drainage area) of mercury to the Caddo Lake sediment core sites (except Carter Lake) indicate that about one-third of the mercury at the Goose Prairie Creek site might result from drainage area sources. No drainage area sources were indicated for the Harrison Bayou and mid-lake sites. Arsenic, cadmium, and zinc concentrations were highest at the Carter Lake site. No relation between the relatively higher trace element concentrations and any potential source of contamination in the Carter Lake drainage area (for example, oil and gas operations, a road, a boat ramp) is indicated.

Wilson, Jennifer T.

2003-01-01

290

History and timing of human impact on Lake Victoria, East Africa.  

PubMed Central

Lake Victoria, the largest tropical lake in the world, suffers from severe eutrophication and the probable extinction of up to half of its 500+ species of endemic cichlid fishes. The continuing degradation of Lake Victoria's ecological functions has serious long-term consequences for the ecosystem services it provides, and may threaten social welfare in the countries bordering its shores. Evaluation of recent ecological changes in the context of aquatic food-web alterations, catchment disturbance and natural ecosystem variability has been hampered by the scarcity of historical monitoring data. Here, we present high-resolution palaeolimnological data, which show that increases in phytoplankton production developed from the 1930s onwards, which parallels human-population growth and agricultural activity in the Lake Victoria drainage basin. Dominance of bloom-forming cyanobacteria since the late 1980s coincided with a relative decline in diatom growth, which can be attributed to the seasonal depletion of dissolved silica resulting from 50 years of enhanced diatom growth and burial. Eutrophication-induced loss of deep-water oxygen started in the early 1960s, and may have contributed to the 1980s collapse of indigenous fish stocks by eliminating suitable habitat for certain deep-water cichlids. Conservation of Lake Victoria as a functioning ecosystem is contingent upon large-scale implementation of improved land-use practices.

Verschuren, Dirk; Johnson, Thomas C; Kling, Hedy J; Edgington, David N; Leavitt, Peter R; Brown, Erik T; Talbot, Michael R; Hecky, Robert E

2002-01-01

291

History and timing of human impact on Lake Victoria, East Africa.  

PubMed

Lake Victoria, the largest tropical lake in the world, suffers from severe eutrophication and the probable extinction of up to half of its 500+ species of endemic cichlid fishes. The continuing degradation of Lake Victoria's ecological functions has serious long-term consequences for the ecosystem services it provides, and may threaten social welfare in the countries bordering its shores. Evaluation of recent ecological changes in the context of aquatic food-web alterations, catchment disturbance and natural ecosystem variability has been hampered by the scarcity of historical monitoring data. Here, we present high-resolution palaeolimnological data, which show that increases in phytoplankton production developed from the 1930s onwards, which parallels human-population growth and agricultural activity in the Lake Victoria drainage basin. Dominance of bloom-forming cyanobacteria since the late 1980s coincided with a relative decline in diatom growth, which can be attributed to the seasonal depletion of dissolved silica resulting from 50 years of enhanced diatom growth and burial. Eutrophication-induced loss of deep-water oxygen started in the early 1960s, and may have contributed to the 1980s collapse of indigenous fish stocks by eliminating suitable habitat for certain deep-water cichlids. Conservation of Lake Victoria as a functioning ecosystem is contingent upon large-scale implementation of improved land-use practices. PMID:11839198

Verschuren, Dirk; Johnson, Thomas C; Kling, Hedy J; Edgington, David N; Leavitt, Peter R; Brown, Erik T; Talbot, Michael R; Hecky, Robert E

2002-02-01

292

Focal mechanisms and the stress regime in NE and SW Tanzania, East Africa  

NASA Astrophysics Data System (ADS)

We report 12 new focal mechanisms from earthquakes in NE and SW Tanzania where the stress regime within the East African rift system is not well constrained. Focal mechanisms for events at the intersection of the Lake Tanganyika and Rukwa rifts in SW Tanzania indicate a complicated stress pattern with possible dextral strike-slip motion on some faults but oblique motion on others (either sinistral on NW striking faults or dextral on NE striking faults). Within the Rukwa rift, focal mechanisms indicate normal dip-slip motion with NE-SW opening. In NE Tanzania where the Eastern rift impinges on the margin of the Tanzania Craton, fault motions are consistent with a zone of distributed block faults and sub E-W extension. All twelve earthquakes likely nucleated within the crust.

Brazier, Richard A.; Nyblade, Andrew A.; Florentin, Juliette

2005-07-01

293

The evolutionary relationships of two families of cottoid fishes of Lake Baikal (East Siberia) as suggested by analysis of mitochondrial DNA  

Microsoft Academic Search

Fragments of mtDNA genes Cyt B, ATPase 6, and ATPase 8 of six cottoid fishes species of Lake Baikal (East Siberia) were amplified and sequenced. In addition mtDNAs of the same fish were subjected to restriction analysis. The data obtained were used to construct phylogenetic trees. The topology of the ATPase tree differs from those of the Res (restriction) and

S. Ja. Slobodyanyuk; S. V. Kirilchik; M. E. Pavlova; S. I. Belikov; A. L. Novitsky

1995-01-01

294

Origin and speciation of haplochromine fishes in East African crater lakes investigated by the analysis of their mtDNA, Mhc genes, and SINEs.  

PubMed

The Western Branch of the East African Great Rift Valley is pocketed with craters of extinct or dormant volcanoes. Many of the craters are filled with water, and the lakes are inhabited by fishes. The objective of the present study was to determine the amount and nature of genetic variation in haplochromine fishes inhabiting two of these crater lakes, Lake Lutoto and Lake Nshere, and to use this information to infer the origin and history of the two populations. To this end, sequences of mitochondrial (mt) DNA control region, exon 2 of major histocompatibility complex (Mhc) class II B genes, and short interspersed elements (SINEs) were analyzed. The results indicate that the Lake Nshere and Lake Lutoto fishes originated from different but related large founding populations derived from the Kazinga Channel, which connects Lake Edward and Lake George. Some of the genetic polymorphism that existed in the ancestral populations was lost in the populations of the two lakes. The polymorphism that has been retained has persisted for some 50000 generations (years). During this time, new mutations arose and became fixed in each of the two populations in the mtDNA, giving rise to sets of diagnostic substitutions. Each population evolved in isolation after the colonization of the lakes less than 50000 years ago. There appears to be no population structure within the crater lake fishes, and their present effective population sizes are in the order of 104 to 105 individuals. Comparisons with the endemic haplochromine species of Lake Victoria reveal interesting parallels, as well as differences, which may help to understand the nature of the speciation process. PMID:12777512

Sato, Akie; Takezaki, Naoko; Tichy, Herbert; Figueroa, Felipe; Mayer, Werner E; Klein, Jan

2003-09-01

295

Distribution of Cr, Pb, Cd, Zn, Fe and Mn in Lake Victoria sediments, East Africa  

SciTech Connect

The presence of many metals at trace or ultra-trace levels in the human environment has received increased global attention. Sediments as a sink for pollutants are widely recognized pollution sources and diagenesis and biochemical transformations within the sediment may mobilize pollutants posing a threat to a wider biological community. The natural (background) concentrations of heavy metals in lake sediments can be estimated either by analysis of surface sediments in non-polluted regions or by analysis of core samples antedating modern pollution. The distribution pattern of heavy metals in tropical freshwater systems has been little studied. The authors found increased concentrations of lead and other trace metals in Lake Victoria. Thus this study was initiated in order to further investigate the distribution patterns of lead and other metals in Lake Victoria.

Onyari, J.M.; Wandiga, S.O. (Univ. of Nairobi (Kenya))

1989-06-01

296

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

Microsoft Academic Search

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

Geoffrey Fryer

1991-01-01

297

[Area changes of emergent herbaceous wetlands in relation to water level in East Dongting Lake, China in 1989-2011].  

PubMed

Based on multi-temporal Landsat MSS/TM/ETM+ images, and by using decision tree method, this paper extracted the areas of emergent herbaceous wetlands with different water levels in 1989-2011 in the East Dongting Lake, China. The change characteristics and change trends of the emergent herbaceous wetlands areas were investigated based on the DEM data and the daily water level data from the Chenglingji Hydrological Station. The area of the emergent herbaceous wetlands was significantly affected by water level (R2 = 0.875, P < 0.001), presenting a significant linear relationship between the two. Moreover, the emergent herbaceous wetlands area decreased with increasing water level. The higher the water level, the smaller the effects of the water level on the emergent area were. The emergent area changed regularly with water level. In January-July, water level increased, and the emergent area decreased; in July-December, it was opposite. In 1989-2011, the areas of emergent herbaceous wetlands had a continual increase. The newly emergent herbaceous wetlands area was mainly transformed from mudflat. The emergent herbaceous wetlands expansion was the co-effects of the increase of the emergent herbaceous wetlands areas at different elevations, and the rapid expansion of the emergent herbaceous wetlands in low bottomland (22-25 m of Yellow Sea elevation) played the most important role in the expansion. The change of water level at different elevations was the dominant cause for the changes of emergent herbaceous wetlands areas in the East Dongting Lake in the past 20 years. PMID:24564154

Tang, Yue; Xie, Yong-Hong; Li, Feng; Chen, Xin-Sheng

2013-11-01

298

Effect of Temporally and Spatially Variable Meteorological Forcing on the Stratification Dynamics of Lake Victoria, East Africa  

NASA Astrophysics Data System (ADS)

The annual cycle of stratification of tropical lakes is driven by seasonal changes in cloud cover as it affects solar radiation and net long wave radiation and seasonal changes in wind speed and relative humidity as they affect latent heat fluxes. For large tropical lakes, latent heat fluxes and net long wave radiation vary across the lake due to lake effects but remain largely unquantified, as are the resulting spatial differences in temperature. Here we present meteorological data and surface energy budgets for six stations around Lake Victoria, East Africa, and time series temperature profiles and transect data taken during different times of day and different seasons. Seasonality is determined by the northeast and southeast monsoons and intervening rainy seasons. Winds were higher in the afternoon to the north in the northeast monsoon and higher at night and in the morning to the south during the southeast monsoon. Cloud cover was least during the monsoons. Lakewide, latent heat fluxes range from 150W m-2 to 250 W m-2 in the afternoon with larger values to the north during the northeast monsoon. Values during the morning range from 100 W m-2 to 150 W m-2 but increase to 200 W m-2 - 300 W m-2 to the south and west during the southeast monsoon. The seasonal thermocline is generated during the northeast monsoon due to the higher afternoon winds which mix heat downwards and overall net heating. Holomixis, but with warmer temperatures to the north, occurs during the southeast monsoon due to the accentuated night time cooling and net heat loss. Wind speeds are lower and the diel range of air temperature and relative humidity is higher inshore than off. Consequently, computed monthly heat losses were at least 30% higher offshore and water temperatures are cooler offshore. Scaling analyses indicate that the stratification induced by inflows of cool water to the north at the end of the southeast monsoon are wind driven and that despite the warmer waters inshore which would enable convective circulation, inshore-offshore exchanges are mediated by wind and internal waves.

MacIntyre, S.; Romero, J. R.

2011-12-01

299

The consortium of the sponge Lubomirskia baicalensis in Lake Baikal, East Siberia  

Microsoft Academic Search

The spatial distribution of the fauna associated with a branched sponge, Lubomirskia baicalensis, endemic of Lake Baikal has been quantitatively studied. The biomass and numbers of three amphipod species which inhabit\\u000a the sponge correlate (linearly or non-linearly) with the weight of the sponge.

R. M. Kamaltynov; V. I. Chernykh; Z. V. Slugina; E. B. Karabanov

1993-01-01

300

Indian Ocean climate event brings floods to East Africa's lakes and the Sudd marsh  

Microsoft Academic Search

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

Charon Birkett; Ragu Murtugudde; Tony Allan

1999-01-01

301

Microcrystalline sphalerite in resin globules suspended in Lake Kivu, East Africa  

USGS Publications Warehouse

The origin and chemical nature of micron-sized spheres found as suspended particles in Lake Kivu are examined. It can be shown that the hollow spheres, with a wall thickness of 500 A??, consist of a complex polymeric resinous material which has little functionality, except for hydroxyl groups. The spheres arise in the process of degassing of water samples at depth. Tiny gas bubbles, about 1 micron in size, act as scavengers of dissolved resinous material. The newly created resinous membrane promotes the selective coordination of zinc dissolved in the water column. In the prevailing H2S regime, formation of sphalerite crystals in induced. The size range of the crystals, 5 to 50 A??, corresponds to 1 to 10 unit cells and suggests that the resinous membrane also acts as a template in sphalerite growth processes. The sources of the zinc and dissolved gases (CO2, CH4, H2S) are hydrothermal springs seeping from the lake bottom into the basin. Water discharge is substantial; about 100 years are required to fill the lake to its present level (ca. 550 km3 water). The average Kivu water contains 2 ppm zinc. Thus, 1 million tons of zinc are contained in Lake Kivu in the form of sphalerite. ?? 1972 Springer-Verlag.

Degens, E. T.; Okada, H.; Honjo, S.; Hathaway, J. C.

1972-01-01

302

Phylogeny of a rapidly evolving clade: The cichlid fishes of Lake Malawi, East Africa  

Microsoft Academic Search

ABSTRACT Lake Malawi contains a f lock of >500 spe- cies of cichlid fish that have evolved from a common ancestor within the last million years. The rapid diversification of this group has been attributed to morphological adaptation and to sexual selection, but the relative timing and importance of these mechanisms is not known. A phylogeny of the group would

R. C. Albertson; J. A. M Arkert; P. D. D Anley; T. D. Kocher

1999-01-01

303

Holistic view to integrated climate change assessment and extreme weather adaptation in the Lake Victoria Basin East Africa  

NASA Astrophysics Data System (ADS)

Extreme weather events have been the leading cause of disasters and damage all over the world.The primary ingredient to these disasters especially floods is rainfall which over the years, despite advances in modeling, computing power and use of new data and technologies, has proven to be difficult to predict. Also, recent climate projections showed a pattern consistent with increase in the intensity and frequency of extreme events in the East African region.We propose a holistic integrated approach to climate change assessment and extreme event adaptation through coupling of analysis techniques, tools and data. The Lake Victoria Basin (LVB) in East Africa supports over three million livelihoods and is a valuable resource to five East African countries as a source of water and means of transport. However, with a Mesoscale weather regime driven by land and lake dynamics,extreme Mesoscale events have been prevalent and the region has been on the receiving end during anomalously wet years in the region. This has resulted in loss of lives, displacements, and food insecurity. In the LVB, the effects of climate change are increasingly being recognized as a significant contributor to poverty, by its linkage to agriculture, food security and water resources. Of particular importance are the likely impacts of climate change in frequency and intensity of extreme events. To tackle this aspect, this study adopted an integrated regional, mesoscale and basin scale approach to climate change assessment. We investigated the projected changes in mean climate over East Africa, diagnosed the signals of climate change in the atmosphere, and transferred this understanding to mesoscale and basin scale. Changes in rainfall were analyzed and similar to the IPCC AR4 report; the selected three General Circulation Models (GCMs) project a wetter East Africa with intermittent dry periods in June-August. Extreme events in the region are projected to increase; with the number of wet days exceeding the 90% percentile of 1981-2000 likely to increase by 20-40% in the whole region. We also focused on short-term weather forecasting as a step towards adapting to a changing climate. This involved dynamic downscaling of global weather forecasts to high resolution with a special focus on extreme events. By utilizing complex model dynamics, the system was able to reproduce the Mesoscale dynamics well, simulated the land/lake breeze and diurnal pattern but was inadequate in some aspects. The quantitative prediction of rainfall was inaccurate with overestimation and misplacement but with reasonable occurrence. To address these shortcomings we investigated the value added by assimilating Advanced Microwave Scanning Radiometer (AMSR-E) brightness temperature during the event. By assimilating 23GHz (sensitive to water) and 89GHz (sensitive to cloud) frequency brightness temperature; the predictability of an extreme rain weather event was investigated. The assimilation through a Cloud Microphysics Data Assimilation (CMDAS) into the weather prediction model considerably improved the spatial distribution of this event.

Mutua, F.; Koike, T.

2013-12-01

304

Temperature and Aridity in Tropical East Africa Over the Past 200,000 Years: Reconstructions from the Lake Malawi Drill Core  

NASA Astrophysics Data System (ADS)

Tropical heating is the driving force behind global atmospheric circulation and thus is an essential component to our understanding of climate dynamics through time. We present a record of temperature and aridity from Lake Malawi, the largest and southern-most of the large East African Rift lakes, which extends from 9 to 14 °S. The temperature record is based on TEX86 (TetraEther indeX of tetraethers with 86 carbon atoms) analyses on a drill core from the central basin of the lake, which provides a new record from 39 to 140 m burial depth, extending to approximately 200kyr BP. (This record will extend to the core bottom at 378 m below lake floor when completed.) Average lake surface temperature during the past 200kyr was ~25.5°C, with temperature values ranging from 22 to 29°C. When compared to earlier studies, the range of temperatures over the most recent glacial-interglacial transition (MIS 2 to 1) exceeds that of any time earlier in this ~ 200kyr record. No consistent relationship exists between temperature and aridity as indicated by Ca (calcite) abundance in the sediments. Cyclic behavior on orbital time scales is apparent in both temperature and Ca records, however not at the same frequencies. Superimposed on the orbital scale variability are higher frequency, millennial shifts of 2 - 3°C, which undoubtedly impacted ecosystem dynamics and hominin migration on the East African landscape, at least in the vicinity of Lake Malawi, over the past 200,000 years. The regional extent of this climate history cannot be ascertained until comparable records are recovered through drilling the other great lakes of the East African Rift Valley.

Abbott, A. N.; Johnson, T. C.; Berke, M. A.; Werne, J. P.; Schouten, S.; Sinninghe Damste, J. S.; Brown, E. T.

2010-12-01

305

Hydrology of the Wolf Branch sinkhole basin, Lake County, east-central Florida  

USGS Publications Warehouse

A 4-year study of the hydrology of the Wolf Branch sinkhole basin in Lake County, Florida, was conducted from 1991-95 by the U.S. Geological Survey to provide information about the hydrologic characteristics of the drainage basin in the vicinity of Wolf Sink. Wolf Branch drains a 4.94 square mile area and directly recharges the Upper Floridan aquifer through Wolf Sink. Because of the direct connection of the sinkhole with the aquifer, a contaminant spill in the basin could pose a threat to the aquifer. The Wolf Branch drainage basin varies in hydrologic characteristics from its headwaters to its terminus at Wolf Sink. Ground- water seepage provides baseflow to the stream north of Wolf Branch Road, but the stream south of State Road 46 is intermittent and the stream can remain dry for months. A single culvert under a railroad crossing conducts flow from wetlands just south of State Road 46 to a well-defined channel which leads to Wolf Sink. The basin morphology is characterized by karst terrain, with many closed depressions which can provide intermittent surface-water storage. Wetlands in the lower third of the basin (south of State Road 46) also provide surface water storage. The presence of numerous water-control structures (impoundments, canals, and culverts), and the surface-water storage capacity throughout the basin affects the flow characteristics of Wolf Branch. Streamflow records for two stations (one above and one below major wetlands in the basin) indicate the flow about State Road 46 is characterized by rapid runoff and continuous baseflow, whereas below State Road 46, peak discharges are much lower but of longer duration than at the upstream station. Rainfall, discharge, ground-water level, and surface-water level data were collected at selected sites in the basin. Hydrologic conditions during the study ranged from long dry periods when there was no inflow to Wolf Sink, to very wet periods, as when nearly 7 inches of rain fell in a 2-day period in November 1994, following an extended wet season. A comparison to long-term rainfall record (40 years) indicates that this range in hydrologic conditions during the 4-year study is representative of the range of conditions expected during a much longer time period. Two dye-trace studies conducted during the study indicated no direct connections between the sink and local wells. The path of a constituent entering the aquifer through Wolf Sink generally would be to the east, following the gradient of the regional ground-water flow system. The conductance of Wolf Sink (the rate at which the sink conducts water to the underlying aquifer) was estimated from streamflow data, ground-water levels, and water levels in Wolf Sink. The range of hydrologic conditions during the study provided a basis for the determination of a representative conductance value. The regression of streamflow as a function of head difference between the sink water level and the potentiometric surface at an observation well (an approximation of the potentiometric level beneath Wolf Sink) resulted in a significant relation r2=0.91, mean square error = 1.60 cubic feet per second); and the slope of the regression line, representing sink conductance, was 1.48 cubic feet per second per foot of head difference. Flow and storm-volume frequency curves for selected time periods (1-day, 7-days, 14-days, 21-days, and 30-days) were generated based on streamflow data from January 10, 1992, to September 30, 1995. These curves indicate that, based on the available record, the volume of water that would have to be stored (in the event that streamflow had to be diverted from Wolf Sink) during a 30-day period would be equal to or less than about 11 acre-fee 30 percent of the time and 161 acre-feet 80 percent of the time. The maximum volume that would be generated during a 30-day period, based on this study, would be about 570 acre-feet.

Schiffer, D. M.

1996-01-01

306

Mass movement deposits in the 3.6 Ma sediment record of Lake El'gygytgyn, Far East Russian Arctic  

NASA Astrophysics Data System (ADS)

This paper focuses on the characterization and genesis of mass movement deposits (MMDs) in the Quaternary and Pliocene sediments of Lake El'gygytgyn, Far East Russian Arctic. Three partly overlapping holes were drilled into the 320 m long sediment record at International Continental Scientific Drilling Program (ICDP) Site 5011-1 in the lake basin, recovering the Quaternary almost completely, and the Pliocene down to 3.6 Ma with 52% recovery. Mass movement deposits were investigated in all three cores, based on macroscopical core descriptions, radiographic images, high-resolution magnetic susceptibility and gamma-ray density. Five different types of MMDs were identified: turbidites, grain-flow deposits, debrites, slumps and slides. These are formed by transitional mass movement processes, and thus can be co-generic. An initial slope failure is thought to transform into a debris flow that deforms frontal sediments, partly disintegrates and dilutes into a turbidity flow. Turbidites are by far the most frequent MMD type in the lake center. They occur throughout the record in all pelagic sedimentary facies, but they are thinner in facies formed during cold climate conditions. All other MMDs, by contrast, incise exclusively the pelagic facies deposited during warm climates. In the 123 m thick Quaternary composite sediment record 230 mass movement events are identified, comprising 33% of the sediment length. Turbidites contribute 93% of the number of Quaternary MMDs, but only 35% of their thickness. In the Pliocene sediments between 123 and 320 m, 181 additional mass movement deposits are identified, which constitute ~33% of the recovered sediments. The mean recurrence interval for MMDs is 11 and 5 ka in the Quaternary and Pliocene, respectively.

Sauerbrey, M. A.; Juschus, O.; Gebhardt, A. C.; Wennrich, V.; Nowaczyk, N. R.; Melles, M.

2013-08-01

307

Lake  

ERIC Educational Resources Information Center

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

Wien, Carol Anne

2008-01-01

308

Phylogenetic diversity of T4-like bacteriophages in Lake Baikal, East Siberia.  

PubMed

Among the tailed phages, the myoviruses, those with contractile tails, are widespread and diverse. An important component of the Myoviridae family is the genus 'T4-like viruses'. The present study was aimed at elucidating the molecular diversity of T4-type bacteriophages in Lake Baikal by partial sequencing of g23 genes of T4-type bacteriophages. Our study revealed that the g23 gene sequences investigated were highly diverse and different from those of T4-like bacteriophages and from g23 clones obtained from different environments. Phylogenetic analysis showed that all g23 fragments from Lake Baikal, except for the one sequence, were more closely related to marine T4 cyanophages and to previously described subgroups of uncultured T4 phages from marine and rice field environments. PMID:20579103

Butina, Tatyana Vladimirovna; Belykh, Olga I; Maksimenko, Svetlana Yu; Belikov, Sergey I

2010-08-01

309

The Shrimp Caridina nilotica in Lake Victoria (East Africa), Before and After the Nile Perch Increase  

Microsoft Academic Search

The shrimp Caridina nilotica is a major prey of the introduced Nile perch in Lake Victoria. In spite of heavy predation, the density of shrimps increased\\u000a after the Nile perch boom and the concomitant disappearance of the haplochromine cichlids. In the same period, the mean size\\u000a of gravid shrimps and the size at first maturity declined. This seems to indicate

Frans Witte; Jan H. Wanink

2006-01-01

310

Recent changes in the level of Lake Naivasha, Kenya, as an indicator of equatorial westerlies over East Africa  

Microsoft Academic Search

A previously unpublished record of lake levels from Lake Naivasha, Kenya from 1880 to 1976 has been analysed and shows little similarity to the level record from nearby Lake Victoria. Level changes from year to year of the two lakes show no significant correlation (at 5%) and spectral analysis of the two records shows no common significant peaks. Both lakes

C. E. Vincent; T. D. Davies; A. K. C. Beresford

1979-01-01

311

Gravity Data from Dry Lake and Delamar Valleys, east-central Nevada  

USGS Publications Warehouse

Cenozoic basins in eastern Nevada and western Utah constitute major ground-water recharge areas in the eastern part of the Great Basin, and our continuing studies are intended to characterize the geologic framework of the region. Prior to these investigations, regional gravity coverage was variable over the region, adequate in some areas and very sparse in others. The current study in Nevada provides additional high-resolution gravity along transects in Dry Lake and Delamar Valleys to supplement data we established previously in Cave and Muleshoe Valleys. We combine all previously available gravity data and calculate an up-to-date isostatic residual gravity map of the study area. Major density contrasts are identified, indicating zones where Cenozoic tectonic activity could have been accommodated. A gravity inversion method is used to calculate depths to pre-Cenozoic basement rock and to estimate maximum alluvial/volcanic fill in the valleys. Average depths of basin fill in the deeper parts of Cave, Muleshoe, Dry Lake, and Delamar Valleys are approximately 4 km, 2 km, 5 km, and 3 km, respectively.

Mankinen, Edward A.; Chuchel, Bruce A.; Moring, Barry C.

2008-01-01

312

Recent land?cover\\/use change associated with land degradation in the Lake Baringo catchment, Kenya, East Africa: evidence from Landsat TM and ETM+  

Microsoft Academic Search

Many parts of East Africa are experiencing dramatic changes in land?cover\\/use at a variety of spatial and temporal scales, due to both climatic variability and human activities. Information about such changes is often required for planning, management, and conservation of natural resources. Several methods for land cover\\/change detection using Landsat TM\\/ETM+ imagery were employed for Lake Baringo catchment in Kenya,

L. M. Kiage; N. D. Walker; N. Lam; O. K. Huh

2007-01-01

313

The bounty of minor lakes: the role of small satellite water bodies in evolution and conservation of fishes in the Lake Victoria Region, East Africa  

Microsoft Academic Search

The Lake Victoria Region (LVR) encompasses the large lakes Victoria, Kyoga, Edward, George and Kivu, as well as scores of small satellite lakes within the parent catchments. Taken as a whole, the LVR originally harbored a unique fish fauna that included in excess of 600 endemic species of cichlid fishes. As a result of human influence, including a commercial fishery

Wilson W. Mwanja; Audrey S. Armoudlian; Silvester B. Wandera; Les Kaufman; Lizhao Wu; Gregory C. Booton; Paul A. Fuerst

2001-01-01

314

East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins  

PubMed Central

The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is known mainly from isolated outcrops and distant marine sediment cores. Here we present results from new scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from the continent itself. Our record shows periods of severe aridity between 135 and 75 thousand years (kyr) ago, when the lake's water volume was reduced by at least 95%. Surprisingly, these intervals of pronounced tropical African aridity in the early late-Pleistocene were much more severe than the Last Glacial Maximum (LGM), the period previously recognized as one of the most arid of the Quaternary. From these cores and from records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa), we document a major rise in water levels and a shift to more humid conditions over much of tropical Africa after ?70 kyr ago. This transition to wetter, more stable conditions coincides with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa, but our records provide evidence for dramatically wetter conditions after 70 kyr ago. Such climate change may have stimulated the expansion and migrations of early modern human populations.

Scholz, Christopher A.; Johnson, Thomas C.; Cohen, Andrew S.; King, John W.; Peck, John A.; Overpeck, Jonathan T.; Talbot, Michael R.; Brown, Erik T.; Kalindekafe, Leonard; Amoako, Philip Y. O.; Lyons, Robert P.; Shanahan, Timothy M.; Castaneda, Isla S.; Heil, Clifford W.; Forman, Steven L.; McHargue, Lanny R.; Beuning, Kristina R.; Gomez, Jeanette; Pierson, James

2007-01-01

315

Dietzia natronolimnaios sp. nov., a new member of the genus Dietzia isolated from an east African soda lake.  

PubMed

Two novel alkaliphilic aerobic organotrophic bacteria have been isolated from a moderately saline and alkaline East African soda lake. The new isolates grow at pH values between 6 and 10, with a pH optimum for growth of 9.0, and at a salt concentration between 0% and 10% (w/v). Phylogenetic analysis based on 16S rDNA sequence shows that these isolates are very closely related (99.6% similarity) and are members of the monospecific genus Dietzia (98.8% and 98.7% similarity). DNA/DNA hybridization revealed a relatedness of 83% between the two isolates, but only 8% between them and the type strain Dietzia maris. The G + C content as measured by thermal denaturation is 66.1 mol%. Phenotypic comparisons between D. maris and one isolate showed that they share very similar morphological and chemotaxonomic properties, but differ significantly in carbon source utilization profiles and halotolerance in alkaline medium. We propose a second species of this genus which we name Dietzia natronolimnaios (type strain 15LN1 = CBS 107.95). PMID:9783184

Duckworth, A W; Grant, S; Grant, W D; Jones, B E; Meijer, D

1998-08-01

316

Vegetation responses to interglacial warming in the Arctic: examples from Lake El'gygytgyn, Far East Russian Arctic  

NASA Astrophysics Data System (ADS)

Preliminary analyses of Lake El'gygytgyn sediment indicate a wide range of ecosystem responses to warmer than present climates. While palynological work describing all interglacial vegetation is ongoing, sufficient data exist to compare recent warm events (the postglacial thermal maximum, PGTM, and marine isotope stage, MIS5) with "super" interglaciations (MIS11, MIS31). Palynological assemblages associated with these climatic optima suggest two types of vegetation responses: one dominated by deciduous taxa (PGTM, MIS5) and the second by evergreen conifers (MIS11, MIS31). MIS11 forests show a similarity to modern Picea-Larix-Betula-Alnus forests of Siberia. While dark coniferous forest also characterizes MIS31, the pollen taxa show an affinity to the boreal forest of the lower Amur valley (southern Russian Far East). Despite vegetation differences during these thermal maxima, all glacial-interglacial transitions are alike, being dominated by deciduous woody taxa. Initially Betula shrub tundra established and was replaced by tundra with tree-sized shrubs (PGTM), Betula woodland (MIS5), or Betula-Larix (MIS11, MIS31) forest. The consistent occurrence of deciduous forest and/or high shrub tundra before the incidence of maximum warmth underscores the importance of this biome for modeling efforts. The El'gygytgyn data also suggest a possible elimination or massive reduction of Arctic plant communities under extreme warm-earth scenarios.

Lozhkin, A. V.; Anderson, P. M.

2013-06-01

317

Nesterenkonia lacusekhoensis sp. nov., isolated from hypersaline Ekho Lake, East Antarctica, and emended description of the genus Nesterenkonia.  

PubMed

An aerobic and heterotrophic isolate, designated IFAM EL-30T, was obtained from hypersaline Ekho Lake (Vestfold Hills, East Antarctica). The isolate consisted of Gram-positive cocci or short rods which occasionally exhibited branching. The organism was moderately halotolerant, required thiamin.HCI and was stimulated by biotin and nicotinic acid. It grew well with glucose, acetate, pyruvate, succinate, malate or glutamate, and hydrolysed DNA but not gelatin, starch or Tween 80. Nitrate was aerobically reduced to nitrite. Chemical analysis revealed diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine and an unidentified glycolipid as the major polar lipids. The cellular fatty acids were predominantly of the anteiso and iso methyl-branched types, and the major menaquinone6 were MK-7 and MK-8. The peptidoglycan type was A4alpha, L-Lys-L-Glu. The DNA base ratio was 66.1 mol% G+C. Comparisons of 16S rRNA gene sequences showed that the unidentified organism was phylogenetically closely related to Nesterenkonia halobia, although a sequence divergence value of > 3% demonstrated that the organism represents a different species. On the basis of phenotypic and genotypic evidence, it is proposed that the unknown bacterium be designated as a new species of the genus Nesterenkonia, namely Nesterenkonia lacusekhoensis sp. nov., the type strain being IFAM EL-30T (= DSM 12544T = CIP 107030T). An emended description of the genus Nesterenkonia is given. PMID:12148619

Collins, Matthew D; Lawson, Paul A; Labrenz, Matthias; Tindall, Brian J; Weiss, N; Hirsch, Peter

2002-07-01

318

Reconstruction of climate and vegetation changes of Lake Bayanchagan (Inner Mongolia): Holocene variability of the East Asian monsoon  

NASA Astrophysics Data System (ADS)

A high-resolution pollen and Pediastrum record, spanning 12,500 yr, is presented for Lake Bayanchagan (115.21°E, 41.65°N, and 1355 m a.s.l.), southern Inner Mongolia. Individual pollen taxa (PT-MAT) and the PFT affinity scores (PFT-MAT) were used for quantitative climatic reconstruction from pollen and algal data. Both techniques indicate that a cold and dry climate, similar to that of today, prevailed before 10,500 cal yr B.P. The wettest climate occurred between ˜10,500 and 6500 cal yr B.P., at which time annual precipitation was up to 30-60% higher than today. The early Holocene increases in temperature and precipitation occurred simultaneously, but mid-Holocene cooling started at approximately 8000 cal yr B.P., 1500 yr earlier than the drying. Vegetation reconstruction was based on the objective assignment of pollen taxa to the plant functional type. The results suggest that this region was dominated by steppe vegetation throughout the Holocene, except for the period ˜9200 to ˜6700 cal yr B.P., when forest patches were relatively common. Inner Mongolia is situated at the limit of the present East Asian monsoon and patterns of vegetation and climate changes in that region during the Holocene probably reflect fluctuations in the monsoon's response to solar insolation variations. The early to middle Holocene monsoon undoubtedly extended to more northern latitudes than at present.

Jiang, Wenying; Guo, Zhengtang; Sun, Xiangjun; Wu, Haibin; Chu, Guoqiang; Yuan, Baoyin; Hatté, Chritine; Guiot, Jöel

2006-05-01

319

Biogeochemistry of a large, meromictic tropical lake (Lake Kivu, East Africa): insights from a stable isotope study covering an annual cycle  

NASA Astrophysics Data System (ADS)

Lake Kivu (East Africa) is a large (2370 km2) and deep (maximum depth of 485 m) meromictic lake. Its vertical structure consists of an oxic and nutrient-poor mixed layer down to 70 m maximum, and a permanently anoxic monimolimnion rich in dissolved gases (methane and carbon dioxide) and nutrients. Seasonal variation of the vertical position of the oxic-anoxic interface is driven by contrasting air humidity and wind speed regimes between rainy (October-May) and dry (June-September) seasons. The latter is characterized by a deepening of the oxic zone, and an increased input of dissolved gases and inorganic nutrients. The mean annual photic depth is 18 m, but water transparency slightly decreases during the dry season. In this study, we present a comprehensive data set covering a full annual cycle at a fortnightly resolution, which combine hydrochemical data, ?13C and ?15N measurements of particulate organic carbon and nitrogen (POC, PN) and zooplankton, ?13C of dissolved organic and inorganic carbon (DOC, DIC), nutrients and gases (CH4) concentrations, phytoplankton biomass and composition. In the euphotic zone, phytoplankton biomass was constant during the rainy season, but doubled during the dry season. In contrast, ?13C-DIC increased linearly with time during the rainy season, deviating from the values expected at isotopic equilibrium with the atmosphere, then suddenly decreased in the dry season due to the vertical mixing with 13C-depleted DIC. Results of mass-balance calculations indicate that the ?13C-DIC increase reflects the net autotrophic status of the mixed layer. Irrespective of the season, the ?13C-POC signatures were constant from the surface to the oxic-anoxic interface, then showed a local and abrupt excursion to values as low as -40o reflecting the incorporation of a 13C-depleted source in the POC. While the large pool of DIC is the main carbon source for POC in surface waters, CH4 contributes significantly to C fixation at the oxic-anoxic interface all year round. The ?13C signature of the DOC pool shows very little variation in the mixolimnion and thus appears to be uncoupled from the POC pool, suggesting that old and refractory compounds constitute the major part of the DOC pool. Also the more labile and freshly produced DOC that reflects the ?13C signature of the POC, is rapidly mineralized. Finally, we noticed a shift toward higher values in the ?15N-PN during the dry season (from 0.5o to 4.0) and ?15N-PN was significantly related to the proportion of cyanobacteria in the euphotic zone. Hence the variation of ?15N-PN in surface waters could either reflects a change in the dominant phytoplankton taxa or in the biogeochemical processes controlling the upward nitrate and ammonium fluxes. Zooplankton ?15N signatures mirrored the seasonal changes in ?15N-PN and were significantly correlated to phytoplankton biomass, highlighting their dependence on autochtonous sources of organic matter in this large lake.

Morana, Cedric; Darchambeau, François; Muvundja, Fabrice; Roland, Fleur; Kelemen, Zita; Commarieu, Marc-Vincent; Leporcq, Bruno; Alunga, Georges; Masilya, Pascal; Descy, Jean-Pierre; Borges, Alberto V.; Bouillon, Steven

2014-05-01

320

The subglacial Lake Vostok (East Antarctica) surface snow is Earth-bound DNA (and dust)-free  

NASA Astrophysics Data System (ADS)

The objective was to assess the microbial cell abundance in the surface snow in Central East Antarctica and the fate of microbial genomic DNA during summer short-time exposure to surface climatic (and radiation) conditions at Vostok using flow cytometry and DNA-based methods. The surface snow (until 4m deep) was collected as clean as possible in the vicinity of the Vostok station (3 sites - courtesy of A Ekaykin and ASC Lebedev Physical Iinstitute RAS) and towards the Progress station (4 more sites with one just 29km from the coast - courtesy of A Ekaykin and S Popov) in specially decontaminated plastic crates or containers of various volumes (up to 75 kg of snow). All subsequent snow treatment manipulations (melting, concentrating, genomic DNA extraction, primary PCR set up) were performed in clean room laboratory facilities (LGGE, UJF-CNRS, Grenoble, France). Cell concentrations were determined on meltwater aliquots prepared under clean room conditions using flow cytofluorometry (Biostation, Roscoff, France). The highly concentrated meltwater (until 10000 times down) was used to extract gDNA which were subjected to bacterial 16S rRNA genes amplification in PCR and sequencing. The gDNA of a complex mesophile microbial community for exposure trials were also prepared and put onto a filter under strict clean room conditions. The filters were got exposed open to solar radiation and surface temperature at Vostok during January for various time duration periods (from 25 to 1 day). As a result no microbial cells were confidently detected in surface snow samples differed by sampling sites and people asked to collect as well. Complementary the mineral dust particle abundance did not exceed 16 mkg per liter with the particle size mode about 2.5 mkm as shown using Coulter counter. Preliminary amongst the microparticles no unusual findings (e.g. spherules of cosmic origin) were observed by shape and element composition using electron scanning microscopy. The gDNA studies came up with only contaminant bacterial phylotypes (mostly of human source). The bioexposure trials showed that even in one day of open exposure the gDNA of rather complex microbial community composition was fatally damaged in terms of long-, mid-range and short-size amplicon generation in PCR. All this testify for very harsh conditions for life to survive the climate conditions of Central East Antarctica which could be considered as a presentday 'zone mortale' or 'polar desert' for known Earthbound microbial life forms. In addition this means that no life seeds are expected to reach subglacial lakes and water reservoirs and establish indigenous lake microbiota during their transit through the thick and aged Antarctic ice sheet upon its bottom melting. In general the subglacial Lake Vostok surface (ice sheet as well) environ represents the unique test area (sterile - in fact Earth-bound DNA-free and clean - in fact Earth-bound dust-free) for advancing extraterrestrial (ET) life detection technologies and searching for ET life indices in AMMs and IDPs.

Bulat, S.; Marie, D.; Bulat, E.; Alekhina, I.; Petit, J.-R.

2012-09-01

321

PCDD/Fs and dioxin-like PCBs in surface sediments from Lake Victoria, East Africa.  

PubMed

Surface sediments (<60 cm) from the Napoleon Gulf and Thurston Bay on the northern shore of Lake Victoria were analyzed for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs). Fifteen PCDD/Fs and eleven dl-PCBs were found in 75.5% of the samples. The maximum concentrations of PCDD/Fs and dl-PCBs were 44.1 and 136 pg g(-1) dry weight (dw), respectively. Octachlorodibenzo-p-dioxin was the predominant PCDD/F congener at the Napoleon Gulf and Thurston Bay area. Regarding the dl-PCBs, a variation in levels was observed between the mono-ortho PCBs and non-ortho PCBs, with the former having higher levels than the latter. The PCDD/F and dl-PCB levels, in the sediments of Napoleon Gulf, which is near urban centers and industrial areas were markedly higher (? ? 0.05) than those from the Thurston Bay, which is offshore, suggesting that human activities could be sources of the pollutants to the surrounding water resources. World Health Organization-toxic equivalency quotients (WHO-TEQs) lay in the range of 0.07-5.53 pg g(-1) dw for PCDD/Fs and 0.01-0.23 pg g(-1) dw for dl-PCBs. 23.1% of samples from the Napoleon Gulf had their results above the set WHOPCDD/Fs-TEQ value. PMID:23567173

Ssebugere, Patrick; Kiremire, Bernard T; Henkelmann, Bernhard; Bernhöft, Silke; Wasswa, John; Kasozi, Gabriel N; Schramm, Karl-Werner

2013-06-01

322

PCDD/Fs and dioxin-like PCBs in fish species from Lake Victoria, East Africa.  

PubMed

Two commercially important fish species, Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus) belonging to different trophic levels were collected from the Napoleon Gulf and Thurston Bay in Lake Victoria. Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) were extracted from the fish muscles and livers using the (13)C isotope dilution method, followed by multiple column chromatography clean-up. Analysis was achieved by a high resolution gas chromatography coupled with a high resolution mass spectrometer. The concentrations of analytes ranged from 0.07 to 0.59pgg(-1) fresh weight (fw) and 0.3-19.0pgg(-1) in L. niloticus and 0.06-0.18 and 0.2-15.7pgg(-1) in O. niloticus, for ?PCDD/Fs and ?dl-PCBs, respectively. Differences in congener concentrations were observed between the two fish species and study sites, and this was attributed to differences in feeding habits and trophic levels. World Health Organization-toxic equivalents (WHO-TEQs) were in the range 0.01-0.16pgTEQg(-1) for the PCDD/Fs and 0.001-0.74pgTEQg(-1) for the dl-PCBs. The TEQ values in the present study were lower compared to those of most fish samples reported in literature and were within permissible levels recommended by the European Union, implying that the fish was fit for human consumption. PMID:23648330

Ssebugere, Patrick; Kiremire, Bernard T; Henkelmann, Bernhard; Bernhöft, Silke; Kasozi, Gabriel N; Wasswa, John; Schramm, Karl-Werner

2013-07-01

323

Multiple episodic evolution events in V1R receptor genes of East-African cichlids.  

PubMed

Fish use olfaction to detect a variety of nonvolatile chemical signals, and thus, this sense is key to survival and communication. However, the contribution of the olfactory sense to social-especially reproductive-interactions in cichlids is still controversial. To obtain insights into this issue, we investigated the genes encoding V1Rs-possible candidates for reproductive pheromone receptors-among East-African cichlids. Interestingly, we found an excess of nonsynonymous over synonymous substitutions in four of six V1R genes in multiple cichlid lineages. First, we found that highly dimorphic V1R2 allele groups were shared among the cichlids inhabiting all East-African Great Lakes emerged through the episodic accumulation of the nonsynonymous substitutions prior to the radiation of the Lake Tanganyika species flock. We further detected such episodic events in V1R1 of the tribe Tropheini, and in V1R3 and V1R6 of the tribe Trematocarini. The excess of nonsynonymous substitutions in these examples were indicated as dN/dS > 1, which were all statistically significant by Fisher's exact test. Furthermore, we speculate that the amino acid changes in these episodic events are likely functional switch because they occurred in the putative ligand-binding pocket. Our finding of the occurrence of multiple episodic events and the unexpected gene diversity in one unique gene family is suggestive of the contribution of the V1R to the species diversification and the social interaction in cichlids. PMID:24803573

Nikaido, Masato; Ota, Tomoki; Hirata, Tadashi; Suzuki, Hikoyu; Satta, Yoko; Aibara, Mitsuto; Mzighani, Semvua I; Sturmbauer, Christian; Hagino-Yamagishi, Kimiko; Okada, Norihiro

2014-05-01

324

Multiple Episodic Evolution Events in V1R Receptor Genes of East-African Cichlids  

PubMed Central

Fish use olfaction to detect a variety of nonvolatile chemical signals, and thus, this sense is key to survival and communication. However, the contribution of the olfactory sense to social—especially reproductive—interactions in cichlids is still controversial. To obtain insights into this issue, we investigated the genes encoding V1Rs—possible candidates for reproductive pheromone receptors—among East-African cichlids. Interestingly, we found an excess of nonsynonymous over synonymous substitutions in four of six V1R genes in multiple cichlid lineages. First, we found that highly dimorphic V1R2 allele groups were shared among the cichlids inhabiting all East-African Great Lakes emerged through the episodic accumulation of the nonsynonymous substitutions prior to the radiation of the Lake Tanganyika species flock. We further detected such episodic events in V1R1 of the tribe Tropheini, and in V1R3 and V1R6 of the tribe Trematocarini. The excess of nonsynonymous substitutions in these examples were indicated as dN/dS > 1, which were all statistically significant by Fisher’s exact test. Furthermore, we speculate that the amino acid changes in these episodic events are likely functional switch because they occurred in the putative ligand-binding pocket. Our finding of the occurrence of multiple episodic events and the unexpected gene diversity in one unique gene family is suggestive of the contribution of the V1R to the species diversification and the social interaction in cichlids.

Nikaido, Masato; Ota, Tomoki; Hirata, Tadashi; Suzuki, Hikoyu; Satta, Yoko; Aibara, Mitsuto; Mzighani, Semvua I.; Sturmbauer, Christian; Hagino-Yamagishi, Kimiko; Okada, Norihiro

2014-01-01

325

Sources of core and intact branched tetraether membrane lipids in the lacustrine environment: Anatomy of Lake Challa and its catchment, equatorial East Africa  

NASA Astrophysics Data System (ADS)

The MBT/CBT palaeotemperature proxy uses the distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs), membrane lipids that are supposed to derive from soil bacteria, to reconstruct mean annual air temperature (MAAT). Applied successfully in coastal marine sediments, its extension to lake-sediment records with potentially high time resolution would greatly expand its utility. Over the last years, however, studies have indicated the presence of additional sources of brGDGTs within lake systems. To constrain the factors influencing the MBT/CBT palaeotemperature proxy in lakes, detailed investigation of brGDGT fluxes in a modern lake system is necessary to identify their potential sources. This study concentrates on Lake Challa, a permanently stratified crater lake in equatorial East Africa with limited catchment area. An almost 3-year time series of approximately monthly samples of settling particles, supplemented with a depth profile of suspended particulate matter (SPM) and sets of profundal surface-sediment and catchment soil samples, were analysed for both the 'living' intact polar lipids (IPLs) and 'fossil' core lipids (CLs) of GDGTs. We found that brGDGTs are produced in oxic, suboxic and anoxic zones of the water column, and in substantial amounts compared to influxes from catchment soils. Additional in situ production within the lake sediments is most probable, but cannot be definitely confirmed at this time. These lacustrine brGDGTs display a different response to temperature variation than soil-derived brGDGTs, signifying either a different physiological adaptation to changing conditions within the water column and/or a different composition of the respective bacterial communities. Using this specific relationship with temperature, a local calibration based on brGDGT distributions in SPM generates relatively accurate water temperature estimates from settling particles but fails for surface sediments.

Buckles, Laura K.; Weijers, Johan W. H.; Verschuren, Dirk; Sinninghe Damsté, Jaap S.

2014-09-01

326

Temporal rainfall variability in the Lake Victoria Basin in East Africa during the twentieth century  

NASA Astrophysics Data System (ADS)

Water resources systems are designed and operated on assumption of stationary hydrology. Existence of trends and other changes in the data invalidates this assumption, and detection of the changes in hydrological time series should help us revise the approaches used in assessing, designing and operating our systems. In addition, trend and step change studies help us understand the impact of man’s activities (e.g. urbanisation, deforestation, dam construction, agricultural activities, etc.) on the hydrological cycle. Trends and step changes in the seasonal and annual total rainfall for 20 stations in the Lake Victoria basin were analysed. The seasonal rainfall for any station in a given year was defined in two ways: (1) fixed time period where the rainy seasons were taken as occurring from March-May (long rains) and from October-December (short rains); and (2) variable periods where the rainy seasons were taken as the three consecutive months with maximum total rainfall covering the period of January-June (long rains) and July-December (short rains), to take into account the fact that the onset of rainy seasons within the basin varies from year to year and from one station to the next. For each station, sub datasets were derived covering different periods (all available data at the station, 1941-1980, 1961-1990, 1971-end of each station’s time series). The trends were analysed using the Mann-Kendall method, while the step changes were analysed using the Worsley Likelihood method. The results show that positive trends predominate, with most stations showing trend being located in the northern part of the basin, though this pattern is not conclusive. In all, 17% of the cases have trends, of which 67% are positive. The 1960s represent a significant upward jump in the basin rainfall. Seasonal rainfall analysis shows that the short rains tend to have more trends than the long rains. The impact of the varying month of onset of the rainy season is that the results from analyzing the fixed-period and variable-period time series are rarely the same, meaning the two series have different characteristics. It may be argued that the variable-period time series are more reliable as a basis for analysing trends and step changes, since these time series reflect more closely the actual variability in rainy seasons from one year to the next. The fixed-period analysis would, on the other hand, find more practical use in planning.

Kizza, Michael; Rodhe, Allan; Xu, Chong-Yu; Ntale, Henry K.; Halldin, Sven

2009-09-01

327

Monthly abundance of rodent and their ectoparasites in newly settled areas, east of lakes, Ismailia Governorate, Egypt.  

PubMed

Rodents and their ectoparasites were studied inside and outside houses in the newly settled areas, east of lakes, Ismailia Governorate, Egypt. Forty traps per month in each of the two sides were used for collecting rodent during 2009. From 221 rodent were collected from inside houses; Mus musculus N=115 (52.04%), Rattus rattus. frugivorous N=54 (24.43%), R. r. alexandrinus N=40 (18.10%) and R. norvegicus N=12 (5.43%). From 177 rodent were collected from outside houses; M musculus N=4 (2.3%), R. r. frugivorous N=29 (16.43%), R. r. alexandrinus N=37 (20.9%), R. norvegicus N=36 (20.3%), Gerbillus pyramidum N= 67 (37.9%) and Jaculus jaculus N=4 (2.3%). Total ectoparasites per rat inside houses were 765 (3.46 E/Rat) which were classified as fleas, N=464 (2.11 F/R); lice N=150 (0.68 L/R) and mites N=151 (0 68 M/R). From outside house, total ectoparasites per rat were 984 (5.5 E/R) which were classified as fleas, N=410(2.31 F/R); lice N=100 (0.56 L/R), mites N=400 (2.23 M/R) and ticks, N=74 (0.42 T/R). From indoors two fleas species were recorded (Xenopsylla cheopis and Ctenopsyllus segnis); one species of lice (Polyplax spinulosa) and four species of mites (Laelaps nuttall, Ornithonyssus bacoti, Dermanyssus gallinae and Eulaelaps stabularis). The outdoors ectoparasites were; six fleas species (X. cheopis, X. ramesis, Pulex irritans, C. segnis, Stenoponia tripectinata and Nosopsylla sinaiensis); one lice species (P. spinulosa); Six mites species (L. nuttalli, O. bacoti, D. gallinae, E. stabularis, Haemogamnasus pontiger and Hirstionyssus isabellinus) and immature stages of two ticks species (Rhipicephalus sp. and Hyalomma sp.). Most of these ectoparasites were recorded infesting G. pyramidum. PMID:24260816

Bahgat, Iman M

2013-08-01

328

The Marine Terraces of the Northeast Coast of Tanganyika.  

National Technical Information Service (NTIS)

The coast of Tanganyika provides an ideal situation for the study of changing land position and changing sea level as these complexly related circumstances combine to form marine terraces. The field work along the north-eastern Tanganyikian coast was unde...

C. S. Alexander

1968-01-01

329

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

330

27. View east, foreground north facade of Forest Hall, background ...  

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

27. View east, foreground north facade of Forest Hall, background north facade of Forest East Suites. - Lake Placid Club, Forest Wing, East side of Mirror Lake Drive, North of State Route 86 & Main, North Elba, Essex County, NY

331

19. View west, foreground, north facade of Forest East Suites, ...  

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

19. View west, foreground, north facade of Forest East Suites, background north & east facades of Forest Hall. - Lake Placid Club, Forest Wing, East side of Mirror Lake Drive, North of State Route 86 & Main, North Elba, Essex County, NY

332

[Effects of environmental factors on the distribution of dominant wintering waterfowl species in east Dongting Lake wetland, South-central China].  

PubMed

East Dongting Lake is one of the national nature reserves in China, and an important habitat for the wintering of waterfowls in China, and even, global wetlands. To study the relationships between waterfowl community and environmental factors is of vital significance in providing useful data and necessary information for the restoration of bird habitat. In the winters of 2010 and 2011, a survey was conducted on the wintering waterfowls in East Dongting Lake wetland, and canonical correspondence analysis (CCA) was adopted to reveal the relationships between the distribution of dominant wintering waterfowl species and environmental factors. The partial CCA was also employed to assess the respective importance of environmental factors on the waterfowl species distribution and diversity. The factors including the distance to roads, distance to residents, patch density, number of vegetation types, water area, and sedge area had significant effects on the waterfowl distribution (P<0.05), with the affecting intensity in the order of sedge area > patch density > distance to residents > number of vegetation types > water area > distance to road. Sedge area and patch density had highly significant effects (P<0.01) on the distribution of the waterfowls, being the two major factors affecting the wintering waterfowls in the wetland, while landscape diversity index and reed area had no significant effects (P>0.05). The regression analysis showed that environmental factors had different effects on the species richness. The richness of Platalea leucorodia, Anas falcata, and Calidris alpina decreased with the increase of sedge area, while increased with the increase of patch density. However, the richness of Anserfabalis, Anser albifrons, Anser erythro- pus, and Anas crecca increased with increase of sedge area while decreased with the increase of patch density. It was suggested that the distribution of wintering waterfowls in East Dongting Lake wetland was affected by a variety of environmental factors, among which, sedge area and patch density played the most important roles. PMID:23705401

Yuan, Yu-Jie; Liang, Jie; Huang, Lu; Long, Yong; Shen, Sheng; Peng, Yu-Ru; Wu, Hai-Peng; Zeng, Guang-Ming

2013-02-01

333

Using multi-source satellite data for lake level modelling in ungauged basins: a case study for Lake Turkana, East Africa  

NASA Astrophysics Data System (ADS)

Managing limited surface water resources is a great challenge in areas where ground-based data are either limited or unavailable. Direct or indirect measurements of surface water resources through remote sensing offer several advantages of monitoring in ungauged basins. A physical based hydrologic technique to monitor lake water levels in ungauged basins using multi-source satellite data such as satellite-based rainfall estimates, modelled runoff, evapotranspiration, a digital elevation model, and other data is presented. This approach is applied to model Lake Turkana water levels from 1998 to 2009. Modelling results showed that the model can reasonably capture all the patterns and seasonal variations of the lake water level fluctuations. A composite lake level product of TOPEX/Poseidon, Jason-1, and ENVISAT satellite altimetry data is used for model calibration (1998-2000) and model validation (2001-2009). Validation results showed that model-based lake levels are in good agreement with observed satellite altimetry data. Compared to satellite altimetry data, the Pearson's correlation coefficient was found to be 0.81 during the validation period. The model efficiency estimated using NSCE is found to be 0.93, 0.55 and 0.66 for calibration, validation and combined periods, respectively. Further, the model-based estimates showed a root mean square error of 0.62 m and mean absolute error of 0.46 m with a positive mean bias error of 0.36 m for the validation period (2001-2009). These error estimates were found to be less than 15 % of the natural variability of the lake, thus giving high confidence on the modelled lake level estimates. The approach presented in this paper can be used to (a) simulate patterns of lake water level variations in data scarce regions, (b) operationally monitor lake water levels in ungauged basins, (c) derive historical lake level information using satellite rainfall and evapotranspiration data, and (d) augment the information provided by the satellite altimetry systems on changes in lake water levels.

Velpuri, N. M.; Senay, G. B.; Asante, K. O.

2011-05-01

334

Using multi-source satellite data for lake level modelling in ungauged basins: A case study for Lake Turkana, East Africa  

USGS Publications Warehouse

Managing limited surface water resources is a great challenge in areas where ground-based data are either limited or unavailable. Direct or indirect measurements of surface water resources through remote sensing offer several advantages of monitoring in ungauged basins. A physical based hydrologic technique to monitor lake water levels in ungauged basins using multi-source satellite data such as satellite-based rainfall estimates, modelled runoff, evapotranspiration, a digital elevation model, and other data is presented. This approach is applied to model Lake Turkana water levels from 1998 to 2009. Modelling results showed that the model can reasonably capture all the patterns and seasonal variations of the lake water level fluctuations. A composite lake level product of TOPEX/Poseidon, Jason-1, and ENVISAT satellite altimetry data is used for model calibration (1998-2000) and model validation (2001-2009). Validation results showed that model-based lake levels are in good agreement with observed satellite altimetry data. Compared to satellite altimetry data, the Pearson's correlation coefficient was found to be 0.81 during the validation period. The model efficiency estimated using NSCE is found to be 0.93, 0.55 and 0.66 for calibration, validation and combined periods, respectively. Further, the model-based estimates showed a root mean square error of 0.62 m and mean absolute error of 0.46 m with a positive mean bias error of 0.36 m for the validation period (2001-2009). These error estimates were found to be less than 15 % of the natural variability of the lake, thus giving high confidence on the modelled lake level estimates. The approach presented in this paper can be used to (a) simulate patterns of lake water level variations in data scarce regions, (b) operationally monitor lake water levels in ungauged basins, (c) derive historical lake level information using satellite rainfall and evapotranspiration data, and (d) augment the information provided by the satellite altimetry systems on changes in lake water levels. ?? Author(s) 2011.

Velpuri, N. M.; Senay, G. B.; Asante, K. O.

2011-01-01

335

A biomarker record of Lake El'gygytgyn, Far East Russian Arctic: investigating sources of organic matter and carbon cycling during marine isotope stages 1-3  

NASA Astrophysics Data System (ADS)

Arctic paleoenvironmental archives serve as sensitive recorders of past climate change. Lake El'gygytgyn (Far East Russian Arctic) is a high-latitude crater impact lake that contains a continuous sediment record influenced by neither glaciation nor glacial erosion since the time of impact 3.58 Ma ago. Prior research on sediments collected from Lake El'gygytgyn suggest times of permanent ice cover and anoxia corresponding to global glacial intervals, during which the sediments are laminated and are characterized by the co-occurrence of high total organic carbon, microscopic magnetite grains that show etching and dissolution, and negative excursions in bulk sediment organic matter carbon isotope (?13C) values. Here we investigate the abundance and carbon isotopic composition of lipid biomarkers recovered from Lake El'gygytgyn sediments spanning marine isotope stages 1-3 to identify key sources of organic matter (OM) to lake sediments, to establish which OM sources drive the negative ?13C excursion exhibited by bulk sediment OM, and to explore if there are molecular and isotopic signatures of anoxia in the lake during glaciation. We find that during marine isotope stages 1-3, direct evidence for water column anoxia is lacking. A ~4‰ negative excursion in bulk sediment ?13C values during the Local Last Glacial Maximum (LLGM) is accompanied by more protracted, higher magnitude negative excursions in n-alkanoic acid and n-alkanol ?13C values that begin 20 kyr in advance of the LLGM. In contrast, n-alkanes and the C30 n-alkanoic acid do not exhibit a negative ?13C excursion at this time. Our results indicate that the C24, C26 and C28 n-alkanoic acids do not derive entirely from terrestrial OM sources, while the C30 n-alkanoic acid at Lake El'gygytgyn is a robust indicator of terrestrial OM contributions. Overall, our results strongly support the presence of a nutrient-poor water column, which is mostly isolated from atmospheric carbon dioxide during glaciation at Lake El'gygytgyn.

Holland, A. R.; Petsch, S. T.; Castañeda, I. S.; Wilkie, K. M.; Burns, S. J.; Brigham-Grette, J.

2013-01-01

336

A biomarker record of Lake El'gygytgyn, far east Russian Arctic: investigating sources of organic matter and carbon cycling during marine isotope stages 1-3  

NASA Astrophysics Data System (ADS)

Paleoenvironmental archives in Arctic regions serve as sensitive recorders of past climate change where summer temperatures hover near freezing and small climate variations may exhibit strong threshold-crossing environment responses. Lake El'gygytgyn (Far East Russian Arctic) is a high-latitude crater impact lake that contains a continuous sediment record influenced by neither glaciation nor glacial erosion since the time of impact at 3.58 Ma. Prior research on sediments collected from Lake El'gygytygyn suggest times of permanent ice cover and anoxia corresponding to global glacial intervals, during which the sediments are laminated and are characterized by the co-occurrence of high total organic carbon, microscopic magnetite grains that show etching and dissolution, and negative excursions in bulk sediment organic matter carbon isotope (?13C) values. Here, we investigate the abundance and carbon isotopic characteristics of lipid biomarkers recovered from Lake El'gygytygn sediments spanning marine isotope stages 1-3, to identify key sources of organic matter (OM) to lake sediments, to establish which compounds and thus OM sources drive the negative ?13C excursion exhibited by bulk sediment OM, and to explore if there are molecular and isotopic signatures of anoxia in the lake during glaciation. We find that during marine isotope stages 1-3, direct evidence for water column anoxia is lacking. A ∼4‰ negative excursion in bulk sediment ?13C values during the local Last Glacial Maximum (LLGM) is accompanied by more protracted, higher magnitude negative excursions in n-alkanoic acid and n-alkanol ?13C values that begin 20 kyr in advance of the LLGM. In contrast, n-alkanes and the C30 n-alkanoic acid do not exhibit a negative ?13C excursion at this time. Our results indicate that the C24, C26 and C28 n-alkanoic acids do not derive entirely from terrestrial OM sources, while the C30 n-alkanoic acid at Lake El'gygytgyn is a robust indicator of terrestrial OM contributions. Overall, our results strongly support the presence of a nutrient-poor water column, which is mostly isolated from atmospheric carbon dioxide during glaciation at Lake El'gygytgyn.

Holland, A. R.; Petsch, S. T.; Castañeda, I. S.; Wilkie, K. M.; Burns, S. J.; Brigham-Grette, J.

2012-09-01

337

Pliocene to Pleistocene climate and environmental history of Lake El'gygytgyn, Far East Russian Arctic, based on high-resolution inorganic geochemistry data  

NASA Astrophysics Data System (ADS)

The 3.6 Ma sediment record of Lake El'gygytgyn, Far East Russian Arctic, represents the longest continuous climate archive of the terrestrial Arctic. Its elemental composition monitored by X-ray fluorescence scanning exhibits significant changes since the Mid-Pliocene caused by climate driven variations in the primary production, postsedimentary diagenetic processes, and current activity in the lake as well as weathering processes in its catchment. During the Mid to Late Pliocene, warmer and wetter climatic conditions are reflected by elevated Si / Ti ratios, indicating enhanced diatom production in the lake. Prior to 3.3 Ma, this signal is highly masked by intensified detrital input from the catchment, visible in maxima of clastic-related proxies such as the K concentration. In addition, calcite formation in the early lake history points to enhanced nutrient flux into the lake caused by intensified weathering in its catchment. Its termination at ca. 3.3 Ma is supposed to be linked to the development of permafrost in the region triggered by a first cooling in the Mid-Pliocene. After ca. 3.0 Ma the elemental data suggest a gradual transition to Quaternary-style glacial / interglacial cyclicity. In the early Pleistocene, the cyclicity was first dominated by variations on the 41 ka obliquity band but experienced a change to a 100 ka eccentricity dominance after the Middle Pleistocene Transition at ca. 1.2 to 0.7 Ma. This clearly demonstrates the sensitivity of the Lake El'gygytgyn record to orbital forcing. A successive decrease of the baseline-levels of the redox-sensitive Mn / Fe ratio and magnetic susceptibility between 2.3 to 1.8 Ma reflects an overall change in the bottom water oxygenation due to an intensified occurrence of pervasive glacial episodes in the early Quaternary. The coincidence with major changes in the North Pacific and Bering Sea paleoceanography at ca. 1.8 Ma implies that the change in lake hydrology was caused by regional cooling and/or changes in the ocean-land moisture transport. Further rising TOC and TN values after ca. 1.6 Ma are attributed to a progressive intensification of the glacial intensity. In the course of the Quaternary glacial/interglacial sequence eight so-called "super-interglacials" occur. Their exceptional warm conditions are reflected by extreme Si / Ti peaks accompanied by lows in Ti, K, and Fe, thus indicating an extraordinary high lake productivity.

Wennrich, V.; Minyuk, P. S.; Borkhodoev, V. Ya.; Francke, A.; Ritter, B.; Nowaczyk, N.; Sauerbrey, M. A.; Brigham-Grette, J.; Melles, M.

2013-10-01

338

Sediment geochemistry and tectonic setting: Application of discrimination diagrams to early stages of intracontinental rift evolution, with examples from the Okavango and Southern Tanganyika rift basins  

NASA Astrophysics Data System (ADS)

In this article, we have applied discriminant diagrams and bivariate plots for tectonic setting to Quaternary sediments from the East African Rift System (EARS). Sediment samples used in this study represent two different phases in early stage intracontinental rift evolution: the alluvial fan of the nascent Okavango system and a lacustrine basin within the relatively more mature Tanganyika system. The diagrams for tectonic setting for major elements place the majority of these EARS sediments within the passive margin (PM) setting. Passive margin sandstones are generally enriched in SiO 2 and depleted in Na 2O, CaO and TiO 2 reflecting their highly recycled nature. Based on major element discriminant diagrams, we propose two new fields for early stage intracontinental rift evolution (alluvial fan and lacustrine basin), within the previously defined passive margin field. The rare earth element (REE) patterns from both Okavango and Tanganyika sediments exhibit patterns similar to PAAS, with ash layers from the Rungwe volcanics in the Tanganyika samples exhibiting an enrichment in REE relative to the bulk sediment.

Huntsman-Mapila, P.; Tiercelin, J.-J.; Benoit, M.; Ringrose, S.; Diskin, S.; Cotten, J.; Hémond, C.

2009-01-01

339

Phylogenetic and antigenic characterization of reassortant H9N2 avian influenza viruses isolated from wild waterfowl in the East Dongting Lake wetland in 2011-2012  

PubMed Central

Background Wild waterfowl are recognized as the natural reservoir for influenza A viruses. Two distinct lineages, the American and Eurasian lineages, have been identified in wild birds. Gene flow between the two lineages is limited. The H9N2 virus has become prevalent in poultry throughout Eurasia, and mainly circulates in wild ducks and shorebirds in North America. Methods In this study, 22 H9N2 avian influenza viruses were isolated from wild waterfowl feces in East Dongting Lake Nature Reserve in November 2011 and March 2012. The phylogenetic, molecular, and antigenic characteristics of these viruses were analyzed based on analyses of the whole genome sequence of each isolate. Results Phylogenetic analyses indicated that these H9N2 viruses were generated by reassortment events. The HA, NA, PA, and NS genes were derived from the American gene pool, and the other four genes were derived from the Eurasian gene pool. Antigenic analyses indicated that these viruses were significantly different from the Eurasian lineage viruses. Conclusions This study presents the isolation of novel intercontinental recombinant H9N2 viruses from wild waterfowl in the East Dongting Lake wetland. The novel genotype H9N2 virus has not been detected in poultry in the region yet, and may be transmitted to naïve birds in poultry farms. Therefore, our results highlight the need for ongoing surveillance of wild birds and poultry in this region.

2014-01-01

340

Spatial co-distribution of neglected tropical diseases in the East African Great Lakes region: revisiting the justification for integrated control  

PubMed Central

Summary OBJECTIVE To determine spatial patterns of co-endemicity of schistosomiasis mansoni and the soil-transmitted helminths (STHs) Ascaris lumbricoides, Trichuris trichiura and hookworm in the Great Lakes region of East Africa, to help plan integrated neglected tropical disease programmes in this region. METHOD Parasitological surveys were conducted in Uganda, Tanzania, Kenya and Burundi in 28 213 children in 404 schools. Bayesian geostatistical models were used to interpolate prevalence of these infections across the study area. Interpolated prevalence maps were overlaid to determine areas of co-endemicity. RESULTS In the Great Lakes region, prevalence was 18.1% for Schistosoma mansoni, 50.0% for hookworm, 6.8% for A. lumbricoides and 6.8% for T. trichiura. Hookworm infection was ubiquitous, whereas S. mansoni, A. lumbricoides and T. trichiura were highly focal. Most areas were endemic (prevalence ?10%) or hyperendemic (prevalence ?50%) for one or more STHs, whereas endemic areas for schistosomiasis mansoni were restricted to foci adjacent large perennial water bodies. CONCLUSION Because of the ubiquity of hookworm, treatment programmes are required for STH throughout the region but efficient schistosomiasis control should only be targeted at limited high-risk areas. Therefore, integration of schistosomiasis with STH control is only indicated in limited foci in East Africa.

Clements, Archie C. A.; Deville, Marie-Alice; Ndayishimiye, Onesime; Brooker, Simon; Fenwick, Alan

2010-01-01

341

WEST PIER OF NORTH GATE (490 NORTH & 900 EAST), ...  

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

WEST PIER OF NORTH GATE (490 NORTH & 900 EAST), SALT LAKE CITY, UT. VIEW LOOKING SOUTH AT THE WEST PIER OF THE CEMETERY'S NORTH GATE. - Salt Lake City Cemetery, 200 N Street, Salt Lake City, Salt Lake County, UT

342

NORTH GATE AT 11TH AVENUE (490 NORTH & 900 EAST), ...  

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

NORTH GATE AT 11TH AVENUE (490 NORTH & 900 EAST), SALT LAKE CITY, UT. VIEW LOOKING SOUTH AT CEMETERY'S NORTH GATE (WPA PROJECT, 1938-1941). - Salt Lake City Cemetery, 200 N Street, Salt Lake City, Salt Lake County, UT

343

Analogy between natural gas found in lakes of rift valley system of east Africa and its allied gas in Japan  

Microsoft Academic Search

The Afar triangle in northeastern Ethiopia is where the Red Sea rift, the Carlsberg Ridge of the Indian Ocean, and the Rift Valley system of east Africa meet. In 1979, J. Welhan and H. Craig reported that hydrothermal vents at 21°N, on the East Pacific Rise, are discharging turbid waters. Mixtures of the plumes with ambient seawater contain significant amounts

Osamu Fukuta

1984-01-01

344

Late Quaternary vegetation changes around Lake Rutundu, Mount Kenya, East Africa: evidence from grass cuticles, pollen and stable carbon isotopes  

Microsoft Academic Search

Woody, subalpine shrubs and grasses currently surround Lake Rutundu, Mount Kenya. Multiple proxies, including carbon isotopes, pollen and grass cuticles, from a 755-cm-long core were used to reconstruct the vegetation over the past 38 300 calendar years. Stable carbon-isotope ratios of total organic carbon and terrestrial biomarkers from the lake sediments imply that the proportion of terrestrial plants using the

M. J. Wooller; D. L. Swain; K. J. Ficken; A. D. Q. Agnew; G. Eglinton

2003-01-01

345

Dynamic diatom response to changing climate 0-1.2 Ma at Lake El'gygytgyn, Far East Russian Arctic  

NASA Astrophysics Data System (ADS)

The Lake El'gygytgyn sediment record contains an abundant diatom flora through most intervals of the lake's history, providing a means to create and test hypotheses concerning the lake's response to changing climates. The 0-1.2 Ma core interval is characterized by shifts in the dominant planktonic genera and events of exceptional concentration and diversity. Warm interglacial intervals have enhanced concentration and diversity of the plankton. This response is most extreme during exceptional events corresponding to marine isotope stages (MIS) 11 and 31. Diatom concentration and diversity also increase during some cold intervals (e.g., MIS 2), suggesting conditions of lake circulation and nutrient cycling promoting diatom production during these events. Short intervals of low plankton concentration accompanied by shifts in the dominant genus of the lake suggest conditions during certain cold events generate a severe impact on plankton production. The absence of these events during extended intervals of low summer insolation variability suggests a muted cold-event response of the lake system linked to regional climate.

Snyder, J. A.; Cherepanova, M. V.; Bryan, A.

2013-06-01

346

High-elevation amplification of warming since the Last Glacial Maximum in East Africa: New perspectives from biomarker paleotemperature reconstructions  

NASA Astrophysics Data System (ADS)

Tropical lapse rate variability on glacial/interglacial time scales has been hotly debated since the publication of CLIMAP in 1976. Low-elevation paleotemperature reconstructions from the tropics have repeatedly shown less warming from the Last Glacial Maximum (LGM) to present than reconstructions from high elevations, leading to widespread difficulty in estimating the true LGM-present temperature change in the tropics. This debate is further complicated by the fact that most paleotemperature estimates from high elevations in the tropics are derived from pollen- and moraine-based reconstructions of altitudinal shifts in vegetation belts and glacial equilibrium line altitudes (ELAs). These traditional approaches rely on the assumption that lapse rates have remained constant through time. However, this assumption is problematic in the case of the LGM, when pervasive tropical aridity most likely led to substantial changes in lapse rates. Glycerol dialkyl glycerol tetraethers (GDGTs) can be used to reconstruct paleotemperatures independent of hydrological changes, making them the ideal proxy to reconstruct high elevation temperature change and assess lapse rate variability through time. Here we present two new equatorial paleotemperature records from high elevations in East Africa (Lake Rutundu, Mt. Kenya and Lake Mahoma, Rwenzori Mountains, Uganda) based on branched GDGTs. Our record from Lake Rutundu shows deglacial warming starting near 17 ka and a mid-Holocene thermal maximum near 5 ka. The overall amplitude of warming in the Lake Rutundu record is 6.8×1.0°C from the LGM to the present, with mid-Holocene temperatures 1.6×0.9°C warmer than modern. Our record from Lake Mahoma extends back to 7 ka and shows similar temperature trends to our record from Lake Rutundu, indicating similar temporal resolution of high-elevation temperature change throughout the region. Combining these new records with three previously published GDGT temperature records from different elevations in East Africa (Sacred Lake, Lake Tanganyika, and Lake Malawi), we are able to reconstruct a continuous record of lapse rates and freezing level heights (FLHs) back to the LGM. We find that tropical lapse rates have varied widely over the last 22 ky, with the largest (lowest) lapse rate (FLH) around the LGM, while the smallest (highest) lapse rate (FLH) occurs during the mid-Holocene, confirming the amplification of warming at high altitudes between the LGM and present. These lapse rate and FLH reconstructions match records of regional hydrological variability, confirming the importance of glacial/interglacial humidity variations on altitudinal temperature gradients in the tropics. Furthermore, the FLH record largely matches records of tropical glacier ELA changes, indicating that warming from LGM-present was likely amplified at high altitudes throughout the tropics.

Loomis, S. E.; Russell, J. M.; Kelly, M. A.; Eggermont, H.; Verschuren, D.

2013-12-01

347

Hydrologic monitoring program in Eldridge-Wilde and East Lake Road well-field areas, Pinellas and Hillsborough counties, Florida, 1978  

USGS Publications Warehouse

This report describes the observation-well network in Eldridge-Wilde and East Lake Road well-field areas, Pinellas and Hillsborough Counties, Florida. Data obtained in 1978 from the network in and adjacent to the two well fields, as well as rainfall and pumpage records, are presented. The Southwest Florida Water Management District has established regulatory water-level limits in four observation wells and water-quality limits in three observation wells. Water levels dropped below regulatory limits in the spring of 1978 in three wells. Chloride concentrations in 1978 remained above regulatory limits for the entire year in one well and exceeded the limit during the late spring in the other two deep wells, both west of Eldridge-Wilde well field. (USGS)

Mills, L. R.

1980-01-01

348

Secondary production and energetics of the shrimp Caridina nilotica in Lake Victoria, East Africa: model development and application  

Microsoft Academic Search

Measurements of body mass, carbon content, respiration, growth, and egestion are combined in a model of secondary production by the tropical freshwater shrimp Caridina. The model is developed to permit its direct application to empirical data for abundances and size frequency distributions of field populations. Model calculations combined with population data for offshore Lake Victoria over a period of two

Marcy Ignatow; Godfrey Mbahinzireki; John T. Lehman

1996-01-01

349

75 FR 53735 - Notice of Final Federal Agency Actions on East Lake Sammamish Master Plan Trail in King County, WA  

Federal Register 2010, 2011, 2012, 2013

...starting at Gilman Boulevard in Issaquah, Washington and ending at Bear Creek Trail in Redmond, Washington. Those actions grant licenses...side of Lake Sammamish from Gilman Boulevard in Issaquah, WA to Bear Creek Trail in Redmond, WA. The project will be an...

2010-09-01

350

Estimation of water pollution sources in Lake Victoria, East Africa: Application and elaboration of the rapid assessment methodology  

Microsoft Academic Search

Pollution resulting from increased human activities is threatening Lake Victoria, its effects being characterised by eutrophication and the occurrence of dramatically low dissolved oxygen levels. This study applies a system of pollution inventory methods to estimate waste loads from pollution sources on the basis of functional variables and pollution intensities. Penetration factors are used to incorporate the effects of treatment

Peter AGM Scheren; H. A Zanting; A. M. C Lemmens

2000-01-01

351

Characterization of a mercury-reducing Bacillus cereus strain isolated from the Pulicat Lake sediments, south east coast of India  

Microsoft Academic Search

Pulicat Lake sediments are often severely polluted with the toxic heavy metal mercury. Several mercury-resistant strains of Bacillus species were isolated from the sediments and all the isolates exhibited broad spectrum resistance (resistance to both organic and inorganic mercuric compounds). Plasmid curing assay showed that all the isolated Bacillus strains carry chromosomally borne mercury resistance. Polymerase chain reaction and southern

Seralathan Kamala Kannan; Subramony Mahadevan; Ramaswamy Krishnamoorthy

2006-01-01

352

A 350 ka record of climate change from Lake El'gygytgyn, Far East Russian Arctic: refining the pattern of climate modes by means of cluster analysis  

NASA Astrophysics Data System (ADS)

Rock magnetic, biochemical and inorganic records of the sediment cores PG1351 and Lz1024 from Lake El'gygytgyn, Chukotka peninsula, Far East Russian Arctic, were subject to a hierarchical agglomerative cluster analysis in order to refine and extend the pattern of climate modes as defined by Melles et al. (2007). Cluster analysis of the data obtained from both cores yielded similar results, differentiating clearly between the four climate modes warm, peak warm, cold and dry, and cold and moist. In addition, two transitional phases were identified, representing the early stages of a cold phase and slightly colder conditions during a warm phase. The statistical approach can thus be used to resolve gradual changes in the sedimentary units as an indicator of available oxygen in the hypolimnion in greater detail. Based upon cluster analyses on core Lz1024, the published succession of climate modes in core PG1351, covering the last 250 ka, was modified and extended back to 350 ka. Comparison to the marine oxygen isotope (?18O) stack LR04 (Lisiecki and Raymo, 2005) and the summer insolation at 67.5° N, with the extended Lake El'gygytgyn parameter records of magnetic susceptibility (?LF), total organic carbon content (TOC) and the chemical index of alteration (CIA; Minyuk et al., 2007), revealed that all stages back to marine isotope stage (MIS) 10 and most of the substages are clearly reflected in the pattern derived from the cluster analysis.

Frank, U.; Nowaczyk, N. R.; Minyuk, P.; Vogel, H.; Rosén, P.; Melles, M.

2013-07-01

353

A 350 kyr record of climate change from Lake El'gygytgyn, Far East Russian Arctic: refining the pattern of climate modes by means of cluster analysis  

NASA Astrophysics Data System (ADS)

Rock magnetic, biochemical and inorganic records of the sediment cores PG1351 and Lz1024 from Lake El'gygytgyn, Chukotka peninsula, Far East Russian Arctic, were subjected to a hierarchical agglomerative cluster analysis in order to refine and extend the pattern of climate modes as defined by Melles et al. (2007). Cluster analysis of the data obtained from both cores yielded similar results, differentiating clearly between the four climate modes warm, peak warm, cold and dry, and cold and moist. In addition, two transitional phases were identified, representing the early stages of a cold phase and slightly colder conditions during a warm phase, respectively. The statistical approach can thus be used to resolve gradual changes in the sedimentary units as an indicator of available oxygen in the hypolimnion in greater detail. Based upon cluster analyses on core Lz1024, the published succession of climate modes in core PG1351, covering the last 250 kyr, was modified and extended back to 350 kyr. Comparison to the marine oxygen isotope (?18O) stack LR04 (Lisiecki and Raymo, 2005) and the summer insolation at 67.5° N, with the extended Lake El'gygytgyn parameter records of magnetic susceptibility (?LF), total organic carbon content (TOC) and the chemical index of alteration (CIA; Minyuk et al., 2007), revealed that all stages back to marine isotope stage (MIS) 10 and most of the substages are clearly reflected in the pattern derived from the cluster analysis.

Frank, U.; Nowaczyk, N. R.; Minyuk, P.; Vogel, H.; Rosén, P.; Melles, M.

2012-10-01

354

Presence of the 54-chromosome common vole (Mammalia) on Olkhon Island (Lake Baikal, East Siberia, Russia), and the occurrence of an unusual X-chromosome variant.  

PubMed

We report a new finding of the 54-chromosome sibling species of the common vole in East Siberia - the first description from Olkhon Island (Lake Baikal). The karyotype of a male specimen revealed by routine staining and C-banding demonstrates the unambiguous presence of Microtus rossiaemeridionalis Ognev, 1924 (recently often regarded as as junior synonym of Microtus levis Miller, 1908). Comparison with conspecific specimens from the European part of the species range (from the left bank of the river Volga) shows that the vole of the island population has a smaller X-chromosome due to a reduced quantity of C-positive heterochromatin. This is just the third example of this type of X-chromosome variant with previous cases on an Arctic island (Svalbard) and the West Siberian lowland (Novosibirsk) and the only one on a lake island. Although Microtus rossiaemeridionalis is largely monomorphic in its karyotype, our data show that one specific type of X-chromosome variant is remarkably widespread, though rare. PMID:24260647

Pavlova, S V; Tchabovsky, A V

2011-01-01

355

Presence of the 54-chromosome common vole (Mammalia) on Olkhon Island (Lake Baikal, East Siberia, Russia), and the occurrence of an unusual X-chromosome variant  

PubMed Central

Abstract We report a new finding of the 54-chromosome sibling species of the common vole in East Siberia - the first description from Olkhon Island (Lake Baikal). The karyotype of a male specimen revealed by routine staining and C-banding demonstrates the unambiguous presence of Microtus rossiaemeridionalis Ognev, 1924 (recently often regarded as as junior synonym of Microtus levis Miller, 1908). Comparison with conspecific specimens from the European part of the species range (from the left bank of the river Volga) shows that the vole of the island population has a smaller X-chromosome due to a reduced quantity of C-positive heterochromatin. This is just the third example of this type of X-chromosome variant with previous cases on an Arctic island (Svalbard) and the West Siberian lowland (Novosibirsk) and the only one on a lake island. Although Microtus rossiaemeridionalis is largely monomorphic in its karyotype, our data show that one specific type of X-chromosome variant is remarkably widespread, though rare.

Pavlova, S.V.; Tchabovsky, A.V.

2011-01-01

356

Mass movement deposits in the 3.6 Ma sediment record of Lake El'gygytgyn, Far East Russian Arctic: classification, distribution and preliminary interpretation  

NASA Astrophysics Data System (ADS)

This paper focuses on the characterization and genesis of mass movement deposits (MMD) in the Quaternary and Pliocene sediments of Lake El'gygytgyn, Far East Russian Arctic. The 320 m long sediment record was drilled by three partly overlapping holes at ICDP Site 5011-1 in the lake basin, representing the Quaternary almost completely, and the Pliocene down to 3.6 Ma with 52% recovery. Mass movement deposits were investigated in all three cores, based on macroscopical core descriptions, radiographic images, and high-resolution magnetic susceptibility and gamma-ray density. Five different types of MMDs were identified: turbidites, grain flow deposits, debrites, slumps and slides. These are formed by transitional mass movement processes, and thus, can be co-generic. An initial slope failure is thought to transform into a debris flow, deforms frontal sediments and partly disintegrates and dilutes into a turbidity flow. Turbidites are by far the most frequent MMD type in the lake center. They occur throughout the record in all pelagic sedimentary facies, but they are thinner in facies formed during cold climate conditions. All other MMDs, by contrast, incise exclusively the pelagic facies deposited during warm climates. In the 123 m thick Quaternary sediment record 238 mass movement events are identified, comprising 37% of the sediment length. Turbidites contribute 92% of the number of Quaternary MMDs, but only 32% of their thickness. In the Pliocene sediments between 123 and 320 m, additional 185 mass movement deposits are identified, which constitute 32% of the recovered sediments. The mean recurrence rate for MMDs is 11 ka and 5 ka in the Quaternary and Pliocene, respectively.

Sauerbrey, M. A.; Juschus, O.; Gebhardt, A. C.; Wennrich, V.; Nowaczyk, N. R.; Melles, M.

2013-01-01

357

Transit losses and traveltimes for reservoirs releases during drought conditions along the Neosho River from Council Grove Lake to Iola, east-central Kansas  

USGS Publications Warehouse

Knowledge of the transit losses and water-wave traveltimes in the Neosho River for varying reservoir-release volumes and durations is necessary for proper management of water supply. Two reaches were studied along the Neosho River in east-central Kansas. The upper reach is from Council Grove Lake to John Redmond Reservoir, a distance of 83.0 river miles. The lower reach is from John Redmond Reservoir to Iola, Kansas, a distance of 56.3 river miles. Channel and aquifer characteristics were estimated from available data and used in a streamflow routing model. These estimated characteristics were verified using the model by comparing simulated reservoir releases to observed reservoir releases. The verified model then was used to simulate transit losses (or gains) and traveltimes for selected reservoir release volumes and durations from Council Grove Lake to Iola. Transit losses and traveltimes were investigated for the selected reservoir releases while under a severe drought antecedent streamflow condition (zero base flow) and a less severe drought antecedent streamflow condition (2% drought base flows). The largest total transit loss from Council Grove Lake to Iola occurred during the severe drought antecedent streamflow condition, small reservoir release rates, and long reservoir release durations. The total transit loss included water that was temporarily lost to bank storage. For a severe drought condition, transit losses ranged from 1,100 acre-ft for a release volume of 1,840 acre-ft for a duration of 50 days to 6 ,280 acre-ft for a release volume of 6,280 acre-ft for a duration of 365 days. For a less severe drought condition, transit losses ranged from 860 acre-ft to 3,234 acre-ft for the same release volumes and durations as for the severe drought condition. (Author 's abstract)

Carswell, W. J.; Hart, R. J.

1985-01-01

358

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

359

Evolution of the mitochondrial DNA control region in the mbuna (Cichlidae) species flock of lake Malawi, East Africa  

Microsoft Academic Search

Considerable controversy has surrounded the application of mitochondrial DNA data to reconstruction of evolutionary relationships\\u000a among the endemic cichlids of Lake Malawi. Central to this debate has been the issue of whether lineage sorting is complete,\\u000a and thus whether these data actually reflect species phylogeny, or simply gene genealogy. Review of all mtDNA control region\\u000a sequences available for members of

Alex Parker; Irv Kornfield

1997-01-01

360

Nutritional vulnerability of older persons living in urban areas of Lake Victoria Basin in East Africa: a cross sectional survey.  

PubMed

The aim of this study was to (1) determine the prevalence of malnutrition and (2) investigate factors affecting nutritional status of older persons living in urban areas of Lake Victoria Basin. The prevalence of underweight was 16.5%, with men (24.1%) being significantly more likely to be underweight (P < 0.05) than women (12.3%). Overall, 61.2% had normal body mass indices, 13.2% were overweight, and 9.1% were obese. Energy intake was low (1596.3-1630.5 Kcal), with only 22% and 38% of men and women, respectively, meeting their daily requirements. Protein intake was adequate in more than half of men and women. Vitamin A, iron, and zinc intakes were moderate, while calcium intake was low (P < 0.05). Inadequate food access, poor health, living arrangements, and poor eating patterns were the main nutritional risk factors. There is a need to plan nutrition programs that can improve living conditions, health, and nutritional status of older adults in these urban areas of the Lake Victoria Basin. PMID:22335442

Cheserek, Maureen J; Waudo, Judith N; Tuitoek, Prisca J; Msuya, John M; Kikafunda, Joyce K

2012-01-01

361

Polybrominated diphenyl ethers and alternative flame retardants in air and precipitation samples from the northern Lake Victoria region, East Africa.  

PubMed

High volume air and precipitation samples were collected close to the shore of Lake Victoria at Entebbe, Uganda, between October 2008 and July 2010 inclusive. Polybrominated diphenyl ethers (PBDEs) and alternative flame retardants (AFRs) were analyzed by GC-MS. BDEs 47, 99, and 209 were the predominant PBDEs with mean concentrations (in air) of 9.84, 4.38, 8.27 pg m(-3) and mean fluxes in precipitation of 3.40, 6.23, and 7.82 ng m(-2) sample(-1), respectively. 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), and hexabromocyclododecane (HBCDD), anti- and syn-Dechlorane plus were detected at levels comparable with those of PBDEs. Both PBDEs and AFRs in air generally increased from 2008 to 2010. Elevated PBDE concentrations in air were associated with slow moving low altitude air masses from the region immediately adjacent to the lake, while low concentrations were mostly associated with fast moving westerly and southwesterly air masses. Analysis of the octa- and nona-BDE profiles suggested photolysis and pyrolytic debromination of BDE-209 in the air samples. The highly halogenated and most abundant PBDEs and AFRs in air also predominated in precipitation samples. This is the first study to report flame retardants in high volume air samples and precipitation in Equatorial Africa. PMID:24400732

Arinaitwe, Kenneth; Muir, Derek C G; Kiremire, Bernard T; Fellin, Phil; Li, Henrik; Teixeira, Camilla

2014-02-01

362

Observed and simulated hydroclimatology using distributed hydrologic model from in-situ and multi-satellite remote sensing datasets in Lake Victoria region in East Africa  

NASA Astrophysics Data System (ADS)

Floods and droughts are common, recurring natural hazards in East African nations. Studies of hydro-climatology at daily, seasonal, and annual time scale is an important in understanding and ultimately minimizing the impacts of such hazards. Using daily in-situ data over the last two decades combined with the recently available multiple-years satellite remote sensing data, we analyzed and simulated, with a distributed hydrologic model, the hydro-climatology in Nzoia, one of the major contributing sub-basins of Lake Victoria in the East African highlands. The basin, with a semi arid climate, has no sustained base flow contribution to Lake Victoria. The short spell of high discharge showed that rain is the prime cause of floods in the basin. There is only a marginal increase in annual mean discharge over the last 21 years. The 2-, 5- and 10-year peak discharges, for the entire study period showed that more years since the mid 1990's have had high peak discharges despite having relatively less annual rain. The study also presents the hydrologic model calibration and validation results over the Nzoia Basin. The spatiotemporal variability of the water cycle components were quantified using a physically-based, distributed hydrologic model, with in-situ and multi-satellite remote sensing datasets. Moreover, the hydrologic capability of remote sensing data such as TRMM-3B42V6 was tested in terms of reconstruction of the water cycle components. The spatial distribution and time series of modeling results for precipitation (P), evapotranspiration (ET), and change in storage (dS/dt) showed considerable agreement with the monthly model runoff estimates and gauge observations. Runoff values responded to precipitation events that occurred across the catchment during the wet season from March to early June. The hydrologic model captured the spatial variability of the soil moisture storage. The spatially distributed model inputs, states, and outputs, were found to be useful for understanding the hydrologic behavior at the catchment scale. Relatively high flows were experienced near the basin outlet from previous rainfall, with a new flood peak responding to the rainfall in the upper part of the basin. The monthly peak runoff was observed in the months of April, May and November. The analysis revealed a linear relationship between rainfall and runoff for both wet and dry seasons. The model was found to be useful in poorly gauged catchments using satellite forcing data and showed the potential to be used not only for the investigation of the catchment scale water balance but also for addressing issues pertaining to sustainability of the resources within the catchment.

Khan, S. I.; Adhikari, P.; Hong, Y.; Vergara, H.; Grout, T.; Adler, R. F.; Policelli, F.; Irwin, D.; Korme, T.; Okello, L.

2010-07-01

363

A new interpretation from geophysical data of the crustal architecture of the East Antarctic craton between Vostok Lake and Adventure Subglacial depression  

NASA Astrophysics Data System (ADS)

Numerical modelling of the Earth surface has been extensively used to investigate regional tectonic settings. The East Antarctic Craton (EAC) is a fragment of the Gondwanaland Precambrian shield as confirmed from the sea floor geophysical reconstruction. Despite the progress achieved in the last decades for the understanding of the tectonic evolution of the EAC, our knowledge of the subglacial geology derives from sparse rocks outcrop around the perimeter of the continent since the ice sheet prevents from direct investigations. Since the onset of the East Antactic Ice Sheet (EAIS), the tectonic activity represents the major modelling agent of the subglacial landscape, due to the mostly dry ice cap-bedrock contact preventing any significant erosional or sedimentary episode. Compressional, extensional, transcurrent tectonic styles of deformation produce characteristic morphological signatures. These landscapes were replicated by a series of numerical Hybrid Cellular Automata (HCA) models. The comparison and tuning of these models with the bedrock morphology allowed to constrain the extensional tectonic style responsible for the formation of the subglacial depressions in the huge region between Vostok and Adventure. Results from the numerical modelling suggest the tectonic origin of the Aurora depression, of the Concordia Trough and of the Adventure Subglacial basin. Crustal listric faults with normal displacements of the order of hundreds to thousands of meters created the necessary space beneath the ice cap to develop the present day subglacial morphologies as derived from RES data and their characteristic geophysical signatures. An original and alternative origin is proposed for the Lake Vostok depression based on the re-interpretation of published geophysical data. The integration of the results allows us to speculate on the existence of an intraplate transtensional deformation belt within the EAC since Cenozoic times.

Cianfarra, Paola; Salvini, Francesco

2013-04-01

364

The species flocks of East African cichlid fishes: recent advances in molecular phylogenetics and population genetics  

NASA Astrophysics Data System (ADS)

With more than 3,000 species, the fish family Cichlidae is one of the most species-rich families of vertebrates. Cichlids occur in southern and central America, Africa, Madagascar, and India. The hotspot of their biodiversity is East Africa, where they form adaptive radiations composed of hundreds of endemic species in several lakes of various sizes and ages. The unparalleled species richness of East African cichlids has been something of a conundrum for evolutionary biologists and ecologists, since it has been in doubt whether these hundreds of species arose by allopatric speciation or whether it is necessary to invoke somewhat less traditional models of speciation, such as micro-allopatric, peripatric, or even sympatric speciation or evolution through sexual selection mediated by female choice. Ernst Mayr's analyses of these evolutionary uniquely diverse species assemblages have contributed to a more direct approach to this problem and have led to a deeper understanding of the patterns and processes that caused the formation of these huge groups of species. We review here recent molecular data on population differentiation and phylogenetics, which have helped to unravel, to some extent, the patterns and processes that led to the formation and ecological maintenance of cichlid species flocks. It is becoming apparent that sexually selected traits do play an important role in speciation in micro-allopatric or even sympatric settings. Species richness seems to be roughly correlated with the surface area, but not the age, of the lakes. We observe that the oldest lineages of a species flock of cichlids are often less species-rich and live in the open water or deepwater habitats. While the species flocks of the Lake Malawai and the Lake Victoria areas were shown to be monophyletic, the cichlid assemblage of Lake Tanganyika seems to consist of several independent species flocks. Cichlids emerge as an evolutionary model system in which many fundamental questions in evolution and ecology can be tested successfully, yet for other fish species flocks the relative importance of alternative mechanisms of speciation is likely to differ from that in cichlid fish.

Salzburger, Walter; Meyer, Axel

365

Regionalisation of the parameters of a conceptual water balance model for Lake Victoria basin in East Africa  

NASA Astrophysics Data System (ADS)

Large parts of the globe are ungauged and even the numbers of gauged basins are declining very fast due to factors like insufficient funding, inadequate institutional frameworks, a lack of appreciation of the worth of long term data and, sometimes, political turmoil. The most common approach for predicting hydrological variables in ungauged basins is regionalisation whereby model parameters are transferred from gauged basins that are deemed similar to the target ungauged basin. In this study, WASMOD, a conceptual water balance model was applied to 9 gauged sub-basins in Lake Victoria basin in order to test the transferability of model parameters between the basins using three regionalisation approaches. The goal was to evaluate regionalisation methods that could be used for modelling catchment inflow into Lake Victoria. WASMOD model was calibrated within the GLUE framework for uncertainty assessment using Monte Carlo simulation with uniformly sampled parameter sets. Nash-Sutcliffe coefficients were used as the likelihoods. The analysis was carried out for the period 1967-2000. Parameter transferability was assessed by comparing the likelihood values of regionalised simulations with the values under calibration for each basin. The results showed that WASMOD performed well for all study sub-basins with NS values during calibration that ranged between 0.70 and 0.82. The transferability results were mixed. For the proxy-basin method, the best performing parameter donor basin was Mara with 4 proxy basins giving acceptable results. Sio, Sondu, Gucha and Duma also performed well. The global mean method gave acceptable performance for 7 of the 9 study basins. The ensemble regionalisation method provides the possibility to consider parameter uncertainty in the regionalisation. Ensemble regionalisation method performed best with an average departure of 40% from the observed mean annual flows compared to 48% and 60% for proxy-basin and global mean methods, respectively. The departure for calibrated mean monthly flow estimates was 26%.

Kizza, M.; Guerrero, J.; Rodhe, A.; Xu, C.

2012-12-01

366

Diversity of the major capsid genes (g23) of T4-like bacteriophages in the eutrophic Lake Kotokel in East Siberia, Russia.  

PubMed

Numerous studies revealed high diversity of T4-like bacteriophages in various environments, but so far, little is known about T4-like virus diversity in freshwater bodies, particularly in eutrophic lakes. The present study was aimed at elucidating molecular diversity of T4-like bacteriophages in eutrophic Lake Kotokel located near Lake Baikal by partial sequencing of the major capsid genes (g23) of T4-like bacteriophages. The majority of g23 fragments from Lake Kotokel were most similar to those from freshwater lakes and paddy fields. Despite the proximity and direct water connection between Lake Kotokel and Lake Baikal, g23 sequence assemblages from two lakes were different. UniFrac analysis showed that uncultured T4-like viruses from Lake Kotokel tended to cluster with those from the distant lake of the same trophic status. This fact suggested that the trophic conditions affected the formation of viral populations, particularly of T4-like viruses, in freshwater environments. PMID:23539063

Butina, Tatyana V; Belykh, Olga I; Potapov, Sergey A; Sorokovikova, Ekaterina G

2013-07-01

367

Hydrologic monitoring program in Eldridge-Wilde and East Lake Road well-field areas, Pinellas and Hillsborough counties, Florida, 1977 water year  

USGS Publications Warehouse

The observation-well network in the vicinity of the two well fields is described in detail. Data obtained from the network from October 1976 through September 1977, as well as rainfall and pumpage records, are presented and discussed. Below-normal rainfall caused the water table and potentiometric surface of the Floridan aquifer in Eldridge-Wilde well field to recover 2 feet less in September 1977 than in the previous September. Water levels in East Lake Road will field were approximately the same in Spetember of both years. The Southwest Florida Water Management District has established regulatory water-level and water-quality limits in several observation wells. Water levels did not drop below regulatory limits during the year. Water from two deep wells west of Eldridge-Wilde well field exceeded the regulatory limits for chloride concentrations. The position of the 250 milligram per liter chloride line is shown in cross section in the vicinity of Eldridge-Wilde well field in September 1977. Network modifications are proposed that would result in a more comprehensive knowledge of the hydrologic system. (USGS)

Joyner, Boyd F.; Gerhart, James M.

1980-01-01

368

GRACE water storage estimates for the Middle East and other regions with significant reservoir and lake storage  

NASA Astrophysics Data System (ADS)

While GRACE (Gravity Recovery and Climate Experiment) satellites are increasingly being used to monitor water storage changes globally, the impact of spatial distribution of water storage within a basin is generally ignored but may be substantial. In many basins, water may be stored in reservoirs, lakes, flooded areas, small aquifer systems, and other localized regions with sizes typically below GRACE resolution. The objective of this study was to assess the impact of non-uniform water storage distribution on GRACE estimates as basin-wide averages, focusing on surface water reservoirs. Analysis included numerical experiments testing the effect of mass size and position within a basin, and application to the Lower Nile (Lake Nasser) and Tigri-Euphrates (TE) basins as examples. Numerical experiments show that by assuming uniform mass distribution, GRACE estimates may under- or over-estimate basin-average water storage by up to a factor of two, depending on reservoir location and extent. Although their spatial extent may be unresolved by GRACE, reservoir storage may dominate in some basins. For example, it accounts for 95% of seasonal variations in the Lower Nile and 10% in the TE basins. Because reservoirs are used to mitigate droughts and buffer against climate extremes, their influence on interannual time scales can be large, for example accounting for 50% of total water storage decline during the 2007-2009 drought in the TE basin. Effects on GRACE estimates are not easily accounted for via simple multiplicative scaling, but in many cases independent information may be available to improve estimates. Accurate estimation of the reservoir contribution is critical, especially when separating groundwater from GRACE total water storage changes. Because the influence of spatially concentrated water storage - and more generally water distribution - is significant, GRACE estimates will be improved when it is possible to combine independent spatial distribution information with GRACE observations, even when reservoir storage is not a major factor. In this regard, data from the upcoming Surface Water Ocean Topography (SWOT) satellite mission should be an especially important companion to GRACE-FO observations.

Longuevergne, L.; Wilson, C. R.; Scanlon, B. R.; Crétaux, J. F.

2012-10-01

369

Gas isotopic signatures (He, C, and Ar) in the Lake Kivu region (western branch of the East African rift system): Geodynamic and volcanological implications  

NASA Astrophysics Data System (ADS)

On 17 January 2002, the city of Goma was partly destroyed by two of the several lava flows erupted from a roughly N-S oriented fracture system opened along the southern flank of Mount Nyiragongo (Democratic Republic of Congo), in the western branch of the East African rift system. A humanitarian and scientific response was promptly organized by international, governmental, and nongovernmental agencies coordinated by the United Nations and the European Union. Among the different scientific projects undertaken to study the mechanisms triggering this and possible future eruptions, we focused on the isotopic (He, C, and Ar) analysis of the magmatic-hydrothermal and cold gas discharges related to the Nyiragongo volcanic system, the Kivu and Virunga region. The studied area includes the Nyiragongo volcano, its surroundings, and peripheral areas inside and outside the rift. They have been subdivided into seven regions characterized by distinct 3He/4He (expressed as R/Rair) ratios and/or ?13C-CO2 values. The Nyiragongo summit crater fumaroles, whose R/Rair and ?13C-CO2 values are up to 8.73 and from -3.5‰ to -4.0‰ VPDB, respectively, show a clear mantle, mid-ocean ridge basalt (MORB)-like contribution. Similar mantle-like He isotopic values (6.5-8.3 R/Rair) are also found in CO2-rich gas emanations (mazukus) along the northern shoreline of Lake Kivu main basin, whereas the 13?C-CO2 values range from -5.3‰ to -6.8‰ VPDB. The mantle influence progressively decreases in (1) dissolved gases of Lake Kivu (2.6-5.5 R/Rair) and (2) the distal gas discharges within and outside the two sides of the rift (from 0.1 to 1.7 R/Rair). Similarly, ?13C-CO2 ratios of the peripheral gas emissions are lighter (from -5.9‰ to -11.6‰ VPDB) than those of the crater fumaroles. Therefore, the spatial distribution of He and C signatures in the Lake Kivu region is mainly produced by mixing of mantle-related (e.g., Nyiragongo crater fumaroles and/or mazukus gases) and crustal-related (e.g., gas discharges in the Archean craton) fluids. The CO2/3He ratio (up to 10 × 1010) is 1 order of magnitude higher than those found in MORB, and it is due to the increasing solubility of CO2 in the foiditic magma feeding the Nyiragongo volcano. However, the exceptionally high 40Ar*/4He ratio (up to 8.7) of the Nyiragongo crater fumaroles may be related to the difference between He and Ar solubility in the magmatic source. The results of the present investigation suggest that in this area the uprising of mantle-originated f luids seems strongly controlled by regional tectonics in relation to the geodynamic assessment of the rift. These fluids are mainly localized in a relatively small zone between Lake Kivu and Nyiragongo volcano, with important implications in terms of volcanic activity.

Tedesco, D.; Tassi, F.; Vaselli, O.; Poreda, R. J.; Darrah, T.; Cuoco, E.; Yalire, M. M.

2010-01-01

370

Distribution and exploitation of Nile perch Lates niloticus in relation to stratification in Lake Victoria, East Africa  

USGS Publications Warehouse

Stratification restricts habitable areas forcing fish to balance between favourable temperature and minimum dissolved oxygen requirements. Acoustic surveys conducted during the stratified and isothermal periods on tropical Lake Victoria indicated that stratification of temperature and dissolved oxygen (DO) affected vertical distribution of Nile perch. There was higher mean temperature (25.6 ± 0.5 °C) and lower DO (6.4 ± 1.8 mg/l) during stratified period compared to the isothermal period (mean temperature 24.9 ± 0.3 °C; mean DO 7.3 ± 0.6 mg/l). Higher mean densities of Nile perch were recorded in the coastal (0.44 ± 0.03) and deep (0.27 ± 0.02 g/m3) strata during the stratified compared to the isothermal season (coastal: 0.24 ± 0.01; deep: 0.12 ± 0.02 g/m3). In addition, Nile perch density in the upper 0–40 m depth layers in the coastal and deep strata increased by over 50% from the isothermal to the stratified season. Daily landings from 65 motorised fishing boats between October 2008 and September 2010 show higher mean catch (26.29 ± 0.17 kg/boat/day) during stratified compared to the isothermal (23.59 ± 0.15) season. Thermal stratification apparently compresses the habitat available to Nile perch and can potentially result in higher exploitation. Managers should evaluate the potential benefits of instituting closed seasons during the stratified period, and stock assessment models should take into account the seasonal niche compression.

Taabu-Munyaho, A.; Kayanda, Robert J.; Everson, Inigo; Grabowski, Timothy B.; Marteinsdóttir, Gudrún

2013-01-01

371

Mormon Lake Cliffs.  

National Technical Information Service (NTIS)

An establishment of a scientific or educational natural area on the east side of Mormon Lake has been proposed. The area supports an unusual floral assemblage and may be important to vertebrates (especially migrating songbirds) as well. The cliffs include...

E. L. Smith G. L. Bender

1973-01-01

372

Simulation of reproductive rate, prey selection and the survival of pelagic fish of the African Great Lakes  

Microsoft Academic Search

Populations of two prey groups of pelagic mainly zooplanktivorous fish with differing life history strategies, were simulated with a Lotka-Volterra model with predation. Group r fish are r-selected species and have a high rate of biomass increase. These comprise of the small pelagic cyprinids of Lakes Malawi and Victoria and the clupeids of Lake Tanganyika. Group K fish are K-selected

A. B. Thompson

1999-01-01

373

42. Peaks of Otter, Abbott Lake. View across lake to ...  

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

42. Peaks of Otter, Abbott Lake. View across lake to peaks of Outter Lodge, completed in 1964. Construction of the lake got underway in 1964. Looking east-northeast. - Blue Ridge Parkway, Between Shenandoah National Park & Great Smoky Mountains, Asheville, Buncombe County, NC

374

3. View northeast, west facade of Lake Forest (original Forest ...  

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

3. View northeast, west facade of Lake Forest (original Forest Cottage structure incorporated into renamed structure) - Lake Placid Club, Forest Wing, East side of Mirror Lake Drive, North of State Route 86 & Main, North Elba, Essex County, NY

375

51. Third Floor, Lake Forest, west center room, looking west, ...  

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

51. Third Floor, Lake Forest, west center room, looking west, part of original Forest Cottage as of 1901. - Lake Placid Club, Forest Wing, East side of Mirror Lake Drive, North of State Route 86 & Main, North Elba, Essex County, NY

376

4. View southeast, west facade of Lake Forest (original Forest ...  

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

4. View southeast, west facade of Lake Forest (original Forest Cottage structure incorporated into renamed structure) - Lake Placid Club, Forest Wing, East side of Mirror Lake Drive, North of State Route 86 & Main, North Elba, Essex County, NY

377

1. View of Lake Hodges Dam showing the origin of ...  

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

1. View of Lake Hodges Dam showing the origin of the flume at left. View is looking east. - Lake Hodges Flume, Along San Dieguito River between Lake Hodges & San Dieguito Reservoir, Rancho Santa Fe, San Diego County, CA

378

Exploring Subglacial Antarctic Lake Environments  

Microsoft Academic Search

While subglacial lakes have been suspected, and speculated about, for more than 50 years, recent analyses of historical and new data have shown that liquid water environments are common beneath the vast Antarctic Ice Sheet. Airborne radar surveys have now documented more than 145 subglacial lakes, the largest being Lake Vostok located 4 km beneath the vast East Antarctic Ice

J. C. Priscu; M. C. Kennicutt III; R. E. Bell; S. A. Bulat; J. C. Ellis-Evans; V. V. Lukin; J.-R. Petit; R. D. Powell; M. J. Siegert; I. Tabacco

2005-01-01

379

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

380

Planning applications in east central Florida. [resources management and planning, land use, and lake algal blooms in Brevard County from Skylab imagery  

NASA Technical Reports Server (NTRS)

The author has identified the following significant results. Lake Apopka and three lakes downstream of it (Dora, Eustis, and Griffin) are in an advanced state of eutrophication with high algal concentrations. This feature has shown up consistently on ERTS-1 images in the form of a characteristic water color for those lakes. As expected, EREP photographs also show a characteristic color for those lakes. What was not expected is that Lake Griffin shows a clear pattern of this coloration. Personnel familiar with the lake believe that the photograph does, indeed, show an algal bloom. It is reported that the algal concentration is often significantly higher in the southern portion of the lake. What the photograph shows that was not otherwise known is the pattern of the algal bloom. A similar, but less pronounced, effect is seen in Lake Tohopekaliga. Personnel stationed at Kissimmee reported that there was an algal bloom on that lake at the time of the EREP pass and that its extent corresponded approximately to that shown on the photograph. Again, the EREP photograph gives information about the extent of the bloom that could not be obtained practically by sampling. ERTS-1 images give some indication of this algal distribution on Lake Griffin in some cases, but are inconclusive.

Hannah, J. W.; Thomas, G. L.; Esparza, F. (principal investigators)

1973-01-01

381

A water index for rapid mapping of shoreline changes of five East African Rift Valley lakes: an empirical analysis using Landsat TM and ETM+ data  

Microsoft Academic Search

Because of the complicated shorelines, inaccessibility and vast spread of some lakes, information on changing shorelines is difficult to acquire. A new water index (WI) has been applied to quantify changes in five saline and non?saline Rift Valley lakes in Kenya using Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) data. The WI is based on a logical combination

Yashon O. Ouma; R. Tateishi

2006-01-01

382

New Proxies from Loess-Paleosols on Mount Kilimanjaro document Late Pleistocene Megadroughts in East Africa  

NASA Astrophysics Data System (ADS)

Innovative, new proxies from loess and paleosol sediments hold great potential to obtain more quantitative information about paleoclimate changes in terrestrial environments. Here we present results from lipid biomarkers (GDGTs) and hydrogen isotopic measurements on long-chain fatty acids and alkanes that we extracted from 69 paleosol samples from Mt Kilimanjaro, Tanzania (~3°S). The respective soil pit and sediment core at ~2700 m above sea level is radiocarbon-dated to 38.4 ka BP, and probably covers most of the Late Pleistocene, making it one of the longest, continuous, terrestrial archives in the East African tropics. Our compound-specific deuterium measurements show lowest ?D values from ~9 to 5 ka in the Early/Middle Holocene, consistent with regional evidence for an “African Humid Period,” followed by a shift towards more arid conditions during the Late Holocene (~5‰ shift). The Younger Dryas is characterized by a ?D enrichment (=aridity) of ~15‰ compared to the Early/Middle Holocene, almost reaching LGM values (~20‰ shift). The enrichment during the LGM is, however, significantly smaller than the 50‰ change as observed in Lake Tanganyika further southwest. At present it is not possible to determine whether these differences result from geographic variations in precipitation and humidity, or isotopic distillation processes along the vapor transport trajectories across East Africa. Much more arid conditions (~40‰ enrichment) can be inferred for the paleosols older than ~60 ka. Although further dating efforts are required to determine the exact timing, this corroborates earlier findings from African lakes that suggested ‘megadroughts’ occurred during Marine Isotope Stages 5 and 4. Acknowledging the general perception that precipitation in East Africa is strongly controlled by ITCZ positioning, we highlight the role of (strong) eccentricity in modulating the precessional forcing, which - in combination with high-latitude glacial boundary conditions - may have caused extreme amplitudes of seasonal ITCZ migration and corresponding variability of climate conditions in the tropics on orbital timescales. Counter-intuitively, our GDGT temperature reconstruction based on MBT and CBT indices shows temperatures ~5°C warmer throughout the LGM and MIS3 than during the Holocene. Although local soil temperature may be affected by vegetation and/or cloud cover, such results advice caution and highlight the necessity to further validate and develop these new biomarker proxies.

Zech, R.; Huang, Y.; Russell, J. M.; Tarozo, R.; Gao, L.; Hemp, A.; Zech, W.

2009-12-01

383

Introduction to Librarianship, with Special Reference to the Tanganyika Library Service.  

National Technical Information Service (NTIS)

Since the inception of the Tanganyika Library Service in 1963, in-service training has been run for newly recruited library staff. All along, however, it has been difficult to find suitable reading material for the training programme. Hence the need for w...

1971-01-01

384

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 fr