Natural Lakes (natural + lake)

Distribution by Scientific Domains


Selected Abstracts


Detection and quantification of microcystins from cyanobacteria strains isolated from reservoirs and ponds in Morocco

ENVIRONMENTAL TOXICOLOGY, Issue 1 2002
B. Oudra
Abstract In Morocco, the occurrence of toxic cyanobacteria blooms is confirmed in some water bodies used for recreational and/or as drinking water reservoirs. According to WHO recommendations, the establishment of a monitoring program for microcystins is a necessity. This paper presents toxicological studies of 19 toxic cyanobacteria strains of Microcystis, Synechocystis, Pseudanabaena, and Oscillatoria. These strains were isolated from various water bodies including natural lakes, reservoirs, and ponds located in central regions of Morocco. The isolation, culture, and biomass production of these strains was made on Z8 or BG13 media under laboratory controlled conditions. The hepatotoxicity of cyanobacterial lyophilized material was confirmed by mouse bioassays. The amount of microcystins produced by each strain was determined by the enzyme-linked immunosorbent assay (ELISA). The detection and identification of microcystin variants was performed by high performance liquid chromatography (HPLC) with photodiode array detection. Almost all strains showed medium to high toxicity, the estimated LD50 i.p mice bioassay ranged between 28 to 350 mg/kg body weight. The concentrations of microcystins varied between 2.16 to 944 ,g/g and 26.8 to 1884 ,g/g dry weight determined by ELISA and HPLC, respectively. The screening of bloom-forming and microcystin producer cyanobacteria strains in these fresh water bodies leads us to propose the need for the establishment of a survey of cyanobacteria and a cyanotoxin-monitoring program. © 2002 by Wiley Periodicals, Inc. Environ Toxicol 17: 32,39, 2002 [source]


Water outflow as a cause of changes in trophic conditions for zooplanktivorous fish in reservoirs

FISHERIES MANAGEMENT & ECOLOGY, Issue 1-2 2000
L. Pehlivanov
The seasonal changes and vertical distribution of zooplankton, the export of zooplankters by outflow through water management installations, and the feeding of zooplanktivorous fish were studied in two Bulgarian reservoirs. In a bottom-draining reservoir, planktonic crustacea >,1.0 mm were found to be selectively exported as a result of their diurnal vertical migrations. Increases in water outflow for irrigation resulted in a decrease in total zooplankton abundance, as well as changes in zooplankton size and species composition at the beginning of the summer. At the same time, major changes occurred in the feeding patterns of bleak, Alburnus alburnus (L.), and juvenile pikeperch, Stizostedion lucioperca (L.), the principal zooplanktivores in this reservoir. It is easy for bleak to switch to feeding on an alternative food, but a lack of available large prey organisms is suggested as the main cause of the downstream movement of pikeperch juveniles. In a surface-draining reservoir, the pattern of zooplankton export corresponded to those in natural lakes. Discharged water carried with it mainly small-sized epilimnetic zooplankton from the most numerous groups (i.e. rotifers, juvenile copepods and cladocerans) in the reservoir. Furthermore, outflow exports represent a relatively small part of total zooplankton number, and thus, do not disturb the natural zooplankton succession, and changes in abundance and composition Coincidental changes in the trophic responses for zooplanktivores (mainly juvenile cyprinids and percids) were not found. [source]


The influence of geographic and morphometric factors on the distribution of water bird species in small high altitude tropical man made reservoirs, Central Rift Valley, Kenya

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2010
Francis Mwaura
Abstract Variability in waterfowl characteristics among eight high altitude (2040,2640 m) small shallow (0.065,0.249 km2; 0.9,3.1 m) reservoirs in the escarpment zone along the central rift valley in Kenya between Naivasha and Nakuru towns were studied between 1998 and 2000. The aim of the study was to establish whether the geographic status of small reservoirs in terms of altitude and surface gradient can affect the characteristics of their birdlife in terms of bird counts and species numbers. The study also aimed at establishing whether reservoir bird counts and species number can be predicted by reservoir morphometric factors especially water depth, surface area, length of shoreline and area-shoreline ratio. The other aim was to determine the influence of local environment especially distance from the nearest natural lakes, and house density on the birdlife. The findings showed that geographic location of the reservoirs in terms of altitude and landscape had a strong influence on birdlife whereby reservoirs in higher altitude and flat plateau landscape were found to support higher bird species and counts. Larger and deeper reservoirs were richer in water bird species but small and shallow reservoirs were superior in terms of both bird species and counts. Reservoirs with more coarse, irregular and highly erratic shorelines had higher species number than those with smooth and well-rounded shorelines. The reservoir birdlife was found to be influenced by the number of farm houses near the waterbodies and also the distance from the nearby rift valley lakes. The results showed that both geographic and morphometric considerations are necessary in the establishment of new reservoirs especially for utilization in birdlife conservation and ecotourism. Résumé Entre 1998 et 2000, nous avons étudié la variabilité des caractéristiques de l'avifaune aquatique de huit petits réservoirs peu profonds (0,065,0,249 km²; 0,9,3,1 m) de haute altitude (2040,2640 m) dans la région de l'escarpement de la Rift Valley située entre Naivasha et Nakuru, au Kenya. L'objectif de cette étude était d'établir si le statut géographique de réservoirs petits en termes d'altitude et de gradient de surface peut affecter les caractéristiques de leur avifaune en ce qui concerne le nombre d'oiseaux et d'espèces. L'étude visait aussi àétablir si l'on peut prédire la densité des oiseaux et le nombre d'espèces d'après les facteurs morphométriques du réservoir, et en particulier la profondeur de l'eau, la superficie de la surface, la longueur des berges et le rapport entre la superficie et la longueur de berges. L'autre objectif était de déterminer plus spécialement l'influence de la distance par rapport aux lacs naturels les plus proches et celle de la densité des habitations sur l'avifaune. Les résultats ont montré que la situation géographique des réservoirs en termes d'altitude et de paysage avait une forte influence sur l'avifaune, en ceci que les réservoirs de plus haute altitude et situés dans un paysage de plateau régulier accueillaient un plus grand nombre d'espèces et une plus forte densité d'oiseaux. Les réservoirs plus étendus et plus profonds étaient plus riches en espèces d'oiseaux d'eau, et les réservoirs plus petits et moins profonds étaient supérieurs en termes de nombre d'espèces d'oiseaux et de densité. Les réservoirs dont les berges étaient accidentées, instables et irrégulières avaient un nombre d'espèces plus élevé que ceux dont les berges étaient bien délimitées et planes. On a découvert que l'avifaune d'un réservoir était influencée par le nombre d'exploitations agricoles situées près du plan d'eau et aussi par la distance qui le séparait des lacs les plus proches de la Rift Valley. Les résultats ont montré qu'il faut tenir compte des données géographiques et morphométriques pour établir de nouveaux réservoirs, spécialement s'ils sont destinés à la conservation de l'avifaune et au tourisme. [source]


The effects of water retention time and watershed features on the limnology of two tropical reservoirs in Brazil

LAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 4 2008
Maria Carolina S. Soares
Abstract Although reservoirs are similar to natural lakes in many respects, such driving forces as water retention time and watershed features can play important roles in the limnology of manmade lakes. With the goal of investigating how these factors influence the limnology of tropical reservoirs, physical and chemical variables were measured at four sampling sites in two reservoirs in southern Brazil, from June 2002 to June 2003. Funil Reservoir is located in one of the most-populated areas in the country, in the Paraíba do Sul river basin, which drains and drastically influences the water quality of the reservoir. In contrast, Lajes Reservoir is located in a well-preserved area, with its water retention time varying from six to 30 times longer than for Funil Reservoir. Funil Reservoir is a turbid (median euphotic zone = 4.3 m), eutrophic reservoir (median total phosphorus (TP) = 3.1 µm), with a high phytoplankton biomass (median chlorophyll- a concentration = 10.0 µg L,1). In contrast, Lajes Reservoir is a transparent (median euphotic zone = 9.2 m), mesotrophic water system (median TP = 1.0 µm), with a low phytoplankton biomass (median chlorophyll- a = 1.9 µg L,1). Both reservoirs were stratified during the summer months, but isothermy was only observed in Funil Reservoir. Because of its short water retention time, Funil Reservoir is a much more dynamic system than Lajes Reservoir, with a pronounced temporal pattern related to changes in its water column and its phytoplankton biomass. Spatial heterogeneity is more evident in Lajes Reservoir, mainly as a consequence of its location in a preserved area, long water retention time and the presence of net cages for fish culture in the waterbody. The typical spatial zonation found in reservoirs, related to nutrient sedimentation and light availability, however, is more evident in Funil Reservoir than in Lajes Reservoir. Despite the similarities between these two water systems, which are in the same geographical region with similar climate, and are comparable in size, the distinct watershed features and water retention time are responsible for marked differences between these reservoirs. [source]


The transcriptomics of life-history trade-offs in whitefish species pairs (Coregonus sp.)

MOLECULAR ECOLOGY, Issue 7 2008
J. ST-CYR
Abstract Despite the progress achieved in elucidating the ecological mechanisms of adaptive radiation, there has been little focus on documenting the extent of adaptive differentiation in physiological functions during this process. Moreover, a thorough understanding of the genomic basis underlying phenotypic adaptive divergence is still in its infancy. One important evolutionary process for which causal genetic mechanisms are largely unknown pertains to life-history trade-offs. We analysed patterns of gene transcription in liver tissue of sympatric dwarf and normal whitefish from two natural lakes, as well as from populations reared in controlled environments, using a 16 006-gene cDNA microarray in order to: (i) document the extent of physiological adaptive divergence between sympatric dwarf and normal species pairs, and (ii) explore the molecular mechanisms of differential life history trade-offs between growth and survival potentially involved in their adaptive divergence. In the two natural lakes, 6.45% of significantly transcribed genes showed regulation either in parallel fashion (2.39%) or in different directions (4.06%). Among genes showing parallelism in regulation patterns, we observed a higher proportion of over-expressed genes in dwarf relative to normal whitefish (70.6%). Patterns observed in controlled conditions were also generally congruent with those observed in natural populations. Dwarf whitefish consistently showed significant over-expression of genes potentially associated with survival through enhanced activity (energy metabolism, iron homeostasis, lipid metabolism, detoxification), whereas more genes associated with growth (protein synthesis, cell cycle, cell growth) were generally down-regulated in dwarf relative to normal whitefish. Overall, parallelism in patterns of gene transcription, as well as patterns of interindividual variation across controlled and natural environments, provide strong indirect evidence for the role of selection in the evolution of differential regulation of genes involving a vast array of potentially adaptive physiological processes between dwarf and normal whitefish. Our results also provide a first mechanistic, genomic basis for the observed trade-off in life-history traits distinguishing dwarf and normal whitefish species pairs, wherein enhanced survival via more active swimming, necessary for increased foraging and predator avoidance, engages energetic costs that translate into slower growth rate and reduced fecundity in dwarf relative to normal whitefish. [source]