Showing papers by "Ghent University published in 1991"
TL;DR: Evidence is provided that E-cadherin acts as an invasion suppressor molecule in epithelial tumor cell lines of dog kidney or mouse mammary gland origin.
1,706 citations
TL;DR: Identification to species level showed that Enterococcus faecalis and Ent.
Abstract: Identification to species level showed that Enterococcus faecalis and Ent. faecium largely dominated the enterococcal and streptococcal gut flora of 1-d-old chicks. Enterococcus faecalis was rare in 3- to 5-week-old broilers. Two species, Ent. faecium and Streptococcus alactolyticus, were isolated from nearly all broilers examined. Enterococcus hirae and Ent. durans were found in the small intestines of this category of poultry.
In layers and parent stock of over 12 weeks of age, Ent. cecorum dominated with Strep. alactolyticus ranking next. Other species were isolated irregularly. Enterococcus avium and Ent. gallinarum, originally described from chickens, were rarely found. These species did not appear to belong to the normal intestinal flora of poultry.
200 citations
TL;DR: In this article, a statistical yield analysis for gain and index-coupled distributed feedback (DFB) laser structures is presented, allowing a comparison of their single longitudinal mode (SLM) yield capabilities.
Abstract: A statistical yield analysis is presented for gain- and index-coupled distributed feedback (DFB) laser structures, allowing a comparison of their single longitudinal mode (SLM) yield capabilities. For the yield calculations, the threshold gain difference and the longitudinal spatial hole burning (SHB) are taken into account. By comparing the experimental and theoretical yield of index-coupled DFB lasers, the significance of SHB for correct yield predictions is illustrated. For the purpose of comparison, yield calculations for various lambda /4-shifted DFB lasers (with low facet reflectivities) are presented. The most emphasis, however, is on partly gain-coupled DFB lasers. Estimations of practical gain coupling coefficient values for gain and for loss gratings are discussed. >
152 citations
TL;DR: Several aspects of the response to toxicants using a standardized toxicity test with the freshwater rotifer Brachionus calyciflorus are described, indicating very consistent test sensitivity and a practical limit on toxicant exposure.
148 citations
TL;DR: Chloroplasts of shootlets grown in a medium without sucrose contained numerous, large plastoglobuli and were lacking in starch granules, which might be used by the in vitro shootlets during the acclimation period.
Abstract: Shootlets of Rosa multiflora L. cv. Montse were cultured in vitro with four different levels of sucrose (0, 1, 3 and 5%). Chloroplasts of shootlets grown in a medium without sucrose contained numerous, large plastoglobuli and were lacking in starch granules. The size and number of starch granules increased with the level of sucrose in the culture medium. Starch content in leaves of shootlets grown with 5% sucrose was higher (ca 1, 3%) than those grown with 3% (ca 0, 45%) and 1% sucrose (ca 0, 27%). Starch might be used by the in vitro shootlets during the acclimation period.
129 citations
TL;DR: Counts of E. coli/faecal streptococci and enterococci were made on faecal specimens from human and animal origin and urban raw sewage waters, with microtiter plates containing selective substances, to distinguish human from animal origin ofFaecal pollution is questionable.
Abstract: Counts of Escherichia coli, faecal streptococci and enterococci were made on faecal specimens from human and animal origin and urban raw sewage waters, with microtiter plates containing selective substances. Escherichia coli was more numerous than faecal streptococci and enterococci in 80% of the samples regardless of the origin. Consequently the use of the ratio E. coli/faecal streptococci to distinguish human from animal origin of faecal pollution is questionable. Enterococcus faecalis was predominant in human and poultry faeces, Streptococcus bovis was typical of the bovine faeces and to a lesser extent also of pig faeces whereas Enterococcus durans, Ent. hirae and Ent. faecium did not characterize any faecal source. Streptococcus bovis could be distinguished in the mictrotiter plate by its inability to reduce triphenyl tetrazolium chloride (TTC) in the medium.
122 citations
TL;DR: In this paper, an examination of the state of the art of nonlinear optical polymeric materials in view of their potential advantages is made, and it is shown that these organic materials have many attractive features compared to LiNbO/sub 3/ and III-V semiconductors with regard to their use in integrated optic circuits, especially since the level of integration is ever increasing.
Abstract: An examination is made of the state of the art of nonlinear optical polymeric materials in view of their potential advantages. It is shown that these organic materials have many attractive features compared to LiNbO/sub 3/ and III-V semiconductors with regard to their use in integrated optic circuits, especially since the level of integration is ever increasing. Considering more specifically electro-optic devices, a description is given of some of the theoretical background and basic properties. These polymers have already demonstrated a very high and extremely fast electro-optic effect compared to LiNbO/sub 3/. It is also shown how low-loss waveguides can be fabricated by using easy techniques such as direct UV bleaching. The performance of phase modulators, Mach-Zehnder interferometers, and 2*2 space switches built with such polymers is already very promising. >
115 citations
TL;DR: The sensitivity of four different enrichment procedures to detect Listeria monocytogenes in the presence of high levels of Streptococcus faecalis was investigated and the so-called cold enrichment techniques were found to be unsatisfactory for samples from natural environments.
Abstract: B. VAN RENTERGHEM, F. HUYSMAN, R. RYGOLE AND W. VERSTRAETE. 1991. The sensitivity of four different enrichment procedures to detect Listeria monocytogenes in the presence of high levels of Streptococcus faecalis was investigated. Defined mixed cultures of Strep. faecalis and L. monocytogenes gave better results with one-stage enrichment techniques. For manure samples, however, two-stage enrichment techniques gave the best performance. The so-called cold enrichment techniques were found to be unsatisfactory for samples from natural environments. The following materials were examined for the presence of L. monocytogenes: fresh pig faeces (16% positive), fresh cattle faeces (20% positive), stored liquid manure (0% positive), manured soil samples (0% positive) and ground water samples (5% positive). After 3 weeks of storage L. monocytogenes could be detected in only one of the initially nine positive fresh facces samples. Two months after inoculation of stored liquid pig manure, stored liquid cattle manure and soil with L. monocytogenes, this bacterium could not be traced in any of these materials. Radishes (Raphanus sativus) and carrots (Daucus carota), sown in soil inoculated with L. monocytogenes, were gathered after 3 months and examined for the presence of L. monocytogenes. Three of six radish samples were found to be positive. Remarkably, however, all carrot samples (six) were free of L. monocytogenes.
101 citations
TL;DR: Meiobenthos densities were measured along a Mediterranean deep-sea transect off Calvi (Corsica) and in an adjacent canyon as mentioned in this paper, and they were significantly and positively correlated with CPE values.
Abstract: . Meiobenthos densities (excluding hard-shcllcd foraminifcrans) were compared along a Mediterranean deep-sea transect off Calvi (Corsica) and in an adjacent canyon. Chloroplastic Pigment Equivalent values (CPE) provided an estimate of the amount of primary production reaching the bottom.
The stations along the transect were characterized by a low CPE content of the sediment, decreasing with increasing station depth. CPE values in the canyon were much higher, which probably resulted from import of material from the adjacent bay of Calvi. Similarly, meiobenthos densities along the transect were much lower than at comparable depths along the canyon.
Meiobenthos density was significantly and positively correlated with CPE values.
Nematodes were the most abundant taxon at all stations, followed by copepods + nauplii and the soft-shelled foraminiferans. The meiobenthos was most abundant in the upper half centimeter. Nematode and foraminiferan densities tended to decline less rapidly with increasing depth into the sediment. Specimens belonging to the recently described phylum Loricifera, larvae of the parasitic crustacean class Tantulocarida, and fragments of an infaunal Xenophyophoria (large protozoans) are reported for the first time from the Mediterranean.
97 citations
TL;DR: The reaction mechanism of the non-specific endo-1,4-beta-glucanase from Trichoderma reesei QM 9414 (endoglucan enzyme I) was investigated using both reducing-end3H-labelled and universally 14C-labelling cellooligosaccharides, as well as reducing- end3H
Abstract: The reaction mechanism of the non-specific endo-1,4-beta-glucanase from Trichoderma reesei QM 9414 (endoglucanase I) was investigated using both reducing-end3H-labelled and universally 14C-labelled cellooligosaccharides, as well as reducing-end3H-labelled xylooligosaccharides. The bond cleavage frequencies of cellooligosaccharides proved to be dependent upon the substrate concentration, especially in the case of cellotriose. In addition to simple hydrolytic cleavage, the enzyme catalyzes reactions along alternative pathways, including transglycosylations leading to products larger than the substrate. Some of these pathways were shown to be reversible. During cellotriose or cellopentaose degradation, substrate resynthesis was demonstrated by incorporation of added radioactive D-glucose or cellobiose. The endoglucanase I is active on xylan and xylooligosaccharides, but less than on soluble cellulose derivatives (e.g. hydroxyethylcellulose) and cellooligosaccharides. The fact that for these different types of substrates the same active site is operative is proven by the ability of the enzyme to utilize cellooligosaccharides and xylooligosaccharides as both glycosyl donors and acceptors. The mixed substrate reactions lead to products composed of D-glucosyl and D-xylosyl residues. The kinetic parameters for cellooligosaccharide degradation can be used for the description of an extended substrate binding site. Of the four putative glycosyl subsites, -II and +II show the highest affinities, 16.7 kJ.mol-1 and 7.1 kJ.mol-1, respectively.
96 citations
TL;DR: The aim of this review is to demonstrate why the management of compliance, although not an explicit feature of the rules of Good Clinical Practice, is essential to the successful conduct of clinical trials and in correct interpretation of the results.
Abstract: The aim of this review is to demonstrate why the management of compliance, although not an explicit feature of the rules of Good Clinical Practice, is essential to the successful conduct of clinical trials and in correct interpretation of the results. Methods to measure compliance in randomized clinical trials are also described. The relevant literature was retrieved by a manual search of the Cumulated Index Medicus 1975–1989 and a MEDLINE computer search of publications in 1990 using the Medical Subject Headings “patient compliance” and “clinical trials”. All retrieved articles are discussed. Research into patient compliance has stagnated because of the lack of a “gold” standard of measurement. Nevertheless, management of compliance at the different stages of clinical trials is necessary; at trial design, compliance should be taken into account in sample size calculations; during the conduct of a trial, compliance should be monitored in order to safeguard the power of the study; and in interpretation of trial results, compliance data are helpful both in order to avoid erroneous conclusions and to enrich the value of the data. Compliance should be measured in all limbs of randomized trials, including the placebo limb, without breaking trial blinding. A classification of compliance behaviour into six types (complier, partial complier, overuser, erratic user, partial dropout and dropout) is proposed, based on the changes in the risk-benefit ratio produced by non-compliance. The use of deuterium oxide, low dose phenobarbitone (2 mg per day), digoxin (2,2 μg per day) and the new electronic monitoring devices are suitable methods for measurement in clinical trials.
TL;DR: The precision and sensitivity of the method in the low-dose range could be improved by the knowledge of individual pre-irradiation baseline values and an increase of the number of cells scored by automation of the technique.
Abstract: The dose response of the number of micronuclei in cytokinesis-blocked lymphocytes after in-vitro irradiation of whole blood with x rays in the dose range 0-4 Gy was studied for a heterogeneous population of 10 donors. One thousand binucleated cells were systematically scored for micronuclei. A linear-quadratic dose dependency of the micronucleus yields was observed. The data were used to derive the accuracy of the dose assessment with the technique in case of a radiation accident. It was shown that for doses of 2 Gy and higher, the uncertainty of the dose was predominantly due to interindividual differences in the x-ray-induced micronucleus yields. At the 95% confidence level, doses lower than 0.3 Gy could not be unequivocally detected with the cytokinesis-blocked micronucleus assay due to the variability of the baseline micronucleus frequency within the donor population and the poor statistical accuracy when scoring 1,000 cells. The precision and sensitivity of the method in the low-dose range could be improved by the knowledge of individual pre-irradiation baseline values and an increase of the number of cells scored by automation of the technique.
TL;DR: In this paper, a study on 512 38-year-old European men selected from 6 different towns was conducted and the authors concluded that indicators of body fat distribution are associated with unfavorable risk profiles for cardiovascular disease in European men covering a large geographical and cultural variety and a wide range of body measurements and cardiovascular risk factors.
TL;DR: In this article, the effects of the urease inhibitors hydroquinone (HQ), phenyl phosphorodiamidate (PPDA), and N-(n-butyl) thiophosphoric triamide (NBPT) in retarding the hydrolysis of urea, in the evolution of mineral N, and in reducing NH3 loss through volatilization, under aerobic and waterlogged conditions, both at 25°C.
Abstract: Two laboratory incubation experiments were conducted to study the effects of the urease inhibitors hydroquinone (HQ), phenyl phosphorodiamidate (PPDA), and N-(n-butyl) thiophosphoric triamide (NBPT) in retarding the hydrolysis of urea, in the evolution of mineral N, and in reducing NH3 loss through volatilization, under aerobic and waterlogged conditions, both at 25°C. NBPT generally exceeded PPDA and HQ in the ability to delay urea hydrolysis and NHinf4sup+accumulation under aerobic conditions, whereas PPDA retarded these activities more effectively under anaerobic conditions. HQ was less effective than the other two urease inhibitors. Under aerobic conditions, 20% of the applied urea was lost through NH3 volatilization after 5 days in the system without an inhibitor. With the addition of HQ and PPDA, the volatilization was delayed by 1 day but not eliminated. NBPT effectively decreased the NH3 loss, from 20 to 3% of the applied urea. A more severe N loss (40%) occurred in the waterlogged system. HQ had little effect on NH3 volatilization. PPDA decreased the NH3 loss from 40 to less than 20% of the applied urea. The effectiveness of NBPT decreased under anaerobic conditions. It was concluded that urease inhibitors can reduce NH3 volatilization following the application of urea. However, environmental conditions might have an important influence on the effectiveness of these inhibitors.
TL;DR: In this article, the capacitance of a simplified model of a via hole is calculated based on an integral equation approach for the surface charge density, and it is found that the via capacitance is proportional to the square root of its height, at least for the range of realistic geometrical data considered.
Abstract: The capacitance of a simplified model of a via hole is calculated based on an integral equation approach for the surface charge density. The formulation of the problem is based on an integral equation for the surface charges combined with an analytical solution at the ground plane opening. The finite ground plane thickness is explicitly taken into account. Numerical data are obtained for a large range of realistic geometrical data. The relative importance of the contribution to the total capacitance coming from the ground plane opening is explicitly evaluated. It is found that the via capacitance is proportional to the square root of its height, at least for the range of geometrical data considered. >
TL;DR: Electrotransformation of Rhodococcus fascians by non‐replicating plasmids containing a suitable resistance marker resulted in stable transformants by integration of these constructs at various sites in the genome, thereby generating different mutations.
Abstract: Electrotransformation of Rhodococcus fascians by non-replicating plasmids containing a suitable resistance marker resulted in stable transformants by integration of these constructs at various sites in the genome, thereby generating different mutations. Tagged genes could be isolated in Escherichia coli owing to the presence of a CoIE1 replicon and an ampicillin resistance gene in the inserted sequences. Southern analysis and nucleotide sequencing revealed that recombination can occur at defined locations in the plasmid, while no site preference for target sequences could be detected. Low homology between the recombining sequences indicates illegitimate recombination. The specificity of the plasmid sites could be explained by assuming a linear recombination intermediate, generated by cleavage of the transformed plasmid.
TL;DR: In this paper, the authors studied the role of the European venture capital industry in the major European countries and found that the most important group of investors are the banks, the pension funds, and the insurance companies.
TL;DR: This work cross-linked actobindin and actin in the 1:1 complex, using the zero-length cross-linker 1-ethyl-3(3-dimethylaminopropyl)carbodiimide, and found a connection between one or more of the acidic residues 1,2, or 3 of actin and Lys-16 and Lys
TL;DR: A comparison of the sensitivity of the rotifer test to that of sea urchin (Arabacia punctulata) early embryo, sea urnin sperm cell, Microtox®, and Mysidopsis bahia tests revealed comparability for several compounds, however, no species is consistently the most sensitive to all compounds.
Abstract: As part of the development of a standardized acute toxicity test, the effect of cyst age, strain, temperature, and exposure time on the toxicity of 21 chemicals to the estuarine rotifer Brachionus plicatilis was investigated. Toxicity was chemical specific, with LC50s ranging from 0.061 mg · L−1 for mecury to 598 mg · L−1 for 2,4-dichlorophenoxyacetic acid. Intralaboratory coefficients of variation averaged 11%, at least three times lower than for other aquatic invertebrate acute tests. The age of rotifer cysts stored up to 27 months had no effect on the sensitivity of test animals, but significant differences in sensitivity were detected among rotifer strains. Test temperatures of 25, 30, and 35°C generally yielded lower LC50s than at 20°C. LC50s decreased by 80–90% for cadmium and pentachlorophenol when toxicant exposure time was increased from 24 to 72 h. Life table analysis of rotifer survival in the controls revealed that 72 h is the longest acute test possible without feeding. A comparison of the sensitivity of the rotifer test to that of sea urchin (Arabacia punctulata) early embryo, sea urchin sperm cell, Microtox®, and Mysidopsis bahia tests revealed comparability for several compounds. However, no species is consistently the most sensitive to all compounds.
TL;DR: It is postulated that pyoverdin production plays an important role in plant growth stimulation, but is not the only factor involved, as root than soil bacteria were able to use Fe-desferal or Fe-pyoverdin to overcome iron-shortage.
Abstract: The P. aeruginosa-related plant growth beneficial strain 7NSK2 was able to increase the yield of barley, wheat, 4 varieties of maize, cucumber, spinach and corn salad from 10 to 24%. Siderophore deficient mutants of 7NSK2, obtained by Tn5-mutagenesis were never able to stimulate plant growth, although their root colonizing capacities were not impaired. The effect of 7NSK2 inoculation on cucumber dry weight was more pronounced in EDDHA-treated soil ( + 18%) than in the control soil ( + 10%). Soil inoculation with 7NSK2 in a FeEDDHA-treated soil had no effect on plant growth.
TL;DR: Using hybrid gene constructions, it is shown that transcriptional readthrough into a downstream gene with opposite orientation substantially reduces expression of this gene both in transient expression and in transgenic plants.
TL;DR: A positive correlation between anti-invasive activity and linking of t-PA to laminin is found and suggests that catechins and citrus flavonoids inhibit invasion in vitro by different mechanisms.
Abstract: Catechins, a group of flavonoid molecules, inhibit invasion of mouse MO4 cells into embryonic chick heart fragments in vitro. The anti-invasive effects can be ranked as follows: (+)-catechin greater than (-)-epicatechin greater than 3-O-methyl-(+)-catechin greater than 3-O-palmitoyl-(+)-catechin. Most of the catechins are unstable in cell culture media, and their spontaneous rearrangement products tend to bind to extracellular matrix (ECM). Due to these interactions proteases such as tissue-type plasminogen activator (t-PA) are linked to the ECM glycoprotein laminin. This leads to a partial inactivation of the enzyme. Within the group of catechins we found a positive correlation between anti-invasive activity and linking of t-PA to laminin. Citrus flavonoids are also anti-invasive in vitro (tangeretin greater than nobiletin greater than hesperidin = naringin). However, these stable molecules show poor affinity for ECM, and do not link enzymes to laminin. These data suggest that catechins and citrus flavonoids inhibit invasion in vitro by different mechanisms.
TL;DR: A patient with some unusual features suggestive of a new variant of the 'carbohydrate deficient glycoproteins syndrome' is presented, which was reported on in five girls manifesting with severe neurological disturbances, variable hepatomegaly, abnormal subcutaneous fat depositions and skeletal anomalies.
Abstract: Recently, Jaeken and colleagues reported on an inherited multisystemic syndrome in five girls manifesting with severe neurological disturbances, variable hepatomegaly, abnormal subcutaneous fat depositions and skeletal anomalies (Jaeken et al., 1980, 1984, 1987, 1989; Stibler and Jaeken, 1990). The neurological picture was characterized by moderate to severe psychomotor retardation, alternating internal strabismus, hypotonia, hyporeflexia and ataxia. Biochemical investigations showed a number of abnormalities such as tubular proteinuria, slightly increased serum transaminases, hypoalbuminaemia, hypo-fl-lipoproteinaemia and decreased serum thyroxin-binding globulin. Moreover, there was retinitis pigmentosa, cerebellar hypotrophy and electrophysiological evidence for a peripheral neuropathy. Abnormal lamellar inclusions were found in the tysosomes of some Schwann cells and also of liver tissue. Additional investigations in four patients revealed deficiencies of sialic acid, galactose and N-acetylglucosamine of plasma glycoproteins. Enzymatic analysis of serum suggested a deficiency of a n N-acetylglucosaminyltransferase, one of the Golgi enzymes intervening in tl~e carbohydrate processing of glycoproteins (Jaeken et at., 1987). Subsequently, Kristiansson. and colleagues (1989) reported a similar condition in seven Swedish patients, and at the Vth International Congress on Inborn Errors of Metabolism (Asilomar, 1-5 JUne 1990) we presented 26 patients and called this the 'carbohydrate deficient glycoproteins syndrome' (Jaeken et al., 1990). In this paper we present a patient with some unusual features suggestive of a new variant.
TL;DR: S. suis was found to be biochemically more heterogenous than originally described and a simple scheme which uses the amylase and the Voges-Proskauer (acetoin) reactions for the identification of S. sui is proposed.
TL;DR: The view that sellar and sphenoidal sealing with fibrin glue instead of muscle or fat tissue does not raise the incidence of postoperative rhinorrhea is supported.
Abstract: Fibrin glue (Beriplast, Behring or Tissucol, Immuno) was used for 126 sublabial transseptal transsphenoidal operations in 119 patients from April 1981 to March 1987 in a variety of sellar pathologies together with septal bone and spongycel to seal the sellar floor and the anterior wall of the sphenoid sinus.
TL;DR: Daphnia magna clones, isolated from different natural populations, were inbred and crossbred and some aspects of the heredity of the phototactic behaviour, quantified by an index, were analysed.
Abstract: Daphnia magna clones, isolated from different natural populations, were inbred and crossbred. Some aspects of the heredity of the phototactic behaviour, quantified by an index, were analysed. Heritability in the broad sense was determined for several assemblages of clones through calculation of the clonal repeatability. Heritability sensu strictu was determined by offspring-parent regressions. Frequency distributions of a phototactic index of several inbred and crossbred families are given.
TL;DR: In this article, the second-order harmonic distortion in the amplitude modulation-response of Fabry-Perot and distributed feedback (DFB) lasers is analyzed for modulation frequencies ranging from a few megahertz to well beyond the resonance frequency of the relaxation oscillation.
Abstract: Numerical calculations of the second-order harmonic distortion in the amplitude modulation-response of Fabry-Perot, and distributed feedback (DFB) lasers are presented, and the influence of several nonlinearities, such as longitudinal spatial hole burning, gain suppression, and relaxation oscillations are considered. This analysis is valid for modulation frequencies ranging from a few megahertz to well beyond the resonance frequency of the relaxation oscillation. The distortion of Fabry-Perot lasers for which the effects of spontaneous emission and gain suppression can be clearly illustrated is investigated. The distortion of DFB lasers where the emphasis is on the influence of spatial hole burning and its combination with other nonlinearities is discussed. Various effects are discussed. >
TL;DR: In this article, an enhanced method to calculate the C, L, and R of a multiconductor bus in a multilayered medium is presented, where surface charge discontinuities are explicitly taken into account which results in reduced computation time.
Abstract: An enhanced method to calculate the C, L, and R of a multiconductor bus in a multilayered medium is presented. Different board technologies, conductors of complicated shape, and conductors embedded in different layers can be handled without loss of accuracy or substantial increase in CPU time compared with existing simulation techniques. Correct determination of skin effect losses is shown to depend critically on surface charge modeling. Surface charge discontinuities are explicitly taken into account which results in reduced computation time. A further reduction of computation time is obtained by a particular treatment of the calculation of the Green's function. >
TL;DR: Comparative HPLC fingerprint analysis of the alkamides from natural plant source, control tissues, and transformed callus and roots indicated that transformedCallus and hairy roots might be a promising source for continuous and standardized production of the dodeca-2E,4E,8Z,10E/Z-tetraenoic acid isobutylamide and related amides.
Abstract: Echinacea purpurea seedlings were inoculated with several Agrobacterium rhizogenes strains in order to obtain hairy roots. Infection with A. rhizogenes strains LMG63 and LMG150 resulted in callus formation. Upon infection with strains ATCC 15834 and R1601 hairy roots were obtained. Opine detection confirmed transformation of E. purpurea. Comparative HPLC fingerprint analysis of the alkamides from natural plant source, control tissues, and transformed callus and roots indicated that transformed callus and hairy roots might be a promising source for continuous and standardized production of the dodeca-2E,4E,8Z,10E/Z-tetraenoic acid isobutylamide and related amides.
TL;DR: In this paper, a 9.21 m section of lake sediments, representing an uninterrupted sequence of lacustrine deposition since 8 290 14C years BP, was used to reconstruct the hydrological and environmental evolution of the crater lake at Malha (Northern Darfur, Sudan).
Abstract: A reconstruction of the hydrological and environmental evolution of the crater lake at Malha (Northern Darfur, Sudan) resulted from the mineralogical and biological study of a 9.21 m section of lake sediments, representing an uninterrupted sequence of lacustrine deposition since 8 290 14C years BP. Important changes in water supply and conditions of sedimentation are reflected in the nature of the sediments and the morphology and stratigraphical distribution of various salt minerals. Additional information on lake circulation patterns and salinity conditions are obtained from associated benthic paleocommunities, represented by ostracods and dipterid larvae. Combining both lines of evidence, the studied sequence can be divided in six distinct sections, which correspond to six successive periods in the lake's Holocene history. The first three periods, generally characterized by high lake levels, represent three generations of a meromictic lake, two of which have ended with a complete desiccation of the lake basin. Meromixis was stable during Period I, due to wind shelter and pronounced density stratification. In the course of Periods II and III stratification was repeatedly interrupted. During Period II, the disruptions were accompanied by important water budget fluctuations; a superimposed gradual decrease in net water supply eventually resulted in holomictic conditions terminating this period. Evidence of turbulence periodically affecting profundal waters is recorded in the sediments of Period III, suggesting that disruptions of stratification were now initiated by very strong winds. Between Period I and Period III, the littoral mixolimnion gradually evolved from near fresh to mesosaline. In Periods IV to VI, lake level was intermediate to low. The lake was holomictic for most of the time and meso- to hypersaline; during Period V, it repeatedly shrunk to a shallow brine pool. The Holocene evolution of Malha Crater Lake illustrates the progressive increase in aridity over most of North Africa following a well-established, early- to mid-Holocene major humid episode. The uninterrupted sedimentary sequence lends itself for detailed reconstruction of Holocene climatic evolution in arid Northeast Africa, a region where records of continuous lacustrine deposition are extremely scarce. As the chronology of critical events in the lake's history remains as yet unsupported by radiocarbon dates, correlation with other Holocene sequences in the eastern Sahara is highly tentative at this point.