Dynamical downscaling of temperature variability over Tunisia: evaluation a 21-year-long simulation performed with the WRF model.

8 pagesInternational audienceThis study evaluates the capabilities of the Weather Research and Forecasting (WRF) model to reproduce the space-time variability of near-surface air temperature over Tunisia. Downscaling is based on two nested domains with a first domain covering the Mediterranean Basin and forced by 21 years of ERA-Interim reanalysis (1991-2011), and a second domain (12 km spatial resolution) centered on Tunisia. Analyses and comparisons are focused on daily average (Tavg), minimum (Tmin) and maximum (Tmax) near-surface air temperatures and are carried out at the annual and seasonal timescales. WRF results are assessed against various climatological products (ERA-Interim, EOBS and a local network of 18 surface weather stations). The model correctly reproduces the spatial patterns of temperature being significantly superimposed with local topographic features. However, it broadly tends to underestimate temperatures especially in winter. Temporal variability of temperature is also properly reproduced by the model although systematic cold biases mostly concerning Tmax, reproduced throughout the whole simulation period, and prevailing during the winter months. Comparisons also suggest that the WRF errors are not rooted in the driving model but could be probably linked to deficiencies in the model parameterizations of diurnal/nocturnal physical processes that largely impact Tmax / Tmin

Tunisian reservoirs : diagnosis and biological potentialities

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Variabilité du phytoplancton en relation avec les facteurs environnementaux dans un lac salé temporaire

To establish a relationship between environmental variables and phytoplankton dynamics, physicochemical characteristics and phytoplankton sampling were performed in Sabkhet El Adhibet (Southeastern Tunisia) monthly from November 2005 to April 2006 and from November 2006 to April 2007 (the site dries annually between May and late October). All measured water quality variables showed considerable seasonal variation, and quantitative and qualitative differences in phytoplankton communities were recorded. The maximum phytoplankton density was recorded in January 2006, whereas lowest values occurred in November 2006. Sixteen species belonging to 6 orders were recorded, among which diatoms (52.1 %) and chlorophytes (39.8 %) were the most abundant. The correlation analysis between phytoplankton (density and composition) and abiotic variables revealed that orthophosphate is the major factor affecting the phytoplankton dynamics, and there were no correlation between phytoplankton and all the other environmental parameters. The PCA analysis of the phytoplankton composition and density revealed two main PCA axis explaining 82.99 % of the variance. The first axis was associated with diatoms, cryptophytes, euglenophytes, dinophytes and total phytoplankton, with a contribution of 21.8, 21.6, 21.3, 17.4 and 17.4 %, respectively. The second axis was correlated with chlorophytes (55.3 %) and cyanobacterias (26.3 %)Dans ce travail, afin de déterminer l'impact des différentes variables environnementales sur le phytoplancton dans un milieu hypersalé, un suivi des paramètres abiotiques et biotiques a été réalisé au niveau de Sabkhet El Adhibet (sud-est Tunisien), durant les périodes allant de novembre 2005 à avril 2006 et de novembre 2006 à avril 2007 (le site étant sec entre le début du mois de mai et la fin du mois d'octobre). Les résultats obtenus ont permis l'identification de 16 espèces de phytoplancton, appartenant aux groupes des diatomées, chlorophycées, dinophycées, euglénophycées, cryptophycées et cyanobactéries. La plus grande densité microalgale a été observée en décembre 2005 et janvier 2006 avec respectivement 8,6 et 14,6 106 cellules.L-1, alors que la plus petite densité a été enregistrée en novembre 2006 avec 0,19 106 cellules.L-1. L'analyse de la composition en phytoplancton révèle que ce sont les diatomées et les chlorophycées qui présentent la fraction la plus importante du phytoplancton, avec respectivement un maximum de 97,8 % (novembre 2006) et 95,7 % (janvier 2007). Le pourcentage moyen décroissant, relatif à chaque groupe de phytoplancton, de toute la période d'investigation est comme suit: diatomées (52,1 %), chlorophycées (39,8 %), dinophycées (3,2 %), euglénophycées (3 %), cryptophycées (1,1 %) et cyanobactéries (0,8 %). Toutefois, nous remarquons une grande variation mensuelle de la composition phytoplanctonique avec les diatomées et les chlorophycées présentes au niveau de tous les échantillons, tandis que les dinophycées, les euglenophycées et les cryptophycées sont absentes au niveau de nos échantillons durant certaines périodes de l'année. L'étude de la corrélation, entre la composition et la densité des phytoplanctons avec les différents paramètres abiotiques, montre que c'est l'orthophosphate qui affecte le plus la dynamique et la variation phytoplanctonique dans le milieu. Par ailleurs, aucune corrélation n'a été observée entre le phytoplancton et les autres paramètres environnementaux

Tunisian reservoirs: diagnosis and biological potentialities

Due to scarcity, irregular rainfall and increasing water demand, several reservoirs have been built in recent decades in Tunisia to meet water needs for essential uses, which is generally done without analysis of their capacity to maintain a high quality of aquatic life and equitable distribution of water resources. Currently, 90% of available water resources are already mobilized and climate change exacerbates the country's aridity which makes it difficult to monitor water needs. With a view to contributing to their effective management and setting future directions for controlling and improving inland fish productivity, a comparative limnological study was carried out on 8 artificial reservoirs that were stocked with mullet fry. This study, based on a review of existing data, provides information on the availability and quality of inland water resources in relation to international standards and the biological potential (plankton, fish and other organisms) of these reservoirs. The satisfactory water quality for aquatic life, as well as the significant growth and production of introduced species associated with the rearing of mullet fry, clearly show that, despite several problems, Tunisian reservoirs represent an important potential that still needs to be developed. To this end, we recommend to improve the fishing techniques and the stocking of mullet fry. In addition, the strengthening of fishermen's groups, the encouragement of private initiative and the quality control of water and fish meat are highly requested

Association study of the trinucleotide repeat polymorphism within SMARCA2 and schizophrenia

BACKGROUND: Brahma (BRM) is a key component of the multisubunit SWI/SNF complex, a complex which uses the energy of ATP hydrolysis to remodel chromatin. BRM contains an N-terminal polyglutamine domain, encoded by a polymorphic trinucleotide (CAA/CAG) repeat, the only known polymorphism in the coding region of the gene (SMARCA2). We have examined the association of this polymorphism with schizophrenia in a family-based and case/control study. SMARCA2 was chosen as a candidate gene because of its specific role in developmental pathways, its high expression level in the brain and some evidence of its association with schizophrenia spectrum disorder from genome-wide linkage analysis. RESULTS: Family-based analysis with 281 complete and incomplete triads showed that there is no significant preferential transmission of any of the alleles to the affected offspring. Also, in the case/control analysis, similar allele and genotype distributions were observed between affected cases (n = 289) and unaffected controls (n = 273) in each of three Caucasian populations studied: French Canadian, Tunisian and other Caucasians of European origin. CONCLUSION: Results from our family-based and case-control association study suggest that there is no association between the trinucleotide repeat polymorphism within SMARCA2 and schizophrenia

Systematic review of a RAMSAR wetland and UNESCO biosphere reserve in a climate change hotspot (Ichkeul Lake, Tunisia)

Tunisia\u27s Ichkeul Lake is among the most productive ecosystems in the Mediterranean, with a great regional value thanks to its diversity of habitats. It is an important overwintering area for waterfowl species. It is a RAMSAR wetland, a National Park, a UNESCO World Heritage, and a Biosphere Reserve. This review paper provides a broad overview of the climatic, hydraulic, biogeochemical features, bio-resources, and bio-productivity of the Lake. The interconnectivity between the different environmental components of the lake is presented, highlighting the main characteristics of this vital ecosystem. Its ecosystem consists of a permanent lake bordered by temporary marshes. It is connected to the Mediterranean Sea via Bizerte Lagoon under a typical semi-arid to sub-humid bio-climate with wet and dry seasons. The winter rainfall fills up the rivers and lake with freshwater that overflows into the Tinja River. In summer, high evaporation reduces the water level and allows seawater to enter the wetland from Bizerte Lagoon. The ecosystem is threatened by pollution, the damming of its main rivers, and climate change. The unsustainable water management has resulted in fundamental environmental modifications, as evidenced by the large variation in the salinity, water level, productivity of water plants, and the decline in venue and stop-overs of waterbirds. The current situation is a warning that indicates a general perturbation of the resources of this particular site and of Tunisian wetlands in general, especially that the Mediterranean region has been designated as a climate change hotspot. Accurate hydrological management is needed to boost the physical functioning of the ecosystem, and to gain deeper knowledge of the different phases of the water cycle and its relationship to other long-term environmental cycles for sustainable water management strategies in the most water-scarce region in the world

Rare mutations in N-methyl-D-aspartate glutamate receptors in autism spectrum disorders and schizophrenia

Pharmacological, genetic and expression studies implicate N-methyl-D-aspartate (NMDA) receptor hypofunction in schizophrenia (SCZ). Similarly, several lines of evidence suggest that autism spectrum disorders (ASD) could be due to an imbalance between excitatory and inhibitory neurotransmission. As part of a project aimed at exploring rare and/or de novo mutations in neurodevelopmental disorders, we have sequenced the seven genes encoding for NMDA receptor subunits (NMDARs) in a large cohort of individuals affected with SCZ or ASD (n=429 and 428, respectively), parents of these subjects and controls (n=568). Here, we identified two de novo mutations in patients with sporadic SCZ in GRIN2A and one de novo mutation in GRIN2B in a patient with ASD. Truncating mutations in GRIN2C, GRIN3A and GRIN3B were identified in both subjects and controls, but no truncating mutations were found in the GRIN1, GRIN2A, GRIN2B and GRIN2D genes, both in patients and controls, suggesting that these subunits are critical for neurodevelopment. The present results support the hypothesis that rare de novo mutations in GRIN2A or GRIN2B can be associated with cases of sporadic SCZ or ASD, just as it has recently been described for the related neurodevelopmental disease intellectual disability. The influence of genetic variants appears different, depending on NMDAR subunits. Functional compensation could occur to counteract the loss of one allele in GRIN2C and GRIN3 family genes, whereas GRIN1, GRIN2A, GRIN2B and GRIN2D appear instrumental to normal brain development and function

Simulated effects of land immersion on regional arid climate: a case study of the pre-Saharan playa of Chott el-Jerid (south of Tunisia)

International audienceThe potential effects on the regional climate induced by partially immersing the arid pre-Saharan playa basin of Chott el-Jerid(south of Tunisia) are investigated by comparing two multi-year (1991–2011) sets of numerical simulations each consisting often-member ensemble and performed using the WRF regional climate model. The first WRF ensemble is performed undercurrent land use and land cover, while the second is carried out after introducing a virtual large and shallow surface waterreservoir (a lake) in Chott el-Jerid. The most pronounced effects generated by the artificial lake are circumscribed over its surfaceand slightly spread downwind to the other parts of the Chott. The lake has a clear moderating effect on near-surface airtemperatures by increasing (decreasing) the wintertime (summertime) air temperatures. Sensible heat fluxes are remarkablyincreased in winter and decreased in summer over the lake following the temperature gradient between the lake surface andthe overlying atmosphere. Latent heat fluxes, moisture convergence, and water vapor mixing ratio are increased over the lakethroughout the year, especially in winter. The lake also induces domain-wide decreased (increased) surface pressures and land(lake) breeze circulation in winter (summer). Simulated rainfall amounts are most increased over the lake in winter likely because of an enhanced atmospheric instability, while they slightly decrease in summer