Asymmetric response of forest and grassy biomes to climate variability across the African Humid Period : influenced by anthropogenic disturbance?

A comprehensive understanding of the relationship between land cover, climate change and disturbance dynamics is needed to inform scenarios of vegetation change on the African continent. Although significant advances have been made, large uncertainties exist in projections of future biodiversity and ecosystem change for the world's largest tropical landmass. To better illustrate the effects of climate–disturbance–ecosystem interactions on continental‐scale vegetation change, we apply a novel statistical multivariate envelope approach to subfossil pollen data and climate model outputs (TraCE‐21ka). We target paleoenvironmental records across continental Africa, from the African Humid Period (AHP: ca 14 700–5500 yr BP) – an interval of spatially and temporally variable hydroclimatic conditions – until recent times, to improve our understanding of overarching vegetation trends and to compare changes between forest and grassy biomes (savanna and grassland). Our results suggest that although climate variability was the dominant driver of change, forest and grassy biomes responded asymmetrically: 1) the climatic envelope of grassy biomes expanded, or persisted in increasingly diverse climatic conditions, during the second half of the AHP whilst that of forest did not; 2) forest retreat occurred much more slowly during the mid to late Holocene compared to the early AHP forest expansion; and 3) as forest and grassy biomes diverged during the second half of the AHP, their ecological relationship (envelope overlap) fundamentally changed. Based on these asymmetries and associated changes in human land use, we propose and discuss three hypotheses about the influence of anthropogenic disturbance on continental‐scale vegetation change

Natural tracers and isotope techniques to definer groundwater recharge and salinization in the Bou Areg coastal aquifer (North Morocco).

The geochemical and isotopic (δ2H, δ18O, δ13C, δ15NNO3, δ18ONO3) characterization of the Bou Areg aquifer (North Morocco) based on samples collected during two surveys in November 2009 and June 2010 allowed the identification of runoff from the mountain regions and agricultural return flows as the main sources of aquifer recharge. The high salinization of the aquifer is not only due to the intensive agricultural activities but it is also associated with the natural quality of the catchment. The isotopic signal of dissolved nitrates allowed for the identification of two main sources of nitrogen in the system: (i) fertilizers and (ii) manure and septic effluents. The study, framed within the UNESCO-IHP sub component of the Strategic Partnership for the Mediterranean Large Marine Ecosystem, represents the first isotopic investigation of the area and will serve as a basis for the promotion of robust science based management practices in the region

Synthesis, crystal structure, antimicrobial activity and docking studies of new imidazothiazole derivatives

International audienceA series of imidazothiazole derivatives were synthesized via Claisen–Schmidt condensation of aldehyde 3, and different methyl ketones and their chemical structures were confirmed using 13C NMR, 1H NMR and LC–MS. In addition, the molecular structure of compound 3 was defined by single-crystal X-ray diffraction. The antibacterial and antifungal activities of synthesized compounds were investigated by diffusion method against three pathogenic bacteria (Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus) and one pathogenic fungus (Fusarium oxysporum). Compound 3 displayed significant antibacterial activity against E. coli and P. aeruginosa (MIC ≤ 0.2 mg/ml). Concerning the antifungal activity, all the molecules show very interesting results versus F. oxysporum (IC50 ≤ 0.07 mg/ml). These results were confirmed by the molecular docking studies such as some compounds showing optimum binding energy and affinity to the active site of the receptor

Processes affecting groundwater quality in arid zones: The case of the Bou-Areg coastal aquifer (North Morocco)

The coastal aquifer of Bou-Areg (Morocco) has been studied to identify the main processes causing groundwater salinization, using a multi tracer (general chemistry and isotopes - delta H-2, delta O-18, delta C-13, delta N-15(NO3), delta O-18(NO3)) geochemical approach. Groundwater is characterized by the widespread occurrence of brackish waters (TDS < 500 mg L-1) with high cation contents, which are balanced by elevated dissolved NO3- (reaching a maximum of 208 mg L-1) and Cl-. Lagoon samples represent a mixture of fresh water and sea water, showing a Na/Cl ratio in agreement with that of sea water and an excess of Ca. The high Ca values represent the main peculiarity of the groundwater-lagoon water system. Two types of groundwater could be identified: (i) freshwater, separated from the whole system and located at the limit of the irrigated area, characterized by low TDS, depleted isotopic composition and relatively high quality; and (ii) water mainly recharged by mountain runoff, interacting with local recharge and acquiring salinity from different sources, thus creating a complex system of dilute waters. Hydrochemical results confirm that the high salinity of the aquifer is caused by the coexistence of dissolution of evaporate rocks and carbonates from Miocene strata, water-rock interaction, and human impacts due to agricultural return flows. The latter represents the main contribution to groundwater salinization, especially in the central part of the aquifer, as well as one of the main causes of the general increase in NO3- concentrations. Only locally, in the southern part of the aquifer, close to the city of Kariat Arkmane, the high salinization observed may be attributed to the presence of lagoon water intrusion. The isotopic composition of dissolved NO3- indicates manure and septic effluents, especially in urban areas and in the central part of the plain, and synthetic fertilizers in the agricultural zone as the main drivers for human induced pollution. The study shows that agricultural return flow has significantly modified the chemistry of the system and it is a prime example of the human-induced changes over coastal environments. Saline water intrusion from the lagoon in the shallow aquifer is negligible, while discharge of polluted groundwater into the lagoon has been found to partially alter its qualit