Ecology under lake ice

Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer ‘growing seasons’. We executed the first global quantitative synthesis on under‐ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter‐summer patterns for dissolved organic carbon (DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake‐specific, species‐specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass

CATALYTIC AND ELECTROCATALYTIC ACTIVITY OF Pt-Ru/C ELECTRODE FOR HYDROGEN OXIDATION IN ALKALINE

The kinetics of the oxidation of H2 on PtRu/C gas-diffusion electrode was studied by interfacing the electrode with aqueous electrolytes at different pH values. The conducting electrolytes were KOH and HClO4 aqueous solutions with different concentrations. It is shown that the nature of the aqueous electrolyte plays the role of an active catalyst support for the PtRu/C electrode which drastically affects its catalytic properties. During the aforementioned interaction, termed electrochemical metal support interaction (EMSI), the electrochemical potential of the electrons at the catalyst Fermi level is equalised with the electrochemical potential of the solvated electron in the aqueous electrolyte. The electrochemical experiments carried out at various pH values showed that the electrochemical promotion catalysis (EPOC) is more intense when the catalyst-electrode is interfaced with electrolytes with high pH values where the OH– ionic conduction prevails. It was concluded that similar to the solid state electrochemical systems EPOC proceeds through the formation of a polar adsorbed promoting layer of , electrochemically supplied by the OH- species, at the three phase boundaries of the gas exposed gas diffusion catalyst-electrode surface

Single-strand conformation polymorphism (SSCP) of mitochondrial genes helps to estimate genetic differentiation, demographic parameters and phylogeny of Glossina palpalis palpalis populations from West and Central Africa

A good understanding of tsetse fly population structure and migration is essential to optimize the control of sleeping sickness. This can be done by studying the genetics of tsetse fly populations. In this work, we estimated the genetic differentiation within and among geographically separated Glossina palpalis palpalis populations from Cameroon, the Democratic Republic of the Congo and Ivory Coast. We determined the demographic history of these populations and assessed phylogenetic relationships among individuals of this sub-species. A total of 418 tsetse flies were analysed: 258 were collected in four locations in Cameroon (Bipindi, Campo, Fontem and Bafia), 100 from Azaguie and Nagadoua in Ivory Coast and 60 from Malanga in the Democratic Republic of the Congo. We examined genetic variation at three mitochondrial loci: COI, COII-TLII, and 16S2. 34 haplotypes were found, of which 30 were rare, since each was present in < 5% of the total number of individuals. No haplotype was shared among Cameroon, Ivory Coast and the Democratic Republic of the Congo populations. The fixation index FST of 0.88 showed a high genetic distance between Glossina palpalis palpalis populations from the three countries. That genetic distance was correlated to the geographic distance between populations. We also found that there is substantial gene flow between flies from locations separated by over 100 km in Cameroon and between flies from locations separated by over 200 km in Ivory Coast. Demographic parameters suggest that the tsetse flies from Fontem (Cameroon) had reduced in population size in the recent past. Phylogenetic analysis confirms that Glossina palpalis palpalis originating from the Democratic Republic of the Congo are genetically divergent from the two other countries as already published in previous studies

Petrological and geochemical study of Birimian ultramafic rocks within the West African Craton : insights from Mako (Senegal) and Loraboue (Burkina Faso) lherzolite/harzburgite/wehrlite associations

In Archean and Paleoproterozoic greenstone belts, ultramafic (UM) rock occurrences are commonly found in close association within basic and differentiated magmatic series. In the Kedougou-Kenieba Inlier (West African Craton), UM rocks are interbedded within the Birimian (2.1 Ga) Mako tholeiitic series (basalts, gabbros). UMs are typically lherzolite, harzburgite and wehrlite, characterized by their cumulative textures and relative pro-portions of chromite, olivine, clinopyroxene, amphibole +/- orthopyroxene. Geochemical study (Major, REE and trace elements in whole rocks and mineral (mainly clinopyroxene and amphibole) and Sr/Nd isotopic records suggest the existence of different types of complexes. The first one consists of lherzolite + harzburgite assemblages whereas the second one consists of isolated wehrlite massifs. Both complexes highlight two different geodynamic environments, the first association being significantly more juvenile or mantle-related than isolated wehrlites which show more evolved geochemical signatures. UM rocks (dunite + wehrlite) of Loraboue (greenstone belt of Boromo, Burkina Faso) associated with calcalkaline series display the same mineralogical composition as the Mako UM rocks but exhibit a different whole rock composition characteristic of mature island-arc magmas and showing U-shaped REE pattern for both clinopyroxene and host rock, and a clear negative Nb anomaly. The Mako UMs suggest that this portion of the Birimian crust was built in an oceanic context evolving from a MORB-like domain to an increasingly mature volcanic arc domain