Assessing dolomite surface reactivity at temperatures from 40 to 120 degrees C by hydrothermal atomic force microscopy

This study investigated the reactivity of the (1 0 4) dolomite surface in the system MgCO3–CaCO3–NaCl–H2O via a suite of aqueous solution–dolomite hydrothermal atomic force microscopy interaction experiments at temperatures from 40 to 120 °C, pH ranging from 4 to 8, pressures up to 5 bars, and over a wide range of aqueous fluid saturation state. Dolomite dissolution was observed in the presence of undersaturated aqueous fluids. Dissolution produced crystallographically well defined etch pits, consistent with the stoichiometric release of ordered lattice cations. In low to moderately saturated fluids, dolomite growth began by the growth of one or two layers of carbonate (layer height <3 Å) which morphologically reproduced the initial surface features, resembling the template effect as previously described by Astilleros et al. (2003, 2006) and Freij et al. (2004). Further growth was strongly inhibited and did not show any systematic crystallographically orientated growth morphologies. At aqueous fluid saturation states exceeding 500, nucleation and growth was observed on the dolomite surfaces at moderate rates, but these did not exhibit the characteristic dolomite crystallographic orientation after the growth of several layers. Taken together these observations suggest that the direct precipitation of dolomite from aqueous solution is disfavored at temperatures to at least 120 °C due to the poisoning of the dolomite surface for further growth by the precipitation of one to four Ca–Mg carbonate layers on these surfaces

Paired comparisons of carbon exchange between undisturbed and regenerating stands in four managed forests in Europe

The effects of harvest on European forest net ecosystem exchange (NEE) of carbon and its photosynthetic and respiratory components (GPP (gross primary production) and TER (total ecosystem respiration)) were examined by comparing four pairs of mature/harvested sites in Europe via a combination of eddy covariance measurements and empirical modeling. Three of the comparisons represented high coniferous forestry (spruce in Britain, and pines in Finland and France), while a coppice-with-standard oak plantation was examined in Italy. While every comparison revealed that harvesting converted a mature forest carbon sink into a carbon source of similar magnitude, the mechanisms by which this occurred were very different according to species or management practice. In Britain, Finland, and France the annual sink (source) strength for mature (clear-cut) stands was estimated at 496 (112), 138 (239), and 222 (225) g C m−2, respectively, with 381 (427) g C m−2 for the mature (coppiced) stand in Italy. In all three cases of high forestry in Britain, Finland, and France, clear-cutting crippled the photosynthetic capacity of the ecosystem – with mature (clear-cut) GPP of 1970 (988), 1010 (363), and 1600 (602) g C m−2– and also reduced ecosystem respiration to a lesser degree – TER of 1385 (1100), 839 (603), and 1415 (878) g C m−2, respectively. By contrast, harvesting of the coppice oak system provoked a burst in respiration – with mature (clear-cut) TER estimated at 1160 (2220) gC m−2– which endured for the 3 years sampled postharvest. The harvest disturbance also reduced GPP in the coppice system – with mature (clear-cut) GPP of 1600 (1420) g C m−2– but to a lesser extent than in the coniferous forests, and with near-complete recovery within a few years. Understanding the effects of harvest on the carbon balance of European forest systems is a necessary step towards characterizing carbon exchange for timberlands on large scales

Speech production deficits in early readers: predictors of risk

Speech problems and reading disorders are linked, suggesting that speech problems may potentially be an early marker of later difficulty in associating graphemes with phonemes. Current norms suggest that complete mastery of the production of the consonant phonemes in English occurs in most children at around 6–7 years. Many children enter formal schooling (kindergarten) around 5 years of age with near-adult levels of speech production. Given that previous research has shown that speech production abilities and phonological awareness skills are linked in preschool children, we set out to examine whether this pattern also holds for children just beginning to learn to read, as suggested by the critical age hypothesis. In the present study, using a diverse sample, we explored whether expressive phonological skills in 92 5-year-old children at the beginning and end of kindergarten were associated with early reading skills. Speech errors were coded according to whether they were developmentally appropriate, position within the syllable, manner of production of the target sounds, and whether the error involved a substitution, omission, or addition of a speech sound. At the beginning of the school year, children with significant early reading deficits on a predictively normed test (DIBELS) made more speech errors than children who were at grade level. Most of these errors were typical of kindergarten children (e.g., substitutions involving fricatives), but reading-delayed children made more of these errors than children who entered kindergarten with grade level skills. The reading-delayed children also made more atypical errors, consistent with our previous findings about preschoolers. Children who made no speech errors at the beginning of kindergarten had superior early reading abilities, and improvements in speech errors over the course of the year were significantly correlated with year-end reading skills. The role of expressive vocabulary and working memory were also explored, and appear to account for some of these findings

Roles of glial cells in synapse development

Brain function relies on communication among neurons via highly specialized contacts, the synapses, and synaptic dysfunction lies at the heart of age-, disease-, and injury-induced defects of the nervous system. For these reasons, the formation—and repair—of synaptic connections is a major focus of neuroscience research. In this review, I summarize recent evidence that synapse development is not a cell-autonomous process and that its distinct phases depend on assistance from the so-called glial cells. The results supporting this view concern synapses in the central nervous system as well as neuromuscular junctions and originate from experimental models ranging from cell cultures to living flies, worms, and mice. Peeking at the future, I will highlight recent technical advances that are likely to revolutionize our views on synapse–glia interactions in the developing, adult and diseased brain

Investigation on the diversity and function of benthic protists in the microbial food web.

The investigation of the benthic food web took place in the Nationalpark Niedersächsisches Wattenmeer (Dorumer) and in Königshafen (Sylt).Experiments were made to test the influence of macrofauna on the microbial benthic community. Natural sediment was placed into cellwells and incubated under controlled conditions for 30 minutes to 24 hours with and without macrograzers. The snail Hydrobia ulvae, the crustacean Corophium volvutator and a mixture of different polychaete species were used as macrograzer. The number of bacteria, cyanobacteria, flagellates (heterotrophic and autotrophic) and diatoms were enumerated after the incubation. Additionally, FLBs (fluorescently labelled bacteria) were added to the experimental samples described above to estimate bacterivory.The results showed no detectable influence of the macrograzers on the abundance of bacteria, cyanobacteria, flagellates and diatoms. The FLB experiment revealed that about 50 to 60% of the bacteria standing stock were consumed each day. There was no difference between the FLB loses in the treatments with and without macrograzers, therefore the consumption of bacteria was mainly due micro- and meiobenthic organisms like flagellates, ciliates, nematodes and copepods

Investigation of the diversity and function of protists in benthic microbial food webs.

This study concentrates on the seasonal composition and trophic dynamics of the benthic microbial community in freshwater and marine systems and on the effect of macrozoobenthos grazing on these communities. Laboratory experiments with and without added macrograzers were carried out with sediments from the North Sea, temperate lakes of Northern Germany and arctic lakes of North East Greenland. Incubation time varied between 30min and 5d. In further experiments, fluorescently labeled bacteria (FLBs) were added as food tracers in order to estimate bacterivory. The abundancec of bacteria, cyanobacteria, protists and meiofauna were determined at the beginning and in the end of all experiments. First results indicate no effect of the macrograzers Hydrobia ulvae (Gastropoda), Corophium volutator (Crustacea), Potamopyrgus antipodarum (Gastropoda), mixed polychaets (Annelida) and chironomid larvae (Insecta) on the abundance of bacteria and flagellates. However, FLB experiments revealed a removal of 40 to 60% of the standing bacterial stock per day, with no differences between the treatments with and without macrograzers. These results point a minor effect of macrograzers as bacterivores. Implications on the structure of the food web will be discussed