SiO2·p-TSA: a green catalyst for solvent-free tetrahydropyranylation of alcohols and thiols

A solvent-free procedure for tetrahydropyranylation of alcohols and thiols based on a simple grinding of the reagents in the presence of silica gel and catalytic amounts of p-TSA is described

Ecological assessment of a southeastern Brazil reservoir

Reservoirs are artificial ecosystems with multiple functions having direct and indirect benefits to humans; however, they also cause ecological changes and influence the composition and structure of aquatic biota. Our objectives were to: (1) assess the environmental condition of Nova Ponte Reservoir, Minas Gerais state, southeastern Brazil; and (2) determine how the aquatic biota respond to disturbances. A total of 40 sites in the littoral zone of the reservoir were sampled to characterize physical and chemical habitat, land use, and benthic macroinvertebrate and fish assemblages. The predominant type of land cover near the reservoir was natural vegetation. A total of 29 fish species and 39 macroinvertebrate taxa were collected, including eight alien species. Most sites had intermediate levels of human disturbance, however, high levels of degradation were associated with high proportions of alien species. Disturbances at multiple scales may alter natural patterns and processes, leading to environmental changes and damaging biological communities. Our results reinforce the importance of assessing reservoir ecological conditions at several scales. The study of land use, littoral zone physical habitat characteristics, water quality, and assemblage structure set the ground for proposing actions to rehabilitate and conserve aquatic ecosystems.Keywords: reservoirs, water quality, physical habitat, environmental quality, bioindicatorsKeywords: reservoirs, water quality, physical habitat, environmental quality, bioindicator

Influence of limnological zones on the spatial distribution of fish assemblages in three Brazilian reservoirs

Reservoirs can have both positive and negative effects on differing fish species depending on the species concerned and reservoir morphology, flow regime, and basin location. We assessed the influence of limnological zones on the ichthyofauna of three large Neotropical reservoirs in two different river basins. We sampled fish through use of gill nets set at 40 systematically selected sites on each reservoir. We used satellite images, algae, and suspended solids concentrations to classify those sites as lacustrine or riverine. We observed significant differences in assemblage composition between riverine and lacustrine zones of each reservoir. We either tested if the same region (lacustrine or riverine) showed the same patterns in different reservoirs. In São Simão, the riverine zone produced greater abundances of native species, long-distance migratory species, diversity, and richness, whereas the lacustrine zone supported greater total and non-native species abundances. Conversely, in Três Marias, the riverine zone supported greater total and non-native species abundances, whereas the others traits evaluated did not differ significantly between zones. Only lacustrine sites occurred in Volta Grande Reservoir. The same zones in the three reservoirs usually had significantly different patterns in the traits evaluated. The differences in spatial patterns observed between reservoirs could be explained partly by the differing morphologies (complex versus linear), the differential influence of tributaries of each reservoir and basin positions (presence or absence of upstream dams) of the reservoirs.Keywords: fish assemblages, upper São Francisco Basin, Upper Paraná Basin, dam effects, zonatio

Tectonic evolution of the southern margin of the Amazonian craton in the late Mesoproterozoic based on field relationships and zircon U-Pb geochronology

New U-Pb zircon geochronological data integrated with field relationships and an airborne geophysical survey suggest that the Nova Brasilândia and Aguapeí belts are part of the same monocyclic, metaigneous and metasedimentary belt formed in the late Mesoproterozoic (1150 Ma-1110 Ma). This geological history is very similar to the within-plate origin of the Sunsás belt, in eastern Bolivia. Thus, we propose that the Nova Brasilândia, Aguapeí and Sunsás belts represent a unique geotectonic unit (here termed the Western Amazon belt) that became amalgamated at the end of the Mesoproterozoic and originated through the reactivation of a paleo-suture (Guaporé suture zone) in an intracontinental rift environment. Therefore, its geological history involves a short, complete Wilson cycle of ca. 40 Ma. Globally, this tectonic evolution may be related with the final breakup of the supercontinent Columbia. Mafic rocks and trondhjemites in the northernmost portion of the belt yielded U-Pb zircon ages ca. 1110 Ma, which dates the high-grade metamorphism and the closure of the rift. This indicates that the breakup of supercontinent Columbia was followed in short sequence by the assembly of supercontinent Rodinia at ca. 1.1-1.0 Ga and that the Western Amazon belt was formed during the accretion of the Arequipa-Antofalla basement to the Amazonian craton