RESUMO
Events such as volcanic eruptions may act as disturbance agents modifying the landscape spatial diversity and increasing environmental instability. On June 4, 2011 the Puyehue-Cordon Caulle volcanic complex located on Chile (2236 m.a.s.l., 40° 02' 24" S- 70° 14' 26" W) experience a rift zone eruption ejecting during the first day 950 million metric tons into the atmosphere. Due to the westerly winds predominance, ash fell differentially upon 24 million ha of Patagonia Argentinean, been thicker deposits accumulated towards the West. In order to analyze changes on stream fish assemblages we studied seven streams 8, 19 and 30 months after the eruption along the ash deposition gradient, and compare those data to pre eruption ones. Habitat features and structure of the benthic macroinvertebrate food base of fish was studied. After the eruption, substantial environmental changes were observed in association with the large amount of ash fallout. In western sites, habitat loss due to ash accumulation, changes in the riparian zone and morphology of the main channels were observed. Turbidity was the water quality variable which reflected the most changes throughout time, with NTU values decreasing sharply from West to East sites. In west sites, increased Chironomid densities were recorded 8 months after the initial eruption as well as low EPT index values. These relationships were reversed in the less affected streams farther away from the volcano. Fish assemblages were greatly influenced both by habitat and macroinvertebrate changes. The eruption brought about an initial sharp decline in fish densities and the almost total loss of young of the year in the most western streams affecting recruitment. This effect diminished rapidly with distance from the emission center. Thirty months after the eruption, environmental changes are still occurring as a consequence of basin wide ash remobilization and transport.
Assuntos
Ecossistema , Monitoramento Ambiental , Rios/química , Salmonidae/classificação , Erupções Vulcânicas , Animais , Chile , Salmonidae/crescimento & desenvolvimentoRESUMO
Background. Sevki's histochemical technique allows specific staining of catechomamine-containing cells, yet discrimiantion between adrenaline-(ADR-) cells and noradrenaline-(NOR-) cells is unrealiable, being based on hue differences. Methods. In this work, histochemical differentiation of ADR- and NOR-cells in rat adrenal medulla was carried out by introducing two modifications to Sevki's technique: 1) employment of aged Giemsa solution, and 2) addition of an alkaline differentiating step. Results. With these changes, ADR-cell stained brown, whereas NOR-cells were deep-green, resulting in a clear-cut differentiation. Conclusions. The modified technique permits to differentiate ADR- from NOR-cells in the adrenal medulla using only a bright field microscope without any sophisticated equipment. The present procedure is inexpensive and easy to carry out