Reservoir longitudinal gradient promotes ordered losses on diversity and density of Ephemeroptera community

Reservoir operations alter, eliminate or restrain the natural hydrologic cycles. Biotic community has become subject to these non-cyclic events, responding by reducing the species diversity. Ephemeroptera species present distinct responses to environmental deterioration such that poses this assemblage between the most useful groups in biomonitoring programs. We hypothesized an alteration in beta diversity at the longitudinal species gradient, which will be influenced mainly by species losses between zones. Changes in temporal beta diversity is also expected, but the main drivers of such alterations will be the species turnover between the sampling period. Ephemeroptera community was monitored in nine sampling points from Itaipu Reservoir, where were installed three sets of substrates composed by a float and 2 wooden substrates. We took biological samples in triplicates monthly, from June-01 to August-02. Our initial hypothesis was partially supported and with significant variations only for spatial approach, between the Reservoir zones. The generated ordering from Non-Metric Dimensional Scale – NMDS - corroborated with spatial analyzes, with the formation of two groups along the gradient zonation of the reservoir. The temporal ordination showed no clear pattern. As expected, the contribution to beta diversity was different for our two approaches, such that the loss of species was more important along the spatial gradient and despite of no significant result, the species replacement was more important among months. The spatial results lead us to infer that differences in limnological characteristics between zones are important for determining differences in Ephemeroptera composition and can reflect the dependency degree of the species in relation to the lentic and sometimes-lotic conditions, mainly in the riverine zone of reservoirs. On the other hand, the absence of a temporal pattern can be result of chaotic variations in the physical and chemical attributes imposed by the reservoir operation, disrupting continuity of the biota and natural succession processes.

Association Convolvulo-Polygonetum aviculare (ass. new) in Weed Vegetation of Vineyard Region in Herzegovina

Floristic-phytocenological research of weed vegetation in vineyards of Bosnia and Herzegovina determined a new association Convolvulo-Polygonetumaviculare (ass. new). Regarding floristic character, the asso­ciation was qualified by numerous thermophilic species, and it was ranked in the mediterranean syntaxonomic unit DiplotaxionBr.-Bl. 1931 em 1936 from ordo ChenopodietaliamediterraneaBr.-Bl. 1931 em 1936. Stands association builds 56 plant species. A complete set of association is built by five species: ConvolvulusarvensisL., PolygonumaviculareL., Cynodondactylon (L.) Pers., PortulacaoleraceaL. and ChenopodiumalbumL. Biological spectrum of association shows dominance of hemi­therophytes (62,50%) and hemikryptophytes which together make up 85,71% of the species. Gradient analysis shows very little dependence of floristic composition in relation to soil moisture medium rich in minerals. The value of the coefficient of correlation points a relatively high degree of dependence floristic composition in comparison to the gradient of light and temperature. Areal spectrum of associations suggests the dominance of cosmopolitan and mediterranean group of floral elements. By means of numerical classification and ordination of stands, there may be distin­guished two groups of stands.

Photothermal Beam Deflection and Photoaction Spectroscopic Study of CdS Photoelectrodes in Polysulfide Electrolyte

A number of experimental photothermal deflection, ac photovoltage, and ac photocurrent spectra for CdS photoelectrochemical cells are presented. The spectra were obtained under various conditions, with the use of modulated light: open circuit and short circuit, and with a dc bias applied across the working and counter electrodes. The measurement of both the photothermal deflection and the photoaction signals allows one to monitor two energy conversion channels, namely optical-to-thermal, and optical-to-electrical. The photothermal deflection technique was found to provide useful information regarding the surface condition of the electrodes, with respect to polishing or corrosion damage. Finally, the effect of a current-induced species gradient at the working electrode/electrolyte interface upon the photothermal deflection signal is also examined.