Hidrodinâmica e transporte de material particulado em suspensão sazonal em um estuário dominado por maré: Estuário de Caravelas (BA)

O objetivo do presente estudo é caracterizar a hidrodinâmica e o transporte de material particulado em suspensão (MPS) no estuário de Caravelas sob diferentes condições de maré e vazão fluvial. Foram realizadas quatro campanhas hidrográficas durante ciclos completos de maré, sendo em condições de maré de sizígia e quadratura, e durante os períodos seco e chuvoso. Dados de nível de água, velocidade e direção de correntes, salinidade, temperatura e turbidez foram obtidos em uma estação fixa próxima da desembocadura do estuário. A partir destes dados foram obtidos os transportes residuais de MPS e calculado os mecanismos de transporte. As maiores concentrações médias de material particulado em suspensão ocorreram em condições de sizígia. Em condições de maré de quadraturao transporte resultante de MPS foi com sentido estuário acima, porém de pequena intensidade. Em condições de sizígia o estuário é caracterizado por correntes mais intensas e assimétricas, com dominância de vazante. Durante a condição de sizígia o estuário pode atuar como importador ou exportador de MPS. O estuário do rio Caravelas foi classificado como bem misturado e fracamente estratificado. A hidrografia e o balanço sedimentar são principalmente modulados pela altura da marée o aporte de água doce é irrelevante.

Retention-favorable timing of propagule release in barnacles and periwinkles

Recent studies on the ecology of marine larvae suggest that retention near coastal areas and self-recruitment are probably much more common than previously thought. In light of this, the advective potential of pelagic stages can be partially determined by the timing of propagule release. We sampled the upper-shore levels of a subtropical coastline in southeastern Brazil to examine the temporal patterns of propagule release for the common barnacle Chthamalus bisinuatus and the periwinkle Nodilittorina lineolata. The release timing in both species was very consistent between sites a few kilometers apart. Barnacles released nauplii in a rhythmic pattern, mostly coinciding with neap tides, when the speed of tidal currents was lowest. There was no variation in propagule release in relation to diel or flood-ebb tidal cycles. Periwinkles released propagules in a very irregular pattern, which remarkably matched a time series of wave heights. Egg capsules were released during periods of rough seas, when onshore surface currents were expected to prevail. Eggs were released mostly during ebb tides, and there was no diel variation. Propagule release rhythms are usually viewed as a means to ensure fast offshore advection, thus avoiding presumed hazardous conditions for larvae. However, propagule release strategies in these upper-shore species would more likely contribute to the retention of offspring close to parental stocks.

Hydrodynamics and suspended sediment transport in the Camboriú estuary - Brazil: pre jetty conditions

Estuarine hydrodynamics is a key factor in the definition of the filtering capacity of an estuary and results from the interaction of the processes that control the inlet morphodynamics and those that are acting in the mixing of the water in the estuary. The hydrodynamics and suspended sediment transport in the Camboriú estuary were assessed by two field campaigns conducted in 1998 that covered both neap and spring tide conditions. The period measured represents the estuarine hydrodynamics and sediment transport prior to the construction of the jetty in 2003 and provides important background information for the Camboriú estuary. Each field campaign covered two complete tidal cycles with hourly measurements of currents, salinity, suspended sediment concentration and water level. Results show that the Camboriú estuary is partially mixed with the vertical structure varying as a function of the tidal range and tidal phase. The dynamic estuarine structure can be balanced between the stabilizing effects generated by the vertical density gradient, which produces buoyancy and stratification flows, and the turbulent effects generated by the vertical velocity gradient that generates vertical mixing. The main sediment source for the water column are the bottom sediments, periodically resuspended by the tidal currents. The advective salt and suspended sediment transport was different between neap and spring tides, being more complex at spring tide. The river discharge term was important under both tidal conditions. The tidal correlation term was also important, being dominant in the suspended sediment transport during the spring tide. The gravitational circulation and Stokes drift played a secondary role in the estuarine transport processes.

Shelf and estuarine transport mechanisms affecting the supply of competent larvae in a suite of brachyuran crabs with different life histories

Supply of competent larvae to the benthic habitat is a major determinant of population dynamics in coastal and estuarine invertebrates with an indirect life cycle. Larval delivery may depend not only on physical transport mechanisms, but also on larval behavior and physiological progress to the competent stage. Yet, the combined analysis of such factors has seldom been attempted. We used time-series analyses to examine tide- and wind-driven mechanisms responsible for the supply of crab megalopae to an estuarine river under a major marine influence in SW Spain, and monitored the vertical distribution of upstream moving megalopae, their net flux and competent state. The species Panopeus africanus (estuarine), Brachynotus sexdentatus (euryhaline) and Nepinnotheres pinnotheres (coastal) comprised 80% of the whole sample, and responded in a similar way to tide and wind forcing. Tidal range was positively correlated to supply, with maxima 0 to 1 d after spring tides, suggesting selective tidal stream transport. Despite being extensively subjected to upwelling, downwind drift under the effect of westerlies, not Ekman transport, explained residual supply variation at our sampling area. Once in the estuary, net flux and competence state matched the expected trends. Net upstream flux increased from B. sexdentatus to P. africanus, favoring transport to a sheltered coastal habitat (N. pinnotheres), or to the upper estuary (P. africanus). Competence state was highest in N. pinnotheres, intermediate in B. sexdentatus and lowest in P. africanus, as expected if larvae respond to cues from adequate benthic habitat. P. africanus megalopae were found close to the bottom, not above, rendering slower upstream transport than anticipated.

Microcystin production by a freshwater spring cyanobacterium of the genus Fischerella

We investigated the production of a hepatotoxic, cyclic heptapeptide, microcystin, by a filamentous branched cyanobacterium belonging to the order Stigonematales, genus Fischerella. The freshwater Fischerella sp. strain CENA161 was isolated from spring water in a small concrete dam in Piracicaba, Sao Paulo State, Brazil, and identified by combining a morphological description with 16S rRNA gene sequencing and phylogenetic analysis. Microcystin (MCYST) analysis performed using an ELISA assay on cultured cells gave positive results. High performance liquid chromatography-mass spectrometry (HPLC-MS) analysis detected 33.6 mu g MCYST-LR per gram dry weight of cyanobacterial cells. Microcystin profile revealed by quadrupole time-of-flight tandem mass spectrometry (Q-TOF-MS/MS) analysis confirmed the production of MCYST-LR. Furthermore, genomic DNA was analyzed by PCR for sequences similar to the ketosynthase (KS) domain of the type I polyketide synthase gene, which is involved in microcystin biosynthesis. This revealed the presence of a KS nucleotide fragment similar to the mcyD and ndaD genes of the microcystin and nodularin synthetase complexes. Phylogenetic analysis grouped the Fischerella KS sequence together with mcyD sequences of the three known microcystin synthetase operon (Microcystis, Planktothrix and Anabaena) and ndaD of the nodularin synthetase operon, with 100% bootstrap support. Our findings demonstrate that Fischerella sp. CENA161 produces MYCST-LR and for the first time identify a nucleotide sequence putatively involved in microcystin synthesis in this genus. (C) 2009 Elsevier Ltd. All rights reserved.

First-order-reversal-curve analysis of Pr-Fe-B-based exchange spring magnets

Ribbons of nominal composition (Pr(9.5)Fe(84.5)B(6))(0.96)Cr(0.01)(TiC)(0.03) were produced by arc-melting and melt-spinning the alloys on a Cu wheel. X-ray diffraction (XRD) reveals two main phases, one based upon alpha-Fe and the other upon Pr(2)Fe(14)B. The ribbons show exchange spring behavior with H (c) = 12.5 kOe and (BH)(max) = 13.6 MGOe when these two phases are well coupled. Transmission electron microscopy revealed the coupled behavior is observed when the microstructure consists predominantly of alpha-Fe grains (diameter similar to 100 nm.) surrounded by hard material containing Pr(2)Fe(14)B. The microstructure is discussed in terms of a calculation by Skomski and Coey. A first-order-reversal-curve (FORC) analysis was performed for both a well-coupled sample and a poorly coupled sample. The FORC diagrams show two strong peaks for both the poorly coupled sample and for the well-coupled material. In both cases, the localization of the FORC probability suggests magnetizing interactions between particles. Switching field distributions were calculated and are consistent with the sample microstructure.

Hopf Bifurcations in a Watt Governor with a Spring

This paper pursues the study carried out in [ 10], focusing on the codimension one Hopf bifurcations in the hexagonal Watt governor system. Here are studied Hopf bifurcations of codimensions two, three and four and the pertinent Lyapunov stability coefficients and bifurcation diagrams. This allows to determine the number, types and positions of bifurcating small amplitude periodic orbits. As a consequence it is found an open region in the parameter space where two attracting periodic orbits coexist with an attracting equilibrium point.