Effect of large- and small- bodied zooplankton on phytoplankton in a eutrophic oxbow

Macrozooplankton and microzooplankton effects on the phytoplankton were measured in situ in a eutrophic lake. Indigenous phytoplankton were incubated for 5 days in 301 mesocosms with either the macro- and microzooplankton (complete), microzooplankton only (micro) or no zooplankton (none). Changes in phytoplankton biovolume were investigated. Rotifer densities became significantly higher in the 'micro' treatment than in the 'complete' and 'none' treatments. Total algal biovolume changed little in the 'complete' and 'none' treatments, but increased significantly in the 'micro' treatment. The results suggest that macrozooplankton (Daphnia magna) suppressed it and microzooplankton (Keratella cochlearis) enhanced it. They had opposite net effects on the phytoplankton. Suppression of microzooplankton by Daphnia probably had an indirect negative effect on the phytoplankton

The measurement of dissolved oxygen today - tradition and topicality

Today, the determination of the dissolved oxygen content of natural waters is practically an essential duty whenever background data is collected for investigations of a hydrobiological, ecological, and nature or environmental protection viewpoint. If the method by which the measurements are carried out is concerned, it can be stated that the 120 year old, classical Winkler-method is inevitable even today. However the development of hydroecological sciences have laid claim to such expectations that the necessity of in situ oxygen determinations have become increasingly important. In our work we present the survival of the traditional Winkler-method in the present practice, we review all those viewpoints which have facilitated the widespread application of in situ oxygen determinations as well as the methods of all the measurements that are presently regularly applied in the investigations of natural waters

Spatially extended OH+ emission from the Orion Bar and Ridge

We report the first detection of a Galactic source of OH+ line emission: the Orion Bar, a bright nearby photon-dominated region. Line emission is detected over ~1' (0.12 pc), tracing the Bar itself as well as the Southern tip of the Orion Ridge. The line width of ~4 km/s suggests an origin of the OH+ emission close to the PDR surface, at a depth of A_V ~0.3-0.5 into the cloud where most hydrogen is in atomic form. Steady-state collisional and radiative excitation models require unrealistically high OH+ column densities to match the observed line intensity, indicating that the formation of OH+ in the Bar is rapid enough to influence its excitation. Our best-fit OH+ column density of ~1x10^14 cm^-2 is similar to that in previous absorption line studies, while our limits on the ratios of OH+/H2O+ (>~40) and OH+/H3O+ (>~15) are higher than seen before. The column density of OH+ is consistent with estimates from a thermo-chemical model for parameters applicable to the Orion Bar, given the current uncertainties in the local gas pressure and the spectral shape of the ionizing radiation field. The unusually high OH+/H2O+ and OH+/H3O+ ratios are probably due to the high UV radiation field and electron density in this object. In the Bar, photodissociation and electron recombination are more effective destroyers of OH+ than the reaction with H2, which limits the production of H2O+. The appearance of the OH+ lines in emission is the result of the high density of electrons and H atoms in the Orion Bar, since for these species, inelastic collisions with OH+ are faster than reactive ones. In addition, chemical pumping, far-infrared pumping by local dust, and near-UV pumping by Trapezium starlight contribute to the OH+ excitation. Similar conditions may apply to extragalactic nuclei where OH+ lines are seen in emission.Comment: Accepted by A&A; 10 pages, 5 figure

Growth features of the Amur sleeper, Perccottus glenii (Actinopterygii: Perciformes: Odontobutidae), in the invaded Carpathian Basin, Hungary

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Optimised selenium enrichment of Artemia Sp. Feed to improve red drum (Sciaenops Ocellatus) larvae rearing

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