Jeroen P.E. Gerritsen

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We investigated four stream types in four different bioregions, classified by catchment area and altitude, and stressed by different degrees of organic pollution and habitat alteration. We examined a macro-invertebrate based multimetric approach for Austrian rivers as a potential assessment method within the European Water Framework Directive. Benthic(More)
Surface chemistry of both particles and animals is important in filter feeding at low Reynolds number. Daphnia magna, fed mixtures of three sizes of polystyrene particles, retained particles that were smaller than the mesh size of the animals (1.0 micrometer) at greater efficiencies than predicted by a sieving model. Retention efficiency of the smallest(More)
Over-enrichment leading to excess algal growth is a major problem in rivers and streams. Regulations to protect streams typically incorporate nutrient criteria, concentrations of phosphorus and nitrogen that should not be exceeded in order to protect biological communities. A major challenge has been to develop an approach for both categorizing streams(More)
We present numerical simulations of isolated disk galaxies including gas dynamics and star formation. The gas is allowed to cool to 10 K, while heating of the gas is provided by the far-ultraviolet flux of all stars. Stars are allowed to form from the gas according to a Jeans instability criterion: gas is unstable when the Jeans mass is smaller than a(More)
The spiral galaxy NGC 6503 exhibits a regular kinematical structure except for a remarkable drop of the stellar velocity dispersion values in the central region. To investigate the dynamics of the disc in general, and that of the central region in particular, a theoretical framework has been described. This includes a mass decomposition of the galaxy into a(More)
The new European assessment system for freshwater ecosystems is based on reference conditions. As the ecological status of rivers must be determined with respect to the near-natural reference conditions focus is given to establish a typological framework. A basic part of this typology is the ecoregion approach. Multivariate analysis of the benthic(More)
We present N -body simulations of Low Surface Brightness (LSB) galaxies and their Interstellar Medium to investigate the cause for their low star formation rates (SFR). Due to their massive halos, stellar disks of LSB galaxies are very stable and thin. Lack of dust makes the projected edge-on surface brightness of LSB galaxies comparable to the projected(More)
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