Transitions in bacterial communities along the 2000 km salinity gradient of the Baltic Sea

Salinity is a major factor controlling the distribution of biota in aquatic systems, and most aquatic multicellular organisms are either adapted to life in saltwater or freshwater conditions. Consequently, the saltwater–freshwater mixing zones in coastal or estuarine areas are characterized by limited faunal and floral diversity. Although changes in diversity and decline in species richness in brackish waters is well documented in aquatic ecology, it is unknown to what extent this applies to bacterial communities. Here, we report a first detailed bacterial inventory from vertical profiles of 60 sampling stations distributed along the salinity gradient of the Baltic Sea, one of world's largest brackish water environments, generated using 454 pyrosequencing of partial (400 bp) 16S rRNA genes. Within the salinity gradient, bacterial community composition altered at broad and finer-scale phylogenetic levels. Analogous to faunal communities within brackish conditions, we identified a bacterial brackish water community comprising a diverse combination of freshwater and marine groups, along with populations unique to this environment. As water residence times in the Baltic Sea exceed 3 years, the observed bacterial community cannot be the result of mixing of fresh water and saltwater, but our study represents the first detailed description of an autochthonous brackish microbiome. In contrast to the decline in the diversity of multicellular organisms, reduced bacterial diversity at brackish conditions could not be established. It is possible that the rapid adaptation rate of bacteria has enabled a variety of lineages to fill what for higher organisms remains a challenging and relatively unoccupied ecological niche

Modeling the radiation of modern sound reinforcement systems in high resolution

Starting from physical theory, a contemporary novel framework is developed for the acoustic simulation of sound radiation by loudspeakers and sound reinforcement systems. A variety of own measurements is presented. These agree very well with the predictions of the computer model considering practical uncertainty requirements. First, small sound sources are discussed. Such a source is used at receive distances much larger than its characteristic dimension. A theoretical foundation is derived for the accurate reproduction of simple and multi-way loudspeakers using an advanced point source model that incorporates phase data. After that the practical implementation of this so-called CDPS model is presented including measurement requirements and the newly developed GLL loudspeaker data format. Subsequently the novel model is validated in detail by means of a number of different measurement results. In the second part, larger systems are analyzed such as line arrays where the receiver is often located in the near field of the source. It is shown that theoretically any line source can be decomposed into smaller elements with a directional characteristic. This approach allows modeling the performance of the complete line source in both near and far field as long as the considered receive location is in the far field of the elementary sources. Several comparisons of measured line arrays display good agreement with predicted behavior and underline the superiority of this model compared to existing simulation methods. At the end theoretical methods and measured results are used to show for the first time that the influence of production variation among supposedly identical cabinets has a measurable but small effect on the overall performance of a line array. The last part of this work deals with the consequences of fluctuating environmental conditions, such as wind and temperature, on the propagation of sound. In the context of this work, it is of particular interest to consider the coherent superposition of signals from multiple sources at the receive location. For this purpose a novel theoretical model is developed that allows predicting the mean variation of the propagation delay of the sound wave as a function of the statistical properties of the environmental parameters. Measurements of these properties as well as of the sound travel time are consistent with corresponding modeling results. Finally, it is discussed how the average total sound pressure level of a line array or loudspeaker arrangement is affected by the random variation of propagation delays. A part of this work was distinguished with the AES Publications Award 2010. Parts of the proposed data format have been incorporated into the international AES56 standard