Vorschlag zur Auswertung von PAK-Kontaminationen

The behaviour of this group of substances may be considered as an example for the ubiquitous occurence of xenobiotics in the environment. Regrettably, the measurements presented in numerous publications often cannot be directly compared with each other. A first step towards harmonization can be achieved by referring the measuring programmes or the presentation of results to the six aromatics of the German Drinking Water Ordinance (TWV) (Σ6) or the sixteen compounds of the EPA list. The tendency of the PAH group to fractionation in air, water, and soil as well as in some cases during analysis must be taken into acount. In this respect, the first six aromatics of the EPA list are only partially suitable for comparisons of results. The six TWV aromatics in soils, sediments, aquatic suspended solids, and sewage sludges, and to a certain extent also in airborne dust, make up a mass portion of C_Σ6=40–50% of the Σ16 according to EPA. For Fluoranthene (Fluo) and Benzo(a)pyrene (Bap) as quide parameters, concentration quotients [single aromatic versus (Σ6)] may be given as estimates, which are on average C_Fluo=33%, and C_Bap=13%. By means of these quotients it is possible to calculate the values for the whole list by means of the data of the single aromatic C_Fluo×3=C_Σ6, or C_Bap×7,7=C_Σ6, and as a check C_Fluo/C_Bap=2,5. For estimating purposes, the relation between the two lists may be assumed als C_Σ6×2=C_Σ16. These estimating values apply to mixes of PAH, which originate from many single sources (emitters), are transported through the atmosphere with dust and settle, and/or enter water bodies after being washed from road surfaces. The estimates serve as plausibility check and for extrapolation, but they cannot replace the analysis for individual substances in the identification of the pollution source or in the study of their environmental behaviour.     

Preliminary Measurements of Turbulence and Environmental Parameters in a Sub-Tropical Estuary of Eastern Australia

In natural systems, mixing is driven by turbulence, but current knowledge is limited in estuarine zones where predictions of contaminant dispersion are often inaccurate. A series of detailed field studies was conducted in a small sub-tropical creek in eastern Australia. Hydrodynamic, physio-chemical and ecological measurements were conducted simultaneously to assess the complexity of the estuarine zone, notably the interactions between turbulence and environment. The measurements were typically performed at high frequency over a tidal cycle. The results provide an original data set to complement long-term monitoring and a basis for a more detailed study of mixing in sub-tropical systems. Unlike many long-term observations, velocity and water quality scalars were measured herein with sufficient spatial and temporal resolutions to determine quantities of interest in the study of turbulence, while ecological indicators were sampled systematically and simultaneously. In particular the results yielded contrasted outcomes, and the finding impacts on the selection process for key water quality indicators.     

The poison gland of the antMyrmicaria eumenoides and its role in recruitment communication

Summary The antMyrmicaria eumenoides is a significant arthropod predator. For rapid attraction of large numbers of nestmates to newly discovered food sources the ants use an efficient recruitment communication system based on the poison gland secretion. Workers exhibit age-based division of labour. Young workers perform brood-care; their poison gland reservoir develops and reaches its final size of 0.5 µl at an age of 6 weeks, when they become foragers. The secretion deposited during combat with enemies or prey is composed of equal amounts of both a high volatile and a low volatile fraction. Within the high volatile fraction (+)—limonene is the main component (97%) and is the only olfactory trigger to alert ants in the vicinity and to recruit them to places of combat, where they assemble. Ants respond to synthetic (+)—limonene in exactly the same way as to the poison gland secretion when applied at the same airborne concentrations. Further components of the high volatile fraction are four additional monoterpene hydrocarbons and hexanoic nitrile. The high volatile and the low volatile fraction of the poison gland secretion each have dual functions: The low volatiles, of which the main component is an alkaloid, serve as a fixative and extend the effective period of the limonene signal by modifying its evaporation kinetics. On the other hand the high volatile recruitment signal (+)—limonene is also the solvent for the alkaloid and enhances its spreading on the surface of the cuticle of arthropod enemies or prey.     

Chemical structure and biological activities of lipid A's from various bacterial families

The endotoxic principle of lipopolysaccharides (LPS) is localized in their lipid A component. Biological effects of LPS on, for instance, body temperature, blood pressure, and blood picture, are also induced by free lipid A. In contrast to the great variability of the 0-specific chains, the chemical structure of lipid A is much more constant. It is common for Salmonella and similar for other genera of the Enterobacteriaceae. Recently, a number of lipid A's have been recognized that exhibited distinct structural features compared with Enterobacteriaceae. These lipid A's were found to be also distinct with regard to some of their biological properties.     

Ritter’s dry-bed dam-break flows: positive and negative wave dynamics

Dam-break flood waves are associated with major environmental disasters provoked by the sudden release of water stored in reservoirs. Ritter found in 1892 an analytical solution to the wave structure of an ideal fluid released during an instantaneous dam failure, propagating over initially dry horizontal terrain. This solution, though ideal, hence frictionless, is widely used to test numerical solutions of the Shallow Water Equations (SWE), and as educational tool in courses of fluid mechanics, given that it is a peculiar case of the Riemann problem. However, the real wave structure observed experimentally differs in a major portion of the wave profile, including the positive and negative fronts. Given the importance of an accurate prediction of the dam break wave, the positive and negative wave portions originating from the breaking of a dam with initially dry land on the tailwater reach are revisited in this work. First, the propagation features of the dry-front are investigated using an analytical boundary-layer type model (Whitham/Dressler/Chanson model) constructed matching an (outer) inviscid dynamic wave to an (inner) viscous diffusive wave. The analytical solution is evaluated using an accurate numerical solution of the SWE produced using the MUSCL-Hancock finite-volume method, which is tested independently obtaining the solution based on the discontinuous Galerkin finite-element method. The propagation features of the negative wave are poorly reproduced by the SWE during the initial stages of dam break flows, and, thus, are then investigated using the Serre–Green–Naghdi equations for weakly-dispersive fully non-linear water waves, which are solved using a finite volume-finite difference scheme.