FRAGILE ESTUARINE SYSTEMS–ECOLOGICAL CONSIDERATIONS1

Studies of fish species and populations indicate a high degree of fragility for estuarine ecosystems. Slight stresses tend to disrupt energy flow systems and lead to lower levels of biological productivity, shortened food chains and poorer diversity of species. For individual species low-level stresses tend to suppress metabolism and growth processes. Minor stresses can also substantially reduce populations. Stress processes are quantifiable and amenable to mathematical modeling.     

Atmospheric transport of atrazine: a simple device for its detection

Thin-layer chromatography plates were exposed at three different locations in Bavaria for 3-week periods during the growing season of maize. The adsorption of traces of atrazine was detected by thin-layer chromatography, GC-MS, and by an enzyme immunoassay. It was restricted to the sowing season, which coincides with the application of atrazine. The herbicide could not be detected after this time. The simplicity of the adsorption device, combined with a serological assay, render this procedure suitable for detecting airborne organic pollutants.     

Modelling the biochemical oxidation processes in artificial conditions of waste treatment plants

For natural water bodies there are many models of biochemical oxidation of organic pollutants, from simple to complicated ones. For the artificial conditions of waste water treatment plants there are numerous models of oxidation processes too. The authors believe that a better understanding of these processes in nature would be gained if the oxidation processes in more simple artificial conditions were understood.An attempt has been made to explain the variety of types of models of waste treatment in an activated sludge system or a biofilm reactor by the diffusion mechanism of oxidation of single substrates on the one hand, and by superposition of the kinetics of oxidation of single substrates in measurements of the dynamics of oxidation of a complex pollutant on the other hand.The conditions in which zero- and first-order models are valid in the oxidation of single substrates are derived. Respective formulae for rate constants are given. Monod's model is valid in a broader range of substrate concentration variations. An approximate formula for the half-saturation constant is proposed. Satisfactory agreement with experimental data for glucose and ammonia substrates is shown.The formal character of models being used at present is claimed for multicomponent substrates. The accuracy of the calculation is largely governed by the number of model coefficients. Similar results obtained by Monod's and Grau's models, often used in practice, are emphasized.