In über 150 Schweizer Trinkwasserwerken wird Ozon vor allem als Desinfektionsmittel und zur Entfernung geruchsbildender Stoffe eingesetzt. zur Zeit wird vermehrt untersucht, wie weit sich der Ozonungsprozess auch dazu eignet, organische Spurenstoffe aus dem Wasser zu eliminieren. Die Kinetik der Eliminationsprozesse wurde in neueren Arbeiten (1, 2) ausführlich untersucht. Die erarbeiteten Grundlagen wurden dabei an Wasserproben überprüft, welche vor der Ozonung mit Spurenstoffen im Konzentrationsbereich von 1-100 μg/l aufgestockt warf . Wie weit diese Ergebnisse auch auf die Elimination von spurenstoffen eines Seewassers im ng/1-Bereich übertragen werden können, musste noch geprüft werden. In dieser Arbeit wird über das Verhalten von ausgewählten Seewasserinhaltsstoffen während der Labor- und Werksozonung berichtet.

The chemical and biological conditions of the Lake of Lucerne and of the lower basin of the Lake of Constance are discussed on the basis of observations on the phosphorus content in the course of the past ten years. The heavy load by suspended solids on two basins on the Lake of Lucerne caused a decrease of soluble P-compounds by adsorption. In two other basins of the same lake considerable phosphorus resolubilization from sediments is on the way since 1968. Phosphorus dynamics in the lower basin of Lake Constance is governed by wash-out and by resolubilization and sedimentation respectively. We recommend to adopt a minimum lower limit of 4 to 6 mg O₂/l at any point and at any time in the water body of a lake as a specific criterion for defining the final aim of lake protection or lake restauration measures. With the fulfillment of this requirement, satisfactory conditions for all utilizations of a lake ecosystem will exist.

The potential utilization of simple chemical and biological models (equilibrium and steady state systems, model of ecological succession) as aids in the systemic evaluation of water quality is investigated. This evaluation must be based, however, on the assessment of the entity of ecologically relevant physical, chemical and biological factors and on the temporal development of the particular aquatic ecosystem. Hence, it is not possible to establish a generally valid index on water quality; specifically, it is impossible to codify water quality by a saprobia index.

Different process combinations which all end up with contact filtration as the last treatment step are shown to be possible ways of advanced removal of phosphorus. The process potential of contact filtration in different process combinations was investigated in pilot scale experiments. The results show that a process with pre- or simultaneous precipitation combined with contact filtration is a feasable process in practice and leads to very low phosphorus and suspended solids concentrations. Chemical conditions and suspended solids characteristics are analysed and conclusions are drawn for the design of contact filters for wastewater treatment.

With the help of theoretical understanding, the results of pilot and laboratory activated sludge experiments are evaluated and interpreted. It is shown how nitrification is influenced by temperature and digester supernatant. A dynamic simulation model is able to describe the performance of nitrifying activated sludge plants from hour to hour and longer periods with high accuracy.

In 1969/70, chemical and physical parameters, phytoplankton and recent sedimentation at different levels were investigated in the mesotrophic Lake of Lucerne (Horw Bay) and in the highly eutrophic Rotsee.<br/> The rates of sedimentation came to 1277.4 g dry matter/m²·year in Horw Bay and to 879.3 g dry matter/m²·year in the Rotsee. The chemical analysis of sediments included the following components: total organic substance (loss on ignition), organic C, clay minerals (HCl-insoluble fraction), Ca, Mg, P, N, Fe and Mn. The Rotsee is distinguished by higher nutrient concentrations, higher rates of sedimentation (exceptions: clay minerals, Fe, to a certain extent N and Mn) and by a greater biomass of phytoplankton.<br/> The distribution and succession of selected species and groups of phytoplankton are discussed, the velocity of sinking, the degradation, the growth dynamics and the measure of trophic state are calculated.<br/> For both lakes, a phosphorus and a nitrogen balance have been drawn up. The N:P ratio continually decreases running through the nutrient cycle from the input to the storing into the bottom sediments. The intrabiocoenotic phosphorus cycle in the epilimnion is very intensive and supplies approximately two thirds of the nutrient requirements for primary production in both the Horw Bay and the Rotsee.

The Lakes of Lucerne (Horw Bay), Thoune (Faulensee region), Lugano (Lugano Bay) and Lake Mauen, a small lake in central Switzerland, were investigated periodically from 1965 to 1967. The water was analysed in view of determining the following components: oxygen, nitrate-nitrogen, phosphate-phosphorus (PO₄-P), phosphorus incorporated in cell mass (PP), Langlier index. Phytoplankton was counted in an inverted microscope with special consideration to quantitative distribution of <I>Oscillatoria rubescens</I> D. C. at various depths. Temperature and light variations in function of depth were measured simultaneously and the production rate was determined by means of the C-14 method.<br/> In over 80% of all cases, the <I>Oscillatoria rubescens</I>-maxima coincided with depths showing temperatures under 14 °C. In over 65% of all cases, the intensity of green light (VG9) in such depths was less than 4% of the surface intensity. The influence of light and temperature on the growth of <I>Oscillatoria rubescens</I> was tested with a light thermostat. It was shown that maximum growth occurred at temperatures around 30 °C and light intensities of 1500 Lux. Increase of light intensities above 1500 Lux had a negative effect on the growth rate at temperatures higher than 29 °C.<br/> Our investigations lead to the conclusion that <I>Oscillatoria rubescens</I> is a eurythermal, oligophotic species and that the occurrence of <I>Oscillatoria rubescens</I>-maxima in the vertical distribution of the phytoplankton in a lake is caused by the combined effects of light and temperature.

While NTA or iron may stimulate phytoplankton photosynthesis on a short-term basis in the mesotrophic Lake of Lucerne, they impede this process in the eutrophic Greifensee. After a few days, however, this reaction tapers off. It is therefore highly unlikely that iron enters into play as a growth-limiting factor; the iron which inevitably gets into lakes through wastewater treatment plant effluents as a result of tertiary treatment (precipitation with Fe³⁺) will not have a long-term stimulating effect on plankton production. Both iron-through adsorption-and NTA-through chelation-reduce the supply of free ions of various metals, especially copper. Since, on the one hand, these free ions are needed for plankton growth and, on the other, have a toxic effect even in small quantities (μg/l), the medium can, through addition of iron or NTA, be disintoxicated or the trace metals limited, with corresponding increase or curtailment of algal production. The different patterns for the two lakes examined can be explained by the influence of the natural organic materials, found in each particular lake, on the free ions.

With one-factor experiments, the drift of larvae of <I>Ecdyonurus venosus</I> has been analysed in a stream model. The distances travelled by drifting animals as a function of water velocity have been determined, as well as some drift rhythms. Drift-inducing factors are principally scarecity of food (lack of periphyton) and movement of substrate. Induction of drift by small water velocities can be caused by insufficient oxygen supply. The typical drift minimum during the final larval instar is said to be caused by a pseudo-pupal stage. After temperature shocks of ±5°C respectively, the animals acclimate within 2 days. An increase in temperature induces a decrease in drift reates and vice versa. Sex, predation and competition do not influence drift. The mean flight range of the imagoes (flight-mill) is 2,794 m, the maximum upstream movement of the larvae 140 m/24 h.

- In der Einleitung werden die Problemstellung dargelegt und die wichtigsten, physiographischen Parameter aufgezählt. Die Notwendigkeit der chemischen Datenerhebung wird gezeigt.<br />- Als wichtige Parameter bei der Prägung der Makroinvertebratenzönose werden beschrieben:<br />· Hochwasserhäufigkeit, die relativ gut mit der Schubkraft korreliert<br />· Temperatur<br />· Strömungsgeschwindigkeit, die sich zwar bei allen Probenahmestellen ähnlich zeigt, jedoch generell eine Teilung des Benthos in drei hydraulisch verschiedene Zonen (strörnungsexponierte Oberseite von Steinen, strömungs schützte Toträume, Interstitialraum) bewirkt.<br />Alle anderen Parameter werden vernachlässigt.<br />- Die Probenahmetechnik (Surbersampler mit 400 cm² Grundfläche und 0.25 mm Maschenweite und mindestens 6 Einzelproben/Probe) wird begründet.<br />- Alle ökologischen Kenntnisse über die häufiger gefundenen Tiere werden zusammengestellt und in einem synökologischen Modell, bei dem die Verhältnisse Räuber:Filtrierer:Substratfresser:Weider:Sammler mit 6:10:18:18:45 vorgegeben werden, eingetragen.<br />- Die beiden Flüsse Töss und Necker und die 6 Probenahmestellen mit ihren physiographischen und chemischen Daten werden beschrieben. Dabei zeigt es sich, dass die beiden Flüsse schwachbis unbelastet sind und sich in vielen Parametern (Temperatur, Strömungsgeschwindigkeit, chemische Konzentrationen) gleichen, sich jedoch in der Hochwasserhäufigkeit stark unterscheiden.<br />- Die biologischen Verhältnisse an den einzelnen Probenahmestellen werden dargestellt, wobei auffällt, dass die oberen beiden Stellen in der Töss schwach besiedelt sind, die unterste in der Töss von <em>Leuctra</em>, diejenige im Necker von <em>Rhithrogena semicolorata</em> dominiert wird.<br />- das oben gezeigte, synökologische Modell wird auf die 6 Probenahrnestellen angewendet, indem alle Tiere einem oder mehreren der fünf Kompartimente "Weider","Sammler", "Filtrierer", "Substratfresser" oder "Räuber" zugewiesen werden.<br />- Bei einem Vergleich zwischen den beiden Flüssen zeigt es sich, dass in der Töss die Sammler häufiger, dafür die Weider und die Filtrierer seltener sind als im Necker, was auf die unterschiedliche Hochwasserhäufigkeit zurückgeführt wird.<br />- Die artenmässige Besetzung der einzelnen Kompartimente wird v.a. auf die Temperatur zurückgeführt.

Of the problems connected with vertical migration, the work described deals with certain aspects which were investigated by a new method. The experimental animals were adult males of the spring and summer populations of Cyclops abyssorum praealpinus (KIEFER) and Cyclops vicinus lobosus (KIEFER). The swimming traces were for the first time observed continually over a period of about eight minutes and photographically recorded, without exposing the animals to additional stimulus from the recording technique. The animals' natural biotope was imitated as closely as possible and experimentally stabilised so that irradiance reductions were the only stimulus. The results can be summarised under three headings: <BR/> The direct result of an intensity reduction was a passive sinking of the animals, which we have called the "wait and see" -effect. It depends mainly on the relative reduction of intensity and, to a small extent, on the basic intensity. <BR/> The later, more prolonged upward movement, which we call the "swimming-up"-effect, depends mainly on the prevailing irradiance. <BR/> Jf the irradiance is constant, the animals swim for a considerable time in a restricted region, termed the "lingering-space". Its dimensions are determined by the direction-dependent swimming velocities. These velocities vary according to the species and the time of the year. <BR/> As expected, the animals showed no horizontal orientation behaviour, nor were they influenced by the short- wavelength infra-red light used for photographing. An endogenous rhythm was only barely perceptible. <BR/> The results were analysed exclusively by modern statistical techniques.