Sichttiefen und Wasserfarben der oberen Seen der Feldberger Seenlandschaft im Jahre 1984 und 1985, sowie ihre Veränderungen seit 1983

A simple device is described for determining the transparency by means of white and black as well as four coloured (450, 525, 575. 625 and 720 nm) Secchi disks. The changes in transparencies and water colours having occurred in the individual years in three lakes are discussed in connection with meteorological data. The differences occurring in a groove lake between three stations indicate the differences of the development of plankton.     

Zustandsentwicklung schleswig-holsteinischer Seen zwischen 1983 und 1993: Eine Betrachtung unter Anwendung der Clusteranalyse

In 1983 the regional authority in Schleswig-Holstein (North Germany) started their long term monitoring programme in 29 lakes. During the following years the number increased to 68 lakes in 1993. The monitoring programme includes the parameter carbon (DOC, TOC), nitrogen (NH₄-N, NO₂-N, NO₃-N, TDN) phosphorus (PO₄-P, TDP), conductivity and temperature. Water samples are taken only once a year during late winter overturn in the main outflow of every lake. In this study TOC, TDN and TDP are chosen as most independent variables by correlation tests. Average concentrations of the years 1983 to 1985 and 1992 to 1993 as well as the concentration difference between 1992/93 and 1983/85 are clustered using the Average Linkage Method. It is necessary to use averages of a few years to reduce effects of interannual variability.Between 1983/85 and 1992/93 the average TDP-concentration in all 29 lakes was reduced by 40% from 0.68 to 0.041 mg/l. TDN-concentrations declined by 13% from 2.6 to 2.3 mg/l. The strong reduction of phosphorus concentrations clearly reflect the success of local sewage purification during the last two decades. The high importance of diffuse input sources for lakes is the reason for the less pronounced decline in TDN concentrations.The increase in TOC-concentrations by 14% (from 9.3 to 10.6 mg/l) between 1983/85 and 1992/93 is no indicator for an increased average annual algae biomass in the lakes. It is a result of unusual algae blooms during the warm winters between 1989 and 1993.Beside some similarities, the dendrogram on the basis of 1983/85 data and the one using 1992/93 values show that a lot of lakes are located to different clusters. The classification on the basis of concentration differences (1992/93–1983/85) yield three larger groups of lakes with a similar development and 5 groups containing only one or two lakes with extraordinary changes in their properties during the decade. To a certain degree, TOC, TDN and TDP can be seen as trophic state indicators. During the decade most lakes have been subject to significant changes and some main cluster with different directions of the trophic development become obvious. On the other hand a considerable number of lakes show a very special behaviour.The results underline that cluster methods are a useful tool to discover and analyse different developments in lakes. The calculation of T-values on the basis of classification results permit the identification of most representative individuals for every group of lakes. Representatives are valuable for a detailed discussion of driving forces and future investigations. They allow to handle a reduced number of lakes with minimal information loss about the entity.Lake Belau is the best representative for the average TOC-, TDN- and TDP-changes in all lakes. Its changes in water qualtity during the decade is discussed in detail. The high interannual variability of Chlorophyll a-, TDP- and TDN-concentrations in this lake clearly reflect the problems of long term analysis on the basis of this very limited monitoring programme.     

Diefischereilichen Verhältnisse im Engadin,in den Seen und im Inn

Ohne Zusammenfassung     

Zur Frage der Karpfenintensivbewirtschaftung von Seen und Eutrophierung

Normally, carp rearing at medium densities is connected with the promotion of daphnia and filtration effects up to “clear-water states”. Therefore and because of the reduction of submerged plants and of the periphyton this form of carp rearing should be possible in eutrophic shallow lakes also at a slight nutrient introduction without any considerable eutrophication. Due to a deterioration of the light climate by re-suspension of the sediment even reductions of the primary production are possible. In the case of the Galenbeck lake a drastic reduction of submerged macrophytes occurred in connection with an increased development of plankton, only general estimations being available of the shares of macrophytes and phytoplankton in the overall production. The phytoplankton increase is are perhaps caused by the absence of filtrating zooplankton due to an insufficient reduction of the indigenous fish stocks. In the Galenbeck lake the structural changes of the ecosystem were due both to the high degree of re-suspension of the very mobile lime sediment and the absence of hard bottom areas, which made the total reduction of the macroflora possible.     

Über die Vertikalverteilung und jahreszeitliche Entwicklung der Larvendichte vonDreissena polymorpha Pallas im Pelagial des unteren Zürichseebeckens im Jahre 1974

The freshwater musselDreissena polymorpha Pallas was sighted for the first time in Lake Zürich about 1969. This meant a real problem for the water treatment of lake water. By means of a pump and vertical net hauls it was tried to add more information to the scarce results on Lake Zürich. Additional dates about temperature, depth of Secchi disk visibility and beam transmittance were collected. There was a first appearance of the larvae ofD. polymorpha at the beginning of June. Following the mean temperature of the epilimnion the number of individuals/m² reached max. 210,000. The greatest concentration measured in 1974 of larvae/m³ was 54,375 at a depth of 4 m. The last appearance ofD. polymorpha was observed at the end of October.

     

Hämatologische,enzymatische und histologische Untersuchungen an Fischen der Weser im Mai 1983

The momentary condition concerning the haematological, physiological, macro-and microscopical constitution of the fishes of the Weser at Grohnde was investigated. The fishes were caught electrically at 22 positions in front of and behind the power-station at Grohnde. In the experiments the blood parameters, the biochemical, enzymatical, parasitological and microscopical changes of several species of fishes were analysed. You can see the details of these changes in the figures and pictures of the publication. It is supposed that organic toxic substances are given into the river in front of the power station, because in this region an industrial undertaking is posted. But also the general water quality of the Weser shows a significant toxicological degree, though the content of salt had been reduced in the former time. One can see that at all positions the blood parameters have changed, we also found haemorrhages in the gills, liver, kidney and spleen, little blood swellings, lymphocysts, necrosis, external and internal parasites, enzymatical changes and inflammations of the liver, kidney and myocard in the fishes. The investigations are being continued.     

Über die Verbreitung von Colikeimen im Bodensee und ihre Zunahme während der letzten zehn Jahre

Zusammenfassung Es gelangen heute rund fünfmal so viele Colikeime in den Bodensee wie vor zehn Jahren. In den nachkontrollierten Einzugsgebieten kommen aber auch gleichzeitig von rund fünfmal mehr Menschen die Abw?sser in den See. W?hrend der Sommerstagnation sind in der obersten Wasserschicht mehr Colikeime zu finden als in der Tiefe. Im Winter bestehen keine vertikalen Differenzen. Bei den niederen Wassertemperaturen im Winter werden mehr coliforme Bakterien nachgewiesen als im w?rmeren Wasser im Sommer. Der in den letzten Jahren stark zunehmende Wasserpflanzenbestand hemmt den Wasseraustausch von Ufer- und Seewasser. Die eingeschwemmten F?kalbakterien verbleiben am Ufer.