Untersuchungen des Phytoplanktons des Göta älv: Ausgeführt im Auftrage vom Wasserwerke in Göteborg. Vorläufige Mitteilung

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Abstract

These investigations were pursued on the initiative of the cheaf of the Waterworks, Mr. P. G. Blidberg.

Samples were taken of the seston by straining known volumes of water through a plankton net (Müller gauze No. 25), and other samples were taken directly out of the water. At the intake this was done in 1935 sometimes daily, in 1936 every fortnight, in 1937 every week. Samples also were taken at different seasons of the year at the other Stations indicated on the map. It has not been the aim of these studies to determine the species of all phytoplankton organisms in the samples. The algae have been counted by means of a microscope of the Utermöhl type (i. e. an inverted microscope).

There are a few copies of some reports available in typescript at the Gothenburg Waterworks, and short summaries have been printed in the annual records (1937 and 1938).

Abioseston abounds all the year round, but particularly in winter. The deposits on the filter-sand in the Waterworks Sand Filters consist, especially in winter, of clay, held together by thread-shaped bacteria (Leptothrix major Dorff?). Among the Plankton algae, the Diatoms are the most prominent. Melosira-maximum, chiefly conditioned by M. helvetica, is found in April and May and also in late autumn. The arrival of the spring-maximum is probably connected with the total spring circulation in Lake Vänern. The Diatoms, and together with them, usually, the total amount of algae, reach their maximum in spring or early summer. In summer and autumn the Diatoms are still abundant, but with them there also appear, in particular, species of Eudinobryon, Sphaerocystis Schroeteri, and also Anabaena and other Cyanophyceae in small numbers. In early spring and late summer monads are sometimes to be found to a maximum of 100–250 per ccm.

During the period 1935–1937, the quantity of phytoplankton was observed to be least in 1936, and greatest in 1935, a fact which may have been related to the running off of the water. The volume of the water-flow, in cubic metres per second, at Lilla Edet, is shown in the table in Fig. 2. The conditions prevalent in 1939 make it dobtful, however, whether „Schroeders Law” can be applied to the river Göta älv.

The differences in the temperature and the chemical condition of the water do not essentially determine the differences in the plankton production for the different years.

Regarded from Lake Vänern to the sea, the river does not show any noticeable tendency to be divided into zones, with regard either to the quantity or the quality of the plankton, except in the case of the Stations No. 3 to No. 1, where sea-water begins to be present and the fresh-water plankton diminishes. Among the stations, at which samples have been taken, only No. 27 (Lake Vassbotten, see map), shows a tendency to be eutrophic. The plankton of the river Göta älv consists chiefly of plankton which has flowed rapidly from Lake Vänern.