AKTIEBOLAGET ATOMENERGI

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1 AE-47 UDC 593.1: Zooplankton from Lake Magelungen, Central Sweden E. Alrnquist This report is intended for publication in a periodical. References may not be published prior to such publication without the consent of the author. AKTIEBOLAGET ATOMENERGI STUDSVIK, NYKOPING, SWEDEN 197

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3 AE-47 ZOOPLANKTON FROM LAKE MAGELUNGEN, CENTRAL SWEDEN Elisabeth Almquist ABSTRACT The investigation of the zooplankton of Lake Magelungen, Central Sweden, was carried out over a period of three years. The aim of the investigation was to illustrate the qualitative and quantitative composition of the zooplankton before the release of waste water from the Agesta Heat and Power Station began. Vertical sampling series were collected once a month at three different stations in the lake. The highest volumes of zooplankton were obtained in the summer. The ciliates predominated when the conditions were unfavourable for other zooplankters, as in winter just below the ice. The rotifers dominated during and immediately after the spring circulation. With one exception the crustaceans reached their peak volume values in August or September. The composition of the zooplankton indicates that Lake Magelungen is highly eutrophic. Printed and distributed in November 197.

4 LIST OF CONTENTS Pa 8 e Introduction Methods List of Species Seasonal and Vertical Distribution of the Zooplankton Species Account Comparison Between the Three Stations In the Lake The Trophic State of the Lake Conclusions References Tables 1-5. Table 6. Table 7. Table 8. Volume of zooplankton, Stations MA, MOB, and MH (average values). The phytoplankton - zooplankton ratio Species regularly occurring in plankton of the three stations. Most common zooplankton species found in earlier investigations in Lake Magelungen Figure captions Figures

5 - 3 - INTRODUCTION Lake Magelungen (map Fig. 1) is situated on the boundary between Stockholm and the municipality of Huddinge, about 1 km S of the centre of Stockholm. It has a length of about 6 km, its area is 2 about 2. 4 km, and the maximum depth about 16.4 m. A more thorough description of the lake is given by Willen [21 J. The investigation of the zooplankton of Magelungen was carried out as part of a team job aiming to provide information about the limnological state of the lake with special respect to future changes due to the outlet of waste water from the Agesta Heat and Power Station. The research work was planned and started by Professor W. Rodhe of the Institute of Limnology, Uppsala, and Dr. P-O. Agnedal and his staff at Studsvik [1 ]. The phytoplankton was investigated by Dr. T. Willen of the Institute of Limnology, Uppsala [21 ]. The zooplankton collections began on March 28, I96, and went on until May 28, To begin with, all sampling was done at the main station MA (map Fig. 2) near the point of the future outlet of waste water. From 1961 on, additional collections were made at two other stations, MH and MOB. During 1962 and 1963 a direct comparison of the three stations was made. METHODS Sampling and preserving The zooplankton samples were collected once a month at the main locality, Station MA (Fig. 2), during the period March 28, I96, to May 28, Samples were taken more frequently in spring and autumn. In order to check the plankton distribution of the lake, samples were also taken, from 1961 on, at Stations MH and MOB.

6 - 4 - Both qualitative and quantitative collections were made. A No. 25 Miiller gauze plankton net was used for the qualitative samplings hauled up from bottom to surface. These samples were mostly examined alive or, when this was not possible, immediately preserved with a portion of formalin to make a 4 per cent solution. The determination of ciliates and rotifers has mostly been performed on living material. Some species, such as the Synchaetae, which are best studied when they are quite relaxed, were treated with a 2 per cent cocaine solution. The quantitative plankton samples were collected simultaneously with a Ruttner 1.51 sampler and a Rodhe 5 1 sampler [1 6 ] at the following depths: at Station MA.2, 1, 3, 5, 8, and 1. 5 m; at Station MH.2, 1, 3, 5, 8, 1.5, and 12.5 m; and at Station MOB at.2, 1, 3, and 4. 5 m. During the first year of investigation all organisms in every sample were counted. From the middle of 1961 the "Vollplankton" samples collected with the Ruttner sampler were used for counting protozoans, rotifers, nauplii, and the smallest crustaceans. The filtered 5 1 Rodhe samples were used for counting all crustaceans but nauplii. All samples were counted in Utermohl chambers with inverted microscope [1 9 J. Plankton volumes The volume of each except the rarer zooplankton species in the Magelungen material has been calculated stereometrically or by weighing (adult copepods and cladocers). It is for many reasons difficult to determine the true volumes of the zooplankters. Besides the seasonal and developmental size variations there is also a variation in size from lake to lake!~9 ". A com-

7 - 5 - parison between my material and the dimensions given, for instance, by Monti, Axelson, and Nauwerck [7, 3, 8] showed the risk of transferring the volume numbers of a species from one water to another without checking and sampling a fairly large material. In this paper I have applied the method introduced by Halme [5 ] to calculate the zooplankton volumes on the basis of the biomass factor ("Biomasse Faktor", BmF) for each species. This may be a way of facilitating comparisons between the standing crops of different waters. Graphical presentation The "cake" diagrams, Figs. 3-6, show the distribution of the zooplankton expressed as per cent of the total volume. These diagrams give no indication of the number of individuals; thus the sample collected from 3 m depth at station MOB on April 8, 1961, contained 28 small ciliates and 1 copepodite of Diaptomus per litre, whereas the sample from the same depth and station collected on May 7, 1963, contained about 52 ciliates of different sizes, 2 rotifers,.2 cladocers, 3.6 copepods, and 25 nauplii per litre. The diagrams, Figs. 7-35, are constructed according to Pejler [l 1, p. 226]. They show the frequencies of the most common species at different depths and on different occasions over the sampling period. Empty circles indicate catches from which the species in question was absent, black dots represent samples containing the species. The diameter of each dot is proportional to the third root of the number of individuals per litre. The isotherms for 6, 1, and 2 C as well as the isopletes for 2 mg? per litre are drawn in the diagrams. The diagrams, Figs , which show the distribution of the total zooplankton volume, are drawn in the same manner, but for technical reasons the

8 - 6 - black dots are replaced by circles. In these diagrams, samples containing no zooplankters are represented by an x. Figs. 39 and 4, showing some typical forms of Daphnia occuring in Magelungen, are drawn from the microscope with the aid of a Treffenberg drawing apparatus constructed by Wild.

9 - 7 - LIST OF SPECIES Rhizopoda Arcella vulgaris Ehrbg Difflugia hydrostatica Zacharias D. limnetica Levander C iliata Coleps sp. Didinium nasutum Mull. 3 3 Epistylis rotans Svec BmF 1 p, E_. sp., on Diaptomus Lionotus cf. folium Duj. 4 3 Metopus es Mull. BmF 1 p. Paramaecium aurelia Ehrbg P. sp. Spirostomum cf. minus Roux Stentor sp. Strombilidium gyrans (Stokes) Kahl Tintinnidium fluviatile (Stein) Kent BmF Tintmnopsis lacustris Entz BmF 1 X 3 3 Vorticella sp., on Microcystis BmF 1 [L j> V_. sp., on Daphnia ^V. sp., on Diaptomus Zoothamnium sp., on Diaptomus 5 3 Ciliata spp., large specimens BmF 1 i Suctoria sp. 4 3 medium sized BmF 1 (j, 3 3 small BmF 1 n

10 - 8 - Rotatoria Anuraeopsis fissa (Gosse) BmF 1 n Ascomorpha saltans Bartsch h 3 Asplanchna priodonta Gosse BmF 1 ji, 5 3 Brachionus angularis Gosse BmF 1 j, ft 3 B. calyciflorus Pallas BmF 1 i B. quadridentatus Hermann 5 3 B. urceolaris Mull. BmF 1 pi, 5 3 Collotheca pelagica (Rousselet) BmF 1 i Colurella sp. i 3 Conochiloides natans (Seligo) BmF 1 \i Conochilus hippocrepis (Schrank) 5 3 C. unicornis Rousselet BmF 1 j[, Euchlanis dilatata (Ehrbg) 5 3 Filinia longiseta (Ehrbg) BmF 1 y, 5 3 Kellicottia longispina (Kellicott) BmF 1 a, 5 3 Keratella cochlearis (Gosse) BmF 1 \x K. quadrata (Mull.) BmF 1 5 \i, 3 Lecane luna (Mull. ) L. nana (Murray) Lepadella patella (Mull.) 5 3 Polyarthra dolichoptera (Idelson) BmF 1 j, P. major (Burckhardt) 5 3 P. remata (Skorikov) BmF 1 ^ 5 3 P. vulgaris Carlin BmF 1 i 5 3 Pompholyx sulcata Hudson BmF 1 i 5 3 Synchaeta oblonga Ehrbg BmF 1 i

11 - 9 - fi 3 S. pectinata Ehrbg BmF 1 [i, 5 3 S. truncata von Hofsten BmF 1 i Trichocerca birostris (Minkiewicz) BmF 1 T. capucina (Wierzejski and Zacharias) T. cavia (Gosse) BmF 1 i T. porcellus (Gosse) 5 3 T. pus ilia (Jennings) BmF 1 j, 5 3 T. rousseleti (Voigt) BmF 1 j, Alona quadrangularis (Mull. ) A. rectangula Sars Cladocera 7 3 Bosmina coregoni Baird BmF 1 i B. longirostris (Mull. ) Ceriodaphnia pulchella Sars C. quadrangula (Mull. ) 7 3 Chydrous sphaericus (Mull. ) BmF 1 fx Daphnia cristata Sars s. str. 7 3 D. cucullata Sars s. str. BmF 1 j, 7 8 D. longispina Mull, s. str. BmF 1-1 Diaphanosoma brachyurum Lievin Graptoleberis testudinaria (Fischer) Leptodora kindti (Focke) BmF [i Pleuroxus uncinatus Baird Sida crystallina (Mull. ) Branchiura Argulus foliaceus (L.)

12 - 1 - Copepoda 7 3 Cyclops ins ignis Claus BmF 1 i 7 3 C. strenuus Fischer s. 1. BmF 1 j, 7 3 Diaptomus gracilis Sars BmF 1 (i. 7 Eucyclops serrulatus (Fischer) BmF Mesocyclops leuckarti (Claus) BmF 1 [i 7 3 M. oithonoides (Sars) BmF 1 \i j, Paracyclops fimbriatus Fischer Ins e eta Chaoborus sp., larvae

13 SEASONAL AND VERTICAL DISTRIBUTION OF THE ZOOPLANKTON Like the phytoplankton the zooplankters reached their highest volumes in the summer. The occurrence of high values varied according to the qualitative composition of the zooplankton (Figs. 3-6). In I96 no marked peak values were observed; it is, however, possible that high values occurred during intervals when no sampling was done. The peak in spring 1961 (Fig. 42) was due to Bosmina coregoni, the peak in autumn 1962 (Fig. 43) mainly to Chydorus sphaericus and Daphnia cucullata, though at Station MH (Fig. 45) preceded by a heavy bloom of rotifers. In spring 1963 (Fig. 43), when the investigation was concluded, the rising values were mainly due to crustaceans, especially nauplii and copepodites of Cyclops. C iliata The ciliates predominated at periods when the conditions were unfavourable for other zooplankters, as in winter just below the ice. In spring at about the time of the break-up of the ice they were more or less evenly distributed throughout the whole water column, in summar they appeared in the deeper more or less oxygen-depleted water layers. Rotatoria The rotifers formed the dominant group in all water layers during and immediately after the spring circulation. In July and August 1962 they were the most abundant group in the topmost water layers. The earliest of these large populations consisted mostly of Synchaetae followed by Polyathrae and Keratella cochlearis. Highest

14 values in the peak of July 1962 were reached by Keratella cochlearis, in August 1962 by Trichocerca pusilla and Pompholyx sulcata. Crustacea Among the cladocers Bosmina coregoni reached a peak in June 1961 at Stations MOB and MA and in July 1961 at Station MOB. These high values were never recorded again during this investigation nor were Bosmina found in such large numbers at Station MH. The most numerous cladocers were Daphnia cucullata and Chydorus sphaericus, the peaks of the latter being always coincident with the bloom of the Cyanophytes [21 fig. 7 J. The occurrence of Daphnia cucullata extended over a longer period of the year: often, as in 1961, Daphnia came earlier than Chydorus and was also found in numbers right on to early winter (December). The Copepods were represented by Diaptomus gracilis and some species of the collective genus Cyclops. Diaptomus gracilis was present practically all the year round; it was volumetrically dominant in many autumn and winter samples. The Cyclops, of which the most important was C. strenuus, reached their highest values in the late spring when their nauplii and copepodites dominated in a great number of samples. The seasonal and vertical distribution of the total volumes or "standing crop" of zooplankton is shown in Figs The annual cycle starts with very low values in early spring in connection with the break-up of the ice. The highest values were always recorded in August or September (tables 1-5), with the exception of 1961 when the early spring caused a high peak of Bosmina coregoni in June. This peak was followed by a lower one in August.

15 SPECIES ACCOUNT Rhizopoda Arcella vulgaris Ehrbg. Occasionally. Station MA. Difflugia hydrostatica Zacharias. Occasionally. Station MA. D. limnetica Levander. Single specimens in net samples from Station MOB. Ciliata Coleps sp. Stations MA and MOB. They were mostly found just under the ice before the break-up and near the bottom immediately after the break-up. Didinium nasutum Mull. Mostly single speciemens. The highest numbers were found at Station MH on May 22, 1962 (1 m: 1 4 inds/l; 8 m: 6 inds/l), and at Station M on May 7, 1963 (. 5 m: 3 inds/l; 1 m: 2 inds/l). Epistylis rotans Svec. Typical summer form found only May- October, always at temperatures above 1 C. The species seems to avoid oxygen values lower than 2 mg/l. Most concentrated in the upper water layers. Peak values in at Station MOB on June 12 (.5 m: 44 inds/l) and at Station MA on July 17 (. 5 m: 1 inds/l), and in 1962 on August 6 Station MOB (. 5 m: 44 inds/l), Station MA (3 m: 32 inds/l), and Station MH (. 5 m: 25 inds/l). E_. sp. Quite frequent on Diaptomus gracilis. Lionotus cf. folium Duj. Mostly found in late winter and early spring in connection with the break-up of the ice. In near-bottom samples also in summer at the oxygen-deficit period. Metopus es Mull. Found only in the deepest water layers at Stations MA and MH at the oxygen-deficit period. Mostly in great numbers (> 12 inds/l).

16 Paramecium aurelia Ehrbg. In net samples from Station MOB. P_. sp. was found during the winter mostly in. 5 m samples (just below the ice cover). Also in deep-water samples during summer. Most frequent at Station MOB. Spirostomum cf. minus Roux. In net samples from Station MOB. Stentor sp. In net samples from Stations MA and MOB. Strombilidium gyrans (Stokes) Kahl. Tintinnidium fluviatile (Stein) Kent was found in fairly great numbers from April to December at all three stations. Peak values August 6, 1962, at Station MOB (1 m: 1 3 inds/l), at Station MA (. 5 m: 1 4 inds/l), and at Station MH (1 m: 3 inds/l). A great outburst occurred simultaneously at all three stations on May 7, 1963, with peak values at Station MOB (3 m: 39 9 inds/l), Station MA (5 m: 3 2 inds/l), and Station MH (3 m: 3 2 inds/l). Only once found below the ice cover (April 16, 1962, Station MOB. 5 m: 2 inds/l). This species is by many authors found to be a cold-water form [cf. 2, pp. 222, 228; 8, p. 4 ]. Halme [5, p. 39, and Abb. 4, p. 38], however, during his investigations in the Pojo bay, found the species to behave as a distinctly stenotherm "mild-water organism" reaching its peak above 18 C. Also during the years of this investigation the species appeared as a summer plankter, most abundant at a temperature of about 18 C or more. Tintinnopsis lacustris Entz (» Codonella crater a (Leidy)). Fig. 7. Eurytherm. Found throughout the year at all three stations. The species seems to avoid periods of low oxygen values. Vorticella spp. Anabaena, Microcystis and other cyanophytes were very often infested with small vorticellae. Other small vorticellae were not infrequently found on Diaptomus and Daphnia.

17 Zoothamnium sp. The most commonly found epizootic ciliate on Diaptomus gracilis. Suctoria sp. A small Acineta-like suctorian was sometimes found on Diaptomus spp. Ciliata spp. As most ciliates were rendered more or less unidentifiable by the preservative, they were all counted together except Codonella cratera, Epistylis rotans, Metopus es, and Tintinnidium f luviatile. Rotatoria Anuraeopsis fissa (Gosse). Found only during the summer period April-October. In quantities only July-September. The highest values were found in the 1-3 m water layers August 6, 1 962, Station MOB (1 m: 6 2 inds/l), Station MA (3 m: 79 inds/l), and Station MH (1 and 3 m: 4 2 inds/l). This is quite in contrast to the findings of Pejler [11, p. 227], who found practically all the specimens of this species in the deepest water layers of Osbysjon. Only on two occasions did I find the Anuraeopsis population to be more or less concentrated to the deepest water layers: on October 1 1, I96, at Station MA (1. 5 m: 2 7 inds/l) and on October 1, 1 962, at Station MH (12.5 m: 1 8 inds/l). These two samples were taken just towards the end of the period of low oxygen content. Ascomorpha saltans Bartsch. Occasionally found at all three stations. Asplanchna priodonta Gosse. Fig. 8. Males November 8, I96, Station MA; eggs November 8, I96, Station MA, and May 1 5, 1961, Stations MOB and MA.

18 Brachionus annularis Gosse. Fig. 9. Common but never in great quantities. Except during the winter 1961 this rotifer appeared as a spring and autumn species. Males February 1 3 and 28, B. calyciflorus Pallas. Fig. 1. B. quadridentatus Hermann. Single specimens at Station MA July 5, 196, and September 21, I96. B. urceolaris Mull. Single specimens at all three stations. Collotheca pelagica (Rousselet). In rather small numbers Station MA July-November. Specimens with 1-2 eggs found in the autumn catches. Colurella sp. Conochiloides natans (Seligo). Fig Conochilus hippocrepis (Schrank). Single specimens, mostly from Station MOB. C. unicornis Rousselet. Fig. 12. No finds from summer I96. Same distributions at all three stations. Euchlanis dilatata Ehrbg. In a net catch from Station MH. Filinia longiseta (Ehrbg. ). Fig. 13. Throughout the year but scarce during the colder seasons. Same distribution at all three stations. Females carrying 1-2 eggs each were found at all seasons. In April 1961 about 1 per cent of the females in the upper water layers were found with 3 eggs each and at Station MOB about 3 per cent with 4 eggs. Kellicottia longispina (Kellicott). Fig. 14. Absent in spring and summer i96, then common but never in great quantities from September 6, I96, to February 26, Absent again during the summer 1962 until November 2.

19 Keratella cochlearis (Gosse). Fig. 15. The most common rotifer of the lake, missing only around the periods of great oxygen deficit. During the present investigation Keratella cochlearis showed a pronounced seasonal variation along the tecta series line: f. macracantha in winter, f. typica in spring and autumn, and ff. micracantha and tecta in summer, Fig. 36. Transitional forms between macracantha and typica and between typica and micracantha were abundant, between, micracantha and tecta much rarer. According to Pejler [12, p. 6 ff. ] this variational pattern is well consistent with the physical and chemical conditions of Magelungen. K. quadrata (Mull. ) Fig Found throughout the year, only avoiding the oxygen deficit periods. Lecane luna (Mull.) Single specimens Stations MOB and MA. L. nana (Murray). Single specimens Station MA. On June 1 2, 1 962, 1 2 inds/l were found at 5 m and 2 inds/l at 1. 5 m. Here we very likely encountered a littoral outflow; other littoral species as well were found at Station MA on this occasion. Lepadella patella (Mull.) Station MA June 12, The specimens found belonged to the quadricarinata type [1 3, p. 347 ff. ]. Polyarthra dolichoptera (Idelson), Fig. 17, and P. vulgaris Carlin, Fig. 18. P. dolichoptera was practically absent during i96. In 1961, however, it increased in numbers and in the samples of April 25 was the dominating rotifer in the upper water layers. Figs. 37 and 38 according to Pejler [9, p. 49; 1, p. 49; see also Amren 2, p. 239]. P. dolichoptera, where they occur together, are mostly driven to the less favourable water layers by P. vulgaris. Perhaps P. dolichoptera got a better start in spring than P. vulgaris, which in summer i96 was very often found infected with small globular bodies [11; p ].

20 P. major (Burckhardt) was found only once, in September I96, at Station MA. P. remata (Skorikov) was found at all three stations but never in great numbers. Pompholyx sulcata Hudson. Fig. 19. Pejler [~\ 4, p. 467 ] points out that this species has a more or less pronounced preference for waters with low transparency values. In the present investigation the peak values of P. sulcata occur at the period when the transparency is lowest [see also 21 j Fig. 4]. Synchaeta oblonga Ehrbg. and S. truncata von Hofsten. Fig. 2. It was not possible to distinguish between these two species in the preserved material. They have therefore been counted together and the diagram is made up of the values so obtained. The net catches, however, showed that S. truncata was by far the most common of the two, causing the peaks in April and May. S. oblonga was mostly found in the autumn to early spring catches. S. pectinata Ehrbg. Fig. 21. Common in spring and autumn but never in quantities. Specimens carrying 1-2 eggs were found in April. This species was often more numerous at Station MA, Station MH showing the lowest values. Trichocerca birostris (Minkiewics). Fig. 22. T. capucina (Wierzejski and Zacharias). Occasional in September, Stations MOB and MA. T. cavia (Gosse). This rotifer was found regularly at all three stations during July to September. Except at the shallow Station MOB it was never found in the bottom layer of the water. T. porcellus (Gosse). Station MA I96, September to November, and 1 961, July 1 7 and September 4. Highest values found: 4 inds/l.

21 T. pus ilia (Jennings). Fig. 23..Quantitatively insignificant during 1 96 and 1 961, it reached a high peak on August 6, 1 962, and was on that date both volumetrically and numerically the dominant zooplankter in the.5 m layer. T. rousseleti (Voigt). Occasionally July-September, Stations MOB and MA. C la doc era Alona quadrangularis (Mull.). Single specimens found at Station MA August 2, i96, and in a net sample November 8, I96, the latter with eggs. A. rectangula Sars. Single specimens Station MA September 4, 1 961, and in a net sample November 1 3, Bosmina coregoni Baird. Figs. 24 and 25. B. longirostris (Mull. ). Occasionally at Stations MOB and MA. Ceriodaphnia pulchella Sars. Station MA on May 1 5, C. quadrangula (Mull. ). Single specimens at Stations MOB and MA August 2 - October 11,1 96, and August October 9, Females carrying ephippii were observed on October 1 1, I96, at Station MA and October 9, 1961, at Station MOB. Two specimens of the var. hamata were caught at Station MH on October 9, Chydorus sphaericus (Mull.). Figs. 26 and 27. Daphnia cristata Sars. s. str. A few specimens were occasionally found at Stations MA and MH. Fig. 39. D. cucullata Sars. s. str. Figs. 28 and 29. This species seems to be the most regularly occurring cladocer of the lake. Males in August and October-November. Females with ephippii were observed in July- August and in November-December. D. cucullata showed a marked seasonal variation. Fig. 4.

22 - 2 - D. longispina Mull. s. str. was found practically throughout the year but never in quantities. In summer, however, it was found mostly in the deeper water layers. Diaphanosoma brachyurum Lievin. Single specimens occasionally at Station MA in late summer. Graptoleberis testudinaria (Fischer). One female with eggs in a net catch, Station MA, September 21, i96. Leptodora kindti (Focke). June-October: Stations MA and MH. Most finds from the upper water layers. 1-2 inds/l. Pleuroxus uncinatus Baird. One specimen, Station MA, September 4, Sida crystallina (Mull. ). Single specimens, Station MA, June 12, 1961, and Station MOB, September 4, Branchiura Argulus foliaceus (L.) was found in a few net catches at Station MH in summer. Copepoda Cyclops spp. Figs C. strenuus was the most important of the Cyclops, found all the year round at Station MA. At Stations MOB and MH, however, it was not caught in samples from early spring. It was always the most numerous Cyclops in the samples from the deeper water layers, often succeeded towards the surface by C. ins ignis (Claus), Mesocyclops leuokarti (Claus) or M. oithonoides (Sars). Fig. 41. Eucyclops serrulatus (Fischer) was only found at Station MA, often in samples which contained other more or less littoral species. Paracyclops fimbriatus Fischer was found in a few net samples.

23 Diaptomus gracilis Sars. Figs The females carried mostly about eggs from summer to late winter. As a rule no females with eggs were caught during March and April. In late spring and early summer, however, they were carrying about 2-3 eggs each. The highest numbers of Diaptomus nauplii were found in late summer, and of copepodites in April. Ins e eta Chaoborus larvae were found in near-bottom water samples, mostly at Station MH, a few finds from Station MA. COMPARISON BETWEEN THE THREE STATIONS IN THE LAKE A mere glance at the map (Fig. 1) reveals a certain difference between the tree stations, MH, MA, and MOB. The roughly 1 3 m deep station MH is surrounded by steep hillsides which give the station a certain shelter from the winds. This condition, its relative depth and the fact that the station is situated off the main flow in the lake, contributes to the pronounced summer stratification of the water of this station. Station MA, which is about 1 1 m deep, is situated within the main flow of the lake. It is more openly situated and consequently more exposed to the winds. Its summer stratification is usually somewhat less accentuated than that of Station MH. Station MOB is also situated within the main flow; the influences of wind, flow and depth (about 5 m), however, cause a more unstable summer stagnation: the stratification is sometimes broken down even in the middle of the summer. Station MOB is further distinguished by the fact that it receives polluted waters from ^.ffluents to the NW part of Magelungen and from Lake Agesta previous to Station MA.

24 As mentioned above, the seasonal distribution of the standing crop of zooplankton is about the same at all three stations (Figs and tables 1-5). Fig. 47 shows the situation during 1962 and 1963, when a direct comparison between the three stations was made. In the diagram the average-value curves for the total volume of zooplankton are drawn for the whole water column from surface to bottom. The ciliate fauna of Station MOB, the most eutrophic (well nourished) of the three stations, was more richly developed and varied than that of the other two stations. The rotifers were the same at all three stations, with the exception of some accidental littoral or rarelyfound species. Also the crustaceans are the same at all three stations with the exception of those indicating high oligotrophy. Daphnia cristata was very rarely found at Stations MA and MH, and Leptodora kindti was not found at all at Station MOB. Chaoborus sp. was also missing in samples from Station MOB. THE TROPHIC STATE OF THE LAKE The trophic degree (nutritional standard) of Lake Magelungen is much higher than would be expected in view of its morphometry. Thus, of its about 36 species regularly occurring in plankton (Table 7), no less than 1 species (Station MA), or 28 per cent, are indicators of eutrophy [l 4, p. 467 ff. ]: Coleps sp., Anuraeopsis fissa, Brachionus angular is, Filinia longiseta, Karatella cochlear is f. tecta, Pompholyx sulcata, Trichocerca birostris, T. pus ilia, Chydorus sphaericus, and Daphnia cucullata, a fact which indicates a very high degree of eutrophy. Also when scoring the lake according to some of the common point systems used in assessing the trophic degree of a lake, we obtain the same

25 result: thus according to the system of Thunmark [l 8, p. 45 ff. and Tab. 1 ] Lake Magelungen is to be placed amongst the "sehr stark eutrophe Seen". The score system of Pejler [14, p. 468] gives for Stations MH and MA 23, for Station MOB 25 points out of possible 2 7, which marks the highest degree of eutrophy. The comparatively low score of Stations MH and MA is due to their depth, which gives only 2 points out of possible 5, which further emphasizes the fact that the lake is more eutrophic than would be expected. The present high eutrophy of Lake Magelungen is undoubtedly due to pollution, mostly from Lake Agesta and the Fagersjo district. That the whole lake suffers from this pollution is illustrated by a comparison with earlier investigations performed by the Stockholm City Municipal Services Department [4] (Table 8). Among 1 5 zooplankton species counted in in samples from Hammartorp (Station MH in the present investigation) only 3 indicators of eutrophy were found. In the years the indicators of eutrophy at Hammartorp had increased to 6, which gives a percentage nearly as high as that for the same years at the sampling station Fagersjo at the NW end of the lake [4]. During the present investigation no less than 9 indicators of eutrophy were regularly found at Station MH (1 at each of Stations MA and MOB). It is interesting to notice how in Magelungen, in contrast to Nauwerck's findings in Lake Erken [8, p. 1 5 J, the zooplankton curve (Fig. 47) follows that of the phytoplankton (Fig. 46), the zooplankton maxima in general appearing somewhat later than the phytoplankton maxima. During the present investigation is was found that the average volume of zooplankton is the same as that of phytoplankton (Station MOB)

26 or somewhat more (Stations MA and MH, Table 6). As a comparison it maybe mentioned that the average phytoplankton: zooplankton (P:Z) ratio of the mesotrophic Lake Erken is.18 [8, p. 14], i.e. about 5. 5 times more zooplankton than phytoplankton volume. Rawson [1 5, p. 2 ] has found values up to 4 times more zooplankton than phytoplankton volume in the oligotrophia Cree Lake in Northern Saskatchewan. CONCLUSIONS As already pointed out by Willen [21, p..28], further additions of nutritional elements to the lake would augment the phytoplankton production. At present the average volume of zooplankton is about the same as that of phytoplankton. It is not likely that an increased growth of phytoplankton would alter this ratio to the advantage of the zooplankton. What could be expected is a continued decrease of the zooplankton in proportion to the phytoplankton and fouling of the shores and bottom as a result of water bloom. The effect of the release of waste water is not easily anticipated. The waste water may stir up mud and water containing hydrogen sulphide during the winter and summer stagnation [cf. 6], which would deteriorate the conditions of animal life in the lake. It is, however, possible that, if the waste water contains a sufficiently high amount of oxygen, the release and the augmented flow might exert a beneficial effect upon the lake during the oxygen-depletion periods and also diminish the risks of an increased unbalance in the production of the lake. An investigation of these problems might give results of vital interest for other lakes which threaten to become unbalanced.

27 AGNEDAL, P-O., (Personal communication.) REFERENCES AMREN, H., Ecological and taxonomical studies on zooplankton from Spitzbergen. Zool. Bidr. Uppsala 36 (1964) p. 29. AXELSON, J., Zooplankton and impoundment of two lakes in Northern Sweden (Ransaren and Kultsj5n). Rep. Inst. Freshw. Res. Drottningholm 42 (1961) p. 84. CRONHOLM, M., (Personal communication.) HALME, E., Planktologische Untersuchungen in der Pojo-Bucht und angrenzenden Gewassern. IV. Zooplankton. Ann. Zool. Soc. "Vanamo" 1 9 (1 958):3. KARLGREN, L. and LINDGREN, O., Luftningsstudier i Trasksjon. Vattenhygien 19 (1963) p. 67. MONTI, R., Numeri, grandezze e volumi degli organismi pelagici viventi nelle aque Italiane, in relatione all'economia lacustre. Mem. 1st. Lombardo di Scienze e Lettere (1936) p. 83. NAUWERCK, A., Die Beziehungen zwischen Zooplankton und Phytoplankton im See Erken. Symbolae Botan. Upsalienses 17 (1963):5. PEJLER, B., On variation and evolution in planktonic rotatoria. Zool. Bidr. Uppsala 32 (1957) p. 1. PEJLER, B., Taxonomical and ecological studies on planktonic rotatoria from Northern Swedish Lapland. Kgl. Sv. Vetenskapsakad. Handi. ser (1 957):5. PEJLER, B., The zooplankton of Osbysjon, Djursholm. I. Seasonal and vertical distribution of the species. Oikos 12 (1961) p. 225.

28 PEJLER, B., On the variation of the rotifer keratella cochlearis (Gosse). Zool. Bidr. Uppsala 35 (1962) p. 1. PEJLER, B., On the taxonomy and ecology of benthic and periphytic rotatoria. Investigations in Northern Swedish Lapland. Ibid. 33 (1962) p PEJLER, B., Regional-ecological studies of Swedish fresh-water zooplankton. Ibid. 36 (1965) p. 47. RAWSON, D.S., Limnology and fisheries of Cree and Wollaston Lakes in Northern Saskatchewan Fisheries Report 4. Dept. of Natural Resources. Saskatchewan. RODHE, W., Zur Verbesserung der quantitativen Plankton-Methodik. Zool. Bidr. Uppsala 2 (1941) p RYLOV, W.M., Das Zooplankton der Binnengewasser. Binnengewasser 15 (1935). THUNMARK, S., Zur Sociologie des Susswasserplanktons. Folia Limnol. Scand. 3 (1 945). UTERMOHL, H.,. Zur Vervollkommung der quantitativen Phytoplankton-Methodik. Mitt. Int. Ver. fur Theor. und Angew. Limnologie, 1958:9. VALIKANGAS, I., Planktologische Untersuchungen im Hafengebiet von Helsingfors. I: liber das Plankton, insbesondere das Netz-Zooplankton des Sommerhalbjahres. Acta Zool. Fennica 1 (1926) p. 1. WILLEN, T., Phytoplankton from Lake Magelungen, Central Sweden, (AE-219) 1966.

29 - 27 Table 1 6 3; Volume of zoopl.inkton, St.ilion MA (average values.2-5. m; in 1 p /l) /3 2/4 1/5 5/7 2/8 6/9 2l/9 ll/l Ciliata Rotatoria C la doc era Copepoda Nauplii Total volume /1 1 6/12 29/ /2 2/2 13/2 28/2 14/3 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume /4 25/4 15/5 12/6 17/7 14/8 4/9 9/1 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume /11 18/ /1 26/2 26/3 16/4 25/4 22/5 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume /6 9/7 6/8 4/9 1/1 29/1 2/11 11/12 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume /1 12/2 11/3 8/4 7/5 28/5 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume

30 Table 2 6 3,, Volume of zooplankton, Station MH (average values.2-5. ra; in 1 ^ /l) /2 28/2 14/ /1 26/2 16/4 22/5 12/6 Ciliata Rotatoria C la doc era Copepoda Nauplii Total volume /8 4/9 1/1 2/11 1 1/ /3 7/5 23/5 Ciliata Rotatoria Cladocera Copepoda Nauplii rs Total volume Table 3 6 3, Volume of zooplankton, Station MOB (average values.2-5. m; in 1 \j. /.) /2 28/2 14/3 25/4 15/5 12/6 14/8 4/9 Cihata Rotatoria C ladocera Copepoda Nauphi I ) I Total volume /1 13/1 1 18/ /1 26/2 26/3 16/4 25/4 C iliata Rotatoria Cladocera Copepoda Xauplii Total volume f /5 12/6 9/7 6/8 4/9 1/1 29/1 1 1/12 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume 17S /1 12/2 11/3 8/4 7/5 28/5 C iliata Rotatoria Cladocera Copepoda Nauplii Total volume

31 29 Table 4 Volume of zooplankton, Station MA (average values m; in 1 6 u 3> /t) /3 2/4 1/5 5/7 2/8 6/9 21/9 11/1 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume /1 1 6/12 29/ /2 2/2 13/2 28/2 14/3 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume /4 25/4 15/5 12/6 17/7 14/8 4/9 9/1 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume /u 18/ /1 26/2 26/3 16/4 25/4 22/5 Ciliata Rotatoria C ladocera Copepoda Nauplii Total volume /6 9/7 6/8 4/9 1/1 29/1 2/11 1 1/12 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume /1 12/2 11/3 8/4 7/5 28/5 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume

32 Table 5 6 3, Volume of zooplankton, Station MH (average values m; in 1 u. /-t) /2 28/2 14/ /1 26/2 16/4 22/5 12/6 Ciliata Rotatoria Cladocera Copepoda Xauplii Total volume /8 4/9 l/lo 2/1 1 11/ /3 7/5 28/5 Ciliata Rotatoria Cladocera Copepoda Nauplii Total volume Table 6 The Phytoplankton - Zooplankton ratio Date Phytoplankton in t 6»>/< volumes Zooplankton in io b n7<. volumes Phytoplankton: Zoo plankton MOB MA MH MOB MA MH MOB MA MH 21/ /2 26/ ' /4 25/ / /6 9/ / / /1 2/ / M (data on phytoplankton from Willen 1 966)

33 TabLe 7. Species regularly occurring in plankton of the three stations. MH MA MOB Indicator of eutrophy E CILIATA Coleps sp. Epistylis rotans Tintinnidium fluviatile Tintinnopsis lacustris E ROTATORIA Anuraeopsis fissa Asplanchna priodonta Brachionus angularis B. calyciflorus Conochiloides natans Conochilus unicornis Filinia longiseta Kellicottia longispina Keratella cochlearis K. cochlearis, f. tecta K. quadrata Polyarthra dolichoptcra P. remata P. vulgaris Pompholyx sulcata Synchaeta oblonga S. pectinata S. truncata Trichocerca birostris T. cavia T. pusilla E E E E E E E E CLADOCERA Bosmina coregoni Chydorus sphaericus Daphnia cucullata D. longispina Leptodora kindti E E COPEPODA Cyclops insignis C. strenuus Diaptomus gracilis Mesocyclops leuckarti M. oithonoides INSECTA Chaoborus sp., larvae Number of species Number of indicators of eutrophy % of indicators of eutrophy

34 Table 8 Most common zooplankton species found in earlier investigations of lake Magelungen. Hammartorp 1945 Hammartorp Fagersjo RHIZOPODA Difflugia limnetic a CILIATA Coleps sp. Epistylis rotans Tintinnidium fluviatile Tintinnopsis lacustris E ROTATORIA Anuraeopsis fissa Asplanchna priodonta Brachionus angularis B. calyciflorus Filinia longiseta Kellicottia longispina Keratella cochlearis K. quadrata Polyarthra remata Pompholyx sulcata Synchaeta pectinata Trichocerca birostris E E E E E 4- CLADOCERA Bosmina coregoni B. longirostris Chydorus sphaericus E Daphnia cristata D. cucullata E Diaphanosoma brachyuum Leptodora kindti Number of species Number of indicators of eutrophy (E) % of indicators of eutrophy

35 FIGURE CAPTIONS Fig. 1 Fig. 2 Figs. 3-6 Figs Fig. 36 Figs Fig. 39 Fig. 4 Fig. 41 Figs. '42-43 Fig. 44 Fig. 45 Map of Lake Magelungen. Map showing the sampling stations. Diagrams showing the distribution of the zooplankton expressed as per cent of the total volume: Fig. 3 Station MA Fig. 4 Station MA Fig. 5 Station MOB Fig. 6 Station MH Diagrams showing the frequencies of the most common zooplankton species over the sampling period. Seasonal variation of Keratella cochlearis in the upper water layers (-5 m) of Stations MA and MOB. Seasonal distribution of the Polyarthra spp. in the surface water layers (-5 m) of Stations MA and MOB. Some Daphnia cristata from Station MA. Some seasonal forms of Daphnia cucullata from Lake Magelungen. Seasonal distribution of the Cyclops spp. (average distribution for the period ). The distribution of the total zooplankton volumes, Station MA. The distribution of the total zooplankton volumes, Station MOB. The distribution of the total zooplankton volumes, Station MH. Fig. 46 Total volume of phytoplankton, average values.2-.5 m (from Willen 1966). Fig. 47 Total volume of zooplankton.

36 - 34 -

37 LAKE MAGELUNGEN Fagersjo From Lake Agesta- MOB w s~\ MA To Lake Drevviken MH Hammartorp 5 1m 1 Fig. 2

38 MAGELUNGEN Station MA Per Cent of Total Volume Zooplankton. ON Fig. 3

39 MAGELUNGEN Station MA m Fi".. J

40 MAGELUNGEN Station MOB to Per Cent of Total Volume Zooplankton. Flj; r >

41 MAGELUNGEN Station MH m 3 m 5 m 8 m 1.5 m 12,5 m PerCent of Total Volume Zooplcmkton. Ciliata Rotatoria Cladocera = Ci J = Ro = Cl : * Hill :::i Copepoda = Co j Nauplii = N ^^^ 1,5 m 12,5 m Fig. 6

42 - 4 - OtPTH rr. 196 V,WWWIIIIII11WI»1»II> TINTINNOPSIS LACUSTRIS 1961 STATION MA ' i' JANIIFCB. IMAR. lapr. I HAY I JUN.I JUL. I AUGlSEP.I OCT I NOV I DEC I JAN ICES I MAR lapp I MA/I JUN I JUL 1 AUS.I3CP. I OCT.I NOV.I DEC. Fig. 7 DEPTH T 196* A5PLANCHNA PRIODONTA 1961 STATION MA * JMAR.IAPO. fwawjun.ljul. I AUS.ISEP.I OCT.I NOV.I DEC.I JAN.IFCB I Fig. 8

43 41 - BRACHIONUS ANGULARIS STATION MA Fig. 9 DZPTU» 136 IVAJW BRACHIONUS CALYCIFLORUS (961 5TATIN MA I JAN.IPEB.lMAR. lapr. I MAY I JUN.IJUL.I AUGlSEP. I OCT NOV I DEC I JAN ifeb.lmar. lapr I MAY I JUN. I JUL. I AUG.ISEP. I OCT I NOV I DEC I Fig. 1

44 CONOCHILOIDES NATAN5 STATION MA JAN.lFEB. IMAR. IAPR.-I MAyljUN.I JUL.I AUSI5EP I OCT. I NOV. I DEC.I JAN IFEB IMAR.IAPR [ MAylJUN jul. I AUGTSEP. I OCT7I NOV.I DEC Fig. 11 OEPTH m 196 i'w vjijtjj>/r//tsj/s///////u CONOCHILUS UNICORNIS STATION MA ' m 1962 lhar. IAPB. I MAY I JUN. I JUL. I AU6.ISEP.I OCT. I NOV.I DEC.I JAN.lFEB. I MAR. I APR. I MAY IJUN I JUL. I AUG. ISEP. I OCT. I NOV.I DEC. Fig. 12

45 FILINIA LONGISETA 1961 STATION MA mg/t imaa ama/e,' m j/',.... lanttra". I MAR. I APR. I MAy IjUN. IjUL. I AUC ISEP. I OCT. I MOV.TDEC.IJAH. IFEB.IMAR. I APR. I MAY IjUN. IjUL. I AUS.ISEP. I OCT. I NOV. I DEC. Fig. 13 OEPTH "> 196 KELLICOTTIA LONGISPINA STATION MA ;n»a/t i»s/t l m s_/*_, tm3 'S ^_ JAN.IFEB. IMAR.IAPR. I MAYI JUN.IJUL. I AUS ISEPTI OCTTNOV.I OEC.I JAN.IFEB.IMAR.IAPRM MAV I JUK. I JUC. / *ue.tscr.l ocrfnoki oec Fig. 14

46 DEPTH m 196 //s/t/tw>/'j//////////jn KERATELLA COCHLEARIS ^ 7 i 1 /}>/>>u/tt/t/rtrrr> STATION MA JAM.lFCB. IMAR, I APR.1 MAVl JUN.I JUL I AUG. I5EP.I OCT. I NOV.! OEC.I JAN. IFE8- I MAR. I APR. I HAY IJUN. jul. I AUC.ISEP. I OCT I NOV.I DEC. Fig. 16 DCPTH m 1J6 Tj*r*rt>rmm KERATELLA QUAORATA u> v 1961 ', -* STATION MA ' OCT. I NOV.I DEC.I JAN. FEB. M»R. AP». I MAY I JUN. I JUL. I AU S.I SEP. I OCT.I NOV. I DEC. Fig. 16

47 POLyARTHRA DOLICHOPTERA STATION MA JAN.lrEB.lMAB. lapb.lmayljun.ijul.i AU*.ljEP. I OCT.I NOV.I OEC.I JAN.lFEB.I MAP.. I AP». I MAV IjUN. IJUL.TAUSJSEP. I OCT.I MOV.l DEC. Fig. 17 m 196 fwrrwrr/?/////?. POLYARTHRA VULGARIS 1361 STATION MA 19G JAN.IFEB 2 "9 A 2ma7< 2m 9/< imab.laps. I MAVIjUN.IjUL. I AU&lsCP. I OCT.I NOV.I DEC.I JAN.IFEB.IMAB.I APB. I MAY IjUN. I JUL. I AUS.ISEP. I OCT.I NOV.I DEC. Fig. 18

48 POMPHOLyX,o SULCATA STATION MA 13GO ' JAN IFE8.IMAR.UPR. I MAy I JON. I JUL. I AU&liEP.I OCT I NOV I DEC I JAN IFEB I MAP. I APR. I MAy IJUN. I JUL. I AUO.ISEP.1 OCT I NOV. I DEC Fig. 19 DCPTU m 196 SYNCHAETA spp. BmF STATION MA ic f JAKl'IFEB. IMAB lapr.i MAY I JUN. I JUL. I AUS. ISEP.IOCT. I NOV. I OEC I JAN. IFEB. IMAR.IAPR.I MAY JUN. I JUL. I AU4 I SEP. I OCT I NOV.I DEC Fig. 2

49 SyNCHAETA PEXTINATA 19G1 STATION nq/t i»]/l iuq/l 2mq/t, ^ & ^ ^ _ ^ N.IFEB.IMAR. IAPB. I MAY I JUN IJUL I AUS.ISEP. I OCT. I NOV.I DEC I JAN IFEB.IMAR UPR MAY I JUN.IJUL. I AU&ISEP. I OCT.I NOV.I DEC. Fig. 21 DEPTH m 196 TRICHOCERCA BIROSTRIS STATION MA * G" 2m3/{ JANIFEB.IHAQ IAPR I MAYIJUN.I JUL.I AUGISEP. I OCTI NOV ' DEC! JAI^FEB'MAR IAPR. 1 MAY! JUN.IJUL. I AUC ISEP ' OCT.I NOVIDEC Fig. 22

50 - 48 DEPTH m I96 TRICHOCERCA 1* c 1361 PUSILLA STATION MA m 1962 \w//i»l/il/iia)>/>//. 2""l/< 2ma/t JmsV* i-s/l OAN.IPEB.IMAR.IAPD. I MAY I JUH.I JUL.I AUSTISEP. t ocff NOV! OECI JAN.IFEB.IMAR IAPR.I MAVIJUNJOUL.! AO«.I»EP.I OCT.I NO«I ote. Fig. 23 DEPTH 9/////'/////J77TmsjJ//MJ/\ I BOSMINA COREGONI 1961 STATION MA " JANIFES. IMAR. I APR. I MAY IjUN. IjUL. I AUS.ISEP I OCT I NOV. I DEC. I JAN. IrEB. MAR. lapr. I MAY IJUN. I JUL. I AUS.ISEP.I OCT. I NOV. I DEC. Fig. 24

51 DEPTH 2mg/« /j. BOSMINA COREGONI Id' 6' ' ( to' 15' STATION MOB m m9/«2mg/«STATION MH JANIPEB.IMAB.UPR I MAyljUN. I JUL. I AUS.ISEP. I OCT. I NOV I DEC I JAN. IrEB IMAO. lapr. I MAY IjUN I JUL I AUGjSED.I OCT. I NOV. I DEC. Fig. 25 IHO CHYDORUS SPHAERICUS STATION MA JANICEB.IMAP IAPP. I MAVI JUN.IJUL.I AUS.ISEP. I OCT NOV I DECljAN.lFEB. imar.lapr.' MAY I JUN. I JUL. FAUGISEP. I OCT I NOV.I DEC. Fig. 26

52 5 DEPTH lma/l m 1961." CHyDORUS SPMAERICUS * f 1' M' STATION MOB ' <' m 1961 y///>t>> />»//>»>>>>/ 1962 STATION MH mjA * m S/' ' m 9/' '"'A JAN,lctB. HAP.lAPB.I MAV IjUN. I JUL. I AU6. S P, I OCT, I NOV.I DEC.I JAN IFEB. IMAR. I APP. I MAyl MH. I JUL. I AUC-ISEP, I OCT, I NOV.! OEC, I Fig. 27 DEPTH "> 196 DAPHNIA CUCULLATA STATION MA JANIFEB MAP I APR. I MAY I JUN.IjUL. I AUGlSEP. I OCT.I NOvl DEC I JAN IFEB IMAR UPQ.I MAyl JUN. I JUL. I AUttlSEP.I OCTl NOV.I OEC. Fig. 28

53 DEPTH 2ms/«f" 1961, r Y.V /}? - [} DAPHNIA CUCULLATA 1962 JfJfl. STATION MOB »-< STATION MH JAN IrEB IMAR.TAPR.I MAyljUN. I JUL. I AUG IsEP I OCT! NOV I DEC. I JAN IFEB. I MAR. IAPR ' MAvl JUN. I JUL. I AUG F3EP I OCT! NOV i DEC Fig. 29 OEPTH m I96 CYCLOPS spp. ADULTS AND COPEPODITES STATION MA JUL I AUGlSEP I OCT NOV DEC JAN.iPEB MAR IAPR I MAyljUN i JUL I AUG.ISEP I OCT I NOV.I DEC Fig. 3

54 52 - eye LOPS spp. ADULTS AND COPEPODITES DEPTH 2mq * m 1961,, i///y]i/j>/j 1 r - if o- I l «* o I I I I I I I I I 1/ "T o J 2m3/t 2- f» 15' r >'»» \ * I \!-V.Ui 2mg/«STATION MOB STATION MH JAN. I CEB. I MAR. lapr. I MAY IjUN. I JUL. I AUG ISEP. I OCT. I NOVTDECTJAN.IFEB" IMAP.TIAPR I MAY IjUN.IjUL I AUS 3EP. I OCT. I NOV I DEC. Fig. 31 OEPTH m 136 cyclops spp. NAUPLII 1961 STATION MA ' C gmg/t 2mq/l lm$jl 2mg"/t JAN VES. IMAR. lapr. I HAyljUN I JUL. I AUGlSEP. I OCT I NOV I DEC I JAN leeb.' MAR. I APR. I MAyl JUN. I JUL. I AUGlSEP. I OCT. I NOV. I DEC. Fig. 32

55 DIAPTOMUS GRACILIS NAUPLII 1361 STATION MA in- t' JANIFEB.IMAR? 8/» 2m97l ii"i/l I APR. I M*y IjUN. I JUL. I AUSlSEP. I OCT I NOV. I OEC I JAN FEB.'MAR. I APB.1 MAy IjUN. I JUL. I AUS I SEP. I OCT.I NOV. I DEC. Fig DIAPTOMUS GRACILIS ADULTS AND COPEPODITES STATION MA AN FEB. IMAR.IAPR. I MAYIJUN.I JUL I AUGlSEP I OCT I NOV I OEC I JAN lfe6.imar.lapr I MAyljUN. I JUL. I AUG.ISEP.I OCT I NOV. I DEC Fig. 34

56 DZPTU!mj/< 1961 " -W 1 4fi ~v~i > I r~i 7 DIAPTOMUS GRACILIS ADULTS AND COPEPOD1TES 1962 STATION MOB ^ ra ItEt _j A m3/t 2mg/» STATION MH '6* JAN 1KB. I MAR. I APR.! MAY IjUN. I JUL. I AUC 1SEP I OCT. I NOV i DEC I JAN IFCB.!HAR. iapp. I MAY,JUN. I JUL. 1 AUSlfiEP. i OCT. I NOV I DEC Fig. 35

57 SEASONAL VARIATION OF KERATELLA COCHLEARIS IN THE UPPER WATER LAYERS (-5m) OF STATIONS MA AND MOB. STATION MA ^ ff MACRACANTHA AND TYPICA f. MICRACANTWA f TECTA STATION MOB ff MACRACANTHA AND TVPICA f MICRACANTHA f TECTA THE DIAMETER OF THE CYLINOER CORRESPONDS TO THE CUBE ROOT OF THE MEAN VALUE OF INOS/l. I JAN. I FEB I MAR. I APR I MAy I JUN I JUL TAUG I SEP TOCTI NOVTDEXI JAN I FETT MARTAPRI MAY I JUN IjUL I AUG I SEP IOCT.INOV.I DEC.I Fig. 36

58 SEASONAL DISTRIBUTION OF THE POLYARTHRA spp IN THE SURFACE WATER LAYERS (-1 m) OF STATION MA STATION MA 196 P OOLICHOPTERA P VULGARIS P REMATA 1963 P DOLICWOPTERA P VULGARIS P REMATA THE DIAMETER OF THE CYLINDER CORRESPONDS TO THE CUBE ROOT OF THE MEAN VALLE OF INDS/L_ I JAN 1 FEB I MAR I APR I MAY I JUN 1 JUL I AUG ISEP I OCT I NOV I DEC i JAN FFEB I MAR 1 APR] MAY I JUN! JUt'I AUGTSEPTOCT PNOVFOEC 1 Fig. 37 SEASONAL DISTRIBUTION OF THE POLYARTHRA spp. IN THE SURFACE WATER LAYERS ( - 1 m ) OF STATION MOB. STATION MOB ! P DOLICWOPTERA P VULGARIS p RE:MATA P DOLICHOPTERA P VULGARIS P REMATA THE DIAMETER OF THE CYL1NER CORRESPONDS TO THE CUBE ROOT OF THE MEAN VALUE OF 1NDS/L JAN I FEB I MAR I APR I MAV T JUN I JUL I AUG i SEP I OCT I NOV I DEC ] JANTFEB MAR ' APR MAV I JUN JUL ' AUG I SEP I OCT! NOV 1 D <P Fig. 38

59 Some seasonal forms of Daphnia cucullata from Lake Magelungen March-May. I96 May May Juv. June.19&1 July-August and August Male. August and September September, 1961 September-November November - December October November AA/W/IAA^AAAA May.1961 Junt July July Juv, July July 1962 July 1962 July-August Sep I ember July July November, 1961 November Dorsal view Fig. 39 Som«Oaphnia crista la from Station MA Fig. 4

60 SEASONAL DISTRIBUTION OF THE CYCLOPS spp (AVERAGE DISTRIBUTION FOR THE PERIOD ) V///X ADULTS EGSBEARINS FEMALES 1 CyCLOPS INSICNIS < X z o v//////;//////////////;//////////a 2 CYCLOPS STRENUUS 3 MESOCYCLOPS LEUCKARTI m^mmmtm A MESOCyCLOPS OITWONOIOES 5 EUCyCLOPS SERRULATUS ^^^^^^ 1 CYCLOPS INS1&NIS 2 CYCLOPS STRENUUS 3 MESOCYCLOPS LEUCKARTI 4 ME5CYCLOPS O1THNIDES (& EUCYCLOPS SERRULATUSj 1 CYCLOPS INSIGNIS V///////////////X gg^^^ 2 CYCLOPS STRENUUS 3 MESOCVCLOPS LEUCKARTI k HESOCVCLOPS OITHONOIDES (5 EUCYCLOPS SERRULATUS) I JAN. FEeT MAR I APRl MAY JUN I JUL I AUG I SEP f OCT I NOV I DEC I Fig. 41

61 Station MA 5 3 Total zooplankton volumes 1 JJ /I 1*C 6'C 6'C^ Fig. 42 Station MA «5 3, Total zooplankton volumes IO'JJ'/I 6'CIO'C ^ ^ ^ ^ 1*C 6'C 6*C1"CL. Fig. 43

62 - 6 - m mg/l 6«c Station MOB 5, Total zooplankton volume 1 JJ /I 22mg/l 2.c.c 6.c g62 6.c,-c r 22mg/l 22 J ' F ' M l_ A r "M" ' J *~S A "^ S ' 6 ' N ' D~Fl ' F r ~M~ ~ 1 A ' M ' J ^J ' A ' S ' ' N ' ~ Fig. 44 Station MH 5 3, Total zooplankton volumes 1 JJ /I 6 C I C ^BBB^_ 1 C 6 C Fig..45

63 U to to Fig A V fn 1963 Total volume (average values) V=1 6,w 3 /l -15m MA -12 5m MH m MOB 12-1 r- / \ : \ ( Jan I Feb I Mar. TApr. TMay I Jun I Jul. I Aug I Sep I Oct I Nov I Dec i Jan I Feb I Mar I Apr TMay"] Fig. 47

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66 LIST OF PUBLISHED AE-REPORTS 1 34 (See back cover earlier reports.) 341. Nonlinear dynamic model of power plants with single-phase coolant reactors. By H. Vollmer p. Sw. cr. 1: Report on the personnel dosimetry at AB Atomenergi during By J. Carlsson and T. Wahlberg p. Sw. cr. 1: Friction factors in rough rod bundles estimated from experiments in partially rough annuli - effects of dissimilarities in the shear stress and turbulence distributions. By B. Kjellstrom p. Sw. cr. 1: A study of the resonance interaction effect between i3, U and u, Pu in the lower energy region. By H. Haggblom p. Sw. cr. 1: Application of the microwave discharge modification of the Wilzbach technique for the tritium labelling of some organics of biological interest. By T. Gosztonyi p. Sw. cr. 1: A comparison between effective cross section calculations using the intermediate resonance approximation and more exact methods. By H. Haggblom p. Sw. cr. 1: A parameter study of large fast reactor nuclear explosion accidents. By J. R. Wiesel p. Sw. cr. 1: Computer program for inelastic neutron scattering by an anharmonic crystal. By L. Bohlin, I. Ebbsjo and T. Hogberg p. Sw. cr. 1: On low energy levels in 1 "W. By S. G. Malmskog, M. Hojeberg and V. Berg p. Sw. cr. 1: Formation of negative metal ions in a field-free plasma. By E. Larsson p. Sw. cr. 1: A determination of the 2 2 m/s absorption cross section and resonance integral of arsenic by pile oscillator technique. By E. K. Sokolowski andr. Bladh p. Sw. cr. 1: The decay of 1 "Os. By S. G. Malmskog and A. Backlin p. Sw. cr. 1: Diffusion from a ground level point source experiment with thermoluminescence dosimeters and Kr 85 as tracer substance. By Ch. Gyllander, S. Hollman and U. Widemo p. Sw. cr. 1: Progress report, FFN, October 1, - September 3, By T. Wiedling p. Sw. cr. 1: Thermodynamic analysis of a supercritical mercury power cycle. By A. S. Roberts, Jr p. Sw. cr. 1: On the theory of compensation in lithium drifted semiconductor detectors. By A. Lauber p. Sw. cr. 1: Half-life measurements of levels in "As. By M. Hojeberg and S. G. Malmskog p. Sw. cr. 1: A non-linear digital computer model requiring short computation time for studies concerning the hydrodynamics of the BWR. By F. Reisch and G. Vayssier p. Sw. cr. 1: Vanadium beta emission detectors for reactor in-core neutron monitoring. By I. O. Andersson and B. Soderlund p. Sw. cr. 1: Progress report Nuclear chemistry p. Sw. cr. 1: A half-life measurement of the kev level in <"Lu. By M. Hojeberg and S. G. Malmskog p. Sw. cr. 1: The application of thermoluminescence dosimeters to studies of released activity distributions. By B-l. Ruden p. Sw. cr. 1: Transition rates in '"Dy. By V. Berg and S. G. Malmskog p. Sw. cr. 1: Control rod reactivity measurements in the Agesta reactor with the pulsed neutron method. By K. Bjoreus p. Sw. cr. 1: On phonons in simple metals II. Calculated dispersion curves in aluminium. By R. Johnson and A. Westin p. Sw. cr. 1: Neutron elastic scattering cross sections. Experimental data and optical model cross section calculations. A compilation of neutron data from the Studsvik neutron physics laboratory. By B. Holmqvist and T. Wiedling p. Sw. cr. 1: Gamma radiation from fission fragments. Experimental apparatus - mass spectrum resolution. By J. Higbie p. Sw. cr. 1: Scandinavian radiation chemistry meeting, Studsvik and Stockholm, September 17-19, By H. Christensen p. Sw. cr. 1: Report on the personnel dosimetry at AB Atomenergi during By J. Carlsson and T. Wahlberg p. Sw. cr. 1: Absolute transition rates in 1u lr. By S. G. Malmskog and V. Berg p. Sw. cr. 1: Transition probabilities in the 1/2 (631) Band in '"U. By M. Hojeberg and S. G. Malmskog p. Sw. cr. 1: E2 and M1 transition probabilities in odd mass Hg nuclei. By V. Berg, A. Backlin, B. Fogelberg and S. G. Malmskog p. Sw. cr. 1: An experimental study of the accuracy of compensation in lithium drifted germanium detectors. By A. Lauber and B. Malmsten p. Sw. cr. 1: Gamma radiation from fission fragments. By J. Higbie p. Sw. er. 1: Fast neutron elastic and inelastic scattering of vanadium. By B. Holmqvist, S. G. Johansson, G. Lodin and T. Wiedling p. Sw. cr. 1: Experimental and theoretical dynamic study of the Agesta nucler power station. By P. A. Bliselius, H. Vollmer and F. AkerhieTm p Sw. cr. 1: Studies of Redox equilibria at elevated temperatures 1. The estimation of equilibrium constants and standard potentials for aqueous systems up to 374 C. By D. Lewis p. Sw. cr. 1: The whole body monitor HUGO II at Studsvik. Design and operation. By L. Devell, I. Nilsson and L. Venner p. Sw. cr. 1: ATOMSPHERIC DIFFUSION. Investigations at Studsvik and Agesta By L-E. Hasggblom, Ch. Gyllander and U. Widemo p. Sw. cr. 1: An expansion method to unfold proton recoil spectra. By J. Kockum p. Sw. cr. 1: The kev lever "Sr, and evidence for 3-neutron states above N=5. By S. G. Malmskog and J. McDonald p. Sw. cr. 1: The low energy level structure of 2 "ir. By S. G. Malmskog, V. Berg, A. Backlin and G. Hedin p. Sw. cr. 1: The drinking rate of fish in the Skagerack and the Baltic. By J. E. Larsson p. Sw. cr. 1: Lattice dynamics of Nacl, KCI, RbCl and RbF. By G. Raunio and S. Rolandson p. Sw. cr. 1: A neutron elastic scattering study of chromium, iron and nickel in the energy region 1.77 to 2.76 MeV. By B. Holmqvist, S. G. Johansson, G. Lodin, M Salama and T. Wiedling p. Sw. cr. 1: The decay of bound isobaric analogue states in "Si and 3! Si using (d. ny) reactions. By L. Nilsson, A. Nilsson and I. Bergqvist p. Sw. cr Transition probabilities in "»Os. By S. G. Malmskog, V. Berg and A. Backlin p. Sw. cr. 1: Cross sections for high-energy gamma transition from MeV neutron capture in " s Pb. By I. Bergqvist, B. Lundberg and L. Nilsson p. Sw. cr. 1: High-speed, automatic radiochemical separations for activation analysis in the biological and medical research laboratory. By K. Samsahl p. Sw. cr. 1: Use of fission product Ru-16 gamma activity as a method for estimating the relative number of fission events in U-235 and Pu-239 in low-enriched fuel elements. By R. S. Forsyth and W. H. Blackadder p. Sw. cr. 1: Half-life measurements in "*l. By V. Berg and A. Hoglund p. Sw. cr. 1: Measurement of the neutron spectra in FRO cores 5, 9 and PuB-5 using resonance sandwich detectors. By T. L. Andersson and M. N. Qazi p. Sw. cr. 1: A gamma scanner using a Ge(Li) semi-conductor detector with the possibility of operation in anti-coincidence mode. By R. S. Forsyth and W. H. Blackadder p. Sw. cr. 1: A study of the 19 kev transition in "'La. By B. Berg, A. Hoglund and B. Fogelberg p. Sw. cr. 1: Magnetoacoustic waves and instabilities in a Hall-effect-dominiated plasma. By S. Palmgren p. Sw. cr. 1: A new boron analysis method. By J. Weitman, N. Daverhog and S. Farvolden p. Sw. cr. 1: Progress report Nuclear chemistry p. Sw. cr. 1: Prompt gamma radiation from fragments in the thermal fission of 33S U. By H. Albinsson and L. Lindow p. Sw. cr. 1: Analysis of pulsed source experiments performed in copper-reflected fast assemblies. By J. Kockum p. Sw. cr. 1:-. 4. Table of half-lives for excited nuclear levels. By S. G. Malmskog p. Sw. cr. 1: Needle type solid state detectors for in vivo measurement of tracer activity. By A. Lauber, M. Wolgast p. Sw. cr. 1: Application of pseudo-random signals to the Agesta nuclear power station. By P-A. Bliselius p. Sw. cr. 1: Studies of redox equilibria at elevated temperatures 2. An automatic divided-function autoclave and cell with flowing liquid junction for electrochemical measurements on aqueous systems. By. K. Johnsson, D. Lewis and M. de Pourbaix p. Sw. cr. 1: Reduction of noise in closed loop servo systems. By K. Nygaard p. Sw. cr. 1: Spectral parameters in water-moderated lattices. A survey of experimental data with the aid of two-group formulae. By E. K. Sokolowski p. Sw. cr. 1: The decay of optically thick helium plasmas, taking into account ionizing collisions between metastable atoms or molecules. By J. Stevefelt p. Sw. cr. 1: Zooplankton from Lake Magelungen, Central Sweden By E. Almquist p. Sw. cr. 1:-. List of published AES-reports (In Swedish) 1. Analysis by means of gamma spectrometry. By D. Brune p. Sw. cr. 6:. 2. Irradiation changes and neutron atmosphere in reactor pressure vesselssome points of view. By M. Grounes p. Sw. cr. 6:-. 3. Study of the elongation limit in mild steel. By G. Ostberg and R. Attermo p. Sw. cr. 6:-. 4. Technical purchasing in the reactor field. By Erik Jonson p. Sw. cr. 8:-. 5. Agesta nuclear power station. Summary of technical data, descriptions, etc. for the reactor. By B. LilliehSok p. Sw. cr. 15:-. 6. Atom Day Summary of lectures and discussions. By S. Sandstrom p. Sw. cr. 15:-. 7. Building materials containing radium considered from the radiation protection point of view. By Stig O. W. Bergstrom and Tor Wahlberg p. Sw. cr. 1:-. Additional copies available from the Library of AB Atomenergi, Fack, S Nykoping 1, Sweden. EOS-tryckerierna, Stockholm 197