vertical distribution of bacteria and algae in a tropical lake

1 Int . Revueges. Hydrobiol. 1 54 5 I 1969 791-797

GOTTFRIED W. SCHMIDT

Cooperation between Instituto Naeional de Pesquisas da Amazonia (INPA), Manaus-Amazonas,

and Max-Planek-Institut fur Limnologie, Abteilung Tropenokologie, P1on

Vertical Distribution of Bacteria and Algae in a Tropical Lake

C o n t e n t s 1. Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791 2. Place and time of investigation. . . . . . . . . . . . . . . . . . . . . . . 792 3. Resul t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792 4. Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 5. Summary, Resumo . . . . . . . . . . . . . . . . . . . . . . . . . . . . 796 6. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797

In another paper (SCHMIDT, 1969b) the relations between the numbers of bacteria and phytoplankton in the surface layers of some waters near Manaus (Amazonas) were reported. As a stratification of phytoplankton is nct possible, due to the strong turbulence in the Rio Solim6es (Amazon River), and since current was also present in the Rio Negro off the bays and littoral regions, the vertical distribution of bacteria and algae was of special interest in the Lago do Castanho, the third of the waterbodies investigated in the paper mentioned above. In the present study, two important fractions of bacteria, their total number, and the fraction of saprophyta (estimated by the number of bacterial colonies), were also differentiated.

1. M e t h o d s This investigation is closely related to the former one mentioned above, and the methods

used have already been described in detail there. The total numbers of bacteria and algae were determined by the membrane filter method

(staining with erythrosin) : 25 ml of each water sample, formalin-fixed, were filtered, and the counts carried out a t 1,250 x magnification (SCHMIDT, 1969 b). The number of saprobiont bacteria (saprophyta) was established from the number of bacterial colonies, which were grown on a nutritive-broth medium (Nahrkartonscheiben, Typ Standard, Membranfilter- gesellschaft Gottingen).

The visibility, shown in the figures presented, was measured with a Secehi disc. I n order to test the membrane filter method for its usefulness under the specific conditions,

a series of test preparations has been investigated. For this, pure and mixed suspensions from different bacterial colonies, which had grown on broth-type plates (NKS-Standard, mentioned above), were prepared (see also SCHMIDT, 1969a). Although only some of the various types of bacteria could be tested by this procedure, there were no fundamental 51 *

792 G. W. SCHMIDT

differences in interpretation of these tests and the preparation made from lake water. Therefore, the conclusion is allowed, that the total bacterial numbers of the investigated water samples were sufficiently representative. This statement is justified b y the good correspondence of the parallel counts, too.

For the interpretation of the algal counts, each cell of the algal colonies was differentiated. Also, samples were collected each time for later taxonomic determination of the algae. I n the first examinations of these samples, only a very few algae were found with soft and easily destructable bodies, which might not be detected during the counting process because of strong deformation by the preparation of the membrane filters. Therefore, this error can be regarded as negligible.

2. P l a c e and t i m e of i n v e s t i g a t i o n

The Lago do Castanho can be regarded as a typical example of the lakes of the varzea region. It is connected with the Rio Solimoes during the whole year and receives no important tributaries from the terra firme. Therefore, its water is practically decanted Solimdes water (SIOLI, 1957, and SCHMIDT, 1968, 196913).

The samples were taken at the same time as those from the two rivers t o guarantee comparable results. I n samples taken a t three-month intervals from October 1967 t o July 1968, a full vegetational cycle was included (SCHMIDT, 1969b). The changes of water level with all their effects are the main cause of the alterations in the life of a water-body in this region in the course of a year. The sinking water level causes R certain isolation of the dissolved and suspended matter of t,he lake water, but with rising water level, new Solimoes water enters the lake again, supplying new plant nutrients to the phytoplankton and mixing with the remaining lake water. The water levels of the Rio Negro near Manaus are shown in fig. 1 (from SCHMIDT, 196933). They are essentially valid for the Lago do Castanho as well, which is situated only 60 km from the city.

3. R e s u l t s I n the Lago do Castanho, a t all times of investigations, significant strytifi-

cation of these organisms occured.

1967 I 1968

d

Fig. 1. Mean water level of the Rio Negro near Manaus during the investigation period (from: SCHMIDT, 196913)

Vertical Distribution of Bacteria and Algae in a Tropical Lake 793

2 -

3 -

I -

In October 1967, a t lowest water level, the highest absolute amount of organisms of any of the four sampling times in that lake was observed. In spite of the extremely low visibility, the number of algae also reached by far its highest level (fig. 2 ) , i. e., about 650,000 cells/ml a t 0.5 m depth. At a greater depth, the quantity of algae decreased, but the numbers were still very high. At the same depth as the algae maximum, there was also an immense development of saprophyta. The total number of bacteria attained its maximum in the layer immediately below the former, a t 1 m depth.

Up to January 1968, the population densities of both the algae and the bacteria decreased strongly (fig. 2). This was rather astonishing, as meanwhile the new Solimhes water had entered, which supplies the lakes every year with fresh mineral nutrients for the phytoplankton. As the visibility had slightly increased, compared to October, lack of light could not have been the cause of the decrease in algal number. A renewed increase of bacterial numbers was observed towards the bottom, a development which was noted a t the following investigation times, too.

I n April, the quantities of algae and bacteria had fallen more (fig. 3). At that time, only about 60,000 algae/ml at most were found, while in January, 190,000 indiv./ml were still present. The total number of bacteria in the upper layers, with a maximum of 400,00O/ml, was only about half as great as the corresponding January value. Only the numbers of saprophyta were little changed. Over the mud, the total number of bacteria was notably higher than that in the euphotic zone, in contrast to normal conditions.

By July, the algae and bacteria had multiplied again (fig. 4). Although the visibility in the Lago do Castanho a t that time was about 2 meters, all maximum values were found close to the surface. The sudden downward slope of the curves of bacteria below this layer allows the conclusion, that the essential remineralisation processes took place there. This strong activity in the upper layers resulted in an oxygen distribution, which also had its maximum (7.6 mg/l) a t a depth of 0.5 m, diminished rigorously, and dropped to 0 a t 4 m, a dept,h

300 400 fifln

1.5 2 0 2!5406 4 5 S a h 5

I I 1

I I I

9 0 0 100 {-IT> 0.5 ';o@ - lvisibility

-

T @, 27.10.1961

I v LAG0 DO CASTANHO 25.1.1968

@ number of algae Irnl

@ totol number of bocterio Iml

@ number o f bacterial colonies /ml

Eig. 2 . Vertical distribution of bacteria and algae in the Lago do Castanho at 27. 10.67 and a t 25. 1. 68

794 G. W. SCHMIDT

100 200 300 400 5uu I

0.5 1.0 1.5 Pi0 m" 2 1 5 ~ 1 0 ~

1 1 2 3 4 5 I I I I I L

6 I 7 -

LAG0 00 CASTANHO 24.4.1968

@ number of algae / ml

@ to ta l number o f bacterio/ml

@ number of bacterial colonieslm

Fig. 3. Vertical distribution of bacteria and algae and oxygen content in the Lago do Castanho a t 24.4.1968

100 200 300 400 500 I I 1

0.5 1.0 1.5 20 a" 25x10'

Fig. 4. Vertical distribution of bacteria and algae and oxygen content in,$he Lago do Castanho a t 26. 7. 1968

still in the euphotic zone. In the oxygen-free layers below, the quantities of bacteria remained steadily a t a high level, whereas the numbers of algae decreased greatly, beginning at 3 m depth.

The essential results of the investigation of the Lago do Castanho are as follows : First, a t each time of sampling, a distinct stratification of the algal and bacterial populations could be proved. Second, in the upper water layers, a maximum of algae was always correlated with a maximum of bacteria, The latter was located either in the same depth of water as that of the algae or just below it. The saprophyta, especially, depended for their development on close proximity to the algae. Their peaks normally coincided, and below this zone of


mass development, the number of saprophyta decreased rapidly. Only a t greater depths did their number increase again.

4. D i s c u s s i o n

Considering the notable lack of plant nutrients in Solimdes water (SIOLI, 1950, KLINGE and OHLE, 1964, WILLIAMS, 1968), which supplies the lake water as mentioned above, the absolute quantities of bacteria and algae in the Lago do Castanho were more abundant than expected, but nevertheless reached only about the lower range of algal and bacterial content of eutrophic lakes in the northern hemisphere. The numbers of saprophyta fell more or less in the range which was found in the contaminated blackwaters in the urban district of Ma- naus (SCHMIDT, 1969a), but in comparison with European lakes, were not, extremely high,

From the close proximity of bacteria and algae in their vertical distribution it can be concluded, that in the upper water layers of the tropical Lago do Ca- stanho a decisive correlation between the organisms in question exists over the whole year. Because of the fundamental importance of bacteria and algae in the trophic system of water bodies, their numbers and interrelations are parti- cularly interesting in limnology. Up to now knowledge about them in tropical waters has been rather scarce, but in the temperate zone of the northern hemisphere, the bacteria and algae in freshwaters and their problems have been studied for some time by such authors as HENRICI (1937), KUSNETZOV (1958), CZECZUQA (1962), etc., and especially by OVERBECK (1965, 1967, 1968)) OVER- BECK and BABENZIEN (1964), and ANAGNOSTIDIS and OVERBECK (1966). They found, in almost all cases, that an abundant development of algae was correlated with a decided increase in bacterial numbers, and that the maximum of bacterial numbers normally occurred shortly after the maximum of algae. Also, clear interrelations between the numbers of bacteria and algae and the dynamics of organic and inorganic matter in the waters they investigated could be seen. HENRICI (1937) observed a striking parallel between the peaks of plankton and bacteria in temporal successions, and KUSNETZOV (1958) published a series of vertical profiles through lakes of different types and demonstrated in oligotrophic Dalny lake a clear vertical succession of algal and bacterial maxima. But in comparison to Lago do Castanho, Dalny lake showed a more distinct separation of their maxima. Probably, the remineralisation of the organic pro- ducts supplied by the algae could not occur as rapidly in Dalny lake, due to much lower temperatures than are found in the tropical Lago do Castanho, where the maxima were always extremely close together. The numbers of organisms in the two lakes are rather similar t o each other.

Numerous aspects of the relations between algae and the bacteria were studied by OVERBECK and his collaborators (cited above). In this paper only a few subjects can be treated. I n a series of examples from German lakes, these authors were able to prove a close relationship between bacteria and algae. They stated that the bacteria depend to a high degree on the organic matter produced by the algae, and can use these substances on the spot. Due to the tropical temperatures this seems t o be even more valid for the Lago do Castanho. Furthermore, OVERBECK (1965) compared the quantities of the two fractions of bacteria mentioned above with corresponding data on the primary production

796 G. W. SCHMIDT

of the phytoplankton in some German lakes, and could demonstrate an obvious relation between the amount of carbon produced by the algae per volume of water, and the population density of these bacteria. By this he introduced important new perspectives into the characterization of natural waters.

A striking difference between the vertical profiles published by OVERBECK (1968) and those of the Lago do Castanho occurs, however. In contrast to the situation in the lakes described by OVERBECK, in general the saprobiont bacterial numbers in Lago do Castanho increased again a t greater depths. Perhaps this growth in numbers was brought about by specially facultative, anaerobic types which had better living conditions towards the bottom. But it is also possible that, due to the frequent complete circulations in these shallow tropical lakes, saprophyta were carried to these depths, and a t renewed stagnation of the lower water layers, they slowly concentrated downwards. There they can be kept alive for varying periods even in the absence of oxygen.

The parallels between the lakes studied by the authors cited above and Lago do Castanho are therefore valid primarily for the upper water layers. Although OVERBECK (1968) described a special case of significant increase of saprophyta numbers with increasing depth (Schohsee), and another case of a slight increase in this direction (Schluen-See), this phenomenon seems to be more decisive for the Lago do Castanho. But stress must be laid on the fact, that in our investigations the so-called water-sediment contact zone could not be taken into account. In the lakes of all climatic zones, certainly higher bacterial numbers can be expected in this place.

The absolute numbers of algae and bacteria ranged in Lago do Castanho between those comparable to oligotrophic lakes up to slightly eutrophic ones of the temperate zone. But the curve of the oxygen content of this lake corre- sponded sometimes rather to that of a more eutrophic water. From this, great metabolic activity can be inferred in these lakes.

The relatively great amplitude of the absolute numbers of bacteria and algae in the Lago do Castanho during the investigation period cannot yet be explained sufficiently, because of the long intervals between the sampling times. The rapidity of the dynamics has been stressed already. In these complicated processes, which are characteristic of a great number of Amazonian lakes with their strong fluctuations of water levels, the entering of new and turbid Solimdes water, its decantation in the lakes, resuspension of the sediments a t very low water levels, etc., there are still many unsolved problems. For some Amazonian waters, the relations between the activity of phytoplankton, i. e., its primary production, and the population densities of the organisms referred to, is being studied.

5 . S u m m a r y

A clear correlation was repeatedly observed between the maxima of bacteria and algae in the upper water layers of the tropical Lago do Castanho (Amazon region), in accordance with the findings of other authors for lakes in the northern temperate zone. On three different occasions, a secondary increase in numbers of saprobionts occurred at greater depths. The absolute numbers of the organisms studied were rather low, reaching only into the lower range of concentrations of bacteria and algae in eutrophic lakes of the temperate zone. From the close proximity of the algal to the bacterial maxima, in conjunction with the high temperatures, a very high rate of bioactivity in these tropical lakes can be inferred.


Resumo No tropical Lago do Castanho (regiao amazhnica brasileira), as camadas superiores da

igua mostram uma correlapao nitida entre 0s miximos dos nlimeros de algas e de bact,itriss. Este fato corresponde aos resultados, obtidos por outros autores, em lagos da zona temperada setentrional. Em profundidades maiores, uni novo aumento em nlimero de sapro- biontes foi observado em tres 6pocas diferentes do ano. 0 nlimero absoluto dos organismos investigados, por6m, era baixo, alcanpando at6 mais ou menos 0s valores inferiores de algas e bactitrias existentes em Bguas eutr6ficas da zona temperada. A estreita vizinhanpa da ocorrbncia mixima de algas i de bact.itrias, em combina.pLo corn as temperaturas altas, indica uma dinimica muito forte de bioatividae em lagos tropicais.

6. References ANAGNOSTIDIS, K., and J. OVERBECK, 1966 : Methanoxydierer und hypolimnische Schwefel-

bakterien. Studien zur okologischen Bioconotik der Gewiisserorganismen. - Ber. Dt. Bot. Ges. 78: 163-174.

CZECZUGA, B., 1962: An attempt a t establishing the production and numerical relations of bacterioplankton biomass. - Acta Hydrobiol. 4: 1-20.

HENRICI, A. T., 1937: Studies on freshwater bacteria. IV. Seasonal fluctuations of lake bacteria in relation to plankt'on production. - J. Bacteriol. 35: 129-139.

KLINGE, H., and W. OHLE, 1964: Chemical properties of rivers in the Amazon area in relation t o soil conditions. - Verh. Internat. Verein. Limnol. 16: 1067 - 1076.

KUSNETZOV, S. I., 1958: A study of the size of bacterial populations and of organic matter formation due to photo- and chemosynthesis in water bodies of different types. - Verh. Internat. Verein. Limnol. 13: 156-169.

OVERBECK, J., 1966 : Primarproduktion und Gewasserbakterien. - Naturwiss. 52: 145. - 1967: Zur Bakteriologie des SiiOwassersees - Ergebnisse und Probleme. - Gas- u.

Wasserfach 108: 1258- 1260. - 1968: Prinzipielles zum Vorkommen der Bakterien im See. - Mitt. Int,ernat. Verein.

Limnol. 14: 134-144. OVERBECK, J., und H. D. BABENZIEN, 1964: Bakterien und Phytoplankton eines Klein-

gewlssers im Jahreszyklus. - Z. Allgem. Mikrobiol. 4: 59-76. SCHMIDT, G. W., 1969: Zum Problem der Bestimmung der Kohlensaure in kalkarmen

tropischen Gewassern. - Amazoniana 1 : 323-326. - 19GYa: Bakterienzahlen im Wasser von Manaus (Amazonas). - Z. Allgem. Mikrobiol.

(in press). - 1969b: Numbers of bacteria and algae and their interrelations in some Amazonian

waters. - Amazoniana 2 (in press). SIOLI, H., 1950: Das Wasser im Amazonasgebiet. - Forsch. u. Fortschr. 26: 274-280. - 1957: Sedimentation im Amazonasgebiet. - Geol. Rundsch. 46: 608-633. WILLIAMS, P. M., 1968: Organic and inorganic constituents of the Amazon river. - Nature

118: 937-938.

Dr. GOTTFRIED W. SCHMIDT Max-Planck-Ins titut fur Limnologie 232 PIon/Holstein Postfach 165

vertical distribution of bacteria and algae in a tropical lake

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