The World's Great Lakes

J. Great Lakes Res. 10(2):106-113 Internal. Assoc. Great Lakes Res., 1984

THE WORLD'S GREAT LAKESl

Alfred M. Beeton Great Lakes and Marine Waters Center The University of Michigan Ann Arbor, Michigan 48109

ABSTRACT. Most of the large lakes lie in glacial scour basins in the northern hemisphere. These lakes are closely similar in physicochemical characteristics and in their biota. Most of the other large lakes are tectonic in origin and they differ greatly among themselves and from other lakes since they occur in a diversity of terrestrial environments under a broad range of climatic conditions. Large lakes have a great diversity of habitats resulting in great species diversity and endemism in an~ient lakes. The pronounced horizontal gradients in physicochemical conditions in large lakes contribute to the diversity of habitats. Conditions found in Lakes Michigan and Skadar are examples. ADDITIONAL INDEX WORDS: Limnology, water quality, morphometry, geography.

INTRODUCTION A review and synthesis of the literature led to the conclusion that large lakes can be grouped according to their morphometry and distribution (Herdendorf 1982), however groupings according to geologic origin, physicochemical characteristics, and similarities in biota should be more useful in understanding how these large systems function. A large number of these lakes can be grouped together but the remainder differ considerably from most other lakes. All large lakes do appear to have pronounced horizontal differences in physicochemical and biological conditions. This horizontal limnology may provide a unifying concept in the study of large lakes. A previous effort to pull together knowledge on large lakes resulted in a general session entitled "World's Great Lakes" held at the Fifteenth International Limnological Congress in Madison in 1961 (Kennedy 1964). The objectives were to: (1) present general and unique characteristics of large lakes, (2) draw attention to certain unusual research opportunities, and (3) describe research on some of them. Unfortunately, large lakes of the USSR were not included, but there were papers published on the

St. Lawrence Great Lakes (Chandler 1964), Canadian large lakes (Larkin 1964), the Rift Valley lakes of Africa (Beauchamp 1964), Lake Maracaibo (Redfield and Doe 1964), and Lake Titicaca (Gilson 1964). Each lake, large or small, is unique, but it was concluded that some characteristics separate large lakes from small. I) The drainage basins of large lakes have less of an effect on them than do the basins of small lakes. 2) Large lakes affect the climate of their region. 3) Physical processes are of much greater importance in large lakes than in small lakes, i.e., (a) waves are of great importance, (b) separate water masses are distinguishable, (c) upwelling and sinking are important, and (d) large lakes are visibly affected by the Coriolis force.

Rather than dwell on how large lakes differ from small, this paper is concerned with large lakes per se, i.e., how are they alike and what are their major differences? Do they have any common characteristics other than size? An affirmative answer is of more than passing interest since if large lakes do have some close similarities then the results of research on one lake can be applied to others with some degree of confidence. I choose to deal primarily with lakes larger than 6,000 km 2 (Table 1), which includes 30 of the world's lakes, although Lake Skadar is included in the discussion on horizontal limnology.

lContribution 366 of the Great Lakes Research Division, Great Lakes and Marine Waters Center. Based on a paper presented at IAGLR Special Winter Meeting, Windsor, Ontario, 1983.

106

THE WORLD'S GREAT LAKES

107

TABLE 1. World's largest lakesJ

Area Rank 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Name

Area (km 2)

Caspian 374,000 Superior 82,100 Aral 64,500 Victoria 62,940 Huron 59,500 Michigan 57,750 Tanganyika 32,000 Baikal 31,500 Great Bear 31,320 Sap 30,000 Great Slave 28,568 Chad 25,900 Erie 25,657 Winnipeg 24,387 Nyasa 22,490 Balkhash 22,000 Ontario 19,000 Ladoga 18,130 Bangweulu 15,100 Maracaibo 13,010 Tungting 12,000 10,140 Patos Onega 9,700 Mai-Ndombe 8,210 Nicaragua 8,150 8,030 Titicaca Athabasca 7,935 Reindeer 6,650 Rudolf 6,400 Issykkul 6,240

Volume Rank

Name

Volume (km3)

Depth Rank

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Caspian Baikal Tanganyika Superior Nyasa Michigan Huron Victoria Great Bear Great Slave Issykkul Ontario Aral Ladoga Titicaca Reindeer Helmand Erie Hovsgol Winnipeg Kivu Nipigon Melville Onega Maracaibo Van Dead Rudolf Vanern Mistassini

78,200 22,995 17,827 12,230 6,140 4,920 3,537 2,518 2,292 2,088 1,738 1,637 1,451 908 827 585 510 483 480 371 333 320 313 292 280 217 188 187 180 170

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Name Baikal Tanganyika Caspian Nyasa Issykkul Great Slave Matana Crater Toba Sarez Tahoe Hornindalsvatn Chelan Kivu Quesnel Adams Fagnano Mjosa Salsvatn Manapouri Nahuel Huapi Dead Tazawa Great Bear Como Superior Hawea Maggiore Chilko Pend Oreille

Maximum Depth (m)

Area (km 2)

1,741 1,471 1,025 706 702 614 590 589 529 505 501 514 489 480 475 457 449 449 445 443 438 433 425 413 413 407 392 372 366 366

31,500 32,000 374,000 22,490 6,240 28,568 190 54 1,150 86 500 51 140 2,220 260 130 590 370 45 140 550 1,020 26 31,326 150 82,100 120 210 160 380

1Adapted from Herdendorf 1982.

MORPHOMETRIC DATA

One of the major problems is the lack of precise morphometric information for the large lakes. Consequently, various conflicting data on morphometric features have been published. Also, some lakes fluctuate widely in area and depth, e.g., Lake Tungting's area ranges from ca. 2,800 to 12,000 km 2 • Nevertheless, these problems are not so great as to preclude ranking the major lakes. The relative ranking of some lakes may be interchanged, e.g., Chad and Erie, when the area of volume data are closely similar. Most of the large lakes (87070) are found in the northern hemisphere. Most of the southern hemisphere large lakes are in Africa (Herdendorf 1982). This distribution reflects the geologic origin. Glacial scour formed the basins of most of the northern hemisphere lakes of North America and

Europe (Table 2). The basins of the African Rift Valley lakes and most of the major Asian lakes are tectonic. GLACIAL SCOUR LAKES

The glacial scour lakes are closely similar in physicochemical characteristics and in biota. Most of them are classified as oligotrophic, although some, e.g., Erie, have been impacted by man's activities in their drainage basins. Their flora and fauna reflect recent glacial origin and most of the species are cosmopolitan. Most of these lakes also have populations of "glacial relict" species, e.g., Mysis relicta, Pontoporeia, Limnocalanus macrurus, and Myoxocephalus quadricornis. These "glacial relicts" are not cosmopolitan but they are circumpolar in their distributions.

108

A. M. BEETON TABLE 2. Geologic origin of large lakes. Not all lakes listed in Table 1 are on Table 2. Glacial Scour Athabasca, N. Am. Erie, N. Am. Great Bear, N. Am. Great Slave, N. Am. Huron, N. Am. Ladoga, Europe Melville, N. Am. Michigan, N. Am. Nipigon, N. Am. Onega, Europe Ontario, N. Am. Reindeer, N. Am. Superior, N. Am. Winnipeg, N. Am.

Coastal Patos, S. Am.

Tectonic Uplift Aral, Asia Caspian, Asia/Europe Titicaca, S. Am. Victoria, Africa

Tectonic Graben Baikal, Asia Balkhash, Asia Dead Sea, Asia Issykkul, Asia Kivu, Africa Malawi, Africa Rudolf, Africa Tanganyika, Africa

Tectonic Downwarp Chad, Africa Maracaibo, S. Am.

Fluviatile Tectonic and Volcanic Sap, Asia Tungting, Asia

Northern Europen lakes, such as Ladoga and Onega, have species associations closely similar to the St. Lawrence Great Lakes and the large Canadian lakes. For example, the profundal fauna of Lake Ladoga includes Peloscolex ferox, StylodriIus heringi, Pisidium conventus, Pontoporeia affinis, Mysis relicta, and Myoxocephalus quadricornis (Zhadin and Gerd 1961). The nearshore zooplankton in both these lakes is rich in Bosmina, Daphinia, and Leptodora. The fish fauna also resembles the native fish fauna of the St. Lawrence Great Lakes and includes the planktivore Coregonus albula, the whitefish C. lavaretus, and trout Salmo salar, as well as burbot and perch. The large glacial scour lakes have not existed long enough to allow the greater species diversity and endemism observed in Baikal and the large African lakes. Nevertheless, these large lakes represent complex systems with many habitats which allow a much greater diversity than seen in small lakes. Patalas (1981) attributed the zooplankton diversity of Lake Winnipeg to the independent water masses and the tributaries entering the lake. These large lakes offer a spatial heterogeneity, ver-

Nicaragua, Central Am.

tically and horizontally, which is important for stabilizing zooplankton populations (McNaught 1978). TECTONIC AND OTHER LAKES The tectonic uplift lakes differ greatly among themselves and from other lakes. The Caspian and Aral seas are saline. Titicaca is the largest lake at high altitude. Victoria has some characteristics of Malawi and Tanganyika, especially in species richness, but it differs in that it is shallower and consequently undergoes vertical mixing (TaIling 1969). There is a wide variety of tectonic graben lakes (Table 2). Several are salt or brackish, e.g., Dead Sea and Balkhash. Issykkul is myxotrophic, i.e., fresh and brackish, on a horizontal gradient (Zhadin and Gerd 1961). Baikal has some physicochemical characteristics of the glacial scour lakes because of the nature of its drainage basin and the climate. In fact, its chemistry is closely similar to that of Lakes Superior and Ladoga. Malawi and Tanganyika are permanently stratified becuase of their great depth although the vertical temperature differences are very small (TaIling

109

THE WORLD'S GREAT LAKES

1969). Lake Malawi is homothermous at 22.5°C and anoxic below 250 m (Eccles 1974). The thermal gradient at 250 m is only O.OI°C/meter over 25 m, but nevertheless it provides an effective barrier. Usually we think of stratification in terms of temperate lakes, but stratification is more persistent and a more important factor in the large African lakes than it is in the large temperate lakes. Large lakes formed by other geologic processes, e.g., coastal, fluviatile, etc. (Table 2), differ from other lakes primarily because of the nature of their basins. HABITAT DIVERSITY AND HORIZONTAL LIMNOLOGY

The truly Great Lakes of the World offer a great diversity of habitats which have given rise to a great number of species. Lake Malawi has more species of fish than any other lake in the world (Turner 1975). Over 200 species are Cichlidae and all but four are endemic (Fryer and lIes 1972). Lakes Victoria and Tanganyika follow Malawi in species richness (Fryer 1969). This species richness is not just a consequence of these lakes occurring in the tropics since temperate Lake Baikal has many endemic species and a great species abundance. For example, Baikal has 105 species of rotifers of which 27 are endemic (Kutikova 1978). Of the 1,200 species which have been recorded for Baikal, more than half are endemic. These include an endemic sponge family, many endemic turbellarians, and oligochaetes (Zhadin and Gerd 1961). Such species abundance has not occurred in the glacial scour lakes since they are very new geologically. The complex of coregonid species which existed in Lakes Michigan and Huron provides some evidence of future speciation in these lakes. One aspect of large lake limnology which hasn't been adequately explored is the importance of horizontal differences in physicochemical conditions and biota which form an important characteristic of large lakes. Throughout the literature dealing with large lakes one finds references to maximum species diversity in the littoral zone. Eccles (1974) mentioned that the inshore waters of Lake Tanganyika are highly productive while the open lake is oligotrophic, and that fish are concentrated in the shallow marginal areas of Lake Malawi. Productivity is two to three times greater inshore than offshore in Lake Onega (Nikolaev 1972) and it is likely that the differences may be enhanced by a thermal bar (Malinina 1972). Zhadin and Gerd

(1961) also referred to a greater abundance of plankton near shore in Lake Onega. Pronounced inshore-offshore differences have been demonstrated for the St. Lawrence Great Lakes (Nalewajko 1967, Stoermer 1968, Holland and Beeton 1972). For example, Beeton and Barker (1974), in their study of the possible impact of thermal discharge from a power plant, concluded that little or no effect of the thermal discharge upon planktonic populations could be found and that the main factor affecting occurrence and abundance of organisms was distance from shore. A significant gradient of total and soluble reactive phosphorus from shore lakeward occurred on all sampling dates as demonstrated by the plot of data for 6 December 1971 (Fig. 1). This

Z ~

I-

a:

£r I-

z

i.J.J

U

Z ~

U

TBTRL PHBSPHBRUS

?O .0 65.0 60.0 55.0 50.0 45.0 40.0 as .0 ao .0 25.0 20.0 15.0 10.0 5.0

\ \ \

\ \ \ \

~

'I ~

---x- _____ .0

2·0

4.0

6.0

8.0

10.0

SBLUBLE RERCTIVE PHB5PHBRUS

3.0 2.7

2.5 Z ~

...... Ia: £r IZ

i.J.J U

Z ~

U

2.2 2.0 1.? 1.5 1.2 1.0 .?

\.)t"--- _--*----------x

.5 .2 .0 .0

DISTRNCE FRBM SHeRE IN MILES FIG. 1. Concentrations of total and soluble reactive phosphorus (p,g/L) as a function of distance from shore on transects 16 miles north (+) and 12 miles south (x) of Milwaukee Harbor, Lake Michigan, 6 December 1971 (Beeton and Barker 1974).

110

A. M. BEETON

nutrient gradient was reflected in the distribution and abundance of the biota. Some diatoms, such as Tabellaria flocculosa, were most abundant near shore whereas other algae, e.g., Rhodomonas, was most abundant off shore (Fig. 2). Zooplankters usually associated with nutrient rich waters, e.g., Bosmina longiristis, were abundant near shore. Limnocalanus macrurus, a copepod of oligotrophic lakes, was most abundant off shore. Temperature certainly would be a factor in the distribution of these organisms, but for the example presented in Figure 2, temperatures varied less than 2°e in shore/off shore (Beeton and Barker 1974). Nearshore conditions apparently favor the occurrence and abundance of certain diatoms. For example Stephanodiscus hantzschii was found only near shore by Holland and Beeton (1972), while other species, e.g., Cyclotella stelligera, were

LIMNCJCALANUS MACRURUS

100.0 90.0 0::::

W I-

W L: U '-'

co

:::J U

"(f)

CD Z

abundant off shore. Not only are the species composition and abundance of the phytoplankton affected by proximity to shore, but the physiological response to conditions near shore or off shore is also affected. Holland and Beeton (1972) demonstrated that for some diatoms species the population doubling times are almost twice as fast in shore as compared to off shore. The importance of nearshore processes has largely been ignored in studies of lakes, and much of our knowledge of limnology has been greatly influenced and dominated by studies of small stratified temperate lakes of the northern hemisphere. This concern with vertical limnology is appropriate when dealing with small aquatic systems, as demonstrated by idealized textbook figures of vertical gradients of dissolved substances (Fig. 3). In large lakes, biological and physicochemical conditions very often differ greatly between near shore and

350.0 325.0 300.0 275.0 260.0 225.0 200.0 175.0 160.0 125.0 100.0 ?5.0 50.0 25.0 .0

X /

80.0

/ /

70.0

/ / /

60.0

/ /

60.0

'"

/ /

40.0

- -><

30.0 20.0 10.0 .0 .0

2.0

4.0

6.0

B.O

0::::

10.0

W

U

co :::J U

"(f) ~

L:

"(f)

?o.o

\ \

l-

W L:

140.0 130.0 120.0 110.0 100.0 90.0 BO.O

\

600.0

I

600.0

%

-l

\ \

400.0

\ \

300.0

---.J ---.J

I

200.0

W

\

U

\ \ \

100.0

Z

2.0

-+

I I

I I I

~~~~-L~' !

2.0

4.0

!

I

! !

!

I

!

6.0

I

!

I

! ! !

I ,

! !

8.0

I

! !

~

10.0

TAOELLARIA FLCJCCULCJSA \

\

\

X \

\ \ \

60.0 60.0 40.0

X,

ao.o 20.0 10.0 .0

.0 .0

""~, - - --x I _____ *-----~~

.0

BeSMINA LeNGIRCJSTRIS 700.0

RHCJOCJMCJNAS SPP.

4.0

6.0

B.O

10.0

.0

2.0

4.0

6.0

8.0

10.0

DISTANCE FRGM SHeRE IN MILES FIG. 2. Concentrations of Limnocalanus macrurus, Bosmina longirostris, Rhodomonas spp., and Tabellaria f1occulosa as a function ofdistance from shore on transects 16 miles north (+) and 12 miles south (x) ofMilwaukee harbor, Lake Michigan, 6 December 1971 (Beeton and Barker 1974).

111

THE WORLD'S GREAT LAKES

, N0 3 , ,

i i

-

i

i

i

I

i i i

I I I

i i

iSi0 2

I

J

I

I

-

,:,

!,

.c;

0.

\'1-.,' . . .......,) ",

Q)

\,

Cl

! ," .'

I

I

"

"

-'-,

I

Temperature and Chemical ContentEUTROPHIC LAKE FIG. 3. Simulated vertical distribution of dissolved substances in a thermally stratified eutrophic lake.

off shore and from bay to bay. Consequently, in large aquatic systems horizontal limnology is of major interest. An example is Lake Skadar, Yugoslavia, a medium size lake which fluctuates in surface area between 370 and 600 km 2 annually. Extensive areas are occupied by submerged macrophytes which apparently use bicarbonates as a carbon source during photosynthesis, resulting in increases in pH and decreases in alkalinity and specific conductance (Beeton and Sikes 1978). The influence of these macrophytes on the water chemistry was demonstrated by sampling on a transect from open water into the submerged macrophyte bed. Alkalinity, conductivity, silica, and nitrate decreased and pH increased as one progressed into the macrophytes (Beeton 1978). This effect on water chemistry was substantiated by a number of experiments with macrophytes enclosed in clear plastic bags (Beeton and Sikes 1978). Decreases. in silica and nitrate were probably due to maSSIve growths of periphytic diatoms on the macrophyte. Emergent macrophytes, such as Nuphar, affected water chemistry much differently since, on a similar sampling transect from open water into the macrophytes, alkalinity, conductivity, and silica increased whereas nitrate and pH decreased. In

Lake Skadar alkalinity, conductivity, and primary productivity are closely related (Beeton and Sikes 1978). Reducing conditions in the dark waters beneath the dense cover of floating macrophytes apparently resulted in decreased pH and nitrate, and increases in alakalinity and conductivity. Lake Skadar is an aquatic system where horizontal limnology is much more important than vertical limnology. Its large surface area and shallow depth (mean 5 m) preclude persistent stratification. The different aquatic macrophyte beds result in horizontal gradients in concentrations of dissolved substances as great as those observed vertically in some small lakes (Fig. 4). CONCLUSIONS On the basis of geologic origin the glacial scour lakes make a cohesive group, while lakes formed by other processes do not. This situation is, however, not merely a consequence of their origin, but of the climactic conditions at latitudes above 40 0 N which resulted in the glaciers. Glaciation in the northern hemisphere resulted in closely similar conditions in northern North America, Europe, and Asia. Tectonic lakes have been subjected to a broad range of climactic conditions and a diversity of terrestrial environments. Consequently, they do not have much in common. The large lakes offer a great diversity of habitats and as a consequence the really ancient lakes have a great number of species, many end.emic. Th~ ?orizontal differences in physicochemIcal condItIOns in large lakes contribute to the diversity of habitats. The importance of horizontal limnology has largely been overlooked because of the emphasis on the vertical limnology of small temperate lakes. Yet pronounced horizontal differ~nces ~re rec~g­ nized in a number of large lakes III Afnca, ASia, Europe and North America, including the St. Lawren~e Great Lakes. The results of studies on Lake Skadar demonstrate that aquatic macropohytes can be a major factor in causing horizontal differences to the extent that the horizontal gradients in dissolved materials are closely similar to the vertical gradients observed in small stratified eutrophic lakes. REFERENCES Beauchamp, R. S. A. 1964. The Rift Valley lakes of Africa. Verh. Internat. Verein. Limnol. 15:91-99. Beeton, A. M. 1978. Effect of pollution on the trophic

A. M. BEETON

112 320

70-~..

30

60

/fl

o 280 E

.c

'<:7 ' \ \ " . .

\

~ ~ v

c

1E

:::>

~ 240

\ .. ~

o u

.- Cl.

30~.

£u 220

3)

Cl>

0l::t

§

a.

..._ •••••

(/)

()I.- •••

••

U

••

. . ,\

3

••• •...

',\,

\\ \\Conduct -

7.3

150 c

7.2

140

7.1

130

-7.0

120

a.

Open Lake

>. ...-

........

...."

. ..

.."0 <[

•

once

I

Emergent Macrophytes

160 ~ E

J:

e.

••

•••.

AlkOlin~-::::-=-=--

10 (/)

7.4

..........

\

~_

200

o

.. N0

••'~\.', • ...

A

0 (f)

~

••

u u

o

............

\ \

(/)

180

•••••

V . · · .....\ \,\

-:J :0

u

7.5- 170

-I

•• ,

,,::::l 0 0

1'0

··X··········· •••••••

'\\

~~

u

180

...-

"" ,

Ci ~

o .....

Si'

190

o

..........•..•••. ..

\\

Ee

7.6-

··PH

.

."_.,,

\\ \\

50~~ 40

•••••••

v\ \ '\."'.p

~

:::l. ~ 260

............• -7.7

••• ·00

---__•

Submersed Macrophytes

FIG. 4. Concentrations ofphosphorus, silica, alkalinity, nitrate, and measurements ofpH and conductivity in emergent and submerged macrophyte beds, and in open Lake Skadar, Yugoslavia, March 1976 (modified from Beeton 1978).

state of lakes. Montenegrin Acad. Sci., Arts, Sci. Meetings. Vol. 4, Sec. Natural Sci., Vol. 2:44-72. ____ , and Barker, J. M. 1974. Investigation of the influence of thermal discharge from a large electric power station on the biology and near shore circulation of Lake Michigan - Part A: Biology. Center for Great Lakes Studies, Univ. Wis.-Milwaukee, Spec. Rept. No. 18. ____ , and Sikes, S. 1978. Influence of aquatic macrophytes on the chemistry of Skadar Lake, YugoVerh. Internat. Verein. Limnol. slavia. 20: 1055-1061. Chandler, D. C. 1964. The St. Lawrence Great Lakes. Verh. Internat. Verein. Limnol. 15:59-75. Eccles, D. H. 1974. Limnology of Lake Malawi. Limnolo Oceanogr. 19:730-742. Fryer, G. i969. Speciation in African lakes. Verh. Int. Verein. XVII:308-322. ____ , and lIes, T. D. 1972. The Chichlid Fishes of the Great Lakes of Africa, Their Biology and Evolution. Edinburgh: Oliver and Boyd.

Gilson, H. C. 1964. Lake Titicaca. Verh. Internat. Verein. Limnol. 15: 112-127. Herdendorf, C. E. 1982. Large lakes of the world. J. Great Lakes Res. 8:379-412. Holland, R. E., and Beeton, A. M. 1972. Significance to eutrophication of spatial differences in nutrients and diatoms in Lake Michigan. Limnol. Oceanogr. 17:88-96. Kennedy, W. A. 1964. The great lakes of the world. Verh. Internat. Verein. Limnol. 15:57-58. Kutikova, L. A. 1978. On the genesis of the rotatorian fauna of Baikal Lake. Verh. Internat. Verein. Limnolo 20: 1108-1110. Larkin, P. D. 1964. Canadian lakes. Verh. Internat. Verein. Limnol. 15:76-90. Malinina, T. I. 1972. Hydrological features of Lake Onega in the annual cycle. Verh. Internat. Verein. Limnol. 18:537-541. McNaught, D. C. 1978. Spatial heterogeneity and niche differentiation in zooplankton in Lake Huron. Verh. Internat. Verein. Limnol. 20:231-346.

THE WORLD'S GREAT LAKES Nalewajko, C. 1967. Phytoplankton distribution in Lake Ontario. In Proc. 19th Conf. Great Lakes Res., pp. 63-69. Internat. Assoc. Great Lakes Res. Nikolaev, I. I. 1972. Seasonal biological structure of Lake Onega. Verh. Internat. Verein. Limnol. 18:542-547. Patalas, K. 1981. Spatial structure of the crustacean planktonic community in Lake Winnipeg, Canada. Verh. Internat. Verein. Limnol. 21 :305-311. Redfield, A. C., and Doe, L. A. E. 1964. Lake Maracaibo. Verh.Internat. Verein. Limnol. 15:100-111. Stoermer, E. F. 1968. Nearshore phytoplankton populations in the Grand Haven, Michigan vicinity during thermal bar conditions. In Proc. 11th Conj. Great Lakes Res., pp. 137-150. Internat. Assoc. Great Lakes Res. TaIling, J. F. 1969. The incidence of vertical mixing and

113

some biological and chemical consequences in tropical African lakes. Verh. Internat. Verein. Limnol. 17:998-1012. Turner, J. L. 1975. Preliminary analysis of demersal trawl fishery of Lake Malawi. In Symposium of

methodology for the survey, monitoring and appraisal of fishery resources in lakes and large rivers. European Inland Fisheries Advisory Commission. Paper No. 23, Supplement 1. Zhadin, V. I., and Gerd, S. V. 1961. Fauna and flora of the rivers, lakes and reservoirs of the U.S.S.R. Gosudarstvennoe Uchebno-Pedagogicheskoe I1datel'stvo Ministerstva Prosveschcheniya RSFSR, Mopskva. (Translated from Russian by A. Mercado, edited by R. Finesilver, Israel Program for Scientific Translations, Jerusalem 1963).