The Lakes Handbook VOLUME 1 LIMNOLOGY AND LIMNETIC ECOLOGY ppt

The Lakes Handbook
VOLUME 1
LIMNOLOGY AND
LIMNETIC ECOLOGY
EDITED BY
P.E. O’Sullivan
AND
C.S. Reynolds

THE LAKES HANDBOOK
Volume 1
Also available from Blackwell Publishing:
The Lakes Handbook
Volume 2 Lake Restoration and Rehabilitation
Edited by P.E. O’Sullivan & C.S. Reynolds
The Lakes Handbook
VOLUME 1
LIMNOLOGY AND
LIMNETIC ECOLOGY
EDITED BY
P.E. O’Sullivan
AND
C.S. Reynolds
© 2004 by Blackwell Science Ltd
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First published 2003 by Blackwell Science Ltd
Library of Congress Cataloging-in-Publication Data
The lakes handbook / edited by P.E. O’Sullivan and C. S. Reynolds.
p. cm.
Includes bibliographical references and index.
ISBN 0-632-04797-6 (hardback, v.1: alk. paper)
1. Limnology. 2. Lake ecology. I. O’Sullivan, P. E. (Patrick E.) II. Reynolds, Colin S.
QH96.L29 2003
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List of Contributors, vii
1 LAKES, LIMNOLOGY AND LIMNETIC ECOLOGY: TOWARDS A NEW SYNTHESIS, 1
Colin S. Reynolds
2 THE ORIGIN OF LAKE BASINS, 8
Heinz Löffler
3 THE HYDROLOGY OF LAKES, 61

Thomas C. Winter
4 CHEMICAL PROCESSES REGULATING THE COMPOSITION OF LAKE WATERS, 79
Werner Stumm
5 PHYSICAL PROPERTIES OF WATER RELEVANT TO LIMNOLOGY AND
LIMNETIC ECOLOGY, 107
Colin S. Reynolds
6 THE MOTION OF LAKE WATERS, 115
Dieter M. Imboden
7 REGULATORY IMPACTS OF HUMIC SUBSTANCES IN LAKES, 153
Christian E.W. Steinberg
8 SEDIMENTATION AND LAKE SEDIMENT FORMATION, 197
Jürg Bloesch
9 ORGANISATION AND ENERGETIC PARTITIONING OF LIMNETIC COMMUNITIES, 230
Colin S. Reynolds
10 PHYTOPLANKTON, 251
Judit Padisák
11 AQUATIC PLANTS AND LAKE ECOSYSTEMS, 309
Jan Pokorn´y and Jan Kveˇt
Contents
vi contents
12 BENTHIC INVERTEBRATES, 341
Pétur M. Jónasson
13 PELAGIC MICROBES – PROTOZOA AND THE MICROBIAL FOOD WEB, 417
Thomas Weisse
14 ZOOPLANKTON, 461
Z. Maciej Gliwicz
15 FISH POPULATION ECOLOGY, 517
Ian J. Winfield
16 FISH COMMUNITY ECOLOGY, 538
Jouko Sarvala, Martti Rask and Juha Karjalainen

17 SELF-REGULATION OF LIMNETIC ECOSYSTEMS, 583
Claudia Pahl-Wostl
18 PALAEOLIMNOLOGY, 609
Patrick O’Sullivan
Index, 667
Blackwell Publishing is grateful to the various copyright holders who have given
their permission to use copyright material in this volume. While the
contributors to this volume have made every effort to clear permission as
appropriate, the publisher would appreciate being notified of any omissions.
Jürg Bloesch Swiss Federal Institute for Envi-
ronmental Science and Technology (EAWAG),
CH-8600 Dübendorf, Switzerland
Z. Maciej Gliwicz Department of Hydrobiolo-
gy, University of Warsaw, ul. Banacha 2, PL 02-
097 Warszawa, Poland
Dieter M. Imboden Zürichstrasse 128, CH-
8700 Küsnacht, Switzerland
Pétur M. Jónasson Freshwater Biological
Laboratory, University of Copenhagen, DK-3400
Hillerød, Denmark
Juha Karjalainen Department of Biological
and Environmental Science, University of
Jyväskylä, FIN-40351 Jyväskylä, Finland
Jan Kvˇet Faculty of Biological Sciences, Uni-
versity of South Bohemia, CZ-37005 C
ˇ
eske Bude-
jovicˇe, Czech Republic Institute of Botany,
Academy of Sciences of Czech Republic, CZ-379
82 Trˇebonˇ, Czech Republic

Heinz Löffler Institute of Limnology, Univer-
sity of Vienna, Althanstrasse 14, A-1090 Wien,
Austria
Patrick O’Sullivan School of Earth, Ocean
and Environmental Sciences, University of Ply-
mouth, Plymouth, PL4 4AB, UK
Judit Padisák Institute of Biology, University
of Veszprém, H-8200 Veszprém, Hungary
Claudia Pahl-Wostl Institute of Environmen-
tal Systems Research, University of Osnabrück,
Albrechtstrasse 28, D-49069 Osnabrück, Germany
Contributors
Jan Pokorn´y Institute of Botany, Academy
of Sciences of Czech Republic and ENKI
o.p.s. Dukelská 145, CZ-379 82 Trˇebonˇ , Czech
Republic
Martti Rask Finnish Game and Fisheries Re-
search Institute, Evo Fisheries Research, FIN-
16900 Lammi, Finland
Colin S. Reynolds Centre for Ecology and
Hydrology Windermere, The Ferry House, Amble-
side, Cumbria LA22 0LP, UK
Jouko Sarvala Department of Biology, Uni-
versity of Turku, FIN-20500 Turku, Finland
Christian E.W. Steinberg Leibniz-Institut
für Gewässerökologie und Binnenfischerei,
Müggelseedamm 310, D-12587 Berlin, Germany
Werner Stumm late of EAWAG/ETH, CH-
8600 Dübendorf, Switzerland
Thomas Weisse Institute of Limnology,

Austrian Academy of Sciences, A-5310 Mondsee,
Austria
Ian J. Winfield Centre for Ecology and Hydrol-
ogy Windermere, The Ferry House, Ambleside,
Cumbria LA22 0LP, UK
Thomas C. Winter Denver Federal Center,
Box 25046 Denver, Colorado 80225, USA

1.1 INTRODUCTION
From the beginnings of modern science, lakes have
fulfilled a focus of attention. Doubtless, this has
something to do with the lure that water bodies
hold for most of us, as well as for long having been a
source of food as well as water. Authors, from Aris-
totle to Izaak Walton, committed much common
knowledge of the freshwater fauna to the formal
written record, so it is still a little surprising to re-
alise that the formal study of lakes
—
limnology
(from the Greek word, limnos, a lake)
—
is scarcely
more than a century in age (Forel 1895). When, yet
more recently, the branch of biology concerned
with how natural systems actually function (ecol-
ogy) began to emerge, ponds and lakes became key
units of study. The distinctiveness of aquatic biota
together with the tangible boundaries of water
bodies lent themselves to the quantitative study

of the dynamics of biomass (Berg 1938) and
energy flow (Lindeman 1942). One of the leading
contemporaneous exponents of limnology, August
Thienemann, was quick to realise the distinctive
properties of individual lakes and the nature of the
crucial interaction of lakes with their surrounding
catchments, in the broader context of what we
now refer to as landscape ecology (Thienemann
1925). Moreover, as the science has developed, it
has been recognised that lakes cannot be studied
without some appreciation of their developmental
history (Macan 1970). Today, we have no difficulty
in accepting that the biology of water bodies is in-
fluenced by geography, physiography and climate;
in the morphometry of basins; in the hydrology
and the hydrography of the impounded water; the
hydrochemistry of the fluid exchanges; and the
adaptations, dynamics and predilections of the
aquatic biota. We may also accept that, just as no
two water bodies are identical, we cannot assume
that they function in identical ways. Yet the search
for underlying patterns and for the underpinning
processes continues apace, moving us towards a
better understanding of the ecology of lakes and
their biota.
The ostensible purpose of The Lakes Handbook
is, plainly, to provide a sort of turn-of-the-century
progress report which brings together the most re-
cent perspectives on the interactions among the
properties of water, the distinguishing features of

individual basins and the dynamic interactions
with their biota. Such reviews are not a new idea,
especially not in limnology where the great Trea-
tise commenced by Hutchinson (1957, 1967 and
later volumes) remains a foundation block in the
limnologist’s firmament. In these two volumes,
we have attempted to bring together limnologists
and hydrobiologists, each a recognised and re-
spected authority within a specialist sub-division
of limnetic science, and invited from each an up-
to-date overview of pattern–process perceptions
within defined areas of the knowledge spectrum.
The contributed chapters address aspects of the
physics, chemistry and biological features of se-
lected (usually phylogenetic) subdivisions of the
biota, while several topics (such as structural dy-
namics and system regulation) are addressed
under general headings. The limnetic biologies of
selected lakes and systems feature in the second
volume.
The immediate inspiration for this book
—
for
1 Lakes, Limnology and Limnetic Ecology:
Towards a New Synthesis
COLIN S. REYNOLDS
2 c. s. reynolds
the publishers, Blackwell Science, as well as for us
as its editors
—

has been the excellent Rivers Hand-
book (Calow & Petts 1992). We have sought to
select a similar balance of in-depth reviews by
leading practitioners in the field, to cover all as-
pects of limnology. Within the two volumes,
we have attempted also a balance between theoret-
ical and applied topics: our objective has been
to provide a point of reference for students and
professionals alike. We have been conscious, of
course, of the challenges these ambitions entail.
Neither the encyclopaedic thoroughness of
Hutchinson’s Treatise nor the robust utility of
Wetzel’s Limnology textbooks (1975, 1983, 2001),
nor the accessibility of Kalff’s (2002) text, nor even
the explicative empiricism of Uhlmann’s (1975)
Hydrobiologie, is yet capable of emulation. We
do not pretend to rival the more specialist com-
pendia, such as Lerman et al. (1995) on the physics
or chemistry of lake waters. Nevertheless, by
drawing on the talents of our respective contribu-
tors, we believe that we have been able to present a
contemporary and accurate reflection of current
understanding about how lakes and lake ecosys-
tems function.
1.2 THE LURE OF LIMNOLOGY
We have also been keen to mirror two further mod-
ern perceptions underpinning current attitudes to
limnology. One of these is the importance of the
freshwater resource. Although over 70% of our
‘blue planet’ is covered by sea, lakes and rivers oc-

cupy only a tiny percentage of the (c.150 million
km
2
) terrestrial surface. Nobody can say for certain
just how many water bodies currently populate the
surface of the Earth. The series beginning with the
world’s largest lakes (Tables 1.1–1.3) progresses
through smaller and smaller water bodies, eventu-
ally to collapse fractally into a myriad of sumps,
melt-water, flood-plain, delta- and other wetland
pools, puddles and ‘phytotelmata’ of rainwater re-
tained in the foliage of terrestrial plants (especially
of Bromeliads). Even restricting ourselves to
natural (i.e., no artificial ponds), permanent (or
seasonally enduring), stillwater-filled bodies,
wholly surrounded by land and exceeding an
arbitrary cut off point (say 0.1km
2
), then the total
number of lakes in the world may be estimated to
be in excess of 1.25 million, having an aggregate
surface area of 2.6 million km
2
(Meybeck 1995).
For smaller lakes, Meybeck (1995) used intensive
regional censuses to extrapolate that there are
likely to be a further 7.2 million water bodies with
areas in the range 0.01–0.1km
2
, contributing a

further 0.2 million km
2
of water surface. Of partic-
ular interest, however, is that the numbers of lakes
in successive logarithmic bands (0.1–1km
2
, 1–
10km
2
, etc., up to >100,000km
2
) diminish by a fac-
tor of about 10 at each step; nevertheless, the aggre-
gate of lake areas within each is broadly similar
between bands (0.35 ± 0.15 million km
2
: see Table
1.1). Only the second category of great tectonic and
glacial scour lakes
—
group (b) in Table 1.1
—
lies
outside this generalisation, but the disparity is not
vast. It is a reasonable deduction that the present
planetary distribution of standing stillwaters (i.e.,
all lakes by definition, discounting extreme differ-
ences in salinity) is very evenly dispersed across
the spectrum of lake areas.
The impression of evenness disappears when

the volume of lakes is considered. Again, the abun-
dance of water on the planet (nearly 1390 million
km
3
) notwithstanding, barely 225,000km
3
(i.e.,
<0.016% of the total) is estimated to be contained
in lakes and rivers. The amount discharged annu-
ally to the sea, c.29,000km
3
, suggests an average
residence of terrestrial surface water of eight years
or so. True, groundwaters boost the planetary ag-
gregate of non-marine liquid water (8 million km
3
)
but the point remains that, if the resource is to be
maintained, its sustainable exploitation is neces-
sarily restricted to the interception of the seaward
flux. Even then, far from all of the terrestrial stor-
age is potentially potable, owing in part to the ex-
cessive salinity or alkalinity of a large proportion
of it (see Williams; Chapter 8, Volume 2) and in part
to anthropogenic despoliation (see Chapter 2, Vol-
ume 2). Variability in the flux rate about the aver-
age determines that the supply is far from evenly
distributed (Meybeck 1995), either in space or in
time, so that problems vary locally, according to
drainage, climate, season, usage demands and the

extent of defilement. Thus, the world-wide distrib-
ution of lakes and of the rivers that feed and drain
them is of crucial social and economic importance.
Reservoirs provide a means of resource conserva-
tion and of balancing ongoing demands against
temporal vagaries of flows, but there needs still to
be a hydraulic flux. Thus, access to adequate sup-
plies of clean, fresh water is already proving to be a
severe social and developmental constraint in sev-
eral arid nations (e.g., the middle and northeast
USA versus Mexico). The risks of a drying local cli-
mate or, simply the impact of an abnormally dry
year, precipitate immediate and widespread public
concern.
However, between-basin differences in the
allocation of the standing water is impressively
Lakes, Limnology and Limnetic Ecology 3
Table 1.1 Global distribution of the world’s aggregate area of lake water among area classes (in km
2
, based on data in
Meybeck, 1995), with the individual areas of those in the first two classes, as presented by Herdendorf (1982). See also
Beeton (1984).
Category Name of lake Area (km
2
) Number in category Total area of category (km
2
)
(a) Inland waters >100,000km
2
Kaspiyskoye More*,† 374,000 1 374,000

(b) Inland waters 10,000–100,000 km
2
Lake Superior 82,100 18 624,000
Aralskoye More†,‡ 64,500
Lake Victoria 62,940
Lake Huron 59,500
Lake Michigan 57,750
Lac Tanganyika 32,000
Ozero Baykal 31,500
Great Bear Lake 31,326
Great Slave Lake 28,568
Lake Erie 25,657
Lake Winnipeg 24,387
Lake Malawi* 22,490
Ozero Balkhash§ 19,500
Lake Ontario 19,000
Ladozhskoye Ozero 18,130
Lac Tchad§ 18,130
Tonle Sap§ 16,350
Lac Bangweolo§ 10,000
(c) Inland waters 1000–10,000 km
2
124 327,000
(d) Inland waters 100–1000 km
2
1380 359,000
(e) Inland waters 10–100 km
2
12,300 319,000
(f) Inland waters 1–10km

2
127,000 323,000
(g) Inland waters 0.1–1 km
2
1,110,000 288,000
(h) Inland waters 0.01–0.1km
2
7,200,000 190,000
Total (a–h) 8.45 ¥ 10
6
2,804,000
* The Caspian Sea (see Chapter 2). Here, lakes are identified by the latinised local names recommended by Herdendorf (1982), except that
Lake Nyasa is now more generally recognised as Lake Malawi.
† As terrestrially enclosed water bodies these saline waters are included as ‘lakes’.
‡ The area cited, from Herdendorf (1982), refers to the full recent extent of the lake. It has diminished greatly in the last decade owing to
exploitative abstraction (see Williams & Aladin 1991).
§ Shallow lakes in typically arid and semi-arid areas are subject to large fluctuations in extent. The area quoted is the arithmetic mean of the
range cited by Herdendorf (1982).
4 c. s. reynolds
skewed: the volume stored in Ozero Baykal,
Russia (c.23,000km
3
), alone represents over 10%
of the total water quantity in the world’s lakes
and rivers. Discounting the salt waters of the
Kaspiyskoye More, the other nine lakes in Table
1.2 together account for 25% of the surface store of
fresh water. So it is that, although most lake habi-
tats are really rather small (each <0.1km
2

), most of
the aggregate volume resides in large, deep lakes.
All this accentuates the need to understand the
role of the standing reserves (lakes, including
reservoirs and groundwaters), how they function
and how they sustain life, within and beyond their
confines. There is an urgent need to grasp the pro-
ductive dependence of fisheries as a source of food,
not as a factor of the carbon fixation capacity of the
primary producers but on the extent to which
physical and chemical processes govern the meta-
bolic transformation into useful food and in the
context of the materials supplied by the entire
hydraulic catchment.
This brings us to the second of the two percep-
tions. It is that lakes hold practical attractions for
the ecological study of systems. This is not to res-
urrect the quaint and rather discredited early no-
tion about lakes providing closed, microcosmic
model ecosystems. Nevertheless, the substantial
integrity of function in the face of seemingly over-
whelming environmental constraints set by the
high density, high viscosity and high specific heat
of the medium is striking. Moreover, despite the
alleged transparent colourlessness and universal
solvent properties of water, the poverty of under-
water light and the extreme dilution of dissolved
resources are recurrent, dominating architectural
features of limnoecology (Lampert & Sommer
1993). Ecosystems are generally acknowledged to

be complex; those of the majority of lakes provide
no exceptions. They do offer, as many terrestrial
ecosystems do not, the advantage of relevant envi-
ronmental fluctuations and responses at the
population and community levels on timescales
convenient to the observer and experimenter. For
instance, a great many international exhortations
and initiatives have been implemented to protect
species diversity and to develop protocols for the
sustainable exploitation of ecosystems. These are
well motivated but have been offered, as a rule,
without an ecosystem-based view of the manage-
ment objective and, very often, without a clear
idea of whence the diversity derives or precisely
how it is maintained. Ecology is still beset with
what are little more than unproven hypotheses.
Lakes (especially smaller ones), on the other hand,
are amenable to the study of such high-order
ecosystem processes as population recruitment,
community assembly, competitive exclusion,
niche differentiation and changing diversity in-
dices. The timescales of ecological interest, which
in aquatic environments occupy the range seconds
to decades, are equivalent to minutes to hundreds
of millennia on land. Though similar scales apply
as in lakes, they are logistically too difficult or too
expensive to research in the oceans.
Table 1.2 The world’s ten largest lakes and inland
waters, by volume retained (in km
3

, based on Herdendorf
(1982) and Beeton (1984)).
Kaspiyskoye More 78,200
Ozero Baykal 22,995
Lac Tanganyika 18,140
Lake Superior 12,100
Lake Malawi 6140
Lake Michigan 4920
Lake Huron 3540
Lake Victoria 2700
Great Bear Lake 2240
Great Slave Lake 2088
Ozero Issyk-kul 1740
Table 1.3 The world’s ten deepest lakes (maximum
depths in metres; based on Herdendorf (1982) and Beeton
(1984), but modified after Reynolds et al. (2000)).
Ozero Baykal 1741
Lac Tanganyika 1471
Kaspiyskoye More 1025
Lake Malawi 706
Ozero Issyk
—
kul 702
Great Slave Lake 614
Lago Gral.Carrera/Buenos Aires 590
Danau Matano 590
Crater Lake 589
Danau Toba 529
Common to water bodies of all sizes and shapes
is their island quality

—
to aquatic organisms they
function as patches of suitable habitat in a sea of an
inhospitable, terrestrial environment. The distrib-
ution and relative isolation of the aquatic islands
are especially challenging in the context of species
dispersion and endemism, while patch size and
the variability to which patches may be subject are
key factors in viability and survival. Of course,
not all lakes are mutually isolated, but fluvial con-
nectivity merely adds to the fascination of fresh-
water systems and the importance to ecological
understanding of their study (Tokeshi 1994).
Limnologists have perhaps advanced furthest
in the development of realistic models of species-
specific successions and their interaction with the
relatively straightforward properties of the lim-
netic environment (Steel 1995; Reynolds & Irish
1997). This might be reason enough for advocating
the study of lakes but we believe that, because
freshwater systems are sufficiently representative
of all ecosystems, the analogous processes are ade-
quately simulated in the functioning of limnetic
biota. Through the pages of the two volumes of this
handbook, we seek to project something of the ex-
traordinary diversity of lake basins and their ecolo-
gies. However, we strive to reveal the common
constraints that link the properties of water, the
movements generated in lakes, the sources of
input water and its chemical composition, the

structure of the pelagic biota, the littoral influence
and the significance of benthic processes. We iden-
tify the fundamental knowledge required to up-
hold the management of quality and biotic outputs
from lakes and reservoirs, drawing on the assess-
ment of case studies and applications from around
the world. Of course, the relevant knowledge em-
anates from our contributors, through whose
writings we are able to convey the excitement
felt by all limnologists about the habitats we are
fortunate enough to study.
1.3 THE ORGANISATION AND
STRUCTURE OF THIS BOOK
This might have been the point at which to con-
clude this introductory chapter. The organisation
of the book is relatively self-evident, the first part
being dedicated to the physical and chemical fea-
tures of lakes and their main biota, the second
much more at the practical applications of limnol-
ogy. The beginning of a book is also the customary
place in which to acknowledge the generous ef-
forts of expert authors, the patience and profes-
sionalism of the publisher and the interest of
readers. We take this opportunity to do just that
but we are bound to do something more in this
introduction. The book’s inordinately long period
in gestation
—
some five years from conception
to its entry into the bookshops

—
is a matter of
deep regret and embarrassment to the editors. We
apologise profoundly to the contributors whose
submissions we received comfortably within
the original schedule. Hindsight confirms that,
whether out of our naivety, incompetence or as a
consequence of other pressures upon us, we did not
provide the assistance and exhortation required by
a minority of contributors who, for whatever per-
sonal difficulties they experienced, were unable to
keep to the schedule. Alternative contributors had
to be found in more than one instance.
Not one but three tragic setbacks further con-
founded the slow progress. We learned with great
sadness of the death, on 14 April 1999, of Profes-
sor Werner Stumm. As the undisputed father of
‘aquatic chemistry’, his profound contributions
and the fundamental research he led in the field of
mineral surface reactions and aqueous phase equi-
libria and kinetics made him a natural choice as a
contributory author. This was a task to which he
readily committed himself. The chapter here is
close to his original draft; however, we are ex-
tremely grateful to Dr Laura Sigg for her careful
and skilful attention to the final manuscript.
Professor W. Thomas Edmondson died on 10
January 2000. Tommy had been passionate about
freshwater life from childhood and his develop-
ment as a scientist had been encouraged by such

great limnologists as G.E. Hutchinson, Chancey
Juday and Edward Birge. His pioneering work on
rotifers continues to be held in very high regard but
he became best known for his long-term study of
the eutrophication of Lake Washington, and for his
successful public campaign to reverse it. The case
is a telling example of how sound limnological un-
Lakes, Limnology and Limnetic Ecology 5
6 c. s. reynolds
derstanding, good communication and collective
appreciation of a natural asset might be harnessed
to bring about one of the most successful exercises
in lake restoration. We feel deeply honoured to be
able to include Tommy’s own perspective on the
unfolding story.
The death of Milan Straˇskraba, on 26 July 2000,
also represents a severe loss to the scientific study
of lakes. Milan had stepped in at a late date to write
the chapter on reservoirs. We had discussed with
him the topics to be covered in his contribution
and he had submitted a first draft for our considera-
tion. Illness slowed his further progress but he re-
mained determined to complete the work. Sadly,
circumstances did not allow him to do so: we are in
possession only of the first draft. It was necessary
to edit it but we have done so as lightly as we rea-
sonably could.
Further tragedy struck close to the final prepa-
ration of Volume 1 for the publishers when we
learned with enormous sadness that Professor

W.D. (Bill) Williams had finally lost his long battle
with myeloid leukaemia and had passed away in
Brisbane on Australia Day, 26 January 2002. His
eminent contribution to the study of lakes, espe-
cially of those saline and temporary waters that he
considered to be as important, on areal grounds, as
the more familiar subjects of the northern temper-
ate zone, is familiar to all. He was enthusiastic in
his support for this project and we are proud to be
able to include his Chapter with the text as he
agreed it.
The delays are not easily excused and we do not
seek this. When it became evident just how long it
would be before the book was finished, all the au-
thors of submissions received on time were given
the opportunity to update their contributions. In
most instances, the landmark quality of the origi-
nal review endures unscathed but topical revision
has brought each of the contributions to the level
of a contemporary overview of its subject.
Nevertheless, it is fortuitous that the gestation
of the Handbook has coincided with the signifi-
cant paradigm shift that is transforming limnetic
ecology and the consensus view of just how lake
ecosystems work. It is becoming increasingly
recognised that the level of net aquatic primary
production in small lakes does not always generate
sufficient organic carbon to sustain the recruit-
ment of heterotrophs at higher trophic levels.
Moreover, the amount that is transferred through

the planktic food chain seems to be altogether too
small to support the measured quantities of fish
biomass produced. Systems that are exclusively
dependent upon pelagic primary and secondary
producers (those of the open water of the oceans
and of large, deep lakes) are, characteristically, able
to maintain only the very low biomass densities
diagnostic of resource-constrained oligotrophic
systems. In contrast, the maintenance of produc-
tive food webs culminating in high areal densities
of fish or macrophytes relies, to varying extents, on
the supplement of inorganic nutrients and the
residues of organic biomass carbon from the terres-
trial catchments. It now seems that, with varying
shortfalls, the functioning of many lake systems is
not self-sufficient upon autochthonous primary
production but is supported by the heterotrophic
assimilation of primary products originating from
the catchment (Wetzel 1995).
This deduction appears to be applicable to a
wide range of smaller lakes where, in fact, gross
primary production cannot be shown to exceed
community respiration and the net production of
the lake appears to be negative. The balance is met
by terrestrial primary products, imported from the
adjacent lands directly or in the hydraulic inflow.
Enhancing in situ primary production through the
direct fertilisation of the water with nutrients does
not prevent the imported materials so that, even if
internal production is raised absolutely and rela-

tively, the system continues to function with a dis-
tinct heterotrophic component (Cole et al. 2000).
Some of the individual chapters represent these
ideas and interpretations of system dynamics.
Others have emphasised the contemporary prob-
lems in limnetic ecology that are propagated by the
recognition and acceptance that wholesome and
supposedly pristine sites may be, on balance, het-
erotrophic. The whole concept of the ecosystem
health of lakes, as well as the way that they can be
managed in order to achieve and maintain a sus-
tainable condition, must now undergo careful
revision.
In more ways than one, we both feel more than a
little wiser. We have experienced, in more than ad-
equate amount, the tribulations of editing a book
of this scale and these ambitions. On the other
hand, we have gained a great deal of new knowl-
edge from the accumulated wisdom of our contrib-
utors. We take this opportunity of congratulating
all of them for their respective submissions, for
the deep knowledge and experienced judgement
that they reveal, and of thanking them for their
co-operation and collaboration with us in bringing
the project to fruition. To the majority of them, we
express our grateful thanks and appreciation for
prompt responses and extreme patience; but
our gratitude is no less for persistence and endeav-
our where these have been the distinguishing
attributes.

We take pleasure in acknowledging the support
afforded to us by Dr Helen Wilson, of the Univer-
sity of Plymouth, copy editor Harry Langford and
the understanding advice and guidance initially
provided by Susan Sternberg and, later, by Ian Fran-
cis and Delia Sandford at Blackwell. The finished
book is a team effort. We are proud to acknowledge
an excellent team.
REFERENCES
Beeton, A.M. (1984) The world’s great lakes. Journal of
Great Lakes Research, 10, 106–13.
Berg, K. (1938) Studies on the bottom animals of Esrom
Lake. Kongelige Danske Videnskabernes Selskabs
Skrifter, 8, 1–255.
Calow, P. & Petts, G.E. (1992) The Rivers Handbook.
Blackwell Scientific Publications, Oxford (2 vols.), 536
+ 522 pp.
Cole, J.J., Pace, M.L., Carpenter, S.R. & Kitchell, J.F.
(2000) Persistence of net heterotrophy in lakes during
nutrient addition and food-web manipulations.
Limnology and Oceanography, 45, 1718–30.
Forel, F.A. (1895) La limnologie, branche de la
Geographie. Comptes Rendues du sixième Congrès
international de Geographie, 1–4.
Herdendorf, C.E. (1982) Large lakes of the World. Journal
of Great Lakes Research, 8, 106–13.
Hutchinson, G.E. (1957) A Treatise on Limnology, Vol. 1,
Geography, Physics, Chemistry. Wiley, New York,
1016 pp.
Hutchinson, G.E. (1967) A Treatise in Limnology, Vol. II,

Introduction to Lake Biology and the Limnoplankton.
Wiley, New York, 1115 pp.
Kalff, J. (2002) Limnology
—
Inland Water Systems.
Prentice Hall, Upper Saddle River, New Jersey, 592 pp.
Lampert, W. & Sommer, U. (1993) Limnoökologie. Georg
Thieme Verlag, Stuttgart, 440 pp.
Lerman, A., Imboden, D.M. & Gat, J.R. (1995) Physics
and Chemistry of Lakes (2nd edition). Springer-Verlag,
Berlin, 352 pp.
Lindeman, R.L. (1942) The trophic dynamic aspect of
ecology.Ecology,23, 399–418.
Macan, T.T. (1970) Biological Studies of the English
Lakes. Longman, London, 260 pp.
Meybeck, M. (1995) Global distribution of lakes. In:
Lerman, A., Imboden, D.M. & Gat, J.R. (eds), Physics
and Chemistry of Lakes (2nd edition). Springer Verlag,
Berlin, 1–35.
Reynolds, C.S. & Irish, A.E. (1997) Modelling
phytoplankton dynamics in lakes and reservoirs; the
problem of in-situ growth rates. Hydrobiologia, 349,
5–17.
Reynolds, C.S., Reynolds, S.N., Munawar, I.F. & Mu-
nawar, M. (2000) The regulation of phytoplankton
population dynamics in the world’s great lakes. Aquat-
ic Ecosystem Health and Management, 3, 1–21.
Steel, J.A. (1995) Modelling adaptive phytoplankton
in a variable environment. Ecological Modelling, 78,
117–27.

Thienemann, A. (1925) Die Binnengewässer, Band I. E.
Schweizerbart’sche, Stuttgart, 255 pp.
Tokeshi, M. (1994) Community ecology and patchy
freshwater habitats. In: Giller, P.S., Hildrew, A.G. &
Raffaelli, D.G. (eds), Aquatic Ecology: Scale, Pattern
and Process. Blackwell Science, Oxford, 63–91.
Uhlmann, D. (1975) Hydrobiologie. G. Fisher, Stuttgart,
345 pp.
Wetzel, R.G. (1975) Limnology. Saunders, Philadelphia,
743 pp.
Wetzel, R.G. (1983) Limnology (2nd edition). Saunders,
Philadelphia, 859 pp.
Wetzel, R.G. (2001) Limnology and Lake Ecosystems
(3rd edition). Academic Press, San Diego, 1006 pp.
Wetzel, R.G. (1995) Death, detritus and energy
flow in aquatic ecosystems. Freshwater Biology, 33,
83–9.
Williams, W.D. & Aladin, N.V. (1991) The Aral Sea:
recent limnological changes and their conservation
significance. Aquatic Conservation, 1, 3–23.
Lakes, Limnology and Limnetic Ecology 7
2.1 LAKE DEFINITION
Given the great variety of bodies of standing wa-
ters, it is not surprising that all lake definitions
must be arbitrary. It is sometimes even difficult to
distinguish between flowing (lotic) and standing
(lentic, lenitic) waters
—
for instance lengthy, shal-
low swellings in a river channel with only short

(weekly) retention times. Many examples of this
kind are known from northern Sweden (e.g. the
Ångermanälven System).
To begin with the definition of Forel (1901), the
founder of limnology, that a lake is ‘a body of stand-
ing water occupying a basin and lacking continuity
with the sea’ (pp. 2–3), one can think immediately
of many lakes subject to marine influence. The
most remarkable example is Lake Ichkeul in
northern Tunisia near Bizerta (Fig. 2.1), where peri-
odic changes in water supply occur. During winter
and spring fresh water from six inflowing rivers
predominates, but during summer and autumn,
seawater enters from the Bizerta Lagoon, when its
outflow (the Tinja River) becomes an inflow of
Lake Ichkeul. Most recently, this remarkable
system has been altered by the damming (and
irrigation) activities in three of its most important
inflows, which has led to a dramatic rise in
salinity of the lake and its marshes (together about
115km
2
) and the destruction of large Phragmites
stands.
Dictionary definitions (Webster 1970; in
Timms 1992) define lakes as ‘large or considerable
bodies of standing (still) water either salt or fresh
surrounded by land’. This still leaves the question
of a lake’s dimensions. More recently, Bayly &
Williams (1973, p. 50) considered that ‘a typical

pond is shallow enough for rooted vegetation to
be established over most of the bottom, whereas
a typical lake is deep enough for most of the
bottom to be free of rooted vegetation’. They add
a further distinction: ‘Most lakes are permanent
and many ponds are temporary’ (p. 50). This
again is unsatisfactory since shallow lakes
completely covered by emergent vegetation are
conveniently considered as marshes (Kvet et al.
1990), and many alkaline (e.g. Lake Nakuru,
Kenya) and saline lakes (e.g. Lake Niriz, Iran) are
devoid of vegetation for ecological (physiological)
reasons. Moreover, the term ‘pond’ is normally
used in connection with certain types of artificial
bodies (e.g. fish ponds, farm ponds, etc.) rather than
shallow lakes. Timms (1992), in his Lake Geomor-
phology is clearly satisfied with the definition
given by Riley et al. (1984; in Timms 1992)
—
that
‘lakes are defined as areas where vegetation does
not protrude above the water surface’ (p. 2), and
‘swamps are defined as areas where vegetation,
usually emergent rooted macrophytes, dominate
the surface’ (p. 2).
All these attempts clearly demonstrate that
difficulties with definitions arise only from the
case of shallow lakes, which are considered by
many authors to be wetlands, with frequent transi-
tions towards marshes, tree swamps, minerogenic

bogs or shallow swellings in a river channel. Shal-
low lakes are, however, merely bodies of water
which are easily mixed down to the bottom by ca-
sual wind, sometimes by evaporation or irradia-
tion, and with respect to their critical depth, are
dependent on their location. Periods of stratifica-
tion may be induced by ice cover (inverse stratifi-
cation), by freshwater tributaries of saline lakes, or
by floating, dense vegetation cover (e.g. Azolla,
Eichhornia, Nuphar, Salvinia, Stratiotes, etc.)
which may minimise wind fetch but much less so
evaporation.
The size of the lake then remains the only ques-
tion which needs to be considered. Very local des-
2 The Origin of Lake Basins
HEINZ LÖFFLER
ignations
—
often arbitrary or connected with his-
torical events
—
may frequently be used. For such
local labelling, the plain east of the Neusiedlersee
(Lake Fertö) in Austria, with about 40 shallow bod-
ies of water, offers an example. The largest lake in
this group is about 2km
2
in area and is called
‘Lange Lacke’ (‘Long Lakelet’), whereas much
smaller bodies in the same area are given the desig-

nation ‘See’ (i.e. ‘Lake’). This distinction is
founded on the past occurrence of large inunda-
tions by the Neusiedlersee, which could amount
up to 500km
2
and include such shallow basins as
distinct parts of the coastal area of the larger lake.
All of these bodies are also called lake.
2.2 LAKES IN THE PAST
Lakes are transitory landscape features. Some-
times they are born of catastrophes (volcanic erup-
tions, floods, landslides and avalanches, meteoric
impacts and major human interventions), some-
times they evolve quietly and over a long period of
time. Most often, they pass imperceptibly away as
they turn into bogs, marshes or tree swamps, or be-
come filled with permanent sediment (see section
2.12 below). Equally, they may also empty via cata-
strophic eruptions, or again, as a result of adverse
human activities. The eruption of Palcacocha
(Cordillera Blanca, Peru) which destroyed a large
Origin of Lake Basins 9
9°30' E
1988
S
e
d
j
e
n

a
n
e
Lac de Bizerte
Tindja
Djebel
lchkeul
Rhezala
Malah
1985
5 km
0
1984
Djoumine
Tine
37°N
Fig. 2.1 Lake Ichkeul, Tunisia, and its connection with Lac de Bizerte (maritime lagoon) by the Tindja River. During
the rainy season (winter) the Tindja River used to flow into the lagoon carrying almost fresh water from the lake,
whereas, with low water level during the dry season, the river used to supply Lake Ichkeul with lagoon water. Owing to
construction of reservoirs (bold bars with year of construction) for irrigation and water supply for municipalities, the
most important rivers no longer reach Lake Ichkeul. Consequently the lake has become highly saline throughout the
year and during the last two decades its formerly luxuriant emergent vegetation belt has disappeared.
10 h. löffler
part of the city of Huaraz in 1941, and the progres-
sive desiccation of the Aral Sea due to human mis-
management (see sections 2.4 and 2.5.1, also Fig.
2.6 and section 2.7, and Volume 2, Chapter 7), are
examples of such events.
Ever since precipitation began to collect on the
terrestrial surface of our planet, lakes must have

been in existence. It is likely that lake basin for-
mation was enhanced by the Precambrian and
Palaeozoic glaciations. Likewise, the subsequent
formation of mountains during the Silurian (Old
and Young Caledonian orogenies) should have con-
tributed to such processes. Although Opabinia,
often discussed as a Cambrian precursor of the
Anostracan Crustacea, has been removed from
this order (Hutchinson 1967), it may be the
Branchiopoda (Negrea et al. 1999) which provide
the earliest evidence for the possible existence of
lakes. The appearance of the Dipnoi and Ostracoda
during the Devonian (as marine groups known
from the Cambrian), gives safe testimony of their
existence.
Evidence for a variety of lakes, and probably
the first wetlands, increases rapidly during the
Carboniferous when the first aquatic insects
(the Palaeodictyoptera, precursors of the Odonata,
and possible ancestors of the Ephemeroptera),
Notostraca and Amphibia appear. A great variety
of ‘tree’ species contributed to the well known
limnic coal-beds. The formation of the Old and
Middle Variscan mountains and, in addition, the
long-lasting Permo-Carboniferous glaciation (as
evidenced from the Southern Hemisphere), must
have created a great many lakes. The Odonata,
Ephemeroptera, Plecoptera, Cladocera and Mala-
costraca all appear during the Permian, and
inland lake fish become abundant. Fossil lakes

from the early Permian have been identified in
central Europe and elsewhere. Many fossil lakes
and wetlands are also known from the Mesozoic,
when, during the Jurassic, the first Trichoptera and
aquatic Rhynchota appeared. The Late Jurassic
saw the first teleosts, which became abundant
during the Cretaceous. This last period is also
characterised by the appearance of the diatoms
(Bacillariophyta).
The oldest lakes existing today came into exis-
tence during the Tertiary. These are mainly re-
stricted to Eurasia, Africa and perhaps Australia
(e.g. Lake Eyre). The Tertiary is also the era of ex-
tremely large transient inland waters which were
largely the remnants of the Tethys and Paratethys
Seas, and which like the Mediterranean (the ‘Lago
Mare’, about 6–5.5 million yr BP), or the Black Sea,
were cut off over long periods from the sea. The lat-
ter, after a changeable history of almost two mil-
lion years, regained its marine connections to the
Mediterranean via the Bosporus only about 7500
years ago (Fig. 2.2). Other sites were located in the
Amazonian Basin, the largest sedimentary area in
the world. Many fossil lakes have been reported
from the Tertiary, among them several classic sites
with excellent preservation of vertebrates. Such
examples include an Eocene lake near Halle (Ger-
many) and a selection of Oligocene, Miocene and
Pliocene sites.
During the Pleistocene (about 1.7 million until

10,000yrBP) most of the world’s present lake
basins (at least 40% of them in Canada) came into
existence within the areas of continental glacia-
tion. In addition, many older lake basins became
reshaped, although very little is known so far
about their extent during the interglacials. This is
evidenced by most of the present Alpine piedmont
lakes. Many of these basins (e.g. Lake Constance,
or the Bodensee) came into existence during the
Early Pleistocene, if not the late Tertiary and must
have undergone major changes during the glacials.
Only recently, results from a profile near Mondsee
(Austria) demonstrate a much higher lake level
than at present. During the pre-Pleistocene, this
lake must therefore have covered an area of about
30km
2
, in contrast to its present 14km
2
.
At the end of each glaciation, large proglacial
lakes developed at the ice fronts. After the most re-
cent glaciation, the Laurentian Ice Lake (with an
area of more than 300,000km
2
), the Baltic Ice Lake
(Fig. 2.3) and the West Siberian Ice Lake, expanded
along the line of withdrawal of the Northern
Hemisphere continental glaciers. In contrast to
the first two, which left behind the Great Lakes

and the Baltic Sea, the West Siberian Ice Lake, as
Origin of Lake Basins 11
Paratethys Sea
Desiccated Mediterranean Basin
Carpathian Lake
Caspian Sea
Aral Sea
Black Sea
Mediterranean Basin
(a)
(b)
Fig. 2.2 The extent of the Sarmatian Sea (a) some 15 million years BP and (b) the remnants of the Tethys and the
Paratethys 6.0–5.5 million years BP. (Modified from Hsü (1972) and Rögl & Steininger (1983).)
well as Lake Agassiz in North America, disap-
peared completely. In addition, at this time, many
volcanic lakes (see section 2.5.2) came into exis-
tence. The crater lakes Lago di Monterosi (formed
about 26,000yrBP) and Lago di Monticchio (about
75,000yrBP) in Italy can be mentioned as such ex-
amples. Finally, as another of the many large-scale
events of the Pleistocene, the Red Sea, part of the
Great Rift Valley system, should be given atten-
tion. Owing to repeated eustatic sea-level changes,
12 h. löffler
(a) (b)
(c) (d)
Fig. 2.3 The post-Weichselian development of the Baltic Sea. (a) As isolated ice-lake until c.10,000 years BP, just before
the Yoldia stage. (b) Ancylus Lake until c.8000 years BP. (c) Littorina Sea until 3000 years BP. This is followed by (d), the
present less saline stage of the Lymnaea–Mya Sea. The two driving forces of this development are (i) the melting of the
Fennoscandian ice sheet and (ii) isostatic recovery of the Fennoscandian Shield.

it became separated from the Indian Ocean and
during such phases was a hypersaline saltwater
basin which lost most of its organisms (Thenius
1977).
2.3 HYDROLOGICAL ASPECTS
AND GLOBAL BUDGET
With respect to the global water budget (Fig. 2.4)
three extreme conditions may be distinguished.
One scenario would be when the oceans prepon-
derate, leaving terrestrial surfaces mainly as
desert. Conditions of this kind, though not world-
wide, occurred during the Devonian, and perhaps
also during the Late Permian. A second, when
maximum humidity for terrestrial surfaces is
available, could be presumed for the early Tertiary.
Finally a third scenario with maximum amounts
of water bound as glaciers, ice and snow may be dis-
tinguished. The well known examples for these
states comprise the Pleistocene, and earlier glacia-
tion periods.
The present condition of our planet demon-
strates a complex situation with the impact of the
Pleistocene leading to the formation of millions of
lakes, mainly as a result of the melting and retreat
of the continental and mountain glaciers (Table
2.1). Accumulation of ice began in Antarctica dur-
ing the late Oligocene, long before the Pleistocene,
when that continent became separated from South
America and moved south towards its present
polar position. An independent circum-Antarctic

current system then developed, and Antarctica
cooled rapidly. Only much later, when Arctic ice
formation was initiated, some 2.5–3.0 million
years ago, did the recognised world-wide Pleis-
tocene glaciation come about. This eventually
ended some 10,000 years ago.
Obviously, plate tectonics and, hence, the shift
of ocean currents, were greatly involved in these
events. It should be kept in mind that, compared
with the Permo-Carboniferous glaciation some
280 million years ago, the Pleistocene has lasted
only a fraction of time. During the last glaciation
(and also earlier ones) many of the present dry and
desert areas (such as the Sahara) experienced wet
‘pluvial’ periods. These contributed greatly to ex-
isting ‘fossil’ groundwater deposits.
Since then, many climatic changes have oc-
Origin of Lake Basins 13
R = 13 Air moisture t = 0.029
347 383
Mixing zone
t = 80
710
Ocean
R = 1,320,000
Deep sea
t = 1600
36
63
Surface waters R = 230

R = 8400
R = 29,000
Groundwater
Ice & snow
99
Fig. 2.4 Global water budget: t, retention time (yr); R, reservoirs [km
3
¥ 1000]. Arrows denote annual water flow [km
3
¥
1000] (Modified from Stumm & Matter-Müller (1984) and other sources.)
14 h. löffler
curred regionally and globally and most recently
global warming and increased desertification have
contributed to the shrinking of many lakes, espe-
cially in Africa. An example of this recent develop-
ment is Lake Turkana which most probably
reached high levels between 9500 and 7500 years
BP. Between this pluvial peak and 3000 years BP,
the lake underwent two regressions and two major
expansions before the final period of falling level
(Richardson & Richardson 1972). Since 1977 this
decrease has amounted to approximately 1m an-
nually (Källquist et al. 1988). Even more dramatic
is the shrinking of the shallow Lake Chad from its
former area of 25,000 km
2
(during the 1960s) to less
than 1000km
2

at present (Fig. 2.5). This body
drains the largest watershed of all African lakes
(about 2.5 millionkm
2
) which extends through six
countries.
Apart from the present configuration of the con-
tinents, the pattern of ocean currents and their ir-
regularities and other stochastic events, global
precipitation (Table 2.2) is greatly influenced by
large atmospheric circulation systems such as the
trade winds and the westerlies. In addition, oro-
graphic features and secondary patterns are of
great regional importance. Among the latter, the
monsoon system, also recognised elsewhere, is
most paradigmatically presented by the thermal
regime of the interior of the Asiatic continent. The
phenomenon of a wet monsoon blowing across the
Indian Ocean during the summer provides for
summer rain in areas which would otherwise be
desert.
As mentioned above, short-interval fluctua-
tions between ‘normal climate’ and different cli-
matic conditions (within one or over several
decades) occur, which most often follow an irregu-
lar pattern. Among the most forceful events of this
kind, with almost a global influence, the ‘El Niño’
of the Pacific region should be mentioned. During
the past 40 years, nine El Niño events have increas-
ingly affected the Pacific coasts of North and South

America, with development of warm ocean cur-
rents off Peru and Ecuador and as far afield as the
Galapagos Islands where normally cold surface
waters are found. Losses in fishery, imprints on the
regional marine life and impacts on the climatic
conditions around the globe, such as the distur-
bance of the Asian monsoon, may be consequences
of strong events of this kind such as that which
occurred in 1982–1983 (Wallace & Vogel 1994).
During this exceptionally warm interval, coastal
deserts in northern Peru experienced more than
2000mm of rain transforming them into grass-
lands dotted with lakes. Further to the west, abnor-
mal wind patterns deflected typhoons off their
natural tracks towards islands such as Hawaii and
Tahiti, which are unaccustomed to such catastro-
phes. They also caused monsoon rains to fall over
the central Pacific instead of in its western parts,
which led to droughts in Indonesia and Australia.
Winter storms in southern California caused wide-
spread flooding across the southern USA while
northern areas experienced unusually mild weath-
er and lack of snow. Overall, the loss in economic
activity in 1982–1983 as a result of the climatic
change amounted to over $1 billion.
In principle, the phenomenon of El Niño origi-
nates in oscillations of high and low barometric
pressure between the eastern and the western
sides of the Pacific. Upwelling cold-ocean water
along the South American (Chile to Ecuador) coast

caused by wind, induces high pressure in the east
whereas weak ‘easterlies’ cause the upwelling to
slow down; the result is low air pressure. The re-
sulting change in ocean temperature causes the
major rain zone off the western Pacific to shift east-
Table 2.1 The existing mass of global water resources
(km
3
¥ 1000).
Ocean 1,319,800
Ice and snow 29,000
Air moisture 12.9 (instantaneous mean)
Rivers 1.1 (instantaneous mean)
Lakes (fresh) 125
Lakes (salt) 104
Soil 6 ?
Groundwater, more than 800m 4200 ?
Groundwater, less than 800m 4200 ?
1983), although some other estimates are as high as
280,000km
3
. A large fraction of this volume, in-
cluding that of the Caspian Sea (78,700km
3
), is
saline. The catastrophic decline of several large
lakes (e.g. the Aral Sea from 69,000km
2
during
the 1960s to less than 30,000km

2
at present, Lake
Chad from 25,000km
2
during the 1970s to about
1000km
2
), is easily compensated for by the rapidly
increasing number of reservoirs and artificial
ponds (e.g. Lake Volta about 8000km
2
and each of
the two dams, Lake Kariba and the Aswan Lake,
with about 5000km
2
). Total global lake volume
amounts to only 0.017% of the total global water
volume (Table 2.1).
Estimates of total global lake surface vary
Origin of Lake Basins 15
13°N
Yobe
14°30' E
Chari
Serbeouel
EI Beid
Fig. 2.5 Lake Chad, which during
the 1960s covered 25,000km
2
, has

recently shrunk to a remnant of less
than 1000km
2
.
ward and the related adjustments in the atmos-
phere cause the rain to fall over the central and
eastern Pacific and a rise of barometric pressure
over Indonesia and Australia, which results in a
further weakening and eastward retreat of the east-
erlies. At present, our improving understanding of
the wind–sea processes allows for better prediction
of El Niño years.
2.4 THE PRESENT CONDITION
OF LAKES
The total volume of water located in natural and
artificial lakes amounts to 229,000km
3
(Margalef