INTRODUCTORY OVERVIEWS

Contents

Inland Waters

Limnology as a Discipline

Aesthetic Values of Lakes and Rivers

Aquatic Ecosystem Services

Water as a Human Resource

Inland WatersG E Likens, Cary Institute of Ecosystem Studies, Millbrook, NY, USA

ã 2009 Elsevier Inc. All rights reserved.

Inland Waters

All life on Earth is dependent in some way on waterfor providing a vital habitat, the milieu for biochemi-cal reactions, electrochemical transformations, repro-duction, transport, and for many other services tobiota. Some 71% of the Earth’s surface is coveredby water, but most of this water is salty and is foundprimarily in oceans and seas. Limnology (from theGreek: limne ¼ pool or pond; logos ¼ discourse orstudy), the study of inland waters, is the scientificdiscipline focused on all inland waters of the Earth.These days, limnology may sometimes be replaced byor subsumed under other terms of scientific inquirysuch as, aquatic ecology, hydrobiology, or evenhydrology. Initially, limnology lagged behind ocean-ography as a scientific discipline, as F.A. Forel in1892, in his book (first volume) on Lac Leman(Lake Geneva, Switzerland), defined limnology asthe oceanography of lakes. Inland waters are thefocus of this Encyclopedia and this article is intendedas an introduction to the subject.Inland waters are distributed among polar ice and

glaciers, actively exchanged groundwater, freshwaterlakes, and human-made impoundments (farm pondsand reservoirs), saline lakes, soil water, marshes/wet-lands, and rivers and streams, in the order of decreas-ing volume (see Table 1). Determining the extent ofinland waters has been done for a long time, butcurrently is an active area of research. The worldwidedimensions are changed frequently because of newtechnology, such as satellite observation of theEarth. As a result, lakes, rivers, and wetlands arelarger in extent and metabolically more active ona global basis than had been thought. Also, it islikely that the estimated volume of lakes andimpoundments may be significantly underestimatedin Table 1.

Most inland waters in lakes, reservoirs, and riversare shallow (less than a few tens of meters in depth),but a few are very deep. Lakes Baikal in Russia andTanganyika in Africa are more than 1000m deep.Lake Baikal with a maximum depth of 1620 m con-tains about 23 000 km3 or 18% of the Earth’s surfacefreshwater in its basin and is one of the oldest fresh-water basins (formed >20 Mya). The five LaurentianGreat Lakes (Superior, Michigan, Huron, Erie, andOntario) in North America contain another 20% orso of the Earth’s surface fresh water in their basins.A very large (possibly the largest) lake, L. Vostock,exists below the ice in Antarctica, but little is knownabout this lake. Antarctica contains some 70% of theEarth’s freshwater, but most of it is locked up as ice.Because of glacial, tectonic, and volcanic activity,many areas have numerous basins now filled withwater, thus forming ‘lake districts.’ Examples includethe Patagonian region of South America, northernEngland, the upper midwestern and St. Lawrenceregions ofNorthAmerica, and theRift Valley ofAfrica.

Many inland waters, such as the Dead Sea in Israel,are highly saline. The Black Sea and Caspian Sea ineastern Europe, Great Salt Lake in USA, and LakeCorangamite in Australia are saline and very large.Inland bodies of water, such as the Black Sea, Aral Seaand Caspian Sea, represent areas of the ocean recentlyisolated geologically from the remainder of the ocean.In many respects, including their name, they are muchmore like an ocean than a lake. Recent human activ-ities, for example water withdrawal, have greatlyreduced the volume and extent of the Dead Sea, andparticularly the Aral Sea.

Scientists have estimated that freshwater lakes andimpoundments (engineered dams and farm ponds)occupy a much larger proportion of the Earth’ssurface than previously thought (Table 2), overall

1

Table 2 Areas of water on the Earth (thousands of km2)a

Area (thousandsof km2)

Percent ofTotal

World (total) 510 230 100

Land area 148925 29Oceans 361305 71

Polar ice caps and glaciers 17 871 3.5

Fresh and saline lakes 4 200 0.82

Inland seas 699 0.14Rivers 360 0.071

Impoundments 335 0.066

aCompiled from Nace (1960), Wetzel (2001), Lehner and Doll (2004),

Downing et al. (2006), and other sources.

Table 1 Water on the Earth (thousands of km3)a

Volume(1000 ofkm3)

Percent oftotalwater

Percentof totalfresh water

Salt water

Oceans 1 338000 96.54Saline/brackish

ground water

12 870 0.93

Saline lakes 85 0.006

Fresh waterGlaciers,

permanent

snowcover

24 064 1.74 68.70

Fresh groundwater

10 530 0.76 30.06

Ground ice,

permafrost

300 0.022 0.86

Freshwater lakesand

impoundments

91 0.007 0.26

Soil moisture 16.5 0.001 0.05Atmospheric water

vapor

12.9 0.001 0.04

Marshes, wetlands 11.5 0.001 0.03

Rivers andstreams

2.12 0.0002 0.006

Incorporated in

biota

1.12 0.0001 0.003

Total water onEarth (1000km3)

1 386000 100 100

Total fresh water

on Earth(1000km3)

35 029

aBased on Shiklomanov (1993) and other sources.

2 Introductory Overviews _ Inland Waters

comprising �3% of the terrestrial surface of theEarth. Twelve of the largest reservoirs, not includingThree Gorges in China, have a larger combined sur-face area than the 12 largest lakes in the world.Some 25% of the freshwater input to the world’s

oceans comes from two rivers, the Congo and theAmazon, both at approximately the same latitude.Unfortunately, there are no good estimates for thetotal area of small rivers and streams, yet the huge

interface between these inland waters and their adja-cent terrestrial drainage areas is one of the excitingand important subject areas in limnology. This inter-face is often occupied by lacustrine and riverine wet-lands consisting of herbaceous-dominated marshesand forest- or shrub-dominated swamps. These wet-lands often occupy much larger surface areas than dolakes and rivers. In addition to these transitional wet-lands, wetlands also occur in depressions, seepageson hill slopes, and on poorly drained flat lands notadjacent to lakes and streams.

Because successful limnological studies dependupon an understanding of the interactions of physics,chemistry, biology, meteorology, and hydrology ofaquatic ecosystems, such as lakes, ponds, reservoirs,rivers, streams, and wetlands, limnological inves-tigations often draw rather uniquely on a team ofscientists with diverse interests and expertise. To dolimnological research well, studies must incorporatebiology, physics, chemistry, hydrology, geology, etc.into a holistic approach in order to make sense of thefunction, structure, and temporal change of a lake,pond, river, stream, or wetland. Such studies, focusedon a systems approach, provide limnology with apowerful and successful framework for addressingcomplicated environmental issues such as eutrophica-tion and anthropogenic acidification. This integrativeapproach to the study of inland waters as complicatedsystems renders it the status as ‘queen’ among thenatural sciences.

The so-called lentic or standing, inland watersinclude lakes, ponds, pools, reservoirs, inland salinesystems, and wetlands (swamps, marshes, bogs, fens).Lakes, ponds, and reservoirs are transient features ofthe landscape because as their basins fill with water,they immediately start to disappear as the basin fillswith sediment. Nevertheless, lakes aesthetically rep-resent some of the most beautiful ‘gems’ of the land-scape, e.g., Lake Tahoe, CA, USA; Lago Grey, Chile;Crater Lake, OR, USA; Lake Atitlan, Guatemala;Lake Pukaki, New Zealand.

Lotic or running inland waters are referred to bydifferent names (e.g., stream, brook, rivulet, river,headwaters, run, fork, creek [crick], kill, chalkstream, tributary) in English depending on the sizeand regional or cultural background. Obviously,water flows downslope by gravity, coalescing fromheadwaters, into large rivers and eventually to theocean. This network of channels with flowing watermay be simple or complicated, but flowing waters arechallenging to study because the water is constantlymoving, often in numerous channels (braided), andbelow ground.

Dr. J.G. Needham was appointed Assistant Profes-sor of Limnology at Cornell University in 1907,

Figure 4 Chandalar Lake, Alaska (photo by G.E. Likens).

Figure 3 Lake Tahoe, California/Nevada (photo by G.E.

Likens).

Figure 1 Crater Lake, Oregon (photo by G.E. Likens).

Figure 2 Tub Lake, Wisconsin (photo by G.E. Likens).

Introductory Overviews _ Inland Waters 3

having offered the first course on limnology in theUnited states in 1906. In 1911, he authored withJ.T. Lloyd the first text book on Limnology – Life ofInland Waters. Although the book is broad in disci-plinary coverage as expected for limnology, its focus

was biological. Other early pioneers in limnologicalstudies in the United States and Canada includedE.A. Birge, C. Juday, A.D. Hasler (Wisconsin),J. Reighard, F.E. Eggleton, P. Welch, H.B. Ward(Michigan), D.S. Jordan, D.G. Frey, S. Gerking (Indi-ana), C.A. Kafoid, S.A. Forbes (Indiana), L. Agassiz,G.C. Whipple, G.E. Hutchinson (New England), andF.R. Hayes, H.B.N. Hynes, F.E.J. Fry, D. Rawson,F. Rigler, J.R. Vallentyne (Canada).

In Europe, academic limnology has a long historywith early, major centers of activity in Sweden(E. Naumann, S. Ekman, W. Rodhe), Germany(A. Thienemann, H. Elster, W. Einsele, W. Numann,W. Ohle, H. Sioli, D. Uhlmann), Denmark (K. Berg,C. Wesenberg-Lund, P. Jonasson), Norway (K. Strom),France (F.A. Forel, A. Delebeque, B. Dussart), Switzer-land (L. Minder, E.A. Thomas), Spain (R. Margalef),Austria (F. Ruttner, I. Findenegg), England (T.T.Macan,W.H. Pearsall, C.H. Mortimer, E.M. Wedderburn,J. Talling, J. Lund, W. Tutin), Japan (S. Yoshimura,S. Horie), Russia (Yu. I. Sorokin; G.G. Winberg), andItaly (E. Baldi, V. Tonolli, L. Tonolli). (This is a non-exhaustive listing of locations of major limnologicalcenters and pioneers in the field.)

Austrian Professor F. Ruttner’s early textbook(Fundamentals of Limnology, 1940) had been a stan-dard for years in Europe and in North America.

Although the areal extent and volume of freshwaterlakes and rivers are relatively small, their interest andvalue to humans is huge, for example, as a source ofdrinking water, for transportation, food, recreation,and aesthetics. Recently, their importance as a signifi-cant source of carbon dioxide and methane flux to theatmosphere, as well as carbon storage in sediments,has become apparent from scientific study because ofincreased interest in the flux and balance of carbon forthe Earth as related to global warming.

Some 39 professional limnological organiza-tions exist in countries throughout the world. The

4 Introductory Overviews _ Inland Waters

International Association for Theoretical and AppliedLimnology (Societas Internationalis Limnologiae) wasfounded in 1922 by E. Naumann and A. Thienemannand represents the international organization for lim-nology and limnologists (www.limnology.org). Thenamewas changed in 2007 to the International Societyof Limnology. It’s mission ‘to. . . work worldwide, tounderstand inland aquatic ecosystems and to useknowledge, gained from research, to manage them,’and it’s Congresses, occurring every 3 years, attractmembers from more than 80 countries throughoutthe world. Other limnological professional soci-eties, such as the American Society of Limnology andOceanography and the Asociacion Espanola de Lim-nologıa, although primarily national in origin andscope, are working to expand international member-ships and activities. Dozens of limnological journalsand periodicals are being published, including, Lim-nology and Oceanography, Journal of Paleolimnol-ogy, Journal of Crustacean Biology, Chinese Journalof Oceanography and Limnology, and Japanese Jour-nal of Limnology, on diverse topics and inmany differ-ent languages.Currently, freshwater ecosystems are much deg-

raded because of pollution, human occupation anddevelopment of shorelines, and increased sedimentloading and sedimentation. This degradation resultsfrom human activity such as agriculture, urbaniza-tion, and industrial activity affecting the airshed orthe catchment of these inland waters.Historically, inland waters have been attractive to

humans as a place to live, providing a convenientsource of water, food, recreation, and transportation.Unfortunately, inland waters have also been a ‘conve-nient’ receptacle for wastes. Flowing waters havebeen used especially for waste removal by humansfollowing the old adage, ‘out of sight, out of mind,’and with little regard for other organisms, includinghumans, living downstream.Water shortages for human use are common in

many areas of Australia, the Middle East, Africa,Asia, and even in areas of eastern North America,long perceived to have abundant water. Seriouswater-quality problems are now occurring becauseof the pollution of surface waters by sediments, excessnutrients such as phosphate and nitrate, acids,mercury, pharmaceuticals, toxic algal/cyanobacterialblooms, human parasites, e.g., Cryptosporidium spp.and Giardia spp., and invasive alien species.Excess nutrient loading to inland waters has led to

eutrophication (nutrient enrichment) of standing andflowing waters worldwide with resultant degradation(changes in species composition and diminishmentof dissolved oxygen). Anthropogenic acidificationfrom acid rain deposited on geologic areas with low

buffering capacity has resulted in widespread degra-dation of lakes and rivers. Pollution of lakes andstreams from atmospheric deposition of mercury, ori-ginating largely from combustion of fossil fuels andincineration of municipal waste, has resulted inhealth advisories for the consumption of fish through-out North America and Europe.

The inland waters of the Earth result from thebalance between precipitation, evapotranspiration,and runoff. Their chemistry is the result of how thechemistry of precipitation is transformed alonghydrologic flowpaths, by the following factors:

. hydrologic factors, e.g., by dilution or concentra-tion such as by evaporation;

. biotic factors, e.g., by plant uptake, storage andrelease, and microbial storage and transformation;and

. geologic factors, e.g., by geochemical reactions.

An ecosystem is a spatially explicit unit of Earththat includes all the organisms along with all compo-nents of the abiotic environment, interacting togetheras a system, within its boundaries. Using the eco-system approach, the boundaries of a lake, pond,or river are ostensibly clear because the shorelineswould appear to make quantitative, mass-balancecalculations easier, but it has become apparent thatthere is a critical need to look ‘beyond the shoreline,’that is, to the airshed and to the watershed or catch-ment, for evaluating human impacts on a body ofinland water. Moreover, it is mostly impossible tojudge the ‘health,’ condition, or value of an aquaticecosystem from a causal observation from the shore-line. It is necessary to get inside the system to learnabout these characteristics.

This Encyclopedia on Inland Waters will focus onthe quantity, chemistry, biology, hydrology, physics,geology, degradation, management, and enjoyment ofinland waters of the Earth. The chapters of this Ency-clopedia will certainly take you ‘inside these systems.’Inland waters are important for life on Earth. Theefforts made in this Encyclopedia to describe as wellas to help the readers understand, value, and enjoythese inland waters and wetlands will certainly makeit an important reference for those who pursue theseendeavors.

Glossary

Inland waters – Waters on or in the terrestrial portionof the Earth.

Saline – Salty; approximating or exceeding the saltcontent of sea water.

Limnology – The scientific study of inland waters.

Introductory Overviews _ Inland Waters 5

Ecosystem – An ecosystem is a spatially explicitunit of Earth that includes all of the organisms,along with all components of the abiotic environ-ment, interacting together as a system, within itsboundaries.

See also: Abundance and Size Distribution of Lakes, Pondsand Impoundments; Climate and Rivers; Ecology ofWetlands: Classification Systems; Ecology of Wetlands;Effects of Climate Change on Lakes; Floods; GlobalDistribution of Wetlands; Limnology as a Discipline;Marshes – Non-wooded Wetlands; Peat and Peatlands;Pressure; Reptiles; Swamps – Wooded Wetlands; TidalFreshwater Wetlands; Wetland Ecology and Managementfor Birds and Mammals; Wetland Ecology andManagement for Fish, Amphibians and Reptiles; WetlandPlants; Wetlands of Large Lakes; Wetlands of LargeRivers: Floodplains.

Further Reading

Abell R, Thieme ML, Revenga C, et al. (2008) Freshwater ecore-

gions of the world: a new map of biogeographic units for fresh-

water biodiversity conservation. Bioscience 58(5): 403–414.Allan JD and Castillo MM (2007) Stream Ecology: Structure

and Function of Running Waters, 2nd edn., 436 pp. New York:

Springer.

Batzer DP and Sharitz RE (2007) Ecology of Freshwater and Estua-rineWetlands, 581 pp. Berkely, CA: University of California Press.

Cushing CE and Allan JD (2001) Streams: Their Ecology and Life,400 pp. New York: Academic Press.

Downing JA, Prairie YT, Cole JJ, et al. (2006) The global abun-

dance and size distribution of lakes, ponds, and impoundments.Limnology and Oceanography 51(5): 2388–2397.

Gleick PH (1998) The World’s Water. Washington, DC: Island

Press.

Hutchinson GEATreatise on Limnology, Vol I Geography, Physicsand Chemistry (1957). Vol II Introduction to Lake Biology and

the Limnoplankton (1967). Vol III Limnological Botany (1975).

Vol IV The Zoobenthos (1993). (ed. Edmondson YH).

Hynes HBN (1970) The Ecology of Running Waters, 555 pp.Toronto: University Toronto Press.

Kalff J (2001) Limnology: Inland Water Ecosystems, 592 pp.

New York: Prentice-Hall.

Keddy PA (2000) Wetland Ecology: Principles and Conservation,632 pp. Cambridge, UK: Cambridge University Press.

Lehner B and Doll P (2004) Development and validation of a global

database of lakes, reservoirs and wetlands. Journal of Hydrology296: 1–22.

Mitsch WJ and Gosselink JG (2007) Wetlands, 4th edn., 600 pp.

New York: Wiley.

Nace RL (1960) Water Management, Agriculture, and Ground-water Supplies, 12 pp. Denver, CO: U.S. Geological Survey.

U.S. Geological Survey Circular 415.

Ruttner F (1940) Fundamentals of Limnology (translated into

English by Frey DG and Fry FEJ [1953]), 242 pp. Berlin: Walterde Gruyter/University of Toronto Press.

Shiklomanov IA (1993) World fresh water resources. In: Gleick PH

(ed.) Water in Crisis: A Guide to the World’s Fresh WaterResources, pp. 13–24. Oxford University Press: New York.

Wetzel RG (2001) Limnology: Lake and River Ecosystems vol. IV.New York: Academic Press.

Wetzel RG and Likens GE (1991) Limnological Analyses, 2nd edn.,391 pp. New York: Springer.