LIMNOLOGY

By AUGUST THIENEMAN

"Limne" u a Greek word meaning "lake." Readers will be surprised to fi-nd,lim limnology-a leN/I few peopla have e-ver heard of---is all. absorlring sciellce coverillga wide field.

The author has for many yea-rs been the director of the Kaiser Wilhelm Institutefor Hydrobiology in Plan and holds the first German professorship for hydrobiologyat the Univer8ity of Kiel.-K.M.

HERE is an essential difference in theeconomic exploitation of the fruits ofthe earth and those of the water.

lany of the green plants growing on land118 used directly for human consumption,IDil are consequently grown by man. Onthe other hand, true water plants are-withI few exceptions in the tropics-not used atill directly for human consumption.

But when we remember the cultivationof rice, we begin to look at these circum·ltances with other eyes. It is true that the~ has its roots in the earth of the riceIelds and draws from it nutritive substanceswhich, after the harvest, are partially re-'~ by artificial fertilizers. But theDTiga.tion wat.er also provides convertible~nt food; the quality and quantity oft.bese latter nutritive substances depend onthe ohemism of the water. The irrigationIf/. the rice fields is an entirely artificial one;'aDd in order to have sufficient water at all'times of the year, especially in southernregions, natural lakes are often used asItorage places or artificial lakes created bymeans of dams. The surface water of thesetakes is carried to the rice fields by means(If canals and ditch systems often extendingmany kilometers in length.

WEALTH LOWER DOWN

This surface water, however, is alreadylargely deprived of its content in nutritiveeubstances by the organisms living in it; itcontains only traces of dissolved nitrogenand phosphorns compounds. On the otherhand, a German limnological expedition tothe Sunda Isles discovered that the waterat the bottom of such lakes, the hypolimnion,(from the Greek hypo= below) contains avast reserve of these substances. Thusevery cubic meter of water from the hypo.

limnion of the small lake of Ranu Lamonganin eastern Java contains an average of 0.35grams of phosphorus and 3.1 grams ofammonic nitrogen. A total amount of1,430 kilograms of phosphorus and 12,170kilograms of ammonic nitrogen are dissolvedin the water more than 8 meters below thesurface of this tiny lake (750 meters di-ameter; 28 meters maximum depth). In thecase of large lakes, these figures take ongigantic proportions. There can hardly beany great technical difficulties in obtainingthe valuable water from the depths of theselakes for the rice fields instead of the poorsurface water. The technical exploitationof this one secondary result of a limnologicalexpedition would be enough to repay thecost of the expedition several times over.

Indirectly the vegetative substances ofthe fresh waters form the basis for all animalproduction of the waters, including fishingand fish breeding. But here again it mustbe emphasized that there is an essentialdifference between cattle raising on landand fish breeding in the water. All animalsused in one way or another by man convertvegetable substances (grass, le&\7es, etc.)directly into meat. It is, however, a greatexception for fish to feed directly off plants;the chain leading from original plant foodto the fish contains many links, including asit does low forms of animal life on whichthe fish feeds. Hence an exact knowledgeof the metabolism in fresh waters is of greatimportance to fishing interests. The many·linked feeding chain also eA-plains the dif·ficulty in finding scientifically correct meth·ods of fertilizing fish ponds. Other wateranimals, such as crabs, mollusks, turtles, andamphibians, are eaten by man, esp.ecially inthe tropics, or exploited in other ways; thesame applies to them as has been said aboutfish.

192 THE XXth CENTURY

FISH, SAND, AND HYGIENE

The total production of fresh-water fitlhingis usually underestimated. In Germany theannual income of fresh-water fishing accord-ing to the last prewar figures amounted to150 million marks, that of coastal and deep-sea fishing to 80 million marks. If, as arule, the production of salt-water fishingseems larger, this is to be explained by thefact that inland lakes, ponds, 8Jld rivers aredistributed over countle88 localities and thattheir products are usually consumed locallywithout previously being concentrated at afew centers, as is the case with sea productsin most countries.

As for the "inorganic" production of in-land waters, we shall only touch upon themvery briefly here; they consist in the mainof lake chalk and lime, lake ores, gravel andsand, travertine, medicinal mud, etc. Justa few figures to show that these productsamount to considerable quantities too: inthe Lake of Zurich an annual quantity of1 million tons of gravel8Jld sand are dredged,and in Lake Constance some 300,000 to600,000 tons. Calculated at a price of 3marks per ton, this would represent anannual turnover of 1 to 2 million marks inthe case of Lake Constance alone.

Much as the various items mentioned hereunder the heading of "production" of fresh-water bodies may differ from each other,one thing holds good for fresh-water produc-tion of any kind: a deeper understanding ofit 8Jld the possibility of its economic devel-opment can be achieved only on the basisof theoretical limnological studies. Wher-ever inland waters are exploited or whereverthey tend to obstruct human endeavors, theresults of limnology gain practical im-purta.nce.

This is especially true of the role playedby inland waters in the hygiene of m8Jland beast. It is a recognized fact in theadvanced countries of Europe and NorthAmerica today that in all matters affectingthe obtaining of drinking water and thehygiene of waterworks a limnologist shouldbe consulted (although in actual fact this isnot always done). In questions regardingthe contamination of water and the removalof waste water the limnologist gives hisadvice on the basis of a biological analysisof the water; indeed, waste-water biology is,next to fishery biology, one of the oldestbranches of applied limnology. There areclose relations between limnology and the

struggle carried on against human aDdanimal diseases in all those places wheredisease carriers either live in fresh water oruse fresh-water animals as intermediaryhosts. In many cases, measures of oombMmust set in at the stage at which the carrierlives in the water, so that intensive limno-logical work becomes necessary.

LIM.NOLOOY VS. DISEASES

Take the case of fasciolose, a cattle dia-ease caused by liver flukes (Fasciola hepatiu.L), which are transmitted by a certain kindof snail. In 1925, in Bavaria alone at least60,000 sheep, 18,000 head of cattle, and3,000 goats fell victim to the liver fluke.In other regiolls, for instance in the NorthCaucasus, where sheep raising is of primaryimportance, the damage done by liver flukea.is considerably greater.

As regards malaria, we need only pointout that that part of its combat which isdirected against its transmitter, the Anoph-eles, is now based entirely on a hydro-biological-limnological foundation. As a reosuIt, malaria has lost its importance in largeareas formerly entirely infected.

Let us not forget disease-causing baoteri&living in water and transmitted to humansand animals with or by water. Limnologicalstudies are bound to gain considerable im-portance in the fight against them as soon88 the normal bacteriology of our inlandwaters has been thoroughly studied. Atpresent we know-strange as it may sound-hardly anything about the true waterbacteria. It is absolutely necessary, if onlyfor practical hygienic reasons, tha.t the studyof the blWteriologioal world of our inlandwaters be undertaken as soon as poBBiblewith the greatest possible intensity, employ-ing methods which have, in part, alreadybeen perfected.

The productivity of inland wa.ters, theirhygienic significance, and their technicalexploitation are the main problems withwhich applied limnology has to deal. Theproblem of the technical exploitation offresh water and inland waters appears tobe limited entirely to the nonbiological partof limnology. As a ma.tter of fact, questionsconcerning hydraulic engineering, the im·portance of certain inland waters as sourcesof power, etc., touch mainly on hydrologyand hydrography, the theory of currents,etc. But E:verywhere biological life, too,influences lakes and streams; one need onlythink of the sedimentation-to be traced in

LIMNOLOGY

to living organisms-in reservoi.rs, ofpowing over and silting up of lakell and

technical significance, the role of iron. in the supply of drinking water,For every body of water is a unity,

.IMality, in which the happeni.ngs of thellirOOlll1eDt and biological processes exert

iaevitable reciprocal effect upon each

FRUSTRATED CAUSEWAY

lIere, too, we can quote an example inthe value of a limnological "inter-n can be expressed in a round figure.

the autumn of 1932 the authorities decided1'8IDove a "death curve" on the motor

from Kiel to PIon. The road circledIIIlA1l bay of the Pion Lake and thus

ed a narrow curve which had been theof many accidents. The idea was toa 4OO-meter causeway across the bay

.... in this way to straighten out the road.e. the baais of some primitive drillings andDDdings made by a firm of contractors,.. building plans were already drawn up.1kn our own knowledge of sedimentationpiitions in that lake made the wholetItierpriae seem rather doubtful. So wetook a hand, without being asked. We dis-IllTere

THE XXth CENTURY194

its main tasks to be the study of the reociprocal effect of the penetration with lifeand the conditioll8 for life in fresh·waterbodies. Geography and geolog)", chemistryand physics, zoology and botany, are thebasic sciences upon which limnology isfounded. It is one of those sciences devel.oping in increasing numhers in recent timeswhich place the total aspect in the fore·ground, which pay no heed to the boundariesof the traditional "academic" sciences butunite partial fields of them in new synthesesand thereby build bridges between thatwhich formerly seemed to ha\'e no connection.

PLL"lS A~D M.o\TERlAL

Only the recognition of relationships as awhole has provided research with a directionand a goal-and this is of tremendous signif·icance to the further development of ourscience. It might be objected that all in.dividual parts must first be studied in detailbefore turning to wider relationships. But,to put it figurativel)", one does not startcarting stones and mortar until the architecthas drawn up the plans of the house. Other·wise the building material would lie aroundunused and perhapli disregarded and mighte\'en become useless; and then the stonesrou t laboriously he hewn again in order tomake them fit into the proper place of thewhole.

Every science must go through periods ofstock.taking, during which it must devoteitself chietty to the collecting of indi\-idualfacts, as well as perioilll in which totals) ntheses are in order. For the way inwhioh the whole of a science developsthroughout history does not depend on anideal plan. Here, too, the tenet holds goodthat it is men who make history. ButC\'oryone is--more or less-a child of histimes, influenced, at least unconsciously, bytheir spiritual trends. They affect thescientific activities of e\'ery torue scientist,whether he admits it or not. Hence it ishardly a coincidence that the consciousemphasis on synthesis is beginning to playan increasing role, especially in Germany.

To give concretc examples of what I havecalled the "totalitarian" attitude in lim·nology, I shall briefly describe two of thestandard types of lake.

THE ALPnfE LAKE

First. there is the oligotrophic (from theGreek oliges=smaH, scant; trophe=nutrition)type represented, for example, by the large

A1pin~ lakes. The water of a lake of thMtype III poor in plant nutrients. This de-pends, of course. on the geological conditiolllof its close environment and of the areu iawhich its tributary streams originate; bertwe see that the lake is not an isolated phenom-enon but part of a greater unity. Scaroiiyof nutrients entails a poor quantitativede\'elopment of plankton, the free.floatimcanimal and plant We in a body of water.As a result, the water is clear and trana-parent, usuaUy colored blue to bluish.green.As light can thus penetrate to relativelygreat depths, the submerged water plantecan grow fairly far down. Tho beds of theyoung Alpine lakes are usually hard androcky; as a result, the shore region is narrow,for the lake has not bad time enough tognaw deeply into its resistant banks. Hencetbe shore "egetation also covers only ,narrow strip and is poorly developed from'quantitative point of view. ThellO lakes aredeep; so the water mass of the hypolimnion,the deep layers which destroy plant nutri·tion, is greater than that of the epilimnion(from the Greek epi=on, upon), the surfacewater that produces nutrients. The deadremain of the scarce plankton productionand scanty shore vegetation sink into a largemass of water; the decay caused by theirdecomposition is, so to speak, very muchdiluted, so that comparatively little oxygenis withdrawn from the stagnant water ofthe lower levels; and since. as a result of thegreat depth of such lakes, the sinking plank.ton arrin,'S at the bottom in a largely de·composed, mineralized state. the sedimentsof the lake contain little in the way oforganic substances. Consequently, animalsrequiring oxygen can live at tho bottoms ofthese Lakes, in tho water as well as in themud. The quantitative development of thefauna at the bottom is directly relat,cd tothe quantitative development o'f the plank.ton; its limiting factor is nutrition. If anoligotrophic lake is \'ery clear and trans·parent, which means tbat its nutrient·producing lovels reach far down and arethus of great volume, there can he a reI·ati\'ely rich fauna at its bottom.

On the whole, the typical oligotrophiclake is at a stage of equilibrium: almost theentire mass of substances contained in thebodies of organisms is dissolved again andreturncd to the water. The entire circula·tion of nutrition represents a more or lesscompletely reversible process. In otherwords, we find a mutual effect of aU themembers of the system of the lake upon

LUlNOLOGY

IICh other, the result of which is the main-tIaanoe of the system'll equilibrium. Thisakea the lake an entity, a unity of lile ofaliigher order.

Now let us turn to tho eutrophic (fromtheOreek eu=well, OR!;y) lake as represented,for example, by the type of large lakes in&be North German plains. Bedded in theIIch dilu\·ial deposits of tbe low plains, itpoeeesses a wealth of plant nutrients andecmequcntly also of plankton. The resultiI turbid water of a green to yellow orIJI'oll'nish-green color and a limitation of~table life to the surface levels. Thelake has been able to eat deeply into its10ft banks, so that a wide shore with richYegetation bas been formed. The lakes areoomparatively shallow; their epilimnion-which, together with the shore, produces thelllpDic substances-is of a greater volume~an their hypolimnion. When it dies, therioh vegetation of the shore and the surface".ter sinks down into the relatively llltlaUDlass of water of the hypolimnion whero itdecomposes. thus in summer withdrawingthe oxygen from the water of the lowerlevels to such an extent that in some casesdie oxygen is entirely used up. As the,Mdiments at the bottom of the lake are alsorich in undecompofolcd, decaying organiclubstances, only stich organisms can existIt the bottom which can remain alive witha minimum of oxygen. Although they ha\'eplenty of food, the oxygen conditions rep-l'et!ent the factor limiting their quantity, afactor which in extremc conditions (whenihere is no froo oxygen whatever) mayreduce the life at the bottom of a lake toa minimum.

Such an extreme eutrophic lake is nolonger in a st,age of equilibrium. In it asurplus of organic substances is built upevery year in organism bodies which cannotbe com pletely decom posed again and reotunle

196 THE XXth CENTURY

Larger climatio fluctuations, which arenever produced by terrestrial factors aloneand whose causes are for the greater part tobe sought beyond our planet, also affect thecourse of all kinds of biological phenomena.For more than thirty years the relationshipbetween the climatic conditions of individualyears and the size of the harvests in Norway,the fishery yield at the Lofoten Islands, andeven the produotion of cod·liver oil has beenknown. It is the periodicity of the sunspots which makes itself felt here, as it doesin the fluctuations of the ground water level,etc. The same periodicity has been provedin the bottom sediments of certain lakes.The sediments, however, are so to speak theexcrements of the great organism "lake"; inthem is mirrored the character of its entiremetabolism. Differences in sediment meandifferences in metabolism; if the rhythmicalchanges in the nature of the sediment coin-cide with the periods of the SUD spots, thisindicates a rhythmical, cosmic effect on thetotality of the lake.

So the life of the lake not only extendsbeyond its borders but is entwined with thelife of the highest totality we know, theC08IIlOS. We see that limnological andbydrobiological work is, after all, more thanjust fishing for plankton or catching newtsand frogs and water bugs.

* • •Thirty years ago, when the cry for syn-

thesis was to be heard only in isolatedcases, limnology was one of the first amongthe natural soiences to work toward synthesisand, in its own sphere, to build bridgesbetween the various parts of biology andthe nonbiological natural sciences. Itsadvance in the years after the Great War-

a development experienced by but a few ofthe other natural sciences-went parallelwith the general trend, especially among theyounger generation, to get away from special.ization toward a uniform conception of thewhole.

It is true, however, that this urge towardsynthesis has not yet been fully recognizedby all representatives of science. Thebridging sciences are still fighting hard fortheir existence. 'fo those, however, whoare convinced of the unity and totality ofscience, the support of such spheres ofscience IDuat be a matter of deep concern.These sciences are working at reassemblingthe specialized dispersion of science and inthis way intervene significantly in the entirespiritual life of the nations.

Regarding life from a totalitarian pointof view does not mean an underratingof analytical work: it builds up on thelatter. But in pursuit of its goals it followanew paths, creates new methods.

We see the essence of limnology in 8.conscious emphasis on synthesis--withoutever overlooking the fundamental analyticaltreatment of its field of subjects-and in thestressing of total traits in the life of nature,traits whioh enable one to understand thedetails too. This manner of regarding na-ture as a whole will play an increasinglyimportant role in the gradual overooming ofthe present spiritual and cultural crisis.

And the final goal of the study of natureseems to us to be-not, as one scientist putit, the uncovering of relationships of law-but, after an analysis of the parts, to rec·ognize the world as an order, a totality, &8a cosmos!

tJ/ficienc!lIn London, the Admiralty Stores List includes:

Pots, Chamber, plain.Pots, Chamber, with Admiralty monogram in blue, for hospital UlMl.Pots. Chamber, fluted with royal cypher in gold, for Flag Officers only.Potll, Chamber, round, rubber, lunatic.

(The New Staluman and NalWn, London)

'Lacficaf eon~iderafionHigh on a ladder in the British Admiralty's war room stood a WREN

(a member of the Women's Royal Naval Service) lIticking pina in a mapwhich marked the progress of a North Atlantio convoy. A crusty British _lord stalked in, glanced upward at the map. Said he:

.. Captain, that WREN will either have to wear p&IlUi or we will haveto move the convoy to the South Atlantic."

LAKE RAPPEN NEAR OBERSTDORF, GERMANY

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