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James G. (James George) Needham.

The life of inland waters; an elementary text book of fresh-water biology for students online

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Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 3 of 26)
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tary foodstuffs necessary for life. Pure water (H 2 O)
is not found. All natural waters are mineralized
waters even rain, as it falls, is such. And a compara-



Natural Waters 41



tively few soluble solids and gases furnish the still
smaller number of chemical elements that go to make
up the living substance. The amount of dissolved
solids varies greatly, being least in rainwater, and
greatest in dead seas, which, lacking outlet, accumulate
salts through continual evaporation. Here is a rough
statement of the dissolved solids in some typical waters :

In rain water 30 40 parts per million

In drainage water off siliceous soils 50 80

In springs flowing from siliceous soils 60 250

In drainage water off calcareous soils 1 40 230
In springs flowing from calcareous

soils 300 660

In rivers at large 120 350

In the ocean 33000 37370

Thus the content is seen to vary with the nature of
the soils drained, calcareous holding a larger portion of
soluble solids than siliceous soils. It varies with
presence or absence of solvents. Drainage waters from
cultivated lands often contain more lime salts than do
springs flowing from calcareous soils that are deficient
in carbon dioxide. Spring waters are more highly
charged than other drainage waters, because of pro-
longed contact as ground water with the deeper soil
strata. And evaporation concentrates more or less
the content of all impounded waters.

All natural waters contain suspended solids in great
variety. These are least in amount in the well filtered
water of springs, and greatest in the water of turbu-
lent streams, flowing through fine soils. At the con-
fluence of the muddy Missouri and the clearer
Mississippi rivers the waters of the two great currents
may be seen flowing together but uncommingled for
miles.

The suspended solids are both organic and inorganic,
and the organic are both living and dead, the latter



42 Nature of Aquatic Environment

being plant and animal remains. From all these non-
living substances the water tends to free itself: The
lighter organic substances (that are not decomposed
and redissclved) are cast on shore; the heavier mineral
substances settle to the bottom. The rate of settling
is dependent on the rate of movement of the water and
on the specific gravity and size of the particles. Fall
Creek at Ithaca gives a graphic illustration of the carry-
ing power of the current. In the last mile of its course,
included between the Cornell University Campus and
Cayuga Lake, it slows down gradually from a sheer
descent of 78 ft. at the beautiful Ithaca Fall to a scarcely
perceptible current at the mouth. It carries huge
blocks of stone over the fall and drops them at its foot.
It strews lesser blocks of stone along its bed for a quar-
ter of a mile to a point where the surface ceases to break
in riffles at low water. There it deposits gravel, and
farther along, beds and bars of sand, some of which
shift position with each flood rise, and consequent
acceleration. It spreads broad sheets of silt about its
mouth and its residual burden of finer silt and clay it
carries out into the lake. The lake acts as a settling
basin. Flood waters that flow in turbid, pass out
clear.

Whipple has given the following figures for rate of
settling as determined by size, specific gravity and form
being constant:

Velocity of particles falling through water
Diameter i. inch, falls 100. feet per minute.

it n (

.01 '" " '.15 " "
.001 " " .0015 " "
.0001 " .000015 "

Suspended mineral matters are, as a rule, highly
insoluble. Instead of promoting, they lessen the
productivity of the water by shutting out the light.



Gases from the Atmosphere 43

Suspended organic solids likewise contribute nothing
to the food supply as long as they remain undissolved.
But when they decay their substance is restored to
circulation. Only the dissolved substances that are
in the water are at once available for food. The soil
and the atmosphere are the great storehouses of these
materials, and the sources from which they were all
originally derived.

Gases from the atmosphere The important gases
derived from the atmosphere are two : carbon dioxide
(CO 2 ) and oxygen (O). Nitrogen is present in the
atmosphere in great excess (N, 79% to O, nearly 21%,
and CO 2 , .03%), and nitrogen is the most important
constituent of living substance, but in gaseous form,
free or dissolved, it is not available for food. The
capacity of water for absorbing these gases varies with
the temperature and the pressure, diminishing as
warmth increases (insomuch that by boiling they are
removed from it), and increasing directly as the pres-
sure increases. Pure water at a pressure of 760 mm. in
an atmosphere of pure gas, absorbs these three as
follows:

Oxygen CO2 Nitrogen

At oC 41-14 J 796-7 2 -35

At 2oC 28.38 901.4 14-03

At double the pressure twice the quantity of the gas
would be dissolved. Natural waters are exposed not
to the pure gas but to the mixture of gases which make
up the atmosphere. In such a mixture the gases are
absorbed independently of each other, and in propor-
tion to their several pressures, which vary as their
several densities: the following table* shows, for



*Abridged from a table of values to tenths of a degree by Birge and Juday
in Bull. 22, Wise. Geol. & Nat. Hist. Survey, p. 20.



44 Nature of Aquatic Environment

example, the absorbing power of pure water at various
temperatures for oxygen from the normal atmosphere
at 760 mm. pressure:

Water at oC 9.7000. per liter at isC 6.96 cc. per liter

" 5C 8.68 cc. " " " 2oC 6.28 cc. " "

1 ioC 7.77 cc. ' " 2 5 C 5.76 cc. " "

The primary carbon supply for the whole organic
world is the carbon dioxide (CO 2 ) of the atmosphere.
Chlorophyll-bearing plants are the gatherers of it.
They alone among the organisms are able to utilize the
energy of the sun's rays. The water existing as vapor
in the atmosphere is the chief agency for bringing these
gases down to earth for use. Standing water absorbs
them at its surface but slowly. Water vapor owing to
better exposure, absorbs them to full saturation, and
then descends as rain. In fresh water they are found in
less vary ing proportion, varying from none at all to con-
siderable degree of supersaturation. Birge and Juday
report a maximum occurrence of oxygen as observed in
the lakes of Wisconsin of 25.5 cc. per liter in Knight's
Lake on Aug. 26, 1909 at a depth of 4.5 meters. This
water when brought to the surface (with consequent
lowering of pressure by about half an atmosphere)
burst into lively effervescence, with the escape of a
considerable part of the excess oxygen into the air.
('n, p. 52). They report the midsummer occurrence
of free carbon dioxide in the bottom waters of several
lakes in amounts approaching 15 cc. per liter.

The reciprocal relations of C0 2 and Carbon dioxide
and oxygen play leading roles in organic metabolism,
albeit, antithetic roles. The process begins with the
cleavage of the carbon dioxide, and the building up of
its carbon into organic compounds; it ends with the
oxidation of effete carbonaceous stuffs and the reappear-
ance of CO 2 . Both are used over and over again.



Carbon Dioxide and Oxygen 45

Plants require CO 2 and animals require oxygen in order
to live and both live through the continual exchange of
these staple commodities. This is the best known
phase in the cycle of food materials. The oxygen is
freed at the beginning of the synthesis of organic mat-
ter, only to be recombined with the carbon at the end
of its dissolution. And the well-being of the teeming
population of inland waters is more dependent on the
free circulation and ready exchange of the dissolved
supply of these two gases than on the getting of a new
supply from the air.

The stock of these gases held by the atmosphere is
inexhaustible, but that contained in the water often
runs low; for diffusion from the air is slow, while
consumption is sometimes very rapid. We often have
visible evidence of this. In the globe in our win-
dow holding a water plant, we can see when the sun
shines streams of minute bubbles of oxygen, arising
from the green leaves. Or, in a pond we can see
great masses of algae floated to the surface on a foam
of oxygen bubbles. We cannot see the disappearance
of the carbon dioxide but if we test the water we find
its acidity diminishing as the carbon dioxide is con-
sumed.

At times when there is abundant growth of algae near
the surface of a lake there occurs a most instructive
diurnal ebb and flow in the production of these two
gases. By day the well lighted layers of the water
become depleted of their supply of CO 2 through the
photosynthetic activities of the algae, and become
supersaturated with the liberated oxygen. By night
the microscopic crustaceans and other plancton animals
rise from the lower darker strata to disport themselves
nearer the surface. These consume the oxygen and
restore to the water an abundance of carbon dioxide.
And thus when conditions are right and the numbers of



46 ilamre of Aquatic Environment

plants and animals properly balanced there occur
regular diurnal fluctuations corresponding to their
respective periods of activity in these upper strata.

Photosynthesis is, however, restricted to the better
lighted upper strata of the water. The region of
greatest carbon consumption is from one to three meters
in depth in turbid waters, and of ten meters or more in
depth in clear lakes. Consumption of oxygen, however,
goes on at all depths, wherever animal respiration or
organic decomposition occurs. And decomposition
occurs most extensively at the bottom where the organic
remains tend to be accumulated by gravity. With a
complete circulation of the water these two gases may
continue to be used over and over again, as in the exam-
ple just cited. But, as we have seen, there is no circula-
tion of the deeper water during two considerable periods
of the year; and during these stagnation periods the
distribution of these gases in depth becomes correlated
in a wonderful way with the thermal stratification of
the water. This has been best illustrated by the work
of Birge and Juday in Wisconsin. Figure 8 is their
diagram illustrating the distribution of free oxygen in
Mendota Lake during the summer of 1906. It should
be studied in connection with figure 7, which illustrates
conditions of temperature. Then it will be seen that
the two periods of equal supply at all levels correspond
to vernal and autumnal circulation periods. The
season opens with the water nearly saturated (8 cc. of
oxygen per liter of water) throughout. With the warm-
ing of the waters the supply begins to decline, being
consumed in respiration and in decomposition. In the
upper six or seven meters the decline is not very exten-
sive, for at these depths the algae continually renew the
supply. But as the lower strata settle into their sum-
mer rest their oxygen content steadily disappears, and
is not renewed until the autumnal overturn. For three



Summer Stagnation



47



months there is no free oxygen at the bottom of the
lake, and during August there is not enough oxygen
below the ten meter level to keep a fish alive.

Correspondingly, the amount of free C0 2 in the
deeper strata of the lake increases rather steadily until
the autumnal overturn. It is removed from circulation,
and in so far as it is out of the reach of effective light,
it is unavailable for plant food.




FIG. 8. Dissolved oxygen at different depths in Lake Mendota in 1906. The
vertical spaces represent cubic centimeters of gas per liter of water and
the figures attached to the curves indicate the depths in meters. (Birge
and Juday.)

Other gases A number of other gases are more or
less constantly present in the water; nitrogen, as
above stated, being absorbed from the air, methane
(CH 4 ), and other hydrocarbons, and hydrogen sulphide
(H 2 S), etc., being formed in certain processes of decom-



48 Nature of Aquatic Environment

position. Of these, methane or marsh gas, is perhaps
the most important. This is formed where organic
matter decays in absence of oxygen. In lakes such
conditions are found mainly on the bottom. In marshes
and stagnant shoal waters generally, where there is
much accumulation of organic matter on the bottom,
this gas is formed in abundance. It bubbles up through
the bottom ooze, or often buoys up rafts of agglutinated
bottom sediment.

Nitrogen The supply of nitrogen for aquatic organ-
isms is derived from soluble simple nitrates (KNO 3 ,
NaNO 3 , etc.) Green plants feed on these, and build
proteins out of them. And when the plants die (or
when animals have eaten them) their dissolution yields
two sorts of products, ammonia and nitrates, that
become again available for plant food. Ammonia is
produced early in the process of decay and the nitrates
are its end products.

Bacteria play a large role in the decomposition of
proteins. At least four groups of bacteria successively
participate in their reduction. The first of these are
concerned with the liquefaction of the proteins, hydroly-
zing the albumins, etc., by successive stages to albu-
moses, peptones, etc., and finally to ammonia. A
second group of bacteria oxidizes the ammonia to
nitrites. A third group oxidizes the nitrites to
nitrates. A fourth group, common in drainage waters,
reduces nitrates to nitrites. Since these processes are
going on side by side, nitrogen is to be found in all
these states of combination when any natural water is
subjected to chemical analysis. The following table
shows some of the results of a large number (415) of
analyses of four typical bottomland bodies of water,
made for Kofoid's investigation of the plancton of the
Illinois River by Professor Palmer.



Nitrogen



49



The relative productiveness in open-water life of
these situations is shown in the last column of the table.





Solids












In parts
per million




Free
Ammonia


Organic

Nitrogen


Nitrites


Nitrates


Plancton
cm3 per
m3


Sus-
pended


Dis-
solved


Illinois River .


61.4


304.1


.860


1.03


.147


i-59


I.9I


Spoon River .


274-3


167.1


245


I.2Q


039


I.OI


39


Quiver Lake .


25.1


248.2


I6S


.61


.023


.66


1.62


Thompson's L.


44.6


282.9


.422


1.05


.048


.64


6.68



The difference between these four adjacent bodies of
water explains some of the peculiarities of the table.
The rivers hold more solids in suspension than do the
lakes, although these lakes are little more than basins
holding impounded river waters. Spoon River holds
the least amount of dissolved solids, and by far the
greatest amount of suspended solids. Since the latter
are not available for plant food, naturally this stream
is least productive of planet on. Illinois River drains a
vast and fertile region, and receives in its course the
sewage and other organic wastes of two large cities,
Chicago and Peoria, and of many smaller ones. Hence,
its high content of dissolved matter, the cities being
remote, so there has been time for extensive liquefac-
tion. Hence, also, its high content of ammonia, of
nitrites and of nitrates.

The two lakes are very unlike ; Quiver Lake is a mere
strip of shoal water, fed by a clear stream that flows in
through low sandy hills. It receives water from the
Illinois River only during high floods. Thompson's
Lake is a much larger body of water, fed directly from
the Illinois River through an open channel. Naturally,
it is much like the river in its dissolved solids, and in its
total organic nitrogen. That it falls far below the
river in nitrates and rises high above it in plancton
production may perhaps be due to the extensive con-



Nature of Aquatic Environment



sumption of nitrates by plancton algae. Nitrates, be-
cause they furnish nitrogen supply in the form at once
available for plant growths, are, in shallow waters at
least, an index of the fertility of the water. As on
land, so in the water, the supply of these may be
inadequate for maximum productiveness, and they may
be added with profit as fertilizer.

The carbonates Lime and magnesia combine with
carbon dioxide, abstracting it from the water, forming




FIG. 9. Environs of the Biological Field Station of the Illinois State Labora-
tory of Natural History, the scene of important work by Kofoid and others
on the life of a great river.

solid carbonates (CaCO 3 and MgCO 3 ). These accumu-
late in quantities in the shells of molluscs, in the stems
of stone worts, in the incrustations of certain pond
weeds, and of lime-secreting algae. The remains of
such organisms accumulate as marl upon the bottom.
The carbonates (and other insoluble minerals) remain;
the other body compounds decay and are removed.
By such means in past geologic ages the materials for
the earth's vast deposits of limestone were accumu-



The Carbonates 51



lated. Calcareous soils contain considerable quantities
of these carbonates.

In pure water these simple carbonates are practically
insoluble; but when carbon dioxide is added to the
water, they are transformed into bicarbonates* and are
readily dissolved, f So the carbonates are leached out
of the soils and brought back into the water. So the
solid limestone may be silently removed, or hollowed out
in great caverns by little underground streams. So
the Mammoth Cave in Kentucky, and others in Cuba,
in Missouri, in Indiana and elsewhere on the continent,
have been formed.

The water gathers up its carbon dioxide in part as it
descends through the atmosphere, and in larger part as
it percolates thru soil where decomposition is going on
and where oxidation products are added to it.

Carbon dioxide, thus exists in the water in three
conditions: (i) Fixed (and unavailable as plant food)
in the simple carbonates; (2) "half-bound" in the
bicarbonates; and (3) free. Water plants use first for
food, the free carbon dioxid, and then the "half bound"
that is in loose combination in the bicarbonates. As
this is used up the simple carbonates are released, and
the water becomes alkaline. Birge and Juday have
several times found a great growth of the desmid
Staurastrum associated with alkalinity due to this
cause. In a maximum growth which occurred in
alkaline waters at a depth of three meters in Devil's
Lake, Wisconsin, on June I5th, 1907, these plants
numbered 176,000 per liter of water.

*CaCOa, for example, becoming Ca(HCOs)2, the added part of the formula
representing a molecule each of CO2 and H2O.

flf "hard" water whose hardness is due to the presence of these bicarbonate 8
be boiled, the CCte is driven off and the simple carbonates are re-precipitated (as,
for example, on the sides and bottom of a tea kettle). This is "temporary
hardness." "Permanent hardness" is due to the presence of sulphates and
chlorides of lime and magnesia, which continue in solution after boiling.

Phenolphthalein, being used as indicator of alkalinity.



52 Nature of Aquatic Environment

Waters that are rich in calcium salts, especially in
calcium carbonate, maintain, as a rule, a more abundant
life than do other waters. Especially favorable are
they to the growth of those organisms which use much
lime for the building of their hard parts, as molluscs,
stoneworts, etc. There are, however, individual pref-
erences in many of the larger groups. The crustaceans
for example, prefer, as a rule, calcium rich waters, but
one of them, the curious entomostracan, Holopedium
gibber urn, (Fig. 10) is usually found in
calcium poor waters, in lakes in the
Rocky Mountains and in the Adiron-
dacks, in waters that flow off
archaean rocks or out of silic-
eous sands. The desmids
with few exceptions are more
abundant in calcium poor
waters. The elegant genus
Micrasterias is at Ithaca espec-
ially ahunrlant in thp npat FIG. 10. A gelatinous-coated mi-
laiiV aDUnaant in tne peat- C rocrustacean, Holopedium gib-

Stained Calcium-pOOr Waters berum, often found in waters

of sphagnum bogs. that are poor in calcium -

Other minerals in the water The small quantities of
other mineral substances required for plant growth are
furnished mainly by a few sulphates, phosphates and
chlorids: sulphates of sodium, potassium, calcium
and magnesium; phosphates of iron, aluminum, cal-
cium and magnesium, and chlorids of sodium, potas-
sium, calcium and magnesium. Aluminum alone of
the elements composing the above named compounds,
is not always requisite for growth, although it is very
often present. Silica, likewise, is of wide distribution,
and occurs in the water in considerable amounts, and
is used by many organisms in the growth of their hard
parts. As the stoneworts use lime for their growth,
some 4% of the dry weight of Chara being CaO, so




Mineral Content



53



diatoms require silica to build their shells. When the
diatoms are dead their shells, relatively heavy though
extremely minute, slowly settle to the bottom, slowly
dissolving; and so, analyses of lake waters taken at
different depths usually show increase of silica toward
the bottom.

Iron, common salt,
sulphur, etc., often
occur locally in great
abundance, notably in
springs flowing from
special deposits, and
when they occur they
possess a fauna and
flora of marked pecu-
liarities and very
limited extent.

An idea of the rela-
tive abundance of the
commoner mineral
substances in lake
waters may be had
from the following
figures that are con-
densed from Birge and

FIG. ii. A beautiful green desmid, M icra- Judav's report of
sterias that is common in bo^r waters. J -

analyses.




74



MINERAL CONTENT OF WISCONSIN LAKES
Parts per million

F1 2 3 +

SiO 2 A1 3 O 3 Ca Mg Na K CO 3 HCO 3
Minimum. 0.8
Maximum 33.0



Average



11.7



0.4

II. 2

2.1



0.6

49.6

26.9



32.7
19.6



0-3

6.2



3.2 2.2



0.0
12.
2.1



49
153-0
91.7



SO 4
o.o

18.7
9.8



C1

i-5

10.

39



This is the bill of fare from which green water plants
may choose. Forel aptly compared the waters of a



54 Nature of Aquatic Environment

lake to the blood of the animal body. As the cells of
the body take from the blood such of its content as is
suited to their need, so the plants and animals of the
water renew their substance out of the dissolved sub-
stances the water brings to them.

Organic substances dissolved in the water may so
affect both its density and its viscosity as to determine
both stratification and distribution of suspended solids.
This is a matter that has scarcely been noticed by
limnologists hitherto. Dr. J. U. Lloyd ('82) long ago
showed how by the addition of colloidal substances to a
vessel of water the whole contents of the vessel can be
broken into strata and these made to circulate, each at
its own level, independent of the other strata. Solids
in suspension can be made to float at the top of particu-
lar strata, according to density and surface tension.

Perhaps the ' 'false bottom" observed in some north-
ern bog-bordered lakes is due to the dissolved colloids
of the stratum on which it floats. Holt ('08, p. 219)
describes the "false bottom" in Sumner Lake, Isle
Royal, as lying six to ten feet below the surface, many
feet above the true bottom; as being so tenuous that a
pole could be thrust through it almost as readily as
through clear water; and as being composed of fine
disintegrated remains of leaves and other light organic
material. "In places there were great breaks in the
'false bottom,' doubtless due to the escape of gases
which had lifted this fine ooze-like material from a
greater depth: and through these breaks one could
look down several feet through the brownish colored
water."

Perhaps the colloidal substances in solution are
such as harden upon the surface of dried peat, like a
water-proof glue, making it for a time afterward imper-
vious to water.




WATER AND
LAND

ICEANS are the earth's
great storehouse of water.
They cover some eight-
elevenths of the surface
of the earth to an average
depth of about two miles.
They receive the off-flow
from all the continents
and send it back by way
of the atmosphere.

The fresh waters of the earth descend in the first
instance out of the atmosphere. They rise in vapor
from the whole surface of the earth, but chiefly from
the ocean. Evaporation frees them from the ocean's
salts, these being non- volatile. They drift about with
the currents of the atmosphere, gathering its gases to
saturation, together with very small quantities of drift-
ing solids; they descend impartially upon water and



Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 3 of 26)