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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vents the growth of chlorophyl-bearing organisms and
renders such waters relatively barren. The lighted top
layer of the water (zone of photosynthesis) is the pro-
ductive area. The other is a reservoir, tending to
stabilize conditions. Lakes may therefore be roughly

72 Types of Aquatic Environment

grouped in two classes: first, those that are shallow
enough for complete circulation of their water by wind
or otherwise at any time ; and second those deep enough
to maintain through a part of the summer season a
bottom reservoir of still water, undisturbed by waves or
currents, and stratified according to temperature and
consequent density. In these deeper lakes a thermo-
cline appears during midsummer. In the lakes of New
York its upper limit is usually reached at about thirty-
five feet and it has an average thickness of some fifteen
feet. Our lakes of the second class may therefore be
said to have a depth greater than fifty feet.

Lakes of this class may differ much among them-
selves according to the relative volume of this bottom
reservoir of quiet water, Lakes Otisco and Skaneateles
(see map on page 65) serve well for comparison in this
regard, since they are similar in form and situation and
occupy parallel basins but a few miles apart.

Max. % of vol.

Area in depth below Trans- Free CO 2 f at Oxygenf at

Lake sq. mi. in ft. 50 ft. parency* surface bottom surface bottom

Otisco 2.64 66 7.0 9.2 2.50-1-3.80 6.72 o.oo

Skaneateles. 13.90 297 70.2 31.8 1.25+1.00 6.75 7.89

*In feet, measured by Secchi's disc.

fin cc. per liter of water. Alkalinity by phenolthalein test is indicated
by the minus sign.

The figures given are from midsummer measure-
ments by Birge and Juday. At the time these observa-
tions were made both lakes were alkaline at the surface,
tho still charged with free carbon dioxide at the bottom.
Apparently, the greater the body of deep water the
greater the reserve of oxygen taken up at the time of
the spring circulation and held through the summer
season. Deep lakes are as a rule less productive of
plancton in summer, even in their surface waters,
because their supply of available carbon dioxide runs
low. It is consumed by algae and carried to the bottom

Currents 73

with them when they die, and thus removed from cir-

Increasing breadth of surface means increasing
exposure to winds with better aeration, especially
where waves break in foam and spray, and with the
development of superficial currents. Currents in lakes
are not controlled by wind alone, but are influenced as
well by contours of basins, by outflow, and by the
centrifugal pull due to the rotation of the earth on its
axis. In Lake Superior a current parallels the shore,
moving in a direction opposite to that of the hands of a
clock. Only in the largest lakes are tides perceptible,
but there are other fluctuations of level that are due to
inequalities of barometric pressure over the surface.
These are called seiches.

Broad lakes are well defined, for they build their
own barrier reefs across every low spot in the shores,
and round out their outlines. It is only shores that are
not swept by heavy waves that merge insensibly into
marshes. In winter in our latitude the margins of the
larger lakes become icebound, and the shoreline is
temporarily shifted into deeper water (compare summer
and winter conditions at the head of Cayuga lake as
shown in our frontispiece).

Increasing breadth has little effect on the life of the
open water, and none, directly, on the inhabitants of
the depths; but it profoundly affects the life of the
shoals and the margins, where the waves beat, and the
loose sands scour and the ice floes grind. Such a beach
as that shown on page 61 is bare of vegetation only
because it is storm swept. The higher plants cannot
withstand the pounding of the waves and the grinding
of the ice on such a shore.

The shallower a lake is the better its waters are
exposed to light and air, and, other things being equal,
the richer its production of organic life.


Types of Aquatic Environment

High and low water Since the source of this water is
in the clouds, all lakes fluctuate more or less with varia-
tion in rainfall. The great lakes drain an empire of
287,688 square miles, about a third of which is covered
by their waters. They constitute the greatest system
of fresh water reservoirs in the world, with an
unparalleled uniformity of level and regularity of
outflow. Yet their depth varies from month to month

ELEVATION 1896 1897 1898 1899 1900 1901 1902 13OS 190V 19OS



















FIG. 19. Diagram of monthly water levels in Lake Ontario for twelve years,
from the Report of the International Waterways Commission for 1910.

and from year to year, as shown on the accompanying
diagram. From this condition of relative stability to
that of regular disappearance, as of the strand lakes of
the Southwest, there are all gradations. Topography
determines where a lake may occur, but climate has
much to do with its continuance. Lakes in arid regions
often do not overflow their basins. Continuous evapora-
tion under cloudless skies further aided by high winds,
quickly removes the excess of the floods that run into
them from surrounding mountains. The minerals dis-
solved in these waters are thus concentrated, and they
become alkaline or salt. We shall have little to say in

High and Low Water


this book about such lakes, or about their population,
but they constitute an interesting class. Life in their
waters must meet conditions physiologically so different
that few organisms can live in both fresh and salt water.
Large lakes in arid regions are continually salt;
permanent lakes of smaller volume are made temporarily
fresh or brackish by heavy inflowing floods; while

FIG. 20. Marl pond near Cortland, N. Y., at low water. The whiteness oif the
bed surrounding the residual pool is due to deposited marl, largely derived
from decomposed snail shells. The marl is thinly overgrown with small
freely-blooming plants of Polygonum amphibium. Tall aquatics mark the
vernal shore line. (Photo by H. H. Knight).

strand lakes (called by the Spanish name play a lakes,
in the Southwest) run the whole gamut of water con-
tent, and vanish utterly between seasons of rain.

Complete withdrawal of the waters is of course fatal
to all aquatic organisms, save a few that have specialized
means of resistance to the drought. Partial withdrawal

7 6

Types of Aquatic Environment

by evaporation means concentration of solids in solu-
tion, and crowding of organisms, with limitation of
their food and shelter. The shoreward population of
all lakes is subject to a succession of such vicissitudes.
The term limnology is often used in a restricted sense
as applying only to the study of freshwater lakes.
This is due to the profound influence of the Swiss
Master, F. A. Forel, who is often called the "Father
of Limnology." He was the first to study lakes
intensively after modern methods. He made the
Swiss lakes the best known of any in the world.
His greatest work "Le Leman" a monograph on
Lake Geneva, is a masterpiece of limnological litera-
ture. It was he who first developed a comprehen-
sive plan for the study of the life of lakes and all
its environing conditions.



the water that finds
no basins to retain it,
forms streams. Ac-
cording as these differ
in size we call them
rivers, creeks, brooks,
and rills. These dif-
fer as do lakes in the
dissolved contents of their waters, according to the
nature of the soils they drain. Streams differ most
from the lakes in that their waters are ever moving in
one direction, and ever carrying more or less of a load
of silt. From the geologist's point of view the work of
rivers is the transportation of the substance of the
uplands into the seas. It is an eternal levelling process.
It is well advanced toward completion in the broad
flood plains of the larger continental streams (see map
on page 63); but only well begun where brooks and
rills are invading the high hills, where the waters seek
outlets in all directions, and where every slope is
intersected with a maze of channels. The rapidity of
the grading work depends chiefly upon climate and rain-
fall, on topography and altitude and on the character
of the rocks and soil.


78 Types of Aquatic Environment

The rivers of America have been extensively studied
as to their hydrography, their navigability, their water-
power resources, and their liability to overflow with
consequent flood damage ; but it is the conditions they

FIG. 21. Streams of the upper Cayuga basin.

A . Taughannock Creek, with a waterfall 211 feet high near its mouth ;
. Salmon Creek; C. Fall Creek with the Cornell University Biological Field
Station in the marsh at its mouth (views on this stream are shown in the initial
cuts on pages 24 and 82) ; D. Cascadilla Creek (view on page 55) ; -E. Sixmile
Creek; F. Buttermilk Creek with Coys Glen opposite its mouth. (View on
page 7 7 ; of the Glen on page 25) ; G. Neguena Creek or the Inlet. The southern-
most of these streams rise in cold swamps, which drain southward also into
tributaries of the Susquehanna River.

Conditions in Streams


J 10 15 20 25 JO

\ ffiKlf-mriOH I

^ A

afford to their plant and animal inhabitants that
interest us here; and these have been little studied.
Most has been done on the Illinois River, at the floating
laboratory of the Illinois State Laboratory of Natural
History (see page 50). A more recently established
river laboratory, more limited in its scope (being
primarily concerned with the propagation of river
mussels) is that of the U. S. Fish Commission at Fair-
port, Iowa, on the Mis-
sissippi River.

In large streams, espec-
ially in their deeper and
more quiet portions, the
conditions of life are most
like those in lakes. In les-
ser streams life is subject
to far greater vicissitudes.
The accompanying figure
shows comparative sum-
mer and winter tempera-
tures in air and in water of
Fall Creek at Ithaca. This
creek (see the figure on
page 24), being much
broken by waterfalls and
very shallow, shows hardly
any difference between sur-
face and bottom tempera- FIG
tures. The summer tem-
peratures of air and water
(fig. 22) are seen to main-
tain a sort of correspond-
ence, in spite of the thermal
conservatism of water, due to its greater specific heat.
This approximation is due to conditions in the creek
which make for rapid heating or cooling of the water.

Diagram showing summer
and winter conditions in Fall Creek
at Ithaca, N. Y. Data on air
temperatures furnished by Dr. W.M.
Wilson of the U. S. Weather Bureau.
Data on water temperatures by Pro-
fessor E. M. Chamot.

8o Types of Aquatic Environment

It flows in thin sheets over broad ledges of dark colored
rocks that are exposed to the sun, and it falls over pro-
jecting ledges in broad thin curtains, outspread in con-
tact with the air.

The curves for the two winter months, show less
concurrence, and it is strikingly apparent that during
that period when the creek was ice-bound (Dec. 15-
Jan. 31) the water temperature showed no relation to
air temperature, but remained constantly at or very
close to oC. (32 P.).

Forbes and Richardson (13) have shown how great
may be the aerating effect of a single waterfall in such
a sewage polluted stream as the upper Illinois River.
"The fall over the Marseilles dam (710 feet long and 10
feet high) in the hot weather and low water period of
July and August, 1911, has the effect to increase the
dissolved oxygen more than four and a half times, rais-
ing it from an average of .64 parts per million to 2.94
parts. On the other hand, with the cold weather, high
oxygen ratios, and higher water levels of February and
March, 1912, and the consequent reduced fall of
water at Marseilles, the oxygen increase was only 18
per cent. from 7.35 parts per million above the dam
to 8.65 parts below * * * The beneficial effect is
greatest when it is most needed when the pollution is
most concentrated and when decomposition processes
are most active."

Ice The physical conditions that in temperate
regions have most to do with the well- or ill-being of
organisms living in running water are those resulting
from the freezing. The hardships of winter may be
very severe, especially in shallow streams. One may
stand beside Fall Creek in early winter when the thin
ice cakes heaped with snow are first cast forth on the
stream, and see through the limpid water an abundant

Ice in Streams 81

life gathered upon the stone ledges, above which these
miniature floes are harmlessly drifting. There are
great black patches of Simulium larvae, contrasting
strongly with the whiteness of the snow. There are
beautiful green drapings of Cladophora and rich red-
purple fringes of Chantransia, and everywhere amber ^
brown carpetings of diatoms, overspreading all the,
bottom. But if one stand in the same spot in the
spring, after the heavy ice of winter has gone out, he
will see that the rocks have been swept clean and bare,
every living thing that the ice could reach having gone.

The grinding power of heavy ice, and its pushing
power when driven by waves or currents, are too well
known to need any comment. The effects may be seen
on any beach in spring, or by any large stream. But
there is in brooks and turbulent streams a cutting with
fine ice rubble that works through longer periods, and
adds the finishing touches of destructiveness. It is
driven by the water currents like sand in a blast, and it
cleans out the little crevices that the heavy ice could
not enter. This ice rubble is formed at the front of
water falls under such conditions as are shown in the
accompanying figure of Triphammer Falls at Ithaca.
The pool below the fall froze first. The winter increas-
ing cold, the spray began to freeze where it fell. It
formed icicles, large and small, wherever it could find a
support above. It built up grotesque columns on the
edge of the ice of the pool beneath. It grew inward
from the sides and began to overarch the stream face;
and then, with favoring intense cold of some days dura-
tion, it extended these lines of frozen spray across the
front of the fall in all directions, covering it as with a
beautiful veil of ice.

The conditions shown in the picture are perfect for
the rapid formation of ice rubble. From thousands of
points on the underside of this tesselated structure


Types of Aquatic Environment

minute icicles are forming and their tips are being broken
off by the oscillations of the current. These broken
tips constitute
the rubble.
They are some-
times remark-
ably uniform in
size those form-
ing when this
picture was
taken were
about the size
of peas and
though small
they are the
tools with which
the current does
its winter clean-
ing. In the
ponds formed by
damming rapid
streams this rub-
ble accumulates
under the solid

"Anchor ice"
forms in the
beds of rapid
streams, and
adds another
peril to their in-
habitants. The
water, cooled

below the freez-
ing point by con-
tact with the air,

FIG. 23. The ice veil on Triphammer Falls, Cornell
University Campus. The fall is at the left, the
Laboratory of Hydraulic Engineering at the right
in the picture, the only open water seen is in the
foaming pool at the foot of the fall.

Anchor Ice

does not freeze in the current because of its motion,
but it does freeze on the bottom, where the current
is sufficiently retarded to allow it. It congeals in
semi-solid or more or less flocculent masses which, when
attached to the stones of the bed, often buoy them up

FIG. 24. A brook in winter. Country Club woods, Ithaca, N. Y.

Photo by John T. Needham.

and cause them to be carried away. Thus the organ-
isms that dwell in the stream bed are deprived of their
shelter and exposed to new perils.

Below the frost-line, however, in streams where
dangers of mechanical injuries such as above men-
tioned are absent, milder moods prevail. In the bed
of a gentle meandering streamlet like that shown in the
accompanying figure, life doubtless runs on in winter

84 Types of Aquatic Environment

with greater serenity than on land. Diatoms grow
and caddis-worms forage and community life is actively

Silt Part of the substance of the land is carried
seaward in solution. It is ordinarily dissolved at or
near the surface of the ground, but may be dissolved
from underlying strata, as in the region of the Mam-
moth Cave in Kentucky, where great streams run far
under ground. But the greater part is carried in
suspension. Materials thus carried vary in size from
the finest particles of clay to great trees dropped whole
into the stream by an undercutting flood. The lighter
solids float, and are apt to be heaped on shore by wave
and wind. The heavier are carried and rolled along,
more or less intermittently, hastened with floods and
slackened with low water, but ever reaching lower
levels. The rate of their settling in relation to size
and to velocity of stream has been discussed in the
preceding chapter.

Silt is most abundant at flood because of the greater
velocity of the water at such times. Kofoid ('03) has
studied the amount of silt carried by the Illinois River
at Havana. Observations at one of his stations
extending over an entire year show a minimum amount
of 140 cc. per cubic meter of river water; a maximum
of 4,284 cc., and an average for the year (28 samples)
of 1,572 cc. Silt in a stream affects its population in a
number of ways. It excludes light and so interferes
with the growth of green plants, and thus indirectly with
the food supply of animals. It interferes with the free
locomotion of the microscopic animals by becoming
entangled in their swimming appendages. It clogs the
respiratory apparatus of other animals. It falls in
deposits that smother and bury both plants and animals
living on the bottom. Thus the best foraging grounds
of some of our valuable fishes are ruined.

Current 85

Professor Forbes ('oo) has shown that the fine silt
from the earlier-glaciated and better weathered soils
of southern Illinois, has been a probable cause of
exclusion of a number of regional fishes from the streams
of that portion of the state.

It is heavier silt that takes the larger share in the
building of bars and embankments along the lower
reaches of a great stream, in raising natural levees to
hold impounded backwaters, and in blocking cut-off
channels to make lakes of them.

Current Rate of streamflow being determined
largely by the gradient of the channel, is one of the
more constant features of rivers, but even this is sub-
ject to considerable fluctuation according to volume.
Kofoid states that water in the Illinois River travels
from Utica to the mouth (227 miles) in five days at
flood, but requires twenty-three days for the journey
at lowest water. The increase in speed and in turbu-
lence in flood time appears to have a deleterious effect
upon some of the population, many dead or moribund
individuals of free swimming entomostraca being
present in the waters at such times.

With the runoff after abundant rainfall a rapid rise
and acceleration occurs, to be followed by a much
slower decline. The stuffs in the water are diluted;
the planet on is scattered. A new load of silt is received
from the land; plant growths are destroyed and even
contours in the channel are shifted.

Current is promoted by increasing gradient of stream -
bed. It is diminished by obstructions, such as rocks or
plant growths, by sharp bends, etc. It is slightly
accelerated or retarded by wind according as the direc-
tion is up or down stream. Even where a stream
appears to be flowing steadily over an even bed between
smooth shores, careful measurements reveal slight and

2 3-9I

3 3-73

4 3-6o

5 3-32

6 3-04

7 2.8 9

8 2.81
10 2.73

12 2.64

14 2.46

i.S 2.17

16 1.73

86 Types of Aquatic Environment

inconstant fluctuations. The current is nowhere uni-
form from top to bottom or from bank to bank. In the
horizontal plane it is swiftest in midstream and is
retarded by the banks. In a vertical plane, it is swift-
est just beneath the surface and is retarded more and
more toward the bottom. The pull of the surface film
Depth Feet retards it a little and

in inches per sec. when ice forms on the

surface, friction against
the ice retards it far more
and throws the point of
maximum velocity down
near middepth of the
stream. A sample meas-
urement made by Mr.
Wilbert A. Clemens in
Cascadilla Creek at

Current and Depth in Cascadilla Ithaca in Open Water
Creek. Measured by W. A. Clemens, seventeen inches deep

gave rate of flow varying from a maximum of 3 . 9 1 feet per
second two inches below the surface down to i . 73 feet per
second one inch above the bottom, as shown in the col-
umns above. Below this, in the last inch of depth the
retardation was more rapid, but irregular. The current
slackens more slowly toward the surface and toward
the side margins of the stream.

Mr. Clemens, using a small Pitot-tube current meter,
made other measurements showing that in the places
where dwell the majority of the inhabitants of swift
streams there is much less current than one might ex-
pect. In the shelter of stones and other obstructions
there is slack water. On sloping bare rock bottoms
under a swiftly gliding stream the current is often but
half that at the surface. On stones exposed to the
current a coating of slime and diatomaceous ooze
reduces the current 1 6 to 32 per cent.

High and Low Water

This accounts for the continual restocking of a stream
whose waters are swifter than the swimming of the
animals found in the open channels. In these more or
less shoreward places they breed and renew the supply.
Except in a stream whose waters run a long course sea-
ward, allowing an ample time for breeding, there is
little indigenous free-swimming population.

FIG. 25. Annually inundated bulrush-covered flood-plain at the mouth of Fall
Creek, Ithaca, N. Y., in 1908. Clear growth of Scirpus fluviatilis and a
drowned elm tree. The Cornell University Biological Field Station at
extreme right. West Hill in the distance.

High and Low Water Inconstancy is a leading char-
acteristic of river environment, and this has its chief
cause in the bestowal of the rain. Streams fed mainly
by springs, lakes, and reservoirs are relatively constant;
but nearly all water courses are subject to overflow;
their channels are not large enough to carry flood
waters, so these overspread the adjacent bottomlands.
Every change of level modifies the environment by


Types of Aquatic Environment

connecting or cutting off back waters, by shifting cur-
rents, by disturbing the adjustment of the vegetation,
and by causing the migration of the larger animals. At
low water the Illinois River above Havana has a width
of some 500 feet; in flood times it spreads across the
valley floor in a sheet of water four miles wide.

The rise of a river flood is often sudden ; the decline
is always much more gradual, for impounding barriers
and impeding vegetation tend to hold the water upon
the lowlands. The period of inundation markedly
affects the life of the land overflowed. Cycles of seasons
with short periods of annual submergence favor the
establishment of upland plants and trees. Cycles of
years of more abundant rainfall favor the growth of
swamp vegetation. Certain plants like the flood-plain
bulrush shown in the preceding figure seem to thrive
best under inconstancy of flood conditions.


GREAT aquatic en-
vironment may be
maintained with
much less water than there is in a lake or a river if only
an area of low gradient, lacking proper basin or channel,
be furnished with a ground cover of plants suitable for
retaining the water on the soil. Enough water must be
retained to prevent the complete decay of the accumu-
lating plant remains. Then we will have, according to
circumstances, a marsh, a swamp or a bog.

There are no hard and fast distinctions between these
three; but in general we may speak of a marsh as
a meadow-like area overgrown with herbaceous aquatic

Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 5 of 26)