Bulletin


STATE OF ILLINOIS

DEPARTMENT OF REGISTRATION AND EDUCATION

DIVISION OF THE

NATURAL HISTORY SURVEY
THEODORE H. PRISON, Chiel

Vol. XIX. BULLETIN Article V.

The Plankton of the Sangamon

River in the Summer

of 1929

BY

SAMUEL EDDY

PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS

URBANA, ILLINOIS

NOVEMBER, 1931



STATE OF ILLINOIS

DEPARTMENT OF REGISTRATION AND EDUCATION

M. F. Walsh, Director

BOARD OP NATURAL RESOURCES AND CONSERVATION

M. F. Walsh. Chairman

William Trelease, Biology Joiix W. Alvord, Engineering

Heney C. Cowles, Forestry Charles M. Thompson, Represent-

Edson S. Bastin, Geology ing the President of the Univer-

William A. Notes, Chemistry sity of Illinois

STATE NATURAL HISTORY SURVEY DIVISION

Theodore H. Prison, Chief

H. C. Oesterling, Editor

ScHNBPp & Barnes, Printers
Springfield, III.

1931

66752—1200



VoLiME XIX. Article V.

THE PLANKTON OF THE SANGAMON
RIVER IN THE SUMMER OF 1929

Samuf.l Eddy

The Sangamon River, a small river in the central part of Illinois,

has special interest to students of aquatic biology because it exhibits

in a remarkable way the effects of the installation of a sewage treatment

plant in alleviating pollution and at the same time the effects of the

erection of a dam to impound water for munici))al and industrial uses.

The present study is an attempt to determine to what extent these ef-

fects are reflected by changes in the abundance of certain kinds of

microscopic organisms, collectively called ]5lankton, which live sus-

pended in the water. As is well known, some kinds of plankton organ-

isms, if present in sufficient numbers in reservoirs, may give diagree-

able flavors to the water ; other kinds may aid in the natural purification

of polluted waters: and in streams and lakes generally plankton plays

a role of more or less importance as food for larger organisms, includ-

ing ti.shes. In our larger streams, such as the Rock River and the Illi-

nois River, the plankton is a very important factor in fish production.

In the Kaskaskia River, as an example of our smaller streams, the

plankton is so scanty that it can have very little importance. The San-

gamon River illustrates an intermediate stage in which the plankton is

abundant enough to enter into the food chains of fishes to some extent

but does not result in a yield of fishes appreciably greater than in the

Kaskaskia. The writer's observations of plankton development in the

upper part of the Sangamon from li)23 to li)2rt were included in a

general study on "Fresh-water Plankton Commimities," submitted as

a thesis in the Graduate School of the University of Illinois but not

yet published. Further collections, made during the summer of 11)2!),

showing the variety and abundance of organisms present at selected

stations along the lower part of the river as well as the ujiper part,

are reported in this paper.

The Sangamon River rises in McLean County and at first flows

eastward into the northwestern part of Champaign County, where it

turns southward and passes the villages of Foosland, Fisher, and

Mahomet. It then Hows in a general S()Uth\\cstwar<l direction acrcjss

[4fi!)]



470 Ii.Li.NOis Xatukal History Suisn-ey Bulletin

Piatt County, passing Monticello, and across Macon County, passing

Decatur. In Sangamon County, it receives its first large tributary, the

South Fork, and passes Riverton and Springfield. It flows northward

across Menard County, passing Petersburg. At its junction with Salt

Creek it turns westward. It continues in a generally westward di-

rection, forming the boundary between ilason County and Cass County,

passing the village of Chandlerville, and finally emptying into the Illi-

nois River about ten miles above Beardstown.

The length of the river is about 237 miles. The distance from the

source to Decatur is about 103 miles, from Decatur to Springfield about

59 miles, and from Springfield to the mouth about 75 miles. The total

drainage area is about 5,390 square miles, of which 1,940 square miles

belong to Salt Creek, and 846 square miles belong to South Fork.

The current of the river at normal levels is never very great, since

it flows through glacial till and occupies a well-worn valley. The river

falls 120 feet in the first 10 miles and 300 feet in the balance of its

course, or less than 2 feet per mile. The fall is far from regular, how-

ever, and there are many stretches where the gradient is very slight.

The bottom is usually sand or fine silt, the latter predominating over

most of the river.

Previous to 1923, no obstructions were encountered in the upper

course of the river except several small ruined mill-dams. At Decatur

a small dam raised the water level a few feet and held back a small

supply for municipal purposes. Below this dam the city of Decatur

discharged all its sewage, which usually was greater in volume than the

water flowing over the dam. During times of low water, the sewage

constituted the entire flow of the river below the dam. as all of the

water above the dam was then tliverted through the city water sujijily

system. As a result of the pollution, the river below Decatur was de-

void of normal aquatic life. Jewell (1920) reported no living organ-

isms immediately below Decatur except those accustomed to conditions

of pollution. Thirty miles below Decatur conditions were found to be

improving, but even at Sprmgfield, almost GO miles downstream, the

normal life was not completely restored. The writer was well acquaint-

ed with the river previous to 1920 and clearly remembers the extreme

condition of pollution existing for at least 20 miles below Decatur. The

bottom was covered with a thick layer of foul sludge, and the opaque

water, which varied in color from inky black to milky white, depending

on the season, contained large ([uantities of floating mouldy wa.stes.

At SpringfieUl a second dam has obstructed the river for many
years, raising the level of the water about six feet and forming a nar-

row pool that extends upstream several miles. Pollution below Spring-



Plaxktox of the Sangamon River 471

field has been largely eliminated since the city's sewage treatment plant

was put into operation, July 10, 193!). The wastes from Petersburg

and Chandlerville are not sufficient to pollute the river to an ajjpreci-

able extent.

In 1923 the city of Decatur, in order to increase its water sujiply,

completed a large dam across the river just above the site of the old

one, creating a lake one-half mile wide and 12 miles long. Later, in

1924, a sewage disposal plant was put into operation, handling one-

third of the city wastes, and in 1928 the plant was enlarged to accommo-

date all the wastes. This relieved the extreme condition of pollution.

The dredging of a new channel from Harristown for 20 miles down-

stream has aided by furnishing a new bed, free from the accumulated

bottom sludge. These changes have resulted in a fairly clean stream,

flowing through a lake-like reservoir in its upper region.

In the writer's previous study of the plankton of the upper river

from 1923 to 1928, inclusive, weekly or semi-monthly collections were

made from the river at Decatur and above. Very little plankton was

found above Lake Decatur in those years. At Mahomet, about 50 miles

from the source, no plankton forms occurred, though bottom organ-

isms, especially diatoms and |)rotozoans, occasionally appeared in the

collections. The same was true at Monticello during the greater part

of the year, but in mid-summer or early autinnn, when the water was

low, a scanty population of plankton organisms was found there. This

was the first point in the course of the stream where plankton ever

appeared. At Rhea's Bridge on the upper end of Lake Decatur, plank-

ton was present in the water during most of the year but was never

as abundant as at Lost Bridge, one mile above the dam. where many

plankton species were abundant from March until December. During

January and February the plankton of the lake was scanty and con-

sisted chiefly of protozoans.

In 1929, trips were made in June, July, and September, for the

purpose of collecting sam])les at intervals of about 20 miles over the

entire river. The collections were made from bridges at or near Ma-
homet, Monticello, Lake Decatur, Harristown, Illioijolis, Ri\'erton,

Springfield, Petersburg, and Ch;uidlerville. The method was to dip

the water fruiii mid-channel b\' JDwering a len-liler bucket on a rojie.

No stratification of ])lrmkton was noticed except at Lake Decatur,

where the current was negligible and the plankton was much heavier

near the surface. The ])rincipa! collecting station on the lake was at

Lost Bridge, and at this station a series of collections was made from

bottom to surface and averaged. Lach set of collections made at the

other stations consisted of a 100-liter silk-net collection and a one-liter



472 Illinois Natikal History SriiVKV Bllletix

collection which was preserved with formalin and allowed to settle and

then decanted iti order to obtain the nannoplankton. The organisms were

counted by the usual method in a Sedgwick-Rafter slide. All data were

computed per cubic meter. The volume of the plankton in the silk-net

collections was obtained by centrifuging for 3 minutes at 2000 revo-

lutions per minute. The volume of the decanted plankton was not de-

termined because of the large amoimt of silt present.

At the times of collecting, the river was 1-2 feet deep and 25-40

feet wide at Mahomet, the uppermost station, and 8-10 feet deep and

200-210 feet wide at Chandlerville, the lowermost station. The deepest

portion from which collections were made was in Lake Decatur \vhere

the depth in the channel ranged from 10 to 18 feet. Below Decatur

the river was quite shallow. It was 2-1 feet deep and 60-75 feet wide

at the Harristown and Illiopolis bridges. At Riverton. after the union

with the South Fork, the river was 4-6 feet deep and 100-111 feet

wide. At the bridge north of Springfield the water (backed up by the

dam) was 5-T feet deep and 100-110 feet wide. At Petersburg the

river was 100-150 feet wide and 7-10 feet deep in mid-channel.

The current, which was moderate at most places, was very slow

in some stretches of the river and somewhat swifter in others with a

greater fall. At JNlahomet and Alonticello, the current averaged about

one-half mile per hour during the summer. In the main part of Lake

Decatur no current could be detected. At Harristown and Illiopolis

the current averaged about one mile per hour; at Riverton one-half

mile per horn- ; and at Springfield just above the dam it was too slow-

to estimate. At Petersburg and Chandlerville it averaged a little more

than one-half mile per hour.

The river level was slightly above normal when the plankton col-

lections were made in Jiuie and July. The readings of the gage at the

Decatur sewage disposal plant averaged 58T.3 feet for June 25-27 and

587.6 feet for July 26-28. April and May were the highest months

for the year 1929, the gage at the disposal plant reaching a maximum
of 593.5 feet in those months. The lowest stage for the year was in

September, although the gage readings on the dates of collections,

Sc])tenil)er 10-12, averaging 581.0 feet, were not the lowest of the

month. Thus the river w;is about 3'/> feet lower in September than it

was when the June and July collections were made. The Decatur lake,

however, did not fiuctuate nnich. as the gage reading above the dam
was (ill). 25 in June and jul\- and ii()9,;i5 in September.

Tlie temperature of the water at the time of collecting was about

what would be expected under normal summer conditions. In June

it ransjvd from 2 1° to 25^C. and in |ul\- from 25' to 28 "C". Xo tem-



PlANKTO.N of TIIH SANliAMOX RiVElt 473

perature data were obtained on the Scpteinlier trip, as the therniuineter

was broken in the field.

Hydrogen ion determinations were made at all stations and were

found to run consistently about pH 7.(i. This seemed normal for the

river, as the readings agreed with those obtained by the writer in pre-

vious observations. On the upper river from 1023 to 192!), the read-

ings in summer always ranged around pH T.G, drop[)ing to pH 7.0 or

lower in winter.

Determinations of dissolved o.xygen in the water at each station

on the June trip were as follows: Alahomet 4."; 5 cc. per liter, Monticello

4.06, Decatur 4.G2, Harristown 4.06, lUiopolis 4.62, Riverton 4.25,

Petersburg 4.25, and Chandlerville 6.4T. No determinations can be

given for Springfield, as the June collections and data from that sta-

tion were accidentally lost. There was only a slight fluctuation in the

amount of dissolved oxygen in the water at the various stations. At

all points examined, the supply seemed sufficient for the support of

abundant aquatic life.

A summary of the plankton collections is given in Taljle I, and

the constituent organisms are listed in Tables II, III, and IV.

The general taxonomic composition of the jilankton found in the

river below Monticello was the same as that observed in most shallow

lakes and larger streams of North America. Certain typical forms

were conspicuous in their proper seasons, namely : two protozoans,

CodoiicUa cratcra and Ccratiuui lurundincUa; rotifers of the genera

Bmcliioiiiis, Syitc/iacta, Polyarthra, and KcratcUa; various cladocerans,

particularh- Moiiia affiiiis, Daplinia loiiijispiiia, and Bosiniiia loiii/i-

rostris; and two copepods, Diaptoiiuis siciloidcs and Cyclops bicnspid-

atus. A few bottom organisms, usually diatoms and protozoans, were

often conspicuous in the plankton collections from the shallow portions

of the river where the current could easily sweep them up from the

liottom. They did not often appear in the collections from Lake De-

catur but were quite common in the collecti(jns from the ntlicr stations,

especially at Alonticello, Idarristown and IlliopoHs.

The collections made in June showed no i)lankton at .Mahomet ;ui(l

only a very scanty plankton at .Monticello. The first heavy plankton

occurred at Lost Bridge in Lake Decatur. Both the volume of the

plankton and the number of species in the collections decreased down-

stream as far as Petersburg and Chandlerville, where the number of

species increased slightly, though the volume of the plankton contiiuied

to decrease. Of the 50 species observed in the collections from the

entire river in June, 36 appeared in Lake Decatur and 12 appeared

farther downstream in relatively small numbers. Evidently a large



474 Illinois Xatt-kal History Surx-et Billetix

amount of the downstream plankton owed its origin to the increase in

Lake Decatur. Characteristic species which were most conspicuous

in Lake Decatur and showed a decrease downstream were DifHugia

lobostouia, CodoucUa cnitcra, Brachionus angiilaris, Polyartlira trigla,

KcmtcUa cochlcaris. Aloiiia affiiiis, Daphnia lonciispina, Bosiuiiia longi-

rostris, Cyclops bicitspidatus, and Lysigomum (Mclosira) gramdatum.

Several other members of the plankton conspicuous in the lake did not

appear at all below. The flagellates, Trachcloiiionas volvociiia and

Euglcna viridis. decreased downstream to Petersburg and then started

to increase. The only form that showed a decided increase below the

lake was one of the algae, Actiiiastruiii liaiitcsclii.

The collections made in July showed that the plankton then had

a distribtition very similar to that of the preceding month. At Ma-

homet there was no plankton at all. and at Monticello it was very scanty.

Of the 58 species found in the July collections, 4T first became abundant

in Lake Decatur. Only S species occurred downstream which did

not occur in the lake, and these were usually rare or inconspicuous.

never forming an important part of the plankton. Many forms which

were conspicuous in Lake Decatur showed a decided decrease below

Decatur and apparently had their origin in the lake. Examples of

these were the following: Paiidorina iiioruiii, Plcodoriiw illiiioiscnsis.

CodoncUa cratcra, Difhugia lobostouia. Trachclonwnas cnsifcra. Eu-

glcna viridis, Ccratiuut liinindiiiclla, Eudoriiia clcgans. three species

of the genus Brachionus and species of FUinia ( Triarflira). Asplaiichiia.

Polyarthra. Synchacfa, Pcdalia. and Trichoccrca. ( Rattiiliis). and Lysi-

goniuui (Mclosira) graiiulatuni. Only a few forms which decreased

below Decatur showed a slight increase at Chandlerville. A peculiar

feature was an increase in the number of Cyclops bicitspidatus. Kcra-

tella cochlcaris, Diaphanosoma brachyiiniiii, and Brachionus aiigularis

at Harristown and Illiopolis. In general, the July plankton showed a

decided decrease below Decatur. Just as in June, the lake apparently

was acting as a reservoir, develoiiing an abinidant jilankton which was

then carried downstream and gradually thinned out in the lower river

as the water was diluted by tributaries.

The September collections were made under somewhat different

conditions from those in June and July, for the level of Lake Decatur

was slightly below the crest of the dam, so that little or no water

])assed over, and the chief source of the water in the river below De-

catur was the effluent from the city's sewage disposal plant. The cur-

rent in the river was not as swift as at higher river levels, and under

such conditions the larger tributaries, jiarticularly the South Fork and

Salt Creek, might he expected to add a small amount of ]ilankton.



Plaxktox of the Sancamox River 475

While there still were no plankton organisms found at Mahomet, the

plankton was more ahundant at Monticello than previously. In Lake

Decatur the collections were found to have a somewhat smaller volume

and to include fewer species than previously. Downstream from the

lake, however, many species, apparently originating in it. especially

protozoans and algae, showed a steady increase in abundance ; and sev-

eral species additional to the lake list make their first appearance just

below Decatur. Many conspicuous members of the plankton, par-

ticularly rotifers, appeared first at Riverton after the union with the

South Fork and were abundant downstream from there. A decided

increase in both abundance and species was noted at Springfield, which

may in part be due to slack water above the dam. A further increase

at Petersburg indicated that other conditions were favorable for greater

])lankton production.

Only a few species abundant in Lake Decatur showed a tendency

to decrease rather than increase downstream. These were Difflitgia

lobostoiiia, Codonclhi cnitcra. Brachio/iiis aiiijiihiris, KcratcUa cochlcaris,

and some of the cladocerans and copepods. Of the GG species found in

the September collections, only 25 occurred in Lake Decatur, and 3:5

species occurred in the downstream collections which did not appear in

the lake. Many of the latter showed a tendency to increase downstream.

The increase was marked at Springfield and Petersburg, indicating that

the lower river was maintaining a plankton population due in part to

the low water stage and the reduction of the current. Such conditions

in the river approach lake conditions, the waters remaining longer in

the pool-like stretches. Since no water was then coming directly down-

stream from the lake, all the water in the river was effluent from the

sewage disposal plant. Agersborg (1929) found this effluent to be

teeming with annelids, rotifers, copepods, protozoans and algae, and

states that these are organisms such as live in small ponds, though fail-

ing to mention any species which are typical of either clean-water or

sewage plankton. It is doubtful if many, or any at all, of the lake forms

survive passage through the sewage disposal plant, comjirising as it does

both sand filters, tanks and Dorr sc]):irators ; and still more doubtful

that there is any important develoijment of additional plankton species

until after the ])assage through the ]ilant is comiileted.

Sphacrotilns nalniis, although \ery aljundant in the sewage dis-

])osal plant, did not ajijiear at any time in the collections. It is probable

that the origin of many of the downstream i)lanklon species at this

period was ir, the quiter stretches of the river, which were seeded by the

plankton originating in the lake at times when the water was passing

over the dam.



476 Ii.i.ixois XATfRAL History SuR^EY Bulletin"

The question often arises whether the plankton in a given part of

a stream is developed there under local conditions or whether it is car-

ried down from u]istream. This survey indicates that, at times, part

of the plankton, at least, is carried downstream. Wiebe (192S) and

the Minnesota State Board of Health (1928) show that clean plankton

from upstream is carried through polluted areas in the Mississippi

below Minneapolis and St. Paul. In the ."^angamon the downstream

decrease oljserved in June and July may be due partly to the fact that

local development was not sufficient to counterbalance the dilution

from tributaries. In September, when the low stage of the water

cut ofT the direct supply from the lake, local conditions down-

stream became more favorable for the development of plankton.

When the current becomes \ery slow, the development of plank-

ton becomes local and is governed by local conditions. If the cur-

rent averaged one-half mile per hour, the time required for water

to flow from the source to the mouth would be about 20 days. How-

ever, at normal stages the river has many pool-like stretches which re-

tard part of the water, and rough estimates of the period of detention

in the lake at Decatur range from two weeks to two months, depending

on the river level. Thus the water remains in the lake at least twice as

long as in the rest of the river. The water and the plankton it bears

as it flows over the dam at Decatur will ordinarily be in the neighbor-

hood of Chandlerville about a week later. In this way. at normal levels,

there is a continual stream of water carrying plankton from the lake

and passing downstream. Even though the downstream conditions are

not favorable for plankton development, it seems possible for the water

to retain part of the original jilankton load for a week or more, so that

a series of collections made at various points in the lower course of

the river do not represent the development of plankton at each point

but give glimpses of various stages of senescence as the plankton moves

away from its source. It may be possible that the plankton observed

downstream in September had originated from the lake wlien the water

was still flowing over the dam, and that it was still progressing down-

stream. This, however, would hardly explain the origin of the plank-

ton observed in the river immediately lielow Decatur.

No evidence of the former pollution was observed in the plankton

of the Sangamon River. No pollutional organisms were found at Har-

ristown, about eight miles below Decatur, where Jewell ten years earlier

had found the plankton to be characterized by Sf'lwcrotihis ihitaiis.

nematodes, ciliatcs, and creejiing rotifers, with desmids and phytofiagel-

lates common when the water was high. In this area in 1!>2!) the plank-

ton was tvpical of clean water and was characterized by Codoiiclla era-



Plankton of the Sangajiox River 477

tcra. Pol\artlini triiila, rotifers of the genus Bracliiniius, Cyclop's biciis-

pidatiis, cladoccraiis. and Lysigonium (Mclosira) grannlatuui. Jewell

found the dissolved oxygen usually low in that part of the river,

especially during periods of low water. The determinations of dis-

solved oxygen made in lil2!) showed an abundant sujiply. The sludge

which was formerly so abundant had nearly disaj)peared, the water

was clear, and a number of fishes were observed.

Very little is known regarding the former condition of the plank-

ton below the jjolluted part of the river. Jewell's studies in 1918-1919,

which extended only as far as Springfield, showed that the influence

of pollution had ])artly ceased there and that a few typical clean-water

plankton organisms were present in the river at that point. The abund-

ant clean-water ]jlankton now found in that part of the stream, includ-

ing many more species than were reported by Jewell, indicates that the

plankton population in the lower river is much greater than formerly,

and this is due, no doubt, to the creation of the lake at Decatur and to

the removal of the jiollution barrier.

BIBLIOGRAPHY.

Agersborg, H. p. K.

1929. The Biology of Sewage Disposal. A Preliminary Study. Trans.

Am. Micros. See, Vol. 4S, pp. 158-lSO.

Greeley, S. A., and Hatfield, W. D.

1928. The Sewage Disposal Works of Decatur, Illinois. Proc. Am. Soc.

Civil Eng., Vol. 92, pp. 2237-22S6.

Jewell, M. E.

1920. The Quality of Water in the Sangamon River. 111. State Water
Surv. Bui. No. 16, pp. 230-246.

Minnesota State Board of Health.

1928. Report of the Investigation of the Pollution of the Mississippi

River from Minneapolis to LaCrosse. Metropolitan Drainage

Commission of Minneapolis and St. Paul, 2nd Annual Report,

pp. 90-102.

WiEBE, A. H.

1927. Biological Survey of the Upper Mississippi River with Special

Reference to Pollution. U. S. Bur Pish. Bui., Vol. 43, pp. 137-167.



478 Illinois Natural HisToity Survey Blxletix

Table I.

SUJIJIABY OI' PlANKTOX COLLECTIONS, Sangamon River. 1929.

station



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