Bulletin STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE NATURAL HISTORY SURVEY THEODORE H. FRISON, Chief Vol. XIX. BULLETIN Article IV. The Plankton of Some Sink Hole Ponds in Southern Illinois BY SAMUEL EDDY PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS SEPTEMBER 1951 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION M. F. Wai.sii, Director BOARD OF NATURAL RESOURCES AND CONSERVATION M. F. Walsh, Chairman William Tkklha.sk, Biology Henry C. Cowi.es, Forestry Edson S. Bastin, Geology William A. Noyes, Clicmistry Joiix W. Alvord, Engineering Ciiakles M. Thompson', Represent- ing the President of the Univer- sity of Illinois STATE NATURAL HISTORY SURVEY DIVISION TiiEODoiiE H. Fiiisox, Chief H. C. OKsri.iiLiNG. Editor ScHiNnri' & Barnes, Printei!; Springfield. III. 1331 5S5S7 — 1200 VoLU.MK XIX. AUTICLf: IV. THE PLANKTON OF 80ME SINK HOLE POND8 IN SOUTHERN ILLINOIS S.\MUEL Eddy Sink holes arc ahuiidant in various parts of Illinois, espccialh' in the extreme southern jiortion of the state. Their circular or oval tun- nels are common in areas underlain with limestone. The general con- ception of their origin is that water moving through the limestone dis- solves away part of it so as to form underground chamhers, the roofs of which settle and cause surface depressions that become filled with water draining from the surrounding land. Cummings (l'J05) ad- vanced the idea that the majority of sink holes, particularly those of southern Indiana, were only enlarged funnels produced by the pene- tration of surface waters into the limestone, and according to this idea such bodies of water have been referred to sometimes as "solution ponds." The sink holes studied in this pajier, however, were probably produced by the first method, which is the more generally accepted among geologists. All such sinks originally have no other drainage than a vertical ])it in the center extending to the subterranean outlet. The younger sinks are usually small and deep with steep sides extending to the pit. In the older sinks drainage from the pit is obstructed by falling rocks and eroded soil, so that the water accumulates to form a jrond, though drainage is frequently maintained to some extent through the j)it. As a result of further erosion of the sides and deposition of the silt washed in after each rain, the pond gradually fills and becomes only a low place containing water in wet seasons. The water from these sinks is generally considered as a source of supply to underground streams and springs. Kofoid (]SI)!)) states that the sink holes in the vicinity of Mammoth Cave, Kentucky, su]5ply the water for tlu- cave streams and the surrounding surface sjirings. All iif the twenty organisms that he fimnd in the water of I'xhn River in Mammoth Cave seemed to l)e characteristic of the surface waters aufl to originate from ])onds in connected sink holes. Plankton organ- i>ins were rare in F.cho River, and only si.K of those fdimd were true |iond forms. Scott (IIJO!)) found that the underground streams in the vicinity of Shawnee Cave in southern Indiana were similarly fed [449] 450 Illinois Xatiflvl Histoi;y Siuvev Billetin l)v water from sink hnlcs and that the jjlankton of these streams origi- nated in the jionds on the surface. Scott (liHl) observed the fauna of a sink hole ]X)nd in southern Inthana over a period of several years and reported a faiinal hst containing a few plankton organisms. A sttidy of the ])lanktMn of such ponds is of interest because of the additional information thus obtained regarding pond organisms and because of the jxissibilities of their relation to cave fauna. .\lso. as the ])onds may l)e the sources of the large springs for which these regions are noted and often jiopular. the contents of their waters are important as possible sources of pollution. Sketch map showing location of ponds (l-H) and spring (7). Scale: 2% inches equals 1 mile. The ponds sludied li\' the writer are located three-fourths of a mile northwest of Wetaug, Illinois, on the farm of -Mr. R. W'iard in Pulaski County. The Lower Mississijipian limestone which underlies this region contains nian\- caves, and the numbers of its subterranean passages are indicated by the numbers of springs in the valleys. More than a dozen large sinks lilled with water and many others small and empt\' are to be found within a radius of one-half mile from the ponds studied. The larger sinks contain water at all seasons of the year. During the rain\ se:i-'ons the le\-el rises a few feet but soon drops to normal. Plankton ok Sink Holk Ponds 4yl Perennial Ponds Three perennial ponds of different sizes were selected for study. They are indicated by the numbers 1, 2, and 3 on the accompanying ma]). ^Ir. \\'iard stated that by ])robing through the ice he had found a pit in the center of each. The largest pond (No. 1 ), located one- eighth mile north of Mr. W'iard's house, is probably the oldest of the group studied. The sides have eroded, enlarging the boundaries of the pond until it covers about five acres, and the deposition of the eroded clay has filled the bottom so that it slopes very gradually to a depth of 20 feet in the center. No vegetation is apparent except a few small willows. The next largest pond (No. 2), aljout 150 feet in diameter, lies alrout oOO feet south of the house. Clay has washed in until the bottom slopes gradually to a depth of about 20 feet in the center. There is no vegetation about this pond. The smallest and deepest, and therefore youngest, pond (No. 3) lies southwest of the house. It is about 1 '> feet in diameter with a steep mud bottom sloping to a reported depth of about 40 feet. Half of this pond is shaded by oak trees on the west bank. Silk-net collections were made from Pond No. 1 on April 17, 1937, and again on .\pril Ki, ID^S. In these preliminary collections the fol- lowing forms were found : Lysigonium varians (Ag.) D. T occasional Synedra ulna (Nitz.) Ehr occasional Coelosphaeriuni kuetzingianum Nag rare Spirogyra spp common Netrium digitus (Ehr.) Itz. & Roth very abundant Closterium acerosum (Schrank) Ehr very abundant Pleurotaenium sp common Micrasterias americana ( Ehr. ) common Difflugia urceolata Carter occasional Ditflugia globulosa Duj occasional Dinobryou sertularia Ehr common Eudorina elegans Ehr common Volvox globator Leeuwenhoek common Rotaria neptunia (Ehr.) rare Conochiloides dossuarius ( Hudson ) occasional Polyarthra trighi Ehr common TrichociTca multicrinis (Kellicolt ) common Lecane ungulata (Gosse) occasional Keratflla cochlearis (Gosse) abundant Notholca longispina (Kellicott) rare Diaphanosoma brachyurum (Lioven) occasional Bosmina loiigirostris (O. P. M.) abundant Alona sp rare Chydorus sphaericus ( O. V. M.) common Diaptonius niississippiensis Marsh common Cyclops bicuspidatiis Claus abundant Copcpods (immaluro) common 452 Illi.noi.s Xatiiial History SritvEY Billetix Table IV shows the results obtained from collections made from Ponds Nos. 1, 2. and :] in July, September, and December. ]!t2.s. and in April. ]!(:^!). Usually filter-jjaper collections were made simultaneously with the silk-net collections and used to furnish data on the smaller planktonts. The abundance of the organisms was determined by the usual counting method in a Sedgwick-Rafter slide. Some of the chemical conditions of the ponds were determined in an effort to find any differentiating factors which might influence plankton distribution. Water samples collected December 1, 1928, were submitted to the Illinois State Water Survey for determination of the chlorine in chlorides and of alkalinity ; determinations of the dis- solved oxygen content were made September 12 and December 1. 1928; and temperature and pH readings were taken on several occasions (Table I). Frf)m these limited data on chemical and jihysical condi- Takle I Phy.sical anm) Chemicai. DAT.^. on Pokd.s Nos. 1, 2. and 3 Date 1928 Determination No. 1 No. 2 No. 3 Dec. 1 Chlorine In chlorides, p. p. m 16 1 Dec. 1 Alkalinity, phenolphthalein, p. p.m.... Dec. 1 Alkalinity, methyl orange, p. p. m 24 10 10 July 20 Temperature, C 29 29 28 Sept. 2 Temperature, C 26 26 26 Dec. 1 Temperature, C 9 9 9 July 20 Hydrogen ion concentration, pH 6.6 6.6 6.8 Sept. 3 Hydrogen ion concentration, pH 7.1 7.6 7.4 Sept. 3 Dissolved oxygen, cc. per liter 4.443 4.99S 3.605 Dec. 1 Dissolved oxygen, cc. per liter 6.424 6.118 5.659 tions, there seems to be little difference in the waters of the various ponds. Some variations occur, but they are not as great as those often found between two streams with the same type of fauna. The dis- solved salt content is partially indicated by the determination of the chlorine in chlorides. This factor was negligible in Ponds No. 2 and No. 3 but quite noticeable in Pond No. 1. It is obvious that the origin of the dissolved salts is in the soil washed by the water draining into the jionds, since the only apparent source of the water of the ponds is rain water from the surrounding basins or slopes. Pond No. 1 not only occupies a larger area but has a nuich larger drainage basin in pro]iortion than the other ponds studied. Conse(|uently. as the water of this pond was subject to more soil wash, it would be expected to have a greater dissolveil salt content. Pr.AXKTox OK Sink Hoi.ii Poxus 453 These three ponds contained a rich planlcton. Many more species were found than were recorded liy Scott (liM 1 ). A total of 128 species was found in the plankton of the three ponds. With slight differences in the lists, 81 species occurred in the north ])ond ( Xo. 1 ) the same number in the south ])ond ( No. 2 ) , while the southwest pond (No. ;!) had 90 species (Table II j. As far as volume was concerned, there was little difference between the total amount of plankton in each pond. The silk-net collections for July and September averaged 18 cc. per cubic meter, and the hlter-i)aper collections for the same dates averaged 183 cc. per culjic meter. The species which were common to all the ponds usually were those which were abundant in each. The exceptions to this will be discussed later. There were no greater dif- ferences in species or in their alnmdance in the collections of the same date from the three ponds than often occur in collections made simul- taneously at short distances from each other in the same pond or T.\BLE II Numbers of Species Pound in Ponds Nos. 1, 2, and 3 Organisms No. 1 No. 2 No. 3 Algae 33 30 31 Protozoa 21 16 25 Nematoda 1 1 Rotatoria 17 20 20 Cladocera 5 9 9 Copepoda 4 3 4 Ostracoda 1 Iiisecta 1 1 Total 81 81 90 stream. Thirty-seven species were common to the three ]3ons ziridis, and Cyclops bicuspidaliis. These are cosmopolitan forms, commonly found in nearly all Ijodies of fresh water. The ]ilankton thus was characterized by the ])resence of certain species abundantly distributed in all the ptjnds and by the absence or scarcity of other species. Diatoms, usually so ainindant in ]iond and stream plankton, were noticeably rare. Syiicdni ulna was the only diatom found in all the ])onds. Syucdra U'liiiissiiiui and species of I'mgilaria and Lysii/diiiiiiii. usualK- found in bodies of fresh water, were either absent or relatively 454 Illinois Xatural History Sukvey Billetin scarce. Pearsall (1923) has noted that a lack of essential mineral elements may be responsible for the decreased diatom population in the plankton of ponds, and that an increase in mineral content usually occurred after rains and was accompanied by an increase in diatoms. It is interesting to note that two common species of the typical plank- ton genus Lysigoniuiii occurred in Pond Xo. 1, which was the only pond with an appreciable dissolved salt content as indicated by the determination of the chlorine in chlorides, and bottom diatoms were particularly abundant in the small temporary pools occupying the basins of the filled sinks, where the water was generally greatly re- duced by evaporation and it is possible that the dissolved salt content may have been rather large. Algae, especially the blue-green forms, were usually abundant. In July and September, Ponds No. 1 and Xo. "2 contained a rich population of blue-greens. Pond Xo. o. whicli was deeper and ecologically younger, did not have these forms in any abundance. Coelosphacrium iiacycliaiium, Anahacna plaiiktouica, and A. spiroidcs formed a bloom on the first two ponds in July and September. The total number of species of algae found in the three ponds was 52. The common phytoplanktonts of the genera Scciicdcsmiis and Pc'd lastruin were never as abundant as in rivers and in ponds generally. Most of the species of rotifers are those which are quite common in rivers and poricls generally, but several were noted which were characteristic of these sinks. Triclwccrca iniilticrinis occurred in all the ponds but was much more abundant in the north ]»nd ( Xo. 1 ) most of the time. Although occasionally found elsewhere in Illinois, this species does not usually occur as abundantly or as uniformly as it did here. It was seldom absent from a collection and was always aliundant in one or more of the ponds. Rotifers of the genus Sviichacta were entireh- absent, and those of the genus Bnicliloiiiis were very scarce with the exception of Bracliioiiiis f^aliihis. whicii is hardly a typical species. Both of these genera usually form a characteristic part of the plankton of ponds and large rivers, and their scarcity here constitutes a negative character of the plankton, 'i'his may be due in part to a lack of necessary mineral elements or to a slight temporary acidity of the water ( Harring and Myers, 1H28). As collections were made from tliree ponds, it is hardly possible that these rotifers could have been abundant in any pond between the dates of collections. In many southern waters in the State of Mississippi, in Reelfoot Lake in Tennessee (Eddy, 1 !);!()), and in the floodplain lakes a few miles to the south of the sink holes under discussion, the writer has found most species of the genus I>ritcliioinis to be rare. In many jionds and lakes in the Plankton of sink Hole Ponds 455 central part of Illinois and in the Illinois and Rock rivers, these forms are very abundant and often are characteristic of the ])lankton. Information cm the geographical distritnUion of these circum-jjolar and supposedly cosmopolitan rotifers is not sufficient to establish their range definitely, hut their rarity in southern c(jl!ections makes it seem possible that thev have a southern limit. Thirty-one species of Protozoa were found in the three ponds. The common pond types, such as Ccratimn hintndincUa and Codonella cratcni. were well distributed. The plankton was further characterized by the rather unusual abundance of various species of Tnichcloinonas and of Pcrid'iuiitm cinctum. Trachcloiuonas voh'ocina was abundant at all times. \n unusually interesting form was found in irachclo- iiioiias iiiagdalciilaiiu, which was descriljed by Deflandre (\'.)'iii) from a single specimen from \'enezuela, but never reported, as far as is known, from any other place. This s])ecies was found commonly in Ponds No. 2 and No. •! in the summer of 1i)28. and in various other waters of the southern part of Illinois during the same season. Copepods were very common. Cyclops z'iridis was observed in most of the collections. Cyclops biciispidatus occurred as a spring form in the .\pril collections. Diaptomus inississippiciisis, generally regarded as a southern species, appeared as a spring form in Pond No. 1 in 1928 and in all the ponds in April, 1929. Temi>ok.'\kv Ponds In Old Sink Holes Random collections were made also from three small sink holes (see 4, 5, and li on the map) which contained shallow temporary pools having an abundance of vegetation, chiefly grasses and cat-tails. These were old sinks that had filled with clay until they had become very shallow. There was no longer any evidence of any \nt or under- ground drainage. Such jwiols. therefore, have no influence on the sub- terreanean waters. A ^niall ])ool (No. o). near Pond No. 1, contained a heavy red bldom (if linglcna sanguinca July 29, 192s. As the water was only alxiut si.x indies dee]J, the plankton was highly concentrated. Bottom diatoms constituted half of the bulk of the forms ])resenl. Protozoa, especially the chlorophyl-bearing forms, constituted the other half. This aggregation of organisms can hardly be called plankton, because the ])of)l was so shallow that they were ]iracticaily living on liie bottom. Nevertheless, except for the bottom diatoms, they were forms which are found normally in plankton, .\lgae were scarce. The plankton here included si.x forms not found at this time in I'oiul .\o. 1 : two rotifers ( Moiiostyla quadyidcutata and LcpadcUa acnininata) . three 456 Illinois Natural History Survey BuLLErrix protozoans (Englena sangiiiiiea, Eugleiia viridis, and Pleodoriiia iUinoiscnsis), and one alga fCosinariiiiii deprcssum). This pool was dry September 3, 1028. .\notlier similar pool (Xo. 6), near Pond No. 3, also had a heavy red bloom of Euylciia sangitinca and contained an abundance of diatoms. Only a few other species, however, were found here. ArccUa z'uhjaris, usually a bottom form, was abundant, though it did not appear in the collections from the nearby perennial pond ( Xo. 3). Another small sink hole ( Xo. ij, near Pond Xo. 1. contained a temporary pool 2 feet deep and 20 feet in diameter in April and July, 1928. This sink was dry in September. 1928. At the time of collecting, the organisms were not as concentrated as in the other temporary pools but represented many more species. The data of this pool are not listed, as they are very similar to those of Pond Xo. 1 for the same date. They comprise 35 species, all of which occurred in the nearby pond (No. 1) at the same times. It is interesting to note that this temporary pool was slightly deeper than the other temporary pools and that the plankton here resembled that of the larger perennial ponds rather than that of the smaller temporary pools. Tahlk III Counts of Okganis.ms per Cubic Meter from Tempokauy Poxns Nos. 5 axd 6 Organisms Pond No. 5 July 20. 192S Pond No. 6 Sept. 3. 192S Undetermined diatoms Cosmarium depre.ssum (Nag.). Spirogyra sp Arcella vulgaris Ehr Difflugia lobostoma Leidy Euglena sanguinea Ehr Euglena spirogyra Ehr Trachelomonas ensifera Daday. Trachelomonas volvocina Ehr.. Trachelomonas hispida (Perty) *PIeodorina illinoisensis Kotoid. Peridinium sp Polyarthra trigla Ehr Lepadella acuminata (Ehr.) .. Monoslyla quadridentata Ehr. . Brachionus patulus O. F. M 12,000.000,000 3.000.000 10,000,000 10,000,000 2.000.000 1,000.000.000 80.000.000 3.000,000 1.000.000 50.000.000 40,000.000 2,000,000 1.000.000 20,000.000.000 10.000,000 10.000.000.000 50.000.000 30.000,000 1,000.000 6.000.000 * Colonies. The plankton of all these temporary remnants of old ponds con- tained the same species of organisms as were found at some time or Dtlier in the younger and dcejier permanent ponds, with the exception (il l:iii/lciia sdiigiiiiu'd and /;. spirogyra. which formed the liloom. Plankton oi- Sink Hoik Ponhs 457 Relation of Sink Hole Ponds to Springs As Scott and Kofoid found that underground waters in the re- gions of sink holes were contaminated by surface pond organisms, an attempt was made to ascertain if there was any evidence that the sjirings of this locality were connected with the surface ponds. The most accessible spring (No. 7 on the map) was located on the road one-fourth mile from Wetaug and one-half mile from the sink holes. Plankton collections were made from this spring on October \'i, 1928. Only a few organisms were found, twelve of which were identified. These are listed below, with average counts of their abundance per cul.)ic meter : Surirella robusta Ehr 800 Undetermined diatoms 400 Oscillatoria sp. ( filaments ) 40,000 Arcella vulgaris Ehr 2,400 Difflugia acuminata Ehr 320 Nematodes 16 Cyclops viridis Jurine 1,600 Cyclops serrulatus Fischer 3,200 Immature copepods 4,800 Cliironomid larvae 160 *I'Mlinia longiseta (Ehr.) 16 *Brachionus angularis Gosse 15 *Keralella cochlearis (Gosse) IS Nine of these were living and. with the exception of Cyclops scrndaliis (a temiiorar)- pond copepod ) , could occur naturally in either the spring or in the sink hole ponds. The other three, which were rare and ])artly disintegrated, were rotifers: biUni.i loiu/iscla, Bracliioiiiis aiii/uhiris. and KcratcUa cochlearis. all of which also oc- citrred in the collections from the sink hole ponds. None of these three forms would be exjiected to live under normal conditions in a spring. It wnulil be difficult to determine whether this sjiring was connected with the particular ponds studied. The use of dyes in the ponds could not be attempted in this brief study. The presence of the three battered rotifers mentioned may be accepted as probalile evi- dence of the origin of the water from these or similar ]ionds. The other species were either tvpical of s])rings or tolerant nf the condi- tions under which they were found. Conclusions .\n abundant plaiiktmi was luund in the sink hdle ponds studied. It was of the same general composiliun in all nf the ]ierennial ponds, * Partly clisiiilcKratirl pluTilOoii oifjani.sm.s bcliiiiKing tn iiond ]ilaiikl(m. 458 Illinois Natuiial History Sup.vet Bvlletix exhibiting only minor variations, which consisted chiefly in the presence of a few species, usually inconspicuous, in one pond that were apparently absent in another. The jj'.anktun of these ponds, though similar in some respects to that of rivers and of other ponds, is distinguished by the abundance of several characteristic species, such as Trichocerca miilticrinis. and by the absence or scarcity of certain other species, notably rotifers of the genus Brachioiius which normally occur in pond jjlankton. The ponds ranged in age, both geologically and ecologically, from a deep perennial pond in an apparently recent sink hole to temporary ponds in old sink holes that had become nearly filled. Though diflfer- ing in their depths and areas, the perennial ponds all contained the same type of plankton ; that is, the predominant forms in each pond were largely of the same kinds. Two of the temporary ponds con- tained plankton which differed distinctly from that of the perennial ponds. In a third temporary pond, which was deeper and apparently younger, the plankton was more like that of the perennial ponds. Some of the species common to the perennial ponds were retained in all these temporary ponds, but they were mingled with bottom species to form a characteristic aggregation which may be called ])Iankton only in a broad sense. To a certain extent, this series shows developmental stages in the trend of the plankton community as the ponds grow old and gradu- ally fill. As long as a pond remains in the perennial stage, containing water throughout the year, the plankton shows little change, but as the depth decreases and the pond reaches the temporary stage, con- taining water onlv in the rainy seasons, the plankton organisms mingle with those from the bottom in an aggregation characteristic of very shallow water. At this stage it is interesting to note how tenacious of their habitat certain pond planktonts are, for they persist almost as long as there is water left in which they can swim. Ultimately these aggregations disappear before an invasion of shore and vegeta- tion organisms as the ]X)nd becomes merely a wet depression in a terrestrial habitat. There is incomplete evidence that the plankton population of nearby sjirings is derived from ]Hinds in sink holes. This is im- portant because in many cases farm buildings are located on the slopes draining into the sink holes and coukl easily pollute the waters fornu'ng the source for nearby springs. b'ach of the ])erennial ponds contained an abundance of algae of numerous species, which seemed to balance the heavy animal ]iopula- F^A.NKTox OF Sink Hole Ponds 459 tion. Thus the plankton community was apparently self-supijorting with regard to producers and consumers. Sink hole ponds, because of their relative stability in regard to water level and plankton content and because of their small size, should offer an interesting opjiortunitv for further study on the dynamics of atjuatic communities. BIBLIOGRAPHY CVMMI.N'G.S, E. R. 1905. On the Weathering of the Subcarboniterous Limestones of In- diana. Proc. Ind. Acad. Sci., Vol. 15, pp. 85-100. Defi-andre, Georges. 1926. Monographie du Genre Trachelomonas Ehr. Thesis, University of Paris, pp. 1-162. Ediiy. S. 1930. The Plankton of Reelfoot Lake. Trans. Amer. Micro. Soc, Vol. 49, pp. 246-251. H.VBRixo, H. K. AND Myers, F. J. 1928. The Rotifer Fauna of Wisconsin. IV. The Dicranophorinae. Trans. Wise. Acad. Sci., Vol. 23, pp. 667-808. KOKOID, ClIAS. A. 1899. The Plankton of Echo River, Mammoth Cave. Trans. Amer. Micro. Soc, Vol. 21, pp. 113-126. Pearsaix, W. H. 1923. A Theory of Diatom Periodicity. Jour, of Ecol., Vol. II, pp. 165-183. Si OTT, Wnx. 1909. An Ecological Study of the Plankton of Shawnee Cave, with Notes on the Cave Environment. Biol. Bull., Vol. 17, pp. 386- 406. 1910. The Fauna of a Solution Pond. Proc. Ind. Acad. Sci., Vol. 20, pp. 395-442. Wi.nki.er, L. W. 1888. Die Bestimmung des im Wasser zelosten Sauerstoffes. Berichte der deutschen chemischen Gesellschaft, XXI, Bd. II, p. 2893. 460 Ii.i.ixnis NATfiiAi, HisToiiV StnvEY BrLi.ETix a. o Plaxktox ok Sink Hole Ponds 461 OOO LS O O to ro o T^ o-s ^' 462 IlJ.I.NOIS XaTLISAL HlSTOIiY SURVEY BULI.ETIX Plaxktox of Sink Hole Ponds 463 ^ CO "-C "r ci to '*^* oT '*^ <=^ C^ C- 464 Illixoi.s XAxriiAf. Histohy Slkvey Bulletix ©JO . t?2 •-= Oh o o o o IS 30 Pi.AXKTON OF Sink Holk Poxds 465 <0 C' O Ci o o o o '>*' o o o m m o CO CO CD^ ^ tH t- C^ O O = c: CD O O L'5 C^l C-; M o^ c>i oT oc — o o !=! O '=>o o so o o in o 5 o o o o c3 ?i CD M O 466 Illinois Xatukal Histouv Slkvey Billetin o o o o o O O <=5 CO o Lfl O -O to 00 c-^ ci o' c:* M to 1-HM i-H rH o o =; -J5 m O to to o o o oo o o -(J. o o C3 O Ci o oO O O iH (M CO Tt* O CO CO ooooo<=>oooooOOOOOOOC'lO'OO o = • Plaxktox of Sink Hulk Ponds 467 ooooooooooocooooo to J"^ Tf CO CD O O li^ 51* CT> CD O lO M o o — O' o o O' o o