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THE

[TEXAS JOURNAL OF SCIENCE

^ a ^ $

STAGE X

SECTION I

MATHEMATICAL SCIENCES

Mathematics, Statistics, Computer Science, Operations Research

SECTION VI ENVIRONMENTAL SCIENCES

SECTION II

PHYSICAL SCIENCES

Astronomy Chemistry Engineering Physics

SECTION V

SOCIAL SCIENCES

Anthropology Education Economics History

SECTION III EARTH SCIENCES

Psychology

Sociology

Geography

Geology

SECTION IV

BIOLOGICAL SCIENCES

Agriculture

Botany

Medical Science Zoology

AFFILIATED ORGANIZATIONS

Texas Section, American Association of Physics Teachers Texas Section, Mathematical Association of America Texas Section, National Association of Geology Teachers

GENERAL INFORMATION

Membership. Any person engaged in scientific work or interested in the pro¬ motion of science is eligible for membership in The Texas Academy of Science. Dues for annual members are $7.00; sustaining members, $15.00; life members, at least $100.00 in one year; patrons, at least $500.00 in one payment; corporation members, $100.00. Dues should be sent to the Secretary-Treasurer.

Texas Journal of Science. The Journal is a quarterly publication of The Texas Academy of Science and is sent to all members. Institutions may obtain the Journal for $7.00 per year. Single copies may be purchased from the Editor.

Manuscripts submitted for publication in the Journal should be sent to the Editor, P.O. Box 5015, North Texas Station, Denton, Texas, 76203.

PUBLISHED QUARTERLY AT AUSTIN, TEXAS (SECOND CLASS POSTAGE PAID AT POST OFFICE,

AUSTIN, TEXAS 78712).

Volume XX, No. 1

MAY 28, 1968

CONTENTS

Earliest Known Eutherian Mammals and the Evolution of Premolar Oc¬ clusion. By Boh H. Slaughter . 3-12

Relationship Between the Chemical Limnology and Raw Water Quality of a Subtropical Texas Impoundment. By R. B. Higgins and E. G.

Fruh . . 13-32

Fauna of the Aransas Pass Inlet, Texas. III. Diel and Seasonal Variations in Trawlable Organisms of the Adjacent Area. By H. D. Hoese,

B. J. Copeland , F. N. Mosely, and E. D. Lane ...... 33- 60

On A Unique Earthworm Species Native to Texas. By G. E. Gates . . 61- 67

Rodent Numbers on Different Brush Control Treatments in South Texas.

By Jeff Powell . . 69-76

Characteristics of Proteolytic Activity of Pepsin from Rana catesbeiana.

By Jim D. Boston and Charles R. Willms . 77-86

NOTES

Chromatic Behavior of Some o-, m-, and p-Derivatives of Phenylalanine.

By Joan Becker and C. G. Skinner . 87- 89

Inhibition of the Conversion of Prothrombin to Thrombin by Choline and

Acetylcholine. By Henry G. Norrid and William A. Cooper . 89- 91

5-OH Tryptamine Content in Rat Brain Tissues X-Irradiated In Vitro.

By J. B. Lott and J. F. Hines . . . . 91- 94

Social Tendencies in Perognathus hispidus. By P. Kelly Williams . . 95- 96

The Importance of Clear Writings. By Junetta Watson Davis . . 97-102

EDITOR’S NOTE

It has been a long-standing policy for the Texas Journal of Science to publish only reports of original research or review articles. This has restricted the scope of the Journal and perhaps limited its usefulness and interest.

With this issue a new section, “Dialectic,” is added in the hope of attracting comments, conversation, and perhaps controversy, from readers anywhere. Do you have an opinion about science, education, conservation, or any other subject of potential interest to members of the scientific community? Do you want to write a letter to the Editor? Carry on a dialogue or exchange opinions? This is your section. I hope you use it. I also hope that the name chosen for this section will encourage the “art or practice of logical discussion.”

“Dialectic” is inaugurated with an article by Junetta Watson Davis on a subject dear to an editor’s heart, “The Importance of Clear Writing.”

Gerald G. Raun

Earliest Known Eutherian Mammals and the Evolution of Premolar Occlusion

by BOB H. SLAUGHTER

Shuler Museum of Paleontology

Southern Methodist University , Dallas , Texas 75222

ABSTRACT

Submolariform premolars recovered from Early Cretaceous (Al- bian) deposits in north-central Texas are offered as evidence of euther- ians or at least protoeutherians. Although certain marsupials have specialized premolars, none are known to have premolars which mimic the molar pattern. Such molarization of eutherian premolars is nearly universal.

Molarization of eutherian premolars apparently began earlier and extended farther forward in the superior series than in the inferior series and primitive forms almost always have one more upper pre¬ molar containing a protocone than lower premolars with metaconids. There is evidence that all major eutherian groups have passed through a stage in which protocones were present on both P3 and P4 and P4 contained a well developed metaconid. Furthermore, it appears that this stage may have been reached by Albian times.

INTRODUCTION

In 1956 Patterson described the oldest fossils referable to mammals of eutherian-metatherian grade, with the possible exception of Endo- therium . His material was collected from the Greenwood Canyon locality in Montague County, Texas about 100 feet below the top of the Trinity Group (Albian). Due to the fragmentary nature of his specimens, he did not propose formal names. More recently I (Slaugh¬ ter, 1965) described fossil material from the Butler Farm locality in Wise County, Texas about 20 miles south of Greenwood Canyon and at about the same horizon. A new family, Pappotheriidae, was pro¬ posed, but the order and infraclass were left incertae sedis. Since that time the Butler Farm locality has produced additional material which leaves little doubt that eutherian mammals are present in the fauna. The evidence consists of premolars which are submolariform a spe¬ cialization unknown in marsupials.

4

THE TEXAS JOURNAL OF SCIENCE

DESCRIPTION OF NEW MATERIAL

The lower premolar (SMP-SMU 61947; Fig. 1; D, E, & F) is con¬ sidered P4. There is a well developed metaconid developed one third the height of the protoconid. Its apex is lingual and slightly posterior to the apex of the protoconid. The metaconid arises from an internal cingulum. The paraconid, if we may so call it, is merely a broadly triangular shelf with its anterior apex truncated. A small ridge con¬ nected with the base of the metaconid and forming the lingual border of the shelf is slightly elevated. An ill-defined blunt cuspule which may have given rise to a more typical paraconid is present in the middle of the shelf. Lingual to this the shelf slopes downward and pos¬ teriorly to become confluent with a cingulum extending back almost to the middle of the protoconid. The talonid is roughly rectangular with a faint ridge squaring its posterior edge. The lingual end of this posterior talonid ridge is connected to the base of the metaconid by the endocrista and its labial end is connected to the trigonid’s midwidth by a ridge ( crista obliqua) . Two talonid cusps are barely visible, one at each end of the posterior talonid ridge. Labial to the crista obliqua the crown slopes steeply to the base of the tooth. The apex of the meta¬ conid is slightly worn on a horizontal plane and there is a wear-facet starting on the posterolingual side of the apex of the protoconid and continuing down the posterior slope of the tringonid almost to the talonid. This may have obliterated a posterior protoconid crest con¬ fluent with the crista obliqua.

The other submolariform premolar in the collection is an upper (SMP-SMU 61948, Fig. 1; A, B, C). The para cone is slightly inclined posteriorly towards its tip. Its anterior edge is broadly rounded not sharply keeled as in Potamogale. There is an antereo-basal cingulum containing a small cuspule which extends downward and posteriorly for a short distance around the lingual side of the paracone. The pos¬ terior edge of the paracone is sharply keeled and there is a shallow sulcus parallel and buccal to this crest. P3 of Potamogale has a slightly better developed sulcus in this same position. Buccal to the base of this crest and posterior to the paracone is a basined area bounded by an elevated ridge. At least 3 cuspules arise from this ridge, the largest of which is just anterior to the postero-buccal corner of the tooth. Al¬ though the single posterior basal cusp on P3 of Potamogale is relatively larger, it is positioned the same and doubtless represents the same cusp. The ridge extends downward and anteriorly from this cusp along the buccal edge of the paracone, almost to the tooth’s anterior-posterior midlength. The other 2 posterior cusps are close together, the most

EARLIEST KNOWN EUTHERIAN MAMMALS

5

Fig. 1 . Sufomolariform premolars from the Albian of Texas. A, B, & C. Referred P3; X25; SMP=SMU 61948. A. Labial View; B. Occlusal view; C. Lingual view. D, E, & F. Referred P4; X25; SMP=SMU 61947. D. Lingual View; E. Occlusal view; F. Labial view.

lingual being at the point where the ridge passes just lingual base of the posterior paraconal keel. The ridge continues on to join with the protocone in much the same manner as a similar cingulum on P3 of Potamogole . In the living form, however, the ridge does not pass lingual to the paracone. Instead the posterior base of the paracone interrupts the ridge. The protocone is broken away in our but the stump reveals some details of that cusp. It is oval in cross section at its connection with the lingual face of the paracone oval is slightly inclined upward at the anterior end.

EVOLUTION OF PREMOLAR MOLARIZATION AND OCCLUSION

The identification of the Butler Farm specimens as being somewhat molarized leads us to the following considerations.

6

THE TEXAS JOURNAL OF SCIENCE

Scott (1892) stated that molarization of premolars started first and usually extended farther forward in the lower series than in the upper series. He apparently refers to independent specialization of premolars not related to the mimicing of the molar patterns (e.g., addition of ac¬ cessory cusps to the premolars of carnivores which are useful in grasp¬ ing and slicing) . If we restrict evidence of molarization to the presence of a lingual metaconid on lower premolars and a protocone on upper premolars, the most primitive members of all placental groups have one more molariform premolar above than below.

It appears the first step taken in the molarization of simple pre¬ molars was the addition of the protocone on the ultimate upper pre¬ molar (P4) (Gregory, 1934). The newly added protocone is not so large or so tall as its counterpart on the molars and could not occlude with the low talonid of the opposing premolar. * Instead, it has a quite different occlusal relationship with the inferior dentition. At this stage, the protocone is slightly inclined posteriorly (opisthoclinalf ) and oc¬ cludes with the anterior portion of the trigonid of the tooth (Ml) be¬ hind the opposing premolar. As molarization progresses, the occlusion of the protocone shifts to the newly developed talonid of the opposing premolar (P4) . At this point it becomes a “mature occlusion. ”$ Simul¬ taneously, an opisthoclinal protocone is added to P3 and a lingual metaconid is added to P4. It is curious that the companion change to the addition of the opisthoclinal protocone to P3 is the development of a lingual metaconid to P4 for it is the paraconid which receives the brunt of the protocone’s occlusion. Perhaps the addition of the lin- gually placed metaconid, forming a true trigonid, provides the width necessary to make such occlusion effective. These simultaneous changes in upper and lower dentitions fit well into the Field Concept developed by Butler (1937). Butler demonstrated that evolution in¬ volving dentition takes place at the same time in both upper and lower series. However, simultaneous changes are not in opposing premolars, but in the upper premolar in front of the changing lower premolar’s opposing tooth. The presence of a submolariform lower premolar (P4) with a well developed metaconid in the Butler Farm assemblage thus

* “Opposing” is used throughout this report for the tooth of the opposite series which carries the same numerical designation (P4 P4; Ml Ml).

f “Opisthoclinal” protocone indicates one occluding with the anterior portion of the trigonid of the tooth behind the opposing tooth. This may be due to the posterior inclination of the protocone relative to the rest of the crown, or to the tilting of the whole tooth by lingual displacement of the tooth’s anterior edge.

t Protocones with a “mature occlusion” are those occluding with the talonid of the opposing tooth and thereby serving the same function as the protocones of the molars.

EARLIEST KNOWN EUTHERIAN MAMMALS

7

suggests the animal had both P3 and P4 molariform to some degree. It is on this basis that the upper premolar from Butler Farm which had a small but separately-rooted protocone, is referred to P2.

We may, therefore, outline the progressive molarization and oc- clusual evolution of premolars of primitive eutherians (Fig. 2) :

Stage /. An opisthclinal protocone is added to P4, which occludes with the trigonid of Ml, and P4 remains simple. Modern Nesophontes has this occlusal relationship but surely represents secondary de- molarization. All possible Late Cretaceous and Early Tertiary an¬ cestors are at Stage II.

Stage II. The talonid of P4 develops and the protocone of P4 trans¬ fers its occlusion there. At the same time there is an opisthoclinal pro¬ tocone added to P3 which occludes with the trigonid of P4, formed by the addition of a lingually placed metaconid and various development of the paraconid. If the Butler Farm specimens are interpreted cor¬ rectly, at least some eutherians had reached Stage II by Albian times and it was from this stage that all degrees of additional molarization or demolarization took origin. The stage is apparent in primitive condy- larths (e.g., Ozyclaneus , T etreclaenodon ) , most Paleoeene and Eocene primates (e.g., Notharctus ), bats (e.g., Icaronycteris) , insectivores (e.g., Geolahis , Procerberus) , and although the development of the ad¬ vanced carnassial pattern is well underway the stage can still be recog¬ nized in most miasids.

At Stage III occlusion of the protocone on P3 matures (occludes with the talonid of P3) and an opisthoclinal protocone is added to P2 which occludes with the newly developed trigonid of P3. This stage was reached by many condylarth-derived mammals before the end of the Paleoeene (e.g., Prodinoceras, Probathyopis , and U intatherium) .

Tapirs and rhinoceroses have even advanced to Stage IV in which molarization is extended to PI and P2.

The relationship between the most anterior premolar containing a protocone and the lower premolar behind its opposing tooth becomes less important as the shearing function gives way to emphasis on crushing and grinding. When this happens the metaconids of lower molars may diminish without accompanying changes of the upper premolars. This outline of the molarization of premolars cannot be ex¬ pected to recapitulate the more ancient development of the therian molar as the Premolar Analogy Theory suggests. It is well known that the metaconid was developed long before the protocone was added to upper molars.

There is no doubt that considerable secondary simplification of pre¬ viously submolariform premolars has occurred in some groups, espe-

8

THE TEXAS JOURNAL OF SCIENCE

STAGE I

EXPLANATION OF FIGURE 2

Schematic diagram showing presumed evolution of eutherian occlusal relationships with regard to the molarization, and in some cases demolarization, of the premolar series.

Although the molars and molariform premolars are drawn triangular, this does not imply position of the paracone and metacone or lack of development of a hypocone. Molars are stippled, premolars are open, and boat-shaped symboles represent premolars without metaconids. Simple premolars are deleted.

Stage I Presumed first step in the molarization of the eutherian premolar series: opistho- clonial protocone on P4 and P4 simple.

Stage II Metaconid added to P4; opisthoclinal protocone added to P3; protocone of P4 occluding talonid of P4.

Stage II- Forms whose ancestors were at Stage II but due to a secondary specialization, such as brachycephaly, has lost the protocone from P3 and the metaconid from P4.

Stage ll-M Forms whose ancestors were at Stage II but the protocone of P3 has shifted its occlusion to the talonid of P3 without the addition of a metaconid to P4 or an opisthoclinal protocone to P2.

Stage ll-S Forms which are still at Stage II by premolar occlusal relationships but in which the carnassials are developed and the posterior molars are reduced.

Stage III Forms whose ancestors were at Stage II but in which the protocone of P3 has switched its occlusion to the talonid of P3 and there has been an addition of a metaconid to P3 and an opisthoclinal protocone to P2.

Stage lll-D Forms whose ancestors were at Stage III but have secondarily lost the metaconid from P3 and the protocone from P2. The resulting dentition is almost exactly like that of Stage ll-M forms and are difficult to interpret without knowledge of the ancestors.

Stage I ll-M Forms whose ancestors were at Stage III but the protocone of P2 has shifted

EARLIEST KNOWN EUTHERIAN MAMMALS

9

dally carnivores, bats, and soricoids. Advanced aeluroids (felids and canids) have a single premolar with a protocone (P4, the carnas- sial), and the metaconid has been lost from P4. In more primitive aeluroids such as the viverrids (e.g., Atilax ) the carnassial is de¬ veloped and P3 has an ophisthoclinal protocone occluding with the fairly well developed trigonid of P4.

During demolarization the same relationship of P3 to P4 is often maintained. The dwindling of the opisthoclinal protocone on P3 us¬ ually is accompanied by the reduction or loss of the metaconid of P4. Propaleosinopa thompsoni is an excellent example. Here the protocone of P3 is just a small opisthoclinal projection, with a very small but functional cuspule. The metaconid is visible on some specimens as a slight protuberance, but not on others. The metaconid here serves a new function, however, in that it has been incorporated in the lingual wall of a sulcus down the posterior face of the protoconid. This allows the protocone of P4 to slice on its way to the talonid.

It is interesting that there is a similar occlusal relationship among marsupials. The ultimate upper premolar (P3) of didelphids has a posterolingual cingulum which occludes with the trigonid of Ml, in the same manner as the opisthoclinal protocone of P3 of primitive placental mammals occludes with triconid of P4. The reduction of this cingulum seems to be correlated with the reduction or loss of the meta¬ conid and paraconid of Ml, as in dasyurids.

When a lineage ceases to extend molarization of its premolars farther forward in its series, occlusion of the most anterior protocone may shift to the talonid of its opposing tooth without the addition of a metaconid to its new partner or a protocone to the upper premolar one place farther forward. There is still one more protocone than meta- conids but considering the new occlusal relationship these are desig¬ nated as Stage II-M, Stage III-M, etc.

An almost identical dentition may result from a partial demolari¬ zation related to some specialization such as a tendency toward brachycephalus condition. I suspect Palaeoryctes may be an example of this. The most anterior protocone in this form is on P4 and it is not opisthoclinal. Instead it occludes with the talonid of P4 which has no metaconid. This condition was probably reached through the loss of an

its occlusion to the talonid of P2 without the addition of a metaconid to P2 or an opistho¬ clinal protocone to PI.

Stage IV Forms whose ancestors were at Stage III but in which the protocone of P2 has switched its occlusion to the talonid of P2 and there has been an addition of a metaconid to P2 and an opisthoclinal protocone to PI .

10

THE TEXAS JOURNAL OF SCIENCE

opisthoclinal protocone from P3 and the metaconid from P4. It there¬ fore would represent a demolarized Stage II rather than a matured Stage I.

Another specialization which causes the rule of one more protocone than metaconid to break down is the development of long rostra. This is usually accompanied by the development of diastemas between the premolars, enhancing their grasping ability. One example is the hedgehog, Erinaceus erisopeus , in which P3 is simple but P4 has a fairly well developed metaconid. The same is true of the viverrid, Eupleres gondoti , although the metaconid is somewhat reduced. That these examples represent secondary simplification is indicated by the fact that the erinaceid, Echinosorex gymnura , and the viverrid, Herp- estes ichneumon , retain the normal Stage II relationship.

Shrews have molariform premolar formulas of 1/0, but when one considers more primitive soricoids demolarization is indicated. Soleno- don has an atypical formula of 1 /I but probably reflects the loss of the protocone of P3 while the metaconid is retained on P4 due to the shear¬ ing function related to extreme zalambdodonty of the form. Neso- phontes , considered closely related to Solenodon by McDowell (1958), with its 1/0 formula would represent one further step towards the shrew condition. Of course, an alternate interpretation could be that soricoids have not been through Stage II, that Solenodon is advanced in the addition of the metaconid to P4, and that soricoids and perhaps other insectivores such as Palaeoryetes were derived directly from a Stage I form. This might be interpreted, however, to indicate that the lineage has been separate from other placentals since the early Cre¬ taceous and this hardly seems probable. Though it is highly improb¬ able, it is not impossible. Deltatheridium has no molarized premolars and could conceivably give rise to Stage I forms later than the Albian. This, however, would cast grave shadows on the relationship between Deltatheridium and Stage II members of the proposed order Delta- theridia. I prefer to believe this genus is merely a specialized form which has been more completely demolarized than all others.

PREMOLAR OCCLUSAL RELATIONSHIPS AS A TOOL TO ASSOCIATE DISASSOCIATED UPPER AND LOWER DENTITIONS

Simpson (1929) referred several isolated and submolariform pre¬ molars from the Upper Cretaceous Lance Formation to Gypsonictops. He admitted the possibility of these teeth being P3s, but considering the age of the form, preferred the P4, interpretation. He also pointed out that all of the submolariform premolars in the collection were of

EARLIEST KNOWN EUTHERIAN MAMMALS

11

the same type; and if they were actually P3s, more advanced P4^s should be represented. He did have atypical molars in the collection, and explained that these could be more-or-less fully molariform pre- molars, but did not feel this was probable in such an early insectivore. He later returned to the subject (1951) when he illustrated hypo¬ thetical upper dentition in occlusion with the lower dentition of Euangelistes . He emphasized that his reconstruction did not represent a known species, or even genus, but felt that it demonstrated fairly well the general form of the group to which Gypsonictops belongs. Looking at the reconstruction from the aspect of premolar occlusion it seems to me that one major correction should be suggested. If the lower dentition of Gypsonictops contained a P4 with a well developed metaconid as in Euangelistes the submolariform upper premolar is almost certainly P3, an alternative Simpson offered. Simpson further inferred that whatever form to which the submolariform upper pre¬ molars belonged could not be congeneric with Telacodon or Batodon because the ultimate lower premolar was simple in these forms. Al¬ though we now know that these genera are not related to Gypsonic- tops , separation on this basis is invalid. If the submolariform premolar were actually P4s, P4 almost certainly would be simple.

SUMMARY

Primitively, placental mammals have one more submolariform pre¬ molar in the upper series than in the lower. Stage II in the molari- zation of the premolar series (protocone on P3 and P4; metaconid on P4) was reached by Albian times. Although there are exceptions re¬ lated to specialization, truly primitive forms generally fall into 2 morphological categories: (1) The most anterior submolariform pre¬ molar has its protocone posteriorly inclined (opisthoclinal) and oc¬ cluding at least partially with the trigonid of the tooth behind the opposing premolar (which has a metaconid). (2) The most anterior submolariform premolar has a protocone oriented as those of the molars and occludes with a talonid of the opposing premolar and this tooth probably does not have a metaconid.

This second type can be reached in 2 very different ways: After ex¬ tension of molarization forward in the series has ceased; or as a first step toward demolarization.

It appears that Stage II in the molarization of premolars was at¬ tained by Albian times. Therefore Stage I and divergence of meta- therian-eutherian mammals predates the Albian.

Molarization of the premolar series of Inseetivora, Carnivora, Ro-

12

THE TEXAS JOURNAL OF SCIENCE

dentia, and Primates never preceded beyond Stage II. However, mo- larization extended forward to P2/P3 (Stage III) and even P1/P2 (Stage IV) in certain condylarth-derivities.

An acquaintance with the occlusal relationship of premolars of primitive eutherians is a useful tool in associating upper and lower dentitions found disassociated.

ACKNOWLEDGMENTS

My sincere appreciation is due Mr. Lee Butler who allowed exten¬ sive excavation on his property and extended other courtesies. I am also most grateful to Dr. C. Lewis Gazin, U.S. National Museum, Drs. Malcolm C. McKenna and Leigh Van Valen, American Museum of Natural History, Dr. Elwyn Simons, Peabody Museum, Dr. Glenn Jepson, Princeton Museum for allowing examination of material under their care.

The Trinity premolars were recovered and the study undertaken under the sponsorship of National Science Foundation Grant No. GB 3805. The drawings were made by Professor Edward Willimon.

LITERATURE CITED

Butler, P. M., 1937 Studies of the mammalian dentition. I The teeth of Centetes ecaudatus and its allies. Proc. Zool. Soc. London, (B), 107: 103-132.

Gregory, W. W., 1934 A half century of trituberculy. The Cope Osborn theory of dental evolution, with a revised summary of molar evolution from fish to man. Proc. Amer. Phil. Soc., 73: 169-317.

McDowell, S. B., Jr., 1958 The Greater Antillean insectivores. Bull. Amer. Mus. Nat. Hist., 115:3: 117-214.

Patterson, Bryan, 1956 Early Cretaceous mammals and the evolution of mam¬ malian molar teeth. Fieldiana: Geology, 13:1: 1-105.

Scott, W. B.. 1892 The evolution of the premolar teeth in the mammals. Proc. Acad. Nat. Sci. Phil., 405-44.

Simpson, G. G., 1929 American Mesozoic Mammalia. Mem. Peabody Mus. Yale Univ., 3:1-235.

- , 1951 Amer. Mus. Nov., no. 1541, 1-18.

Slaughter, B. H., 1965 A new therian from the Lower Cretaceous (Albian) of Texas. Postilla, 93: 1-18.

Relationship between the Chemical Limnology and Raw Water Quality of a Subtropical Texas Impoundment

by R. B. HIGGINS and E. GUS FRUH

Environmental Health Engineering

The University of Texas , Austin , Texas 78712

ABSTRACT

Data are presented for the chemical limnology of a relatively un¬ polluted deep-storage impoundment in central Texas. The tempera¬ ture profiles for the different seasons exhibit characteristics typical of subtropical lakes. Although relatively unpolluted, oxygen deficits are present below the epilimnion for a substantial part of the year. Oxygen depletion and absence first occurred at the thermoeline. Other data show chemical and nutrient stratification throughout the summer and fall. The effects of these water quality changes with depth are dis¬ cussed in view of the proposed Texas Water Plan and the lack of lim¬ nological data needed for the optimum water quality management of this plan.

INTRODUCTION

Cole (1963) and Clark (1966) point out in their reviews that little limnological data is available for the artificial impoundments of Texas. In addition, nearly all of the impoundments that have been studied are located in north and northeast Texas. In view of this lack of data in a state where there is a growing concern for water quantity and quality management, studies are needed on various impoundments in other sections of the state.

The purpose of this paper is to furnish limnological data for Lake Travis, a large deep-storage impoundment on the Colorado River in central Texas (Fig. 1). It is the largest of a series of 7 reservoirs lo¬ cated within a 150 mile reach of this river. The major inflows are from Marble Falls Lake and the Pedemales River. At normal opera tiing levels, Lake Travis has a capacity of 1,170,000 acre-feet, with a sur¬ face area less than 19,000 acres. Thus, the impoundment has the lowest ratio of surface volume of any present Texas impoundment. An additional 830,000 acre-feet are available for flood control.

Lake Travis was constructed for flood control and hydroelectric

14

THE TEXAS JOURNAL OF SCIENCE

power. At the present time, it also serves as a local water supply source. Furthermore, its releases are utilized downstream for municipal water supply by Austin and for irrigation. The economy of the surrounding area is now based on the aesthetic and recreational benefits of the impoundment.

METHODS OF SAMPLING AND MEASUREMENT

Temperature was measured by lowering a temperature probe to the desired water depth. The data were obtained in amperes and converted to degrees centigrade from a calibration curve which was checked be¬ fore each sampling date. A dissolved oxygen probe was lowered with the temperature probe. The lead-silver probe was covered with a pad and plastic membrane. The pad was saturated with potassium hy¬ droxide. The ampere reading from the probe was converted to mg/1 dissolved oxygen from a calibration curve. Occasionally as a check, water samples were “fixed” in the field, and the dissolved oxygen was determined using the azide modification of the Winkler method (Stan¬ dard Methods, 1960).

Samples for chemical and biological analysis were obtained by a Kemmerer sampler. The pH was measured immediately using a Beck¬ man Model N Meter. Part of the water sample was preserved using

CHEMICAL LIMNOLOGY AND RAW WATER QUALITY

15

chloroform. Immediately upon return to the laboratory, total phos¬ phate was determined (Standard Methods, 1960). Kjeldahl nitrogen, nitrate plus nitrite nitrogen, and ammonia nitrogen were determined using Technicon Autoanalyzer Procedures (1966). Hardness, alka¬ linity, chlorine demand, color, turbidity, and conductivity were meas¬ ured as described in Standard Methods (1960) . Bacteria were counted using the membrane filter technique of Standard Methods (1960). Total bacteria were defined as those cells growing on Nutrient Broth and coliform on M-HO-Endo Broth.

The data obtained in this 1966-67 investigation were collected at a single sampling station. To validate such sampling, a cross-section of the pool behind Mansfield Dam (See line A on Figure 1 ) was sampled for both temperature and oxygen. As indicated by the sampling sta¬ tions’ depth (Fig. 2) , the old river channel wound throughout the pool. The data showed that the temperature and oxygen profiles at one sta¬ tion in the old river channel reasonably represented the entire cross- section of the pool area. The slight variations in temperature were un¬ doubtedly due to the different times of day at which the samples from the various stations were obtained.

o

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Station

Station

Station

Station

Stotion

In Main

In Main

In Main

In Main

In Main

Channel

Chonnel

Channel

Channel

Channel

(175 'deep)

( 39'deep)

(140'deep)

(54* deep)

( 175 'deep)

Cross - Section of Lake Trovis

Fig. 2. Temperature and dissolved oxygen profiles at various sampling stations on Lake Travis.

16

THE TEXAS JOURNAL OF SCIENCE

TEMPERATURE

Sampling was started in early June. Unfortunately, temperature data (Figs. 3 and 4) could not accurately be obtained below 90 feet throughout the summer months. This operating difficulty was cor¬ rected by October.

The thermocline was located at approximately 25 feet below the surface in early June and dropped to 35 feet by the end of August. During this time the water temperature in the top 90 feet increased by approximately 5°C. By mid-September the thermocline dropped to approximately 50 feet below the water surface. At the end of October, the surface water temperature decreased to 23 °C, and the thermocline was at least 90 feet below the water surface. On November 22 the thermocline was at the penstock outlets (elevation 560 feet). In De¬ cember and February no thermocline existed, although the tempera¬ ture profile was still not isothermal. By March 20 the temperature trend had reversed as an exceptionally warm spring began.

To determine whether the 1966-67 temperature profiles were typ¬ ical, data were obtained from the literature. The University of Texas

Temperature ®C

18 19 20 21 22 23 24 25 26 27 28 29 30 31

Fig. 3. Temperature profile of Lake Travis from June through August.

CHEMICAL LIMNOLOGY AND RAW WATER QUALITY

17

II 12 13 14 15 16 17 18 IS 20 21 22 23 24 2 5 26 27 28 29 30 31

Fig. 4. Temperature profile of Lake Travis from August through March.

Defense Research Laboratory recently published its 1966 temperature profiles which were obtained at least once a week in the old river channel immediately behind Mansfield Dam (See Fig. 1). It was re¬ ported that an isothermal temperature profile was first obtained on January 11, 1966, and this isothermal situation persisted through Feb¬ ruary 15. Only small temperature differences were found between surface and bottom waters until the end of March. During the re¬ mainder of the spring a number of temperature gradients appeared, probably because of alternate warm