Generalized Hydrology

of Prairie Potholes on the

Coteau du Missouri, North Dakota

Prepared as part of the program o and a rnnTrllnlmnn

Aerial view of prairie potholes on the Coteau du Missouri, The water surfaces reflect the morning sun, Photo~raph by Wm, S, Eisenlohr, Jr,, May 1967, Generalized Hydrology of Prairie Potholes on the Coteau du Missouri North Dakota Generalized Hydrology of Prairie Potholes on the Coteau du Missouri, North Dakota

By Wm. 5. Eisenlohr, Jr., and Charles E. Sloan

GEOLOGICAL SURVEY C I R C U L A R 558

Prepared as part of the program of the U.S. Department of the Interior for the development of the Missouri River Basin and a contribution to the International Hydrological Decade

Washington 1968 United States Department of the Interior STEWART L. UDALL, Secretary

Geological Survey William T. Pecora, Director

Free on application to the U.S. Geological Survey, Washington, D.C. 20242 CONTENTS

Page Page Abstract______1 Ground-water movement______6 Introduction______1 Quality of water ------7 Water supply ______·-______3 Vegetation ______8 Geology------6 References______11

ILLUSTRATIONS

Page Frontispiece. Aerial view of prairie potholes on the Coteau du Missouri. Figure 1. Map of North Dakota showing the Coteau du Missouri, location of study areas, average annual precipitation, and average annual lake evaporation------2 2. Graphs showing relation of precipitation to basin inflow at an individual pothole _ _ 4 3. Charts showing variations in basin inflow from similar storms------5 4. Photograph of a dense stand of cattail and bulrush in a pothole, September 1964 __ 9 v

Generalized Hydrology of Prairie Potholes on the Coteau du Missouri, North Dakota

By Wm. S. Eisenlohr, Jr., and Charles E. Sloan

ABSTRACT County. This report presents all the informa­ tion that can be generalized with some assur­ This report presents a II the information, obtained during the investigation, that lends itself to generalization. It describes ance that later work will not make major re­ conditions on that part of the Coteau du Missouri where there visions necessary. is little integration of drainage systems. The surface of the glacial drift in this region is dotted with shallow depressions The Coteau du Missouri (fig. 1), as cefined known as prairie potholes that hold water for varying lengths of time. Preci pi tat ion directly on a pothole is the basic by the U.S. Geographic Board (1933), is a source of its water supply, but it is only about half the po­ "narrow plateau beginning in the northwest tential evaporation; therefore, potholes tend to go dry. Basin corner of North Dakota between Missouri inflow from melting snow or rain occurs only when the soil is River and River des Lacs and Souris River frozen or saturated, a condition so erratic in occurrence that seasonal or annual precipitation is of little value as an indi­ and running southeast and south, with its cation of basin inflow. Net seepage outflow occurs from southern limit not well defined; and its west­ potholes on the higher parts of the Coteau at very low rates, ern escarpment forming the bluffs on the but it can amount to 20 to 30 percent of the toto I water loss Missouri." Many other definitions are in use; from a pothole. Net seepage inflow occurs at the potholes on the lower parts of the Coteau. for the latest discussion of boundaries of this feature see Winters (1967). The present re­ The phreatic surface (water table) tends to be a subdued port is concerned with the eastern part of the image of the topography and is generally very near the land area just defined where there is little or no surface. The water surfaces of the potholes are part of the phreatic surface, and therefore they can be used to pre­ integration of drainage systems. The Coteau pare a contour map of the phreatic surface; wells usually is mantled with a layer of glacial drift that in act as piezometers and thus are useless for such a purpose. places is several hundred feet thick; there are few outcrops of bedrock. The surface of Generally, potholes with water relatively low in dissolved sol ids have net seepage outflow, and those with water con­ the glacial drift is dotted with shallcw de­ taining high concentration of dissolved solids have net see­ pressions (see frontispiece) known as prairie page inflow. The direction of ground-water movement can potholes that hold water for varying lengths of therefore be inferred from the quality of water in potholes. time. There are more than 660,000 of them The total salinity of water in a pothole is largely a func­ tion of the rate of ground-water flow and the relationship of that contain water in the spring of a normal seepage inflow to outflow. year (Schrader, 1955).

The species of emergent aquatic vegetation that grow in a The ponds in these pra1r1e potholes, and pothole are directly related to the permanence and salinity of the water at the particular site of each species. The re­ some associated larger bodies of water usu­ port contains a to ble of the common species that con be used ally termed lakes, constitute the surface water as indicators of these conditions. supply of the Coteau. These ponds also make ideal breeding areas for migratory waterfowl. INTRODUCTION Prairie potholes can be classified in several The hydrology of prairie potholes in North ways by broad groups, but they also have indi­ Dakota was investigated by the U.S. Geological vidual characteristics that make strict classi­ Survey from 1959 to 1967. Three study areas fication difficult. Furthermore, some of the were used as shown in figure 1. The evapo­ characteristics of prairie potholes change transpiration studies were made mostly in with changing hydrologic conditions, not only Ward and Dickey Counties and the ground­ from year to year, but also within a year. The water studies were made mostly in Stutsman reasons for the individualistic and ch~nging

1 1:..:1

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Precipitation directly on a pothole is the Saturated soil has an effect similar to fro­ basic source of water for a pothole; it is not zen soil in producing overland flow. Saturated influenced by the many factors that make basin soil in this sense refers to the inabilit~' of the inflow so erratic. Figure 1 shows that the top layers of the soil to absorb additional ratio of annual precipitation to annual lake moisture, or to do so at a higher rate of ab­ evaporation ranges from slightly less than a sorbtion, and does not refer to any ccndition half in the western part of the State to some­ of the soil at depth. In a strict sense it is the what more than a half in the eastern part. The infiltration capacity of the soil that is satu­ range of this ratio between the study areas in rated rather than the soil itself. Saturated Ward and Dickey Counties is less than the soils are the result of previous rains or in­ range for the entire State, but great enough tense rains. That such conditions are very that throughout the study, potholes in Ward erratic is shown in figure 2 where basin in­ County were generally drier than those in flow, resulting from less than normal rainfall Dickey County. The fact that, by chance, the in the summers of 1961 and 1963, was greater annual evaporation rate is about the same in than inflow from 60 percent above normal rain­ Ward and Dickey Counties does not affect the fall in 1962. conclusion. For a water body to be permanent in this region, basin inflow must be at least The general conclusion reached concerning great enough to make up the difference be­ the prairie potholes, and supported by figure 2, tween precipitation and all the water losses. is that seasonal or annual precipitaticn is of That it is frequently insufficient for this pur­ little value as a measure of water replenish­ pose is shown by the tendency for potholes to ment in a pond from basin inflow. become dry. In some years, however, it is more than adequate and a pothole will receive The importance of saturated soil in produc­ enough water for its pond to persist for sev­ ing basin inflow is illustrated in the following eral years. There is no regularity in such oc­ examples. First, consider a pothole in Dickey currences and no way of predicting them for County (pothole 5, fig. 3). This pothole received a specific year. 0.18 foot of rain on July 5, 1964, and 0.05 foot about 24 hours later. There had been no pre­ Overland flow reaches a pothole only when vious rain since 0.07 foot fell on July 1. Some the condition of the ground is such that water drying of the soil undoubtedly took place in the can flow over it without being absorbed; that 3-day interval, so that the effect of soil mois­ is, the ground must be either frozen or satu­ ture on producing basin inflow on July f is not rated. Snowmelt flowing over frozen ground is known. It is known that on July 5 the rainfall believed by many people to be the largest was very heavy, so heavy that it is not ex­ source of water supply of prairie potholes. It pected to occur at that rate and duration of­ does occur every year, but rarely is it as tener than once in 10 years, on the average 4 GENERALIZED HYDROLOGY OF PRAIRIE POTHOLES ON THE COTEAU DU MISSOURI, NORTH DAKOTA 60

_J <{ ~ 40 .. 0:: zo oz ~ lL 20 0 ~ 1- £1.. z 0 w 0 w 0 0:: 0:: £1.. w £1.. -20 z EXPLANATION

-40

November - April

0.15

~ May- October 0 _J 0.10 lL w~ z w z lL (f) c::{ z 005 {])

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Figure 2, -Relation of precipitation to basin inflow at an individual pothole.

(U.S. Weather Bur., 1955). This storm raised second on August 20 that produced no basin the water level in the pond by 0,385 foot, 45 inflow at all. It is interesting to note also that percent from precipitation and 55 percent the 0.05 foot of rain that fell about midnight from basin inflow. The second storm was not July 5 was far more effective in producing especially heavy, but coming so soon after a basin inflow than the 0.18 foot of rain that fell heavy rain, 0,05 foot of rain caused a rise of less than 24 hours previously. 0.156 foot in the pond on July 6. The lower part of figure 3 shows a second In contrast to these responses are those example (pothole 1), but the time relationship August 17-20, a little over a month later. is reversed and rainfall intensit~T probably had There had been no rain for more than a week no effect. The chart for June 13-14, 1965, and less than 0.04 foot since the first of the shows that rain of 0.12 foot produced a rise of month. There was 0.04 foot of rain in the 0.146 foot in the pond, 0.021 foot of which was morning of August 17, 0.06 foot in the after­ basin inflow or less than 0.2 of the amount of noon, and 0.05 foot about noon of August 20. direct precipitation. There had been no rain There was no basin inflow from any of these for more than 2 weeks prior to the rain on rains, and the first rain of 0,04 foot fell in June 13. The chart for July 20-23 shows that about half an hour. a rain of 0.11 foot on July 22-23 caused the pond to rise 0.495 foot, 0.387 foot of which was We thus have two storms that produced basin inflow or 3.6 times the amount of direct 0.05 foot of rain each; one that produced basin precipitation on the pond. The difference is inflow on July 6 equal to twice the amount of seen as the effects of the rain of 0.05 foot on rain that fell directly on the pond, and a WATER SUPPLY 5

July 20, only 42 hours before the rain em water, presumably because much of the drain­ July 22. age area did not contribute in those yeF.rs.

Potholes that have very large drainage areas Seasonal evaporation (May~ctober) from may have areas that are noncontributing ex­ potholes clear of emergent aquatic vegetation cept in years of high basin inflow. In those was found to be very close to the values given years, however, the normally noncontributing by Kohler, Nordenson, and Baker (1959) for areas may overflow into the pothole and add lake evaporation. Kohler shows seasond evap­ enough water to assure a water supply in the oration to average about 84 percent of annual pothole for several years. evaporation from lakes in North Dakota (fig. 1 ).

This condition is believed to be the expla­ Seasonal evapotranspiration from p0tholes nation of a sequence of events that occurred in with vegetation averaged about 10 percent less ¥lard County. There, a pothole went dry in than seasonal evaporation from equivalent 1964, 3 years after other potholes around it potholes clear of vegetation. There is, of went dry. When the other potholes received course, a great variation in transpiration dur­ an appreciable amount of water in 1965 and ing the season as the vegetation grows, 1966, the subject pothole, although it has by reaches maturity, and then becomes dormant far the largest drainage area, received little or dies. Evaporation is directly related to the

z 0 .,. 0 I' I I' -+­ I ~w 0.1 -7.7 a..LL v ~~0.2 -7.6 0::: CL POTHOLE 5, 1964 7.5 ~ z I .. 1-­ 7.4 7.3 ww (.!)W ~I.J_r-= 7.3 7.2 I ---- en w-- -' 7.2 7.1 JULY 4 JULY 5 JULY6 AUG.I7 AUG. IS AUG.I9 AUS. 20 ~ 0 1--1-­ 'If r I'

Figure 3. -charts showing variations in basin inflow from similar storms. 6 GENERALIZED HYDROLOGY OF PRAIRIE POTHOLES ON THE COTEAU DU MISSOURI, NORTH DJ\KOTA rate at which water vapor is removed from the was deposited directly from the glacial ice vicinity of the evaporating surface by air cur­ with little modification by running water. That rents or wind. In a pothole filled with vegeta­ is, there is little stratification within the till. tion, there is practically no wind, most of the It consists of a heterogeneous, unsorted mix­ time, at the water surface. Therefore, evapo­ ture of clay, silt, , , cobbles, and ration rates are very low. They are so low boulders that is poorly permeable. Cracks that even with high rates of transpiration that and joints that have developed through weath­ occur in midsummer the total evapotranspira­ ering processes have increased the permea­ tion for a season is less than that of a pothole bility of the till in the surficial unsaturated clear of vegetation in a comparable situation. zone. In addition, permeable deposits of sand and gravel are locally enclc sed by poorly Seepage rates were computed only for till permeable till in many places. terranes. It had been expected that seepage in till would be negligible. Net seepage outflow Outwash were deposited by melt­ occurred in all potholes where seepage was water from the glacier and consist largely of computed. The rates were very low, seldom permeable sand and gravel. Areas of outwash exceeding 0.01 foot of water per square foot of have a less irregular topography than the till pond area per day and frequently being less terrane and generally contain 1arger and more than half that rate. However, these are not widely scattered lakes. negligible rates because they often represent 20 to 30 percent of the total loss of water from GROUND-WATER MOVEMENT a pothole. The movement of ground water on the Seepage outflow rates computed for the veg­ Coteau is related to the surface topography etated potholes were much greater than those and the permeability of the underlying earth for the potholes clear of vegetation. They materials. The top of the zon

The Coteau du Missouri was an extensive Because much of the glacial till on the area of glacial stagnation during several ad­ Coteau is at relatively high elevations, pot­ vances of the Late Wisconsin Glacier, and it is holes in till generally lose water through largely covered by deposits of glacial till and seepage outflow. Conversely, because much outwash. of the outwash on the Coteau is at relatively low elevations, many of the potholes and lakes The areas of till on the Coteau are charac­ in outwash gain water through seepage inflow. terized by a hummocky knob-and-kettle topog­ raphy, abounding in prairie potholes and lack­ A well that has been dug or drilled below ing an integrated drainage pattern. The till the phreatic surface, and cased for most of its GENERALIZED HYDROLOGY OF PRAIRIE POTHOLES ON THE COTEAU DU MISSOURI, NORTH DAKOTA 7 length, will act as a piezometer. That is, the QUALITY OF WATER water level in the well will represent the aver­ age head or fluid potenital in the uncased part All natural waters contain some dissolved of the well. Because the change in head with solids. The concentration of these dis solved depth can be substantial, water levels in wells solids affects the usefulness of a water supply. cannot be used to map the phreatic surface. Normally, the chief interest in a water supply However, as the water levels in potholes are is in relation to direct human use. In th" pot­ part of the phreatic surface (with few excep­ hole region, however, the major interest in the tions), they can be used to prepare a contour salinity of water is its use by migratory wa­ map of the phreatic surface. terfowl. R. E. Stewart has chosen a slightly different classification than that used by the In areas underlain by poorly permeable till, U.S. Geological Survey as being more appro­ the phreatic surface may be steeply inclined, priate for waterfowl applications, and his clas­ but there is little evidence to suggest appreci­ sification has been adopted for this report. able lateral movement of water in the direction (See table under the section "Vegetation.") of the inclination; the dominant direction of ground-water flow appears to be vertical. Sev­ The salinity of water is usually expressed eral lines of evidence suggest vertical move­ as the number of milligrams of solic1 s dis­ ment in till: (1) Large difference in water solved in a liter of solution. An approximation levels in closely spaced observation wells that of the number of milligrams per liter of dis­ have been cased to different depths, (2) large solved solids can be obtained quickly and eas­ and rapid water level changes in observation ily by measuring the specific electrical con­ wells, (3) relative independence of water levels ductance of a sample. If the conductance is in potholes and adjacent wells, and (4) the oft­ expressed in micromhos per square centime­ times steep configuration of the phreatic sur­ ter per centimeter at 25°C (frequently '"ritten face. micromhos per centimeter}, the number is close to the number of milligrams per liter of The water levels in shallow observation dissolved solids in prairie pothole waters. wells in till rise several feet every spring at There is a difference between the two, and the a time when recharge is far too small to ac­ difference for fresh water and for brine is count for it. Declines in water levels in near­ very significant for most purposes, the num­ by potholes have been observed during parts her of milligrams per liter ranging fr')m 0. 7 of the period in which the water levels in wells times the number of micromhos per centime­ are rising. The reason is probably the rapid ter for fresh water to more than 1. 2 times the return to the phreatic zone, during the spring number for brines. For the broad classifica­ thaw, of water that had migrated as water va­ tions used in this report, however, it is prac­ por slowly upward to the frost zone during the tical to ignore the difference. previous winter (Willis and others, 1964). The salinity of water varies from pond to In areas of outwash, there is substantial lat­ pond and over the Coteau covers mos1 of the eral movement of ground water. Springs and range of salinity found in nature, from. very seeps are numerous. Commonly this ground­ fresh water, less than 100 micromhos per water discharge is fresh to slightly saline. centimeter, to brines of more than 70,000 Many of the springs are artesian, and, in some micromhos per centimeter, or double the con­ of the s·aline lakes, they are sites for the centration of sea water. The salinity of water growth of fresh-water vegetation. Spring in­ found in any particular pond is frequently a flow in a few potholes is great enough to main­ good indicator of whether the pothole is in a tain permanent water bodies. region of ground-water recharge or dis­ charge, as explained later. There are many potholes that go dry every year, either because they do not get enough in­ As it was stated previously, the evaporation flow, or because outflow seepage is too great, potential is much greater than the precipita­ or a combination of the two. Potholes that tion. Therefore, for the region as a w}'')le, it have very high rates of outflow seepage in till would be possible to remove by evaporation terranes are usually underlain in part by per­ (and transpiration} all the water supplied to meable sand deposits. 8 GENERALIZED HYDROLOGY OF PRAIRIE POtHOLES ON THE COTEAU DU MISSOURI, NORTH DAKOTA the region if that water were uniformly avail­ prior to 1962, precipitation anc outflow seep­ able for evaporation. Water evaporated from age had diluted and removed roost of the dis­ a pothole leaves behind the solids that it dis­ solved solids brought in by that overflow. solved on its way to the pothole. If there is no This indicates also that there is little lateral mechanism available for removing these sol­ movement of ground water between the two. ids, then they will continue to accumulate. According to the foregoing c1iscussion, pot­ Wind has been observed as an agent for re­ holes in highland areas, where seepage outflow moving saline deposits from potholes and generally prevails, could be expected to, and lakes. It is questionable, however, whether do, contain mostly fresh or slightly saline wa­ this has any large effect on the salinity of wa­ ter. Likewise, potholes in lowland areas, ter. If wind were truly an effective force in where seepage inflow generally prevails, could removing salts from potholes that go dry, not be expected to, and do, contain water much so many potholes that go dry would remain more saline than in the highland areas. This consistently saline. statement is about water in the potholes, but as stated in the section on "Grourd-water move­ Seepage outflow removes dissolved solids ment," numerous springs in the glacial out­ from potholes. All the dissolved solids will wash provide good water in lowland areas. be removed from a pothole if the pond goes dry before the water reaches such concentra­ VEGETATION tions that parts of some dissolved constituents are precipitated and remain on the bottom of Many potholes contain emergent aquatic the pothole or within the shallow sediments vegetation (fig. 4). This vegetation exerts a covering the bottom. significant effect on water losses. It is also a good indicator of the quality of water in which In contrast, if there is no seepage outflow, it grows and of the length of time it is inun­ either because the bottom of the pothole is dated. watertight (which probably never occurs) or because over the entire bottom there is a The presence of emergent aquatic vegeta­ ground-water potential for seepage inflow, tion affects the water loss to the air in two then there is no mechanism for removal of ways. It reduces evaporation by reducing wind dissolved solids and their concentration can at the water surface and it ac1ds to the water be expected to increase. The total salinity of loss through the transpiration process (Eisen­ water in such a pothole is largely a function lohr, 1966a). The effects vary throughout the of the rate of seepage inflow and the salinity year, but the total effect on an annual basis is of the inflowing water. that evapotranspiration from a pothole filled with emergent aquatic vegetation is somewhat Surface inflow can be very irregular. Dur­ less than evaporation from a pothole clear of ing periods of great inflow to potholes, some vegetation, perhaps by 10 percent or more. of them overflow and produce inflow to the pothole next downstream, which may increase The reduction in water loss to the air in or decrease the concentration of solids there. potholes with vegetation, compared with those Few observations have been made to evaluate without, seems to be more than offset by sub­ this effect, which is illustrated by the follow­ stantially greater loss by seepage. The rea­ ing example. There is a small pond within 50 son for this greater seepage is not known. feet of a larger one whose water level is at There is no evidence to indicate whether the least 3 feet higher. Both ponds are in till. The increase is cause or effect. One might theo­ higher, larger pond di,d not overflow into the rize that vegetation only grows in soils per­ lower one (during the study) until 1964. How meable enough to allow the greater seepage long it had been since the previous overflow is and another might theorize tl'at products of not known. In 1962 the concentration of dis­ decaying vegetation may aggregate the finer solved solids in the lower pond was less than particles underlying the pothc1.e and thereby 20 percent of that in the upper one. After the increase soil permeability and reduce the re­ overflow occurred, the concentrations were sistance to flow below the pond. about the same. The lower pond has a very small and, before the overflow, The species of vegetation that grow in a it usually went dry by the middle of the sum­ pothole are directly related to the permanence mer. Presumably, since the last overflow and salinity of the water at the particular site VEGETATION 9

Figure 4. -Dense stand of cattail and bulrush in a pothole, September 1964. As a result of the high water levels in 1964 and 1965, this pothole was clear of vegetation in 1965. of each species. The term "permanence" is tion continually subject to change, but less used extensively in the classification of prai­ rapidly. The way these factors affect emer­ rie potholes to indicate the extent to which a gent vegetation is indicated in the accompany­ pothole water body is permanent. As used in ing table prepared by R. E. Stewart on the connection with vegetation, it indicates the basis of hundreds of observations extending period of time, usually within a year, that the over several field seasons. The table lists ground on which the vegetation grows is sub­ only those species that were found in enough merged or inundated. As this permanence and potholes to be classed as commonly present. salinity are continually subject to change, so For a more detailed table see Stewart and also are the species and densities of vegeta- Kantrud (1968).

Common species of emergent vegetation as indicators of permanence and salinity of water in potholes on the Coteau du Missouri, N. Oak.

[Prepared by R. E. Stewart, Bureau of Sport Fisheries and Wildlife]

Salinity and range in Permanence of water at site of indicated species2 specific conductance1~------T------T------­ (micromhos per em) Less than 1 month 1-4 months More than 4 months

Fresh P oa pa Ius tris A lisma triviale Scirpus heterochaetus 0-700 Calamagrostis canadensis Polygonutti coccineurn Sc irpus fluviati lis Carex praegracilis Glyceria grandis Typha latifolia Carex lanuginosa Carex atherodes ]uncus dudleyi Sparganium eurycarpum I

10 GENERALIZED HYDROLOGY OF PRAIRIE PO~OLES ON THE COTEAU DU MISSOURI, NORTH DAKOTA i Common species of emergent vegetation as indicators of permanence and salinity of water in potholes on the Coteau du Missouri, N. Dak.-Continued Salinity and range in Permanence of water at site of indicated species2 specific conductance1 (micromhos per em) Less than 1 month 1-4 months More than 4 months

Slightly saline Calamagrostis inexpansa Alisma gramineum "Typha glauca;;a 700-31000 Juncus balticus Beckmannia syzigachne Scirpus acutus Juncus torreyi Scolochloa festucacea Spartina pectinata Carex atherodes Hordeum jubatum Eleocharis palustris Carex sartwellii

I Moderately saline Hordeum. jubatum i Eleocharis palustris Scirpus acutus 31000-121000 Distichlis stricta Scirpus americanus Scirpus paludosus Muhlenbergia asperifolia Puccinellia nuttalliana Spartina gracilis

Very saline or briny Distichlis stricta Salicornia rubra Scti'pus paludosus 12,000-70.000 Muhlenbergia asperifolif Puccinellia nuttalliana Suaeda depressa

I Scirpus nevadensis

: 1These ranges in specific conductance dif1fer somewhat from those used by the Geological Sur­ vey which are based on other needs~ especially that of defining fresh water for domestic use. 2The time divisions used here are purely arbitrary; large deviations from them can be expected. 3 Recent investigations show this species to be a hybrid of T. latifolia and T. angustifolia.

There are no common names for many of composed of several species. Each species the species listed; therefore~ it is necessary seems to be associated with a range of salinity to consult a manual of plants to make full use and permanence of water to such an extent of the above table. For the casual reader some that it can be used as an indicator of those conditions in this area. Where species of dif­ common names of the genera listed are1 al­ phabetically: ferent ranges in salinity are growing together~ the salinity indicated is the range common to

Alisma1 waterplantain both species. For example, a pothole may con­

Beckmannia 1 sloughgrass contain both Carex atherodes and Eleocharis palustris. Calamagrostis, reedgrass As shown in the table~ Carex atherodes grows in Carex. sedge fresh to slightly saline water and Eleocharis Distichlis, saltgrass palustris grows in slightly saline to moderately Eleocharis~ spikerush saline water. This would indicate that the pot­ Glyceria1 mannagrass Hordeum~ wild barley hole has slightly saline water. Juncus, rush

Muhlenbergia1 muhly As the water level in a pothole fluctuates it Poa, meadowgrass covers and uncovers vegetation on its shores. Polygonum~ smartweed Therefore~ vegetation that grows in the center Puccinellia, alkaligrass of a shallow pothole can also grow near the Salicornia~ glasswort~ samphire shore of a deep pothole where the permanence Scirpus~ bulrush Scolochloa~ sprangletop, whitetop of water is about the same. In using the table Sparganium~ burreed to estimate the permanence of water, the user Spartina, cordgrass should be careful to apply it only to the site of Suaeda~ sea blite the particular plant species observed. Typha, cattail Stewart's table may be incomplete because The table is very useful in making a firtst it does not include a permanence beyond which approximation of the salinity of any particul~r no vegetation, or only a very few well adapted pothole. Vegetation in any pothole usually'is species, will survive. Such a condition is REFERENCES 11

described by Harris and Marshall (1963) who flow of this fresher water as it mixes w~th the also cited many references to the effect that main and becomes more Paline. continuously flooded emergent vegetation sel­ dom survives for more than 5 years, or less The depth of water in a pothole and the if subjected to increased wave action or species of emergent vegetation that may be greater depth of flooding. With respect to present or absent represent the total eL~ect of their own investigation (p. 342) they reported: current hydrologic events combined with un­ usual events of the past. Undoubtedly the ef­ "Spike rush[Eleocharis palustris] and soft-stem fect of the extremely high stages reached by bulrush[Scirpus validus]were destroyed by flood­ the water in 1950 lasted for a long time. To ing with over 15 inches of water in 3 years what extent it governed the order in which pot­ and in any continuously flooded area in 4-5 holes went dry in the early 1960's is not years. These species persisted only in shore­ known. line evaporation zones. Common cattail [Typha latifolia] and sedges [Car ex atherodes, C. pseudo­ REFERENCES cyperus, and C. lacustris] were gone from con­ tinuously flooded areas in 4-5 years and also Eisenlohr, Wm. S., Jr., 1966a, Water losE from persisted only in shoreline evaporation zones. a natural pop.d through transpiration by hy­ 'Hybrid' cattail remained unchanged in 24 drophytes: Water Resources Research, v. 2., inches of water throughout 5 years of flooding." no. 3, p. 443-453. ---1966b, Determining the water balance of Whether such a situation exists for the com­ a lake containing vegetation: Internat. Assoc. mon species of the open prairie on the Coteau Sci. Hydrology Pub. 70, Symposium of Garda, du Missouri is uncertain. No specific obser­ 1966, v. 1, p. 91-99. vations were made for this purpose. It was Harris, S. W., and Marshall, W. H., 1963, Ecol­ definitely observed, however, that permanence ogy of water-level manipulations on a north­ and depth of water have a controlling effect on ern marsh: Ecology, v. 44, no. 2, p. 331-343. emergent vegetatiOn. Such vegetation disap­ Kadlec, J. A., 1962, Effects of a dr:awdown 0n pears rapidly once it is inundated beyond the a waterfowl impoundment: Ecology, v. 43, critical depth. no. 2, p. 267-281. Kohler, M. A., Nordenson, T. J ., and Baker, Once emergent vegetation has died as are­ D. R., 1959, Evaporation maps for t,he United sult of flooding, rapid regrowth will not take States: U.S. Weather Bur. Tech. Parer 37, place until the soil is again uncovered. As pls. 2 and 4. stated by Kadlec (1962), "many emergent Meyboom, P ., 1963, Patterns of groundwater plants, including cattail and bulrush, must have flow in the prairie profile, in P roce

tions in the United States, Alaska, Hawaiian Winters, Harold A., 1967~ ThE. extent of the Islands~ and Puerto Rico: U.S. Weather Bur. Coteau du Missouri in soutr-central North Tech. Paper 25, p. 34. Dakota, in Glacial geology of the Missouri Willis, W. 0.~ Parkinson, H. L., Carlson, C. W., Coteau and adjacent areas-Midwest Friends and Haas, H. J., 1964, Water table changes of the Pleistocene~ Field Conf. 1967 Guide­ and soil moisture loss under frozen condi­ book: North Dakota Geol. Survey Misc. Ser. tions: Soil Sci., v. 98, no. 4, p. 244-248. 30, p. 63-70.

-1< U. S. GOVERNMENT PRINTING OFFICE : 1968 0 - 310-344