Hydrology and Chemistry of Selected 

Prairie Wetlands in the Cottonwood Lake 

Area, Stutsman County, North Dakota, 

1979-82

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1431
Hydrology and Chemistry of Selected 

Prairie Wetlands in the Cottonwood Lake 

Area, Stutsman County, North Dakota, 

1979-82

By J. W. LABAUGH, T. C. WINTER, V. A. ADOMAITIS, and G. A. SWANSON

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1431

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 198?
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging-in-Publication Data

Main entry under title:

Hydrology and chemistry of prairie wetlands, in the Cottonwood Lake area, Stutsman County, North Dakota, 1979-82.

(U.S. Geological Survey professional paper ; 1431)

Bibliography : p.

Supt. of Docs, no.: I 19.16:1431

1. Hydrology North Dakota Cottonwood Lake (Stutsman County) 2. Wetlands North Dakota Cottonwood Lake

(Stutsman County) 3. Water chemistry. I. LaBaugh, J. W. II. Series: Geological Survey professional paper ; 1431. 

GB705.N9H83 1987 551.48'09784'52 85-600279

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, 

Federal Center, Box 25425, Denver, CO 80225
CONTENTS

	Page

Conversion factors ----------------------------------------- m

Abstract -------------------------------------------------- i

Introduction ---------------------------------------------- i

Purpose and scope ------------------------------------.- 2

Environmental setting of the study area ---------------- 3

Methods of investigation ----------------------------------- 3

Hydrologic conditions -------------------------------------- 5

Calendar year 1979 ----------------------------------- 5

Calendar year 1980 ----------------------------------- 7

Calendar year 1981 ----------------------------------- 9

Calendar year 1982 ----------------------------------- 13

Water chemistry ------------------------------------------ 13

Ground water ----------------------------------------- 13

Water chemistry Continued

Wetlands --------------------------------------------- 17

Relation to aquatic vegetation -------------------------- 20

Implications of the interaction of prairie wetlands and

ground water ---------------------------------_.... 22

Hydrologic relations ----------------------------------- 22

Water-chemistry relations ----------------------------- 23

Major ions ---------------------------------------- 23

Phosphorus and nitrogen -------------------------- 23

Conclusions ----------------------------------------------- 24

References cited ------------------------------------------- 25

ILLUSTRATIONS

FIGURE 1. Map showing hydrologic instrumentation and location of wetlands and wells sampled for chemical analysis ----------

2. Diagrams showing design for sampling water in wetlands ---------------------------------------------------------

3. Hydrographs of water levels in wetlands sampled for chemical analysis --------------------------------------------

4. Hydrographs of water levels in wells sampled for chemical analysis ------------------------------------------------

5. Hydrologic sections showing relation of wetland water levels to water-table levels for four dates in 1979 -------------

6. Hydrologic sections showing relation of wetland water levels to water-table levels for five dates in 1980 --------------

7. Map showing altitude and configuration of the water table for April 25 and November 26, 1980 ---------------------

8. Hydrologic sections showing relation of wetland water levels to water-table levels for five dates in 1981 --------------

9. Hydrologic sections showing relation of wetland water levels to water-table levels for five dates in 1982 --------------

10. Schoeller diagrams showing average annual major-ion composition of the water in wells ----------------------------

11. Schoeller diagrams showing seasonal and annual changes in the major-ion composition of the water in wetlands ------

12. Piper diagrams showing the range in chemical composition of water in the wetlands, 1981 --------------------------

13. Diagrams summarizing regression analyses showing the relation between water level and major-ion concentration in 

	each wetland ----------------------------------------------------------------------------------------------

14. Graphs summarizing phosphorus and nitrogen data from wells and wetlands showing differences along the hydrologic 

	section ----------------------------------------------------------------------------------------------------

Page

4

5

6

7

8

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11

12

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15

16

18

19

21

CONVERSION FACTORS

For the convenience of those readers who prefer to use U.S. customary units rather than the International System of Units (SI), the conversion factors for terms used in this report are listed below:

Multiply SI unit By To obtain U.S. customary unit

centimeter (cm) 0.393 inch

meter (m) 3.281 feet

kilometer (km) .621 mile

HYDROLOGY AND CHEMISTRY OF SELECTED PRAIRIE

WETLANDS IN THE COTTONWOOD LAKE AREA, STUTSMAN

COUNTY, NORTH DAKOTA, 1979-82

By J. W. LABAUGH.T. C. WINTER, V. A. ADOMAiTis,1 and G. A. SwANSON 1

ABSTRACT

The relation of hydrologic setting and temporal variability in hydrology to nutrient content and geochemical characteristics of a 

group of prairie wetlands and adjacent ground water was studied 

during the period 1979-82. Although data were collected from many 

wetlands and wells at the study site, emphasis in this report primarily is on four wetlands two seasonal and two semipermanent and 

four wells contiguous to them along a hydrologic section. The seasonal wetlands, T8 and T3, contained water only for a few weeks to 

months after filling in spring and early summer; both were completely dry by August. The semipermanent wetlands, PI and P8, 

contained water throughout each year and were ice covered in winter. One wetland, T8, recharges ground water. Wetlands PI and P8 

are in areas of ground-water discharge. None of the wetlands received water by channelized surface-water inlets. Only wetland P8 

had a channelized surface-water outlet. Ground-water-level data 

showed that high points of the water table did not always occur 

beneath land-surface highs. Reversals of ground-water flow occurred 

occasionally between two of the wetlands, T3 and PI.

Significant differences existed in the chemical composition of the 

wetlands based on their hydrologic setting. In general, the dominant 

cation and anion in the wetlands were potassium and bicarbonate in 

wetland T8, calcium and sulfate in wetland T3, magnesium and 

sulfate in wetland PI, and magnesium and bicarbonate in wetland 

P8. Significant seasonal differences existed in the water chemistry of 

the wetlands in ground-water discharge areas. Water in three of the 

wetlands, T3, Pi, and P8, was most dilute while they filled in spring 

after icemelt. Concentration increased during the open-water period, 

and two of the wetlands, PI and P8, became most concentrated under 

ice cover. Concentrations of total phosphorus and total nitrogen were 

greatest in wetlands in areas of ground-water recharge and least in 

wetlands in areas of ground-water discharge. Differences in the 

chemistry of water from wells in the adjacent ground water resulted 

primarily from the positions of the wells in the ground-water flow 

system. The chemical type of water from well 12, which was located 

in a ground-water recharge area, was calcium sodium bicarbonate. 

Water from well 4, located downgradient from wetland T8, and from 

well 16, located downgradient from wetland PI, typically was a calcium sulfate type. Water from well 13, located between wetlands T3 

and PI in an area of changing ground-water flow directions, was a 

magnesium sulfate type. Data from this study show that an understanding of hydrologic conditions is important in the interpretation 

of the water chemistry of wetlands in the study area.

1U.S. Fish and Wildlife Service.

INTRODUCTION

Numerous studies published in the proceedings of 

symposia on the subject of wetlands have indicated that 

the relation between hydrologic processes and the function and structure of wetland ecosystems is poorly 

understood (Good and others, 1978; Greeson and others, 1979). Probably the principal reason for this lack of 

understanding is that comprehensive, multidiscipline 

studies of wetlands rarely have been done; hydrologic 

studies seldom include comprehensive analyses of 

chemical and ecological processes, and, conversely, few 

ecological studies of wetland ecosystems include comprehensive investigations of hydrologic processes.

Some ecological studies of wetlands have presented 

evidence that the structure of biological communities is 

affected by hydrologic processes. Gooselink and Turner 

(1978) indicated that plant communities change because the frequency of inundation of wetland soils affects the availability of oxygen in the root zone. Studies 

of wetland seed banks were used by van der Valk 

(1981) to show how changes in water level alter plantcommunity structure. The ability of seeds or propagules to become established in areas of either standing 

water or no standing water was attributed to waterlevel changes.

Hydrologic setting also can affect structure of plant 

communities in wetlands, through its relation to wetland water chemistry; for example, Stewart and 

Kantrud (1972) determined that the composition of 

plant communities in prairie wetlands is correlated 

with specific conductance of water in those wetlands. 

Wetland water chemistry is related to hydrologic processes because those processes are a major factor in controlling the movement of chemical constituents to and 

from wetlands. Hemond (1980) noted that information 

on the movement of water to and from wetlands is essential for biogeochemical studies.

The wetland-biogeochemical studies most dependent 

on investigation or measurement of hydrologic proc-
HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

esses are those of chemical mass balance. Quantification of water inputs and outputs is an integral part of 

determining chemical inputs and outputs in massbalance studies; for example, Valiela and Teal (1978) 

indicated that the quantification of water and nutrient 

inputs and outputs is important in understanding nu 

trient dynamics of wetlands. Yet, in only a few studies 

have nearly all relevant hydrologic processes been 

measured as a basis for understanding biogeochemical 

processes in wetlands (Crisp, 1966; Valiela and others, 

1978; Mitsch and others, 1979; Hemond, 1980; Verry 

and Timmons, 1982). However, even in these studies, 

at least one hydrologic process that was a component 

of the water budget was measured some distance away 

from the study area or was calculated as the difference 

between measured inputs and outputs.

Ground water commonly is calculated as the difference between measured inputs and outputs in chemical 

mass-balance studies of lakes (Winter, 1981); this approach also commonly is used in the study of wetlands. 

A major problem with using the approach of calculating ground water as a residual in wetland studies is 

that hydrologic instrumentation usually is not optimal 

in either accuracy or placement relative to the wetland; 

the difference between measured inputs and measured 

outputs can have little hydrologic meaning because of 

errors in hydrologic measurement (Winter, 1981).

Conceptual models of ground-water flow systems 

near wetlands have been developed primarily by Canadian hydrologists; for example, Meyboom (1966, 1967) 

studied the interaction of ground water with several 

prairie wetlands and lakes in Saskatchewan. Many of 

Meyboom's study sites were of wetlands that received 

ground-water inflow because water-table highs underlaid land-surface highs. In some cases, the water table 

beneath hills would decline to the point where the wetland would have seepage from it to ground water for 

part of the year. Meyboom also conducted studies of 

open-water evaporation (1967) and of transpiration 

from phreatophytes near wetlands (1966,1967). Lissey 

(1971) also studied ground-water flow near prairie wetlands in Canada; he proposed that most ground-water 

recharge and discharge in that environment takes 

place in land-surface depressions that commonly are 

occupied by wetlands.

A few studies of wetlands have attempted to relate 

wetland water chemistry to the hydrologic concepts of 

Meyboom (1966,1967) or Lissey (1971). These few studies have been confined to prairie potholes in western 

Canada (Rozkowska and Rozkowski, 1969; Rozkowski, 

1967, 1969; Sunde and Barica, 1975) and have indicated that a relation exists between the water chemistry of lakes and wetlands and nearby ground water. 

Hydrologic data were not available in those studies. 

Consequently, water chemistry was interpreted by

using a conceptual model of hydrologic processes instead of in conjunction with directly measured hydrologic processes.

In most cases, wetlands have been studied individually rather than as a group within a hydrologic unit, 

such as a ground-water flow system. Many ecologists 

are unaware of ground-water flow systems and associated theory on the way ground water may effect the 

wetlands under investigation. This is manifested in 

studies of wetland biogeochemistry, where chemical 

mass-balance calculations include estimates of ground 

water by difference. Before chemical mass balances, 

including direct measurement of ground water, can be 

determined, wetlands need to be shown to be an integral part of ground-water flow systems. Such a system 

then can be used to begin to examine the relation between the water chemistry of wetlands and adjacent 

ground water.

Wetlands in the prairies of North America are ideal 

systems for such an investigation because many have 

no channelized surface-water inlet or outlet. Therefore, 

the hydrologic processes most likely to effect such 

ecosystems are those related to atmospheric exchange 

(rainfall-evaporation-evapotranspiration) and groundwater flow.

Hydrologic process research is being conducted in the 

Cottonwood Lake area of North Dakota (Winter and 

Carr, 1980). This area includes numerous wetlands 

within the same ground-water flow system. Concurrent 

investigation of ecological processes is part of the research program. For this report, the scarcity of interpretive studies of wetland water chemistry, based on 

comprehensive analysis of hydrologic processes, led us 

to ask the following questions: What is the hydrogeologic function of prairie wetlands? and what is the effect of hydrogeologic .setting on wetland water chemistry?

PURPOSE AND SCOPE

The objective of this report is to examine the relation 

of ground-water flow and related hydrologic characteristics to differences in major ions, total phosphorus, and 

total nitrogen among prairie wetlands in the Cottonwood Lake area, Stutsman County in North Dakota. 

During the period of study, 1979-82, the area had a 

small climatic cycle that began with a wet year (1979), 

followed by two dry years (1980 and 1981), followed by 

another wet year (1982). The hydrologic setting of the 

study site is analyzed to show the important features 

affecting selected wetlands. The chemical composition 

of water in the wetlands then is placed in the context of 

hydrologic setting, climatic cycle of the study period, 

and chemical composition of ground water in the study 

area.
INTRODUCTION

ENVIRONMENTAL SETTING OF THE STUDY AREA

Wetlands in the Cottonwood Lake area are being 

studied by the U.S. Geological Survey and the U.S. 

Fish and Wildlife Service because they are believed to 

be typical of the vast region of prairie wetlands in the 

Missouri Coteau region. Largely because of the wetlands, this region has long been recognized as a primary waterfowl breeding habitat in North America.

The Cottonwood Lake area is located in east-central 

North Dakota (fig. 1). It is situated in one of the higher 

parts, near the eastern edge, of the Coteau du Missouri 

(Winter and Carr, 1980). The coteau is a large glacial 

drift complex transecting north-south through North 

and South Dakota and consisting of end and stagnation 

moraine, ice contact, and outwash deposits (Colton and 

others, 1963). At the study site, the glacial drift is 

greater than 130 meters (m) thick. It consists largely of 

clayey, silty till, but a few thin lenses of sand of unknown lateral extent also were observed when test 

drilling for the water-table wells.

Local relief of the study area is about 30 m; the 

highest part is in the southeastern corner, and the lowest is in the northwestern corner (fig. 1). This magnitude of local relief is typical of the Coteau du Missouri. 

The higher part of the area, where wetlands T9, T8, 

and T5 are located, is separated from an intermediate 

level by a steep slope about 15 m high. The slope is most 

pronounced between wells 1 and 10. Wetlands T4, T3, 

P7, P6, PI, P2, P4, and Tl are situated at this intermediate level. The lowest part of the area has the appearance of a north-south-trending valley, which is separated from the intermediate level by a sharp slope 

about 10 to 15 m high. Wetlands T2, P8, and P9 are 

located in the valley.

Nearly all wetlands in the intermediate and high 

parts of the area do not have surface-water outlets. One 

exception is wetland T3, which occasionally overflows 

to wetland PI for a week or two after snowmelt. Wetlands T2 and P8, in the valley along the west edge of 

the area, are connected by surface-water channels that 

contain water intermittently. Location and identification of wetlands, wells, and instruments in the Cottown wood Lake area are shown in figure 1.

Four wetlands were selected for the detailed study 

presented here. Two, T8 and T3, were seasonal, containing water for only part of the year. Two, PI and P8, 

were semipermanent, containing water throughout the 

year. Although data were collected from many wetlands, these four wetlands were selected because they 

were representative of the variety of wetlands at the 

site. They also were along a line of water-table wells 

designed to determine the water-table configuration 

between the highest and lowest parts of the study area 

(Winter and Carr, 1980). Four of these wells (4,12,13,

and 16) were chosen for detailed study because of their 

location with respect to the four wetlands selected for 

the study. Because of the location of these selected wetlands within this network of water-table wells, the position of these wetlands within the local ground-water 

flow system could be defined.

Vegetation in the general area consists of a variety of 

prairie herbs and grasses. A few small patches of aspen 

and chokecherry occur on north-facing slopes. A comprehensive report on the aquatic vegetation of the wetlands of the area is given by Stewart and Kantrud 

(1972). Because wetlands T8 and T3 are dry part of the 

year, they are dominanted by shallow-marsh plant species that occupy the central part of the wetlands. 

Slough sedge (Carex atherodes) and marsh smartweed 

(Polygonum cuccineum) are found in the shallowmarsh zone of wetland T8. Whitetop (Scolochloa festucacea) is a dominant plant species of the shallow-marsh 

vegetation in wetland T3. Wetlands PI and P8 retain 

water year around; as a result, these two wetlands support deep-marsh plant species and submerged vascular 

plants in the central part of the wetland. Hardstem 

bulrush (Scirpus acutus) and cattail (Typha latifolia 

and T. glauca) usually dominate the deep-marsh zone 

of wetland PI. Cattail species are the dominant vegetation in the deep-marsh zone of wetland P8.

METHODS OF INVESTIGATION

Hydrologic characteristics of the wetlands and their 

watersheds that are important for this paper are precipitation, water depth of the wetlands, and groundwater flow. Precipitation was measured at the study 

site by using a recording tipping-bucket gage. A standard nonrecording gage was used as a backup instrument. Both gages, located between wetlands T3 and PI, 

were operated only during the open-water season. For 

the remainder of the year, precipitation data were obtained from a National Weather Service station in 

Woodworth, about 16 kilometers west-northwest of the 

study area. These latter data were used only to obtain 

general estimates of precipitation.

Water levels in wetlands were measured by using 

staff gages that were read weekly to biweekly. A 

recording stage gage was installed on wetland PI in 

July 1980. Altitude of the water table, which is the 

upper surface of the ground-water system, was determined by measuring water levels in water-table wells. 

[Details of well construction were given by Winter and 

Carr (1980).] A steel tape was used to measure water 

level in wells weekly to biweekly during spring 

through fall and monthly during winter.

Water samples for chemical analysis were collected 

from the wetlands on approximately a biweekly basis 

from spring thaw to formation of ice cover for wetlands
HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

PI and P8 and from spring thaw to a condition of being 

completely dry for wetlands T3 and T8. In addition, 

water was collected occasionally from wetlands PI and 

P8 when they were ice covered. During the period of 

open water, three samples of water were obtained from 

each wetland. The wetlands were divided by three transects into six zones of 60° each from the center of the 

wetland. The first transect always started at 158° with 

respect to magnetic north. In wetlands PI and P8, 

water samples were collected along each of the three 

transects 1 m outside the deep-marsh zone (fig. 2). In 

wetlands T8 and T3, samples were collected along each 

transect at a point one-half the distance between shore 

and the center of the wetland.

The entire water column was sampled at each site, 

using a 65-centimeter (cm)-internal-diameter acrylic 

tube column sampler described by Swanson (1978). The 

contents then were transferred to acid-cleaned

polyethylene bottles and brought to the chemical laboratory of the U.S. Fish and Wildlife Service Northern 

Prairie Wildlife Research Center Jamestown, N. 

Dak., for analysis.

Because of the low permeability of the glacial till at 

the study site, ground water for chemical analysis was 

collected by bailing the wells. Water standing in the 

wells was removed before sampling to assure that the 

sample collected was representative of ground water 

and that it had minimal contact with the well screen 

and casing. Water was collected in acid-cleaned 

polyethylene bottles before being brought to the chemical laboratory of the U.S. Fish and Wildlife Service 

Northern Prairie Wildlife Research Center for analysis.

Anions and Kjeldahl nitrogen were analyzed by 

using standard methods (American Public Health Association, 1980). Cations were determined by plasma

99°06' 99°05'30"

47°05'46"

EXPLANATION

WETLANDS

STAFF GAGE-Letter and number is 

designation of wetland

WATER TEMPERATURE AND 

WINDSPEED GAGES 

ON RAFT

D AIR TEMPERATURE,HUMIDITY.AND

PRECIPITATION GAGES 

.9

WATER-TABLE WELL AND NUMBER

O PIEZOMETER NEST

 LINE OF SECTION-Figures 5.6.8.and 9

Base from U.S. Geological Survey,Goldwin S.E., 1958

NORTH DAKOTA 

Study area

0 200 400 600 FEET 

CONTOUR INTERVAL 3 METERS 

DATUM IS SEA LEVEL

FIGURE 1. Hydrologic instrumentation and location of wetlands and wells sampled for chemical analysis.
HYDROLOGIC CONDITIONS

LOCATION OF SAMPLING TRANSECTS

WETLANDS T3 AND T8 WETLANDS P1 AND P8

Wet-meadow zone

\Fen zone

Low-prairie zone

SAMPLING POINT AT 

MIDPOINT OF TRANSECT

Wet-meadow zone

Shallow-marsh zone

Deep-marsh zone

SAMPLING POINT ALONG TRANSECT 

1 METER INTO OPEN-WATER ZONE

FIGURE 2. Design for sampling water in wetlands.

emission spectrometry. Total phosphorus was determined from unfiltered samples by the method used for 

cations. Specific conductance and pH were determined 

electrometrically in the laboratory.

Statistical analyses used in the study were linear 

regression, analyses of covariance, and analysis of variance (Helwig and Council, 1979). A significance level of 

P < 0.05 was accepted in all analyses unless otherwise 

stated.

HYDROLOGIC CONDITIONS

The following detailed description of ground-water 

levels and wetland water levels is given to emphasize 

the great variability in the mechanisms that control

direction of water flow between the ground-water system and the wetlands. The process changes annually 

and seasonally depending on the quantity of snow before snowmelt, timing of snowmelt, and quantity and 

timing of rainfall. Results show that it would be misleading to assume general processes exist, particularly 

if data are collected for only 1 or 2 years.

CALENDAR YEAR 1979

Winter 1978-79 had normal to greater-than-normal 

snowfall, resulting in an extensive snowpack that averaged 0.3-m depth before snowmelt in spring 1979. Melting of this snow resulted in high water levels in the 

wetlands (fig. 3). At wetland T8, which is at the highest
HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

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1979 1980 1981 1982 

FIGURE 3. Water levels in wetlands sampled for chemical analysis.

altitude of all the wetlands, the water level declined 

throughout May, and the wetland dried up in early 

June. A brief period of water-level decline in early June 

at all the wetlands was interrupted by intense rainfall 

June 19-22. As a result of this rainfall, water levels 

rose in all the wetlands, including wetland T8, which 

contained water until it again dried up near mid-July. 

After the June rainfall, water levels in all wetlands 

gradually receded throughout the summer. Wetland T3 

dried up in late August. Water levels in the semipermanent wetlands, PI and P8, receded to their lowest 

level in late October, at which time they froze.

All ground-water wells showed rapid response to 

spring recharge in 1979, as indicated in figure 4. After 

the spring water-table high in mid-May, the water 

table receded in altitude throughout the remainder of 

the year. A reversal in this water-level recession was 

caused by the intense rainfall in June and by another 

period of rainfall in early August.

To examine the interrelation of ground and surface 

water, it is useful to examine a hydrologic section 

(fig. 5) from the highest part of the study area to the 

lowest. The section transects the 15-m-high slope that 

occurs between wells 1 and 10. Wetland T5 is located at 

the top of the slope; wetlands T4 and T3 are at the base 

of it.

Starting at the topographically highest part along 

the hydrologic section, the water level in well 4 is always lower than that in wetland T8, indicating that 

this wetland has seepage from it on its downgradient 

side whenever it held water. Wetland T5 also shows a 

water-table gradient away from it on both sides for the 

entire period it held water. Water-level information 

from well 1 shows a depression in the water table similar to that near well 24 (fig. 5). These data indicate 

that, in the higher parts of the area, water-table highs 

do not underlie land-surface highs and that water-table 

highs are created by seepage from wetlands.

A mechanism to explain the mounds near wetlands 

and the water-table depressions beneath hills, which 

are controlled largely by the low permeability of the 

till, has been presented by Winter (1983), who used 

numerical simulation. These numerical simulations 

showed that, in porous media of low permeability, 

water-table lows are common beneath land-surface 

highs. Depending on the magnitude of recharge and 

permeability of the porous media, this condition can 

persist for considerable periods of time. Numerical simulation of unsaturated-saturated flow in porous media 

(Winter, 1983) also has shown that ground water is 

recharged quickest directly next to surface water.

The phenomenon of water-table lows underlying
HYDROLOGIC CONDITIONS

land-surface highs was observed in the Cottonwood 

Lake area, as shown by the very low position of the 

water table between wetlands T8 and T5. At first, it 

was believed that the water-table low was a result of 

poor well construction. However, four wells in place 

between wetlands T8 and T5 confirm this low position 

of the water table in this area. Again, numerical simulation of the interaction of lakes and ground water 

(Winter, 1976) indicates that, if an area is underlain by 

a more permeable unit, recharge to the lower unit significantly affects water movement in the upper unit 

and that it would tend to cause the water table to be 

lower. Sand was observed in the bottom of the test hole 

drilled for well 24, but the extent of the sand unit has 

not been mapped.

In the intermediate level of the study area, the water 

table slopes toward wetland T3 from wells 11 and 12 

(upgradient side of wetland T3). Water-table levels on 

the side of wetland T3 toward wetland PI (downgradient side) were always lower than the wetland level, 

indicating seepage from wetland T3 to the groundwater system. Thus, wetland T3 and probably wetland 

T4 are flow-through-type wetlands; ground water enters one area of the wetland and exits from another 

area of the wetland.

For a time during late winter and early spring, wetland PI had seepage to ground water on its upgradient 

side, the side toward wetland T3 (fig. 5A). This appears 

to be a late-winter condition only because, as late as 

mid-October (fig. 5D), the water-table gradient was toward wetland PI, even after wetland T3 dried up.

On the downgradient side of wetland PI, the side 

toward wells 15 and 16, the water table had a mound 

higher than wetland PI during the period of study at 

well 16. However, water-level information from well 15 

shows a water table lower than in wetland PI before 

spring recharge (fig. 5A) and after late August.

These data from 1979 show the wetlands selected for 

detailed study are in a ground-water flow system in 

which water moves from an area of recharge, wetland 

T8, through an intermediate area, wetland T3. Available 1979 data from wells in the vicinity of wetlands PI 

and P8 were insufficient to clearly define their position 

in the flow system. A seasonal reversal in groundwater flow occurred between wetlands T3 and PI at the 

location of well 13.

CALENDAR YEAR 1980

Winter 1979-80 had very little precipitation; by 

April 1,1980, only a small quantity of snow was on the

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measurement

11,1,1 o I I I I I I I I I I I I I

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1979 1980 1981 1982

FIGURE 4. Water levels in wells sampled for chemical analysis.
HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

A April 25

METERS

585 -i

575- 

565- 

555- 

545- 

535

P8 P1 

B

Water table

B May 31

METERS 

585-i

575- 

565- 

555- 

545- 

535

C July 12

METERS 

585-,

575- 

565-

555- 

545- 

535

D October 15

METERS 

585-i

575- 

565-

555- 

545-

535

DATUM IS ARBITRARY VERTICAL EXAGGERATION X5

150 METERS

0 500 FEET 

TRACE OF SECTION SHOWN IN FIGURE 1

Figure 5. Relation of wetland water levels to water-table levels for four dates in 1979 (modified from 

Winter and Carr, 1980). A, April 25. B, May 31. C, July 12. D, October 15.

ground. Because of minimal snowmelt in 1980, water 

levels in the wetlands generally were lower than in 

1979, and the seasonal wetlands dried up by the end of 

April (fig. 3). As in 1979, however, more than 10 cm of 

rainfall in June resulted in water being present in the 

seasonal wetlands and in water-level peaks in the

semipermanent wetlands. After the wet June, seasonal 

wetlands quickly dried up again, and water levels in 

semipermanent wetlands receded sharply through 

July. Greater-than-normal rainfall in August and September caused water levels in permanent wetlands to 

rise slightly and to remain stable into October when
HYDROLOGIC CONDITIONS

they froze. A late-summer rainfall did not cause water 

to be present in seasonal wetlands.

Recharge to ground water in 1980 began in April, but 

the water table reached a lower peak in 1980 than that 

of 1979 (fig. 4). The water level in well 16 showed no 

spring rise (fig. 4). Ground-water levels in most wells 

responded to the greater-than-normal late-summer 

rainfall. Well 13 showed particularly large rises in 

water level in contrast to the water level in well 16, 

which merely ceased to decline.

In the higher part of the area, ground-water flow 

directions between wetlands and ground water in 1980 

were much like those determined for 1979 (fig. 6). In 

the immediate level of the area, water seeped from 

wetland PI on the side toward wetland T3 during most 

of April (fig. 6A). At this time, wetland T3 also had 

seepage from it on its upgradient side, toward well 12, 

which is a relatively rare condition. By May 19 

(fig. 6B ), the water table between wetlands PI and T3 

(at well 13) was higher than the water level in wetland 

PI, thereby reversing the direction of ground-water 

flow in this area. The same is true of wetland T3 and 

well 12. This latter flow condition continued through 

the remainder of 1980 (fig. 6C-E).

Ground-water flow conditions between wetlands PI 

and P8 in 1980 were considerably different from those 

in 1979. During 1979, the water level in well 16 was 

always higher than that in well 15. In the early part of 

1980, the water level in well 16 was higher than that in 

well 15, but, by November, it was lower. In addition, 

the relation of the water level in well 16 to that in 

wetland PI was much different in 1980 compared to 

1979. In 1979, the water level in well 16 was always 

higher than the level of wetland PI; but, in 1980, it was 

lower from early spring to midfall. By November, water 

levels in wells 15 and 16 were higher than the water 

level in wetland PI. The significance of the 1980 data 

for wells 15 and 16 and wetland PI is that the groundwater system in this area also had reversals of groundwater flow similar to, but not as short term as, that of 

the area between wetlands PI and T3.

Construction of additional water-table wells (wells 

17-29) in August 1980 made it possible for the first 

time to determine the areal configuration of the water 

table in the study area. Water-table maps for many 

dates were constructed; the general configuration was 

consistent for periods of high and low ground-water 

levels (fig. 7). The maps show that wetland PI was 

principally in a ground-water discharge area and that 

the reversals of flow discussed for this 4-year period 

apply only to the low areas in the intermediate level 

along the hydrologic section.

As in the previous year, data from 1980 showed wetland T8 to be an area of ground-water recharge and 

wetland T3 to be intermediate, receiving ground-water 

discharge and, then, recharging ground water. Additional wells in the vicinity of wetlands PI and P8 indicated that they were in areas of ground-water discharge. Reversals in ground-water flow again occurred 

between wetlands T3 and PI; however, these reversals 

were of shorter duration than those of 1979. Unlike 

1979, reversals of flow also were determined between 

well 12 and wetland T3 and between wetlands PI and 

P8. Reversals in flow between wetlands PI and P8 were 

of longer duration than reversals between wetlands 

T3 and PI.

CALENDAR YEAR 1981

During winter 1980-81, only small quantities of 

snow fell in the study area; virtually no snow was on 

the ground before icemelt. Consequently, water levels 

in the wetlands in early spring 1981 were at low levels 

for the second consecutive year. Further, because of the 

warmer winter, ice in the wetlands melted in early 

March, which was at least 1 month earlier than in any 

other year of the study period.

Precipitation in late March caused rises in water levels in all wetlands (fig. 3). These rises were followed by 

declines of water levels through April, when wetland 

T8 dried up, and May, until a wet period in late May 

through June caused a second, but lower, water-level 

peak in June. After late June, water levels in the wetlands declined for the remainder of the open-water season. Wetland T3 dried up in late July.

The fluctuation pattern of ground water, indicated 

by the well data (fig. 4), was similar to that in 1980 

with respect to magnitude and shape of spring peaks. 

The only exception was well 16, in which the water 

level rose to a peak in July, whereas, in 1980, no rise in 

water level occurred (fig. 4). Because no major rainfall 

occurred in late summer 1981, in contrast to 1980, no 

significant interruption of the summer-through-winter 

recession occurred.

Unlike the previous 2 years, because of the unusually low water levels in the wetlands, especially in wetland PI, no seepage occurred from wetland PI on the 

side toward wetland T3 (fig. 8A). Thus, throughout the 

part of 1981 that wetland T3 held water, ground-water 

flow always was from wetland T3, past well 13, to wetland PI (fig. 8A-D). Reversal of ground-water flow in 

the area between wells 15 and 16 again occurred in 

1981, but that reversal was of a much longer duration 

than that of 1980. A reversal of ground-water flow from 

well 15 to wetland PI also occurred in 1981; in 1980, 

however, no reversal occurred.
10 HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

A April 1

METERS

585-1 

- P8 T1 P1 T3 T4

Land surface 13

Water table

1211

B May 19

METERS 

585-i

575- 

565- 

555- 

545- 

535

C June 30

METERS 

585-i

575- 

565- 

555- 

545- 

535

D August 26 

METERS 

585-1

575-

565- 

555- 

545- 

535

o ,_;

£ November 26

METERS 

585-i

575- 

565- 

555- 

545- 

535

DATUM IS ARBITRARY VERTICAL EXAGGERATION x5

150 METERS

0 500 FEET 

TRACE OF SECTION SHOWN IN FIGURE 1

FIGURE 6. Relation of wetland water levels to water-table levels for five dates in 1980. A, April 1. B, 

May 19. C, June 30. D, August 26. E, November 26.
AUGUST 25, 1980

47° 06' 00"

47°05'45"

HYDROLOGIC CONDITIONS 

99° 06' 00"

11

99°'05' 30'

NOVEMBER 26, 1980

47° 06' 00'

47° 05'45"

99° 06' 00" 99° 05'30"

to WETLAND AND 

iP DESIGNATION

 WATER-TABLE WELL

EXPLANATION

563.8 WATER-TABLE CONTOUR-Shows altitude of water on 

CTi ' |Ta indicated date. Dashed where inferred. Hachures indicate

depression. Contour interval, in meters, is variable.

Datum is sea level

FIGURE 7. Altitude and configuration of the water table for August 25 and November 26, 1980.
12 HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

A March 16 

METERS 

585 -

575- 

565- 

555- 

545- 

535

T1

in Land surface

P1

 Water table

B April 30 

METERS 

585-,

C June 10

METERS 

585-i

575- 

565-

555- 

545- 

535

in in

8 in

D Julv 20 

METERS 

585-i

575- 

565- 

555 ~ 

545- 

535

£ November 3 

METERS

585-,

575- 

565- 

555- 

545- 

535

DATUM IS ARBITRARY VERTICAL EXAGGERATION x5

150 METERS

0 500 FEET 

TRACE OF SECTION SHOWN IN FIGURE 1
HYDROLOGIC CONDITIONS 13

As in 1979 and 1980, wetland T8 was an area of 

ground-water recharge. Wetland T3 had ground water 

flowing through it. Wetlands PI and P8 were in areas 

of ground-water discharge. No reversals of flow occurred between wetland T3 and well 12, between wetlands T3 and PI, or between wetlands PI and P8. The 

only reversal in ground-water flow occurred between 

wetland PI and well 15.

CALENDAR YEAR 1982

Although snowfall during winter 1981-82 was not as 

great as that of 1978-79, about 0.3 m of snow was on 

the ground in early March just before snowmelt. This 

accumulation resulted in early spring water levels in 

the wetlands being higher than they had been the two 

previous years; water levels were similar to those of 

spring 1979 (fig. 3).

Precipitation in May and June was sufficient either 

to maintain stable water levels in the wetlands or to 

cause them to have only minor declines, followed by a 

second, lower, peak in June. Steady water-level declines continued through the remainder of the summer 

and fall. Wetland T8 held water longer than at any 

time during the study period; then it dried up in midJuly. Wetland T3 also held water until mid-July.

In early October, an exceptionally large rainfall, 

about 13 cm, occurred, which is about two to five times 

greater than normal for October. This rainfall caused 

sharp water-level rises in wetlands PI and P8; it also 

resulted in wetland T3 again holding water until the 

wetlands froze in late October.

Ground-water levels also responded to recharge from 

the large snowmelt in 1982 by showing sharp spring 

rises to peaks that were equivalent in some wells, such 

as 4 and 13, to the peaks of 1979 (fig. 4). In other wells, 

such as 12 and 16, the peaks were lower than in 1979. 

Ground-water levels receded throughout the remainder of summer and fall, but all wells showed a rise in 

water levels in response to the large October rainfall. 

The water-table rise in October was especially sharp in 

wells 4 and 13 (fig. 4).

Examination of the hydrologic section for 1982 

(fig. 9) shows that wetlands T5 and T8 continued to 

have seepage to ground water on all sides, just as in the 

other 3 years of the study. In the area between wetlands T3 and PI, seepage from wetland PI moved toward well 13 only during a brief period in April (which 

is not shown on sections in fig. 9). In the area between 

wetlands P8 and PI, reversals of ground-water flow

FIGURE 8. Relation of wetland water levels to water-table levels for 

five dates in 1981. A, March 16. B, April 30. C, June 10. D, July 

20. E, November 3.

again occurred. The pattern of reversals was similar to 

those of 1981, although 1982 had a much wetter spring. 

Data from the 4 years show the wetlands selected for 

intensive study lie within a ground-water flow system 

that includes recharge and discharge areas. Wetland 

T8 is an area of recharge to the ground-water flow 

system. Between wetlands T8 and T3, configuration of 

the water table does not follow the topography of the 

land surface. Wetlands PI and P8 are in areas of 

ground-water discharge. In the low areas between wetlands T3, PI, and P8, configuration of the water table 

is dynamic. Reversals of ground-water flow are common between wetlands T3 and PI in the vicinity of well 

13. Timing and duration of these reversals are affected 

by seasonal and annual fluctuations in snowpack 

recharge and by rainfall. Less pronounced or frequent 

reversals of flow occur between wetlands PI and P8. 

Rare reversals in flow happen higher in the groundwater flow system.

WATER CHEMISTRY 

GROUND WATER

Distinct quantitative and qualitative differences 

occur in the dissolved major ions of water from wells 

sampled during the study (fig. 10). With respect to 

major ions, water in well 12 is the least concentrated, 

and water in well 13 is the most concentrated. Geochemical types of water in the wells were calcium 

sodium bicarbonate in well 12, calcium sulfate in wells 

4 and 16, and magnesium sulfate in well 13. Based on 

major-ion analysis, ground water at the study site is 

neither quantitatively nor qualitatively uniform.

To provide a ready means of comparing both water 

type and concentration, major ion data will be presented in the form of Schoeller diagrams (Schoeller, 

1959). Although some seasonal variation occurred in 

the concentration of some of the major ions in water 

from each well, differences in average annual concentration were more pronounced (fig. 10). Despite these 

changes in concentration, with the exception of well 12, 

no difference was apparent in the geochemical type of 

water from year to year in the wells. Sodium replaced 

calcium as the most abundant cation only in 1981 in 

water from well 12.

Before examining differences in the geochemical 

type of water present in the wells, the positions of the 

wells in the ground-water system will be reviewed. 

Well 4 is downgradient along a ground-water flow path 

from a recharge area, wetland T8 (figs. 5-9). Well 12 is 

located in an area where ground-water was affected 

substantially by localized recharge to the ground-water 

system (figs. 5, 6, 8, 9). Although ground water in this 

vicinity would be expected to show evidence of dis-
14 HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

A April 30 

METERS 

585-1

575-

565- 

555 - 

545- 

535

T1

Q Land surface

P1 T3

Water table

B May 26

METERS 

585-,

575- 

565-

555- 

545- 

535

C July 19

METERS 

585-i

575- 

565-

555- 

545- 

535

D September 29

METERS 

585-1

575- 

565-

555- 

545- 

535

E October 27 

METERS

585-i

575-

565- 

555- 

545-

535

DATUM IS ARBITRARY VERTICAL EXAGGERATION X5

150 METERS

0 500 FEET 

TRACE OF SECTION SHOWN IN FIGURE 1
WATER CHEMISTRY 15

FIGURE 9. Relation of wetland water levels to water-table levels for 

five dates in 1982. A, April 30. B, May 26. C, July 19. D, 

September 29. E, October 27.

charge from adjacent ground-water highs (fig. 7), 

ground-water flow from these highs might be moving 

preferentially to wetlands rather than to the groundwater system between wetlands. The ground-water 

system in the vicinity of well 13 is in a discharge area 

for water moving from water-table highs in the adjacent valley walls (fig. 5). It also is in an area of alternating direction of ground-water flow between wetlands 

T3 and PI. Well 16 is in an area of ground-water discharge with some flow reversals between two wetlands 

that contained water throughout each year. Thus, each 

of the four wells was in a different position in the 

ground-water flow system.

If no chemical interaction occurs between water and 

the geologic material through which it moves along the 

ground-water flow path, then water in the four wells 

would be chemically identical and indistinguishable 

from water recharging the ground-water system. Data 

from the wells (fig. 10) and snowmelt recharge (fig. 11) 

show the water is neither chemically identical in the 

wells nor chemically indistinguishable from snowmelt 

at the Cottonwood Lake area.

The data shown in figures 10 and 11 indicate that 

some chemical interaction must occur between water 

and the geologic material through which it moves. It is 

assumed that, as water moves through geologic material along a ground-water flow path, interaction with 

that material takes place, as long as the ionic assemblage in the water is undersaturated with respect to the 

mineralogical composition of the geologic material. 

Thus, if water recharging the ground-water system 

was moving through gypsum, then the concentration of 

calcium and sulfate in the water would continue to 

increase until saturation for gypsum was achieved. 

Saturation could occur within a short distance along 

the ground-water flow path, if ground-water movement 

was slow, or within a longer distance along the flow 

path, if ground-water movement was fast. Consequently, composition of the water in a well is affected 

by geologic material in the flow path and by the position of the well in the ground-water flow system.

At the Cottonwood Lake area, geologic material in 

the area is assumed to be uniform. This assumption is 

based on results of drilling in the study area. The simplest explanation for the differences in the major-ion 

chemistry of the water in the wells then becomes one of 

a well's position in the ground-water system. Well 12 is 

in an area of ground-water recharge; therefore, water 

in well 12 has the least concentration of dissolved 

major ions (fig. 10) and is most similar qualitatively to 

snowmelt recharge of the wells sampled in this study 

(fig. 11). Well 13 is in an area of frequent flow reversals 

in a ground-water discharge area; so, water in well 13 

is the most concentrated (fig. 10). Comparisons of data 

from wells 13 and 12 indicate that, as water moved 

from a recharge area to a discharge area, the water 

became more concentrated with respect to sulfate and 

major cations, particularly magnesium.

Water from wells 4 and 16 is more concentrated than 

snowmelt recharge (fig. 11) or than ground water in a

1000,=-

1980 1981 1982

100

10

1

y 1

0.1

Well 13

UJ UJ

CO ^C/3

UJ dyj

Z Q<

C3 01-

< COO

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00 

m m DC DC

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mm DC DC

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m +

FIGURE 10. Average annual major-ion composition of the water in wells.
16 HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

recharge area, as represented by well 12 (fig. 10), particularly for calcium, magnesium, and sulfate. Because 

water in these wells is intermediate in concentration 

between a recharge area (well 12) and a discharge area 

(well 13), the wells must be along a flow path between 

recharge and discharge areas of the ground-water system. Although this is obvious for well 4 from the hydrologic sections and water-table contours presented in

figures 5 through 9, the same is not true for well 16. 

Based on water-table configuration data, well 16 definitely is in an area of ground-water discharge with 

some flow reversals. Yet, the chemical composition of 

water in well 16 is distinctly different from that in well 

13, which is in a similar position in the flow system, 

and statistically indistinguishable from water in well 

4, which is in a very different part of the ground-water

1979 1980 1981 1982 10 

1

0.1 

50

10

1 

CC 

LU

cc 0.1

£ 100

CO

z

LU

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$

D

a

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0.1>: 

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0 CO §CO g ^ ZZ U CO ^w o ^ 11 CJ CO §CO g "j ZZ <-> CO 2tn g u. zz 

< Z D< ° 3 °° < z QCO 3 D 00 ^ £ 5^ 3 D 00 ^ £ O CO 3 ^ O O

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< cop « < o « < '"o « $ o «

5J °- OCJ 5J Q. CJ CJ 5J °- CJCJ 2 °- CJ CJ

5+ m+ m+ CQ +

EXPLANATION

............... .. OMr\\A/KACI T t- A 1 1 / nt OO \ MI-AD PlDV / TO TO \

ooivy vv ivu

SPRING

-i- 1 r«i_i_ \ r i , ro ; IN

MIDWINTER ( ICE

c/^n uni \ i u , i *J /

E COVER PRESENT )

 85-100 PERCENT POTASSIUM »»»»»»»»»- NEAR COMPLETE DRYNESS

FIGURE 11. Seasonal and annual changes in the major-ion composition of the water in wetlands.
WATER CHEMISTRY 17

system. These chemical data indicate that well 16 could 

be affected by localized recharge not evident from the 

available hydrologic information on the existing well 

network.

Chemical equilibrium analyses of water from the 

wells support the conceptual model used here to explain ground-water chemistry. These analyses were 

done using the computer program WATEQ (Truesdell 

and Jones, 1974). Water in the wells differed in the 

degree of saturation for certain minerals typically 

found in the till of the area. These analyses indicated 

that supersaturating conditions existed for calcite in 

the four wells. Supersaturation of the calcium sulfate 

mineral, gypsum, was evident in water from wells 13 

and 16 throughout the study and in water from well 4 

only in the driest year, 1981. Conditions of supersaturation did not exist for any magnesium sulfate minerals. These analyses indicated that the increase in calcium, magnesium, and sulfate in ground water may be 

a result of dissolution of calcium sulfate and magnesium sulfate minerals; for example, when water 

reaches a ground-water discharge area, as in the vicinity of well 13, magnesium increases relative to calcium 

because supersaturating conditions exist for calcium 

sulfate minerals but not for magnesium sulfate minerals.

In contrast to major-ion chemistry, no significant difference in concentrations of nitrite, nitrate, total Kjeldahl nitrogen, or total phosphorus occurred from year 

to year in water from each well. A statistically significant difference was shown to exist only in 1981 and 

1982 between the ground water in each well on the 

basis of total Kjeldahl nitrogen alone; water from well 

13 had the maximum concentration both years. Although total phosphorus concentration was least in 

water from well 4 and greatest in water from well 16 in 

the 3 years data were obtained from the wells, this 

difference in concentration statistically was significant 

only in 1981. Concentration of nitrite (when detected) 

was always equal to or greater than concentration of 

nitrate. This relation of nitrate to nitrite was most pronounced in water from well 13. These nitrogen and 

phosphorus data indicate the mechanisms controlling 

concentrations of nutrients along the ground-water 

flow path are different from those controlling major-ion 

concentrations at the site.

WETLANDS

As in the case of the wells previously discussed, distinctly different geochemical types of water existed in 

each of the wetlands (fig. 11). In general, the dominant 

cation and anion in waters of the wetlands were potassium and bicarbonate in wetland T8, calcium and sulfate in wetland T3, magnesium and sulfate in wetland

PI, and magnesium and bicarbonate in wetland P8. 

Chloride was the least abundant major ion in the four 

wetlands. In contrast to the wetlands T3, PI, and P8, 

sodium and sulfate concentrations commonly were less 

than the detection limits in wetland T8.

Differences existed between the wetlands for majorion concentration as well as water type (fig. 11). Based 

on these major-ion data, waters in the wetlands showed 

the following general relation with respect to concentration: wetland T8 is less than wetland P8 is less than 

wetland T3 is less than wetland PI. Water in wetland 

T8 consistently had the least specific conductance 

[110-600 microsiemens per centimeter (jjtS/cm)] of the 

wetlands. The greatest value of specific conductance 

(7,140 |xS/cm) was measured under ice cover in wetland 

PI.

Very little seasonal change in concentration and 

water type occurred in wetland T8 when it contained 

water each year; similarity of concentration in early 

spring to concentration just before drying is shown in 

figure 11. A distinct change in water type occurred only 

when the wetland was almost dry, as in late May 1981. 

Sulfate was more abundant than bicarbonate.

Wetland T3 showed pronounced increases in concentration, particularly for calcium, magnesium, and sulfate, from the time it filled with water until it dried up 

in 1979, 1981, and 1982. The wide separation of points 

representing concentration in those years is shown in 

figure 11. Similar changes in concentration did not 

occur in 1980. A seasonal change in water type was 

measured only in 1980 and 1982, when magnesium 

increased slightly in abundance compared to calcium 

just before the wetland dried up.

Distinct seasonal patterns of changes in concentration of major ions were shown each year in wetland PI. 

Greatest concentrations were measured under ice 

cover; these concentrations were two to five times 

greater than the average concentration during the 

open-water season of 1981 (fig. 11). Water in the wetlands was most dilute during spring snowmelt; this was 

most evident at wetland PI for the snowmelt period of 

1979 (fig. 11) when concentrations of major ions were 

an order of magnitude less than during the rest of the 

year. Also, during snowmelt measured in 1979, water 

in wetland PI was a sodium bicarbonate type, in contrast to other times of the year when the water typically was a magnesium sulfate type. Concentrations, 

particularly of the most abundant anions and cations, 

steadily increased from early April to ice cover in late 

fall. This increase was most distinct in 1981, particularly for wetland PI.

Concentrations of major ions in wetland P8 increased 

slightly from April to ice cover in late fall; the most 

marked increase was measured in 1981 (fig. 11). Great-
18 HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

est concentrations of calcium, magnesium, and bicarbonate were in samples collected under ice cover in 

1981. Wetland P8 showed the most noticeable seasonal 

changes in major-ion type of all the wetlands; sodium 

became more abundant from spring to fall and was the 

dominant cation in October 1979 and 1981 (fig. 11). An 

example of the pronounced change in major-ion type in 

wetland P8, relative to the other wetlands, is shown by 

data from 1981 (fig. 12).

These data indicate that the wetlands differ qualitatively and quantitatively in the geochemical type of 

water present in each and that seasonal changes occurred in some wetlands. Hydrologic data presented in 

figures 5 through 9 show the wetlands are located in 

different positions in the ground-water flow system. 

Based on these data, the wetlands appear to be similar 

to the wells in that they differ chemically and in hydrogeologic setting. This study indicates that the chemical

Figure 12. Range in chemical composition of water 

in the wetlands, 1981.

composition of water in the wetlands is related to the 

position of the wetlands in the ground-water flow system, as was the case for the wells.

If the position of a wetland in the ground-water system does affect the geochemical type of water in the 

wetland, then water in wetlands in ground-water 

recharge areas would be similar to atmospheric deposition, and those in discharge areas would be similar to 

ground water in the discharge area. At the study site, 

wetland T8 was in a ground-water recharge area, and 

the water was a monovalent-cation bicarbonate type 

and relatively dilute, like snowmelt measured at wetland PI. Wetland PI was in a ground-water discharge 

area, and the geochemical type of water in the wetland 

was magnesium sulfate like ground water in a discharge area (well 13). The geochemical type of water in 

wetland T3 was similar to that found in ground water 

in a position along a flow path between ground-water 

recharge and discharge areas, represented by well 4. 

Water in both was a calcium sulfate type. Although 

wetland P8 was in a ground-water discharge area, it 

was not characterized by a magnesium-sulfate-type 

water; instead, it was a magnesium-bicarbonate-type 

water. The dominant cation, magnesium, was typical of 

ground-water discharge in the flow system at the site, 

as represented by water in well 13 and wetland PI. 

Unlike wetland PI, wetland P8 has an intermittent 

surface-water outlet.

Other hydrological processes can affect the type of 

water found in each wetland, in addition to the wetlands' position in the ground-water flow system, as 

shown by geochemical data from wetland P8. Water 

and chemical elements were supplied to the wetlands 

by snowmelt, rainfall, overland runoff, and groundwater inflow. Water and chemical elements were lost 

from the wetlands by outflow to ground water and by 

evaporation. In addition, losses occurred by an intermittent channelized surface-water outlet from wetland 

P8. The quantitative importance of each of these processes in determining the chemical composition of water 

in each wetland is beyond the scope of this report.

However, it is possible to examine indirectly the effect of concentration by evaporation. Each of the wetlands had some seasonal changes in the concentration 

of major ions; these changes were most pronounced in 

wetland PI and almost negligible in wetland T8 (fig. 

11). Typically, water in the wetlands was most dilute 

during snowmelt and loss of ice cover. Water in the 

wetlands became more concentrated while they contained open water; it became most concentrated under 

ice cover in wetlands PI and P8. Because water levels 

in the wetlands declined concurrently with the increase in concentration, change in water level and 

change in concentration appear to be correlated.
WATER CHEMISTRY 19

If concentration by evaporation alone was the process responsible for the seasonal changes measured in 

the major-ion composition of the water in the wetlands, 

then a significant statistical relation could exist between water level and concentration. Most of the variability in concentration then could be accounted for by 

changes in water level, providing evaporation alone 

resulted in water-level changes. Water-level changes 

were assumed to be an indirect estimate of changes in 

water volume of the wetlands because stage-volume 

data were unavailable. Results of regression analyses 

to examine the relation between changes in water level 

and in concentration are presented in figure 13.

Results of the regression analysis shown in figure 13 

do not support the statement that concentration by 

evaporation alone is responsible for the seasonal

WETLAND T8

changes in chemical composition shown in figure 11. 

These regressions, based on intercept, slope, and regression coefficient data, rarely were consistent from 

year to year. In many cases, water-level changes could 

account for only 60 to 70 percent of the variability in 

concentration. No significant regressions occurred for 

wetland T8, which was consistent with the fact that no 

statistically significant seasonal increase in concentration was determined for that wetland, in contrast to 

wetlands T3, PI, and P8. These statistical analyses 

indicate that processes other than concentration by 

evaporation were occurring in these wetlands. To confirm this, change-in-mass calculations would have to 

be performed to show changes in mass with time. 

Water-volume data necessary for such calculations 

were unavailable.

WETLAND T3

1980

1981

1982

EXPLANATION

NOT SIGNIFICANT

SAMPLE SIZE 3 

OR LESS

SLOPE NEGATIVE

SLOPE POSITIVE

R2<0.5

0.5 <R2 $ 0.75

0.75 <R2< 0.95

FIGURE 13. Relation between water level and major-ion concentration in each wetland.
20 HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

Comparison of data from wetlands T8, T3, PI, and P8 

(fig. 13) indicated changes in water level were statistically related most often to changes in concentration for 

wetland PI, most likely because it was in a groundwater discharge area with no surface outlet and only a 

narrow area of outflow by ground water. No quantitatively significant hydrologic process exists that could 

transport ions out of the wetland, thereby affecting 

measured concentration in the water remaining in the 

wetland. Thus, concentration by evaporation would be 

expected to be an important mechanism controlling 

major-ion concentrations in wetland PI in comparison 

to the other wetlands.

The relative importance of evaporation as a mechanism controlling major-ion concentrations in water 

within wetland PI varied from year to year. In the 

driest year of the study, 1981, the effect of groundwater inflow-outflow on major-ion concentration would 

be less than in the other, wetter, years. In 1981, the 

most abundant ions in wetland PI had nearly twice the 

increase per unit change in water level compared to 

any other year. Changes in water level accounted for 

greater than 85 percent of the variability in magnesium and sulfate, indicating that the effect of changes 

in water level on changes in concentration was most 

pronounced in a dry year.

To examine further statistical relations between 

changes in concentration and changes in water level 

between wet and dry years, analyses of covariance were 

used to compare regressions. Analyses showed differences between wet and dry years only in wetland PI 

and only for specific conductance. A statistically identical relation existed between changes in water level and 

specific conductance for 1980 and 1981, based on comparison of regressions. This regression relation for 

1980 and 1981 was different from regressions of water 

level and specific conductance in 1979 and 1982; 

changes in water level accounted for 72 to 74 percent of 

the variability in specific conductance in wetland PI 

for 1980 and 1981, whereas, in 1979 and 1982, these 

changes accounted for 61 percent.

In contrast to the major ions, changes in the concentration of total phosphorus and total Kjeldahl nitrogen 

in the wetlands did not have a steady increase from 

ice-melt to the formation of ice cover. Wetland T3 

had a marked increase in total phosphorus and total 

Kjeldahl nitrogen just before becoming completely dry 

only in 1981 and 1982. The concentration of total phosphorus just before complete dryness was more than 

double the concentration measured when wetland T3 

contained substantial standing water. In 1980 and 

1981, the concentrations of total phosphorus in wetland 

PI were greatest just after loss of ice cover, and the 

concentrations decreased to one-third of those maxima

from June to the formation of ice cover. This decrease 

did not occur in 1982. Patterns of change in concentration of phosphorus and nitrogen in wetlands T8 and P8 

showed no similarity in any of the 4 years of the study.

With respect to concentration of phosphorus and nitrogen, based on analysis of variance, significant 

statistical differences occurred between the wetlands 

in each year of the study. The concentration of total 

phosphorus was greatest in wetland T8 and least in 

wetland PI (fig. 14). The concentration of total phosphorus in wetland PI was nearly an order of magnitude 

less than that in wetland T8. Wetlands T8 and T3 always had significantly greater concentrations of total 

Kjeldahl nitrogen than did wetlands PI and P8.

These data for phosphorus and nitrogen for the wetlands indicate that mechanisms controlling concentrations of nutrients in the wetlands are different from 

mechanisms controlling major-ion concentrations. 

Phosphorus and nitrogen data do not show a steady 

increase in concentration with time beginning at 

snowmelt and loss of ice cover. Wetlands with the 

greatest phosphorus concentration had the least concentration of major ions. If the same mechanisms were 

controlling concentrations of major ions and nutrients, 

then concentrations of nutrients should have shown 

the same seasonal patterns and differences among wetlands as shown by the major-ion data.

RELATION TO AQUATIC VEGETATION

Plant communities of key wetlands examined in the 

Cottonwood Lake study area demonstrate the response 

of plant species to wetland hydrologic regimes, which 

determine the length of time water is present in the 

wetlands and chemical characteristics of the water. 

Wetlands in the study area were representative of different hydrologic regimes.

Wetland T8, located on a topographic high, receives 

precipitation and perhaps surface runoff as the dominant water sources; it functions as a recharge wetland 

that maintains a relatively small specific conductance. 

Indicators of water with relatively small specific conductance, slough sedge (Carex atherodes) and marsh 

smartweed (Polygonum cuccineum) (Stewart and 

Kantrud, 1972), are found in wetland T8.

Wetland T3 is located lower in the topographic profile; as a result, it receives ground water that increases 

the specific conductance of the water. Whitetop 

(Scolochloa festucacea), an indicator of increased 

specific conductance, is a dominant plant species of 

wetland T3.

Wetland PI is a closed system to channelized surfacewater outflow that establishes a dynamic hydrologic 

regime in response to changing climatic conditions.
WATER CHEMISTRY 21

oc

ULl

cc

Ul

e?

- 3

o

K 2 

<

CC

UIJ

o

U 7

1980

1981

I

1982

P8 W16 Pt W13 T3 W12 

WELLS AND WETLANDS

W4 T8

Figure 14. Phosphorus and nitrogen data from wells and wetlands showing 

differences along the hydrologic section.

Changes in water level are followed by major changes 

in dissolved chemical constituents of the water. 

Wetland vegetation zones respond to changing water 

levels by constantly adjusting to drawdown and reflooding cycles that are accompanied by changes in 

specific conductance. The central part of wetland PI

has varied from open water dominated by submerged 

vascular plants during high-water conditions to shallow marsh dominated by whitetop during low-water 

conditions.

Wetland P8 is an open system to surface-water outflow that tends to stabilize water levels and to main-
22 HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

tain a minimal specific conductance relative to its position in the ground-water flow system. This type of 

water regime provides conditions that support cattail 

dominance in the central part of the deep-marsh zone. 

Zonation tends to remain stable, and cattail has established a floating mat that is extending toward the central part of the wetland.

IMPLICATIONS OF THE INTERACTION OF 

PRAIRIE WETLANDS AND GROUND WATER

HYDROLOGIC RELATIONS

Results of this study indicate that the hydrologic interaction of wetlands and ground water in the glacial 

prairie environment is considerably more complicated 

than was indicated by some earlier studies (Meyboom, 

1966; Eisenlohr, 1972; Sloan, 1972). The reason for 

these differing views of complexity is most likely the 

result of differences in project design. Some of the earlier studies were of individual wetlands that did not 

give the complete range of wetland-ground-water interactions, as do studies of wetland systems situated at 

different altitudes along a topographic (and groundwater) slope.

The concept of depression-focused ground-water 

recharge and discharge as proposed by Lissey (1971) is 

a natural outgrowth of studying a series of wetlands on 

a valley side. This concept is substantiated fairly well 

in this study of the Cottonwood Lake area However, 

even the depression-focusing concept needs to be 

viewed with a perspective on the size of depressions 

needed to concentrate the surface water; for example, 

the water-table highs north and south of wetlands Tl 

and PI (by wells 28 and 29 on the north and wells 18 

and 22 on the south; fig. 7) did not show obvious depressions. Yet, water-table highs persisted in these areas. 

Although depressions for focusing recharge were not 

large, recharge to ground water apparently occurred in 

these uplands.

Study of the Cottonwood Lake area permitted synthesis of a number of concepts of the interaction of 

wetlands and ground water in the till-prairie environment. As stated before, Lissey's (1971) concept of 

depression-focused recharge and discharge was demonstrated clearly in the study area. Depression-focused 

recharge was particularly evident in the higher part of 

the area. Here, wetlands T8 and T5 served primarily as 

ground-water recharge pits. If either of these wetlands 

would be studied individually and if they were assumed 

to be representative of all prairie wetlands, then a serious misconception would result because they clearly 

represent only one possibility for the interaction of wetlands and ground water.

Wetlands in the intermediate and lower levels of the 

study area serve different functions with respect to 

ground water than wetlands in the higher area. Wetlands in these levels of the study area function either as 

areas of ground-water movement in and out of the wetland or as areas of ground-water discharge. The fact 

that the water chemistry from well 12 was so different 

from that of wetland T3 is an indication of depressionfocused ground-water discharge. Wetland T3 was an 

excellent example of a flow-through wetland; that is, 

most of the time, ground water seeped into one side, 

and wetland water seeped out the other side. Wetlands 

PI and P8 are good examples of ground-water discharge areas. Individual study of either of these wetlands and their contiguous ground-water system would 

result in the concept that water-table highs underlie 

land-surface highs and that the flow system is simply 

from these water-table highs to the adjacent lowland, 

which is occupied by a wetland. This concept, as seen in 

the Cottonwood Lake study area, also would be misleading if it were applied to all prairie wetlands. Results of studies in the Moose Mountain area of southern 

Saskatchewan (Rozkowska and Rozkowski, 1969; 

Rozkowski, 1967, 1969) need to be viewed from this 

perspective.

In addition to the implications of this study for 

understanding the interaction of wetlands and ground 

water, the results also add perspective to understanding ground-water flow in till of low permeability. 

Water-table lows underlying land-surface highs in the 

higher part of the study area provide onsite evidence 

for phenomena observed in theoretical modeling studies, as previously discussed in the section "Hydrologic 

Conditions."

Another aspect of theoretical numerical simulation 

studies with application to this study is the effect 

of water-table mounds between certain wetlands 

on ground-water flow and seepage. Studies of 

unsaturated-saturated porous media (Winter, 1983) 

also show that the depth of penetration into the 

ground-water system of local ground-water flow systems is related to water-table mounds of various 

heights. This relation is important to understanding 

the effect of ground-water recharge on seepage to and 

from surface water.

Finally, no discussion of ground-water flow in materials of low permeability is complete without mentioning flow in fractures. Clay-rich material commonly is 

fractured, particularly in the unsaturated zone. Grisak 

and others (1976) have discussed the hydrologic and 

geochemical properties of fractured till that is similar 

to till in the Cottonwood Lake area. Processes occurring in this till that affect water chemistry are described in the following section.
IMPLICATIONS OF THE INTERACTION OF PRAIRIE WETLANDS AND GROUND WATER 23

WATER-CHEMISTRY RELATIONS

MAJOR IONS

Geochemical interpretation by Rozkowski (1967, 

1969) of wetland interactions with ground water was 

based on the simplest hydrologic concepts of recharge 

under land-surface highs and discharge to adjacent depressions. Consequently, in a series of papers on prairie 

wetlands in Canada, Rozkowski (1967,1969) indicated 

that, in glacial moraine, ground water in recharge 

areas is a calcium magnesium sulfate type and that 

ground water in discharge areas is a magnesium sulfate type. Rozkowski (1967, 1969) also found calcium 

bicarbonate waters in sandy glacial deposits on slopes 

of hills. He did not interpret the calcium bicarbonate 

water type in the context of ground-water flow systems, 

as was done for calcium magnesium sulfate and magnesium sulfate water types.

Rozkowski's (1967,1969) interpretation of the hydrogeochemical patterns of prairie wetlands in Canada 

was based on assumptions of the local hydrology, following Meyboom's (1966, 1967) concepts of groundwater movement, and not on actual concurrent invesgation of the hydrology of his study area. The wetlands 

Rozkowski (1969) found to be a calcium bicarbonate 

type or a calcium magnesium bicarbonate type correspond to wetland T8 in the Cottonwood Lake area. The 

calcium magnesium sulfate waters of Rozkowski's 

"recharge" areas are similar to the waters found in 

wells 4 and 16 in the Cottonwood Lake area; both are 

some distance along the path of ground-water flow.

The increase in concentrations of magnesium, calcium, and sulfate along the ground-water flow path in 

the Cottonwood Lake area is similar to their occurrence 

in glacial till in other parts of the North American 

Prairie (Grisak and others, 1976). Based on calculations of saturation indices, Grisak and others (1976) 

suggested that the dissolution of soluble carbonates 

and sulfate minerals is the process responsible for the 

increase in these major ions as ground water moves 

through glacial till. This process occurs in the groundwater system at the Cottonwood Lake area, based on 

data from WATEQ chemical equilibrium analyses.

The effect of concentration under ice cover of the 

major ions followed by dilution of icemelt in wetlands 

PI and P8 is similar to that reported by Barica (1975) 

for prairie-pothole lakes in Canada. Although the hydrology of their area was not studied by Barica, Sunde 

and Barica (1975) indicated that Lissey's (1971) model 

of depression-focused recharge and discharge was representative of ground-water conditions in their study 

area. Barica (1975) measured the chemical composition 

of water from local farm wells and indicated that a

direct relation occurs between the composition of lake 

water and ground water.

Data from the Cottonwood Lake area provide some 

insight concerning the hydrogeological problem related 

to specific conductance and major-ion chemistry of 

lakes in the North-Central United States, as noted by 

Gorham and others (1983). In that study, they determined that lakes in the North-Central United States 

could be classified into five groups (I-V) on the basis of 

specific conductance. Of these five groups, only two (III 

and IV) occurred in the Cottonwood Lake area. According to the classification of Gorham and others (1983), 

Group III lakes had specific-conductance values between 141 and 501 |xS/cm. The specific-conductance 

range for Group IV lakes was 501 to 7,079 |xS/cm. A 

distinct geographical boundary existed between Group

III and Group IV lakes. Bicarbonate is dominant in 

Group III lakes, whereas sulfate is dominant in Group

IV lakes. Gorham and others (1983) stated the hydrogeological problem as not knowing (1) how much of the 

III-IV boundary could be explained by the effect of 

local versus regional ground-water flow and (2) how 

much of the III-IV boundary resulted from mineralogical and chemical differences in the glacial deposits.

Wetlands from the present study of the Cottonwood 

Lake area fell into two distinct groups, based on the 

classification of Gorham and others (1983) wetland 

T8 into Group III and wetlands T3, PI, P8 into Group 

IV. However, based on seasonal changes, the four wetlands could be put into either group. During ice loss 

and snowmelt, wetlands T3, PI, and P8 would be classified as Group III. When nearly dry, wetland T8 would 

be classified as Group IV. Gorham and others (1983) 

pointed out that, in arid areas (North Dakota and western Minnesota), seasonal variability in concentration 

and composition of lakes would occur. Consequently, a 

lake could be classified as either Group III or IV depending on what time of year it was sampled for analysis. This variation in classification based on time of 

sampling also was verified in this study for wetlands in 

the Cottonwood Lake area.

Data from the Cottonwood Lake area indicate that 

position within local ground-water flow was the major 

determinant of concentration and chemical composition with respect to major ions of surface-water bodies 

and of ground water. These data indicate that the effect 

of local flow systems can be important in the interpretation of the Group III-IV boundary described by 

Gorham and others (1983).

PHOSPHORUS AND NITROGEN

During an investigation of the nutrient regime of 

prairie-pothole lakes in Manitoba, Barica (1975) also
24 HYDROLOGY AND CHEMISTRY, SELECTED PRAIRIE WETLANDS, NORTH DAKOTA

found considerable seasonal variation in nutrient concentrations in the lakes. Total phosphorus and total 

nitrogen were inversely related to specific conductance. 

A similar relation was found in wetlands of the Cottonwood Lake area. Total phosphorus and total Kjeldahl 

nitrogen varied on a seasonal basis in wetlands of the 

Cottonwood Lake area. Wetland T8 had the least 

specific conductance and the greatest phosphorus and 

nitrogen concentrations during the period 1979-82.

The fact that wetland T8 had the greatest concentrations of total phosphorus and total Kjeldahl nitrogen 

can be explained, in part, on the basis of its position in 

the local ground-water system and its seasonal hydrologic cycle; wetland T8 has one or more periods of filling and drying annually. Macrophytes in wetland T8 

are subjected to a more rapid cycle of filling and drying 

than in the other wetlands. Standing dead 

macrophytes result from three conditions in wetland 

T8 flooding, drying, and freezing.

Ulehlova (1978) indicated phosphorus and nitrogen 

are leached rapidly from standing, dead, aquatic 

macrophytes. Rapid loss of phosphorus and nitrogen by 

leaching also has been measured by Davis and van der 

Valk (1978). They also noted that plant fragmentation 

accounts for the remainder of phosphorus and nitrogen 

losses from standing dead macrophytes. Because standing dead material would be produced more commonly 

in wetland T8 than in wetlands T3, PI, and P8, more 

frequent inputs of phosphorus and nitrogen to this wetland from the macrophytes would occur.

If the filling and drying of wetland T8 is responsible 

for greater concentrations of phosphorus and nitrogen, 

then other seasonal wetlands (for example, T3) should 

have greater concentrations of these elements than the 

semipermanent wetlands (PI, P8). Also, if the duration 

of standing water in seasonal wetlands is related to 

nitrogen and phosphorus concentrations, then wetland 

T3 should have lesser concentrations of these nutrients 

than does wetland T8. Both of these results actually 

occurred in the study area during the period 1979-82. 

The concentration of total Kjeldahl nitrogen was less in 

wetland T8 than that in wetland T3 only in 1982, when 

the duration of standing water was nearly equal for 

both wetlands.

Loss of elements from standing dead macrophytes in 

wetland T8, as suggested by phosphorus and nitrogen 

data, also might have been responsible for the relatively large concentration of potassium in that wetland. Potassium also is lost readily from dying or dead 

aquatic macrophytes (Chamie and Richardson, 1978; 

Davis and van der Valk, 1978; Ulehlova, 1978). The 

short cycle of filling and drying in wetland T8 would 

produce conditions favorable for the input of potassium 

from dead or dying macrophytes, thereby contributing

to the potassium bicarbonate water characteristic of 

the wetland. This condition is indicated by the fact 

that, in the wet years (1979, 1982), the abundance of 

potassium relative to the other cations was less than 

that in the dry years (1980,1981).

Being a recharge area to ground water explains why 

major ions do not show a pronounced increase with 

time due to concentration by evaporation in wetland T8 

relative to the other wetlands. These elements are lost 

through the wetland sediments to the ground-water 

system or to plant uptake. In the latter case, the elements are not lost completely from the system, but this 

will affect concentration in the water of the wetland 

only through leaching or during decomposition of the 

macrophytes, as indicated by the data for potassium. It 

is probable that most of the phosphorus and, to a lesser 

extent, the nitrogen in water moving from the wetland 

through its sediments are taken up by the 

macrophytes, rather than by entering the ground 

water. This would account for phosphorus and nitrogen 

concentrations being much less in the nearby ground 

water represented by water in well 4.

Many studies of wetlands have been done to determine what percentage of nutrient input is retained in 

the wetland (Valiela and Teal, 1978; Kadlec and 

Kadlec, 1979; van der Valk and others, 1979). However, only a few nutrient budget studies have attempted to measure most components of the water budget (Crisp, 1966; Valiela and others, 1978; Mitsch and 

others, 1979; Hemond, 1980; Verry and Timmons, 

1982). As noted by Richardson and others (1978), comprehensive nutrient budgets are essential to determine 

what fraction of input is not lost by output. Calculation 

of chemical budgets for the wetlands in the Cottonwood 

Lake area was not possible for the scope of this study. 

However, comparisons of a wetland (P8) with a surfacewater outlet, a wetland (T8) recharging ground water, 

and wetlands with no surface-water outlet and in a 

ground-water discharge area indicate that retention of 

phosphorus, nitrogen, and major ions in those wetlands 

would be a function of their hydrologic settings.

CONCLUSIONS

This study has shown that, in the glacial prairie environment, the hydrologic interaction of wetlands and 

ground water is considerably more complex than previously conceived. Ground-water recharge and discharge 

are depression focused, but water-table highs were 

found under broad land-surface highs in parts of the 

system. Study of hydrologic interactions for several 

years has indicated that predictions based on shorter 

term studies would produce misleading information
REFERENCES CITED 25

about the relation between wetlands and adjacent 

ground water. Reversals in ground-water flow between 

some wetlands were measured in this study, which indicate the need to study the adjacent ground water, as 

well as more than one wetland in a system of wetlands. 

Position within the local ground-water flow system 

primarily was responsible for the chemical composition 

of wetlands and the adjacent ground water. Seasonal 

and annual changes in the hydrologic conditions of the 

wetlands in ground-water discharge areas resulted in 

seasonal and annual differences in major-ion chemistry 

within those wetlands. Changes in phosphorus and nitrogen in water of the wetlands were unrelated to seasonal changes in hydrologic conditions of the wetlands. 

Differences between the wetlands on the basis of phosphorus and nitrogen appeared to be related to the effect 

of hydrologic variability on aquatic macrophytes. 

These data indicate that comprehensive knowledge of 

hydrologic setting is essential for chemical flux studies 

of prairie wetlands.

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