Distribution of Selected Nitrogen 

Compounds in Ground Water and the 

Unsaturated Zone, Superior-Hardy 

Special Protection Area, Nuckolls County, 

Nebraska, 1991-93
Distribution of Selected Nitrogen 

Compounds in Ground Water and the 

Unsaturated Zone, Superior-Hardy 

Special Protection Area, Nuckolls County, 

Nebraska, 1991-93

By ABRAHAM H. CHEN

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 96-4239

Prepared in cooperation with the

NEBRASKA DEPARTMENT OF ENVIRONMENTAL QUALITY;

LOWER REPUBLICAN NATURAL RESOURCES DISTRICT;

LITTLE BLUE NATURAL RESOURCES DISTRICT; and the

CONSERVATION AND SURVEY DIVISION,

UNIVERSITY OF NEBRASKA-LINCOLN

Lincoln, Nebraska 

1996
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

The use of firm, trade, and brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Geological Survey.

For additional information write to:

District Chief 

U.S. Geological Survey 

Room 406 Federal Building 

100 Centennial Mall North 

Lincoln, NE 68508

Copies of this report can be purchased 

from:

U.S. Geological Survey 

Branch of Information Services 

Box 25286 

Denver, CO 80225-0286
CONTENTS

Abstract.......................,......................................^ 1

Introduction.......................................................................................................................................... 2

Purpose and Scope...............................................................~...................................................................................... 2

Previous Investigations.............................................................................................................................. 2

Acknowledgments...................................................-^ 2

Description of the Study Area............................................................................................................................................... 3

Hydrogeology.............................................................................................^^ 3

Soils............................................................................................................................ 8

Land Use ...................................................................................................................................... 8

Ground-Water Quality .. ....---- -...----- ..---.----. ...-... ---.-....--............-.---.....-..--...........--.......--... 8

Methods................................................................................................................................................................................. 11

Site Selection and Monitoring-Well Installation......................................................................................................... 11

Water-Quality Sampling and Analysis........................................................................................................................ 13

Unsaturated-Zone Sampling and Analysis.................................................................................................................. 15

Statistical Data Analysis.............................................................................................................................................. 15

Distribution of Selected Nitrogen Compounds..................................................................................................................... 16

Nitrate in Ground Water.............................................................................................................................................. 16

Areal Distribution.............................................................................................................................................. 16

Vertical Distribution.......................................................................................................................................... 16

Temporal Variation............................................................................................................................................ 19

Nitrate and Ammonium in the Unsaturated Zone....................................................................................................... 23

Vertical Distribution and Change in Nitrogen Content..................................................................................... 23

Estimation of Rate of Vertical Transport of Nitrate........................................................................................... 23

Summary..........................................................................................._^ 33

Selected References.............................................................. 34

Additional Water-Quality and Sediment Data....................................................................................................................... 37

FIGURES

1 7. Maps showing:

1. Location of study area, Superior-Hardy Special Protection Area, Nuckolls County, Nebraska........................ 4

2. Generalized geology of the study area, Nuckolls County, Nebraska................................................................. 5

3. Altitude and configuration of the base of the aquifer system in the study area, Nuckolls County,

Nebraska....,.....................,..............................^ 6

4. Altitude and configuration of the water table and direction of ground-water flow in the study area,

Nuckolls County, Nebraska, fall 1992............................................................................................................... 7

5. Soil associations in the study area...................................................................................................................... 9

6. Agricultural land use in the study area, Nuckolls County, Nebraska, 1989...................................................... 10

7. Location of monitoring wells in the study area, Nuckolls County, Nebraska................................................... 12

8. Boxplot of nitrate concentrations from year 1 baseline data prior to the implementation of the management

plan and year 2 data after implementation of the plan in the study area, Nuckolls County, Nebraska...................... 18

9. Map showing areal distribution of median nitrate concentrations in ground water from 16 fully

penetrating wells in the study area, Nuckolls County, Nebraska, July 1991 through March 1992............................ 20

10-15. Graphs showing:

10. Stratification of nitrate concentrations in water samples from wells 9 and 13 in the study area,

Nuckolls County, Nebraska, 1991-93................................................................................................................ 21

11. Difference in median nitrate concentrations between year 2 and year 1 in ground water from fully

penetrating monitoring wells in the study area, Nuckolls County, Nebraska, 1991-93.................................... 22

12. Distribution of ammonium and nitrate concentrations and organic matter and silt-clay content with

depth at site 1 of the study area, Nuckolls County, Nebraska, spring 1991-93................................................. 26

CONTENTS IN
13. Distribution of ammonium and nitrate concentrations and organic matter and silt-clay content

with depth at site 9 of the study area, Nuckolls County, Nebraska, spring 1991-93 ........................................ 28

14. Nitrate content and total nitrogen and ammonium content beneath a corn field at site 1 in the

study area, Nuckolls County, Nebraska, spring 1991-93.................................................................................. 30

15. Nitrate content and nitrate and ammonium content beneath a corn field at site 9 in the study area,

Nuckolls County, Nebraska, spring 1991-93 .................................................................................................... 31

TABLES

1. Land use in the study area, Nuckolls County, Nebraska, 1989............................................................................... 11

2. Statistical summary of chemical quality of ground water in the study area, Nuckolls County,

Nebraska, 1988..................................................^ 11

3. Summary of monitoring-well characteristics in the study area, Nuckolls County, Nebraska, 1991....................... 14

4. Nitrate concentrations in samples from monitoring wells in the study area, Nuckolls County,

Nebraska, 1991-93..................................................._ 17

5. Summary of the sum of squares, the mean sum of squares, and its ranking for monthly nitrate

concentrations in water samples from 16 wells in the study area, 1991-93........................................................... 23

6. Mean organic-matter content, silt-clay content, and ammonium and nitrate concentrations as nitrogen

in multiple sediment cores for site 1 in the study area, Nuckolls County, Nebraska, spring 1991-93................... 24

7. Mean organic-matter content, silt-clay content, and ammonium and nitrate concentrations as nitrogen

in multiple sediment cores for site 9 in the study area, Nuckolls County, Nebraska, spring 1991-93................... 25

8. Summary of nitrate and ammonium contents in the unsaturated zone, sites 1 and 9 in the study area,

Nuckolls County, Nebraska, spring 1991-93.......................................................................................................... 29

9. Concentrations of bromide in sediment cores and estimated content for site 1 in the study area,

Nuckolls County, Nebraska, winter 1992 and spring 1993..................................................................................... 32

10. Concentrations of bromide in sediment cores and estimated content for site 9 in the study area,

Nuckolls County, Nebraska, winter 1992 and spring 1993..................................................................................... 32

11. Water-quality data for samples from 20 monitoring wells in the study area, Nuckolls County,

Nebraska, 1991-93...................................................._ 38

12. Nitrate and ammonium concentrations as nitrogen in sediment cores for site 1 in the study area,

Nuckolls County, Nebraska, spring 1991................................................................................................................ 46

13. Nitrate and ammonium concentrations as nitrogen and organic-matter content in sediment cores for

site 1 in the study area, Nuckolls County, Nebraska, spring 1992.......................................................................... 47

14. Nitrate and ammonium concentrations as nitrogen and organic-matter content in sediment cores for

site 1 in the study area, Nuckolls County, Nebraska, spring 1993.......................................................................... 48

15. Estimation of nitrate and ammonium content in sediment for site 1 in the study area, Nuckolls County,

Nebraska, spring 1991-93......................................................... 49

16. Nitrate and ammonium concentrations as nitrogen in sediment cores for site 9 in the study area,

Nuckolls County, Nebraska, spring 1991................................................................................................................ 50

17. Nitrate and ammonium concentrations as nitrogen and organic-matter content in sediment cores for

site 9 in the study area, Nuckolls County, Nebraska, spring 1992.......................................................................... 50

18. Nitrate and ammonium concentrations as nitrogen and organic-matter content in sediment cores for

site 9 in the study area, Nuckolls County, Nebraska, spring 1993.......................................................................... 51

19. Estimation of nitrate and ammonium content in sediment cores for site 9 in the study area,

Nuckolls County, Nebraska, spring 1991-93.......................................................................................................... 51

20. Grain size and nitrate and ammonium concentrations as nitrogen in sediment cores for site 1 in the

study area, Nuckolls County, Nebraska, spring 1991............................................................................................. 52

21. Grain size and nitrate and ammonium concentrations as nitrogen in sediment cores for site 9 in the

study area, Nuckolls County, Nebraska, spring 1991............................................................................................. 54

IV CONTENTS
CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

Multiply

acre

foot (ft)

foot per mile (ft/mi)

gallon per minute (gal/min)

gallons per day per foot [(gal/d)/ft)]

inch per hour

inch per inch

mile

pound (Ib)

pound per acre (Ib/acre) 

square inch (inch2) 

square mile (mi2) 

square foot per day (ft^d)

By

4,047

0.3048

0.1894

0.00006309

0.0124

25.4

25.4

1.609

0.4536

1.120 

645 

2.590 

0.0929

To obtain

square meter

meter

meter per kilometer

cubic meter per second

square meter per day

millimeter per hour

millimeter per millimeter

kilometer

kilogram

kilogram per hectare 

square millimeter 

square kilometer 

square meter per day

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F-32)/1.8

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD 

of 1929) a geodetic datum derived from a general adjustment of the first-order level nets of both 

the United States and Canada, formerly called Sea Level Datum of 1929.

ADDITIONAL ABBREVIATIONS

mg/L, milligrams per liter 

jiig/L, micrograms per liter 

mg/kg, milligrams per kilogram

CONTENTS
Distribution of Selected Nitrogen Compounds in 

Ground Water and the Unsaturated Zone, 

Superior-Hardy Special Protection Area, 

Nuckolls County, Nebraska, 1991-93

By Abraham H. Chen

Abstract

A ground-water-quality monitoring 

network of 20 wells located at 16 sites was 

established in 1991 in the 32-square-mile 

Superior-Hardy Special Protection Area in 

Nebraska. The purpose of this network was to 

monitor long-term trends in concentrations of 

nitrate in ground water after a management plan 

was implemented in 1991. Nested monitoring 

wells were installed at two sites to examine 

vertical distribution of nitrate concentrations in 

the area.

Nitrate concentrations greater than 

5 milligrams per liter were detected in 81 percent 

of the ground-water samples collected from the 

shallow aquifer during 1991-93. The occurrence 

of nitrate in ground water is related to groundwater flow direction and land-use patterns in the 

area. Nitrate concentrations ranged from 

5 milligrams per liter in the northern part of the 

study area to 15 milligrams per liter in the 

southern part. Most of the large nitrate concentrations were found in areas of irrigated farmland, 

particularly in lowland areas.

Difference in nitrate concentration with 

depth was measured at two sites in the lowland 

area. Nitrate concentrations are largest at the top 

of the saturated zone and decline with depth; 

therefore, the fully penetrating, fully screened 

wells yield samples most representative of the 

entire saturated thickness of the aquifer.

Two sites were chosen for sediment coring 

during 3 consecutive years (1991-93) prior to 

fertilizer application in the spring to estimate the 

nitrate and ammonium, organic matter, and siltclay content of the unsaturated zone. Maximum 

concentrations of nitrate were detected at or 

within 13 feet of the land surface at both sites, 

suggesting that the major source of nitrogen at 

these sites is from the land surface. Bromide 

tracer experiments were conducted to estimate the 

annual rate of movement of nitrate in the unsaturated zone. Bromide tracer had leached to 9 and 

13 feet below the land surface at the two sites. 

Thus, an annual rate of downward movement of 

nitrate was estimated to be about 11 feet. It may 

take about 2 years and more than 9 years for 

nitrate to reach ground water in the lowland and 

the upland, respectively.

Because of very slow ground-water 

movement and the time lag between the 

implementation of the management plan and 

water-quality improvement, significant changes in 

concentrations of nitrate in ground water were not 

detected during the study period (3 years). To 

identify changes in concentrations of nitrate in the 

ground water, long-term repetitive sampling over 

the spatial network is necessary. Such changes 

will be detected most quickly in the shallow 

ground water beneath the lowland area.

Abstract
INTRODUCTION

Continued detections of nitrate as nitrogen 

(nitrate) in the shallow aquifer in excess of the 

U.S. Environmental Protection Agency's (USEPA) 

Maximum Contamination Level (MCL) of 

10 milligrams per liter (mg/L) (U.S. Environmental 

Protection Agency, 1994) in parts of the Lower 

Republican and Little Blue Natural Resources 

Districts (NRD) led to a request for a Special Protection Area (SPA) designation. After conducting a 

ground-water-quality investigation during the spring 

and summer of 1988, the Nebraska Department of 

Environmental Quality (NDEQ) concluded that nitrate 

concentrations in ground water were sufficiently 

widespread and large enough to justify establishment 

of Nebraska's first SPA in 1990. This designation 

required the Lower Republican and the Little Blue 

NRDs to create and implement a management plan in 

1991 that would either improve or prevent more 

serious degradation of ground-water quality in the 

SPA. The management plan prepared for the SPA 

includes educational, regulatory, and long-term 

ground-water-quality monitoring elements. This plan 

was implemented within the SPA and includes 

practices such as crop fertilization, crop rotation, 

integrated pest management, irrigation, and livestockwaste, tillage, and buffer-zone management activities 

(Lower Republican and Little Blue Natural Resources 

Districts, 1990). The purpose of the ground-waterquality monitoring was to document changes in 

ground-water quality over time and to determine if the 

educational and regulatory elements will be effective 

in improving ground-water quality during the 10-year 

period of designation as an SPA.

In 1991, the U.S. Geological Survey (USGS) 

entered into a cooperative agreement with the NDEQ, 

the Lower Republican and Little Blue NRDs, and the 

Conservation and Survey Division, University of 

Nebraska-Lincoln (UNL), to:

1. Identify acceptable sites for monitoring-well 

locations and install a network of monitoring 

wells within the SPA;

2. Determine the variability of nitrate concentrations 

in ground water;

3. Examine possible timing of ground-water sample 

collection; and

4. Estimate the nitrate and ammonium content of the 

unsaturated zone at representative sites.

Purpose and Scope

This report identifies locations for monitoring 

wells and unsaturated-zone sampling sites and 

describes the results of monitoring for nitrate and 

ammonium during 1991-93. The report describes 

variations in concentrations of nitrate in ground water, 

describes nitrate and ammonium content of the 

unsaturated zone at two sites prior to fertilizer application, and describes possible timing of ground-water 

sample collection.

Previous Investigations

Several geologic and hydrologic studies during 

the past 50 years have described the study area. Miller 

and others (1964) reported on the geography, geology, 

structural, historical, and economic geology of the 

study area. Bedrock geologic maps showing thickness 

of overlying Quaternary-age deposits were 

constructed by Burchett and others (1972) and 

Dreeszen and others (1973). Ground-water resources 

for Nuckolls County were described by Waite and 

others (1944). A hydrogeologic reconnaissance of the 

Republican River Basin was completed by Ellis 

(1981). A study of ground-water quality in southern 

Nuckolls County, which documented concentrations 

of nitrate and detections of atrazine, was completed by 

Ehrman (1989).

Acknowledgments

The assistance and cooperation of the following 

are greatly appreciated: personnel of the NDEQ for 

assistance with well logging; personnel of the Lower 

Republican and the Little Blue NRDs for assistance in 

well selection, logging and sampling; the drilling team 

of the Conservation and Survey Division, University 

of Nebraska-Lincoln; and numerous land owners and 

tenants who permitted access for the installation and 

sampling of monitoring wells.

Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-93
DESCRIPTION OF THE STUDY AREA

The Superior-Hardy SPA is located in southern 

Nuckolls County, south-central Nebraska, along the 

Kansas-Nebraska border (fig. 1). Superior, with a 

population of 2,397 in 1990 (U.S. Bureau of the 

Census, 1993), is located along the Republican River 

in the western part of the SPA. Hardy, with a population of 206 in 1990, is the only other population center 

within the study area. The SPA encompasses 

32 square miles (mi2), and is under jurisdiction of the 

Lower Republican and Little Blue NRDs.

The study area lies within the Plains Border 

Section of the Great Plains Physiographic Province 

(Fenneman, 1946). The area is characterized by 

moderate relief and dissected topography in the upland 

area, which gradually changes to a low relief in the 

lowlands of the Republican River Valley (fig. 1). The 

study area has an overall relief of about 160 ft, with 

the highest elevation in the northwest portion, and the 

lowest in the Republican River Valley at the KansasNebraska border. Major streams in the area are the 

Republican River and its tributaries, and Blakely and 

Crosby Creeks. Water is diverted from the Republican 

River upstream from the study area through the 

Superior Canal for surface-water irrigation in the 

Republican River Valley.

Hydrogeology

The geology of the Superior-Hardy SPA 

consists of Carlile Shale of Late Cretaceous age 

unconformably overlain by sand, silt, and clay 

deposits of Quaternary age (fig. 2). However, the 

Ogallala Formation of Tertiary age is absent in the 

study area. Carlile Shale is a mostly gray, clayey shale 

in the lower portion, capped by a fossiliferous, yellowbrown, sandy siltstone.

In the Republican River Valley, the Carlile Shale 

is unconformably overlain by deposits of Quaternary 

age. Alluvial deposits of Pleistocene age consist of 

alluvial material composed of unconsolidated silt, 

sand, and some gravel, some of which are nearly 50 ft 

thick. Loess deposits of Pleistocene age overlie the 

alluvial deposits along the margins of the river valley 

and in the terrace and upland portions of the study 

area. The loess deposits are yellowish to grayish 

orange and may contain up to 10 percent sand and may 

exceed 100 ft in thickness in the eastern portion of the

study area. Terrace deposits, which consist of clayey 

to sandy silt of Holocene age, directly overlie the 

coarser alluvial deposits in the river valley and also the 

loess deposits along the margin of the river valley and 

in small stream channels cut into the loess. The 

shallow aquifer (part of the High Plains aquifer) is 

within alluvial and loess deposits of Quaternary age.

The altitude of the base of the shallow aquifer 

was assumed to be identical to the top of the Carlile 

Shale and was mapped using geologic information 

from 53 test holes, irrigation wells, and monitoringwell logs (fig. 3). The base of the aquifer system 

ranges in altitude from about 1,580 ft above sea level 

in the northern part of the study area to about 1,480 ft 

in the southern part. The slope is toward the south, 

and averages about 40 feet per mile (ft/mi). The 

aquifer extends to the northern edge of the study area, 

where the altitude of the top of the Carlile Shale is 

similar to the altitude of the water table and the 

shallow aquifer is absent or very thin. As a result, the 

bedrock creates a boundary along the north side of the 

study area that isolates the study area from subsurface 

flow from the north.

The shallow aquifer in the study area is 

unconfined. The configuration of the water table 

(fig. 4) was produced from water-level measurements 

in 49 wells and 6 stream stage measurements during 

the fall of 1992. The altitude of the water table ranges 

from 1,590 ft above sea level in the northern part of 

the study area to 1,520 ft above sea level in the 

southern part of the study area, indicating a general 

north-to-south direction of ground-water flow and an 

average hydraulic gradient of about 30 ft/mi. Ground 

water generally discharges into the Republican River 

in the southern part of the study area. However, 

municipal ground-water withdrawals in the 

northwestern part of the study area have caused local 

depressions in the water table.

Based on well data from the 54 wells, depth to 

water ranged from near zero in the Republican River 

Valley and two perennial stream valleys, Blakely 

Creek in the western part and Crosby Creek in the 

central part of the study area, to about 160 ft in upland 

areas in the eastern part of the study area. Depths to 

water in upland areas generally were about 130 ft in 

the eastern part of the upland area, 48 ft in remaining 

upland areas, and 16 ft in the lowland.

Saturated thickness was measured by 

subtracting the elevation of the base of the aquifer 

from the elevation of the fall 1992 water-table surface.

DESCRIPTION OF THE STUDY AREA
98°15' R5W

40°07'30" 

40°00'

Little Blue

Natural Resources

District

Lower Republican 

Natural Resources 

District i

KANSAS

Base from U.S. Geological Survey 1:100,000 DIG data

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian-96°00'

6 MILES 

I

6 KILOMETERS

EXPLANATION

LOWLANDUPLAND

Figure 1. Location of study area, Superior-Hardy Special Protection Area, Nuckolls County, Nebraska.
98°00'

40°or -- Base from U.S. Geological Survey 1:100,000 DIG data Albers Equal-Area Conic Projection Standard parallels 29°30'and 45°30', central meridian-96°00' JEWELL CO REPUBLIC CO KANSAS

4 MILES

0 1 3 4 KILOMETERS

EXPLANATION

GEOLOGIC UNIT 

Flood-plain alluvium

Terrace Deposits 

Loess 

GEOLOGIC CONTACT

Figure 2. Generalized geology of the study area, Nuckolls County, Nebraska (geology modified from Miller and others, 1964).

oi

2
o>

S

n i.

40°or 

98°00'

97°50'

Base from U.S. Geological Survey 1:100,000 DIG data

Albers Equal-Area Conic Projection

Standard parallels 29°30'and 45°30', central meridian-96°00'

JEWELL CO

NUCKOLLS CO ___g

REPUBLIC'CO KANSAS

4 MILES

4 KILOMETERS

EXPLANATION

 7 500 BASE-OF-AQUIFER CONTOUR Shows altitude of 

base aquifer. Contour interval is 20 feet. Datum is sea level

. WELL OR TEST-HOLE LOCATION

N

I

Figure 3. Altitude and configuration of the base of the aquifer system in the study area, Nuckolls County, Nebraska.

s. o
98°00'

40°or 

Base from U.S. Geological Survey 1:100,000 DIG data

Albers Equal-Area Conic Projection

Standard parallels 29°30'and 45°30', central meridian-96°00

JEWELL CO REPUBLIC CO KANSAS

4 MILES

0 1 4 KILOMETERS

EXPLANATION

 7550 WATER-TABLE-CONTOUR-Shows altitude of 

water table. Hachures indicate depression area. Contour interval is 10 feet. Datum is sea level

DIRECTION OF GROUND-WATER FLOW

WELL LOCATION

STREAM STAGE MEASURED

m

Figure 4. Altitude and configuration of the water table and direction of ground-water flow in the study area, Nuckclls County, Nebraska, fall 1992.

s5
Saturated thickness at well locations ranged from 3 to 

33 ft, with a mean of 16 ft in the lowland areas, and 

from 2 to 55 ft, with a mean of 24 ft, in upland areas. 

Transmissivity (T) is a measure of the ability of 

the aquifer to transmit water, and is largely dependent 

on the nature of the pore space and thickness of the 

aquifer. T values in the Republican River Valley near 

Superior and on the terraces east of Hardy range from 

about 3,000 to more than 13,000 square feet per day 

(f^/d) (Lower Republican Natural Resources District, 

1990). In the upland area, T values range from zero to 

about 3,000 f^/d. T values in the extreme eastern part 

of the study area, where some saturated sand and 

gravel are present, exceed 13,000 ft2/d (Lower 

Republican and Little Blue Natural Resources 

Districts, 1990).

Soils

Major soil associations within the study area are 

shown in figure 5. The Crete-Hastings Soil Association (fig. 5) is located in the extreme northeastern 

portion of the study area and is formed in loess on 

nearly level to gently sloping upland. The association 

consists of silt loam to silty-clay loam soils that have 

permeabilities less than 1.0 inch per hour and a waterholding capacity of about 0.19 inch per inch (Dugan, 

1984). It contains soils with a moderate to high 

shrink-swell potential. Large cracks are commonly 

found during dry periods and offer potential routes for 

the rapid movement of water into the subsurface.

The Geary-Hastings Soil Association also is 

formed in loess and is located in the northern and 

eastern parts of the study area (fig. 5). Hydrologic 

properties of this association are similar to soils of the 

Crete-Hastings Soil Association. Slopes are nearly 

level to moderately steep with an average maximum 

soil slope of 14 percent.

The Hord Soil Association (fig. 5) contains 

silty-clay loams to silt loams with permeabilities from 

1 to 2 inch per hour. These soils are present on the 

stream terraces north of the Republican River and 

have a moderate to low shrink-swell potential. The 

water-holding capacity of these soils is about 0.20 inch 

per inch.

The McCook-Wann-Inavale Soil Association is 

located along the Republican River in the study area 

(fig. 5). The association consists of silt-loam to loamy 

sands with high permeabilities of 5 to 10 inches per

hour. The water-holding capacity of these soils is 

about 0.12 inch per inch.

Land Use

The principal land use in the study area is 

agricultural, with about 89 percent of all land used for 

crop or livestock production (fig. 6, table 1). This land 

use consists primarily of irrigated (29 percent) and 

nonirrigated (38 percent) cropland, and rangeland 

(22 percent). A summary of land use in the area 

during 1989 is presented in table 1.

Crops raised in the area include corn, sorghum, 

soybeans, wheat, oats, alfalfa, and hay. The irrigated 

cropland is dominated by corn and soybeans, whereas 

the nonirrigated cropland is dominated by corn, 

sorghum, and small grains. Pasture and rangeland are 

utilized mainly for cattle production.

Within lowlands of the study area, 3,690 acres 

of cropland (or 63 percent of irrigated land) were 

irrigated by surface water diverted from the 

Republican River through the Superior Canal. 

Remaining irrigation was by sprinkler systems using 

ground water.

Current corn-production techniques often 

require significant quantities of nitrogen fertilizers, 

pesticides, and irrigation water to achieve optimum 

yields. Farmers commonly apply from 80 to 250 Ib of 

total nitrogen per acre annually, mostly as anhydrous 

ammonia, to supplement available nitrogen in the soil 

(University of Nebraska, 1989).

Ground-Water Quality

Ground water in the study area is of the calcium 

bicarbonate type (Engberg, 1984) and contains 

moderate amounts of sulfate, sodium, chloride, nitrate, 

and other constituents. Results from 10 ground-waterquality samples retrieved from the USGS Water Data 

Storage and Retrieval System (WATSTORE), 

collected prior to irrigation (pre-1950) in the lowland, 

indicated that nitrate concentrations in ground water 

were less than 1 mg/L. Thirty-seven water-quality 

samples were collected within the study area during 

the spring and summer of 1988 (Ehrman, 1989). Two 

water samples were considered to be affected by 

point-source contaminants and were eliminated from

8 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolis County, Nebraska, 1991-93
97°50'

40°01' vBase from U.S. Geological Survey 1:100,000 DLG data Albers Equal-Area Conic Projection Standard parallels 29°30'and 45°30', central meridian-96°00' JEWELL CO REPUBLIC CO KANSAS

4 MILES

01234 KILOMETERS

EXPLANATION

1 CRETE-HASTINGS SOIL ASSOCIATION

2 GEARY-HASTINGS SOIL ASSOCIATION3 HORD SOIL ASSOCIATION

4 McCOOK-WANN-INAVALE SOIL ASSOCIATION

Ijj Figure 5. Soil associations in the study area (modified from Dugan, 1984). 

m
. i

Z g I!(0 =* 

to toi1

98°00'

40°01'

97°50'

I

Land use is 1989 data from Nebraska Natural Resources Commission data bank

Albers Equal-Area Conic Projection Standard parallels 29°30' and 45°30', central meridian-96°00'

4 MILES

EXPLANATION

NONIRRIGATED CROPLAND SPRINKLER IRRIGATED CROPLAND

FURROW IRRIGATED CROPLAND 

RANGELAND

OTHER

0 1 4 KILOMETERS

Figure 6. Agricultural land use in the study area, Nuckolls County, Nebraska, 1989 (modified from Nebraska Natural Resources Commission).
the data set. A statistical summary of these waterquality data is presented in table 2.

Table 1. Land use in the study area, Nuckolls County, 

Nebraska, 1989

[Data from Nebraska Natural Resources Commission]

Land use

Irrigated cropland

Sprinkler irrigated

Furrow irrigated

Nonirrigated cropland

Rangeland

Forest land

Other farmland

Built-up land

Water

Total

Acreage

5,845

1,418

4,427

7,844

4,571

450

400

1,280

90

20780

Percentage

28.5

6.9

21.6

38.3

22.3

2.2

2.0

6.3

0.4 "TOO"

Data from Ehrman (1989) indicate that most 

concentrations of the dissolved constituents analyzed 

were within recommended limits for public drinkingwater supplies (U.S. Environmental Protection 

Agency, 1994). However, concentrations of nitrate in 

12 out of 35 samples (34 percent) exceeded the 

USEPA's MCL of 10 mg/L for nitrate. Nitrate as 

nitrogen concentrations ranged from about 3 to 

17 mg/L, with a mean of 8.3 mg/L (table 2).

The areal distribution of nitrate in ground water 

(Ehrman, 1989) indicates that nitrate concentrations 

were highest in the central and eastern parts of the

study area. The distribution of higher nitrate values 

correlates with the location of irrigated cropland in the 

study area (Ehrman, 1989). Pesticides such as atrazine 

were detected in seven of eight samples, ranging from 

2.4 to 4 micrograms per liter (j*g/L). Three samples 

collected by Ehrman (1989) exceeded the USEPA 

proposed MCL for atrazine of 3 |*g/L (U.S. Environmental Protection Agency, 1994).

METHODS

Site Selection and Monitoring-Well 

Installation

Sixteen monitoring sites were selected 

(fig. 7). Criteria used in determination of the number 

and locations of monitoring wells included geologic 

setting, saturated thickness, depth to water, groundwater flow direction, soil characteristics, land use, 

water-quality data, accessibility, and cost. The 16 sites 

were subdivided into three groups according to landuse intensity. Monitoring sites 4,6,8,12, and 14 were 

located within nonirrigated upland (cropland and 

rangeland); sites 1,2,3, and 5 were located in irrigated 

upland, closely situated downgradient from irrigated 

cropland; and sites 7,9,10,11,13, 15, and 16 were 

located within surface-water furrow-irrigated 

cropland, on the lowland.

Table 2. Statistical summary of chemical quality of ground water in the study area, Nuckolls County, Nebraska, 1988

[Data from Ehrman, 1989; °C, degrees Celsius; nS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter]

Properties, constituents, 

and units

Temperature, °C

pH, standard units

Specific conductance, (iS/cm

Calcium, dissolved, mg/L

Magnesium, dissolved, mg/L

Sodium, dissolved, mg/L

Chloride, dissolved, mg/L

Sulfate, dissolved, mg/L

Potassium, dissolved, mg/L

Nitrate as nitrogen, mg/L

Number 

of 

analyses

35

35

35

35

35

35

35

35

35

35

Minimum

12

6.7

111

65

8.6

10

5.6

17

3.8

2.9

25th 

percentlle

13

6.9

587

81

10

35

21

26

4.8

4.8

50th 

percentiie

14

7.0

639

93

13

45

34

47

5.3

8.3

Uttan iviocin

14

7.2

665

94

13

47

36

49

5.9

8.3

75th 

percentlte

14

7.1

768

104

15

58

41

64

6.6

10

Maximum

15

8.1

997

136

20

80

134

96

12

17

METHODS 11
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Standard parallels 29°30'and 45°30', central meridian-96°00'

JEWELL CO REPUBLIC CO

EXPLANATION

4 MILES

4 KILOMETERS

. 1 WELL LOCATION AND NUM

A'

ff

Figure 7. Location of monitoring wells in the study area, Nuckolls County, Nebraska.
Twenty monitoring wells were installed at the 

16 sites in May 1991 to monitor overall regional water 

quality. In this report, each monitoring well is identified by the same number as the corresponding 

numbered site. Nests of three wells were installed at 

sites 9 and 13 with various screened depths (A, B, and 

C) to monitor vertical distribution of nitrate in the 

area. Well A was screened throughout most of the 

aquifer; well B was screened at the bottom 2 ft of the 

aquifer; and well C was screened at the top 5 ft of the 

aquifer. Extensions of casing below the screens of 

three wells (4,9C, and 13C) were designed to facilitate sampling of ground water during low water-table 

conditions.

A reverse-circulation, rotary drilling method 

was used in drilling the wells to eliminate possible 

contamination of ground-water samples with drilling 

fluids and to minimize reduced permeability from 

injection of drilling fluids into the aquifer. All wells 

were completed with full penetration of the aquifer, 

except wells 9B, 9C, 13B, and 13C.

Four-inch outside diameter, schedule 40, flushthreaded polyvinyl chloride casing and screen were 

installed in all monitoring wells. Continuous-slot 

screen with 0.012-inch slots, providing 8.160 square 

inches of open area per linear foot, permitted effective 

well development without plugging and facilitated 

rapid recharge to the well. Table 3 summarizes the 

characteristics of the 20 monitoring wells.

Gravel from a local source was used to backfill 

around the screened intervals to a height of 2 to 3 ft 

above the top of the screen. The remainder of the 

annular space was filled to 3 ft below the land surface 

with bentonite slurry that was pumped in with a tremie 

pipe. The uppermost part of the 3-ft annular space 

was filled with a cement seal to prevent downward 

seepage along the well casing. Steel well protectors 

with locking caps were cemented in place around the 

tops of the well casing. The wells were developed by 

surge pumping with a suction-lift centrifugal pump 

until the water was free from suspended participate.

Water-Quality Sampling and Analysis

During June 1991, pumps for monitoring wells 

were installed and samples were collected once during 

the months of July, September, and November, and 

twice during August at each well. A bimonthly 

(January, March, May, July, September, and 

November) sampling schedule was established in 

January 1992. A stainless-steel, submersible pump

was installed permanently in all wells except 1,6, and 

8, which avoided the potential problem of cross 

contamination between wells during sampling and 

reduced labor costs. A bailer was used to sample 

wells 1, 6, and 8, where the aquifer is thin and/or 

composed of sediment with low permeability. 

Samples were sent to the National Water Quality 

Laboratory (NWQL) in Arvada, Colorado, for analysis 

of dissolved nitrate as nitrogen. Nitrogen 15N stable 

isotope analysis was also done by the NWQL's 

contract laboratory.

Water samples were collected after 3 to 10 

casing volumes had been purged to ensure that 

stagnant water was removed from the well prior to 

sample collection. A flow-through chamber fitted 

with field instrument probes was used to monitor pH, 

specific conductance, dissolved oxygen, and temperature of the water during well purging. A sample was 

collected only after the field measurements 

stabilized. General sample collection, treatment, 

preservation, and storage and shipping procedures 

conformed to those described by Kolpin and Burkart 

(1991).

Quality assurance and quality control of the 

analytical data were maintained through an integration 

of procedures at the NWQL, field-sampling protocols, 

and data reviews by the USGS. All bottles and 

preservatives used for water samples were subjected to 

quality-control measures at the NWQL to decrease the 

chance of sample contamination. A minimum of 

15 percent of all analyses performed for any given 

constituent at the NWQL consists of reference 

materials from the USEPA and the National Bureau of 

Standards, spiked samples, blanks, and samples split 

between different laboratories as recommended by 

Fishman and Friedman (1989).

Ten percent of the samples collected for nitrate 

analysis were duplicate quality-assurance samples. 

The duplicate samples were collected in separate 

containers immediately following collection of the 

regular sample and sent to the NWQL for analysis. 

Precision, which is the measure of the variability of 

individual sample measurements, was assessed from 

analyses of duplicate samples and expressed as 

standard deviation for the concentration data.

Analytical results were compared with previous 

results for each site and with other study sites to 

identify possible inconsistencies. If inconsistencies 

were identified, checks for transcribing errors were 

performed at the NWQL, and analytical reruns were 

requested as appropriate.

METHODS 13
Table 3. Summary of monitoring-well characteristics in the study area, Nuckolls County, Nebraska, 1991

Ibutlon ofS

, Nuckolls C

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Well 

number

1

2

3

4

5

6

7

8

9A

9B

9C

10

11

12

13A

13B

13C

14

15

16

Site ID

400009097503601

400101097503601

400035097513201

400125097534601

400008097545301

400101097553501

400045097560901

400127097574701

400041097574301

400041097574302

400041097574303

400032097595901

400031098003401

400213098011601

400101098012901

400101098012902

400101098012903

400130098030501

400042098032001

400019098040201

Landsurface 

altitude 

(feet)

1,657

1,653

1,640

1,633

1,530

1,610

1,557

1,580

1,548

1,548

1,548

1,550

1,549

1,595

1,570

1,570

1,570

1,630

1,562

1,552

Drilling 

date

5-15-91

5-15-91

5-20-91

5-16-91

5-16-91

5-21-91

5-21-91

5-22-91

5-21-91

5-21-91

5-21-91

5-16-91

5-20-91

5-14-91

5-20-91

5-20-91

5-20-91

5-14-91

5-13-91

5-13-91

Well 

depth 

(feet)

124

155

148

63

33

40

45

18

36

36

23.5

28

20

57

38

38

32.5

66

32

36

Depth to 

water 

(feet)

123

130

118

59

14

35

26

8

13

13

13

16

12

42

24

24

24

45

15

7

Casing and 

screen type

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

4-inch PVC

Casing length 

(feet)

From

0

0

0

0

61

0

0

0

0

15

0

0

0

21

0

0

0

0

0

0

30

0

0

0

To

69

68

55

41

63

23

20

26

10

18

16

34

16

23.5

18

10

32

18

36

25

32.5

46

17

10

Scre

From

69

68

55

41

23

20

26

10

16

34

16

18

10

32

18

36

25

46

17

10

TJ 

O
Unsaturated-Zone Sampling and Analysis

Sediment cores were collected and analyzed to 

provide estimates of the amounts and vertical distribution of residual nitrogen in the unsaturated zone at two 

sites in the study area. These results provided the 

basis for estimating the amount of nitrogen potentially 

available for eventual leaching into the ground water. 

Measurements of a conservative tracer through the soil 

and sediment profiles provided an estimate of the 

potential rate of nitrogen transport within the unsaturated zone.

Two sites, located in corn fields representative 

of surface-irrigated lowland (site 9) and sprinklerirrigated upland (site 1), were selected for sediment 

coring and nitrogen analysis. Both sites had been in 

continuous corn production, had 150 to 200 Ib of 

nitrogen per acre applied annually, and utilized 

minimum tillage practices prior to 1991. In this 

report, site numbers used in reference to sediment 

coring-site locations correspond to numbers used to 

identify well-site locations.

Sediment cores of the unsaturated zone were 

collected annually from 1991 to 1993, prior to fertilizer application in the spring with a hollow-stem auger 

drilling rig operated by the Conservation and Survey 

Division, UNL. The sediment cores at sites 1 and 9 

were collected at locations approximately 200 ft 

from wells 1 and 9, respectively, on April 3, 1991, 

February 4,1992, and April 27,1993. Replicate cores 

also were collected at the sediment- coring sites each 

year two holes at each site in 1991 and three holes at 

each site in 1992 and 1993. Approximately 3-inch 

portions of core samples were collected every 3 ft, or 

at each major lithological change, in each hole through 

depths of about 73 and 20 ft for sites 1 and 9, respectively. Core samples were analyzed by the Geology 

Department, UNL, for grain size, and by the Soil 

Testing Laboratory, Department of Agronomy, UNL, 

to determine organic matter content, nitrate-N, and 

ammonium-N concentrations.

To determine the approximate rate at which 

nitrate may be transported through the unsaturated 

zone, two tracer experimental plots, 30 x 30 ft, were 

located in corn fields at well sites 1 and 9 (fig. 7). 

Both plots were flat with a 0- to 1-percent slope. 

Bromide (as potassium bromide), a conservative tracer 

whose transport behavior is similar to nitrate, was 

applied at a rate of 267.6 Ib/acre to each of the plots on 

May 19, 1992. Bromide was not detected in core

samples of the unsaturated zone prior to fertilizer and 

bromide application in February 1992.

Bromide analyses of core samples collected in 

February 1992 and April 1993 for the tracer experiments were conducted by the UNL Soil Testing 

Laboratory. Bromide was extracted from sediment 

cores using potassium chloride and analyzed using a 

cadmium-reduction method. An ion chromatograph 

using an ion-exchange resin in combination with a 

specific effluent was used to analyze for bromide.

Concentrations of nitrate-N, ammonium-N, and 

bromide were converted to pounds per acre using the 

following formula (Follett and others, 1991):

NO3-N (Ib/acre) = 

NO3 (mg/L) x 0.3 x interval thickness (inches)

(corresponding calculations can be done for 

ammonium and bromide),

where 0.3 is a unit conversion factor, and the interval 

thickness is bounded by the midpoints between core 

sample depths in the core above and below the 

recorded sample depth.

Statistical Data Analysis

Descriptive statistical analysis, boxplots, and 

nonparametric statistical tests were used to summarize 

and evaluate data collected during 1991 93. Descriptive statistics such as the mean, median, maximum, 

minimum, standard deviation, and percentile aided in 

the interpretation of data. Percentiles show the 

percentage of analyses equal to or less than the 

indicated value. Boxplots present the median and the 

10th, 25th, 75th, and 90th percentiles in graphical 

form.

The Mann-Whitney and Wilcoxon tests 

(Conover, 1989), nonparametric hypothesis tests 

involving rank-transformed data, were used when 

comparing two independent groups of data. Hypothesis tests are done to examine to what extent differences in data may be due to chance variability. The 

hypothesis tests involve a null hypothesis, which 

states that no real difference exists. The alpha value, 

or level or significance, that is used in hypothesis 

testing in this report is 0.05. This value represents the 

maximum probability of rejecting the null hypothesis 

when it actually is true. For each test, the probability 

(given as a p-value) representing the attained significance level also is presented. If the p-value is smaller 

than or equal to the alpha value, the null hypothesis is

METHODS 15
rejected and the tested data groups are considered to 

be significantly different.

DISTRIBUTION OF SELECTED NITROGEN 

COMPOUNDS

The following analysis is based on the data 

collected from 20 wells and from two selected 

unsaturated-zone sampling sites during 1991-93. 

Precision of data for water-quality analysis was 

expressed as a standard deviation of 0.3 mg/L. This 

indicates that multiple analysis of duplicate samples 

coincides.

Nitrate in Ground Water

Results of detailed chemical and physical 

analyses of ground-water samples collected during 

this study are listed in table 11 at the back of the 

report. Concentrations of nitrate in ground water 

collected during this study are statistically 

summarized in table 4. Average yearly nitrate concentrations were computed by averaging all samples 

collected during a growing season (April to 

September) and a nongrowing season (October to 

March).

Nitrate data collected during the growing and 

nongrowing seasons of 1991 92, were reported as 

year 1 data. Because these data were obtained just 

prior to implementation of the management plan, they 

are regarded as baseline data. These data provide a 

basis for comparison of nitrate concentrations in the 

study area over time. Baseline nitrate year 1 data 

(July 1991-March 1992) and year 2 nitrate data 

(April 1992-March 1993) are illustrated in figure 8.

Results indicate that ground-water samples from 

all fully penetrating monitoring wells in the aquifer 

contained detectable concentrations of nitrate, and that 

samples from 12 of 16 (75 percent) wells contained 

median concentrations greater than 5 mg/L. Samples 

from 7 of 16 (44 percent) wells contained median 

concentrations that exceeded 10 mg/L. Median nitrate 

concentrations of 5 mg/L or more also were found in 

ground-water samples from three upland sites 

(wells 1,2, and 3) at depths as much as 100 ft or more 

below the land surface.

Baseline data (year 1) (table 4) indicate that 

nitrate concentrations in ground water for the entire

study area ranged from 0.08 to 30 mg/L, with a 

median of 8.7 mg/L. Nitrate concentrations for the 

same period in nonirrigated uplands ranged from 

1.9 to 25 mg/L, and had the smallest median value of 

5.2 mg/L. Within irrigated land, median concentrations of nitrate for upland and lowland areas were 

9.0 and 9.5 mg/L, respectively, whereas the extremes 

ranged from 5.0 to 15.0 mg/L, and from 0.08 to 

30 mg/L, respectively.

Areal Distribution

Figure 9 indicates that the distribution of nitrate 

concentrations in ground water relates to ground-water 

flow direction (fig. 4) and land use (fig. 6). Median 

nitrate concentrations ranged from 5 mg/L in the 

northern part of the study area, where nonirrigated 

land use is dominant, to 15 mg/L in the Republican 

River Valley, where irrigated com is the dominant land 

use. Most monitoring wells in which greater nitrate 

concentrations were detected were located within or 

near the areas of irrigated com, which is generally 

associated with high-nitrogen fertilizer and water 

applications.

Relatively large concentrations of nitrate were 

present in water samples in year 1 from wells 4 and 

15, with median concentrations of 24 mg/L (table 4). 

Isolated large nitrate concentrations are a possible 

indication of a point source. Therefore, additional 

samples were collected and analyzed for isotopic 

nitrogen to help identify potential nitrate sources. 

Nitrate derived from human and animal wastes 

typically has a nitrogen isotopic ratio (815N) in the 

range of 10 to 22 parts per thousand (%o); nitrate 

derived from natural organic material in soil has 

from 4 to 9%o (Aravena and others, 1993); and nitrate 

derived from commercial fertilizers has 815N from 

-4 to 4%o (Gormly and Spalding, 1979; Komor and 

Anderson, 1993). The 8f5N of nitrate in samples 

collected from wells 4 and 15 was 8.9 and 12.2%o, 

respectively, which indicates that nitrate in water 

samples from these wells originated from soil-organic 

nitrogen and human and/or animal wastes rather than 

commercial fertilizer.

Vertical Distribution

The variability of nitrate concentrations in water 

samples from monitoring wells screened at different 

depths (table 3) was examined at well sites 9 and 13

16 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-83
Table 4. Nitrate concentrations in samples from monitoring wells in the study area, Nuckolls County, Nebraska, 1991-93

[mg/L, milligrams per liter]

Well number 

(table 3, fig. 8) Year1

Number of 

analyses

Minimum 

(mg/L)

25th 

percentlle Median

75th 

percentlle

Maximum 

(mg/L)

Mean 

(mg/L)

Standard 

deviation 

(mg/L)

NONIRRIG ATED UPLAND

4

6

8

12

14

All analyses,

nonirrigated upland

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

7

6

7

5

7

6

7

6

7.

6

35

29

23

22

6.5

6.6

2.2

1.7

4.5

3.9

1.9

2.2

1.9

1.7

24

22

6.5

6.7

2.2

2.2

4.5

4.1

2.1

2.3

3.1

2.9

24

23

6.9

6.9

4.0

2.9

4.7

4.5

2.4

2.8

5.2

4.7

24

24

7.1

11

5.3

4.7

5.2

7.1

2.7

3.2

7.4

12

25

25

10

14

5.8

6.1

7.4

9.3

3.1

3.4

25

25

24

23

7.3

8.5

3.9

3.4

5.2

5.5

2.4

2.8

8.6

8.6

0.58

1.3

1.2

3.1

1.4

1.6

1.0

2.1

.39

.46

8.1

7.9

IRRIGATED UPLAND

1

2

3

5

All analyses,

irrigated upland

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

7

6

7

6

7

5

7

6

28

23

5.0

6.0

7.0

6.0

8.6

8.2

9.9

8.0

5.0

6.0

5.6

6.0

7.6

6.6

9.0

8.2

11

8.4

6.5

6.5

5.9

6.1

8.3

7.2

9.3

8.3

12

9.9

9.0

7.6

6.2

6.6

9.0

7.5

9.4

8.9

13

13

9.0

8.9

6.4

7.0

9.9

7.6

9.9

8.9

15

13

15

13

5.8

6.3

8.4

7.1

9.2

8.5

12

10

8.9

8.0

.45

.40

.94

.62

0.40

.37

1.7

2.2

2.5

2.0

IRRIGATED LOWLAND

7

9A

10

11

ISA

15

16

All analyses,

irrigated lowland

All analyses,

irrigated land

All analyses

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

Yearl

Year 2

7

6

7

5

7

6

7

6

7

6

7

6

7

6

49

41

77

64

112

93

5.2

6.0

8.8

13

8.1

10

16

17

8.6

10

18

20

.10

.25

.08

.25

.08

.25

.08

.25

5.9

6.0

10

14

9.2

10

17

18

9.6

10

19

22

.20

.30

6.5

6.0

6.5

6.1

5.4

6.0

6.4

6.0

11

14

9.5

11

18

18

10

11

24

27

.30

.30

10

11

9.5

9.9

8.7

8.2

6.6

6.1

12

15

9.9

11

19

18

11

12

27

33

.70

.43

17

18

12

14

12

14

7.2

6.1

13

15

11

11

20

19

11

13

30

34

.70

.50

30

34

30

34

30

34

6.3

6.0

11

14

9.6

11

18

18

10

11

23

27

.40

.30

11

12

10

11

9.8

10

.62

.05

1.4

.84

.87

.54

1.4

.63

.83

1.2

4.2

5.5

.23

.09

7.2

8.3

6.1

7.1

6.8

7.4

1: April 1991 to March 1992; Year 2: April 1992 to March 1993.

DISTRIBUTION OF SELECTED NITROGEN COMPOUNDS 17
NONIRRIGATED UPLAND

26

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EXPLANATION

-p 90th percenti le 

pL, 75th percenti le 

M Median

M 25th percenti le

-L 10th percenti le

Year 1 Year 2 Year 1 Year 2 Year 1 Year 2 Year 1 Year 2 Year 1 Year 2

WELL 4 WELL 6 WELLS WELL 12 WELL 14

16

tr 14

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QIRRIGATED UPLAND 

6 7

~ 10

Year 1 Year 2 

WELL1

Year 1 Year 2 

WELL 2

Year 1 Year 2 

WELL 3

Year 1 Year 2 

WELL 5

Figure 8. Nitrate concentrations from year 1 baseline data prior to the implementation of the management plan and year 2 data after implementation of the plan in the study area, Nuckolls County, 

Nebraska: (A) nonirrigated upland; (B) irrigated upland; (C) irrigated lowland.

18 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckoiis County, Nebraska, 1991-93
IRRIGATED LOWLAND

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O

LU

1 5

Z

n

- 1 1 1 1 1 1 1 1 1 1 1

-

r

_

-

1

[

]

1 :

_

-

_

-

j

'- B - :

H n n R

1 B I

-

5

1 2 -

-

1 1 1 1 ! 1 i 1 1 1 i 4. -

EXPLANATION

90th percentile 

75th percentile 

Median

25th percentile 

10th percentile

Year 1 Year 2 Year 1 Year 2 Year 1 Year 2 Year 1 Year 2 Year 1 Year 2 Year 1 Year 2 Year 1 Year 2 

WELL? WELL9A WELL 10 WELL 11 WELL 13A WELL 15 WELL 16

Figure 8. Nitrate concentrations from year 1 baseline data prior to the implementation of the management plan 

and year 2 data after implementation of the plan in the study area, Nuckolls County, Nebraska: (A) nonirrigated 

upland; (B) irrigated upland; and (C) irrigated lowland Continued.

(fig. 10), which are located in the lowland area. At 

well 9, median nitrate concentration for year 1 was 

26 mg/L in the water from the well screened at the top 

of the aquifer, 8.0 mg/L in water from the well 

screened at the bottom of the aquifer, and 11.1 mg/L in 

water from the well screened through the entire 

aquifer. Median nitrate concentrations for the three 

depths in year 2 were 26.2,11.3, and 14.2 mg/L, 

respectively. Similarly, for well 13, the median nitrate 

concentrations at the three different depths were 11.7, 

9.6, and 10.3 mg/L for year 1, and 12.3,10.1, and 

10.8 mg/L for year 2, respectively.

The observed stratification of nitrate concentration is likely the result of (1) a relatively short transit 

time for nitrate to leach through the shallow unsaturated zone to the water table, compared to the slower 

rate of ground-water flow and dispersion, and 

(2) possible denitrification of nitrate at depth as 

conditions become more reducing.

The vertical distribution of nitrate concentrations at the nested wells demonstrates the stratification 

of nitrate concentrations within the aquifer. Therefore, 

the wells open to the entire aquifer are considered to

yield samples most representative of the entire aquifer. 

In areas where wells are screened near the top section 

of the saturated zone, variations in nitrate concentrations most likely were related to short-term or seasonal 

differences in precipitation, irrigation recharge, and 

agricultural practices.

Temporal Variation

Because of slow ground-water movement and 

the resulting time lag between the adoption of the 

management plan and water-quality improvement, a 

comparison of nitrate concentrations at each 

monitoring well for years 1 and 2 shows little change 

(table 4, figs. 8 and 11). Examining upland and 

lowland areas separately, nitrate concentrations 

generally decreased slightly in the upland and 

increased slightly in the lowland (fig. 11). Changes in 

nitrate concentrations in the ground water are expected 

to be detected more quickly in the lowland area than 

the upland area because of the sandy-textured soils 

and shallow water table that are present in the lowland 

area. A Mann-Whitney test (Conover, 1989) indicated

DISTRIBUTION OF SELECTED NITROGEN COMPOUNDS 19
>5 

li

98°00'

 ' o

ie

40°or 

Q. 

(A

O

5

Base from U.S. Geological Survey 1:100,000 DIG data

Albers Equal-Area Conic Projection

Standard parallels 29°30'and 45°30', central meridian-96°00'

JEWELL CO REPUBLIC CO KA

4 MILES

4 KILOMETERS

EXPLANATION

LINE OF EQUAL NITRA

IN GROUND WATER 

as nitrogen. Contour i

per liter

MONITORING WELL L

N

% Figure 9. Area! distribution of median nitrate concentrations in ground water from 16 fully penetrating wells in the study area, Nuc

-* through March 1992.

c

to
cc 

^2 20

FULL-SCREEN INTERVAL, WELL 9A 

BOTTOM-SCREEN INTERVAL, WELL 9B 

TOP-SCREEN INTERVAL, WELL 9C

J A S 0 N D 

1991

J F M A

TIME, IN MONTHS

M J J 

1992

A S 0 N D J F M 

1993

FULL-SCREEN INTERVAL, WELL 13A 

BOTTOM-SCREEN INTERVAL, WELL 13B 

TOP-SCREEN INTERVAL, WELL 13C

i i i i i i i i i i i i i i i

JASONDJFMAMJJASOND JFM

TIME, IN MONTHS

Figure 10. Stratification of nitrate concentrations in water samples from wells 9 and 13 in the study area, Nuckolls 

County, Nebraska, 1991-83.

DISTRIBUTION OF SELECTED NITROGEN COMPOUNDS 21
.ZERO LINE 

(YearD

LUQ

NONIRRIGATED 

UPLAND

IRRIGATED 

UPLAND

IRRIGATED 

LOWLAND

12 14 235 

WELL NUMBER

9A 10 11 13A 15 16

Figure 11. Difference in median nitrate concentrations between year 2 and year 1 in ground water from fully 

penetrating monitoring wells in the study area, Nuckolls County, Nebraska, 1991-93.

no significant difference in nitrate concentrations 

between the two years of data (p = 0.46).

The amount of variation in nitrate concentration 

for a 2-year period for all wells was also evaluated. 

This variation may be an appropriate consideration 

when selecting sampling times to effectively define 

long-term trends with fewer samples. Substantial 

variation in nitrate concentrations would make it more 

difficult to identify long-term trends. The amount of 

variation in nitrate concentration can be determined 

using:

where:

SS = the sum of squares, 

x = monthly nitrate data, 

x = annual average concentration for a single well

(table 4).

subscripts 1 and 2 indicate years 1 and 2, and 

i = well number, 1 16.

Based on limited (years 1 and 2) data, samples 

collected in January and August had the least amount 

of variation (table 5).

22 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckoils County, Nebraska, 1991-93
Table 5. Summary of the sum of squares, the mean sum of 

squares, and its ranking for monthly nitrate concentrations in 

water samples from 16 wells in the study area, 1991-93

r 2 2~i 

[SS, the 2-year combined sum of squares Z [_ (x I / ~~ * 1) + (*2; ~~ *l) J;

N, sample size; MSS, the mean sum of squares of SS/N]

Month

August

January

March

November

July

September

May

SS

9.3

51.6

66.7

71.4

92.6

96.9

53.8

N

15

30

31

32

32

32

16

MSS

0.6

1.7

2.2

2.2

2.9

3.0

3.4

Rank

1

2

3

4

5

6

7

It may also be relevant to identify times during 

which maximum or minimum concentrations 

occurred. This information could indicate sampling 

times most likely to identify recurring seasonal 

extremes, which may also be useful in identifying longterm trends.

Nitrate and Ammonium in the Unsaturated 

Zone

Important to the issue of monitoring programs is 

the nitrate content of the unsaturated zone. The amount 

of nitrogen present in the unsaturated zone and the rate 

at which it is transported to the water table determines 

the time required for a management plan to have an 

impact on nitrate concentrations in the ground water.

Most of the nitrogen applied to the field is in the 

form of anhydrous ammonia, which is ionized to 

ammonium and tends to sorb to organic matter and clay 

particles in the soil (Bonn and others, 1985). Nitrification within the soil zone converts most of the ammonia 

to nitrate that is highly mobile under aerobic conditions 

and is leached by recharge water downward toward the 

water table. Tables 11-20 at the back of the report 

contain the basic data of organic matter and silt-clay 

content and nitrate and ammonium concentrations 

derived from sediment cores.

Vertical Distribution and Change in Nitrogen 

Content

The mean organic matter, nitrate and ammonium 

concentrations as nitrogen, and mean silt-clay content 

from analyses of replicate sediment cores at two 

monitoring sites (1 and 9) for 3 consecutive years

(1991-93) are presented in tables 6 and 7. Distribution patterns of these constituents with depth in the 

sediment profile are depicted in figures 12 and 13.

Small concentrations of nitrate and ammonium, 

with overall means of 1.6 and 2.5 mg/kg (mg/L) for 

site 1, and 2.4 and 2.0 mg/kg for site 9, were found in 

the unsaturated zone (tables 6-7). Although nitrate 

concentrations in the unsaturated zone are small 

compared to those in ground water, leaching over time 

is apparently sufficient to increase the nitrate concentrations in ground water to relatively high levels. 

Maximum concentrations of nitrate were detected at or 

within 13 ft of the land surface in both sites, 

suggesting that the major source of nitrogen at these 

sites is from the surface. When correlating nitrate, 

ammonium, organic matter, and silt-clay content with 

depth for all sediment samples at site 1, the correlations ranging from 0.40 to 0.69 show that nitrate 

concentrations, organic matter, and silt-clay content 

decreased with depth, whereas, ammonium increased 

with depth. Likewise, at site 9, ammonium concentrations and organic matter decreased with depth, 

whereas the nitrate concentrations and silt-clay 

content seemed to be independent of depth. An 

estimation of nitrate and ammonium contents in the 

unsaturated zone for 3 consecutive years at sites 1 and 

9 is summarized in table 8. Distribution patterns and 

changes with depth in the sediment profile at sites 1 

and 9 are depicted in figures 14 and 15.

At site 1, total nitrate and ammonium content of 

the unsaturated zone was 25 percent less for spring 

1992 compared to spring 1991 contents. The total 

nitrate and ammonium content in spring 1993 at site 1 

showed no change compared to spring 1991. At site 9, 

nitrate and ammonium content of the unsaturated zone 

at site 9 was 444 Ib/acre in spring 1991,228 Ib/acre 

(48 percent less compared to spring 1991) in spring 

1992, and 271 Ib/acre (39 percent compared to 1991) 

in spring 1993.

Estimation of Rate of Vertical Transport of Nitrate

Tracer experiments were conducted to estimate 

the annual rate of movement of nitrate in the unsaturated zone and to estimate the retention rate of nitrate in 

the unsaturated zone. Bromide was applied on two 

irrigated corn-field plots (sites 1 and 9) prior to fertilizer application in the spring 1992. The background 

levels of bromide concentration at the two sites prior 

to bromide treatment (February 4, 1992) were less

DISTRIBUTION OF SELECTED NITROGEN COMPOUNDS 23
Table 6. Mean organic-matter content, silt-clay content, and ammonium and nitrate concentrations as nitrogen in multiple 

sediment cores for site 1 in the study area, NuckoNs County, Nebraska, spring 1991-33

[--, no data; mg/kg, milligrams per kilogram; silt-clay, grain size < 0.063 millimeter]

Sample 

depth 

(feet)

0.3

3.0

6.0

9.0

11.4

13.0

16.0

19.0

22.0

25.0

28.0

31.0

34.0

37.0

41.0

43.0

46.0

49.0

51.3

52.0

55.0

56.0

58.0

62.0

64.0

65.0

68.0

70.0

73.0

Organic matter 

(percent)

1992

2.28

.37

.20

.22

1.11

.99

.39

.16

.14

.16

.18

.10

.12

.10

.07

.09

.14

.13

.09

.11

.11

.15

.13

.12

.09

.07

.23

.05

.04

1993

1.44

.90

.21

.46

.58

.82

.36

.22

.16

.15

.16

.12

.10

.07

.09

.12

.12

.10

.12

.12

.16

.17

.12

.14

.09

.12

.13

.07

.11

Silt-clay 

content 

(percent)

1991

77.8

70.1

75.2

68.2

68.7

51.7

50.5

63.4

64.6

58.1

52.9

59.2

62.7

45.3

63.5

68.5

60.3

42.3

54.8

82.2

81.9

48.7

68.6

33.6

35.1

42.7

46.6

47.5

40.1

Nitrate as nitrogen 

(mg/kg)

1991

-

1.98

1.73

2.16

2.55

2.58

2.42

2.14

2.19

1.96

1.37

1.68

1.94

2.22

1.75

2.04

2.09

1.98

1.49

1.29

1.70

1.42

1.42

2.06

.93

.68

.24

.29

.34

1992

2.36

4.08

1.37

1.37

2.01

1.93

1.52

1.33

1.25

1.78

1.68

1.20

1.30

1.36

1.09

1.51

.83

1.61

1.15

.93

1.16

1.15

1.31

.91

.70

.70

.53

.51

.53

1993

2.28

3.36

4.14

1.91

2.31

1.77

1.27

1.34

1.25

1.25

1.40

1.47

1.63

2.49

1.52

1.84

1.49

1.44

1.76

1.55

1.59

1.63

1.47

1.47

.92

1.36

1.50

1.48

1.58

Ammonium as nitrogen 

(mg/kg)

1991

2.29

1.74

1.80

1.95

1.86

1.43

1.61

2.63

2.57

2.26

2.97

3.12

3.56

3.27

2.54

3.09

2.67

2.60

2.69

3.00

2.75

3.52

1.80

5.21

4.45

4.94

2.32

2.13

2.63

1992

1.65

1.31

1.40

.63

.56

.77

.87

1.17

1.52

1.82

1.51

1.58

2.32

1.77

1.70

1.74

2.02

2.45

2.60

2.35

3.12

3.21

3.00

3.04

3.71

2.96

3.53

2.17

1.53

1993

1.93

1.92

1.86

1.30

3.78

1.17

1.45

1.90

2.20

2.53

1.66

2.35

2.26

2.47

2.90

2.59

3.43

3.36

3.33

2.39

3.54

3.91

3.14

3.76

3.29

3.03

3.83

3.22

4.44

24 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-93
Table 7. Mean organic-matter content, silt-clay content, and ammonium and nitrate concentrations as nitrogen in multiple 

sediment cores for site 9 in the study area, Nuckolls County, Nebraska, spring 1991-93

[--, no data; mg/kg, milligrams per kilogram; silt-clay grain size < 0.063 millimeter]

Sample depth 

(feet)

Organic matter 

(percent)

Silt-clay 

content 

(percent)

Nitrate as nitrogen 

(mg/kg)

Ammonium as nitrogen 

(mg/kg)

1992 1993 1991 1991 1992 1993 1991 1992 1993

0.3

2.0

3.0

5.0

7.0

9.0

ll.O

1 3.0

1 5.0

1 7.0

1 8.6

19.0

20.0

1.94

1.05

.48

.50

.54

.25

.21

.22

.18

.31

.41

.46

.42

1.67

0.97

.48

.36

.45

.35

.22

.20

.19

.19

.35

.42

.44

57.8

44.1

53.1

38.8

45.0

57.4

78.7

44.3

58.4

60.0

31.3

33.7

--

5.50

1.78

1.26

2.81

6.65

8.40

9.78

5.00

2.64

2.45

2.32

2.04

-

2.28

1.88

1.24

1.08

1.22

1.39

1.91

1.41

1.53

1.69

2.19

1.74

1.71

1.86

1.09

.93

1.09

1.17

1.30

1.14

1.30

1.40

1.70

1.45

1.50

1.47

2.17

2.47 :

2.53 :

1.32

1.23

2.10

1.75

1.35

2.28

2.08

1.61

1.11

1

1.73

114

124

.60

.40

.51

.53

.49

.25

.29

.53

.89

.11

2.34

3.38

3.97

3.68

2.19

2.35

1.76

1.67

1.90

2.00

2.51

2.24

2.62

than the analytical detection limit of 0.4 mg/kg 

(tables 9 and 10).

Bromide in sediment cores that were obtained 

343 days (April 27,1993) after bromide application 

indicate that the tracer had leached to 9 ft (core 3) and 

13 ft (core 1) below the land surface at sites 1 and 9, 

respectively (tables 9 and 10).

Assuming transport of the conservative bromide 

tracer in the unsaturated zone is similar to that of 

nitrate, and assuming an annual rate of downward 

movement of 11 ft, it would take about 2 years for 

nitrate to travel through a 22-ft-thick unsaturated zone 

in the lowland and reach ground water. However, in

parts of the upland where thickness of the unsaturated 

zone is greater than 100 ft, it would take more than 

9 years for nitrate to reach ground water. Total 

bromide retained in the unsaturated zone was considerably less than the level of bromide applied. The 

bromide within the unsaturated zones was estimated to 

be about 28 percent of the amount applied at site 1 and 

19 percent at site 9. However, about 46 and 91 percent 

of those amounts were retained in 5-ft unsaturated 

zones at sites 1 and 9, respectively. A large portion of 

bromide probably was removed by runoff and uptake 

by the corn plants (P.L. Barnes, Kansas State University Agronomy Department, written commun., 1993).

DISTRIBUTION OF SELECTED NITROGEN COMPOUNDS 25
30 35

SILT AND CLAY CONTENT, IN PERCENT 

40 45 50 55 60 65 70 75 80 85

5

10

15

S 20

LL

^25

LU 

U

< 30 

cr

w 35 

Q

<j 40 

O 45

LU

"50

LU 55 

Q

60

65

70

75

% 1991 =

*'" I I 1*1 I I I I "~ i i i i I i i i i I i i i I I i M I I I I I i I i i i i I i i M I i i i i I i i i r

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

NITRATE AND AMMONIUM AS NITROGEN CONCENTRATION,

IN MILLIGRAMS PER KILOGRAM

5.5

Figure 12A. Distribution of ammonium and nitrate concentrations 

and organic matter and silt-clay content with depth at site 1 of the 

study area, Nuckolls County, Nebraska, spring 1991.

ORGANIC MATTER CONTENT, IN PERCENT 

0.5 1.0 1.5 2.0

 ORGANIC MATTER 

CONTENT

1992 d

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ! I I I I I 1 I I I I I I i I

NITRATE AND AMMONIUM AS NITROGEN CONCENTRATION, 

IN MILLIGRAMS PER KILOGRAM

Figure 12B. Distribution of ammonium and nitrate concentrations 

and organic matter and silt-clay content with depth at site 1 of the 

study area, Nuckolls County, Nebraska, spring 1992.

26 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-93
ORGANIC MATTER CONTENT, IN PERCENT 

0.5 1.0 1.5 2.0 2.5

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

NITRATE AND AMMONIUM AS NITROGEN CONCENTRATION, 

IN MILLIGRAMS PER KILOGRAM

Figure 12C. Distribution of ammonium and nitrate concentrations 

and organic matter and silt-clay content with depth at site 1 of the 

study area, Nuckolls County, Nebraska, spring 1993.

DISTRIBUTION OF SELECTED NITROGEN COMPOUNDS 27
SILT AND CLAY CONTENT, IN PERCENT 

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

ffi 6

10

12

O

14

16

18

20

22

 SILT-CLAY

 - N03-N

 -- NH4-N

1991H

lllllllllllllMMllllllMMlMMlMl.lllMlM

10

NITRATE AND AMMONIUM AS NITROGEN CONCENTRATION, 

IN MILLIGRAMS PER KILOGRAM

Figure 13A. Distribution of ammonium and nitrate concentrations 

and organic matter and silt-clay content with depth at site 9 of the 

study area, Nuckolls County, Nebraska, spring 1991.

0

2

4

LLJ

LU ,,

LL. 6

z

B 8

ORGANIC MATTER CONTENT, IN PERCENT 

0.5 1.0 1.5 2.0 2.5

O

i i i r

 ORGANIC MATTER 

CONTENT

I i i i i I i i i i I i i i i I i i i i I i i i i I i i i i I i i i i I i i i i I i i i i I i i i

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

NITRATE AND AMMONIUM AS NITROGEN CONCENTRATION, 

IN MILLIGRAMS PER KILOGRAM

Figure 13B. Distribution of ammonium and nitrate concentrations 

and organic matter and silt-clay content with depth at site 9 of the 

study area, Nuckolls County, Nebraska, spring 1992.

28 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-93
ORGANIC MATTER CONTENT, IN PERCENT 

0.5 1.0 1.5 2.0 2.5

LLJ

z 

S 8

QC

ORGANIC MATTER 

CONTENT

N03-N 

NH4-N

1993 J

iln

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

NITRATE AND AMMONIUM AS NITROGEN CONCENTRATION, 

IN MILLIGRAMS PER KILOGRAM

Figure 13C. Distribution of ammonium and nitrate concentrations 

and organic matter and silt-clay content with depth at site 9 of the 

study area, Nuckolls County, Nebraska, spring 1993.

Table 8. Summary of nitrate and ammonium contents in the 

unsaturated zone, sites 1 and 9 in the study area, Nuckolls 

County, Nebraska, spring 1991-93

[lb/acre, pounds per acre; total sample depths are 73 and 20 feet below land 

surface at sites 1 and 9, respectively]

Nitrogen _____________ Sltel ___________ Slte9

compound 1991 1992 1993 "1991 1992 1993

Nitrate as 484 370 467 314 IB92~ 

nitrogen, 

lb/acre

Arnmon- 682 507 699 130 115 179 

iumas 

nitrogen, 

lb/acre

Total 1,166 877 1,166 444 228 271

DISTRIBUTION OF SELECTED NITROGEN COMPOUNDS 29
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 

NITRATE CONTENT, IN POUNDS PER ACRE

Figure 14A. Nitrate content and total nitrogen and ammonium 

content beneath a com field at site 1 in the study area, Nuckolls 

County, Nebraska, spring 1991-33.

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

NITRATE PLUS AMMONIUM CONTENT, 

IN POUNDS PER ACRE

Figure 14B. Nitrate content and total nitrogen and ammonium 

content beneath a corn field at site 1 in the study area, Nuckolls 

County, Nebraska, spring 1991-33.
10

fj 12

S

uj 14

16

18

20

22

20 40 60 

NITRATE CONTENT, IN POUNDS PER ACRE

80

Figure 15A. Nitrate content and nitrate and ammonium content 

beneath a corn field at site 9 in the study area, Nuckolls County, 

Nebraska, spring 1991-93.

UJ c

uj b

10

3 12

I

uj 14

CD

I

Sl6

20 40 60 80

NITRATE PLUS AMMONIUM CONTENT,

IN POUNDS PER ACRE

100

Figure 15B. Nitrate content and nitrate and ammonium content 

beneath a corn field at site 9 in the study area, Nuckolls County, 

Nebraska, spring 1991-93.

DISTRIBUTION OF SELECTED NITROGEN COMPOUNDS 31
Table 9. Concentrations of bromide in sediment cores and estimated content for site 1 in the study area, Nuckolls County, 

Nebraska, winter 1992 and spring 1993

[lb/acre, pounds per acre; N, less than detection level of 0.4 mg/kg; mg/kg, milligrams per kilogram]

Sample depth 

(feet)

Sample date: 02-07-92 

(pretreatment)

Concentration

Corel 

(mg/kg)

0.3 N 

3 N 

6 N 

9 N 

11.4-73 N 

Total content (lb/acre) 

Percent

Core 2 

(mg/kg)

N 

N 

N 

N 

N

Mean 

(mg/kg)

N 

N 

N 

N 

N

Content 

(lb/acre)

N 

N 

N 

N 

N

N

Corel 

(mg/kg)

2.52 

1.56 

2.48

N 

N

Sample date: 04-27-93

Concentration

Core 2 

(mg/kg)

1.53 

2.52 

5.23

N 

N

CoreS 

(mg/kg)

1.16 

2.31 

2.37 

1.24

N

Mean 

(mg/kg)

1.74 

2.13 

3.36 

.41

N

Content 

(lb/acre)

3.65 

30.03 

36.29 

3.98

N

73.95 

28

Table 10. Concentrations of bromide in sediment cores and estimated content for site 9 in the study area, Nuckolls County, 

Nebraska, winter 1992 and spring 1993

[lb/acre, pound per acre; mg/kg, milligrams per kilogram; N, less than detection level of 0.4 mg/kg]

Sample

depth

/<«k«h*\ (feet)

0.3

2

3

5

7

9

11

13

15-20

Sample date: 02-04-92 

(pretreatment)

Concentration

Corel

(mg/kg)

N

N

N

N

N

N

N

N

N

Core 2

(mg/kg)

N

N

N

N

N

N

N

N

N

Mean

(mg/kg)

N

N

N

N

N

N

N

N

N

Total content (lb/acre)

Percent

Content

(lb/acre)

N

N

N

N

N

N

N

N

N

N

Corel

(mg/kg)

N

4.71

1.76

N

N

N

N

.63

N

Sample date: 04-27-93

Concentration

Core 2

(mg/kg)

0.527

8.27

4.31

.43

N

N

N

N

N

CoreS

(mg/kg)

0.68

.60

.93

.43

.40

.42

N

N

N

Mean

(mg/kg)

0.42

4.53

2.33

.29

.13

.14

N

.21

N

Content

(lb/acre)

0.88

31.26

12.58

2.09

.94

1.01

N

1.51

N

50.27

19

32 Distribution of Selected Nitrogen Compounds In Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-93
SUMMARY

During the late 1980's, nitrate concentrations in 

ground water in excess of the U.S. Environmental 

Protection Agency's Maximum Contaminant Level for 

drinking water of 10 milligrams per liter occurred in 

the southern part of Nuckolls County, Nebraska. To 

help reduce this local ground-water contamination, the 

Nebraska Department of Environmental Quality 

designated the State's first Special Protection Area in 

1989 the Superior-Hardy Special Protection Area. 

The Special Protection Area designation requires that 

a management plan be implemented and that concentrations of nitrate in the ground water be monitored 

during the 10-year period of designation as a Special 

Protection Area.

A ground-water-quality monitoring network of 

20 wells located at 16 sites was established in 1991, in 

the 32-square-mile Superior-Hardy Special Protection 

Area. The purpose of this network was to monitor 

long-term trends in concentrations of nitrate in ground 

water after a management plan was implemented in 

1991. The 16 sites were selected based on geologic, 

hydrogeologic, soil, land-use, and physiographic 

factors, cost considerations, and accessibility. Nested 

monitoring wells were installed at two sites (wells 9 

and 13) to examine vertical distribution of nitrate 

concentrations in the area.

Nitrate concentrations greater than 5 mg/L were 

detected in 81 percent of the ground-water samples 

collected from the shallow aquifer during 1991 93. 

Approximately 44 percent of the samples exceeded 

10 mg/L, the U.S. Environmental Protection Agency 

Maximum Contaminant Level for nitrate as nitrogen 

in drinking water. The mobility of nitrate in the 

ground-water system was demonstrated by detection 

of high nitrate concentrations at three upland sites 

(1,2, and 3) at depths as much as 100 feet below the 

land surface. The presence of nitrate in ground water 

is related to ground-water flow direction and land-use 

patterns in the area. Nitrate concentrations ranged 

from 5 mg/L in the northern part of the study area to 

15 mg/L in the southern part. Most of the large nitrate 

concentrations were found in areas of irrigated 

farmland, particularly in lowland areas.

Difference in nitrate concentration with depth 

was measured at two sites in the irrigated lowland

area. Data indicate that the aquifer is not well mixed 

vertically. Nitrate concentrations are largest at the top 

of the saturated zone and decrease with depth; 

therefore, the fully penetrating, fully screened wells 

yield samples most representative of the entire 

saturated thickness of the aquifer.

Because of very slow ground-water movement 

and the time lag between the implementation of the 

management plan and water-quality improvement, 

significant changes in concentrations of nitrate in 

ground water were not detected during the study 

period (3 years). To identify changes in concentrations of nitrate in the ground water, long-term repetitive sampling over the spatial network is necessary. 

Such changes will be detected most quickly in the 

shallow ground water beneath the lowland area.

Two sites were chosen for sediment coring 

during 3 consecutive years (1991 93) prior to fertilizer application in the spring to estimate the nitrate and 

ammonium, organic matter, and silt-clay content of the 

unsaturated zone. Both nitrate and ammonium forms 

of inorganic nitrogen were found throughout the entire 

sediment profile in the unsaturated zone. Maximum 

concentrations of nitrate were detected at or within 13 

feet of the land surface at both sites, suggesting that 

the major source of nitrogen at these sites is from the 

land surface. Correlation analysis indicated that 

nitrate, organic matter, and silt-clay content decreased 

with depth, whereas ammonium increased with depth 

at site 1. At site 9, ammonium concentrations and 

organic matter decreased with depth, whereas the 

nitrate and silt-clay content appeared to be independent of sampling depth. Nitrate plus ammonium as 

nitrogen loads were estimated as 1,166, 877, and 

1,166 Ib/acre at site 1 and 444,228, and 271 Ib/acre at 

site 9, for the 3-year period.

Bromide tracer experiments were conducted to 

estimate the annual rate of movement of nitrate in the 

unsaturated zone. Bromide tracer had leached to 9 and 

13 feet below the land surface at sites 1 and 9, respectively. Thus, an annual rate of downward movement 

of nitrate was estimated to be about 11 feet. It may 

take about 2 years and more than 9 years for nitrate to 

reach ground water in the lowland and the upland, 

respectively.

SUMMARY 33
SELECTED REFERENCES

Aller, Linda, 1991, Handbook of suggested practices for the 

design and installation of ground-water monitoring 

wells: Dublin, Ohio, National Water Well Association, 

398 p.

Aravena, R., Evans, ML., and Cherry, J.A., 1993, Stable 

isotopes of oxygen and nitrogen in source identification of nitrate from septic systems: Ground Water, 

v. 31, no. 2, p. 180-S6.

Bohn, H.L., McNeal, B.L., and O'Connor, G.A., 1985, Soil 

chemistry (2d ed.): New York, John Wiley and Sons, 

341 p.

Burchett, R.R., Dreeszen, V.H., Reed, E.G., and Prichard, 

G.E., 1972, Bedrock geologic map showing thickness 

of overlying Quaternary deposits, Lincoln quadrangle 

and part of Nebraska City quadrangle, Nebraska and 

Kansas: U.S. Geological Survey Miscellaneous 

Investigations Series Map 1-729, scale 1:250,000.

Chen, H.H., and Druliner, A.D., 1987, Nonpoint-source 

agricultural chemicals in ground water in 

Nebraska Preliminary results for six areas of the 

High Plains aquifer: U.S. Geological Survey WaterResources Investigations Report 86-4338, 68 p.

Conover, W.J., 1989, Practical nonparametric statistics: 

New York, John Wiley and Sons, 493 p.

Conservation and Survey Division, 1953, Logs of test holes, 

Nuckolls County, Nebraska: Lincoln, University of 

Nebraska, Conservation and Survey Division, Test 

Hole Report THR-48,13 p.

Conservation and Survey Division, 1980, Configuration of 

base of principal aquifer, Nebraska, 1979: Lincoln, 

Nebraska, Conservation and Survey Division, Institute 

of Agriculture and Natural Resources, University of 

Nebraska, Groundwater Map 52, scale 1:250,000.

Crawford, C.G., Slack, J.R., and Hirsch, R.M., 1983, 

Nonparametric tests for trends in water-quality data 

using the statistical analysis system: U.S. Geological 

Survey Open-File Report 83-550, 102 p.

Dreeszen, V.H., Reed, E.G., Burchett, R.R., and Prichard, 

G.E., 1973, Bedrock geologic map showing thickness 

of overlying Quaternary deposits, Grand Island 

quadrangle, Nebraska and Kansas: U.S. Geological 

Survey Miscellaneous Investigations Series 

Map 1-819, scale 1:250,000.

Dugan, J.T., 1984, Hydrologic characteristics of Nebraska 

soils: U.S. Geological Survey Water-Supply Paper 

2222, 19 p.

Ehrman, Richard, 1989, A study of nonpoint-source 

ground-water contamination in southern Nuckolls 

County, Nebraska Special Protection Area Report: 

Nebraska Department of Environmental Control 

(Quality), 54 p.

Ellis, M.J., 1981, Hydrogeologic reconnaissance of the 

Republican River Basin in Nebraska: U.S. Geological 

Survey Open-File Report 81-531, scale 1:500,000, 

1 sheet.

Engberg, R.A., 1984, Appraisal of data for ground-water 

quality in Nebraska: U.S. Geological Survey WaterSupply Paper 2245, 54 p.

Fenneman, N.M., 1946, Physical divisions of the United 

States: Washington, D.C., U.S. Geological Survey 

special map, scale 1:7,000,000.

Fishman, M.J., and Friedman, L.C., (eds.), 1989, Methods 

for determination of inorganic substances in water and 

fluvial sediments: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 5, chap. Al, 

545 p.

Follett, R.F., Kenney, D.R., and Cruse, R.M., (eds.), 1991, 

Managing nitrogen for ground-water quality and farm 

profitability: Madison, Wisconsin, Soil Science 

Society of America, 357 p.

Gormly, J.R., and Spalding, R.F., 1979, Sources and

concentrations of nitrate-nitrogen in ground water of 

Central Platte Region, Nebraska: Ground Water, 

v. 7, no. 3, p. 291-301.

Harris, J., Loftis, J.C., and Montgomery, R.H., 1987, Statistical methods for characterizing ground-water quality: 

Ground Water, v. 25, no. 2, p. 185-93.

Hirsch, R.M., Slack, J.R., and Smith, R.A., 1982,

Techniques of trend analysis for monthly water-quality 

data: U.S. Geological Survey Open-File Report 

81-488, 30 p.

Kleiner, B., and Graedel, T.E., 1980, Exploratory data 

analysis in the geophysical sciences: Reviews of 

Geophysics and Space Physics, v. 18, no. 3, 

p. 699-717.

Kolpin, D.W, and Burkart, M.R., 1991, Work plan for 

regional reconnaissance for selected herbicides and 

nitrate in ground water of the mid-continent United 

States, 1991: U.S. Geological Survey Open-File 

Report 91-59,18 p.

Komor, S.C., and Anderson, H.W, Jr., 1993, Nitrogen 

isotopes as indicators of nitrate sources in Minnesota 

sand-plain aquifers: Ground Water, v. 31, no. 2, 

p. 260-70.

Lower Republican Natural Resources District and Little 

Blue Natural Resources District, 1990, Superior-Hardy 

Special Protection Area Action Plan, 120 p.

McBean, E.A., and Rovers, F.A., 1984, Alternatives for 

assessing significance of changes in concentration 

levels: Groundwater monitoring review, summer 

1994, p. 39-41.

Miller, R.D., Van Horn, R., Dobrovolny, E., and Buck, L.P., 

1964, Geology of Franklin, Webster, and Nuckolls 

Counties, Nebraska: U.S. Geological Survey Bulletin 

1165, 91 p.

34 Distribution of Selected Nitrogen Compounds In Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolis County, Nebraska, 1991-93
Montgomery, R.H., Loftis, J.C., and Harris, J., 1987, Statistical characteristics of ground-water quality 

monitoring: Ground Water, v. 25, no. 2, p. 176-84.

SAS Institute, Inc., 1990, SAS/STAT user's guide: 

Version 6, (4th ed.), Gary, North Carolina, v. 2.

Soil Conservation Service and University of Nebraska 

Cooperative Extension, 1994,1993 field demonstrations of best management practices to protect groundwater quality: SCREC94/2, 104 p.

Spruill, T.B., 1990, Monitoring regional ground-water 

quality Statistical considerations and description of 

monitoring network in Kansas: U.S. Geological 

Survey Water-Resources Investigations Report 

90-4159, 41 p.

Tukey, J.W, 1977, Exploratory data analysis: Reading, 

Massachusetts, Addison-Wesley, 688 p.

U.S. Department of Commerce, Bureau of the Census, 

1993,1990 Census of population and housing:

Summary population and housing characteristics, 

Nebraska, 303 p.

U.S. Environmental Protection Agency, 1994, Drinkingwater regulations and health advisories: U.S. Environmental Protection Agency, Office of Water, 11 p.

University of Nebraska, 1989, Adjusting nitrogen fertilizer 

for corn based on nitrate levels hi soil and irrigation 

water: Cooperative Extension Service, NebGuide 

89-913,4 p.

Waite, H.A., Reed, B.C., and Jones, D.S., Jr., 1944, Ground 

water in the Republican River Basin, Nebraska, part 1, 

Nuckolls, Webster, Franklin, and Harlan Counties: 

Lincoln, Nebraska, Conservation and Survey Division, 

Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln, Water Resources Survey 

Water-Supply Paper 1.

SELECTED REFERENCES 35
ADDITIONAL WATER-QUALITY AND SEDIMENT DATA

ADDITIONAL WATER-QUALITY AND SEDIMENT DATA 37
Table 11. Water-quality data for samples from 20 monitoring wells in the study area, Nuckolls County, Nebraska, 

1991-93

[-, no data; °C, degrees Celsius; mg/L, milligrams per liter; nS/cm, microsiemens per centimeter]

Well 

number

1

1

1

1

1

1

1

1

1

1

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

3

3

3

3

3

3

3

3

3

3

3

Date

7-02-91

8-02-91

8-21-91

9-04-91

11-12-91

1-17-92

3-17-92

5-19-92

7-09-92

9-16-92

11-19-92

1-26-93

3-24-93

5-19-93

7-13-93

9-07-93

7-02-91

8-06-91

8-21-91

9-04-91

11-12-91

1-17-92

3-17-92

5-19-92

7-09-92

9-15-92

11-19-92

1-26-93

3-24-93

5-19-93

7-13-93

9-08-93

7-10-91

8-02-91

8-21-91

9-05-91

11-12-91

1-17-92

3-17-92

5-20-92

7-09-92

9-15-92

11-19-92

Time

20:18

11:30

12:22

16:30

12:05

9:30

14:00

11:20

J4:00

8:00

10:10

13:44

14:05

15:55

14:05

15:00

18:47

17:50

11:23

18:15

13:30

10:20

15:08

13:29

14:53

18:20

11:00

15:18

13:40

16:39

14:47

14:00

14:51

15:20

13:08

9:16

14:20

8:50

13:33

9:11

13:17

17:30

9:25

Depth to 

water 

(feet)

123.00

121.60

122.00

122.56

122.05

-

124.16

126.15

126.05

126.00

124.28

125.45

125.49

125.56

124.49

122.50

130.40

137.00

136.55

136.25

135.61

134.98

135.40

134.13

126.80

134.72

134.70

134.34

134.01

133.31

133.47

118.40

121.50

123.70

122.70

122.40

-

122.27

122.28

122.78

115.30

122.22

Temperature (°C)

17.1

16.8

14.1

13.1

13.0

12.5

13.0

15.5

12.4

13.2

11.8

12.4

12.8

12.6

14.3

13.3

13.7

13.3

13.3

13.2

13.1

12.8

13.1

14.0

13.3

13.4

12.9

12.6

13.3

13.0

13.6

13.4

14.2

13.3

13.3

13.2

13.3

12.8

13.8

13.8

13.3

13.6

13.0

PH 

(standard 

units)

7.3

7.4

7.5

6.4

7.4

7.1

7.4

7.2

7.3

7.3

7.4

7.1

7.2

7.1

7.2

6.9

7.2

7.2

7.2

6.1

7.2

7.0

6.9

7.2

7.12

7.1

7.3

7.2

7.1

7.2

7.2

7.1

7.2

7.0

7.2

7.1

7.0

7.0

6.9

6.8

7.0

7.1

7.2

Specific 

conductance 

(nS/cm at 

25°C)

805

908

906

915

938

939

951

928

952

940

926

894

875

863

849

864

630

732

740

722

758

747

732

716

695

673

677

664

652

640

640

638

964

658

658

666

664

657

655

663

656

652

649

Dissolved 

oxygen 

(mg/L)

6.6

5.9

6.6

6.4

6.7

6.8

6.1

7.6

6.6

7.2

6.8

8.0

6.3

6.5

6.2

8.2

6.8

7.7

7.1

7.1

7.4

6.9

7.0

9.2

9.2

10.9

9.0

9.3

9.6

9.0

9.6

10.4

11.1

6.8

6.9

6.4

6.7

6.1

5.4

8.9

8.7

9.8

8.5

Nitrate 

as 

nitrogen 

(mg/L)

5.9

5.0

6.4

6.0

5.8

6.2

5.6

6.0

6.0

6.1

6.5

6.1

7.0

5.9

6.1

6.0

7.0

8.1

8.3

8.6

9.0

9.9

7.6

7.5

7.6

7.5

6.8

6.0

6.9

5.7

5.6

5.4

9.9

9.3

9.4

9.0

9.1

9.4

8.6

8.8

8.2

8.2

8.3

38 Distribution of Selected Nitrogen Compounds In Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-93
Table 11. Water-quality data for samples from 20 monitoring wells in the study area, Nuckolls County, Nebraska, 

1991-93 Continued

[--, no data; °C, degrees Celsius; mg/L, milligrams per liter; ^S/cm, microsiemens per centimeter]

Well 

number

3 1

3

3

3

3

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

5

5

5

5

5

5

5

5

5

5

5

5

5

5

5

5

6

6

6

6

6

6

Date

1-26-93

3-24-93

5-19-93

7-13-93

9-07-93

7-10-91

8-02-91

8-21-91

9-05-91

11-12-91

1-17-92

3-17-92

5-20-92

7-09-92

9-15-92

11-19-92

1-26-93

3-24-93

5-19-93

7-14-93

9-08-93

7-01-91

8-01-91

8-19-91

9-05-91

11-12-91

1-16-92

3-18-92

5-20-92

7-10-92

9-15-92

11-19-92

1-26-93

3-23-93

5-19-93

7-13-93

9-08-93

7-10-91

8-06-91

8-21-91

9-05-91

11-12-91

1-16-92

Time

13:03

15:21

15:15

15:50

15:41

20:10

14:43

10:10

15:07

11:00

15:50

9:53

15:33

16:00

11:43

16:43

12:23

14:40

10:37

14:30

15:30

10:35

14:00

11:10

16:00

14:22

15:00

11:24

8:57

14:48

12:27

11:54

11:35

15:25

13:30

13:15

16:50

16:10

15:15

12:10

16:33

14:40

Depth to 

water 

(feet)

~

122.07

123.27

121.20

121.26

58.70

58.50

58.70

59.65

58.80

58.80

59.08

59.03

58.60

58.30

59.40

58.26

57.64

56.90

55.58

14.00

19.20

18.70

18.60

17.00

~

14.39

13.98

13.82

13.00

11.59

11.50

8.03

10.63

7.76

8.45

35.35

35.30

35.29

35.47

35.43

..

Temperature (°C)

~

13.3

13.1

13.5

13.3

15.0

13.3

13.3

13.2

13.3

13.1

13.7

13.7

13.2

13.5

13.0

13.0

13.3

13.1

13.3

13.3

13.7

12.2

12.5

12.3

12.8

12.9

13.2

13.2

12.6

12.8

12.6

12.7

12.8

12.4

12.3

12.2

14.1

15.2

14.4

12.9

12.9

12.5

pH 

(standard 

units)

7.0

7.1

7.0

7.0

6.8

6.7

6.9

6.7

6.7

6.7

6.6

6.5

6.8

6.8

6.8

6.7

6.7

6.8

6.8

7.0

6.9

7.3

7.0

7.0

7.0

6.9

6.9

6.8

6.6

7.0

7.0

6.9

7.0

7.0

7.0

7.0

7.2

7.2

7.3

7.2

7.1

7.3

Specific 

conductance 

(nS/cm at 

25°C)

~

654

651

656

648

959

1,040

1,050

1,050

1,070

1,060

,060

,070

,060

,060

,050

,030

980

880

723

648

950

1,010

984

966

991

1,020

1,060

1,050

1,040

929

918

947

936

996

1,010

956

592

582

1,070

1,090

1,140

1,150

Dissolved 

oxygen 

(mg/L)

-

9.4

8.4

9.2

9.8

8.4

5.4

5.4

5.3

5.6

5.1

4.8

7.5

7.3

8.4

7.0

7.3

7.1

7.2

8.6

9.8

3.1

.1

.3

.3

.3

.1

.04

.1

.1

0.2

.2

.1

.2

.1

.2

.4

13.0

6.1

5.3

4.9

5.2

5.2

Nitrate 

as 

nitrogen 

(mg/L)

-

8.9

7.6

7.2

7.6

24

24

24

25

24

23

24

22

22

22

25

23

24

23

17

-

13

12

11

9.9

11

13

15

13

13

8.0

8.5

9.8

10

12

13

11

10

6.9

7.1

6.9

6.5

7.0

ADDITIONAL WATER-QUALITY AND SEDIMENT DATA 39
Table 11. Water-quality data for samples from 20 monitoring wells in the study area, Nuckolls County, Nebraska, 

1991-93 Continued

[-, no data; °C, degrees Celsius; mg/L, milligrams per liter; nS/cm, microsiemens per centimeter]

Well 

number

6

6

6

6

6

6

6

6

6

6

7

7

7

7

7

7

7

7

7

7

7

7

7

7

7

7

8

8

8

8

8

8

8

8

8

8

8

8

8

8

8

8

Date

3-17-92

5-20-92

7-10-92

9-15-92

11-19-92

1-26-93

3-23-93

5-19-93

7-14-93

9-07-93

7-01-91

8-02-91

8-21-91

9-05-91

11-12-91

1-16-92

3-18-92

5-19-92

7-10-92

9-15-92

11-19-92

1-27-93

3-24-93

5-19-93

7-14-93

9-08-93

7-10-91

8-02-91

8-21-91

9-05-91

11-13-91

1-16-92

3-17-92

5-20-92

7-09-92

9-15-92

11-18-92

1-26-93

3-24-93

5-19-93

7-12-93

9-07-93

Time

16:30

14:12

9:30

15:26

14:55

12:25

12:35

13:55

11:08

13:50

17:50

18:50

15:45

13:00

17:18

15:25

14:15

17:27

8:15

13:39

15:55

10:15

11:19

12:45

11:50

12:05

21:35

13:10

16:18

14:30

9:20

11:30

12:30

16:58

12:00

12:30

16:57

10:30

14:58

11:45

18:28

14:20

Depth to 

water 

(feet)

35.88

35.36

33.19

35.10

36.80

34.40

33.94

34.61

32.50

31.52

26.45

26.65

25.25

25.02

25.68

-

25.04

25.06

25.44

22.90

23.02

22.70

20.87

21.62

18.22

18.72

8.15

9.55

9.83

9.90

11.10

-

12.09

12.70

10.94

7.90

6.87

6.80

2.38

3.86

3.33

2.66

Temperature 

(°C)

12.4

13.5

13.4

15.5

11.8

12.5

13.4

12.8

14.0

12.9

12.9

12.7

12.6

12.5

12.6

12.5

13.1

13.4

12.7

12.8

12.5

12.5

12.9

12.7

12.7

12 .4

13.3

13.3

13.8

13.3

13.4

12.6

11.6

13.8

12.3

14.6

12.9

10.0

8.0

9.3

13.0

13.8

PH 

(standard 

units)

7.2

7.2

7.1

7.4

7.3

7.0

7.1

7.0

7.0

6.9

6.7

6.8

7.0

6.8

6.8

6.7

6.7

6.6

6.5

6.9

6.9

6.7

6.8

6.8

6.8

6.8

7.1

6.9

6.8

6.8

6.2

6.7

7.1

7.0

6.91

7.0

6.9

7.2

7.1

6.8

7.2

7.0

Specific 

conductance 

(nS/cm at 

25°C)

1,150

1,170

1,170

1,050

1,020

1,130

1,130

1,060

498

1,180

800

832

823

832

844

827

828

834

814

799

812

820

829

853

892

914

709

1,300

1,340

1,320

1,260

1,160

1,150

1,140

595

1,300

1,350

1,330

1,300

1,280

1,190

1,140

Dissolved 

oxygen 

(mg/L)

3.8

7.1

6.2

7.1

6.2

7.9

7.5

7.1

8.1

-

2.4

2.8

3.0

2.6

2.3

2.3

3.2

3.2

3.5

4.1

2.8

2.6

2.4

2.4

2.8

3.3

10

4.9

4.4

3.4

2.6

3.1

2.2

5.1

5.0

5.0

5.0

5.8

3.5

4.2

3.3

Nitrate 

as 

nitrogen 

(mg/L)

6.5

6.6

6.9

6.9

8.3

14

18

17

~

7.2

6.5

6.6

6.3

5.2

6.4

5.9

6.0

6.1

6.1

6.0

6.0

6.0

6.2

7.4

8.5

4.6

4.0

5.8

5.3

3.2

2.2

2.2

2.4

3.4

6.1

4.3

2.5

1.7

1.0

1.1

1.3

40 Distribution of Selected NHrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-93
Table 11. Water-quality data for samples from 20 monitoring wells in the study area, Nuckolls County, Nebraska, 

1991-93 Continued

[ , no data; °C, degrees Celsius; mg/L, milligrams per liter; nS/cm, microsiemens per centimeter]

Well 

number

9A

9A

9A

9A

9A

9A

9A

9A

9A

9A

9A 

9A1

9A

9A

9A

9B

9B

9B

9B

9B

9B

9B

9B

9B

9B

9B 

9B1

9B

9B

9B

9B

9C

9C

9C

9C

9C

9C

9C

9C

9C

9C

9C 

9C1

Date

7-10-91

8-01-91

8-20-91

9-05-91

11-13-91

1-16-92

3-17-92

5-19-92

7-09-92

9-15-92

11-18-92 

1-26-93

3-24-93

5-18-93

7-12-93

7-10-91

8-01-91

8-20-91

9-05-91

11-13-91

1-16-92

3-17-92

5-19-92

7-09-92

9-15-92

11-18-92 

1-26-93

3-24-93

5-18-93

7-12-93

9-08-93

7-10-91

8-01-91

8-20-91

9-05-91

11-13-91

1-16-92

3-17-92

5-19-92

7-09-92

9-15-92

11-18-92 

1-26-93

Time

20:46

12:00

20:32

15:30

8:14

12:35

11:23

15:55

10:45

11:20

15:57

9:58

14:47

17:15

20:27

12:20

20:07

15:50

8:30

12:50

11:45

16:19

11:05

11:42

16:13

10:16

15:05

17:35

12:25

20:29

12:40

19:51

16:10

8:44

13:15

12:05

16:40

11:25

12:01

16:30

Depth to 

water 

(feet)

13.50

12.90

13.00

13.60

15.18

15.63

15.79

15.83

12.70

13.78

13.13

12.27

10.93

_

~

-

-

_

-

~

Temperature (°C)

13.9

13.0

13.0

13.5

13.3

13.4

13.8

13.7

13.1

13.1

12.9

12.8

12.8

12.9

14.0

13.1

13.1

13.2

13.3

13.2

13.8

14.2

13.4

13.4

13.0

13.0

13.0

13.2

12.8

13.6

12.9

13.1

13.2

13.9

13.9

13.8

13.3

12.7

13.2

13.3

PH 

(standard 

units)

7.3

7.3

7.1

7.0

6.8

7.0

6.8

6.7

6.8

7.1

6.8

6.9

7.1

7.2

7.0

7.3

7.1

7.0

6.

6.8

6.9

6.7

6.9

7.1

6.8

6.9

7.1

7.1

6.9

7.0

7.3

7.3

7.1

6.7

7.1

7.1

6.9

7.2

7.1

7.0

Specific 

conductance 

(nS/cm at 

25°C)

811

795

850

807

842

846

861

901

953

905

913

913

891

841

486

748

737

715

762

813

807

856

947

842

859

846

821

730

808

505

1,120

1,130

1,160

1,210

1,140

1,110

1,170

1,120

1,150

1,120

Dissolved 

oxygen 

(mg/L)

9.4

.8

1.3

1.1

1.4

1.4

2.2

2.3

2.3

2.3

2.5

2.4

2.2

1.8

2.5

.5

.7

1.9

2.2

2.5

3.2

3.8

4.5

5.8

3.6

2.3

2.5

.7

2.9

3.6

2.4

2.3

2.5

2.2

1.8

2.2

3.0

2.9

3.2

2.6

Nitrate 

as 

nitrogen 

(mg/L)

11

8.8

12

10

11

13

12

13

15

14

15

14

13

12

9.3

7.1

7.5

5.6

7.4

10

8.8

9.9

14

11

12

9.5

9.6

6.3

12

26

26

25

29

26

25

25

26

25

28

28

ADDITIONAL WATER-QUALITY AND SEDIMENT DATA 41
Table 11. Water-quality data for samples from 20 monitoring wells in the study area, Nuckolls County, Nebraska, 

1991-93 Continued

[--, no data; °C, degrees Celsius; mg/L, milligrams per liter; (iS/cm, microsiemens per centimeter]

Well 

number

9C

9C

9C

9C

10

10

10

10

10

10

10

10

10

10

10

10

10

10

10

10

11

11

11

11

11

11

11

11

11

11

11

11

11

11

11

11

12

12

12

12

12

12

Date

3-24-93

5-18-93

7-12-93

9-07-93

7-01-91

8-01-91

8-20-91

9-05-91

11-13-91

1-16-92

3-17-92

5-20-92

7-10-92

9-16-92

11-20-92

1-27-93

3-24-93

5-19-93

7-13-93

9-07-93

7-10-91

8-01-91

8-20-91

9-05-91

11-13-91

1-16-92

3-17-92

5-20-92

7-10-92

9-16-92

11-20-92

1-26-93

3-24-93

5-19-93

7-13-93

9-07-93

7-09-91

8-02-91

8-21-91

9-06-91

11-13-91

1-17-92

Time

10:35

15:23

17:55

12:45

19:27

9:20

16:20

17:50

10:35

16:30

17:15

12:08

14:49

12:10

13:30

12:15

9:15

11:15

17:07

16:35

12:23

8:15

14:30

19:00

11:10

17:10

18:00

12:51

13:07

12:49

12:45

9:23

8:28

10:33

14:22

17:10

15:25

18:05

17:48

10:30

12:40

12:30

Depth to 

water 

(feet)

-

-

-

16.00

16.20

16.30

16.30

16.23

15.55

16.04

16.47

14.60

13.25

15.00

14.73

15.73

13.41

11.81

12.00

12.00

12.00

12.10

12.04

-

11.88

12.08

12.08

11.40

11.20

12.00

11.66

13.30

7.92

9.51

42.50

43.40

43.75

44.55

45.15

Temperature 

(°C)

12.7

12.3

12.4

12.5

12.5

12.4

12.4

12.5

12.9

13.0

13.6

13.4

12.7

12.7

12.8

13.1

13.0

12.6

12.4

12.2

13.9

13.0

13.5

13.7

14.0

12.8

12.4

12.8

12.9

14.0

13.6

12.4

11.7

11.8

13.2

12.8

13.6

12.7

12.9

12.7

12.7

12.5

PH 

(standard 

units)

7.0

7.3

7.2

7.1

7.0

7.3

7.1

7.1

7.0

6.9

6.6

6.7

6.8

6.8

6.7

6.7

6.8

6.8

6.8

6.8

7.1

7.3

7.0

7.2

7.0

6.9

6.8

6.9

6.9

6.9

6.9

6.9

7.0

7.0

7.0

6.9

6.6

6.8

7.1

7.0

6.8

6.7

Specific 

conductance 

(nS/cm at 

25°C)

1,120

1,180

1,180

1,200

800

872

850

828

824

803

797

798

776

754

751

770

769

751

684

740

878

914

911

913

904

880

880

8%

886

877

875

866

853

856

858

853

308

749

763

797

822

750

Dissolved 

oxygen 

(mg/L)

3.1

3.8

3.8

3.9

3.6

3.2

2.8

2.6

1.9

1.6

.9

1.2

.8

.7

1.8

1.2

2.7

2.4

2.6

2.4

8.3

5.4

5.3

5.2

4.8

4.8

2.8

6.5

6.7

6.6

6.8

7.2

7.2

6.5

6.6

6.5

7.5

4.7

4.3

4.4

4.1

4.3

Nitrate 

as 

nitrogen 

(mg/L)

24

28

28

31

11

9.5

9.9

9.2

8.1

9.4

9.7

10

10

10

11

11

11

10

10

10

18

19

20

19

17

18

16

18

18

18

19

17

18

15

16

16

4.5

4.5

5.1

4.7

4.7

5.2

42 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckoiis County, Nebraska, 1991-83
Table 11. Water-quality data for samples from 20 monitoring wells in the study area, Nuckolls County, Nebraska, 

1991-93 Continued

[~, no data; °C, degrees Celsius; mg/L, milligrams per liter; nS/cm, microsiemens per centimeter]

Well 

number

12

12

12

12

12

12

12

12

12

12

13 A

13A

ISA

13A

13A

13A

13A

13A

13A

13A

13A

13A

13A

13A

13A

13A

13B

13B

13B

13B

13B

13B

13B

13B

13B

13B

13B

13B

13B

13B

13B

13B

Date

3-18-92

5-20-92

7-09-92

9-16-92

11-20-92

1-25-93

3-23-93

5-18-93

7-14-93

9-08-93

7-02-91

7-31-91

8-19-91

9-06-91

11-13-91

1-17-92

3-18-92

5-19-92

7-09-92

9-16-92

11-19-92

1-25-93

3-23-93

5-18-93

7-13-93

9-08-93

7-02-91

7-31-91

8-19-91

9-06-91

11-13-91

1-17-92

3-18-92

5-19-92

7-09-92

9-16-92

11-19-92

1-25-93

3-23-93

5-18-93

7-13-93

9-08-93

Time

10:10

16:22

17:50

15:15

9:45

15:05

15:48

18:13

9:40

8:10

08:10

17:56

18:23

09:10

11:40

11:35

12:50

19:05

16:35

13:27

16:35

13:51

13:37

16:05

11:10

10:45

12:08

18:20

18:35

09:26

11:55

11:55

13:08

19:23

16:53

13:43

16:52

14:09

14:00

16:23

11:27

11:05

Depth to 

water 

(feet)

45.27

45.80

46.65

46.10

45.75

46.30

43.90

44.28

42.02

41.07

24.00

22.80

22.42

22.50

23.58

~

24.29

24.50

25.75

21.90

22.55

23.30

22.26

21.39

20.97

16.35

..

~

«

Temperature 

<°C)

13.2

13.3

12.9

13.0

12.5

12.6

12.7

12.7

12.9

12.5

12.6

12.3

12.5

12.3

12.6

12.5

13.2

13.2

12.7

12.7

12.5

12.6

12.8

12.7

12.7

12.4

12.8

12.3

12.5

12.4

12.6

12.5

13.1

13.2

12.8

12.9

12.4

12.5

12.8

12.8

13.0

12.5

pH 

(standard 

units)

6.8

6.6

6.8

6.7

6.7

6.8

6.8

6.9

6.9

6.7

7.1

7.4

7.1

7.3

7.1

7.1

7.0

6.8

7.2

7.1

7.1

6.9

7.1

7.2

7.2

7.1

7.1

7.4

7.1

7.3

7.1

7.1

7.1

6.9

7.2

7.1

7.2

7.0

7.1

7.3

7.8

7.1

Specific 

conductance 

(itS/cm at 

25°C)

684

656

698

769

813

834

838

861

888

883

710

791

790

795

776

791

787

801

807

784

764

795

809

801

799

767

700

775

769

770

782

773

774

790

785

766

760

773

790

787

782

746

Dissolved 

oxygen 

(mg/L)

7.6

7.2

6.7

6.1

5.2

4.7

5.0

5.8

8.1

6.5

5.3

5.4

5.5

5.2

4.6

4.6

6.3

6.4

6.7

6.5

6.1

6.3

6.7

6.7

6.4

6.5

5.0

5.1

5.1

4.8

4.2

4.3

6.0

5.8

6.2

6.0

5.8

5.7

6.3

6.3

5.9

6.0

Nitrate 

as 

nitrogen 

(mg/L)

7.4

9.3

6.4

4.7

4.3

3.9

4.2

6.2

8.9

9.1

10

8.6

11

10

10

11

9.6

10

11

10

10

11

13

11

11

9.4

9.5

10

10

9.6

9.2

9.8

8.9

9.7

10

9.3

9.6

10

12

10

10

8.9

ADDITIONAL WATER-QUALITY AND SEDIMENT DATA 43
Table 11. Water-quality data for samples from 20 monitoring wells in the study area, Nuckolls County, Nebraska, 

1991-83 Continued

[--, no data; °C, degrees Celsius; mg/L, milligrams per liter; nS/cm, microsiemens per centimeter]

Well 

number

13C

13C

13C

13C

13C

13C

13C

13C

13C

13C

13C

13C

13C

13C

13C

13C

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

b

15

15

15

15

15

15

15

15

Date

7-02-91

7-31-91

8-19-91

9-06-91

11-13-91

1-17-92

3-18-92

5-19-92

7-09-92

9-16-92

11-19-92

1-25-93

3-23-93

5-18-93

7-13-93

9-08-93

7-09-91

8-02-91

8-21-91

9-06-91

11-13-91

1-16-92

3-18-92

5-20-92

7-10-92

9-16-92

11-20-92

1-25-93

3-23-93

5-18-93

7-13-93

9-08-93

7-10-91

7-31-91

8-20-91

9-06-91

11-13-91

1-17-92

3-18-92

5-20-92

7-10-92

Time

12:37

18:45

18:51

09:48

12:09

12:05

13:29

19:51

17:11

14:00

17:09

14:25

14:19

16:41

11:44

11:25

11:20

17:20

17:00

11:30

13:22

17:45

9:20

15:45

12:22

14:35

10:25

15:45

15:05

17:35

10:05

08:50

11:40

16:30

11:52

12:50

14:08

14:45

12:05

14:53

10:20

Depth to 

water 

(feet)

-

«

~

45.15

45.90

45.95

47.95

51.27

51.50

51.58

51.73

46.00

47.32

49.60

48.83

46.32

42.85

42.92

15.15

14.80

14.40

16.30

17.22

15.62

16.96

16.61

Temperature (°C)

12.6

12.4

12.3

12.3

12.6

12.6

13.1

13.1

12.6

13.0

12.5

12.6

12.8

12.6

13.1

12.3

14.6

13.9

13.9

13.9

13.8

13.5

13.9

14.2

14.0

14.1

13.6

13.4

13.7

13.8

14.3

14.3

15.0

14.3

14.1

14.2

14.6

14.6

14.6

14.8

14.2

PH 

(standard 

units)

7.2

7.3

7.2

7.3

7.1

7.1

7.1

6.8

7.2

7.1

7.2

7.1

7.2

7.3

7.1

7.1

7.3

7.1

7.0

7.2

7.1

7.0

7.0

7.0

6.9

7.0

7.0

7.1

7.2

7.2

7.1

7.0

7.1

8.4

7.1

7.2

7.0

7.0

7.0

7.0

6.8

Specific 

conductance 

(nS/cm at 

25°C)

740

808

836

833

826

822

818

843

840

812

805

815

818

818

790

780

643

653

652

654

663

655

706

837

653

643

642

645

649

652

673

669

,120

,180

,180

,180

,170

,110

,090

1,140

1,100

Dissolved 

oxygen 

(mg/L)

5.6

5.6

5.8

5.4

4.9

4.9

6.8

6.8

7.1

6.7

6.5

6.9

7.2

7.4

6.6

6.8

10.2

6.2

6.1

6.0

6.0

5.4

7.1

7.1

7.5

7.7

7.4

7.5

7.7

8.0

7.8

7.3

2.2

.1

.4

.4

.4

0.5

.4

.3

.4

Nitrate 

as 

nitrogen 

(mg/L)

12

10

13

12

11

13

11

12

13

12

12

12

13

12

11

10

2.4

1.9

2.1

2.3

2.4

3.1

2.7

2.2

2.8

2.3

2.8

3.1

3.4

3.0

2.9

1.8

19

24

27

30

24

22

18

22

20

44 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckoils County, Nebraska, 1991-53
Table 11. Water-quality data for samples from 20 monitoring wells in the study area, Nuckolls County, Nebraska, 

1991-93 Continued

[--, no data; °C, degrees Celsius; mg/L, milligrams per liter; nS/cm, microsiemens per centimeter]

Well 

number

15

15

15

15

15

15

15

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

16

Date

9-16-92

11-20-92

1-27-93

3-24-93

5-19-93

7-13-93

9-08-93

7-10-91

7-31-91

8-20-91

9-06-91

11-13-91

1-17-92

3-18-92

5-20-92

7-10-92

9-16-92

11-20-92

1-25-93

3-24-93

5-19-93

7-14-93

9-08-93

Time

11:05

12:03

14:15

15:53

9:45

9:25

10:05

10:35

15:05

9:04

14:35

14:43

14:15

11:00

14:12

11:10

15:53

11:21

16:29

16:29

9:00

8:53

9:30

Depth to 

water 

(feet)

16.70

16.39

16.50

15.95

17.29

11.50

14.21

7.60

7.40

8.07

8.70

9.40

8.52

8.54

8.69

7.80

7.82

7.70

5.51

5.93

4.31

6.28

Temperature <°C)

14.7

14.6

14.7

14.6

13.8

13.7

13.3

13.2

12.7

13.0

13.2

13.8

13.5

13.5

13.5

13.3

13.5

13.5

13.0

12.6

12.2

12.5

13.0

PH 

(standard 

units)

7.0

6.9

6.9

7.0

7.0

7.1

7.0

7.3

7.8

7.3

7.2

7.2

7.2

7.1

7.0

7.1

7.0

7.0

7.1

7.1

7.2

7.23

7.1

Specific 

conductance 

(nS/cm at 

25°C)

1,250

1,240

1,230

1,210

1,200

1,270

1,330

941

980

946

953

975

949

984

1,000

989

978

968

978

974

970

969

990

Dissolved 

oxygen 

(mg/L)

.2

.4

.3

.2

.6

.3

1.0

1.2

.1

.2

.3

.2

.2

.5

.2

.4

.2

.5

.5

.3

.2

.2

.5

Nitrate 

as 

nitrogen 

(mg/L)

32

34

28

25

25

31

37

.70

.70

.10

.30

.20

.40

.30

.50

.40

.30

.30

.30

.30

.20

.10

.50

Well inaccessible.

ADDITIONAL WATER-QUALITY AND SEDIMENT DATA 45
Table 12. Nitrate and ammonium concentrations as nitrogen in sediment cores for site 1 in the study area, 

Nuckolls County, Nebraska, spring 1991

[-, no data; mg/kg, milligrams per kilogram]

Sample depth 

(feet)

0.3

3.0

6.4

9.4

11.4

13

16

19

22

25

28

31

34

37

40.6

43.8

46

49

51.3

52

55

56

58

61.5

62

64

65

67

68

70

73

Nitrate as nitrogen 

(mg/kg)

Corel

-

1.85

1.39

-

2.47

2.83

2.16

2.01

2.01

1.75

1.24

1.65

1.96

2.22

2.37

2.47

2.63

2.47

1.49

-

2.27

1.80

1.85

-

-

2.37

2.11

1.75

-

1.24

1.34

Core 2

~

2.11

2.06

2.16

2.63

2.32

2.68

2.27

2.37

2.16

1.49

1.70

1.91

2.22

1.13

1.60

1.55

1.49

1.49

1.29

1.13

1.03

0.98

1.24

2.06

1.49

1.24

-

1.24

1.34

-

Mean

~

1.98

1.73

2.16

2.55

2.58

2.42

2.14

2.19

1.96

1.37

1.68

1.94

2.22

1.75

2.04

2.09

1.98

1.49

1.29

1.70

1.42

1.42

1.24

2.06

1.93

1.68

1.75

1.24

1.29

1.34

Ammonium as nitrogen 

(mg/kg)

Corel

2.19

1.83

1.33

~

2.44

1.33

1.58

1.70

3.12

2.38

2.75

3.92

4.11

3.61

3.12

3.43

3.18

2.75

2.93

2.44

3.06

1.64

~

5.03

5.34

3.00

2.07

2.63

Core 2

2.38

1.64

2.26

1.95

1.27

1.52

1.64

3.55

2.01

2.13

3.18

2.32

3.00

2.93

1.95

2.75

2.19

2.44

2.44

3.00

3.06

3.98

1.95

4.17

5.21

3.86

4.54

~

2.32

2.19

-

Mean

2.29

1.74

1.80

1.95

1.86

1.43

1.61

2.63

2.57

2.26

2.97

3.12

3.56

3.27

2.54

3.09

2.67

2.60

2.69

3.00

2.75

3.52

1.80

4.17

5.21

4.45

4.94

3.00

2.32

2.13

2.63

46 Distribution of Selected Nitrogen Compounds In Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-83
Table 13. Nitrate and ammonium concentrations as nitrogen and organic-matter content in sediment cores for site 1 in the 

study area, Nuckolls County, Nebraska, spring 1992

[mg/kg, milligrams per kilogram; --, no data]

Sample 

depth 

(feet)

0.3

3.0

6.0

9.0

11.4

13.0

16.0

19.0

22.0

25.0

28.0

31.0

34.0

37.0

41.0

43.0

46.0

49.0

51.3

52.0

55.0

56.0

58.0

62.0

64.0

65.0

68.0

70.0

73.0

Nitrate as nitrogen 

(mg/kg)

Corel

3.08

3.81

2.24

2.19

3.03

2.45

2.13

2.19

1.61

2.24

1.45

1.08

1.45

1.29

1.19

1.77

-

2.34

1.45

1.29

1.35

1.08

1.40

1.29

.51

.40

.61

.51

.14

Core 2

2.03

4.02

1.03

1.03

1.50

1.64

1.14

.61

.74

1.24

1.27

.98

1.27

1.29

1.35

1.27

1.61

1.56

1.03

.93

.93

1.19

1.08

.77

.61

.56

.56

.14

.40

CoreS

1.96

4.42

.83

.88

1.50

1.70

1.29

1.19

1.40

1.86

2.32

1.55

1.19

1.50

.73

1.50

.88

.94

.99

.58

1.19

1.19

1.45

.68

.99

1.14

.42

.88

1.04

Mean

2.36

4.08

1.37

1.37

2.01

1.93

1.52

1.33

1.25

1.78

1.68

1.20

1.30

1.36

1.09

1.51

.83

1.61

1.15

.93

1.16

1.15

1.31

.91

.70

.70

.53

.51

.53

Ammonium as nitrogen 

(mg/kg)

Corel

2.30

1.00

.83

.41

.77

1.00

.41

1.12

1.54

1.48

1.89

2.01

1.65

1.00

1.83

1.65

2.01

2.60

2.30

1.77

2.95

2.48

3.01

3.48

3.07

2.13

3.54

2.42

1.30

Core 2

1.36

1.00

2.19

.62

.59

.74

1.24

1.30

1.45

1.65

1.21

1.36

1.86

1.77

1.42

1.54

1.77

2.30

2.30

2.83

3.72

3.75

2.83

3.66

4.61

3.49

3.19

1.48

1.24

CoreS

1.28

1.94

1.18

.87

.32

5.7

9.7

1.08

1.58

2.34

1.43

1.38

3.46

2.55

1.84

2.04

2.29

2.44

3.20

2.44

2.70

3.41

3.15

1.99

3.46

3.26

3.87

2.60

2.04

Mean

1.65

1.31

1.40

.63

.56

.77

.87

1.17

1.52

1.82

1.51

1.58

2.32

1.77

1.70

1.74

2.02

2.45

2.60

2.35

3.12

3.21

3.00

3.04

3.71

2.96

3.53

2.17

1.53

Corel

2.13

.42

.20

.22

1.12

1.05

.37

.17

.15

.15

.18

.12

.09

.02

.07

.11

.20

.13

.09

.13

.12

.15

.13

.15

.07

.07

.18

.04

.02

Organic matter 

(percent)

Core 2

2.37

.31

.17

.22

1.09

1.05

.37

.15

.15

.15

.19

.07

.11

.12

.07

.07

.11

.15

.11

.12

.11

.16

.15

.17

.13

.08

.29

.06

.04

CoreS

2.34

.39

.22

.22

1.12

.88

.42

.16

.13

.17

.17

.13

.15

.15

.07

.09

.12

.10

.07

.09

.12

.15

.11

.04

.07

.07

.22

.06

.05

Mean

2.28

.37

.20

.22

1.11

.99

.39

.16

.14

.16

.18

.10

.12

.10

.07

.09

.14

.13

.09

.11

.11

.15

.13

.12

.09

.07

.23

.05

.04

ADDITIONAL WATER-QUALITY AND SEDIMENT DATA 47
Table 14. Nitrate and ammonium concentrations as nitrogen and organic-matter content in sediment cores for site 1 in the 

study area, Nuckolls County, Nebraska, spring 1993

[--, no data; mg/kg, milligrams per kilogram]

Sample 

depth 

(feet)

0.3

3.0

6.0

9.0

11.4

13.0

16.0

19.0

22.0

25.0

28.0

31.0

34.0

37.0

41.0

43.0

46.0

49.0

51.3

52.0

55.0

56.0

58.0

62.0

64.0

65.0

68.0

70.0

73.0

Nitrate as nitrogen 

(mg/kg)

Corel

1.91

2.32

3.11

1.91

2.68

1.68

1.37

1.77

1.77

1.77

2.01

1.91

1.82

1.68

2.01

1.87

2.01

1.48

1.58

1.82

1.72

1.77

1.63

1.58

1.68

2.01

1.48

1.58

Core 2

2.87

2.06

3.45

2.01

2.01

1.96

1.24

1.25

.10

.01

.10

.25

.48

.77

.81

.43

.29

1.48

1.05

.67

.81

.67

.62

.10

-

-

-

-

CoreS

2.06

5.70

5.87

1.82

2.25

1.68

1.20

1.01

.88

.96

1.10

1.24

1.58

2.49

2.12

2.71

2.17

2.02

2.31

2.02

2.27

2.36

1.97

2.17

1.09

1.04

.99

~

-

Mean

2.28

3.36

4.14

1.91

2.31

1.77

1.27

1.34

1.25

1.25

1.40

1.47

1.63

2.49

1.52

1.84

1.49

1.44

1.76

1.55

1.59

1.63

1.47

1.47

.92

1.36

1.50

1.48

1.58

Ammonium as nitrogen 

(mg/kg)

Corel

2.41

1.92

1.54

1.08

8.50

1.14

1.31

2.06

2.06

1.66

.91

2.24

1.83

3.17

2.01

2.12

3.28

2.53

1.54

1.78

2.47

2.76

2.91

2.41

2.70

3.05

3.22

4.44

Core 2

1.66

2.30

2.06

1.58

1.83

1.19

1.31

1.57

1.83

2.76

1.31

2.07

1.60

2.01

2.41

2.30

3.17

2.35

2.93

2.64

4.09

4.27

4.73

3.75

-

-

~

-

CoreS

1.72

1.54

1.98

1.25

1.02

1.19

1.72

2.06

2.71

3.17

2.76

2.73

3.34

2.47

3.53

3.36

5.86

3.64

5.12

5.69

6.20

5.18

2.40

3.64

3.70

3.36

4.61

-

Mean

1.93

1.92

1.86

1.30

3.78

1.17

1.45

1.90

2.20

2.53

1.66

2.35

2.26

2.47

2.90

2.59

3.43

3.36

3.33

3.39

3.54

3.91

3.14

3.76

3.29

3.03

3.83

3.22

4.44

Corel

0.29

1.77

.20

.97

.39

.22

.28

.28

.15

.15

.17

.12

.09

.07

.09

.07

.07

.11

.07

.15

.15

.15

.16

.12

.09

.15

.07

.11

Organic matter 

(percent)

Core 2

1.93

.47

.20

.19

.76

1.20

.42

.19

.17

.15

.15

.13

.07

.11

.11

.15

.13

.09

.412

.15

.20

.17

.18

.07

~

-

CoreS

2.09

.47

.23

.22

.59

1.05

.39

.20

.16

.15

.15

.12

.13

.07

.09

.15

.15

.09

.15

.16

.17

.16

.04

.09

.09

.14

.10

--

Mean

1.44

.90

.21

.46

.58

.82

.36

.22

.16

.15

.16

.12

.10

.07

.09

.12

.12

.10

.12

.12

.16

.17

.12

.14

.09

.12

.13

.07

.11

48 Distribution of Selected Nitrogen Compounds in Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-83
Table 15. Estimation of nitrate and ammonium content in sediment for site 1 in the study area, Nuckolls County, Nebraska, spring 1

[--, no '

gg

z

\L WATER-

|^

3

> 

O

E

O

5

ft

Sample 

depth 

(feet)

0.3

3

6

9

11.4

13

16

19

22

25

28

31

34

37 

41 

43

46 

49 

51.3

52

55

56

58 

62

64

65

68 

70

73

Total

Interval 

range 

(feet)

0-0.6

0.6-4.5

4.5-7.5

7.5-10.2

10.2-12.2

12.2-14.5

14.5-17.5

17.5-20.5

20.5-23.5

23.5-26.5

26.5-29.5

29.5-32.5

32.5-35.5

35.5-39.0 

39.0-42.0 

42.044.5

44.5-47.5 

47.5-50.2 

50.2-51.7

51.7-53.5

53.5-55.5

55.5-57.0

57.0-60.0 

60.0-63.0

63.0-64.5

64.5-66.5

66.5-69.0 

69.0-71.5

71.5-73.0

Interval 

thickness 

(inches)

7

47

36

32.4

24

27.6

36

36

36

36

36

36

36

42 

36 

30

36

32.4 

18

21.6

24

18

36 

36

18

24

30 

30

18

876

Nitrate as nitrogen content 

(pounds per acre)

1991

-

27.92

18.68

21.00

18.36

21.36

26.14

23.11

23.65

21.17

14.10

18.14

20.95

27.97 

18.90 

18.36

22.57 

19.25 

8.05

8.36

12.24

7.67

15.34 

17.82

10.42

12.10

11.16 

11.61

7.24

484.32

1992

4.96

57.53

14.80

13.32

14.47

15.98

16.42

14.36

13.50

19.24

18.14

12.96

14.04

17.14 

11.77 

13.59

8.96 

15.65 

6.21

6.03

8.35

6.21

14.15 

9.83

3.78

5.04

6.30

4.77

2.75

370.23

1993

4.79

47.38

44.71

18.57

16.63

14.66

13.72

14.47

13.50

13.50

15.12

15.88

17.60

31.37 

16.42 

16.56

16.09 

14.00 

9.50

10.04

11.45

8.80

15.88 

15.88

4.97

9.79

13.50 

13.32

8.53

466.62

Ammonium as nitrogen content 

(pounds per acre)

1991

-

24.53

19.44

18.95

13.39

11.84

17.39

28.40

27.76

24.41

32.08

33.70

38.45

41.20 

27.43 

27.81

28.834 

25.27 

14.53

19.44

19.80

19.01

19.44 

45.04

24.03

35.57

20.88 

19.17

4.21

682.00

1992

3.47

18.47

15.12

6.12

4.03

6.38

9.40

12.64

16.42

19.66

16.31

17.06

25.06

22.30 

18.36 

15.66

21.82 

23.81 

14.04

15.23

22.46

17.33

32.40 

32.83

20.03

21.31

31.77 

19.53

8.26

507.28

1993

4.05

27.07

20.07

12.64

27.22

9.69

15.66

20.52

23.76

27.32

17.93

25.38

24.41

31.12 

31.32 

23.31

37.04 

32.66 

17.98

21.97

25.49

21.11

33.91 

40.61

17.77

21.82

34.47 

28.98

23.98

699.27

199

-

52.4

38.

39.9

31.7

33.2

43.5

51.5

51.4

45.5

46.8

51.8

59.4

69.

46.3

46.

51.4

44.5

22.5

27.8

32.0

26.6

34.7

62.

34.4

47.6

32.0

30.7

11.

1,166.
Table 16. Nitrate and ammonium concentrations as nitrogen in sediment cores for site 9 in the study area, Nuckolls County, 

Nebraska, spring 1991

Sample depth 

(feet)

0.3

2.0

3.0

5.0

7.0

9.0

11.0

13.0

15.0

17.0

18.6

19.0

Nitrate as nitrogen 

(milligrams per kilogram)

Corel

3.92

1.65

1.13

4.23

11.50

13.90

11.80

4.74

3.23

3.09

2.73

2.58

Core 2

7.07

1.91

1.39

1.39

1.60

2.89

8.56

5.26

2.04

1.81

1.91

1.49

Mean

5.50

1.78

1.26

2.81

6.65

8.40

9.78

5.00

2.64

2.45

2.32

2.04

Ammonium as nitrogen 

(milligrams per kilogram)

Corel

2.26

2.13

2.19

1.61

1.21

2.93

2.04

1.21

2.01

2.32

1.58

1.31

Core 2

2.08

2.81

2.87

1.02

1.24

1.27

1.46

1.49

2.54

1.83

1.64

0.90

Mean

2.17

2.47

2.53

1.32

1.23

2.10

1.75

1.35

2.28

2.08

1.61

1.11

Table 17. Nitrate and ammonium concentrations as nitrogen and organic-matter content in sediment cores for site 9 in the 

study area, Nuckolls County, Nebraska, spring 1992

Sample 

depth 

(feet)

0.3

2.0

3.0

5.0

7.0

9.0

11.0

13.0

15.0

17.0

18.6

19.0

20.0

Nitrate as nitrogen 

(milligrams per kilogram)

Corel

2.93

1.65

1.19

.63

.88

1.14

1.29

.73

.73

1.45

1.35

1.70

1.70

Core 2

2.01

1.88

.94

1.32

.88

1.12

1.96

1.58

1.81

2.42

2.57

2.32

2.47

Core3

3.70

2.11

1.60

1.29

1.91

1.91

2.47

1.91

2.06

1.19

1.29

1.19

.97

Mean

2.88

1.88

1.24

1.08

1.22

1.39

1.91

1.41

1.53

1.69

2.19

1.74

1.71

Ammonium as nitrogen 

(milligrams per kilogram)

Corel

2.29

2.70

2.60

1.33

2.19

.62

.57

1.38

.32

.42

.92

.92

.97

Core 2

.97

1.99

1.33

1.63

1.89

1.71

1.48

1.36

1.20

1.36

1.94

1.43

1.23

Core3

1.94

1.73

2.80

1.84

1.63

2.19

2.55

1.73

2.24

2.09

1.73

.32

1.13

Mean

1.73

2.14

2.24

1.60

1.40

1.51

1.53

1.49

1.25

1.29

1.53

.89

1.11

Organic-matter content 

(percent)

Corel

1.76

1.05

.57

.57

.55

.22

.22

.18

.22

.42

.44

.44

.44

Core 2

1.76

.98

.44

.44

.57

.29

.22

.22

.14

.22

.44

.44

.37

Core 3

2.30

1.11

.44

.50

.51

.25

.18

.25

.17

.29

.35

.51

.44

Mean

1.94

1.05

.48

.50

.54

.25

.21

.22

.18

.31

.41

.46

.42

50 Distribution of Selected Nitrogen Compounds In Ground Water and the Unsaturated Zone, Superior-Hardy Special Protection 

Area, Nuckolls County, Nebraska, 1991-43
Table 18. Nitrate and ammonium concentrations as nitrogen and organic-matter content in sediment cores for site 9 in the study ar

spring 1993

o 

g

5

z

3D

O

C

r~

3

z

o

5

I

5

o

3

2

Sample

depth

(feet)

0.3

2.0

3.0

5.0

7.0

9.0

11.0

13.0

15.0

17.0

18.6

19.0

20.0

Table 19.

[ , no data]

Sample

depth 

(feet)

0.3

2

3

5

7

9

11

13

15

17

18.6

19

20

Total

Nitrate as nitrogen

(milligrams per kilogram)

Corel

1.63

.70

.60

.60

.55

.60

.55

.70

.75

.80

.60

.70

.75

Core 2

2.22

1.24

.60

.60

.90

1.29

.99

1.19

1.14

1.49

.99

1.14

1.14

Core 3

1.73

1.34

1.58

2.07

2.07

2.02

1.88

2.02

2.31

2.80

2.76

2.66

2.51

Mean

1.86

1.09

.93

1.09

1.17

1.30

1.14

1.30

1.40

1.70

1.45

1.50

1.47

Ammonium as nitrogen

(milligrams per kilogram)

Corel

2.40

3.42

4.33

2.97

1.77

1.88

1.66

1.91

1.49

1.49

1.77

2.17

2.62

Core 2

2.05

3.02

3.70

3.53

2.79

2.96

1.83

1.49

2.05

2.30

1.88

2.11

2.45

Core 3 Mean

2.57 2.34

3.70 3.38

3.87 3.97

4.55 3.68

2.00 2.19

2.22 2.35

1.80 1.76

1.60 1.67

2.17 1.90

2.22 2.00

3.87 2.51

2.45 2.24

2.79 2.62

Corel

1.66

.74

.48

.39

.38

.38

.22

.18

.24

.15

.22

.37

.42

Orga

Co

1

1

Estimation of nitrate and ammonium content in sediment cores for site 9 in the study area, Nuckolls County, Nebraska, sp

Interval

range 

(feet)

0-0.6

0.6-2.5

2.5-4.0

4.0-6.0

6.0-8.0

8.0-10.0

10.0-12.0

12.0-14.0

14.0-16.0

16.0-18.0

18.0-18.8

18.8-19.5

19.5-20.0

Interval

thickness 

(inches)

7

23

18

24

24

24

24

24

24

24

9.6

8.4

6

240

Nitrate as nitrogen content

(pounds per acre)

1991

11.55

12.28

6.80

20.23

47.88

60.48

70.4

36.00

19.0

17.64

6.68

5.14

~

314.11

1992

6.0

12.97

6.70

7.78

8.78

10.01

13.75

10.15

11.02

12.17

6.31

4.39

3.08

113.14

1993

3.91

7.52

5.02

7.85

8.42

9.36

8.21

9.36

10.08

12.22

4.18

3.78

2.65

92.55

Ammonium as nitrogen content

(pounds per acre)

1991 1992

4.56 3.63

17.04 14.77

13.66 12.10

9.50 11.52

8.86 13.68

15.12 10.87

12.60 11.02

9.72 10.73

16.42 9.00

14.98 9.29

4.64 4.41

2.80 2.24

2.00

129.89 115.25

1993

4.91

23.32

21.44

26.50

15.77

16.92

12.67

12.02

13.68

14.40

7.23

5.65

4.72

179.22

Nit

19

16

29

20

29

56

75

83

45

35

32

11

7

444
Table 20. Grain size and nitrate and ammonium concentrations as nitrogen in sediment cores for site 1 in the study area, Nuckolls 

g SJ, [-, no data; mm, millimeters; mg/kg, milligrams per kilogram; <, less than]

button ofSelNuckolls C

C ( > 3 |

" 1 .

?i

«r * 

5 '

ff 

<o 9 

2 3

"§.

5"

O

|

f

I

1

I

1

f

i

1"

#

Sample 

depth 

(feet)

0.3

3

6.4

11.4

13

16

19

22

25

28

31

34

37

41

43

46

49

51.3

55

56

58

64

65

67

70

73

Percent in indicated size class

Upper limit of size class 

(mm)

2.000

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1.410

0

0

.21

0

0

0

0

0

0

0.05

0

0

.05

0

0

.10

0

0

0

.26

0

0

0.46

0

0

0

1.000

0.06

0

.26

0

0

0.06

0.05

0

.05

.26

0

.06

.72

0

0

1.45

.25

.11

.71

3.23

.25

.06

2.60

.99

.10

.09

0.707

.06

.05

.31

.15

.05

.17

.10

.11

.41

.83

.05

.28

2.11

.05

0

5.11

1.83

1.05

1.71

8.35

0.25

0.67

6.52

3.32

0.29

0.66

0.500

.11

.61

.72

.20

.14

1.32

.15

.33

1.73

1.88

.26

.67

3.22

.42

.05

7.61

6.00

4.18

2.18

9.34

0.51

3.18

8.30

4.83

1.64

1.51

0.354

.39

1.52

1.74

.24

.38

3.03

.60

1.17

3.56

3.39

1.11

1.18

3.17

.16

.09

8.91

11.05

6.93

5.42

8.66

0.66

8.03

5.65

6.54

8.61

2.40

0.250

CORE1

1.23

2.33

2.36

.83

1.48

4.24

1.20

1.89

5.19

4.43

2.33

1.57

3.55

.26

.24

9.83

14.87

9.63

2.59

8.45

0.86

12.99

10.30

10.38

31.74

3.44

0.177

1.40

2.23

2.56

1.52

2.57

4.13

1.40

1.95

4.43

3.96

3.07

1.35

3.22

.26

.52

7.51

11.69

7.65

2.12

5.53

1.11

13.38

8.25

9.66

20.51

3.72

0.125

2.07

3.30

3.08

3.09

5.43

5.23

2.84

2.83

5.14

4.74

1.75

1.41

4.80

.52

1.19

6.36

9.91

7.15

2.00

4.49

1.52

11.98

6.93

7.58

7.98

10.18

0.088

6.77

9.33

6.10

10.93

13.82

11.94

9.98

11.01

10.53

11.46

12.39

6.52

15.94

6.13

10.62

5.59

11.50

9.08

3.77

3.96

3.39

14.60

6.88

8.00

6.63

17.07

0.063

10.25

11.41

7.07

13.13

15.87

14.03

14.16

14.29

12.72

14.96

18.26

13.04

22.18

28.08

18.26

5.44

8.62

15.80

4.83

4.90

22.38

10.70

8.30

10.75

6.34

20.79

<0.0

77

69

75

69

60

55

69

66

56

54

60

73

41

64

69

42

24

38

74

42

69

24

35

37

16

40
Table 20. Grain size and nitrate and ammonium concentrations as nitrogen in sediment cores for site 1 in the study area, Nuckolls 

1991 Continued

>

g

1

i

?§31

1

i

o

W

§£

m

o

5>

8

Sample 

depth 

(feet)

0.3

3

6.4

9.4

11.4

13

16

19

22

25

28

31

34

37

40.6

43.8

46

49

51.3

52

55

56

58

62

64

65

68

70

74

Percent in indicated size class

Upper iimit of size ciass 

(mm)

2.000

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1.410

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1.000

0

0

0.15

0

0.22

0.05

0

0

0

0.10

0.10

0.39

0.05

0

0.05

0.05

0.15

0.05

0.24

0.05

0

0.05

0

0.06

0.05

0

0

0

0.707

0.25

0.23

1.38

0.54

0.11

0.82

0.75

0.28

0.44

0.21

0.10

0.25

0.90

0.48

0.05

0.11

0.21

0.20

0.22

0.33

0.15

0.28

0.20

0.36

0.06

0.16

0.11

0

0.09

0.500

0.76

0.75

2.10

1.47

0.23

2.21

2.45

1.22

1.31

1.36

0.74

1.06

1.46

2.19

0.05

0.32

0.31

0.50

1.53

0.57

0.26

1.47

0.20

2.50

0.12

1.04

0.43

0.05

0.27

0.354

1.82

1.51

2.81

1.36

0.86

4.85

4.48

2.83

2.46

3.25

2.36

2.28

2.25

4.86

0.05

0.90

0.62

1.25

2.03

0.67

0.51

4.19

0.20

6.20

1.37

3.21

1.19

0.10

1.17

0.250

CORE 2

2.73

2.15

3.37

5.23

1.94

8.27

6.64

3.93

3.93

4.71

4.42

3.39

3.04

7.26

0.09

1.49

1.03

2.54

2.74

0.77

0.62

7.01

0.20

10.17

4.54

6.37

2.32

0.36

5.07

0.177

2.37

2.09

3.22

5.34

2.62

9.05

7.07

3.60

3.71

3.88

4.57

3.39

3.43

6.52

0.27

1.65

1.23

3.83

2.41

0.86

0.62

6.67

0.15

10.32

6.09

6.83

4.70

0.73

6.86

0.125

2.12

2.38

3.17

4.96

4.39

9.92

8.67

4.54

4.48

3.93

6.15

4.71

4.22

5.88

0.27

2.34

1.65

5.08

2.74

1.24

0.56

6.05

0.41

10.69

6.81

7.87

6.81

1.19

12.87

0.088

4.80

9.40

3.68

5.45

10.10

10.22

11.83

10.97

8.57

10.53

13.91

10.37

13.55

12.29

3.43

8.24

6.38

11.11

7.50

2.58

3.23

10.46

6.24

14.13

18.75

12.47

11.13

8.39

18.16

0.063

7.78

10.56

5.26

7.41

12.32

11.30

12.96

15.35

12.23

12.26

15.98

16.90

19.35

10.90

32.97

17.02

10.03

14.94

9.53

10.57

4.93

9.33

24.26

11.99

16.42

12.47

18.15

10.36

20.49

<0.0

77.

70.

74.

68.

67.

43.

45.

57.

62.

59.

51.

57.

51.

49.

67.

67.

78.

60.

71.

82.

89.

54.

68.

33.

45.

49.

55.

78.

35.
k

3 [mm, millimeters; mg/kg, milligrams per kilogram; <, less than]

r Sample - 

t depth 

> (feet) -

» 

[ 0.3

L .35

f 2

! 3

i 5

? 5.1

! '

i 9

> 11.3

i 13

L 15 

F 15.3

! 17 

! 18.6 

f 18.9

Percent in indicated size class

Upper limit of size class 

(mm)

2.000

0

0

0

0

0

0

0

0 

0

0

0

0 

0

0 

0 

0

0

1.410

.05

.48

.58

.04

.04

0

0

0 

0

0

0

.09 

0

.16

.97 

0

0.50

1.000

.38

1.34

3.01

.18

1.74

.05

.05

0 

0

.05

.05

1.48 

0

3.36 

5.65 

0.11

4.51

0.707

4.09

4.11

8.15

1.70

7.41

.05

.10

.05 

.05

.05

.10

4.76 

.11

5.71 

9.85 

0.27

10.10

0.500

5.81

6.30

9.60

3.94

11.68

.05

.05

.19 

.05

.55

.25

6.88 

.33

6.55 

9.51 

1.34

11.15

0.354 0.250 0.177

CORE1

6.03 5.81 3.93

6.06 5.78

8.00 6.98

4.64 5.20

12.53 12.44

.25 1.82

.25 1.13

.72 1.25 

.31 1.05

1.19 2.02

.65 3.15

7.16 7.34 

.89 1.67

6.91 6.99 

9.90 10.86 

3.60 7.36

11.11 11.48

3.68

4.51

3.21

8.51

3.00

2.50

1.64 

1.36

2.48

14.12

5.36 

1.95

5.35 

8.06

7.74

8.23

0.125

3.07

3.01

3.73

5.31

8.17

5.27

5.30

2.31 

1.78

2.80

20.18

4.76 

2.51

4.87 

6.81 

8.28

6.81

0.088

4.09

3.72

4.56

5.27

6.86

15.07

15.75

8.90 

5.97

6.94

17.88

4.43 

8.04

5.07 

6.42 

12.20

6.43

0.063

8.99

8.83

6.40

7.96

6.39

14.58

14.43

11.26 

8.12

7.72

16.88

5.73 

10.21

6.79 

7.19 

13.86

6.51

<0.063

57.75

56.69

44.47

62.55

24.25

59.85

60.45

73.68 

81.29

76.19

26.74

52.01

74.27

48.22 

24.77 

45.24

23.17

| CORE 2

I Is

\ 2

i 3

? 5

i 7

1 7.1

( 13.2 

> ^

L 15.3

; i?

17.

. 18.6 

! 18.9

0 

0 

0

0

0 

0

0 

0

0 

0

0

0

0

0 

0

0 

0.09 

0.18

1.50

0.12 

0.14

0.09 

0

0.05 

0.60

0.09

0

0.04

0.05 

0.30

0.36 

0.23 

1.23

3.46

0.52 

1.29

0.14 

0.19

0.27 

1.14

0.26

0.29

0.71

0.70 

1.99

2.14 

2.51 

5.56

2.64

4.73 

5.92

1.61 

2.66

1.38 

3.55

2.14

1.26

2.40

2.41 

6.45

4.45 

5.53 

8.10

8.97

9.64 

9.60

5.39 

6.90

2.88 

5.84

4.45

2.00

4.05

4.73 

8.09

5.87 6.35 

6.70 7.07 

8.49 8.49

8.56 8.33

11.55 12.24 

10.75 11.28

9.36 12.06 

9.66 11.32

4.74 7.03 

7.10 7.88

6.42 7.70

2.92 3.15

5.16 6.37

9.71 11.67 

9.48 10.87

4.51 

4.47 

5.74

5.87

8.89

7.74

9.27 

8.18

5.64 

5.60

6.12

2.63

4.99

8.55 

7.74

3.80 

4.00 

4.95

4.64

7.10 

6.31

7.42 

6.66

4.90 

4.87

5.22

2.69

4.32

7.19 

6.55

4.45 

4.33 

5.39

5.10

6.24 

5.92

6.86 

6.33

4.95 

5.05

5.22

5.43

4.72

7.65 

7.05

7.06 

9.49 

8.32

7.24

6.76 

6.69

7.52 

6.99

6.23 

6.68

6.63

8.07

6.95

9.61 

8.93

61.03 

55.58 

43.56

43.67

32.22 

34.35

40.28 

41.10

61.93 

51.68

55.77

71.57

60.28

37.73 

32.56