Water-Quality Assessment of the Central Nebraska Basins—-

Entering a New Decade

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 013–03

March 2003

-—Ronald B. Zelt and Jill D. Frankforter

In 2001, the U.S. Geological

Survey’s (USGS) National WaterQuality Assessment (NAWQA)

Program began its second decade of

intensive water-quality assessments

(Cycle II). NAWQA scientists plan to

revisit 42 major river-basin and

aquifer systems (called study units)

that were assessed in the first decade

(Gilliom and others, 2001).

The NAWQA Program is a

primary source for long-term,

nationwide information on the quality

of streams, ground water, and aquatic

ecosystems. The goals of NAWQA

are to assess the status and trends of

water quality and to understand the

factors that affect it, thus addressing

the questions:

What is the condition of our

Nation’s streams and ground water?

How is water quality changing over

time?

How do natural features and human

activities affect the quality of

streams and ground water?

For Cycle II assessments, study

units were selected that represent a

wide range of important hydrologic

environments; contain critical contaminant sources, including agricultural,

urban, and natural sources; and

include more than 60 percent of

national water use for drinking and

irrigation (Gilliom and others, 2001).

Many of the predominantly

agricultural study units and most of

the large urban areas included in the

first cycle of NAWQA assessments

were retained for Cycle II. Central

Nebraska (fig.1) is one of the most

intensively agricultural areas being

examined in Cycle II, as determined

from the extent of agricultural land

and intensity of estimated pesticide

and fertilizer use.

Figure 1. Central Nebraska Basins study unit showing studies planned for Cycle-II revisit.

Base from U.S. Geological Survey digital data, 1:100,000, 1989,

and 1:2,000,000, 1972, Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30'

North American Datum of 1983 (NAD 83)

EXPLANATION

0

0 25 50 KILOMETERS

25 50 MILES

101°

102°

41°

42°

99°

100° 98°

97°

96°

Study area for agricultural chemicals in shallow ground water

Study area for transport of agricultural chemicals

Study area for effects of nutrient enrichment

Surface-water trends station

Mercury occurrence station

Area shown on map

Index map

NEBRASKA

Boundary of

study unit

Elkhorn

Loup

Platte

Missouri

River

River

River

River

Maple Creek

Middle

Loup

River

Dismal River

Lincoln

North Platte

Omaha

Columbus

Nickerson

Waterloo

Louisville
Central Nebraska Basins

The Central Nebraska Basins

assessment focuses on the area

drained by the Platte River

downstream of the confluence of its

forks near North Platte, Nebraska

(fig. 1). Within this approximately

30,000-mi2 (square-mile) study unit,

USGS scientists collect and analyze

information on water chemistry,

hydrology, land use, stream habitat,

and aquatic life. By continuing this

study-unit assessment during Cycle II

as an interdisciplinary and long-term

resource evaluation, findings will

describe the general health of water

resources, as well as current and

emerging water-quality issues. Such

information is essential for developing

management strategies for protecting

and restoring water quality.

Through adherence to the NAWQA

national design and use of nationally

consistent sampling and analytical

methods, water-quality conditions in

the Central Nebraska Basins can be

compared to those in other geographic

regions, and to those documented

during Cycle I, to advance an understanding of water-quality changes

through time.

Although NAWQA is a comprehensive effort to assess the quality of

streams and ground water, no single

program can address or anticipate all

relevant water-resource issues. Only

through collaboration with numerous

government agencies, researchers, and

interest groups can the program

address the information needs of

local, State, regional, and national

stakeholders. Input from these

partners continues to be critical and

helps to define the key water-quality

issues on which to focus as the

Central Nebraska Basins assessment

moves into its second cycle.

Major Water-Quality Issues

Agriculture is the dominant land

use in central Nebraska (Zelt, 1996),

and agricultural practices can affect

the quantity and quality of water

resources. For example, agricultural

nonpoint sources have been linked to

contamination of streams by runoff

containing fecal bacteria and nutrients

(that is, forms of nitrogen and

phosphorus) (Nebraska Department of

Environmental Quality, 2002). During

1992–95, nitrate levels in the Platte

River alluvial aquifer averaged among

the highest of any NAWQA study

unit, and nutrient concentrations in

streams draining central Nebraska

cropland where corn and soybeans

predominate were among the largest

in the Nation (Frenzel and others,

1998). Sources of nutrients include

raw or treated sewage, commercial

fertilizers, and animal manure. In

2000, Nebraska ranked second

nationally in total numbers of cattle

and cattle on feed (National

Agricultural Statistics Service, 2000),

and cattle waste, together with wastes

from other livestock, wildlife, and

pets, constitutes a major nutrient

source in the environment. Pesticide

concentrations in Nebraska streams

during 1992–95 were among the

largest measured at any NAWQA site,

and pesticides were detected in all

water samples from the Platte River

alluvial aquifer (Frenzel and others,

1998). Mercury contamination of fish

tissue exceeded water-quality criteria

during 1997–2000 in five streams and

five lakes in the study unit (Nebraska

Department of Environmental Quality,

2002).

Several water-quality concerns are

most evident in eastern parts of the

study unit. NAWQA results from

Cycle I indicated that the Elkhorn

River Basin contributed the majority

of herbicides transported from the

Platte River Basin (Frenzel and others,

1998). Infiltration of herbicides and

other surface-water contaminants to

shallow alluvial ground water

concerns some municipal water

suppliers along the Platte Valley

(Verstraeten and others, 1999; Heberer

and others, 2001). Recent legislation

requires State inspections of livestock

feeding operations—more common in

eastern Nebraska than in western

Nebraska—to identify water

contamination by livestock wastes,

primarily from cattle and hogs.

Nebraska’s pork industry, primarily in

eastern Nebraska, was the sixth largest

in the country in 2000 (National

Agricultural Statistics Service, 2000).

Sedimentation is especially common

in eastern parts of Nebraska where

fine-textured soils predominate.

Recovery efforts for the pallid

sturgeon in Nebraska are focused on

the lower Platte River and the

Missouri River.

Central Nebraska Basins

Revisited

As part of the second cycle of

NAWQA assessments in the Central

Nebraska Basins, efforts will focus on

five major activities, including

(1) water-quality trends in streams

draining cropland, grassland, and

mixed land uses; (2) agricultural

chemicals in shallow ground water

underlying the lower Elkhorn River

Basin; (3) transport and fate of

agricultural chemicals in the

intensively farmed drainage of Maple

Creek; (4) effects of agriculture and

associated nutrient enrichment on

stream biology; and (5) occurrence of

mercury contamination in stream

ecosystems.

Aerial view of a sandy, braided channel of the

Platte River.
Water-Quality Trends in Streams

The trends component of NAWQA

is intended to identify significant time

trends in water-quality conditions in

streams through long-term monitoring

from 2002 through 2010, which can

enable resource managers and

policymakers to assess the value of

programs such as conservation,

farming practices, and planned urban

growth. Data are being collected at

four surface-water trends stations in

the study unit (fig. 1) where NAWQA

monitoring began in 1992.

Two of the surface-water trends

stations represent the effects of a

specific land use. The Dismal River

near Thedford represents grazing of

mostly undeveloped grassland in the

Sand Hills region. Because overland

flow is minimal and base flow is

maintained by ground-water discharge

from the High Plains aquifer system,

streamflow varies little. With just

3 percent of its drainage area used for

cropland, effects of agriculture on

stream-water quality are minimal.

Maple Creek near Nickerson

represents agricultural production of

corn and soybeans. Its drainage area

of 370 mi2 is 85-percent cropland,

mostly underlain by fine-textured soils

that produce its runoff-dominated

hydrology.

The remaining two surface-water

trends stations represent effects of

mixed land uses across large drainage

basins. The Elkhorn River at Waterloo

is located immediately upstream from

the confluence of the Elkhorn and

Platte Rivers. Principal land uses in

this drainage area of 6,900 mi2 are

cropland (56 percent) and pasture and

rangeland (33 percent). The Platte

River at Louisville is downstream

from the confluence of the Platte River

with the Elkhorn River and integrates

the water quality of the entire Platte

River Basin. Mean annual streamflow

from its drainage area of 85,400 mi2 is

7,160 ft3/s (cubic feet per second), or

5.19 million acre-feet. Within the

study unit, the Platte River drains

chiefly cropland (36 percent) and

pasture and rangeland (54 percent).

Continuous monitoring of water

quality began in April 2002 at all four

surface-water trends stations. Specific

conductance, water temperature, pH,

and dissolved oxygen are being

monitored at three stations. Continuous monitoring of the Platte River at

Louisville is currently limited to

recording specific conductance and

temperature because the single

monitoring point may not be

representative of the highly varied

conditions across the channel.

During 2002, from 12 to 25 water

samples were collected at each

surface-water trends station. Samples

were submitted for laboratory

analyses of chloride, sulfate, nutrients,

organic carbon, pesticides, and

suspended sediment. In subsequent

years, fewer samples will be collected

and, in some cases, fewer analytical

determinations will be made per

sample or selected additional

contaminants of concern (glyphosate

and endosulfan) will be determined.

Ecological monitoring at the four

trends stations includes NAWQA’s

standard ecological reach assessment—samples of fish, invertebrate,

and algal communities; and habitat

characterization. Biological samples

are being collected annually during

low-flow conditions in late summer.

Agricultural Chemicals in Shallow

Ground Water

Studies of agricultural land-use

effects in the NAWQA Program track

the changes in contaminant levels in

shallow ground water in selected

important agricultural areas of the

Nation where contaminant sources are

intense and where drinking-water

sources may be affected. Specifically,

the agricultural land-use effects study

begun in Nebraska in 2002 will help

determine if agricultural contaminants

are moving from the land surface into

the shallowest part of the groundwater system underlying areas of corn

and soybean production. The study

area (fig. 1) is in the lower Elkhorn

River Basin, a region characterized as

semiarid to subhumid plains with a

poorly permeable surface and

subsurface. The study area includes

cropland with land use of greater than

20 percent corn production and

20 percent soybean production.

Sampling locations were selected

throughout the study area and

31 monitoring wells were installed.

Ben Dietsch, USGS hydrologist, lowers a water sampler into the Platte River near Louisville. Soil samples were collected from the
soil column removed during drilling to

determine how soil characteristics

varied with depth. Soil samples will

be analyzed for nutrients, chloride,

and physical properties related to

permeability and soil moisture.

Ground-water samples will be

collected from each monitoring well

in spring 2003 and analyzed for major

ions, nutrients, trace elements,

dissolved organic carbon (DOC), and

pesticides. In addition, one-quarter of

the samples will be analyzed for

indicators of the age of the ground

water. Beginning in October 2003,

samples will be collected quarterly

from a subset of these wells, and

beginning in 2005 they will be

sampled only once every 2 years to

monitor trends.

The results of the sample analyses

will be evaluated to address four

questions: (1) Occurrence—which

constituents were detected and at what

frequency? (2) Magnitude—which

constituents occurred in the largest

concentrations, and which were at

concentrations of concern relative to

water-quality criteria? (3) Spatial

distribution—are there spatial patterns

of constituent occurrence and do the

patterns correlate with the factors that

affect shallow ground-water quality?

(4) Background—how do the levels of

constituent concentrations compare

with those found at sites in noncropland areas (reference sites)?

Transport and Fate of Agricultural

Chemicals

In 2002, NAWQA began a new

study addressing the questions, “How

do environmental processes and

agricultural practices interact to affect

the transport and fate of agricultural

chemicals in the hydrologic system of

nationally important agricultural

settings, and what are the effects on

water quality and implications for

management of water resources?”

Each agricultural setting is a unique

combination of a particular

agricultural system (management of

crops, soil, and water) and hydrologic

setting (precipitation, soil surface, soil

water, shallow ground water,

subsurface drains, and streamflow).

The specific objectives of the study

are to (1) determine the residence

times and rates of movement of water

and agricultural chemicals in each

component of the hydrologic system;

(2) identify the important chemical

transformation and transfer processes

for selected agricultural chemicals;

(3) interpret, extrapolate, and predict

the fate and transport of water and

selected agricultural chemicals; and

(4) identify the implications of study

results for water management,

agricultural systems, and water-quality

policy.

In Nebraska, the study will include

sampling most components of the

hydrologic setting. The study area is

in the intensively agricultural drainage

of Maple Creek (fig. 2). A small

research watershed has been selected

and will be studied intensively from

2003 to 2005. Planned data-collection

activities in the small research

watershed include operating a weather

station equipped with a precipitation

sampler, overland-flow sampling sites,

lysimeters for soil-water (vadosezone) monitoring, ground-water

monitoring wells, and a streamsampling station at the outlet (fig. 2A).

Near the Maple Creek surface-water

trends station, a series of monitoring

wells along a ground-water flow path

will lead to lysimeters and shallow

wells at a ground-water/surface-water

interaction study site (fig. 2B).

Additionally, sampling of tile-drain

flow is planned in a second small

research watershed yet to be selected.

The types of planned analyses

dictate which laboratory determinations are required for each type of

sample. Precipitation samples will be

analyzed for pesticides. Surface-water

samples will be analyzed for nutrients,

trace metals, organic carbon,

pesticides, and suspended sediment.

Ground-water samples will be

analyzed for major ions, nutrients,

pesticides, and dissolved gases. Flow

from tile drains will be analyzed for

major ions, nutrients, organic carbon,

pesticides, and suspended sediment.

Soil-core samples will be analyzed for

bulk density, particle size, percentage

of organic matter, soil moisture,

chloride, and nitrate.

Geographic data on crop types,

cropland management practices, and

pesticide-, fertilizer-, and water-use

patterns will be collected for the

Maple Creek and small research

watersheds. Also, numerical groundwater and surface-water models are

being developed to address the study

objectives. Process-based models are

used at multiple scales to refine

understanding of the transport and

transformation of agricultural

chemicals along hydrologic pathways.

Effects of Nutrient Enrichment on

Stream Biology

The goal of a new NAWQA study

for Cycle II is to determine how

biological communities and processes

respond to varying levels of nutrient

enrichment among agricultural

streams from contrasting environmental settings. This study currently

involves six NAWQA study units to

represent different environmental

Brenda Woodward, USGS field assistant,

measures flow velocity for physical habitat

characterization of Maple Creek.
settings affected by agricultural

activities, including the Central

Nebraska Basins. The study has four

objectives:

Determine how biological

communities are related to nutrient

conditions in streams.

Evaluate the relations between

nutrients, algae, and stream

metabolism, or the processes

whereby (1) carbon dioxide and

nutrients are consumed by algae,

producing oxygen, and (2) algal

decomposition consumes oxygen

and recycles nutrients.

Determine how algae, stream

metabolism, and nutrient dynamics

are interrelated within short

lengths of a few representative

streams.

Determine the extent to which

relations between biological

communities and nutrient

conditions can be generalized to

larger regions by using analyses of

geographic factors.

For the Nebraska component of the

study, a list of potential study sites

was compiled, and their respective

drainage areas were characterized

using geographic data. Following

field reconnaissance sampling, an

integrated nutrient index was

constructed. Study sites will be

selected early in 2003 to characterize

the range of the nutrient index and

will be focused within a single

nutrient ecoregion (U.S. Environmental Protection Agency, 2000).

However, the selected sites will

Figure 2. Study area for transport of agricultural chemicals and approximate locations of expected sampling sites.

Eas

Wes

t

t

Dry

Maple Creek

For

F

k

ork

Maple

Maple

Creek

Cree

C

k

reek

41°45'

41°

97°15'

97°

96°45'

0 0.5 1.0 MILE

0 0.5 1.0 KILOMETER

0 0.5 1.0 MILE

0 0.5 1.0 KILOMETER

T

EXPLANATION

Small research watershed

Ground-water flow path transect

Weather station

Stream-sampling station

Tile-drain sampling site

Irrigation sampling site

Vadose-zone monitoring site

Ground-water monitoring well

Ground-water/surface-water interaction sampling site

Ground-water flow path well cluster

Overland-flow sampling site

T

I

Base from U.S. Geological Survey digital data, 1:100,000, 1989,

and 1:2,000,000, 1972, Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30'

North American Datum of 1983 (NAD 83)

0 5 10 MILES

0 5 10 KILOMETERS

Maple

Creek

(A)

(B) 96 ̊34' 96 ̊33'

41 ̊03'

41 ̊04'

I

97 ̊09' 97 ̊08'

41 ̊02'

41 ̊03'
For more information, contact:

U.S. Geological Survey

Federal Building, Room 406

100 Centennial Mall North

Lincoln, NE 68508

Telephone: (402) 437–5082

Home page: http://ne.water.usgs.gov/

include as narrow a range of stream

size, type, and hydrologic setting as is

practical for that region.

Data for assessments of water

quality, algae, invertebrates, and

physical habitat will be collected from

about 28 Nebraska streams during

summer 2003. At each sampling site,

plans include measurements of

specific conductance, pH, water

temperature, and dissolved oxygen on

a continuous basis for a 48-hour

period to allow the calculation of

stream metabolism.

Mercury in Stream Ecosystems

Methylmercury, the most toxic

form of mercury, accumulates in lowlevel members of aquatic food webs,

and its concentration in tissue

progressively increases as higher level

predators consume lower level

organisms. At the top of the food

web, fish, wildlife, and humans that

consume fish can be exposed to

harmful levels of methylmercury. As

part of NAWQA, a recently begun

study of mercury contamination in

streams across the Nation will

describe the occurrence of total

mercury and methylmercury in water

and sediment, and total mercury in

fish. Sampling sites were selected to

represent the large national range of

mercury deposition and across the

ranges of the transport and

methylation of mercury in differing

aquatic ecosystems. The study of

mercury occurrence complements

additional NAWQA work that will

examine in detail the cycling of

mercury in the

environment and food

webs at a small subset

of the sites sampled

nationally in 2002.

Of approximately

112 sites sampled

nationally in 2002, 8 are

in Nebraska (fig. 1).

Samples of fish fillets,

water, and bed

sediments were

collected during lowflow conditions in July 2002. Widely

available predacious fish species, of

approximately 3 to 4 years of age,

were targeted for sampling. Channel

catfish were sampled at five Nebraska

sites, and black crappie, creek chub,

and largemouth bass were sampled at

one site each. Laboratories will

determine mercury concentrations and

fish-specimen age.

References

Frenzel, S.A., Swanson, R.B.,

Huntzinger, T.L., Stamer, J.K.,

Emmons, P.J., and Zelt, R.B.,

1998, Water quality in the Central

Nebraska Basins, Nebraska,

1992–95: U.S. Geological Survey

Circular 1163, 33 p.

Gilliom, R.J., Hamilton, P.A., and

Miller, T.L., 2001, The National

Water-Quality Assessment

Program—entering a new decade

of investigations: U.S. Geological

Survey Fact Sheet 071–01, 6 p.

Heberer, Thomas, Verstraeten, I.M.,

Meyer, M.T., Mechlinski, Andy,

and Reddersen, Kirsten, 2001,

Occurrence and fate of

pharmaceuticals during bank

filtration—preliminary results from

investigations in Germany and the

United States: Water Resources

Update, no. 120, p. 4–17.

National Agricultural Statistics

Service, 2000, “Cattle,” “Cattle on

feed,” and “Hogs and pigs” reports:

Washington, D.C., National

Agricultural Statistics Service,

reports available on the World

Wide Web, accessed October 28,

2002, at http://www.usda.gov/nass/

aggraphs/graphics.htm

Nebraska Department of Environmental Quality, 2002, 2002

Nebraska water quality report:

Lincoln, Nebraska Department of

Environmental Quality, Water

Quality Division, 164 p.

U.S. Environmental Protection

Agency, 2000, Aggregations of

level III ecoregions for the National

Nutrient Assessment and

Management Strategy: U.S.

Environmental Protection Agency

digital map data available on the

World Wide Web, accessed June

2002, at ftp://ftp.epa.gov/wed/

ecoregions/us/us_nutr_agg.e00.Z

Verstraeten, I.M., Carr, J.D., Steele,

G.V., Thurman, E.M., Bastian,

K.C., and Dormedy, D.F., 1999,

Surface water-ground water

interaction—herbicide transport

into municipal collector wells:

Journal of Environmental Quality,

v. 28, no. 5, p. 1396–1405.

Zelt, R.B., 1996, Basin-level habitat

characteristics of selected streams

in central Nebraska: U.S.

Geological Survey Open-File

Report 96–361, 25 p.

NAWQA Data are Readily

Available

The large NAWQA database about

water-quality conditions and other

information is accessible on the World

Wide Web (http://water.usgs.gov/

nawqa/data). The NAWQA Program

encourages use of these data for a

wide range of analyses.

NOTE: Parts of this fact sheet were

modified from USGS Fact Sheet 071–

01.

Algal growth in Clear Creek near Columbus.