Sources and Concentrations of Phosphorus in the Cheney

Reservoir Watershed, South-Central Kansas

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 010–02

March 2002

—Larry M. Pope and Chad R. Milligan

Prepared in cooperation with the

CITY OF WICHITA, KANSAS

Heimerman Point at Cheney Reservoir, April 2001.

Introduction

Phosphorus is a nutrient required

by plants for growth and reproduction

and often is added to agricultural soils

to increase crop yields. However, the

agricultural application of phosphorus

historically has been greater than crop

requirements and has led to a buildup

of soil phosphorus (Carpenter and

others, 1998). The buildup of soil

phosphorus has increased the potential

for phosphorus transport to surface

water in runoff from agricultural

fields (Sharpley and others, 1999).

Excess phosphorus in surface

water may contribute to eutrophication (nutrient enrichment) of surface

water, particularly lakes and

reservoirs. Nutrient enrichment can

overstimulate algal production

creating algal blooms that may reduce

the aesthetic and recreational value of

the water, create taste-and-odor

problems in drinking water, and, in

severe cases, stress or kill aquatic

organisms as a result of dissolved

oxygen depletion or the release of

toxins when algal blooms die

(Sharpley, 1995).

The Cheney Reservoir watershed

is a 933-square-mile contributing

drainage area of Cheney Reservoir

located on the North Fork Ninnescah

River in an agricultural area of southcentral Kansas (fig. 1). The watershed

is used almost exclusively for crop

and livestock production. Since 1965

when Cheney Reservoir was

constructed, the percentage of the

watershed used for crop production

has averaged about 52 percent

annually. Cattle inventories have

averaged about 64,000 animals since

1965. Crop production and cattle

inventories were estimated from

county data presented in Kansas State

Board of Agriculture and U.S.

Department of Agriculture (1964Ð94)

and Kansas Department of Agriculture

and U.S. Department of Agriculture

(1995Ð97).

The human population in the

Cheney Reservoir watershed is less

than 4,000, many of whom are

associated with the approximately

1,000 farms in the watershed (Cheney

Significant Findings

Human-related activities in the predominantly

agricultural watershed of Cheney Reservoir have

substantial effects on the quality of water in the

reservoir.

Agricultural activities have accounted for 65 percent of

the phosphorus transported by streams to Cheney

Reservoir, and most of that phosphorus was

transported when streamflow consisted predominantly

of runoff from agricultural fields.

On a long-term basis, surface water from five waterquality sampling sites in the watershed exceeded the

established goal for phosphorus by about two to five

times.

Substantial reductions in phosphorus concentrations in

streams could involve a combination of approaches

such as reducing the application of phosphorus in the

watershed and more extensive implementation of

land-management and agricultural practices to limit

its movement to streams.
Figure 1. Location of Cheney Reservoir watershed, surface-water-quality sampling sites, and nonagricultural soil-coring sites, south-central Kansas.

C heney R eservoir

North Fork

R iver

S ilver

C reek

Goose C reek

Irish C r

R ed R oc k

Arkansas R iver

C reek

Ninnescah

0 5 10 15 20 MILES

0 5 10 15 20 KILOMETERS

R eno C ounty

K ingman C ounty

Edwards C ounty

K iowa C ounty

Pawnee C ounty

S edgwick

C ounty

S tafford C ounty

Pratt C ounty

Stafford

Sylvia Abbyville Zenith

Penalosa

Pretty Prairie

Haven

Kingman Pratt

Langdon

Castle- ton

Turon

Preston

99 45' 30' 15' 98 97 45'

38

37 45'

50 Partridge

54

61

14

14

17

96

Base from U.S. Bureau of Census digital data, 1992, scales vary from 1:24,000 to 1:100,000, Geographic projection and U.S. Geological Survey digital data, 1:100,000, 1983, Universal Transverse Mercator projection, Zone 14 Converted to Albers Equal-Area Conic projection, standard parallels 29 30' and 45 30', central meridian -96

EX PLANAT ION

Hutchinson

Index map

C ontributing drainage area

Noncontributing drainage area

B oundary of C heney R eservoir watershed

S urface-water-quality sampling site

and number

Nonagricultural soil-coring site

1

2

3

4

5

6

5 C heney R eservoir watershed

Wichita

K ANSAS

Reservoir Watershed Task Force

Committee, written commun., 1996).

Populations of the six largest towns in

the watershed range from less than

200 to slightly more than 1,200 people

(Helyar, 1994). Because of the small

population in the watershed, the

potential for substantial point-source

contamination is small as determined

in a previous low-flow investigation

(Christensen and Pope, 1997).

Cheney Reservoir is a watersupply source for the city of Wichita

and the surrounding area. Currently

(2001), the city obtains 60 to

70 percent of its daily water supply

for about 350,000 people from

Cheney Reservoir (Jerry Blain, city of

Wichita Water and Sewer Department, oral commun., 2000). Cheney

Reservoir also provides for downstream flood control, wildlife habitat,

and recreational opportunities.

In 1996, the U.S. Geological

Survey entered into a cooperative

study with the city of Wichita to

assess the occurrence and transport of

selected water-quality constituents,

including phosphorus, within the

Cheney Reservoir watershed. As part

of that study, six surface-water-quality

sampling sites were established in the

watershed (fig. 1). Sites 1Ð5 were

located on the main stem of the North

Fork Ninnescah River or its tributary

streams. Sampling site 6 was located

immediately downstream from the

Cheney Reservoir Dam.

Sources of Phosphorus

Because the Cheney Reservoir

watershed is used almost exclusively

for agricultural purposes, the two

major sources of phosphorus are

naturally occurring soil phosphorus

and phosphorus contributed from

agricultural activities (fertilizers and

livestock waste). Quantification of

these source contributions can provide

information related to the extent of

agricultural effects on the occurrence

of phosphorus in streams of the

watershed and the potential to achieve

a meaningful reduction in the amount

of phosphorus transported to Cheney

Reservoir. On the basis of results

from a previous investigation conducted during low flow (Christensen

and Pope, 1997), point-source

discharges (municipal wastewater

discharges) probably are not a

substantial source of phosphorus to

surface water in the Cheney Reservoir

watershed.

Historical (1965Ð98) percentages

of phosphorus transported into

Cheney Reservoir from natural and

agricultural sources were calculated

by Pope and others (2002) (fig. 2).

These calculations were performed on

the basis of a comparison between a

mean concentration of phosphorus in

soil from 43 nonagricultural coring

sites, mostly cemeteries, in and near

the Cheney Reservoir watershed

(fig. 1) and a mean concentration of

phosphorus in reservoir bottom

sediment. Cemeteries were selected

for soil sampling because they

represent unique locations where soils

have been protected from agricultural

enrichment of phosphorus for

extended periods. The comparison

determined an agricultural-enrichment

factor of 2.9 for phosphorus. This

enrichment factor indicates that the

phosphorus enrichment of watershed

soil from agricultural activities has

resulted in the transport of 2.9 times
Agricultural

sources

(65 percent)

Natural

sources

(35 percent)

Figure 2. Percentages of phosphorus transported to Cheney Reservoir from natural and

agricultural sources, 1965–98.

1 2 3 4 5

0.50

0.30

0.25

0.36

0.23

0.17

0.10

0.12

0.08

0.09

0

0.10

0.20

0.30

0.40

0.50

0.60

S urface-water-quality sampling site (fig. 1)

Phosphorus concentration, in milligram per liter

E stimated mean

natural phosphorus

concentrations

Long-term water-quality

goal for streams

Mean phosphorus concentrations (1997–2000)

Figure 3. Comparison of mean phosphorus concentrations in water samples from five surface-waterquality sampling sites in Cheney Reservoir watershed to mean concentrations estimated on the basis

of an agricultural-enrichment factor of 2.9. The long-term water-quality goal for phosphorus in

streams was established by the Cheney Reservoir Watershed Task Force Committee (written

commun., 1996).

the amount of phosphorus to Cheney

Reservoir than would have been

expected under conditions where the

watershed soil contained natural

concentrations of phosphorus.

Reference to phosphorus concentrations (soil or water) in this fact

sheet denotes total phosphorus

concentrations (suspended plus

dissolved in the case of water).

Agricultural activities accounted

for 65 percent of the phosphorus

transported to Cheney Reservoir

between 1965 and 1998 (fig. 2). This

percentage is a historical average and

may not accurately describe current

(2001) conditions. However, this

percentage does indicate that changes

to agricultural or land-management

practices that would mitigate the

movement of phosphorus from

agricultural fields or changes in

phosphorus application and

distribution in the watershed have a

large potential for reducing the

amount of phosphorus transported to

Cheney Reservoir.

Concentrations of Phosphorus

Long-term (1997Ð2000) mean

concentrations of phosphorus in water

(fig. 3) were determined (Milligan and

Pope, 2001) for the five surfacewater-quality sampling sites upstream

from Cheney Reservoir (fig. 1).

These mean concentrations were

calculated from the analyses of

surface-water samples collected

during base flow (low flow) and

runoff (high flow) (table 1). On

average, phosphorus concentrations

were 2.0 (sampling site 2) to 4.4

(sampling sites 3 and 5) times larger

in samples collected during runoff

than in samples collected during base

flow. Most phosphorus is transported

to Cheney Reservoir during runoff.

For example, at sampling site 4

(fig. 1), the main inflow site to

Cheney Reservoir, it was estimated

that 72 percent of the phosphorus in

streamflow at this site during

1997Ð2000 was transported in runoff

(Pope and others, 2002). This

determination provides additional

evidence that nonpoint sources

(agricultural sources) are the main

contributors of phosphorus in the

Cheney Reservoir watershed.

Long-term (1997Ð2000) mean

concentrations of phosphorus in water

from the five sampling sites upstream

from Cheney Reservoir (fig. 3) were

2.3 (sampling site 2) to 5.0 (sampling

site 5) times larger than the 0.10-mg/L

(milligram per liter) goal established

by the Cheney Reservoir Watershed

Task Force Committee (written

commun., 1996). The 0.10-mg/L goal

is the same as that recommended by

the U.S. Environmental Protection

Agency (1986) for limiting problems

associated with nutrient enrichment of

lakes and reservoirs.

The differences in long-term mean

concentrations of phosphorus among

the five sampling sites (fig. 3) probably is the result of a combination of

natural and human-related factors.

Natural factors may include

differences in rainfall, topography,

and soil characteristics such as texture

(particle size), permeability, and

erodibility. Human-related factors

include land use, land management,

and agricultural practices. Agricultural practices include the extent and

magnitude of fertilizer applications

and distribution of livestock manure.

Little can be done to control the

effects of the natural factors, but

modifications to the human-related

factors may reduce phosphorus inputs

to the watershed and limit its

movement to surface water.

To estimate how the watershed

system might respond to reduced

phosphorus inputs, the long-term

(1997Ð2000) mean concentrations of

phosphorus (fig. 3) were divided by

the previously determined 2.9 agricultural-enrichment factor for

phosphorus. This calculation, in

effect, simulated (estimated) longterm mean phosphorus concentrations

in the watershed under natural soil

phosphorus conditions. Results of this

simulation (fig. 3) indicated that even

if soil in the watershed were maintained at natural concentrations of

phosphorus, some streams (sampling

sites 3 and 5) still would not meet the
Table 1. Number of samples analyzed and mean concentrations of total phosphorus in surface

water during base-flow, runoff, and long-term streamflow conditions at sampling sites 1–5 in

Cheney Reservoir watershed, south-central Kansas, 1997–2000

For more information contact:

District Chief

U.S. Geological Survey

4821 Quail Crest Place

Lawrence, Kansas 66049Ð3839

(785) 842Ð9909

email: dc_ks@usgs.gov

http://ks.water.usgs.gov

water-quality goal of 0.10 mg/L. The

implication of this finding is that

reductions in the agricultural use of

phosphorus alone may not provide the

water-quality improvement necessary

to meet the established phosphorus

goal. Instead, it could involve a

combination of approaches such as a

reduction in use of phosphorus and

more extensive implementation of

land-management and agricultural

practices to mitigate phosphorus loss

from agricultural fields and movement

to surface water.

Conclusions and Implications

Cheney Reservoir is a watersupply source for about 350,000

people in south-central Kansas and

provides for downstream flood

control, wildlife habitat, and

recreational opportunities. As such,

water quality in the reservoir is of

great importance. The introduction of

excessive amounts of phosphorus in

the reservoir can degrade the water

quality and result in treated drinking

water that is aesthetically objectionable to consumers.

Agricultural activities in the

Cheney Reservoir watershed have

accounted for 65 percent of the

phosphorus transported into Cheney

Reservoir. Much of this phosphorus

(72 percent) was transported by

streams during runoff (high-flow)

conditions. The positive implication

of this large percentage of humanrelated phosphorus is that the

possibility exists for substantial

reductions in phosphorus to Cheney

Reservoir through changes in human

activities.

Long-term mean concentrations

of phosphorus in water from five

surface-water-quality sampling sites

in the Cheney Reservoir watershed

ranged from 0.23 to 0.50 mg/L, about

two to five times the established

water-quality goal for phosphorus.

An estimation of mean concentrations of phosphorus at these sampling

sites relative to the watershed with

natural (nonagriculturally enriched)

soil phosphorus conditions indicated

that water from two of the five

sampling sites still would not meet

the water-quality goal for phosphorus. The implication of this

finding is that reductions in the

agricultural use or distribution of

phosphorus alone may not be

sufficient for some streams to meet

the water-quality goal. Instead, it

could involve a combination of

approaches such as reducing

phosphorus applications in the

watershed and more extensive

implementation of practices to inhibit

phosphorus movement to streams.

References

Carpenter, S.R., Caraco, N.F., Correll, D.L.,

Howarth, R.W., Sharpley, A.N., and

Smith, V.H., 1998, Nonpoint pollution of

surface waters with phosphorus and

nitrogen: Ecological Applications, v. 8,

no. 3, p. 559Ð568.

Christensen, V.G., and Pope, L.M., 1997,

Occurrence of dissolved solids, nutrients,

atrazine, and fecal coliform bacteria

during low flow in the Cheney Reservoir

watershed, south-central Kansas, 1996:

U.S. Geological Survey Water-Resources

Investigations Report 97Ð4153, 13 p.

Kansas Department of Agriculture and U.S.

Department of Agriculture, 1995Ð97,

Kansas farm facts: Topeka, Kansas,

published annually.

Kansas State Board of Agriculture and U.S.

Department of Agriculture, 1964Ð94,

Kansas farm facts: Topeka, Kansas,

published annually.

Helyar, Thelma, ed., 1994, Kansas statistical

abstract 1992Ð93: Lawrence, University

of Kansas Institute for Public Policy and

Business Research, 420 p.

Milligan, C.R., and Pope, L.M., 2001,

Occurrence of phosphorus, nitrate, and

suspended solids in streams of the Cheney

Reservoir watershed, south-central

Kansas, 1997Ð2000: U.S. Geological

Survey Water-Resources Investigations

Report 01Ð4199, 18 p.

Pope, L.M., Milligan, C.R., and Mau, D.P.,

2002, Historical contributions of

phosphorus from natural and agricultural

sources and implications for stream water

quality, Cheney Reservoir watershed,

south-central Kansas: U.S. Geological

Survey Water-Resources Investigations

Report 02Ð4021, 25 p.

Sharpley, A.N., 1995, Fate and transport of

nutrientsÑphosphorus: U.S. Department

of Agriculture, Agricultural Research

Service Working Paper No. 8, 28 p.

Sharpley, A.N., Gburek, W.J., Folmar, G., and

Pionke, H.B., 1999, Sources of phosphorus exported from an agricultural watershed in Pennsylvania: Agricultural Water

Management, v. 41, no. 2, p. 77Ð89.

U.S. Environmental Protection Agency, 1986,

Quality criteria for water, 1986: U.S.

Environmental Protection Agency

Report 440/5Ð86-001, unnumbered pages.

Samplingsite number

(fig. 1) N N N

Long term

Base flow Runoff (1997–2000)

1

2

3

4

5

36

38

40

32

37

0.13

.14

.11

.10

.14

92

78

78

85

106

0.29

.28

.48

.38

.62

128

116

118

117

143

0.25

.23

.36

.30

.50

Mean

concentration (mg/L)

Mean

concentration (mg/L)

Mean

concentration1 (mg/L)

[Data from Milligan and Pope (2001). N, number of samples analyzed; mg/L, milligram per liter]

1

Calculated using all available base-flow and runoff analyses.