1

Effects of Lawn Fertilizer on Nutrient Concentration in Runoff

from Lakeshore Lawns, Lauderdale Lakes, Wisconsin

U.S. Department of the Interior

U.S. Geological Survey

USGS Water-Resources Investigations Report 02–4130

July 2002

Figure 1. Site locations surrounding Lauderdale Lakes, Wis.

Figure 2. Lakeshore development and lawns at Lauderdale Lakes, Wis.

Introduction

Transport of nutrients (primarily forms of nitrogen and

phosphorus) to lakes and resulting accelerated eutrophication

are serious concerns for planners and managers of lakes in

urban and developing suburban areas of the country. Runoff

from urban land surfaces such as streets, lawns, and rooftops

has been noted to contain high concentrations of nutrients;

lawns and streets were the largest sources of phosphorus in

residential areas (Waschbusch, Selbig and Bannerman, 1999).

The cumulative contribution from many lawns to the amount

of nutrients in lakes is not well understood and potentially

could be a large part of the total nutrient contribution.

Why study runoff from lawns?

The shorelines of many lakes are already highly developed,

and the potential water-quality effects of this development are

increasing. Many lawn-care professionals and homeowners

hold a common belief that runoff from lawn surfaces is minimal and that phosphorus movement from lawns is not a

problem (Barth, 1995). The homeowners’ goal to maintain

lush green lawns may conflict with the lake manager’s goal to

minimize nutrient inputs. In cooperation with the Lauderdale

Lakes Lake Management District and the Wisconsin Department of Natural Resources, the U.S. Geological Survey (USGS)

conducted a study during 1999–2000 to determine the magnitude of nutrient runoff from nearshore residential lawns surrounding a lake and to determine whether fertilizer application

and the type of fertilizer (regular or nonphosphorus types)

affect the amount of nutrients in runoff from lawns. Such

information is important for developing stormwater best-management practices and for developing or improving shoreland

zoning ordinances and other local regulations to protect or

improve the water quality of lakes (Wisconsin Department of

Natural Resources, Wisconsin Shoreland Management Program, http://www.dnr.state.wi.us/org/water/wm/dsfm/shore/

title.htm, accessed February 8, 2002).

The study area was located at Lauderdale Lakes in Walworth County,

a chain of lakes in the more populated southeastern part of Wisconsin (fig.

1). The 15-mile shoreline of the lakes is about 70 percent developed,

primarily as single-family housing, and is the focus for additional residential development. Most of the lakefront homes have sloping lawns that are

maintained to the water’s edge (fig. 2). Information about the specific

sources and amounts of phosphorus entering the lakes was needed to

develop a plan for reducing the input of phosphorus. The lakes are

phosphorus limited, meaning that phosphorus is the nutrient limiting plant

growth and affecting lake productivity. A previous study (Garn and others,

1996) found that surface-water inflow from the small nearshore contributing drainage area accounted for only 4 percent of the water inflow to the

lake but represented 51 percent of the total annual phosphorus input from

all sources. The Lake Management District is in the process of installing

Green Lake

Middle

Lake

Mill Lake

Pleasant

Lake

T.4N.

T.3N.

R.16E.

R.16E. R.17E.

T.4N.

T.3N.

Road base from U.S. Geological Survey 1:100,000 digital data;

modified by Wisconsin Department of Natural Resources.

Don Jean 

Bay

Territorial Rd

Honey Creek

12

12

Streamflow station 

Runoff sampling site and number 2

EXPLANATION .5

.5 1 KILOMETER

0 1

0

MILE

5

2

3

4

10

12

1

6

14

13

11

15-18

7

8,9

Pleasant Lake Rd

Plantation Rd

Westshore Dr

Lost Nation Rd

Lost Nation Rd

Plantation Rd

Country Club Dr

Surfwood Dr

Stewart Dr

Shagbark Ln

Green Lake Dr

Hickory Rd

Pleasant Lake Rd

Plantation Rd

Westshore Dr

Lost Nation Rd

Lost Nation Rd

Plantation Rd

Country Club Dr

Surfwood Dr

Stewart Dr

Shagbark Ln

Green Lake Dr

Hickory Rd

Country club

Location of study area 

in Wisconsin
2

Figure 3. Tube-type lawn sampler (site 2).

Figure 4. Edging-type lawn sampler (site 5).

and implementing various measures to reduce the phosphorus input to the

lakes, among which is a “lake-friendly” fertilizer program that encourages

residents to apply nonphosphorus turf fertilizer. The Lake Management

District has been supplying residents with phosphorus-free fertilizer for

purchase for about 3 years, and data were needed to evaluate the effectiveness of the program.

Equipment and Methods

In 1999 and spring 2000, lawn samplers designed to collect surface

runoff were installed using methods described in Waschbusch, Selbig, and

Bannerman (1999, p. 7). The samplers collect runoff through two 5-foot

pieces of 1/2-inch-diameter PVC tubing placed flush with the surface of

the ground, on a sloping lawn, with an angle of about 150 degrees between

the two tubes (fig. 3). Runoff entered the tubing through a 1/8-inch slot cut

at intervals along the length of the tube; each tube was then wrapped with

fiberglass screen to prevent insects and large debris from entering. The

tube was held in place on the lawn surface with wire staples. At the end of

each tube, a connecting piece of 1/2-inch silicone tubing directed the

collected runoff into a covered 1-quart glass jar placed in the ground in a

4-inch-diameter protective PVC sleeve with a cover.

During the summer of 2000, the original sampler design was modified

to increase sample volumes at sites that did not generate sufficient runoff

samples and to minimize contamination problems caused by insects and

earthworms entering the samples despite the fiberglass screen. One variation to increase runoff-collection efficiency was to enlarge the slots cut in

the pipes to 1/4-inch. Another technique used at sites with the least runoff

production was to replace the tubing with two lengths of 4-foot-long plastic

lawn edging that directed runoff toward the collecting jar (fig. 4); this

solution was more effective at increasing captured runoff and minimizing

contamination than increasing the slot size.

Clean sample bottles were placed in the lawn samplers before each

expected storm or at about 2-week intervals when sites were inspected if

there was no rain. Samplers were cleaned and rinsed with deionized water

during each visit to remove any accumulated dirt or debris. Notes were kept

on volume of runoff in the collection bottle; color and noticeable sediment,

debris, or insects in the bottle; and site condition. Sample bottles were

collected as soon as possible after each storm (usually within 1 to 5 days)

and brought to Madison, where the contents were filtered with a 0.45-

micrometer filter, preserved with sulfuric acid, and then delivered to the

Wisconsin State Laboratory of Hygiene for nutrient analyses. Samples

were analyzed according to standard laboratory methods (Wisconsin State

Laboratory of Hygiene, written commun., 2001) for concentrations of total

phosphorus (TP), total dissolved phosphorus, total Kjeldahl nitrogen

(TKN), dissolved ammonia nitrogen, and dissolved nitrate plus nitrite

nitrogen. When insufficient sample volume was collected from a storm to

analyze for all nutrients, analyses were done first for total phosphorus.

Description of Sampling Sites

The Lauderdale Lakes are a chain of three interconnected lakes with a

surface area of 807 acres. The lakes are ground-water drainage lakes in

which more than 90 percent of the water inflows are from ground water and

direct precipitation. Some surface water enters the lakes by way of a few

ephemeral drainageways or as overland flow from the nearshore area. Lake

and drainage-basin characteristics are described in detail by Garn and

others (1996). Lakeshore developments include about 1,010 single-family

homes, of which about 30 percent are year-round residences. Other

developments include a golf course, a boat marina, and two recreational

camps.

In the lakeshore area within 300 feet of the shoreline, soils consist

primarily of the Casco-Rodman Complex (60 percent of the area), Rodman-Casco Complex (12 percent of the area), and Casco-Fox Silt Loam (6

percent of the area). The Casco-Rodman Complex is found on 20–30

percent slopes; surface textures range from loam to silt loam, and subsoils

are clay loam to sandy loam. The Rodman-Casco Complex is found on

slopes of 30 to 45 percent formed in loamy deposits over sand and gravel.

The Casco-Fox soils are found on slopes of 6 to 12 percent and have a silt

loam texture (Haszel, 1971). Soil disturbance can be severe during building

construction in suburban areas, commonly resulting in subsoil compaction

by heavy equipment followed by layering with topsoil. Such disturbance

has the potential for greatly increasing runoff and nutrient losses.

Samplers were installed at 18 locations along the lakeshore (fig.1),

representing different types of lawn-fertilizer use, undeveloped areas, and

one area of mixed land use (part agricultural, ditched paved roads, and

lawns). Sites were grouped into three categories: regular-fertilizer sites,

nonphosphorus-fertilizer sites, and unfertilized sites. Samplers were installed at 12 sites and operated during the growing season in 1999. In 2000,

six additional sites were installed, including two samplers in a swale.

Samplers were installed at seven lawn sites where traditional fertilizer was

applied, three sites where nonphosphorus fertilizer was applied, and six

control sites where no fertilizer was applied (three steep, wooded sites; two

lawns; and an undeveloped grass field). Much of the area is wooded, and

many of the lawns have an overhead canopy of hardwood trees. Two

samplers were installed in a swale area on the south side of Mill Lake (Don

Jean Bay) that collected mixed runoff from an agricultural field, lawns, and

streets. The drainage area of the upgradient sampler was 8 acres and of the

downgradient sampler was 38 acres, of which about 25 percent was

cropland.

Property owners were asked to participate in the runoff study. It was

assumed that most lawn fertilizer users followed usual manufacturer

recommendations of four applications per season made in about April–

May, June–July, August–September, and October at 3 to 3.5 pounds per

1,000 square feet. Homeowners applying regular fertilizer fertilized their

lawns two or more times per year. Each participant’s property was

inspected to ensure that lawn slope was at least 20 feet long, grade was at
3

Table 1. Physical characteristics of sampling sites at Lauderdale Lakes, Wis. [P, phosphorus; ppm, parts per million; %, percent, turf-quality values are defined

in text; ft2, square feet; --, no data]

Figure 5. Estimated monthly precipitation at Lauderdale Lakes, Wis., during

1999–2000 compared to normal monthly precipitation.

Table 2. Storm information and number of sites with

runoff samples at Lauderdale Lakes, Wis., 1999–2000

[est, estimated]

least 5 percent, and sample catchment area was not affected by runoff from

rain gutters, driveways, or other lawns or sources. A soil sample collected

at the time of sampler installation was analyzed for soil texture, pH, and

phosphorus content by the University of Wisconsin Soil and Plant Analysis

Laboratory. A visual vegetative soil-cover density, in percent, and a turfquality rating were assigned to each lawn during visits. Turf quality was

based on a 1 to 10 scale: for example, a score of 10 represented 100 percent

best-quality green grass cover, 5 represented 50 percent grass cover with

bare spots, weeds, and dead grass providing additional cover, and 1

indicated no turfgrass cover, with dead grass, weeds, and other vegetation

providing primary soil cover. The more heavily fertilized sites (5, 8, 9, 12)

had the best turf-quality ratings. Various physical characteristics of the

sampling sites are summarized in table 1.

Nutrient Concentration in Runoff

Rainfall and Runoff

Long-term precipitation records from the National Weather Service

stations at Whitewater (about 9 miles northwest of Lauderdale Lakes) and

Lake Geneva (about 13 miles southeast) were used to estimate rainfall at

Lauderdale Lakes (National Oceanic and Atmospheric Administration,

1999–2000). Data from a recording rain gage at a USGS streamflowgaging station at Jackson Creek near Elkhorn (9 miles south) was used after

the rain gage was installed on May 25, 1999. Rainfall was above the 1961-

90 average for April, May, and June 1999 and near or below average the

remainder of the season. In 2000, rainfall amounts for May, June, and

September were substantially above average (fig. 5). Ten runoff events

occurred from 12 storms in the 1999 sampling season and 13 runoff events

occurred from 15 storms in 2000; generally, the storms in 2000 were larger

than those in 1999. A storm event was defined as more than 0.3 inches of

rain, and a runoff event as one that resulted in at least two runoff samples

with sufficient volume for analysis (about 100 ml). A summary of the storm

dates and precipitation amounts is given in table 2.

Although measurement of quantity of runoff was not part of this study,

a qualitative evaluation of runoff may be obtained by comparing the

0

1

2

3

4

5

6

7

8

PRECIPITATION (INCHES)

Estimated precipitation

Normal precipitation

Apr-99May-99June-99July-99Aug-99Sept-99Oct-99Nov-99Dec-99

Jan-00Feb-00

Mar-00

Apr-00May-00June-00July-00Aug-00Sept-00

Site ID Station number Site type Soil type/texturea

Soil P concentrationb

 (ppm) Slope (%)

Vegetative cover

density (%)

Turf

quality Runoff area (ft2

)

Regular fertilizer application sites

2 424652088333901 Wooded lawn Hebron loam, gravelly 68 21 65 150 10 67

3 424650088333501 Lawn Hebron loam 32 9 90 180 8 80

5 424616088334201 Wooded lawn Casco-Rodman loam-silt loam 66 20 100 114 8 33

8 424541088334602 Golf course lawn Casco-Rodman loam-silt loam 35 20 100 250 15 63

9 424541088334601 Golf course lawn Casco-Rodman loam-silt loam 78 24 100 186 9 54

12 424519088334101 Lawn Casco-Fox silt loam 28 16 100 104 1 8

15 424654088343103 Lawn Fox silt loam 11 11 60 152 5 24

Nonphosphorus-fertilizer application sites

6 424611088334001 Wooded lawn Casco-Rodman loam-silt loam 20 14 80 250 18 67

13 424603088340201 Wooded lawn Casco-Rodman loam-silt loam 21 34 60 140 15 54

14 424623088345101 Wooded lawn Casco-Rodman loam-silt loam 70 14 85 225 8 30

Unfertilized sites

1 424652088334401 Grass field Fox sandy loam 65 9 100 128 2 13

4 424643088333601 Wooded lawn Casco-Rodman loam-silt loam 38 12 85 188 6 47

7 424543088334001 Wooded lawn Casco-Rodman loam-silt loam 14 22 70 209 12 46

16 424654088343101 Wooded Rodman-Casco loam/sand,gravel 28 41 95 200 9 33

17 424654088343102 Wooded Rodman-Casco loam/sand,gravel 24 33 95 300 13 48

18 424654088343104 Wooded Rodman-Casco sandy, gravelly 16 30 65 140 7 28

10 424514088334001 Swale Casco-Fox silt loam -- 5 -- 8 acres 9 69

11 424518088334301 Swale Casco-Fox silt loam -- 4 -- 38 acres 10 77

aFrom Haszel, 1971. b50–75 ppm P optimum recommendation for turfgrass.

 Analysis by Soil and Plant Laboratory, University of Wisconsin, Madison.

6

8.5

9

9.5

9.5

10

6

7.5

5

8

7

8

6

1

1

2

--

--

Number

of samples

Percentage

of storm events

99S1 4/9/1999 0.86 a 4

99S2 4/22/1999 3.73 a 9

99S3 5/12/1999 0.63 a 3

99S4 5/16/1999 0.80 a

 est 4

99S5 5/17/1999 0.66 a

 est 3

99S6 6/1/1999 0.70 8

99S7 6/10/1999 3.35 6

99S8 7/17/1999 1.11 4

99S9 8/13/1999 0.37 5

99S10 9/27/1999 3.66 11

00S1 2/21/2000 2.0 b 11

00S2 4/19/2000 2.59 2

00S3 5/9/2000 1.36 9

00S4 5/18/2000 1.95 5

00S5 5/27/2000 3.85 14

00S6 6/11/2000 1.95 9

00S7 7/2/2000 1.40 12

00S8 7/10/2000 1.33 5

00S9 7/31/2000 1.62 3

00S10 8/5/2000 1.17 16

00S11 8/17/2000 0.70 5

00S12 9/11/2000 1.94 17

00S13 9/22/2000 1.89 9

a Measured at Whitewater.

b From 6 inches snowmelt and light rain.

Storm

number

Storm

start date

Total precip

amount

(inches)

Number of

sites with

runoff

samples
4

Figure 6. Site 12 at Lauderdale Lakes, Wis.—an example of high-quality

turfgrass.

Figure 7. Nutrient concentrations in runoff from different categories of

sampling sites at Lauderdale Lakes, Wis.

number of sites where runoff was sampled for each storm (table 2) and the

number of storms sampled at each site (table 1). The magnitude of runoff is

dependent on a combination of factors including rainfall amount and

intensity, soil-surface storage and detention, and infiltration rate. Infiltration is affected by soil type, vegetative cover, slope, and other factors (Haan,

Barfield, and Hayes, 1994, p. 52–54). In general, sites with dense vegetative

cover and coarse soils with high infiltration rates produced less runoff.

Specifically, site 12 of the fertilized sites (fig. 6), which had the best-quality

turf and fertilizer applications of 4 times per year, produced the least runoff

(only 8 percent of all storms). Other sites (5, 8, 9) with high turf quality and

density produced more frequent runoff samples, possibly because of steeper

slopes or other factors. At six of the lawn sites, more than 50 percent of the

storm events produced runoff.

The phenomenon of soil-water repellency, or hydrophobicity, was

observed at many of the lawn sites, especially after dry periods. Water

repellency of soils reduces affinity to water so that the soil resists wetting,

thus reducing infiltration capacity, decreasing plant growth, and increasing

surface runoff. The phenomenon has been widely accepted as a problem for

many soils in seasonally dry climates. Soils with grass cover in temperate

climates have recently been found to develop resistance to wetting—a

common problem known as “localized dry spot” on golf courses (Doerr,

Shakesby and Walsh, 2000; Kostka, 2000). Therefore, water repellency

could be an additional factor influencing runoff from residential lawn soils

(L.F. DeBano, University of Arizona, oral commun., 2001). At Lauderdale

Lakes, there was also some indication that lawn shading by trees and less

frequent use of fertilizer (sites 6, 7, and 13) resulted in less dense and patchy

turf cover, increasing runoff. In ongoing turf studies at the University of

Wisconsin (W.R. Kussow, Department of Soil Science, written commun.,

2000), researchers found that not fertilizing turfgrass caused thinning of the

turf, increased the amount of runoff, and increased nitrogen and phosphorus

loss. Generally, the percentage of storms resulting in surface runoff from

many of the lawns was higher than expected. Runoff from lawns may occur

more frequently than previously thought because of the complex interaction

of many factors.

Nutrient Concentrations in Runoff and Effects of Fertilizer Use

Summary statistics of nutrient concentrations measured in runoff from

different site categories are given in table 3 and compared in figure 7.

Detailed data for each of the sites were published annually in the U.S.

Geological Survey Water-Data Reports (Holmstrom and others, 2000; Garn

and others, 2001). There was a wide range in concentration of most nutrients

among storms during the study period. Given this variability, geometric

means or medians are more meaningful for comparison because they are

better estimates of central tendency than arithmetic means. The nonparametric Kruskal-Wallis test was used to test for overall differences in

concentration distributions, and the Wilcoxon rank sum test was used to test

for differences in medians between pairs of lawn categories (P.W. Rasmussen,

Wisconsin Department of Natural Resources, written commun., 2001). A

confidence level of 10 percent (p = 0.10) was chosen to evaluate the results

of the statistical tests. The difference in medians for samples from two

different lawn categories was considered statistically significant if p values

were less than 0.10.

A quality-control study was done to determine nutrient-concentration

effects of grass clippings, earthworms, and insects that managed to get into

water samples. All of these contamination sources had a large effect by

increasing nitrogen and phosphorus concentrations. Samples that were

affected by these contamination sources, identified from field notes, were

excluded from data analysis, but the exclusions did not significantly change

the overall results.

No significant differences in concentration among lawn categories were

found for any of the nitrogen species. Fertilizer use did not affect total

nitrogen concentrations in runoff. In addition, nitrite plus nitrate concentrations in runoff were generally low.

Dissolved phosphorus concentrations were significantly different (p =

0.02) among the lawn categories. Moreover, the median concentration of

dissolved phosphorus from regular-fertilizer sites (0.77 milligram per liter

(mg/L)) was significantly greater than that from nonphosphorus-fertilizer

sites (0.33 mg/L) and unfertilized lawn sites (0.38 mg/L). Total phosphorus

in runoff from regular-fertilizer sites compared to nonphosphorus-fertilizer

and to unfertilized-lawn sites had p-values of 0.11 and 0.14, respectively.

Thus, median total phosphorus concentrations were not significantly different at p < 0.1. Dissolved phosphorus was a fraction of total phosphorus, and

its concentrations ranged from 22 to 45 percent of total phosphorus for all

lawn categories.

SITE CATEGORY

0.0

0.5

1.0

1.5

2.0

2.5

DISSOLVED PHOSPHORUS

0.0

2.5

5.0

7.5

10.0

12.5

TOTAL PHOSPHORUS

0

20

40

60

TOTAL KJELDAHL NITROGEN

EXPLANATION

CONCENTRATION, IN MILLIGRAMS PER LITER

Outliers not shown

Outlier

1.5 x interquartile range

1.5 x interquartile range

75th percentile

Median

25th percentile

Regularfertilizer

lawns

Nonphosphorusfertilizer lawnsUnfertilized

lawns

Unfertilized

wooded
5

Table 3. Statistical summary of nutrient concentrations in runoff from

different site categories, Lauderdale Lakes, Wis. [n, number of samples; TKN,

total Kjeldahl nitrogen; NO2, nitrite nitrogen; NO3, nitrate nitrogen; TP, total

phosphorus; Diss P, dissolved phosphorus; all concentrations in milligrams

per liter]

Figure 8. Dense understory vegetation on wooded slope of sites 16 and 17 at

Lauderdale Lakes, Wis.

The median dissolved phosphorus concentration in lawn runoff from

regular-fertilizer sites was twice that for unfertilized and nonphosphorusfertilizer sites. Runoff from lawn sites with nonphosphorus-fertilizer applications had a median dissolved phosphorus and total phosphorus concentration that was similar to unfertilized sites. Dissolved phosphorus in runoff

is important because it is readily available for plant growth. Although not

significant at p < 0.1, lawn sites with regular fertilizer applications had a

median total phosphorus concentration in runoff that was 1.6 times that for

unfertilized sites and 1.8 times that for nonphosphorus-fertilizer sites.

In comparison with other studies, phosphorus concentrations in lawn

runoff at Lauderdale Lakes were slightly higher than concentrations found

in runoff from urban lawns in Madison, Wis. (Waschbusch, Selbig and

Bannerman, 1999), but were similar to those in lawn runoff from suburban

lawns in Minneapolis/St. Paul, Minn. (Barten and Jahnke, 1997). Surprisingly, nutrient concentrations in runoff from the unfertilized, steep, wooded

hillsides (sites 16, 17, and 18) were higher than those from the lawn sites and

thus were separated from the unfertilized lawn sites in the data comparisons.

These wooded sites (fig. 8) may be different from other wooded sites

because of their steep slopes, thick surface organic and litter layer, and

dense understory vegetation (crown vetch) planted for erosion control.

Waschbusch, Selbig, and Bannerman (1999) found a direct relation between phosphorus concentration and percentage of overhead tree canopy

that could affect source-area concentrations. In the Lauderdale Lakes study,

however, all lawn categories contained sites with overhead tree canopy, and

the lawn sites treated with regular fertilizer had the fewest trees; therefore,

differences between regular-fertilizer sites and the other lawn sites could be

even greater if there was an effect from tree cover.

Total phosphorus concentration in lawn runoff had a significant (p =

0.08) relation to soil-phosphorus concentration (table 1); total dissolved

phosphorus had no significant relation. The low category of soil-phosphorus concentration (0 to 24 parts per million (ppm)) had a significantly lower

median concentration of total phosphorus in lawn runoff (about half) than

the medians from medium (25-65 ppm) or high (66 ppm or more) soilphosphorus concentration lawns. There was no significant difference

between runoff concentrations from medium and high soil-phosphorus

concentration lawns. Barten and Jahnke (1997) also found a significant

difference in concentration of phosphorus in runoff from different categories of lawn soil fertility. In their study, total and soluble reactive phosphorus concentrations in runoff from high soil-phosphorus concentration lawns

were twice as large as the concentrations in runoff from low soil-phosphorus concentration lawns.

Median nutrient concentrations from the Don Jean Bay swale area with

mixed land use were more similar to those from the unfertilized wooded

sites and fertilized lawn sites than to those from other lawn sites (table 3).

The range in concentrations for ammonia nitrogen and total Kjeldahl

nitrogen in runoff from the swale, however, was greater than those for the

other sites.

Although it was not within the scope of this study to measure runoff

volumes from each of the sites and quantify the mass of nutrients transported offsite, the concentration data will be useful for future computations

of unit-area loads (that is, mass of a particular nutrient species per unit

contributing area). Concentrations of nutrients from lawns observed in this

Regular-fertilizer lawn sites

Ammonia N TKN NO2 + NO3 TP Diss P

Geometric mean 1.11 5.9 0.09 2.57 0.7

Median 1.07 5.9 0.12 2.85 0.77

Mean 2.18 8.6 0.17 4.02 0.93

Max 14.5 34 0.56 23.2 3.32

Min 0.05 1.5 0.01 0.31 0.17

n 23 23 23 58 23

Nonphosphorus-fertilizer lawn sites

Ammonia N TKN NO2 + NO3 TP Diss P

Geometric mean 1 6.5 0.14 1.89 0.34

Median 0.93 5.2 0.14 1.58 0.33

Mean 3.95 12.2 0.57 3.3 0.45

Max 36.2 55 5.22 23.5 1.29

Min 0.04 1.5 0.14 0.14 0.12

n 14 14 14 38 15

Unfertilized lawn sites

Ammonia N TKN NO2 + NO3 TP Diss P

Geometric mean 0.76 4.08 0.12 1.73 0.4

Median 0.63 5.1 0.14 1.81 0.38

Mean 1.12 5.85 0.17 2.33 0.43

Max 2.98 11 0.4 6.69 0.74

Min 0.22 0.53 0.01 0.36 0.23

n 9 9 9 19 8

Unfertilized wooded sites

Ammonia N TKN NO2 + NO3 TP Diss P

Geometric mean 2.95 12.7 0.16 3.52 1.04

Median 4.38 9.8 0.24 3.98 1.99

Mean 5.33 29.3 0.9 6.78 1.4

Max 11.6 130 2.24 30.6 2.26

Min 0.41 4.1 0.01 0.3 0.33

n 5 6 5 28 5

Don Jean Bay swale sites

Ammonia N TKN NO2 + NO3 TP Diss P

Geometric mean 3.48 14.5 0.06 2.46 0.49

Median 3.96 19 0.04 2.66 0.41

Mean 11.91 31.3 0.15 3.55 0.91

Max 88.1 160 0.6 9.07 3.33

Min 0.56 2 0.01 0.37 0.18

n 11 11 10 19 9
6

For information on this study or on other USGS programs in Wisconsin, contact:

District Chief

U.S. Geological Survey

8505 Research Way

Middleton, WI 53562

(608) 828-9901

http://wi.water.usgs.gov/ Printed on recycled paper

Author: Herbert S. Garn

Layout and illustrations: Michelle Greenwood and James Kennedy

Information

study are much greater (by 3 to 5 times) than the estimated concentrations

used to calculate total phosphorus load from surface runoff to Lauderdale

Lakes in a previous study by Garn and others (1996, p. 16). All of the

nutrient load from lawn runoff may not actually reach or be deposited in the

lake because of varying flowpaths, soil permeability, breaks in slope,

vegetative buffers, and other obstructions; however, in many cases, lawns

extend and slope continuously to the water’s edge to provide a direct source

of loading.

The annual phosphorus load from the nearshore area of Lauderdale

Lakes may be greater than the 430 pounds previously estimated. Using a

revised median concentration of 2.3 mg/L for surface runoff from an

estimated 220 acres of developed shoreline (67 percent of shoreline) within

200 feet from the edge of water, annual total phosphorus load from

residential lawns could be as much as 370 pounds (assuming all of the

phosphorus reaches the lake). If a delivery of 50 percent of the load is

assumed, and the total surface-water load is recomputed using the surface

runoff values from the previous study, the total annual surface-water load

from the nearshore drainage area would be 620 pounds, which represents

60 precent of the total annual phosphorus input from all sources. Studies at

Lauderdale Lakes and several other ongoing studies by the USGS in

Wisconsin will provide additional information on the effects of lawns and

shoreline development on nutrient loads to lakes.

Limitations of Results

• Many runoff samples (about 30 percent) overflowed the collecting

bottle and may not be truly representative of the mean concentration

from each storm. According to T.D. Stuntebeck (U.S. Geological

Survey, unpub. data, 2002), overflow samples for suspended solids and

total phosphorus had higher concentrations than those from samples

that did not overflow the container, but the opposite was true for

dissolved phosphorus. Barten and Jahnke (1997) also found that overflow samples had lower concentrations for some constituents. Overflow

occurred, however, for all categories of sites, and differences noted

could potentially be even greater.

• The number of samples for some categories was relatively small for

rigorous statistical analysis, and the small numbers could lead to

inconsistencies among comparisons for different pairs of categories.

• Nutrient-concentration data are for onsite runoff and should be used

with caution when making offsite interpretations. Not all of the nutrient

load from lawn runoff may actually enter the lake.

• Some changes in nutrient species composition affecting dissolved

constituents may have occurred in those samples that were not collected

within 2 days after a storm.

Conclusions

• A high percentage of storms resulted in surface runoff from many of the

lawns. Runoff from lawns may occur relatively frequently, more than

50 percent of the storms for many lawns.

• Fertilizer use did not affect nitrogen concentrations in runoff. Nitrite

plus nitrate concentrations in runoff were generally low.

• Total phosphorus concentration in lawn runoff was directly related to

the phosphorus concentration of lawn soils.

• Dissolved phosphorus concentrations were significantly different among

the lawn categories; the median from regular-fertilizer sites was twice

that from unfertilized or nonphosphorus-fertilizer sites.

• Runoff from lawn sites with nonphosphorus fertilizer applications had

a median total phosphorus concentration that was similar to that of

unfertilized sites, an indication that nonphosphorus fertilizer use may

be an effective, low-cost practice for reducing phosphorus in runoff.

Acknowledgments

Thanks are extended to Scott Mason of the Lauderdale Lakes Lake

Management District for his assistance in this study; to the lakeshore

homeowners that allowed us to install sampling equipment in their lawns;

and to the Wisconsin Department of Natural Resources, Lake Protection

Grant Program.

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