Otter Creek 

lfway Prairie Creek 

U.S. Department of the Interior 

U.S.� Geological Survey 

����Fact Sheet FS-221-95 

Lonsdorf 

Evaluating Barnyard Best Management Practices in Wisconsin using
 

Upstream-Downstream Monitoring
 

by Todd D. Stuntebeck 

Introduction 

The Nonpoint Source Water Pollution 

Abatement Program was created in 1978 by 

the Wisconsin Legislature. The goal of the 

program is to improve and protect the water 

quality of lakes, streams, wetlands, and 

ground water within selected priority watersheds by controlling sources of nonpoint 

pollution. For each selected watershed, the 

Wisconsin Department of Natural Resources drafts a management plan that 

guides the implementation of pollutioncontrol strategies known as Best Management Practices (BMP’s). This plan summarizes resource and land-use inventories, 

describes the results of pollution-source 

modeling, and suggests pollution reduction 

goals. The U.S. Geological Survey, through 

a cooperative effort with the Wisconsin 

Department of Natural Resources, is monitoring water-quality improvements that result from the implementation of BMP’s. 

The data collected are then compared to the 

watershed plans to assess progress and determine whether goals are being realized. 

This fact sheet describes the data-collection efforts, preliminary results, and planned 

that same source. The barnyards investigated were identified by each watershed 

plan as critical nonpoint sources based on 

herd size, lot size, proximity to the stream, 

and downslope overland flow characteristics. 

Otter Creek is within the Sheboygan 

River Priority Watershed, 15 miles west of 

Lake Michigan, in east-central Wisconsin 

(fig. 1). The drainage area of Otter Creek is 

9.2 square miles at the downstream sampling station, and land use in the watershed 

is 67 percent agricultural (Bachhuber and 

Foye, 1993). Upstream and downstream 

sampling stations, each of 

which are equipped to 

continuously monitor 

streamwater levels 

and collect discrete water 

samples, 

were installed at Otter Creek in March 

1994. Water samples are collected with a 

refrigerated water-quality sampler that is 

activated by the rise and fall of streamwater 

levels. 

Halfway Prairie Creek is within the 

Black Earth Creek Priority Watershed, 20 

miles northwest of Madison, in south-central Wisconsin (fig. 1). The drainage area of 

Halfway Prairie Creek is 16.1 square miles 

at the downstream sampling station, and 

land use in the watershed is 60 percent 

agricultural (Eagan and Morton, 1989). 

Upstream and downstream sampling stations were installed at Halfway Prairie Creek 

in April 1995. The upstream sampling station continuously monitors streamwater 

levels and precipitation and collects discrete water samples with a refrigerated 

water-quality sampler. The downstream 

station is equipped to collect water samples 

only. 

Upstream-downstream sampling 

schemes have the inherent potential for 

upstream loading sources to mask the effects of the investigated source, because 

data-analysis techniques of monitoring individual inputs are often small comprojects for pre-BMP conditions at two pared to the cumulative inputs from upbarnyards, one each on Otter Creek and 

Halfway Prairie Creek. 

Data Collection 

Two sampling stations were established 

on each stream (fig. 1). One station is upstream from a single barnyard-runoff source 

and the other station is downstream from 

91°
 

92°
 0 50 100 MILES 

90° 89° 0 50 100 KILOMETERS 

▲ 

EXPLANATION 

Sampling station 

▲ 

▲ 

stream (Spooner and others, 1985). To 

reduce the potential for this problem, 

project investigators added two enhancements to the sampling design used at Otter 

Creek in order to improve the isolation of 

0 1 2 MILES 

0 1 2 KILOMETERS 

Ha

88° 46° ▲▲ 

87° 

45° WISCONSIN 

Figure 1. Location of upstream 44° Otter Creek 

Watershed and downstream sampling stations 

for Otter Creek (above) and EXPLANATION 0 1 2 3 MILES

43° Halfway Prairie Creek (right). Halfway Prairie Creek ▲ Sampling station 

Watershed 0 1 2 3 KILOMETERS 

1 
barnyard runoff at Halfway Prairie Creek.
 

First, the water-quality samplers are acti- 21
 

vated by precipitation and are programmed 14 

to collect time-integrated samples for an 

initial period. This enhancement will be 7 

added to the Otter Creek sampling design 

for the post-BMP monitoring period. 0 

NO DATA 

BOD 

AMMONIA NITROGEN 

RUNOFF, EVENT-MEAN CONCENTRATION, IN MILLIGRAMS PER LITER

IN CFS-DAYS* 

Samples are then collected in response to 

the rise and fall of streamwater levels in a 

manner similar to that at the Otter Creek 

stations. 

Two benefits of this approach are that 

(1) it allows for sampling of barnyard runoff in the receiving stream before 

streamwater level increases can be sensed, 

thereby effectively isolating the barnyard 

runoff from nonpoint-pollution sources 

upstream, and (2) it allows sampling during 

small storms in which local inputs from the 

barnyard are apparent, but little storm runoff from the upstream areas of the watershed is observed. A second enhancement to 

the Otter Creek sampling design is that the 

upstream and downstream stations at Halfway Prairie Creek are located close enough 

together to allow a direct electronic con1.2 

0.8 

TOTAL PHOSPHORUS 

0.4 

0 

1.8 

1.2 

0.6 

RUNOFF VOLUME 

0 

60 

30 

0 

1 2 3 4 5 6 7 8 9 10 nection and, hence, the collection of concurrent samples from both water-quality 

samplers. This design allows for statistical 

comparisons between concurrent individual 

STORM NUMBER 

EXPLANATION 

*�CFS-day (cubic foot 

per second-day) is UPSTREAM STATION 

equivalent to

�86,400 cubic feet or DOWNSTREAM STATION upstream and downstream concentrations 

in water samples. �2,447 cubic meters 

Samples of streamflow were collected 

during 10 storms between April 1994 and 

June 1995 at Otter Creek, and 10 storms 

during April-June 1995 at Halfway Prairie 

Creek. Samples were analyzed for total 

phosphorus, ammonia nitrogen, biochemical oxygen demand (BOD), suspended solFigure 2. Event-mean concentrations and runoff volume for selected storms, 

Otter Creek, Wisconsin. 

ids, and fecal coliform bacteria. All are 

known to be potential indicators of nonpoint 

pollution from barnyards. 

Data collected before implementation of BMP’s indicate that at each 

site, average downstream eventmean concentrations of total 

phosphorus, ammonia nitrogen, and 

BOD were significantly greater than 

average upstream event-mean 

concentrations. 

Results 

The continuous streamflow and instantaneous water-quality data were used to 

estimate mass transport (load) during individual storms. Loads were computed for 

total phosphorus, ammonia nitrogen, and 

BOD by summing the product of instantaneous concentration and streamflow for 

each period of storm runoff (Porterfield, 

1972). Runoff volumes were computed by 

summing the streamflow rate for each period of storm runoff. Event-mean concentrations were computed by dividing the 

▲ Barnyard-runoff study site at Otter Creek. load by the runoff volume.

2 
18 

BOD 

Concurrent upstream and downstream samples collected early in 12 

6 

NO DATA
NO DATA
NO DATA


periods of storm runoff will likely 

allow improved detection of differences in concentrations, even for 

RUNOFF, EVENT-MEAN CONCENTRATION, IN MILLIGRAMS PER LITER

IN CFS-DAYS* 

0 

AMMONIA NITROGEN 

large storms. 

1.2 

0.8 

0.4 

0 

TOTAL PHOSPHORUS 

trends observed during the other eight 

storms. The most likely reason for this 

observation is that the threshold for initiation of sampling was set too high for the 

first two storms. Based on this experience, 

1.2 it was realized that the threshold could be

0.8 

0.4 

0 

30 

RUNOFF VOLUME 

set lower. If sampling is initiated sooner, 

the downstream site is more likely to capture the higher pollutant concentrations expected in the early part of the barnyard 

runoff. 

Event-mean concentrations of total 

phosphorus, ammonia nitrogen, and BOD 

15 

0 

1 2 3 4 5 6 7 8 9 10 

STORM NUMBER 

EXPLANATION 

*�CFS-day (cubic foot 

per second-day) is UPSTREAM STATION 

equivalent to

�86,400 cubic feet or DOWNSTREAM STATION

 �2,447 cubic meters 

Figure 3. Event-mean concentrations and runoff volume for selected storms, 

Halfway Prairie Creek, Wisconsin. 

downstream from the barnyard on Halfway 

Prairie Creek were also generally higher 

than those upstream (fig. 3). Average downstream event-mean concentrations of total 

phosphorus, ammonia nitrogen, and BOD 

were significantly greater than average upstream event-mean concentrations at the 

95-percent confidence level. Differences 

between upstream and downstream eventmean concentrations at Halfway Prairie 

Creek were less variable than those at Otter 

Creek. Time-integrated samples collected 

early in the storms at Halfway Prairie Creek 

In general, event-mean concentrations 

of total phosphorus, ammonia nitrogen, and 

BOD were greater at the downstream station than at the upstream station for most 

periods of storm runoff at Otter Creek (fig. 

2). Using a paired Student’s t-test, it was 

determined that for each constituent, the 

average of the differences between upstream 

and downstream event-mean concentrations 

was significantly different from zero at the 

95-percent confidence level. In other words, 

average downstream event-mean concentrations of total phosphorus, ammonia nitrogen, and BOD were significantly greater 

than average upstream event-mean concentrations. The statistically significant increases in event-mean concentrations downstream from the barnyard suggest that the 

investigated barnyard-runoff source is an 

important contributor to the concentrations 

of total phosphorus, ammonia nitrogen, and 

BOD in Otter Creek for the storms monitored. 

Upstream and downstream event-mean 

concentrations of total phosphorus, am- may have helped to isolate barnyard runoff 

monia nitrogen, and BOD during storms 1 from other upstream sources of pollution 

and 2 did not follow the same general loads. Similar runoff volumes among the 

▲ Barnyard-runoff study site at Halfway Prairie Creek. 

3 
The pollutant reductions expected 

from the BMP’s at each site are 

greater than the changes needed to 

observe a statistically significant 

improvement in water quality. 

storms and minimal seasonal changes between storms also may explain this lower 

variability. 

The difficulty in finding differences 

between upstream and downstream eventmean concentrations during large periods 

of storm runoff is apparent for storm 8 at 

Halfway Prairie Creek. Because concurrent samples were collected, however, individual concentration comparisons may highlight changes between the upstream and 

downstream differences over time. Such 

comparisons would likely focus on the beginning of the storms, when most of the 

runoff is local and from the barnyard source. 

Although discrete comparisons have not 

yet been conducted, the statistically significant increases in event-mean concentrations downstream from the barnyard suggests that the investigated barnyard-runoff 

source is an important contributor to the 

concentrations of total phosphorus, ammonia nitrogen, and BOD in Halfway Prairie 

Creek for the storms monitored. 

Planned Data Analysis 

Upon completion of monitoring during 

the post-BMP period, the U.S. Geological 

Survey and the Wisconsin Department of 

For more information contact: 

District Chief 

U.S. Geological Survey, 

Water Resources Division 

6417 Normandy Lane 

Madison, WI 53719 

Natural Resources will determine whether kept constant, minimum detectable changes 

the barnyard-runoff controls have improved for significance at the 95-percent confithe water quality in these streams. The dence level are the following: 

event-mean concentration data will be analyzed in a manner similar to that described MINIMUM DETECTABLE CHANGE 

by Spooner and others (1985) to test for Total Ammonia 

upstream and downstream differences. Creek Phosphorus Nitrogen BOD 

These differences will be computed for pre- Otter 50 50 40 

and post-BMP storms, resulting in two independent data sets. These two data sets Halfway Prairie 10 30 40 

will then be compared to determine whether 

a statistically significant decrease in the To clarify, the average downstream 

average of the differences has occurred. post-BMP event-mean concentrations of 

Analysis of the pre-BMP data revealed that total phosphorus at Otter Creek would have 

average downstream event-mean concen­ decrease by at least 50 percent for the 

trations exceeded average upstream event- change to be considered statistically sigmean concentrations before BMP’s were nificant at the 95-percent confidence level. 

implemented. If, after implementation, the These values are conservatively high bemanagement practice has reduced the down- cause variance in the downstream-upstream 

stream concentrations, a corresponding differences for average pre- and post-BMP 

decrease in the average difference between event-mean concentrations was assumed to 

upstream and downstream event-mean con- remain constant. One would expect the 

centrations for the post-BMP period would actual variance to decrease after BMP 

be expected. implementation, thus decreasing the miniUsing the Student’s t-test to find differ- mum detectable changes. As discussed earences between two independent data sets, lier, the differences in event-mean concenone can develop an equation to estimate the trations between upstream and downstream 

minimum amount of decrease in post-BMP samples for Halfway Prairie Creek were 

downstream event-mean concentrations less variable than those for Otter Creek. 

necessary to be considered statistically sig- This is reflected in lower minimum detectnificant. This “minimum detectable change” able changes. According to the watershed 

is usually expressed as a percentage. If the plans (Bachhuber and Foye, 1993; Eagan 

pre- and post-BMP sample sizes are as- and Morton, 1989), the minimum detectsumed to be equal (10 storms) and the able changes are smaller than the pollutant 

variance in the differences between up- reductions expected from BMP implemenstream and downstream concentrations is tation at each site. 

References Cited 

Bachhuber, J., and Foye, K., 1993, Nonpoint source control plan for the Sheboygan River 

Priority Watershed Project: Wisconsin Department of Natural Resources Publication 

WR-265-93 [variously paginated]. 

Eagan, L.L., and Morton, A., 1989, A plan for the control of nonpoint sources and related 

resource management in the Black Earth Creek Priority Watershed: Wisconsin Department of Natural Resources Publication WR-218-89 [variously paginated]. 

Porterfield, George, 1972, Computation of fluvial-sediment discharge: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 3, chap. C2, 66 p. 

Spooner, J., Maas, R.P., Dressing, S.A., Smolen, M.D., and Humenik, F.J., 1985, Appropriate designs for documenting water quality improvements from agricultural NPS 

control programs, in Perspectives on nonpoint source pollution: Washington, D.C., U.S. 

Environmental Protection Agency, EPA 440/5-85-001, p. 30-34. 

U.S. Department of the Interior 

U.S. Geological Survey 

Fact Sheet FS-221-95 

4