walnut creek watershed monitoring project, iowa monitoring water quality in response to prairie...

JOURNAL OF TilE AMERICAN WATER RESOURCES ASSOCIATIONVOL. 36, NO.5 AMERICAN WATER RESOURCES ASSOCIATION OCTOBER 2000

WALNUT CREEK WATERSHED MONITORING PROJECT, IOWA MONITORINGWATER QUALITY IN RESPONSE TO PRAIRIE RESTORATION'

Keith E. Schilling and Carol A. Thompson2

ABSTRACT: Land use and surface water data for nitrogen and pes-ticides (1995 to 1997) are reported for the Walnut Creek WatershedMonitoring Project, Jasper County Iowa. The Walnut Creek projectwas established in 1995 as a nonpoint source monitoring programin relation to watershed habitat restoration and agricultural man-agement changes implemented at the Neal Smith National WildlifeRefuge by the U.S. Fish and Wildlife Service. The monitoring pro-ject utilizes a paired-watershed approach (Walnut and Squawcreeks) as well as upstream/downstream comparisons on Walnutfor analysis and tracking of trends. From 1992 to 1997, 13.4 per-cent of the watershed was converted from row crop to native prairiein the Walnut Creek watershed. Including another 6 percent ofwatershed farmed on a cash-rent basis, land use changes have beenimplemented on 19.4 percent of the watershed by the USFWS.Nitrogen and pesticide applications were reduced an estimated 18percent and 28 percent in the watershed from land use changes.

Atrazine was detected most often in surface water with frequen-cies of detection ranging from 76-86 percent. No significant differ-ences were noted in atrazine concentrations between Walnut andSquaw Creek. Nitrate-N concentrations measured in both water-sheds were similar; both basins showed a similar pattern of detec-tion and an overall reduction in nitrate-N concentrations fromupstream to downstream monitoring sites. Water quality improve-ments are suggested by nitrate-N and chloride ratios less than onein the Walnut Creek watershed and low nitrate-N concentrationsmeasured in the subbasin of Walnut Creek containing the greatestamount of land use changes. Atrazine and nitrate-N concentrationsfrom the lower portion of the Walnut Creek watershed (includingthe prairie restoration area) may be decreasing in relation to theupstream untreated component of the watershed. The frequenciesof pesticide detections and mean nitrate-N concentrations appearrelated to the percentage of row crop in the basins and subbasins.

Although some results are encouraging, definitive water qualityimprovements have not been observed during the first three yearsof monitoring. Possible reasons include: (1) more time is needed toadequately detect changes; (2) the size of the watershed is too largeto detect improvements; (3) land use changes are not located in thearea of the watershed where they would have greatest effect; or(4) water quality improvements have occurred but have beenmissed by the project monitoring design. Longer-term monitoring

will allow better evaluation of the impact of restoration activitieson water quality.(KEY TERMS: watershed restoration; nonpoint source pollution;water quality; nitrate, atrazine.)

INTRODUCTION

Nonpoint Source Pollution (NPS) is a major causeof impairment to water quality in the United States.In an agricultural state such as Iowa this is particu-larly true. Of Iowa's 35.8 million acres, 27.2 millionacres (76 percent) are in row crop, most of whichreceive chemical treatments (Iowa AgriculturalStatistics, 1997). Recent assessments show that agri-cultural land use is the source of diffuse, NPS pollu-tion affecting approximately 96 percent of Iowa'sstream miles and the majority of lakes and wetlands(Agena et al., 1991). Of particular concern has beenwater quality degradation from nitrogen and pesti-cides.

Numerous programs employing a variety of bestmanagement practices (BMPs) have been implement-ed in Iowa to mitigate NPS pollution from agriculture.However, monitoring NPS water-quality improve-ments is not an easy task. Pollution results fromrunoff across a landscape which has varied land-management practices, with the resultant impactsmeasured in perennial streams typically a m:ix ofeffects from many different parcels of land, many dif-ferent components of management, integrated overmany time scales. It has been difficult to documentthe relationship between improvements in water

'Paper No. 99045 of the Journal of the American Water Resources Association. Discussions are open until June 1, 2001.2Respectively, Research Geologist, Iowa Department of Natural Resources, Geological Survey Bureau, 109 Trowbridge Hall, Iowa City,

Iowa 52242-1319; and Assistant Professor, Tarleton State University, Box T-0390, Stephenville, Texas 76402 (E-MailiSchilling:kschilhingigsb.uiowa.edu).

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 1101 JAWRA

Schilling and Thompson

quality and changes in management practices on awatershed scale. Many projects implemented undersection 319 of the Clean Water Act have had little orno monitoring associated with them. Benefits areoften calculated on the basis of models utilizing datacollected on small-scale field studies or from general-ized watershed models. Other watershed studieswhich have had adequate monitoring have been lessthan successful at demonstrating an improvement(Hallberg et al., 1983; Libra et al., 1991; Rowden etal., 1995; Seigley et al., 1994, 1996; Gale et al., 1993;USEPA, 1990). Thus the question remains, have thechanges made in these watershed projects on thelandscape been incomplete and/or not enough to showan effect, or do water-quality responses to land usechanges occur over very long time periods?

The Walnut Creek Watershed Monitoring Projectwas established in 1995 as a NPS monitoring pro-gram in conjunction with watershed habitat restora-tion and agricultural management changesimplemented by the Neal Smith National WildlifeRefuge and Prairie Learning Center (Refuge) inJasper County Iowa (Figure 1). A portion of the Wal-nut Creek watershed is being restored to nativeprairie and/or savanna; riparian zones and wetlandswill be restored in context, with riparian zones grad-ing from prairie waterways, to savanna, to timberedstream borders (Drobney, 1994). Although it is notexpected that large-scale prairie restoration will everbe used as an NPS management practice, the magni-tude of the land use changes within Walnut Creek islarge compared to other watershed projects. This mayallow a baseline to be established against which to setexpectations for other projects and allow assessmentof the amount of non-agricultural land that might beneeded to reach a given water quality objective. Inaddition, for the Refuge-owned lands remaining inrow-crop production during the restoration period,improved agricultural management practices aremandatory, altering chemical inputs and ensuringsoil-conservation compliance to the entire Refuge-controlled area. Because the restoration work andthese improved management measures are imple-mented under U.S. Fish and Wildlife Service(USFWS) control they are implemented much moreuniformly than in many other projects, both in timeand spatially across the watershed. Hence, they willconstitute an important demonstration of the water-quality accomplishments that can be compared toother NPS projects.

The monitoring project utilizes a paired-watershedas well as upstream/downstream comparisons foranalysis and tracking of trends. The Walnut Creekwatershed is paired with Squaw Creek watershed,which shares a common basin divide with WalnutCreek, to minimize precipitation variation. Land

restoration activities began in the Walnut Creekwatershed in 1992, and by 1993, full scale restorationand improved agricultural management was beingimplemented on Refuge-owned lands. Monitoring inthe Walnut Creek and Squaw Creek watershedsbegan on a limited basis in 1994 and full-scale moni-toring commenced in 1995. Data from the first threeyears of land use and surface water monitoring fornitrogen and pesticides (1995 to 1997) are presentedin this paper; additional data regarding other moni-toring components can be found in Schilling andThompson (1999).

WATERSHED CHARACTER:[STICS

Walnut and Squaw Creeks are warm-waterstreams located in Jasper County, Iowa (Figure 1).Walnut Creek drains 30.7 mi2 (19,500 acres) and dis-charges into the Des Moines River at the upper end ofthe Red Rock Reservoir. Only the upper part of thewatershed (12, 890 acres) is included in the monitor-ing project because of possible backwater effects fromthe reservoir. The Squaw Creek basin, adjacent toWalnut Creek, drains 25.2 mi2 (16,130 acres) aboveits junction with the Skunk River. The watershedincluded in the monitoring project is :L8.3 mi2 (11,714acres) and does not include the wide floodplain areanear the intersection with the Skunk River. Basincharacteristics of the Walnut and Squaw Creek water-sheds are very similar and make theni well suited fora paired watershed design (Table 1). Both watershedsare located on the Southern Iowa Drift Plain, a pre-Illinoian glacial landscape characterized by steeplyrolling hills and well developed drainage (Prior, 1991).

Three pre-project water quality studies were com-pleted at Walnut Creek from 1991 to 1994 (Schillingand Thompson, 1999). Nitrate-N concentrations in themain stem of Walnut Creek ranged from 2.3 to 20mg/L (n = 48; mean = 9.14 mg/L; sd = 4.03). Atrazineconcentration ranged from < 0.1 to 2.7 ug/L in WalnutCreek and was slightly higher in the tributaries (upto 3.1 ug/L). These concentrations are typical forsmall streams in Iowa.

METHODS

Land use practices for both Walnut and SquawCreeks have been tracked on a yearly basis through-out the life of the project. Land cover data from bothwatersheds was compiled using a combination of platmaps, NRCS crop data, aerial photographs and fieldsurveys. USFWS personnel have tracked prairie

JAWRA 1102 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION

Walnut Creek Watershed Monitoring Project, Iowa: Monitoring Water Quality in Response to Prairie Restoration

A Water Quality Monitoring Siteo USGS Gauge• Biomonitoring Sitee Wells

,'\/ Refuge BoundaryBasin

/\,/ StreamsSubbasin

3 4 Miles

planting areas and locations of rental ground in theWalnut Creek watershed. Historical land use in thewatersheds (pre-restoration) was compiled from1:24,000 scale color-infrared aerial photographs takenin 1992. Data was entered into a Geographic Informa-tion System (GIS) using ArcView and coupled with

the water quality, flow, and sediment data for analy-sis. USGS gaging stations are located at the bottom ofeach watershed and an additional gage is located atthe upper end of the Walnut Creek watershed wherethe majority of refuge land begins. Surface-waterchemistry is monitored weekly to monthly at ten sites

SQW2

Squaw CreekWatershed

Watershed

0 1 2

Figure 1. Location Map of Walnut and Squaw Creek Watersheds.


Schilhing and Thompson

TABLE 1. Basin Characteristics of Walnut and Squaw Creek Watersheds.

Basin Characteristics Walnut Creek Squaw Creek

Total Drainage Area (sq mi) 20. 142 18.305

Total Drainage Area (acres) 12,890 11,714

Slope Class:

A (0-2%) 19.9 19.7

B (2-5%) 26.2 26.7

C (5-9%) 24.4 25.0

D (9-14%) 24.5 22.2

E (14-18%) 5.0 6.5

Basin Length (mi) 7.772 6.667

Basin Perimeter (mi) 23.342 19.947

Average Basin Slope (ft/mi) 10.963 10.981

Basin Relief(ft) 168 19].

Relative Relief (ft/mi) 7.197 9.575

Main Channel Length (mi) 9.082 7.605

Total Stream Length (mi) 26.479 26.1:11

Main Channel Slope (ft/mi) 11.304 12.623

Main Channel Sinuosity Ratio 1.169 1.141

Stream Density (mi/sq mi) 1.3 15 1.426

Number of First Order Streams (FOS) 12 13

Drainage Frequency (FOS/sq mi) 0.596 0.7 10

in the Walnut and Squaw Creek basins and analyzedfor nitrate, ammonium-nitrogen, pesticides (in sea-son), anions, cations, BOD, DO, turbidity, alkalinity,fecal coliform, conductivity, and temperature (Thomp-son et al., 1995). Sampling stations located in Walnutand Squaw Creek basins are shown on Figure 1.Table 2 shows the current sampling scheme for waterquality parameters. Temperature, conductivity, DO,and alkalinity are measured in the field; all otheranalyses are performed by The University of IowaHygienic Laboratory (UIIL) using standard methodsand an EPA-approved QA/QC plan. Statistical com-parisons between data sets (t-tests, regression analy-ses) were performed using a statistical softwarepackage (SPSS 8.0 program).

Land Use Tracking

RESULTS

In 1992, prior to land restoration activities, landuse in the Walnut Creek watershed consisted of 69percent row crop and 27 percent grass (Schilling andThompson, 1999). These values were similar to rowcrop and grass percentages measured in Squaw Creek(71 percent and 27 percent, respectively). Headwater

areas in both basins (areas upstream of WNT1 andSQW1 sampling points) continue to be the most heav-ily row cropped areas of the basins (greater than 80percent).

From 1992 to 1997, 1,729 acres or 13.4 percent ofthe watershed (approximately 288 acres/year), wereconverted from row crop to native prairie in the Wal-nut Creek watershed (Figure 2). Land currentlyowned by the USFWS but still farmed is rented toarea farmers on a cash-rent basis. Nearly all of theland restored to native prairie from 1992 to 1997 wasderived from USFWS ground previously in row crop.In 1997, 773 acres or 6 percent of the watershed wasfarmed on a cash-rent basis. Refuge-owned croplandis managed by annual crop rotation of corn and beans.No-till production methods are mandatory whereasother management methods are mo:re prescriptive,including soil conservation practices, nutrient man-agement through soil testing, yield goals, and nutri-ent credit records. All chemicals and application ratesare approved prior to application to minimize adverseimpacts on non-target plants and an:imals. In accor-dance with the Cropland Management Plan for therefuge (USFWS, 1993): (1) no fall application of fertil-izer is allowed; (2) a maximum of 100 pounds of nitro-gen per acre is allowed on conventional rotation cornacres; and (3) no pre-emergent herbicide is allowed(this includes common Iowa herbicides, atrazine,

JAWRA 1104 JOURNAL OF THE AMERICAN WATER RESOuRCES ASSOCIATION


TABLE 2. Summary of Sampling Locations, Parameters, and Frequency.

Sampling Location Parameters Frequency

WNT1, WNT2, SQW2 Stage/Discharge, Suspended Sediment Daily

WNT1, WNT2, WNT3, WNT5, WNT6,SQW1, SQW2, SQW3, SQW4, SQW5

Fecal Coliform, Ammonia-Nitrogen, BOD, Anions,Temperature, Conductivity, Dissolved Oxygen,Turbidity, Alkalinity, pH

April (2), May(4),June(4), July(2),August(2), September(2)

Cations May, September

Common Herbicides April, May (4), June (4),July, August, September

Acid Herbicides, Insecticides May, June

WNT1, WNT2, SQW1, SQW2 Fecal coliform, Ammonia-nitrogen, BOD, Anions,Temperature, Conductivity, Dissolved Oxygen, Turbidity,Alkalinity, pH,

January, March, July,August, September,October, November

Rain Gage Station Pesticides Precipitation Events

Groundwater Stations Water LevelsTemperature, Conductivity, Alkalinity, pHPesticides, AnionsCations

DailyQuarterlyQuarterlyBi-annually

Biomonitoring Stations Biomonitoring Bimonthly (April-October)

Note: Number of samples collected per month indicated under frequency column.

cyanazine, metolachlor, alachior, metribuzin, and ace-tochior). This mandate resulted in the complete elim-ination of pre-emergent pesticide use on refuge landsby 1993.

Combining the prairie planting areas and restrict-ed application areas, land use changes have beenimplemented on 19.4 percent of the Walnut Creekwatershed above the WNT2 gaging station. Theremainder of USFWS land in the watershed consistsof areas that have remained unchanged since refugeactivities began in 1992. These lands consist of main-ly grass or woods and comprise another 14.3 percentof the watershed. All told, the USFWS controls 4,343acres, or 33.7 percent, of the Walnut Creek watershedabove the WNT2 gaging station.

In the monitored subbasins, a large percentage ofthe restored prairie is located in the WNT5 subbasin(23.2 percent). Prairie plantings account for much lessland in the other subbasins (16.4 percent in WNT3and 7.2 percent in WNT6). A large percentage of landin the WNT6 subbasin consists of USFWS farmground with application restrictions (32.6 percent).Less USFWS cropland is located in the WNT5 sub-basin (9.2 percent) and none is located in the WNT3subbasin (Figure 2).

Nitrogen Reductions

Estimating reductions in nitrogen appl:icationsfrom land use changes first requires that baselineconditions be established. Using a simplifyingassumption that nitrogen is applied only to corn fieldsand not soybean fields, land use data were used toestimate the typical percentage of row crop areasunder corn rotation in the Prairie City area. In 1992,prior to restoration, 68.7 percent of the watershed, or8,856 acres, was in row crop. Land cover data from1995 to 1997 in the Squaw Creek watershed (typicalof highly agricultural areas in the region) show that,in any given year, corn was the predominant row cropapproximately 57 percent of the time (Schilling andThompson, 1999). Applying this typical percentage tothe 1992 Walnut Creek row crop area suggests thatabout 5,048 acres of the watershed were in corn rota-tion before the refuge was established. Typical nitro-gen application in the farmland around Prairie City isabout 150 lbs/acre, although this can range from 100to 200 lbs/acre based on site-specific factors (source:local coop dealer in Prairie City area). Applying anaverage estimate of 150 lbs/acre over the watershedunder corn rotation suggests that about 757,198 lbs ofnitrogen was normally applied to the Walnut Creek


—IIIIftft

Figure 2. Summary of Annual Prairie Plantings and Cash Rent Areas.

watershed before restoration activities began (Table3).

Considering that the USFWS placed the followingrestrictions on refuge-owned land: (1) corn and beansmust be rotated on an annual basis (indicating thatthe percentage of corn in rotation is 50 percent in anygiven year), and (2) use of nitrogen on refuge-ownedcrop land is restricted to 100 lbs/acre; nitrogen usewas reduced, on average, 50 lbs/acre for each acre ofrefuge land under corn production. Therefore, in1992, following USFWS acquisition of the refugelands, nitrogen application was immediately reducedto 664,027 lbs, or by 12.3 percent in the watershed.With removal of additional lands from row crop pro-duction, each successive year reduced nitrogen loadsby another 1.0 to 3.4 percent (Table 3). From 1992 to1997, the load of applied nitrogen was reduced fromthe baseline condition before 1992 (757,198 ibs) to581,918 lbs in 1997 (76.9 percent of the baseline).

Basin

Refuge Boundary

Farm Rental Unit

1997 Farm Rental Unit

1997 Plantings

1996 Plantings

1995 Plantings

1994 Plantings

1993 Plantings

This represented an 18.1 percent reduction of nitro-gen in the watershed over the six-year period (Table3).

Pesticide Reductions

Pesticide use on refuge-owned lands was drastical-ly curtailed in 1993 (USFWS, 1993). Because pesti-cides detected in the Walnut Creek watershed areassociated with controlling weeds and grasses undercorn rotation, pesticide load reductions can be esti-mated based on the amount of corn acres in therefuge. From previous discussion, 2,502 acres ofrefuge land was in row crop in 1992 before restorationactivities began. This translates to approximately1,425 acres of corn on refuge-owned lands (2,502 rowcrop acres multiplied by 57 percent corn). Based onthe ratio of corn acres in the refuge compared to the



Subbasin WNT3

Subbasin WNT

0 2 miles


TABLE 3. Estimated Nitrogen Application Reductions in the Walnut Creek Watershed.

Applied Nitrogen Data 1992 1993 1994 1995 1996 1997

Baseline Condition - AnnualApplied N of 757,198 1,514,396 2,271,594 3,028,792 3,785,990 4,543,188757,198 lbs per year (no prairie restoration)

Annual Applied N (ibs) (see text) 664,027 649,502 623,882 603,435 596,009 581,918

Total Applied N (ibs) 664,027 1,313,529 1,937,411 2,540,846 3,136,855 3,718,773

Annual Applied N/Baseline (in percent) 87.7 85.8 82.4 79.7 78.7 76.9

Total Reduction of Applied N Compared to 12.3 13.3 14.7 16.1 17.1 18.1Baseline (in percent)

TABLE 4. Summary of Pesticides Most Commonly Detected in Walnut and Squaw Creek Surface Water, 1995 to 1997.

Atrazine Cyanazine Acetochlor DeethylatrazineDetection Median Detection Median Detection Median Detection Median

Sample Frequency Conc. Frequency Conc. Frequency Conc. Frequency Conc.Site (percent) (ugh) (percent) (ugh) (percent) (ugfl) (percent) (ugfl)

WNT1 82.7 0.28 55.2 0.17 10.3 0.54 61.3 0.14WNT2 75.9 0.31 44.8 0.30 24.1 0.16 59.3 0.14WNT3 72.7 0.20 31.8 0.14 4.5 0.30 52.3 0.11

WNT5 77.3 0.29 27.3 0.15 13.6 0.24 57.1 0.11

WNT6 81.8 0.25 54.6 0.18 18.2 0.26 61.9 0.:L7

SQW1 85.7 0.35 38.1 0.21 40.0 0.17 71.4 0.:[7

SQW2 80.0 0.32 44.8 0.18 24.1 0.23 60.7 0.12

SQW3 85.0 0.32 60.0 0.16 15.0 0.23 50.0 0:13

SQW4 50.0 0.27 15.0 0.27 20.0 0.28 0.0 —

SQW5 80.0 0.21 50.0 0.26 50.0 0.32 15.0 0.12

corn acreage in the watershed (5,048 acres), pesticideapplication in the Walnut Creek watershed wasreduced by 28 percent in 1993 following implementa-tion of the Cropland Management Plan.

Surface Water Monitoring Results

Pesticides. Six different compounds and twodegradation products were detected between 1994and 1997 in Walnut and Squaw Creek surface waters.Atrazine was by far the most frequently detected com-pound, as is true across Iowa, with the frequency ofdetection ranging between 76 percent to 86 percent inthe main channels (Table 4). Concentrations rangedbetween < 0.1 to 3.4 ugh at Walnut Creek and < 0.1 to5.2 ugh at Squaw Creek, with median concentrationsat the downstream stations nearly equal (0.31 ugh vs.0.32 ugh, respectively).

For statistical analyses of atrazine concentrationand load data, concentrations reported as < 0.1 mg/Iwere considered to be one-half the detection limit (0.5ug/l). Atrazine data were highly skewed and required

log transformation before t-tests or regression analy-ses were conducted. T-tests found no significant differ-ence between the means of atrazine concentrationsand loads in the two watersheds (p = 0.85 and p =0.29, respectively). A comparison of atrazine loads atthe Walnut Creek upstream and downstream gagessuggests a possible reduction in atrazine loadsbetween the upstream basin sampled at WNT1 andthe remainder of the basin (subtracting the contribu-tion of the upstream basin). Regression analysis ofatrazine loads over time were not found to be statisti-cally significant at the p = 0.05 level. However, thecalculated p-value of 0.17 suggests that a gradualdecrease in atrazine loads may be occurring, but thereis insufficient data to adequately substantiate orquantify the change. Subsequent data added to theexisting data set may reveal the same trend at highersignificance. Overall, the high degree of variability inatrazine concentrations as well as the number ofobservations below the measurable detection limit (27percent of atrazine observations) will make detectingchanges in atrazine difficult over the course of theproject.



In the subbasins, lowest peak and median atrazineconcentrations were found in a small watershed inthe Squaw Creek basin (SQW4) that historically hasbeen less intensely row-cropped than other basins. Inthe subbasin containing most of the prairie refuge(WNT5), concentrations of atrazine continue to bedetected at levels typical of the entire basin (WNT2).

After atrazine, cyanazine was the most frequentlydetected pesticide with median concentrations gener-ally less than 0.3 ugfl (Table 4). Detection frequenciesof cyanazine were the same for both downstreammain stem sites (45 percent) and ranged between 15percent at SQW4 to 55 percent at WNT1 in the sub-basins. Both degradation products of atrazine werefound with desethylatrazine (DEA) more commonlydetected than deisopropylatrazine (DIA). Concentra-tions for both degradation products were generallybelow 0.2 ugh. Acetochlor was detected at approxi-mately the same frequency in both basins with medi-an concentrations from 0.16-0.54 ugh (Table 4).Metolachlor was. detected only once in the SquawCreek basin and detected six times in the WalnutCreek basin.

The detection frequencies of the three most com-monly detected pesticides, atrazine, cyanazine, andacetochlor (these were the only pesticides detected atall sampling sites) appear to relate differently to theamount of row crop present in the combined Walnutor Squaw Creek basins and subbasins (Figure 3).This is likely related to their use and applicationrates in either watershed. Atrazine exhibits thestrongest relationship Cr2 = 0.672; p =0.004) and isalso the pesticide used most consistently, spatiallyand temporally, in the area (Schilling and Thompson,1999). Application rates for atrazine have alsoremained stable over the last five years between 0.5and 1.0 lbs per acre. More scatter is evident in thecyanazine data Cr2 = 0.396; p =0.051) although thebest fit line follows the same general trend asatrazine. Although cyanazine use is relativelywidespread in the area, its use has been declining thelast five years and typical application rates have beenreduced by half (4.5 to 2.2 lbs/acre) (source: local coopdealer in Prairie City area). The similar slopes foratrazine and cyanazine are noteworthy and suggestthat cyanazine use may have been more widespreadin the past (similar to atrazine). Perhaps the variabil-ity in the data may be reflective of its declining useand application rate on a differential basis in thewatersheds. There is poor correlation between fre-quency of detection of acetochlor and percent row crop(r2 = 0.007; p =0.821) (Figure 3). Although acetochloruse is increasing in the area, typical application ratesfor acetochlor vary considerably based on formulation(from 2.3 pints to 2.7 quarts per acre). Differential

use, combined with various application rates, mayhave produced more variability in the data.

Figure 3. Relationship Between the Frequency of PesticideDetections and the Percentage of Row Crop in Walnut

and Squaw Creek Basins and Subbasins.

Nitrogen. Nitrate-N concentrations measured inboth Walnut and Squaw Creek watersheds are similar(Table 5). Annual mean nitrate-N concentrationsranged between 7.8 to 8.3 mg/i at the downstreamWalnut Creek station (WNT2) and 8.1 to 8.5 mg/i atthe downstream Squaw Creek stations (SQW2). At-test found no significant difference between themeans of the two data sets (p = 0.51). Both basinsshow a similar temporal pattern of d.etection and anoverall reduction in nitrate-N concentrations fromupstream to downstream monitoring station (Figure4). Higher concentrations are noted in the spring andearly summer months coinciding with periods ofapplication, greater precipitation and higher streamflows.

Decrease in nitrogen concentrations betweenupstream and downstream stations observed in bothwatersheds can be caused by biological uptake, deni-trification, or dilution by water lower in nitrogen.Ratios of upstream to downstream samples for chlo-ride and nitrate-N can be used to clarify which ofthese processes contribute to concentration differ-ences. Ratios of one indicate no in-st:ream change inconcentration between upstream and downstreamstations, whereas ratios greater or less than one indi-cates additional inputs or reductions. In both Walnutand Squaw Creeks, nitrate-N ratios are less than one,suggesting in-stream reductions caused by denitrifica-tion and biological processes (Figure 5). However, inWalnut Creek, chloride ratios are also less than one,suggesting that inputs of both nitrate-N and chloride


100

80-C00

60

0. 4.

ca)

20

0

• Atrazine, r2=O.672• Cyanazine, ?=o,396a Acetochior, r2=0007

S

U U• .e

• aa

I I I I I I I I —

0 10 20 30 40 50 60 70 80 90 100

Percent Row Crop in Basin


are reduced in this watershed. Reduced chlorideinputs may be associated with decreased use of potas-sium chloride (KC1) fertilizer in the watershed or pos-sibly dilution from other water sources (surface wateror groundwater) with low chloride concentrations.

SampleLocation

WaterYear n

RangeN03-N(mgIL)

MeanN03-N(mgfL)

WNT1 199519961997

91520

2.3-15.04.1-15.85.3-16.0

9.510.611.4

WNT2 199519961997

91520

1.8-12.02.1-13.02.5-13.0

7.87.88.3

WNT3 199519961997

41114

2.9-12.04.5-15.06. 1-15.0

8.611.511.9

WNT5 199519961997

41114

0.6-12.03.8-15.02.5-14.0

8.010.710.4

WNT6 199519961997

41114

1.0-6.30.5-9.70.5-13.0

3.36.06.6

SQW1 199519961997

21419

13.0-14.06.8-17.07.9-19.0

13.512.612.4

SWQ2 199519961997

91519

2.1-12.03.9-12.92.2-13.0

8.18.58.1

SQW3 199519961997

21113

10.0-10.05.7-13.15.6-15.0

10.010.211.0

SQW4 199519961997

21114

1.8-3.00.55-4.50.56-3.0

2.42.72.0

SQW5 199519961997

21114

7.6-7.73,6-11.03,6-12.0

7.77.88.2

Comparison of upstream andWalnut Creek basin suggestsnitrate-N concentrations may be occurringthe upstream subbasin sampled at WNT1remainder of the basin. A linear regression of the dif-ference in concentrations between WNT1 and WNT2(i.e., WNT1-WNT2) over time indicates a statisticallysignificant increase (p = 0.04). If this divergence were

simply due to increasing concentrations at WNT1, anincreasing trend would be expected at the down-stream site. However, regression analysis of theWNT2 nitrate concentrations over time was not sig-nificant (p = 0.83). Increasing divergence suggeststhat nitrate-N concentrations in the lower portion ofthe watershed are not changing in the same manneras the area above WNT1, possibly a result of land usechanges occurring in the core of the watershed. Therelationship between headwater areas and theremainder of the watershed bears further scrutiny asit has implications for determining the sources ofnitrate-N and choosing areas for implementation ofBMPs.

Some differences in nitrate-N concentrations areobserved among the subbasins (Table 5). Highestnitrate-N concentrations are measured in the head-waters of both watersheds with yearly means rangingbetween 9.5-11.4 mg/i at WNT1 and 12.4-13.5 mg/i atSQW1. Both of these headwater areas have a highpercentage of row crop, with the SQW1 basin slightlyhigher (82.6 percent) than WNT1 (76.2 percent) overthe last three years. Mean nitrate-N concentrationshave increased at WNT1 since 1995, which may beassociated with an increasing percentage of landunder corn rotation observed in the subbasin. Lowestnitrate-N concentrations in either basin are observedat SQW4 which is the smallest basin monitored andhas the lowest percentage of land in row crop (averageof 27.7 percent between 1995-1997). On the otherhand, even though the smallest watershed monitoredin the Walnut Creek basin (WNT6) also has the low-est nitrate-N concentrations, it has the highest per-centage of row crop (83.5 percent). Lower nitrate-Nconcentrations in the WNT6 basin may beattributable, in part, to the high percentage of landunder USFWS management either through prairierestoration (7.2 percent) or cooperative farm arrange-ment (32.6 percent). In 1997, approximately 63 per-cent of the corn acres in the WNT6 basin we:re beingfarmed by cash-rent farmers using, a minimum, one-third less nitrogen than other area farmers. WalnutCreek subbasin WNT5 has shown little or no reduc-tion in nitrate-N concentration to date, even though23.2 percent of the land in the subbasin has been con-verted from row crop to prairie. This amount of con-version represents 32 percent of the pre-refuge (1992)row crop acres.

Mean nitrate-N concentrations are lower in theWalnut and Squaw creek basins and subbasins withless row crop (p = 0.011; Figure 6). Concentration datafrom the WNT6 subbasin were not included in thetrend analysis (Figure 6). Although this subbasin ishighly row-cropped (84 percent), 63 percent of the rowcrop acres are owned by the USFWS where reductionin nitrogen application rates has been mandatory.


TABLE 5. Summary of Nitrate-N Concentrations in Walnut andSquaw Creek Surface Water, 1995 to 1997.

downstream data forthat a reduction in

betweenand the

-J

0

-J

C0

18


Figure 4. Nitrate-N Concentrations at Upstream and DownstreamSampling Sites in Walnut and Squaw Creeks.

Reduced nitrogen loadings in the subbasin may havecontributed to lower nitrate concentrations measuredin surface water. Because nitrate is typically found as

a result of baseflow or tile discharge to surface water,two other baseflow constituents are included inFigure 6 for comparison (data from Schilling and

16

14

12

10

8

6

4

2

0

18

16

14

12

10

8

6

4

2

0

Water Year


35

30


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0C/)

C',

0(0

0)C,)

0000Ce

Figure 6. Relationship Between Mean Nitrate-N Concentrationsand the Percentage of Row Crop in Walnut and Squaw Creek

Basins and Subbasins. Data from subbasin WNT6not used for correlation coefficients (see text).


2

0

—1

Squaw Creek

iJNO3-N

—-- CIliii I I II II II III I

J FMAMJ J ASONDJ FMAMJ J ASONDJ FMAMJ J ASOND1994 1995 1996

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Figure 5. Ratios of upstream to Downstream Samples for Nitrate-Nand Chloride in Walnut and Squaw Creeks.

E25'020

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150o 10C0) 5.

0

• Nitrate-N, r=O.6892• Chloride, r2=O.3297 aa Sullate, r2=0.0047

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•WNT6S.

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0 10 20 30 40 50 60 70 80 90Percent Row Crop

100

Thompson, 1999). Chloride exhibits a similar, but lesssignificant (p = 0.090), trend as nitrate-N, possiblyreflecting both agricultural and non-agriculturalsources. Sulfate is a baseflow component with fewagricultural sources and does not exhibit any correla-tion with row crop percentage.

DISCUSSION

The Walnut Creek Watershed Monitoring Projectwas initiated in 1995 with the expectation that con-version of row crop to native prairie and improvedcropland management would result in measurableimprovements in surface water quality. Haveimprovements been observed during the first threeyears of full-scale monitoring (1995-1997)? At this


point in the monitoring program, the answer is proba-bly no, although some preliminary trends haveemerged that are encouraging and bear furtherscrutiny. If the answer is no, then why haven't waterquality improvements been observed thus far? Possi-ble explanations include: (1) improvements are occur-ring but more time is needed to adequately detectchanges; (2) the size of the watershed is too large todetect changes; (3) land use changes are not located inthe area of the watershed where they would havegreatest effect; or (4) water quality improvementshave occurred but have been missed by the projectmonitoring design.

Are Improvements Only a Matter of Ti me?

Are there indications of change in the WalnutCreek watershed that suggest that it is only a matterof time before water quality improvements are fullyrealized? Monitoring data from 1995-1997 suggestthat changes in land use and nutrient loading may bebeginning to improve water quality in the WalnutCreek watershed. Although atrazine loads have notvaried between paired basins, loads may be startingto decrease in the lower portion of the Walnut Creekwatershed (including the prairie restoration area)compared to the upstream untreated area of thewatershed (above WNT1 gage). However, without anupstream gaging station on Squaw Creek, it is notpossible to verify whether this trend is truly a func-tion of restoration activities in Walnut Creek orwhether this trend is also found in the control water-shed.

Indications of change also appear evident innitrate-N data. Similar to atrazine, nitrate-N concen-trations from the headwater areas above WNT1appear to be increasing relative to the downstreamareas (WNT2). This suggests that prairie restorationand cropland management activities may be servingto decrease nitrate-N concentrations in the lower por-tion of the Walnut Creek watershed. Ratios of nitrate-N and chloride at upstream/downstream samplingpoints on Walnut Creek are both less than one. Doesthis indicate less agricultural input in Walnut Creekthan Squaw Creek, or is it related to in-stream bio-processing and dilution from other sources? In thesubbasins, evidence from WNT6 suggests that landuse changes may be improving water quality. In thishighly row-cropped subbasin, low nitrate concentra-tions in surface water may be attributable, in part, tothe high percentage of land under USFWS control(nearly 40 percent).

Does Watershed Size Matter?

Atrazine and nitrate-N loads are not differentbetween the downstream sampling points in thetreatment (Walnut) and control (Squaw) watersheds.Because these downstream monitoring sites integratemuch larger areas of the landscape and do not isolateareas of change, is the watershed too large forimprovements to be detected in a short timeframe?Even though land use changes have been made in19.4 percent of the Walnut Creek watershed (includ-ing row crop conversions and farm unit management)and atrazine and nitrogen loads were reduced by 28percent and 18 percent, respectively, does the factthat over 80 percent of the land remains unchangeddilute the improvements on a watershed scale? Per-haps incremental improvements in water qualityresulting from land use changes in large basins areobscured by normal land use practices and other cli-matic factors.

Data from pesticide detection frequencies (Figure3) and mean nitrate-N concentrations (Figure 6) sug-gest that water quality improvements are more relat-ed to the percentage of row crop in the watershedthan to watershed size. These relationships suggestthat reducing the amount of row crop in the WalnutCreek watershed should result in a decrease in pesti-cide detection frequencies and mean nitrate-Nconcentrations in surface water. For example, therelationship for atrazine (Figure 3) suggests thatreducing the percentage of row crop in the watershedby another ten percent would reduce atrazine detec-tion frequencies by approximately five percent. How-ever, reducing row crop percentages another tenpercent in the Walnut Creek watershed would requireconversion of nearly 1,300 acres of row crop to prairie.Given a smaller watershed that exhibits this relation-ship, fewer acres of row crop conversion may berequired to achieve water quality improvements.This may explain why the small subbasin WNT6shows evidence of reduced nitrate-N concentrationswhereas the larger Walnut Creek wate:rshed does not.

Where Are Land Use Changes Occurring?

Should water quality improvements be expectedwhen land use changes occur in the core of the water-shed rather than headwater areas? Currently, nearlyall of the patchwork assemblage of prairie restorationand land management controls are located in the coreof the watershed near the Walnut Creek channel andtributaries rather than in the headwater areas of thebasins and various subbasins. Headwater areas inboth Walnut and Squaw Creek basins are more highly



row cropped than the remainder of the watersheds,averaging more than 80 percent in 1997. Headwaterareas are also more heavily tiled compared to the restof the watershed, and pesticides and nitrogen are stillbeing applied at normal rates in these areas. Consid-ering that atrazine and nitrogen applications werereduced in the Walnut Creek watershed by 28 percentand 18 percent, respectively, there remain no differ-ences in loads between the treatment and controlwatersheds. Is this due to the contribution of headwa-ter areas to the main channel? In the only locationwhere headwater effects can be accounted for(WNT1), the headwater area of Walnut Creekaccounts for a significant percentage of the load ofatrazine and nitrate in the channel. On a per acrebasis, the percentage of total nitrate-N load from theheadwater area above WNT1 has ranged from 40 tomore than 60 percent (Schilling and Thompson,1999). Mean nitrate-N concentrations at both WNT1and SQW1 are higher than in the remainder of thewatersheds and even appear to be increasing atWNT1. Headwater influences may also explain whythe subbasin containing the highest percentage ofrestored prairie (WNT5) does not show any improve-ment in atrazine or nitrate-N concentration.

Because the location of the proposed acquisitionboundaries for the Neal Smith Refuge are focused inthe core of the watershed, this study has the uniqueopportunity to examine the effects from headwaterareas relative to placement of BMPs for water qualityimprovements. Further studies are planned to exam-ine the contributions from headwater areas in theWalnut Creek watershed.

Have Changes Been Missed by Sampling Design?

Has water quality sampling been conducted toolong after implementation of cropland managementactivities to see the water quality improvements, orhave water quality changes actually occurred buthave been missed by infrequent sampling? Whenprairie restoration was initiated in 1992, pesticide usewas halted on refuge-owned lands in 1993. This repre-sented an immediate 28 percent reduction in pesticideapplication in the watershed, in contrast to nitrogenapplication reductions which have occurred on a grad-ual basis over the years. Considering that projectsampling for pesticides began in earnest in 1995,there was over a two-year time gap between the pesti-cide reduction and initiation of sampling. Did pesti-cide reductions occur during this time period, and ifso, why do atrazine loads remain so similar betweenthe Walnut and Squaw Creek watersheds today? Ifwater quality improvements did occur during this

period, the watersheds must have been very dissimi-lar in pesticide loads before restoration and havesince become equivalent only after the extensive con-versions. Pre-restoration sampling data do not indi-cate differences in water quality between the twowatersheds (Schilling and Thompson, 1999). In anycase, unless another large reduction in applicationloads occurs in the coming years that can be used toevaluate immediate effects, this question will remain.However, data from other monitoring programs inIowa where sampling has coincided with BMP imple-mentation have also shown few noticeable imp:rove-ments (Rowden et al., 1995; Seigley et al., 1994; 1996).

In terms of sampling frequency, the annual sam-pling schedule outlines 23 collection events per yearon the Walnut and Squaw Creek main stem.s and 16collection events per year on the subbasins (Table 2).Is this sufficient to detect changes in water qualitydue to land restoration? For water quaLity con-stituents associated with ground water baseflow con-tributions to surface water (i.e., nitrate-N, ions), thefrequency may be adequate. However, it should benoted that discharge of groundwater to surface waterthrough tiles can bypass the normal groundwater flowpaths from upland areas to discharge points instreams. During large rainfall events, concentrationsof pollutants in tile discharge may be more closelyrelated to surface runoff concentrations than normalbaseflow discharge. For parameters associated withrunoff events, such as pesticides and fecal coliform,the sampling frequency may be inadequate. Theseparameters often require more detailed samplingassociated with precipitation and runoff events to beassessed accurately. Future sampling frequency willbe expanded in the monitoring program to includeevent sampling in the spring and summer to evaluatethe quality of runoff entering the streams. Event sam-pling will include both surface water and tile dis-charges to the main channel and tributaries.

CONCLUSION

The Walnut Creek Monitoring Project began withan ambitious goal to implement a water quality pro-gram to document water quality improvementsresulting from large-scale watershed restoration andmanagement. After three years of monitoring, thereare some preliminary indications of improvements,although more questions have been raised thananswered by the project thus far. Clearly, a consider-ably longer term monitoring record will be needed toevaluate fully the effects of restoration activities onwater quality in the Walnut Creek watershed.



ACKNOWLEDGMENTS

The Walnut Creek Nonpoint Source Pollution Monitoring Pro-ject is supported, in part, by Region VII of the U.S. EnvironmentalProtection Agency through a 319-Nonpoint Source Program Grantto the Iowa Department of Natural Resources. Pauline Drobneyand the rest of the staff at the Neal Smith National Wildlife Refugeare gratefully acknowledged for their support of field activities.Mary Skopec of the Iowa DNR-Geological Survey Bureau andKevin Tweedy of the NCSU Water Quality Group assisted with sta-tistical analyses. Constructive comments from two anonymousreviewers improved the manuscript.

LITERATURE CITED

Agena, U., B. Bryant, and T. Oswald, 1990. Agriculture: Environ-mental Problems and Directions. Proceedings of the 1990 CropProduction and Protection Conference, pp. 219-229.

Drobney, P. M., 1994, Iowa Prairie Rebirth, Rediscovering NaturalHeritage at the Walnut Creek National Wildlife Refuge.Restoration and Management Notes 12(1):16-22.

Gale, J. A., D. E. Line, D. L. Osmond, S. W. Coffey, J. Spooner, J. A.Aronold, T. J. Hoban, and R. C. Wimberley, 1993. Evaluation ofthe Experimental Rural Clean Water Program: Abbreviated Ver-sion. National Water Quality Evaluation Project, NCSU WaterQuality Group, Biological and Agricultural Engineering Depart-ment, North Carolina State University, Raleigh, North Carolina,lO9pp.

Hallberg, G. R., B. E. Hoyer, E. A. Bettis III, and R. D., Libra, 1983,Hydrogeology, Water Quality and Land Management in the BigSpring Basin, Clayton County, Iowa. Iowa Geological SurveyOpen File Report 83-3, 191 pp.

Iowa Agricultural Statistics, 1997. 1997 Iowa Agricultural Statis-tics. U.S. Department of Agriculture, National AgriculturalStatistics Service, Washington, D.C., 131 pp.

Libra, R. D., G. R. Haflberg, J. P. Littke, B. K. Nations, D. J. Quade,and R.D. Rowden, 1991. Groundwater Monitoring in the BigSpring Basin 1988-1989: A Summary Review. Technical Infor-mation Series 21. Iowa Department of Natural Resources, Geo-logical Survey Bureau, 109 pp.

Rowden, R. D., R. D. Libra, and G. R. Hallberg, 1995. SurfaceWater Monitoring in the Big Spring Basin, 1986-1992: A Sum-mary Review. Technical Information Series 33. Iowa Depart-ment of Natural Resources, Geological Survey Bureau, 109 pp.

Prior, J. C., 1991. Landforms of Iowa. University of Iowa Press,Iowa City, Iowa, 153 pp.

Schilling, K. E. and C. A. Thompson, 1999. Walnut Creek NonpointSource Monitoring Project, Jasper County, Iowa: Water Years1995-1997. Technical Information Series 39, Iowa Department ofNatural Resources, Geological Survey Bureau, 169 pp.

Seigley, L.S., M. D. Schueller, M. W. Birmingham, G. Wunder,L. Stahl, T. F. Wilton, G. R. Hallberg, R. D. Libra, and JO.Kennedy, 1994. Sny Magill Nonpoint Source Pollution Monitor-ing Project, Clayton County, Iowa: Water Years 1992 and 1993.Technical Information Series 35, Iowa Department of NaturalResources, Geological Survey Bureau, 103 pp.

Seigley, L. S., G. Wunder, S. A. Gritters, T. F. Wilton, J. E. May,M. W. Birmingham, M. D. Schueller, N. Rolling, and J. Tisl,1996. Sny Magill Nonpoint Source Pollution Monitoring Project,Clayton County, Iowa: Water Year 1994. Technical InformationSeries 36, Iowa Department of Natural Resources, GeologicalSurvey Bureau, 85 pp.

Thompson, C. A., J. 0. Kennedy, and G. R. Haliberg, 1995. WalnutCreek Watershed Restoration and Water Quality MonitoringProject Work Plan. Iowa Department of Natural Resources, Geo-logical Survey Bureau, 20 pp.

USFWS (U.S. Fish and Wildlife Service), 1993. Cropland Manage-ment Plan, Walnut Creek National Wildlife Refuge, Prairie City,Iowa. U.S. Fish and Wildlife Service, Department of the Interior,Prairie City, Iowa, 19 pp.

U.S. Environmental Protection Agency, 1990. Rural Clean WaterProgram: Lessons Learned From a Voluntary Nonpoint SourceControl Experiment. U.S. Environmental Protection Agency,Nonpoint Source Control Branch, Washington, D.C., 29 pp.


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