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The Walnut Creek Watershed Restoration and Water Quality Monitoring Project began in April 1995 and is designed as a nonpoint source (NPS) monitoring program in relation to the watershed habitat restoration and agricultural management changes implemented by the U.S. Fish and Wildlife Service (USFWS) at Walnut Creek National Wildlife Refuge and Prairie Learning Center (WNT) in central Iowa. The watershed is being restored from rowcrop to native prairie, including restoration of native fauna (Figures 1 and 2). This monitoring project is part of the U.S. Environmental Protection Agency's National Monitoring Program.


Photo Photo
Figure 1. Native prairie. Photo by Carol Thompson.
Figure 2. Bison at Walnut Creek. Photo by Jim Heemstra.


Unlike many other projects, landuse changes will be implemented over a large percentage of the basin. The Walnut Creek watershed includes 12,860 acres (20.1 mi2) and contains the majority of the WNT Refuge area; approximately 63% of the watershed is within refuge boundaries (Figure 3). Currently, about 5,000 acres (7.8 mi2) are owned by the USFWS. Because the restoration work and improved management practices are being implemented by the USFWS, they will be implemented much more uniformly than at most other projects, both in time and spatially across the watershed. Thus, documentation of landuse and management changes within Walnut Creek watershed may allow an improved evaluation of the amount of change within a watershed that is needed to bring about significant water quality improvements and the time lags associated with any improvement.

Figure 3. Map of Walnut Creek (WNT) and Squaw Creek (SQW) watersheds. Green area shows the extent of USFWS-owned land.

Table 1. Land management changes.
System Restoration Cropland Management



Integrated Crop Management

Restricted Pesticide Use

Mandatory Crop Scouting

Nutrient Management

Mandatory No-Till Production

There are two components to the landuse changes being implemented by USFWS: ecosystem resources restoration to prairie/savanna; and mandatory (contractual) use of improved agricultural management practices on farmlands prior to conversion (Table 1). All the remaining WNT Refuge cropland will be restored during the next three years. In the riparian areas, one hundred foot-wide vegetative filter strips will be seeded along all of the streams in the Refuge that are not already in grass or timber. Riparian and upland wetlands will also be restored, or allowed to revert to wetlands. Tile lines will be eliminated gradually as acreage is converted providing for restoration of wetlands in various settings. These areas will serve as important demonstration areas for local riparian and wetland restoration projects and will allow an evaluation of the effectiveness of the filter strips on a landscape scale and will provide documentation of their water-quality benefits.

Cropland management within the WNT Refuge is also controlled by the USFWS management team. Farming is done on a contractual, cash-rent basis, with various management measures specified; some are flexible, some more prescriptive. The measures include soil conservation practices, nutrient management through soil testing, yield goals, and nutrient credit records, and integrated pest management. Crop scouting for pest management is mandatory for all farms on Refuge lands, as are no-till production methods. Insecticide use is highly restricted and herbicide use is also controlled, to minimize adverse impacts on non-target plants and animals.

Watershed Characteristics

Walnut Creek, a warm-water stream located in Jasper County, Iowa, drains an area of 30.7 mi2 (19,500 acres) and discharges into the Des Moines River at the upper end of the Red Rock Reservoir. The project watershed includes 20.1 mi2 (12,862 acres) and includes the majority of the WNT Refuge area; approximately 63% of the watershed is within the Refuge boundaries. The Walnut Creek watershed and the WNT Refuge are located in the Southern Iowa Drift Plain, an area characterized by steeply rolling hills and well-developed drainage. Most of the soils are silty clay loams, silt loams, or clay loams formed in loess and many are classified in the moderate to high erosion potential category (Figure 4). The upper portion of the Walnut Creek watershed, above the WNT Refuge, is the more gently sloping headwaters portion of the basin; the majority of Highly Erodible Land (HEL) in the watershed occurs in the Refuge area (Figure 5). Pre-Illinoian till underlies most of the Refuge area and is 50 to 100 feet thick.


Map Map Click on image to view full size.

Data from digital soils maps and associated Iowa Soil Properties and Interpretations Database (ISPAID; Iowa Cooperative Soil Survey).

Figure 4. Parent material.
Figure 5. Slope classes.

For this monitoring project a paired-watershed design will be used. The Squaw Creek basin(SQW), adjacent to Walnut Creek (WNT), will be used as a control watershed. Squaw Creek drains 25.2 mi2 (16,130 acres) above its junction with the Skunk River. The watershed included in the monitoring project is 18.3 mi2 (11,683 acres) and does not include the wide floodplain area near the intersection with the Skunk River. The soils and geology of the Squaw Creek watershed are similar to those in the Walnut Creek basin.

Both creeks have been extensively channelized and are incised into their valleys. A thick package of post-settlement alluvium is present in both valleys. Discharge is similar in both streams, although Walnut Creek experiences slightly lower flows (Figure 6). Both streams are flashy (displaying rapid responses to precipitation; Figure 7). Baseflow percentages for Water Year 1996 (WY96; a water year is a 12-month period, from October 1 through September 30, designated by the calendar year in which it ends) are Walnut Creek (upstream) - 41%, Walnut Creek (downstream) - 29%, and Squaw Creek (downstream) - 37%.


Figure 6. Graph of discharge for Walnut and Squaw creeks.
Figure 7. Typical storm hydrographs.


Water Resource Problems and Earlier Data

Walnut Creek drains into a segment of the Des Moines River that is classified as Not Supporting its designated uses in the Iowa Department of Natural Resources' (IDNR) water-quality assessments (IDNR, 1997); Squaw Creek and the Skunk River are classed as Partially Supporting. Assessments in this area cite agricultural nonpoint source (NPS) pollution as the principal concern.

Walnut and Squaw Creek are affected by many agricultural NPS water pollutants, including sediment, nutrients, pesticides, and animal waste. Water quality in these streams is typical for many of Iowa's small warm water streams; water quality varies significantly with changes in discharge and runoff.

Data was collected in the Walnut Creek basin from 1992 to 1994 as part of the Tri-State Monitoring Project (Figures 8 and 9). Data was also collected during the pre-implementation period by the USFWS. Nitrate shows a slight decrease over the period, but this is not statistically significant. It may be related to climatic patterns. Turbidity, fecal coliform, and atrazine show no differences.


Figure 8. Previous data -atrazine and nitrate.
Figure 9. Previous data - fecal coliform and turbidity.


Monitoring Plan Design

There are five basic components to the project: 1) tracking of land cover and land management changes within the basins, 2) stream gaging for discharge and suspended sediment at two locations on Walnut Creek and one on Squaw Creek, 3) surface water quality monitoring of Walnut and Squaw creeks, 4) biomonitoring for aquatic macroinvertebrates and fish in Walnut and Squaw creeks, and 5) groundwater quality and hydrologic monitoring (Table 2).


Table 2. Water quality monitoring plan.

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-N, BOD, Anions, Temperature, Conductivity, Dissolved Oxygen, Turbidity, Alkalinity, pH


Common Herbicides

Acid Herbicides, OP Insecticides

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

May, September

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

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 Levels

Temperatures, Conductivity, Alkalinity, pH

Pesticides, Anions






Biomonitoring Stations



Invertebrate monitoring

Fish sampling

Sediment sampling

4x (Mar - Oct)

1x (Sept)

1x (Sept)


Land Cover

Current land use practices for both Walnut and Squaw Creeks will be tracked throughout the life of the project (Figure 10). Yearly flight pictures as well as crop plats will be obtained and analyzed for land cover changes. Data on terraces, buffer strips, grassed waterways, and other conservation practices will be included. Data will be entered into a Geographic Information System (GIS) using ARC/INFO software and coupled with the water quality, flow, and sediment data for analysis.


Map Click on image to view full size.
Figure 10. Land cover for 1997.

Data on the geomorphic characteristics of the basins will also be collected. Data related to the physical nature of the stream (length, width, gradient, etc.) will be measured. In addition, analysis of post-settlement deposition will be done for both basins to enhance our understanding of sediment transport in surface water in small Iowa basins.

Stream Gaging

Three stream gaging stations have been installed by the U.S. Geological Survey (USGS). Stage is monitored continuously with bubble-gage sensors (fluid gages) and recorded by automated data collection platforms (DCP) and analog recorders. Depth-integrated sediment samples are collected daily by local observers and by USGS staff during high flow events. Suspended-sediment concentrations are determined by the USGS Sediment Laboratory using standard filtration and evaporation measurements.

Surface Water Monitoring

Surface-water chemistry will be monitored weekly to monthly at ten sites in the basin and analyzed for nitrate, ammonium-nitrogen, pesticides (in season), anions, cations (sampled twice; 2X), biological oxygen demand (BOD), dissolved oxygen (DO), turbidity, alkalinity, fecal coliform, conductivity, and temperature.


Biomonitoring is done at four sites, one at each of the lower gaging stations and two mid-reach samples. The stream reach for aquatic vegetation and fish collection will be a length seven times the stream width. The aquatic vegetation in this reach will be observed, identified, and recorded annually. Aquatic macroinvertebrates will be collected bi-monthly from April through October. A combination of natural and artificial substrates may be used to identify all aquatic macroinvertebrates present. Summary metrics will be used for comparisons with time and between sites. Stream corridor habitat changes will also be recorded.

Demonstration and Education

The WNT's educational commitment and resources will allow for educational and demonstration activities far beyond the scope of those that could typically be accomplished by the U.S. Environmental Protection Agency (EPA) Section 319 (Clean Water Act) projects. Of particular note, the anticipated linkages between landuse changes and water quality improvements will be an integral part of these educational efforts. In addition, existing curriculum creates opportunities for interested visitors to acquire, enter, and interpret hydrologic and water quality data from the watershed. Both streamside and visitor center-based activities and educational stations are planned. Information presentations could readily be tailored to school, environmental, or agricultural interest groups. It is anticipated that visitors to the WNT will number in the tens of thousands annually, offering a uniquely wide exposure to the landuse changes and monitoring activities in the watershed.

USFWS will utilize the WNT as a demonstration area for landscape restoration projects. Information will be disseminated to visitors and invited groups, the public, through published reports, and to the news media. Of broader interest, the project is also serving as a demonstration site for riparian restoration and small wetland restoration. Having a linked water-quality evaluation program makes these demonstrations more effective for general use and translation to broader audience.

Monitoring Results


There have been detections of six different compounds between 1995 and 1997 in Walnut and Squaw Creek surface waters. Atrazine was by far the most frequently detected compound, as is true across Iowa, with frequency of detections from 77% to 89% in the main stems (Figure 11). No significant differences have been noted in atrazine concentrations from 1995 through 1997 (Figure 12).


Figure 11. Atrazine concentrations.
Figure 12. Basin comparisons of atrazine.



Nitrate concentrations are high, but typical for streams in Iowa. A comparison of data from the upstream and downstream paired sites show that the basins are very similar. Ranges and averages for the four main stem sampling sites are in Table 3.

A comparison of data from the three years shows no statistical differences (Figure 13). Concentrations in Walnut Creek are usually slightly less than in Squaw Creek. In addition both creeks show downstream declines in nitrate concentrations (Figure 14). This can be attributed to in-stream reductions, perhaps caused by denitrification, or by dilution from larger flow volumes (surface water and/or groundwater). Chloride and nitrate ratios are shown and may indicate that nitrate in Squaw Creek is reduced more downstream than nitrate which may be indicative of bioprocessing. Chloride and nitrate ratios in Walnut Creek both show declines which may be attributable to dilution (Figure 15).


Table 3. Nitrate-N concentrations.


Range Nitrate-N (mg/L)

Average Nitrate-N (mg/L)

WNT1 (upstream)

4.1 - 15.8


WNT2 (downstream)

2.1 - 13.0


SQW1 (upstream)

6.8 - 17.0


SQW2 (downstream)

3.9 - 13.0



Figure 13. Nitrate loads - basin comparison, yearly comparison.
Figure 14. Nitrate concentrations.
Figure 15. Nitrate - chloride ratio data.



Sediment loads in both streams are similar (Figure 16). No significant differences have been noted in sediment loads from 1995 to 1996. Most sediment moves during large runoff events. For Walnut Creek, 18 days accounted for 90% of the total annual sediment load during WY96; only 13 days were needed in Squaw Creek to carry 90% of the annual load.


Figure 16. Sediment loads from Walnut and Squaw creeks for 1995 and 1996.



The biomonitoring data indicate stream communities in both streams are indicative of disturbed habitat with at least some level of organic pollution (Table 4). The fish communities also reflect this in that all species present are tolerant of degraded conditions (Table 5).

Walnut Creek is characterized by a macroinvertebrate community that was dominated by relatively few taxa with occasional new taxa appearing at low frequencies and abundances. For example, a total of 20 taxa of Ephemeroptera have been collected in two years of sampling, but 15 of those taxa have comprised less than four percent of the specimens. This indicates the presence and the potential of other macroinvertebrates to move into the creek and become a more integral part of the biological community structure. However, because of the long term effects of disturbance of the watershed, it is likely that an adaptive community has developed that exploits this condition to maintain its dominance. The macroinvertebrate trends that occurred in both Squaw and Walnut Creek watersheds (based on 1995 and 1996 data) were similar and continued to respond in equivalent ways seasonally and approximated each other in community structure and population. The Hilsenhoff Biotic Index (HBI) values continue to show good water quality, but other metrics (percent dominant taxon; Ephemeroptera, Plecoptera, Trichoptera - EPT index, and total taxa) indicate unbalanced communities, or a community dominated by few species. Additionally, from an ecoregion perspective, both creeks rate in the lower quartile with respect to two metric indicators (EPT taxa, total number of taxa) of macroinvertebrate community health.

The fish communities retained the same dominant species as 1995, however, the less frequent species were sporadic in their occurrence. The variability of uncommon species is reasonable considering the proximity of the sampling sites to major river systems. The Des Moines River and the South Skunk River provide a pool of species of which some migrate up the respective creeks. It is apparent that the diversity of fish collected from Walnut Creek can vary dramatically and is heavily influenced by Red Rock reservoir. The dominant resident fish species are likely populations that have relied historically on the habitat for shelter and food while the infrequent species are likely just transients. It is noteworthy, however, that at any given time quite a few species may rely on the habitat of Walnut Creek.

The 1996 field season, as the previous field season, showed that aquatic macrophyte populations are not present at the biomonitoring sites and based on field observations were not likely present anywhere in the stream reaches located within the refuge.


Table 4. Benthic macroinvertebrate data from Walnut and Squaw creeks for 1995 and 1996.


Table 5. Fish data from Walnut and Squaw creeks for 1995 and 1996.


Participating Agencies and Organizations

Iowa Department of Natural Resources - Geological Survey Bureau
Provides overall monitoring project coordination and management, including annual project reporting, conducts the water quality sampling, and analyzes all data.

U.S. Fish and Wildlife Service
Provide all funds and staff necessary for implementation of landuse changes, restoration and reconstruction of habitats, monitor farming activities to ensure compliance with previously stated requirements, assist with field sampling and provide the coordination link to other monitoring and investigations underway at WNT.

U.S. Geological Survey - Water Resources Division
Install and operate surface water gages, conduct the suspended sediment sampling, provide expertise for interpretation and analysis of monitoring data.

Hygienic Laboratory, The University of Iowa
Provide laboratory analytical work, and lab QA/QC, conduct the biomonitoring and related QA/QC and provide an annual report.

Farm Service Agency
Provide access to crop plats and land use in the basins.

Iowa Department of Natural Resources - Environmental Protection Division
Provide project funding.

U.S. Environmental Protection Agency
Provide funding for project and review project progress.


IDNR, 1997, Water quality in Iowa during 1994 and 1995: Water Resources Section, Water Quality Bureau, Iowa Department of Natural Resources.

For further information contact Keith Schilling (kschilling@igsb.uiowa.edu) at (319)335-1575.

Walnut Creek Watershed Study Publications:

Reports on the Walnut Creek Watershed Monitoring Project, Jasper County, Iowa:  Water Years 1995-2000:  GSB Technical Information Series 46 (Introduction)

Walnut Creek Nonpoint Source Monitoring Project, Jasper County, Iowa:  Water Years 1995-1997: GSB Technical Information Series 39 (Abstract)

Detailed GPS Survey of Walnut Creek:  Channel Characteristics and Spatial Relationships (Poster)

Sediment Transport Studies at Walnut Creek (Iowa Geology, 2000)

Patterns of Discharge and Suspended Sediment Transport in the Walnut and Squaw Creek Watersheds, Jasper County, Iowa:  Water Years 1996-1998:  GSB Technical Information Series 42 (Abstract)