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Watershed Work Leads to Improvement in Silver Creek
Waterbody Improved
Silver Creek, located in Clayton County, was placed on Iowa's Clean
Water Act (CWA) section 303(d) list of impaired waters in 2002
due to a decline in the biological community based on biological index scores. In 2007, the Iowa
Department of Natural Resources' (DNR) Stressor Identification (SI) process found that increased
sedimentation from the watershed was the primary cause of impairment. Through the Silver
Creek Watershed Project, farmers and landowners installed conservation practices that reduced
the amount of sediment reaching the creek and improved the habitat for aquatic life. Further
monitoring now shows major improvements in biotic index scores, demonstrating the ongoing
recovery of the biological community due to the locally led efforts.
Problem
Silver Creek is a warm water stream in Clayton County,
Iowa, within the Turkey River basin. The Silver Creek
watershed includes a total of 17,909 acres (28.1 square
miies) (Figure 1). The watershed represents one of the
most intensely cropped portions of Clayton County,
and steep cropland slopes are the dominant feature.
The karst (shallow, fractured limestone bedrock)
geology of the watershed further amplifies the threat
of agricultural pollutants. Over 60 sinkholes have been
found in the watershed, including locations in or near
to the stream channel that can divert streamflow
underground and cause the stream to lose water.
The 2007 SI identified sedimentation as a primary
cause of the low index of biotic integrity (IBI) scores for
both fish (FIBI) and benthic macroinvertebrates (BMIBI)
in Silver Creek (Figure 2). Benthic macroinvertebrates
are aquatic animals like insects, snails, mussels and
crayfish that live on the stream bottom.
Sediment in waterways can completely bury or ffil
in gaps around many stream habitat types like rocks
and gravel that are Important to fish and benthic
macroinvertebrate survival. This metric is also known
as stream embeddedness, which is often evaluated
in riffles or shallow runs where currents are normally
high enough to prevent excessive fine sediment
accumulation. As embeddedness increases, the large
and small spaces between rocks become filled with
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Figure 1. i he Silver Creek watershed with biosampling site.
sediment, making this important habitat less suitable
for invertebrates and fish, which use the spaces for
feeding, shelter, spawning and egg incubation.
Sedimentation is caused by soil erosion and runoff
from tilled agricultural ground, streambank collapse,
and from active gullies across steep terrain, all of
which were found in the Silver Creek watershed.
Sediment delivery to the stream was estimated to be
14,930 tons per year in 2007.

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~	2006
~	2018






~ delisting criteri




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I































FIBI	BMIBI
Story Highlights
The watershed project was launched in 2007 by the
Clayton County Soii and Water Conservation District
(SWCD). The interest demonstrated by Silver Creek
landowners and farm operators over the 14 years of
the project has been outstanding (Figure 3).
Practices adopted included terraces (238,190 feet),
cover crops (11,484 acres), grassed waterways
(35 acres) and streambank protection (830 feet). New
filter strips now buffer over two miles of the stream
and its tributaries, and cattle were excluded from a
mile of the stream corridor. The diversity and number
of practices adopted far exceeded expectations and
have reduced sediment delivery to Silver Creek by an
estimated 60 percent.
Results
Improvements have been seen in all sediment-related
measures. Embeddedness of rocky substrates
decreased by half. Additionally, the percent stream
bottom as silt and the percent composed of soft
sediment both decreased by one third. The decrease in
sedimentation is responsible for much of the improve-
ment seen in the FIBI and BMIBI scores (Figure 4). Based
on the biological monitoring, scores have more than
doubled. Silver Creek now meets the impairment delist-
ing criteria for the benthic macroinvertebrates, but is
remains just below the minimum threshold for fish.
Partners and Funding
The Silver Creek Watershed Project was funded and
supported by Iowa DNR through U.S. Environmental
Protection Agency CWA section 319 grants
($1,106,700) and the Clean Water State Revolving
Fund ($410,000) and local landowners/farmers
($1,385,806). This money was used to leverage an
additional $2,125,727 for the project. Other major
project partners included the Clayton SWCD, the
U.S. Department of Agriculture's Natural Resources
Conservation Service and Farm Service Agency, and
Iowa Department of Agriculture and Land Stewardship.
Funding from all sources totaled $5,028,233.
Figure 4. Index of biotic integrity scores for Silver Creek
(FIBI=fish, BMIBl=benthic macroinvertebrates).
Figure 2. Silver Creek is in Clayton County.
Figure 3. Silver Creek Project Coordinator Eric
Palas moderates a panel on soil health with three
conservation farmers from the Silver Creek watershed.
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U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-20-0Q1DD
November 2020
For additional information contact:
Jennifer Kurth
Iowa Department of Natural Resources
515-725-8381 • jennifer.kurth@dnr.iowa,gov

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