South Fork of the Iowa River, Iowa
An ARS Benchmark Research Watershed
Collaborators and cooperating Agencies and Groups
The watershed of interest is the South Fork of the Iowa River (Hardin
and Hamilton Counties, Iowa). The total drainage area of this watershed
is approximately 78,000 ha, and the watershed area to be evaluated is about
76,250 ha. Major sub-basins or Tipton Creek (19,850 ha), Beaver Creek (18,200
ha), and the upper South Fork (25,600 ha) are instrumented with separate
gaging stations. Instrumentation of two small drainage districts (500 –
2500 ha) in Tipton Creek is planned for 2005.
The Clarion-Nicollet-Webster soil association (Typic Hapludolls – Aquic
Hapludolls –Typic Haplaquolls) dominates the landscape, with Harps soils
(Typic Calciaquolls) occupying glacial potholes with the Webster soil.
The landscape is composed of glacial till deposited 10-15,000 years ago.
The terrain is poorly dissected and internally drained “prairie potholes”
are common in the upper parts of the watershed. The low relief creates
poor drainage conditions, and hydric soils occupy 54% of the watershed
area. A major lateral moraine of the Des Moines Lobe crosses the upper
part of the watershed. Subsurface tile drains and ditches were installed
beginning more than 100 years ago. The artificial drainage accelerates
transport of several dissolved contaminants. Normal annual precipitation
is 750 mm with 60% falling during May through August in relatively short,
but intense events. Annual baseflow constitutes 60% of the total stream
discharge. Much of the remaining runoff is derived from subsurface drain
inlets. About 85% of the watershed is under corn and soybean rotation,
and about 6% in grass (CRP) and pasture. Most of the remainder is roadways
and developed land cover, only about 1% is forest or wetland. There are
about 100 confined swine-feeding operations, most of which are located
in Tipton Creek and the upper South Fork.
1. Water Quality: Nitrate loads from subsurface drainage systems, phosphorus,
and sediment in runoff, and pathogens in streamflow are major water quality
2. Soil Quality: Trends in carbon sequestration as practices are implemented,
and buildup of phosphorus in soils receiving frequent manure applications.
1. Conservation tillage (329A and 329B)
2. Riparian Buffers (391)
3. Nutrient management (590)
4. Waste utilization (633)
5. Constructed wetlands (656)
6. Grass waterway (412)
7. Subsurface Drainage (606)
Evaluate watershed and river basin responses to conservation practices
including those supported by USDA conservation programs.
1. Evaluate loads of sediment, nitrate, phosphorus, and E. coli from the South Fork watershed and the capacity of the above conservation
practices to reduce those loads.
2. Identify locations where conservation practices should be most effective
in meeting water quality goals.
3. Assess the impact of current tillage and cropping practices on soil
quality using the NRCS Soil Conditioning Index (SCI) and the Soil Management
Assessment Framework (SMAF) being developed by the ARS and NRCS Soil Quality
The capacity of in-field and edge-of-field conservation practices to achieve
water quality goals will be evaluated in large watersheds. Landscape assessment
will use terrain-modeling techniques, applied to widely available data
on topography, soils, and climate to conceptualize areas where conservation
practices will be most effective. A comprehensive evaluation of the distribution
of existing conservation practices in the watershed will be undertaken,
with assistance from NRCS.
Synoptic sampling and long-term monitoring will be used to determine nutrient,
sediment, and pathogen loads in streams draining watersheds at nested scales,
and assess retentions and losses associated with conservation practices.
The distribution of practices and sensitive areas within the watershed
and its sub-basins will guide the final experimental design. Increased
funding for new conservation practices (e.g., EQIP), if available, along
with collaboration with the Southfork Alliance will help encourage implementation
of new conservation practices. Paired watershed comparisons and/or water
quality trends will be evaluated to determine the impact of new practices
that producers volunteer to implement. Results will also be used to parameterize
models (EPIC, SWAT) that predict the effects of management systems on watershed
processes and water quality.
Soil quality assessments will be made using existing data, and employing
two different approaches. First, recognizing that soil organic matter is
a primary indicator of soil quality and an important factor in carbon sequestration
and global change, the NRCS Soil Conditioning Index (SCI) will be used
to assess the consequences of the tillage and cropping systems being used
within the watershed. The SCI will provide estimates on whether the applied
conservation practices are maintaining or increasing soil organic matter.
The predictions will be verified with the available data being collected
by either the farmer-cooperators (i.e. through their soil test records)
or other researchers contributing to the overall CEAP database. A more
comprehensive assessment of soil quality will be made using the Soil Management
Assessment Framework (SMAF) that is currently being developed by the ARS
and the NRCS Soil Quality Institute. SMAF is designed to evaluate the dynamic
impact of soil management practices on soil function and consists of three
steps: indicator selection, indicator interpretation, and integration into
an index. Designed as a framework, SMAF allows researchers to continually
update and refine the interpretations for many soils, climates, and land
use practices. Therefore, in addition to providing soil quality assessments
for CEAP, the project will provide data for further improvements of the
SMAF. This will occur by applying decision rules based on management goals
and other site-specific factors in the selection step for each watershed.
The interpretation step will provide site-specific indicator scores. Individually
and collectively (through the index), the indicator scores will be correlated
to critical endpoints including crop yield, water quality (i.e. nitrate,
phosphorus, and sediment loads), and air quality indicators.
Tomer, M.D., and D.E. James. 2004. Do soil surveys and terrain analyses
identify similar priority sites for conservation? Soil Sci. Soc. Am. J.
Tomer, M.D., D.E. James, and T.M. Isenhart. 2003. Optimizing the placement
of riparian practices in a watershed using terrain analysis. J. Soil &
Water Conserv. 58(4):198-206.
Collaborators and Cooperating Agencies and Groups
Southfork Watershed Alliance, a local organization, is working to encourage implementation of conservation
practices that can protect and improve water quality.
NRCShas identified the physiographic region as the focus of their CREP program
in Iowa and is using methods developed by NSTL to locate appropriate sites
for wetland restoration.
USGSmaintains continuous discharge stations at two sites where the NAWQA program
found nitrate concentrations to be among the highest observed in the US.
Measurements of pharmaceuticals have been a subject of recent research.
USEPAhas expressed interest in coordinating ORD research with that of ARS to
answer questions related to Clean Water Act program administered by Region
NRCS Soil Quality Institute (Dr. Susan Andrews)will work with the SMAF, contributing refinements in and developing new
scoring curves for critical indicators within the various watersheds.