Processes Controlling the Source, Movement, and Release of Soil Phosphorus in Midwestern Streams from Pasture and Crop Land
1. College of Agriculture and Life Sciences
Processes Controlling the Source, Movement, and Release of Soil
Phosphorus in Midwestern Streams
Richard Schultz, Thomas Isenhart, and Michael Thompson
Iowa State University
Mark Tomer and John Kovar
USDA – National Laboratory for Agriculture and Environment
Keith Schilling
IIHR - Iowa Geological Survey
USDA-AFRI Foundational Program
2. Iowa Nutrient Reduction Strategy
• Stream banks are known to be a potentially large source of stream
sediment.
• However, accurately accounting for stream bank sources of P is
extremely difficult.
• Therefore, evaluating strategies to reduce P losses from eroding
stream banks are beyond the scope of this effort.
Phosphorus Transport in Iowa Streams:
The Importance of Stream Bed and Bank Erosion
29. College of Agriculture and Life Sciences
Tentative Conclusions
Entire study reach within Stage IV
Simon and Hupp, 1986, Simon and Rinaldi, 2006
Slow transition from initial 20th century
disturbance
Simon and Rinaldi, 2000 (could take 40-100+ years)
Cohesive Gunder bed and banks
30. College of Agriculture and Life Sciences
Distance downstream (km)
0 2 4 6 8 10 12
m3
m-1
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
Channelized
Meandering
Total In-Channel Sediment Storage
31. College of Agriculture and Life Sciences
N
ovem
ber2014M
arch
2015April2015M
ay
2015June
2015July
2015
August2015
Septem
ber2015
O
ctober2015
Volume(m3)
0
200
400
600
800
1000
1200
1400
1600
1800
Walnut Creek Cumulative Streambank ErosionCumulative Streambank Erosion
Volume(m3)
32. College of Agriculture and Life Sciences
Image adapted from Schilling et al., 2012
Walnut Creek Watershed
• Perennial, third order stream
• 5218 ha
• Agricultural headwaters, subsurface
drainage
• Extensive channelization
• Water Quality Data 1995 –
• Neal Smith NWR (2225 ha)
• 1991 - Present
33. College of Agriculture and Life Sciences
Distance (m)
0 2 4 6 8 10 12
Elevation(m)
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
2014
1998
1998
2014
Change in Cross-Sectional Area, 1998-2014