Processes Controlling the Source, Movement, and Release of Soil Phosphorus in Midwestern Streams...

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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 ThompsonIowa State University

Mark Tomer and John KovarUSDA – National Laboratory for Agriculture and Environment

Keith SchillingIIHR - Iowa Geological Survey

USDA-AFRI Foundational Program

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

Altered hydrology

Tile drainageChannelization

Severely & Very Severely Erosive Banks (USDA-NRCS, 1998)

Percent Total Channel Length Classified as Erosive, by Year

Channel Cross-Sectional Area

Distance (m)

0 2 4 6 8 10 12

Elevation (m

20141998

Change in Cross-Sectional Area, 1998-2014

Distance downstream (km)0 2 4 6 8 10 12 14

Percent change

IncreaseDecrease

Recession Rates

Full Set Biannually

Focus Set Monthly, or by Flow Event

Robert’s Creek Member

3500 – 500 YBP

Gunder Member10,500 – 4500 YBP

Camp Creek Member

400 YBP - Present

Slump Material

Recession Estimation with LiDAR

Assessing In-Channel Sediment Storage

Bankfull

In-Channel Sediment Storage by Feature

Event Sampling at Guage Stations

Silt Loams, Coarser with Depth

Camp Creek Roberts Creek

Gunder Till

Photo courtesy of John L Kovar

Sediments pHOM Sand Silt Clay Fe-CBD Fe-ox Ca-M3

---------------- % --------------- -------------mg/kg-----------

Camp Creek 6.2 3.4 11 63 25 6,825 3,348 1,975

Roberts Creek

6.3 4.5 13 60 27 5,682 3,947 2,983

Gunder 7.4 1.5 6 72 22 3,813 1,967 2,135

Till 8.1 1.7 49 31 21 10,124 743 6,750

Stream Bank Soil Characteristics

Sequential Phosphorus Extraction

Soils Sampled for P Adsorption-Desorption Studies

Upland restoration, yet no trends in sediment load, eroding streambank length, streambank recession rate

Observed Processes

Simon and Hupp, 1986, Simon and Rinaldi, 2006

Tentative Conclusions

Entire study reach within Stage IVSimon 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

Distance downstream (km)0 2 4 6 8 10 12

1.21.41.61.82.02.22.42.62.83.03.2

Channelized Meandering

Total In-Channel Sediment Storage

November 2014

March 2015

April 2015

May 2015

June 2015

July 2015

August 2015

September 2015

October 2015

Volume (m

Walnut Creek Cumulative Streambank ErosionCumulative Streambank Erosion

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

Distance (m)

0 2 4 6 8 10 12

Elevation (m

20141998

Change in Cross-Sectional Area, 1998-2014