1. College of Agriculture and Life Sciences
Denitrification within Saturated Riparian Buffers Re-designed to
Remove Nitrate from Artificial Subsurface Drainage
Thomas Isenhart
Iowa State University
Dan Jaynes and Tim Parkin
USDA – National Laboratory for Agriculture and Environment
Kirsten Hofmockel
DOE – Pacific Northwest National Laboratory
USDA-AFRI Foundational Program

5. College of Agriculture and Life Sciences
2015 average 15.5 mg/L Nitrate-N

6. College of Agriculture and Life Sciences
Tile Nitrate Concentrations in Perspective
• Iowa Drinking Water Standard
• 10 mg L-1 Nitrate-N
• Aquatic Life Criteria
• 2.18 mg L-1 Nitrate-N
• Hypoxia in the Gulf of Mexico
• 45% Total N Load Reduction

7. Alternatives for Tile-drained Landscapes?
Nutrient-Removal
Wetland
Bioreactor
USDA-NRCS
IDALS - DSC
IA Soybean Association

8. Question
Could reconnecting tile flow to riparian
buffers remove substantial amounts of
nitrate before it reaches surface waters?
USDA-NRCS

9. Saturated Buffer
Christianson et al.

11. Lynn Betts

12. USDA-ARS

13. College of Agriculture and Life Sciences

14. Tile Flow Diverted Through Buffer

15. Average Nitrate in Buffer Wells

16. Annual Nitrate Removed in Buffer

17. Nitrous Oxide in Shallow Groundwater

18. Soil Greenhouse Gas Emissions
2015 Nitrous Oxide Emissions
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
KgN2O-Nha
-1
yr
-1
0
1
2
3
4
5
Bear Creek
South Skunk
Saturated Buffers
Conventional Buffers

20. College of Agriculture and Life Sciences

21. Measured Flow from Tile Outlet and to Stream

22. Denitrification Estimates
5000
Bear Creek
5/1/15
7/1/15
9/1/15
11/1/15
1/1/16
3/1/16
5/1/16
7/1/16
mgN2O-Nm
-3
hr
-1
0
1000
2000
3000
4000
5000
Unsaturated Grass Core
Saturated Grass Core
Unsaturated Woods Core
Saturated Woods Core
5
Bear Creek 2