College of Agriculture and Life SciencesDenitrification within Saturated Riparian Buffers Re-designed

to Remove Nitrate from Artificial Subsurface Drainage

Thomas IsenhartIowa State University

Dan Jaynes and Tim ParkinUSDA – National Laboratory for Agriculture and Environment

Kirsten HofmockelDOE – Pacific Northwest National Laboratory

USDA-AFRI Foundational Program

College of Agriculture and Life Sciences

2015 average 15.5 mg/L Nitrate-N

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

Alternatives for Tile-drained Landscapes?

Nutrient-Removal Wetland

Bioreactor

USDA-NRCS

IDALS - DSC

IA Soybean Association

Question

Could reconnecting tile flow to riparian buffers remove substantial amounts of nitrate before it reaches surface waters?

USDA-NRCS

Saturated Buffer

Christianson et al.

Lynn Betts

USDA-ARS

College of Agriculture and Life Sciences

Tile Flow Diverted Through Buffer

Average Nitrate in Buffer Wells

Annual Nitrate Removed in Buffer

Nitrous Oxide in Shallow Groundwater

Soil Greenhouse Gas Emissions

2015 Nitrous Oxide Emissions

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Kg N

2O-N

ha-1

yr-1

0

1

2

3

4

5

Bear CreekSouth Skunk

Saturated Buffers

Conventional Buffers

College of Agriculture and Life Sciences

Measured Flow from Tile Outlet and to Stream

Denitrification Estimates

mg N

2O-N

m-3

hr-1

0

1000

2000

3000

4000

5000

Bear Creek

mg N

2O-N

m-3

hr-1

0

1000

2000

3000

4000

5000Unsaturated Grass CoreSaturated Grass CoreUnsaturated Woods CoreSaturated Woods Core

South Skunk

Bear Creek 2