Nitrate-nitrogen export: magnitude and patterns from drainage districts to downstream river basins

Area of Science:

• Agricultural Science
• Environmental Science
• Hydrology

Background:

• Subsurface tile drainage enhances U.S. Corn Belt agricultural productivity.
• This drainage system contributes to significant nitrogen losses into surface waters.
• Limited in-depth studies exist on nitrate export from small, tile-drained agricultural catchments.

Purpose of the Study:

• To quantify hydrology and nitrate-nitrogen (NO3-N) export patterns from three tile-drained catchments and a downstream river over five years.
• To compare findings with previous plot-, field-, and watershed-scale studies.
• To discuss implications for improving water quality in agricultural drainage districts.

Main Methods:

• Monitoring of water yield and nitrate-nitrogen concentrations in three tile-drained catchments and a downstream river.
• Data collection over a five-year period.
• Comparative analysis with existing literature data from various scales.

Main Results:

• Annual average water yield was 247 mm/yr.
• Flow-weighted nitrate-nitrogen concentration averaged 17.1 mg/L.
• Average nitrate-nitrogen loss was approximately 40 kg/ha/yr, with over 97% of export occurring during the highest 50% of flows.

Conclusions:

• Nitrate losses from these tile-drained catchments are among the highest reported, exceeding those in small watersheds.
• Effective nitrate reduction requires management strategies at the drainage district scale.
• Implementing strategies addressing both hydrology and nitrogen supply is crucial for tile-drained landscapes.