Reactive nitrogen in a clay till hill slope field system

Area of Science:

• Environmental Science
• Soil Science
• Hydrogeology

Background:

• Reactive nitrogen in groundwater is a key factor influencing surface water quality.
• Glacial till systems beneath agricultural fields require further study regarding nitrogen cycling.
• Understanding nitrogen behavior in subsurface environments is essential for managing agricultural impacts.

Purpose of the Study:

• To investigate the fate of reactive nitrogen, specifically nitrate, within glacial till.
• To determine the depth and mechanisms of nitrate removal in groundwater beneath agricultural land.
• To assess the role of redox conditions in the transformation of nitrogen species in till.

Main Methods:

• Groundwater sampling using suction cups and piezometers installed in glacial till.
• Analysis of nitrate concentrations at various depths below the ground surface (mbg).
• Utilizing a 2D dataset to map the spatial variability of the redox zone.

Main Results:

• Nitrate concentrations leached to depths greater than 2 m below ground surface (mbg) were approximately 60 mg L^-1.
• Complete nitrate removal was observed within 5 mbg, occurring within a redox zone.
• The redox zone depth varied between 3 and 5 mbg, with negligible ammonium release.

Conclusions:

• Nitrate reduction in glacial till is primarily driven by pyrite oxidation within a diffuse redox zone.
• Localized organic matter lenses also contribute to nitrate reduction.
• Variations in infiltration likely influence the undulating depth of the redox zone.