Contrasting Nitrogen Fate in Watersheds Using Agricultural and Water Quality Information

Area of Science:

• Environmental Science
• Agricultural Science
• Hydrology

Background:

• Nitrogen (N) surplus in agricultural watersheds is a significant environmental concern.
• Understanding nitrogen fate and transport is crucial for managing water quality.

Purpose of the Study:

• To compare nitrogen surplus and its fate across diverse agricultural watersheds.
• To identify sources and transport pathways of nitrogen in streamflow and nitrate (NO) load.

Main Methods:

• Applied Principal Component Analysis-End-Member Mixing Analysis (PCA-EMMA) across 10 agricultural watersheds.
• Calculated watershed surplus nitrogen (N) by quantifying inputs and outputs (crop uptake, volatilization).
• Analyzed solute concentrations in various water sources (streams, runoff, tile drainage, groundwater).

Main Results:

• Watershed surplus N ranged from 11 to 52 kg N/ha, representing 9–32% of N input.
• Higher surplus N was observed in watersheds with permeable soils, where oxic groundwater was a primary NO source.
• Less permeable watersheds showed rapid NO transport via tile drainage and runoff with minimal removal, while larger watersheds exhibited streambed NO removal.

Conclusions:

• Soil permeability significantly influences nitrogen surplus and transport pathways.
• Denitrification and benthic processes contribute to nitrogen removal, particularly in larger or more permeable watersheds.
• Effective nitrogen management strategies must consider watershed characteristics and hydrological pathways.