A Field-Scale Approach to Estimate Nitrate Loading to Groundwater

Area of Science:

• Environmental Science
• Hydrology
• Agricultural Science

Background:

• Assessing groundwater quality improvements requires accurate quantification of nitrate (NO) loading from agricultural fields.
• Existing methods face challenges in objectively measuring NO export linked to specific management practices.

Purpose of the Study:

• To investigate the magnitude and timing of NO export from a raspberry agricultural field.
• To combine high-resolution groundwater NO concentration data with Darcy's flux estimation for robust mass flux assessment.

Main Methods:

• Utilized passive diffusion samplers for high-resolution groundwater NO concentration profiles.
• Employed Darcy's flux estimation using field-measured hydraulic gradients and laboratory-determined hydraulic conductivity.
• Validated mass flux estimation using chloride (Cl) application and export rates.

Main Results:

• Estimated annual groundwater recharge at 1002 mm using Darcy's law.
• Quantified an annual NO-N export of 80 kg/ha from the agricultural field.
• Observed peak monthly groundwater mass flux of NO in February and March, linked to autumn precipitation leaching.

Conclusions:

• The combined approach of groundwater sampling and flux estimation provides a robust method for quantifying NO loading.
• This methodology enables objective assessment of groundwater quality improvements related to agricultural management.
• Effective isolation of groundwater recharge within a vertical profile is key for accurate, spatially integrated NO loading estimates.