Field experiment and numerical simulation of point source irrigation with multiple tracers.

Area of Science:

• Soil Science
• Environmental Science
• Hydrology

Background:

• Organic contaminants and fertilizers pose risks to soil and water quality.
• Understanding solute transport in soils is crucial for sustainable agriculture.
• Dyes and bromide ions can serve as tracers for organic contaminants and nitrate-nitrogen (NO3-N), respectively.

Purpose of the Study:

• To investigate the mobility of dye (simulating organic contaminants) and bromide ions (simulating fertilizer) in sandy soil under drip irrigation.
• To assess the effectiveness of drip irrigation in enhancing water and soil nutrient adsorption.
• To validate numerical simulations of tracer transport using HYDRUS-2D/3D.

Main Methods:

• Field experiments in semiarid Tunisia using sandy soil plots.
• Irrigation with a high-saline solution containing Brilliant Blue dye and bromide ions.
• Analysis of dye patterns, bromide concentration, and soil water content after infiltration.
• Numerical simulation using HYDRUS-2D/3D with inverse parameter estimation for soil hydraulic properties.

Main Results:

• Preferential flow was observed but did not dominate solute transport.
• Bromide ions exhibited greater mobility than the Brilliant Blue dye.
• Dye mobility was retarded approximately twice by volume compared to bromide.
• Numerical simulations accurately replicated field observations of tracer mobility.

Conclusions:

• Drip irrigation shows promise for improving water and nutrient adsorption in sandy soils.
• HYDRUS-2D/3D is a valuable tool for studying tracer mobility under point source irrigation.
• The differential mobility of dye and bromide supports their use as surrogates for organic contaminants and fertilizers, respectively.