Model demonstrating the potential for coupled nitrification denitrification in soil aggregates.

Area of Science:

• Environmental Science
• Soil Science
• Biogeochemistry

Background:

• Nitrogen (N) transformations in soil aggregates are complex, influenced by physical and chemical factors.
• Irrigation with reclaimed wastewater introduces elevated nutrient loads and alters soil conditions, impacting N cycling.
• Understanding these processes is crucial for managing soil health and water quality.

Purpose of the Study:

• To develop a reactive, multi-species diffusion model for N transformations in spherical soil aggregates.
• To investigate the effects of reclaimed wastewater irrigation on N cycling within soil aggregates.
• To analyze the influence of aggregate size, respiration, and oxygen availability on nitrification and denitrification.

Main Methods:

• Development of a reactive, multi-species diffusion model.
• Incorporation of kinetic models for mineralization, nitrification, and denitrification.
• Simulation of N transformations under varying conditions, including wastewater irrigation and aggregate characteristics.

Main Results:

• Aggregate size and soil respiration rate are primary drivers of anaerobic conditions within aggregates.
• Nitrification is predominantly limited to smaller aggregates (<0.25 cm), while denitrification peaks in medium-sized aggregates supporting coupled nitrification/denitrification (CND).
• Wastewater irrigation enhances predicted nitrite formation in small aggregates, a difference that diminishes with increasing aggregate size.

Conclusions:

• Soil aggregate characteristics significantly control the spatial distribution and rates of N transformations.
• Wastewater irrigation alters N cycling dynamics, particularly enhancing nitrification and denitrification in smaller aggregates.
• The developed model provides insights into aggregate-level N cycling, essential for predicting soil ecosystem responses to environmental changes.