Soil nitrogen accumulation, denitrification potential, and carbon source tracing in bioretention basins

Area of Science:

• Environmental Science
• Soil Science
• Water Quality Management

Background:

• Bioretention basins are key green infrastructure for stormwater management.
• While nitrogen removal via inflow/outflow is studied, long-term soil accumulation and denitrification remain less understood.
• Understanding temporal nitrogen dynamics is crucial for optimizing bioretention performance.

Purpose of the Study:

• To investigate the temporal variation of total nitrogen (TN) accumulation and denitrification potential in bioretention basin soils.
• To assess the influence of site age, soil texture, and carbon sources on nitrogen dynamics.
• To provide recommendations for enhancing bioretention basin efficiency in subtropical Australia.

Main Methods:

• Studied 25 bioretention basins over a 13-year chronosequence in a subtropical Australian climate.
• Analyzed total nitrogen accumulation in soil profiles (top 5 cm vs. deeper soils).
• Measured denitrification potential, soil characteristics, and stable isotopes (δ13C, δ15N) in a subset of basins.

Main Results:

• Total nitrogen accumulated faster in the top 5 cm of soil, reaching densities of 1.4 kg N m⁻³.
• Site age and soil texture were significant predictors of soil TN density and denitrification rates (1–9.7 mg N m⁻² h⁻¹).
• Stable isotope analysis indicated nitrogen fixation in young basins and increased denitrification in older basins; plant material was the primary carbon source.

Conclusions:

• Bioretention basins effectively accumulate nitrogen, with significant denitrification potential increasing with basin age.
• Recommendations include increasing initial vegetation and promoting anaerobic conditions to enhance denitrification and water quality improvement.
• Site age and soil texture are critical factors influencing the long-term nitrogen removal capacity of bioretention systems.