Identification of carbon and nitrogen multimedia fate in bioretention based on 13C and 15N isotope tracers

Bioretention is one of the widely used green stormwater infrastructural measures for the efficient removal of pollutants from stormwater runoff. However, the multimedia fate of carbon and nitrogen within these systems is still not completely understood. In this work, we employed ¹³C and ¹⁵N isotope tracers to investigate the chemical transformation of carbon and nitrogen across different media layers in the bioretention. The results of ¹³C isotope tracing revealed that carbon was predominantly lost via CO₂ emission, from 36 to 46 %, while other forms of carbon loss contributed by 23–42 %. On the other side, ¹⁵NH₄⁺-N was primarily retained in the soil, comprising from 25 to 67 %; microbial adsorption was identified as the main pathway for ¹⁵NO₃⁻-N, with a contribution from 31 to 54 %, while other forms of nitrogen loss contributed by 7–37 %. This work identified the multimedia fate of carbon and nitrogen across different media layers in the bioretention, providing a theoretical foundation for bioretention-mediated pollutants removal from stormwater runoff.