Comprehensive evaluation of the hydrology, pollutant removal, and carbon sequestration performance of...

Low impact development (LID) systems effectively reduce stormwater runoff and improve water quality. In addition, their potential contributions to carbon sequestration and climate change adaptation have attracted growing research attention. This study investigated the influence of biochar content on the performance of bioretention cells. A series of experiments was conducted to evaluate eight key indicators: saturated hydraulic conductivity (K_sat), water holding capacity, removal efficiencies for ammonium nitrogen (NH₄-N), nitrate nitrogen (NO₃-N), phosphate (PO₄^3--P), and chemical oxygen demand (COD); CO₂ sequestration flux; and soil organic carbon content. The results indicate that biochar amendments significantly improve the functionality of LID systems. Furthermore, the addition of 2.5 % biochar effectively enhances soil hydrological properties, creating favorable conditions for plant growth. The addition of 5 % biochar results in optimal pollutant removal and water purification, thus serving as a well-balanced and efficient treatment strategy. Moreover, the addition of 10 % biochar results in optimal carbon sequestration, demonstrating the role of biochar in strengthening soil carbon sinks. However, excessive biochar content may affect microbial activity and nutrient pathways, potentially leading to reductions in NO₃-N and COD removal efficiencies. This study provides practical guidance for optimizing biochar use in LID systems to support stormwater management, water quality improvement, and long-term climate mitigation through soil-based carbon storage.