Influence of plant dynamics on phosphorus removal in bioretention systems under different internal and external conditions

Abstract

Bioretention systems are widely used to remove phosphorus from urban runoff, contributing to aquatic ecosystem restoration. Although plant uptake plays a pivotal role in enhancing total phosphorus (TP) removal, few studies have investigated influences of dynamic plant phosphorus uptake on TP removal under varying internal (e.g., gravel layer depth) and external (e.g., catchment area ratios and influent phosphorus concentration levels) conditions. This study proposes a bioretention system model that integrates plant growth (e.g., phosphorus uptake, leaf area index, and biomass), hydrology (e.g., soil moisture and evapotranspiration), and phosphorus dynamics (e.g., soil phosphate concentration) through their interactive processes. The model was validated against two-year field data from a bioretention system planted with Canna indica L. in Shenzhen, China. Key findings include: (i) The model accurately simulates plant dynamics and effluent phosphorus processes, with Nash-Sutcliffe Efficiency coefficients exceeding 0.5 for leaf area index, biomass, monthly plant phosphorus uptake, and effluent TP concentrations; (ii) Neglecting dynamic plant phosphorus uptake leads to misestimation of TP removal, especially in systems with shallower gravel depths, where daily efficiency overestimation can reach 21.8 %; and (iii) Under lower influent phosphorus concentrations, failure to account for plant uptake results in greater inaccuracies in TP removal estimates, with daily removal efficiency deviations as high as 31.2 %. This study provides a tool for long-term TP removal assessment that accounts for dynamic plant uptake and quantifies its impact across different bioretention conditions.