Modeling multi-year phosphorus dynamics in a bioretention cell: phosphorus partitioning, accumulation, and export

Abstract: Nutrient phosphorus (P) export from urban areas via stormwater runoff contributes to eutrophication of downstream aquatic ecosystems. Bioretention cells are a Low Impact Development (LID) technology promoted as a green solution to attenuate urban peak flow discharge, as well as the export of excess nutrients and other contaminants. Despite their rapidly growing implementation worldwide, a predictive understanding of the efficiency of bioretention cells in reducing P runoff remains limited. Here, we present a reaction-transport model data and codes that was used to simulate the fate and transport of P in a bioretention cell facility in the greater Toronto metropolitan area. The model incorporates a representation of the biogeochemical reaction network that controls P cycling within the cell. We used the model as a diagnostic tool to determine the relative importance of processes immobilizing P in the bioretention cell. The model predictions were compared to multi-year observational data on 1) the outflow loads of total P (TP) and soluble reactive P (SRP) during the 2012-2017 period, 2) TP depth profiles collected at 4 time points during the 2012-2019 period, and 3) sequential chemical P extractions performed on core samples from the filter media layer obtained in 2019. According to the modeling results, groundwater recharge was principally responsible for decreasing the surface water discharge from the bioretention cell (63% runoff reduction). From 2012 to 2017, the cumulative outflow export loads of TP and SRP only accounted for 1% and 2% of the corresponding inflow loads, respectively. Accumulation in the filter media layer was the predominant mechanism responsible for the reduction in P outflow loading (57% retention of TP inflow load) followed by plant uptake (21% TP retention). Of the P retained within the filter media layer, 48% occurred in stable, 41% in potentially mobilizable, and 11% in easily mobilizable forms. There were no signs that the P retention capacity of the bioretention cell would approach saturation in the near future. The design of this bioretention facility seems therefore especially efficient at controlling urban P runoff. This Dataset includes the model scripts and modelled results dataset for Elm Drive bio retention cell.

摘要：城市区域通过雨水径流流失的营养态磷（P）会加剧下游水生生态系统的富营养化。生物滞留池（bioretention cell）是一种低影响开发（Low Impact Development, LID）技术，被推广为可减缓城市峰值流量排放、削减过量营养物及其他污染物流失的绿色解决方案。尽管全球范围内该技术的应用正快速普及，但学界对生物滞留池减少磷径流的效率仍缺乏具备预测性的认知。本研究提供了用于模拟大多伦多都会区内某生物滞留池设施中磷归趋与输运过程的反应输运模型数据与代码。该模型纳入了调控池内磷循环的生物地球化学反应网络表征。我们将模型作为诊断工具，以明确生物滞留池内固持磷的各类过程的相对重要性。模型预测结果与三类多年观测数据进行了对比：1）2012-2017年时段内总磷（TP）与可溶性反应态磷（SRP）的流出负荷；2）2012-2019年时段内4个时间点采集的TP深度剖面；3）2019年获取的过滤介质层岩心样品的连续化学磷提取数据。模型结果显示，地下水补给是削减生物滞留池地表水排放量的主要原因（径流削减率达63%）。2012-2017年，总磷与可溶性反应态磷的累积流出负荷仅分别占对应流入负荷的1%与2%。过滤介质层的磷累积是减少磷流出负荷的主要机制（截留总磷流入负荷的57%），其次为植物吸收（截留21%的总磷流入负荷）。在过滤介质层截留的磷中，48%以稳定形态存在、41%以潜在可迁移形态存在、11%以易迁移形态存在。尚无迹象表明该生物滞留池的磷截留容量会在近期接近饱和。因此，该生物滞留设施的设计在控制城市磷径流方面表现出尤为优异的效率。本数据集包含埃尔姆道生物滞留池的模型脚本与模拟结果数据集。