Phytoremediation patterns of riparian macrophytes along a spatial pollution gradient: an integrated risk–performance assessment in the Riva stream, Türkiye

Assessing the phytoremediation efficiency of riparian macrophytes in natural stream systems remains challenging because plant performance is often evaluated using metal concentrations alone, without considering biomass-driven removal or spatial contamination variability. This study evaluated four macrophytes (Typha latifolia, Phragmites australis, Lythrum salicaria, and Persicaria lapathifolia) along a pollution gradient in the Riva Stream. A novel Remediation Efficiency Index (REI) was developed to integrate contamination risk with plant performance and classify species into site-specific management zones. Five sites were sampled during the 2025 vegetation season, and water and aboveground plant biomass were analyzed using ICP-OES. Results revealed clear spatial patterns. Midstream sites represented key potentially toxic element hotspots. P. lapathifolia showed the highest Cu and Fe concentrations (184.6 and 465.3 mg kg−1), while L. salicaria accumulated the highest Zn and Pb (119.5 and 2.83 mg kg−1). P. australis dominated Cr uptake (10.3 mg kg−1) and, due to its higher biomass (1145 g DW m−2), achieved the greatest total metal removal. REI classification placed P. australis in the Sustainable Remediation zone, whereas the other species fell into Adaptive Management or High-Risk Intervention zones. These findings show that integrating biomass-driven removal with spatial contamination patterns can guide phytoremediation strategies in contaminated streams.