Growth of <i>Chrysopogon zizanioides</i> in Floating Treatment Wetlands with Different Substrates for the Remediation of an Urban River

Urban river degradation demands remediation strategies that are both environmentally sustainable and technically feasible. This study evaluated the performance of Floating Treatment Wetlands (FTWs) vegetated with <i>Chrysopogon zizanioides</i> (vetiver) and incorporating four substrate configurations: leaf litter (LL), red volcanic rock (RVR), corn cobs (CC), and a composite mixture of all three, for the rehabilitation of the “Paseo de Los Ahuehuetes” River in Veracruz, Mexico. Over a 182-day monitoring period, in situ water quality parameters and plant growth responses were systematically assessed. The results indicate that substrate selection is a decisive design factor governing the establishment and development of <i>C. zizanioides</i> in FTWs. Among the substrates tested, LL exhibited the most favorable performance, achieving the highest plant survival (82%), enhanced shoot elongation (71.5 ± 12.1 cm), greater root development (49.7 ± 10.0 cm), and the highest relative growth rate (0.028 g g⁻¹ d⁻¹), with statistically significant differences (<i>p</i> < 0.05) compared to CC. Additionally, localized improvements in water quality within the FTW zone were observed, including an increase in dissolved oxygen (2.07%) and a reduction in total dissolved solids (5.65%), likely associated with intensified rhizospheric processes. Overall, these findings identify leaf litter as a low-cost, locally available, and environmentally sustainable substrate that enhances vetiver establishment in FTWs. The study provides practical, evidence-based criteria for the design of nature-based phytoremediation systems aimed at the restoration of urban river ecosystems.