Evaluating and screening the dosage-dependent bioremediation efficiency of seaweeds and a halophyte species

Aquatic macrophytes play a critical role as natural bio-remediators of nutrient-enriched aquatic bodies. We aimed to evaluate the nutrient absorption efficiency and growth rate of four seaweeds (Caulerpa lentillifera, Codium fragile, Betaphycus gelatinus, Gracilaria confervoides) and a halophyte (Sesuvium portulacastrum). G0: with no addition of chemicals; G1: with 10 mg/L NH₄Cl and KH₂PO₄; G2: with 20 mg/L; and G3: with 30 mg/L. The study revealed variable growth rates, with C. lentillifera consistently showing the highest growth indicators, i.e., weight gain, specific growth rate, and weight gain, achieving the highest biomass and fastest growth; conversely, S. portulacastrum showed the lowest performance. WGR reached 289% in C. lentillifera at G3, significantly outperforming other species. Across various nutrient treatments, plant-based bioremediation consistently exceeded the G0 group in absorbing NO₂^-N, NO₃^-N, NH₄⁺-N, PO₄³^-, TSS, and COD (Chemical Oxygen Demand). C. lentillifera was mainly responsible for efficient nutrient removal, whilst B. gelatinus and G. confervoides had moderate nutrient removal efficiencies. Conversely, the halophyte S. portulacastrum exhibited relatively low nutrient assimilation, and all the removal rates were lower in each treatment. Overall, the C. lentillifera and C. fragile confirmed the highest nutrient uptake despite an increase in the chemical dosage used for eutrophic water synthesis.