Phytoindication and Phytoremediation of Water Quality Using the Local Duckweed Plant Lemna aequinoctialis

Abstract

Environmental pollution exacerbates global freshwater scarcity. In Harare, sewage pollution drives freshwater pollution, compromising its quality and security. Here, we uniquely explored the dual role of Lemna aequinoctialis as a phytoindicator and phytoremediator of freshwater quality. Using a purposive sampling strategy targeting common household freshwater abstraction sites in selected communities of Harare (Tafara and Manyame), 12 water samples and an L. aequinoctialis culture were collected from the field and incubated in the laboratory. Biochemical oxygen demand (BOD), electrical conductivity (EC), and potential hydrogen (pH) were determined by probes, while total suspended solids (TSS) and turbidity were analyzed by UV-Vis Spectrometry. Chemical oxygen demand (COD), nitrates (NOˉ₃), nitrites (NOˉ₂), and orthophosphates were analyzed by colorimetric techniques. An analytical balance measured the plant fresh weights and root lengths were measured via microscopy. Akin to ⁺raw sewage, River B (Tafara) exhibited the highest initial pollutant load; BOD (3.8 mg/L), COD (38 mg/L), TSS (96 mg/L), NOˉ₃ (0.134 mg/L), NOˉ₂ (0.058 mg/L), orthophosphates (0.524 mg/L), turbidity (87 FTU), with notably reduced mean fresh biomass (2.9 g) and root length (7.3 mm) which were moderately and negatively correlated with NOˉ₂ and orthophosphates, respectively. Only EC failed to improve after L. aequinoctialis incubation significantly. Despite spatial-temporal limitations, we present limited evidence suggesting a potential real-time, dual utility role that can help track, redress pollution, and suppress algal blooms enhancing public health and transcending the typical role of duckweeds. Long-term applicability of this phytotechnology requires further attention for sustainable freshwater management in resource-limited regions like Zimbabwe.