Interspecific competition and their impacts on the growth of macrophytes and pollutants removal within constructed wetland microcosms treating domestic wastewater

Eight free water surface constructed wetland microcosm (CWM) units are designed with single as well as mixed planting of Pistia stratiotes, Phragmites karka, and Typha latifolia with control to assess their competitive value (CV), relative growth rates (RGR), and pollutants removal efficiency. Further, the total dry biomass production and other growth parameters such as number of macrophytes, above-ground biomass, below-ground biomass, and root length were also measured to understand the dominant characteristics of the macrophytes. The CWM units with species mixture out-performed species monocultures. Removal of BOD, TP, SRP, NH₄ ⁺-N, NO₃ ⁻-N, and NO₂ ⁻-N by mixed planting of P. stratiotes and P. karka was higher at most of the time. Typha latifolia was the superior competitor against both P. stratiotes and P. karka due to its aggressive characteristics that inhibits the growth of neighboring macrophytes. However, P. karka was the superior competitor against P. stratiotes. The RGR of T. latifolia in all experimental units was almost two times more than that of P. karka. Novelty Statement The CWM units with species mixture out-performed species monocultures. CWMs with more than one macrophytic species are less vulnerable to seasonal fluctuations and more effective in contaminants removal as compared to single macrophyte wetlands. Removal of BOD, TP, SRP, NH₄ ⁺-N, NO₃ ⁻-N, and NO₂ ⁻-N by mixed planting of P. stratiotes and P. karka was higher at most of the time. The CWMs with P. stratiotes and P. karka are superior choice due to their higher wastewater nutrients removal capacity. The application of these three macrophytes in mixed cultures in free water surface constructed wetland is rare. The results are useful in designing large-scale multi-species wetlands which are less susceptible to seasonal variation and more effective in pollutants removal than single-species wetlands.