Mixed cropping enhances the nitrogen and phosphorus purification efficiency of sewage in wetland ecosystems

Although the water purification performance of individual species and their removal mechanisms have been thoroughly documented, the potential enhancement of sewage nitrogen and phosphorus removal rates through the combined effects of different plant species has yet to be comprehensively investigated. This study opted for Canna indica and Thalia dealbata, two characteristic wetland plants from the Three Gorges Reservoir Area, as the test subjects. The impact of cropping patterns (single-cropping and mixed-cropping) on the efficiency of nitrogen and phosphorus removal from sewage at varying concentrations was explored. The findings unveiled that the mixed-cropping pattern considerably heightened the total nitrogen (TN) absorption of plants in sewage environments, though it did not appreciably affect total phosphorus absorption. Moreover, sewage concentration influenced the nitrogen and phosphorus absorption patterns of plants, potentially exhibiting a threshold phenomenon. Mixed cropping significantly augmented the removal rates of sewage nitrogen and phosphorus. Under the single cropping arrangement, C. indica displayed superior pollutant removal performance in comparison to T. dealbata. Furthermore, the wetland plants significantly diminished the TN content of the soil matrix. The results indicated that the mixed planting pattern enhanced the purification efficiency of effluent nitrogen and phosphorus in the artificial wetland, probably due to the better purification by mixed species under competition for nutrients or the dilution effect of multiple species on effluent nitrogen and phosphorus nutrient salts following mixed planting. These results should guide planting selection for efficient and sustainable wastewater purification in wetland ecosystems.