Nutrient Removal Potential of Selected Aquatic Macrophytes

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Abstract
The role of eight aquatic macrophytes in removing N and P from nutrient enriched waters was evaluated using microcosm retention ponds. The aquatic macrophytes included water hyacinth (Eichhornia crassipes), water lettuce (Pistia stratiotes), pennywort (Hydrocotyle umbellata), duckweeds (Lemna minor and Spirodela polyrhiza), azolla (Azolla caroliniana), salvinia (Salvinia rotundifolia), and a submersed macrophyte, egeria (Egeria densa). Nitrogen removal by aquatic macrophyte systems was in the order of water hyacinth > water lettuce > pennywort > Lemna > Salvinia > Spirodela > egeria during the summer season, while pennywort ranked first during the winter followed by water hyacinth, Lemna, water lettuce, Spirodela, Salvinia, and egeria. Phosphorus removal in summer was highest by water hyacinth and egeria systems, while pennywort and Lemna showed high P removal rates during the winter compared to other plants. Nitrogen and P removal were generally higher in summer than winter. Plant uptake accounted for 16 to 75% of total N removal, and 12 to 73% of total P removal, indicating the possibility of N and P removal by the mechanisms other than assimilation by plants.