Abstract: We evaluated the single and synergistic effects of Ulva lactuca and Sesuvium portulacastrum on the purification of mariculture wastewater. The results showed that the water quality was significantly improved by U. lactuca with different planting densities after 12 days treatment. The treatment with a density of 2.0 g·L^-1 showed the highest removal rates of COD, inorganic phosphorus, ammonium nitrogen and total nitrogen, with values being 41.7% 76.9%, 81.8%, and 67.2%, respectively. Similarly, S. portulacastrum with different planting densities also significantly improved water quality after 12 days treatment. The planting density of 4.8 g·L^-1 had the highest removal rates of COD, inorganic phosphorus, ammonium nitrogen and total nitrogen, which were 49.0% 20.8%, 98.5%, and 55.9%, respectively. In the treatment with combined U. lactucaand S. portulacastrum, the removal rates of COD, inorganic phosphorus, ammonium nitrogen and total nitrogen reached 36.7%, 100%, 100.0%, and 88.8% respectively, indicating that their combination enhanced the purification ability. Our results suggest that both  U. lactuca and S. portulacastrumcan improve water quality, and appropriate planting density and suitable combination of plant species would promote the phytoremediation effects.

Key words: Haloxylon ammodendron plantation, carbon flux, desert ecosystem, eddy covariance