Effects of salinity on removal of nitrogen and phosphorus from eutrophic saline water in plantedLythrum salicariaL. microcosm systems

Treatment of eutrophic saline water is problematic due to high concentrations of nitrogen and phosphorus often combined with high salinity levels. In this paper, microcosm systems planted with Lythrum salicaria L. (purple loosestrlfe) were set up to evaluate the capacity of the systems to remove excessive nutrients from fresh water (0.05% salinity), and saline water (0.5% and 1.0% salinity). The average removal efficiencies were 30.6%–45.3% for total nitrogen (TN), 31.4%–55.4% for ammonia nitrogen ( - N), 28.0%–45.9% for nitrate nitrogen (-N), and 9.1–16.2% for total phosphorus (TP) at different salinities, respectively. It was observed that the treatment performance was significantly inhibited by increasing salinity. However, increasing salinity could promote the -N removal in the systems. In addition, the elevated salinity of eutrophic saline water was found to induce a stress response that could be quantified by a series of metabolic assays measuring the chlorophyll (Chl), proline (Pro), and malondialdehyde (MAD). At different salinities, no significant differences were observed in pigments' content on the third day of the experiment. But on the seventh day of the experiment, 0.5 and 1.0% salinity resulted in sharp decrease in the levels of chl b, total chl, and total chl/carotenoids. Compared to 0.05% salinity, proline accumulation and MAD increased significantly with increasing salinity, but the content of MAD was still very low (<0.1 μmol g−1 FW). The results of this study indicate that the planted salt-tolerant aquatic macrophytes systems can be a low-cost ecological phytoremediation technology to treat eutrophic saline water, and the application of cellular stress assays can provide useful tools to monitor salt-induced responses in aquatic macrophytes.