Efficacy of different phytoremediation methods for removing nitrogen and phosphorus in drainage ditches of the Wuliangsuhai watershed

【Objective】Nitrogen (N) and phosphorus (P) leaching from the Hetao Irrigation District have led to eutrophication and water pollution in Wuliangsuhai Lake. Over the past decade, various phytoremediation techniques have been developed to address this issue. This study compares the effectiveness of different vegetative buffer strips in removing N and P from drainage ditches. 【Method】Drainage ditches were constructed to evaluate the effectiveness of various vegetative buffer strips in removing N and P. The plants and phytoremediation techniques compared in this study included Astragalus membranaceus var. obliquus (T1), Melilotus officinalis (T2), Medicago sativa (T3), microbial biological ropes (T4), and microbial biological sheets (T5). The control group had no remediation (CK). In each treatment, we measured changes in N and P concentrations in the water, sediment, and plant tissues.【Result】T1 (Astragalus membranaceus var. obliquus) was the most effective in reducing N and P, with total nitrogen (TN) and total phosphorus (TP) reduction rates in the water reaching 71.61% and 80.51%, respectively. It also adsorbed the highest amounts of N and P into the sediments, with adsorption rates of 48.81% for TN and 71.31% for TP. The associated absorption by plant tissues was 20.44% for TN and 69.21% for TP. Among all the plant species tested, Astragalus membranaceus var. obliquus was the most effective for removing TN and TP from the drainage. Our results also showed that a hydraulic retention time of 0-6 hours was most effective for pollutant removal, with TN and TP removal rates of 39.18% and 35.41%, respectively. Nutrient balance analysis indicated that, under the same conditions, T1 had the highest N and P uptake, reaching 5.25 g/kg and 3.08 g/kg, respectively, and the lowest nitrogen loss and changes in the water bodies (7.64 mg/L). 【Conclusion】Our results demonstrate that Astragalus membranaceus var. obliquus is the most effective plant species for removing N and P from drainage ditches. It is therefore a promising phytoremediation method to mitigate eutrophication and water pollution in the Hetao Irrigation District.