Study on the economic advantages of ecological ditch and the impact of removing nitrogen and phosphorus from paddy field drainage

In modern agriculture, fertilizers and pesticides not absorbed by crops contribute significant total nitrogen (TN) and total phosphorus (TP) to water bodies, leading to agricultural non-point source pollution (ANSP). This study presents a novel ecological ditch utilizing Vallisneria natans (V. natans) to purify TN and TP in farmland drainage while enhancing economic efficiency. Ecologically, the ecological ditch effectively intercepted TN and TP in the drainage water, achieving removal rates of 94.8–97.0 % for TN and 88.8–94.0 % for TP. Economically, the net profit and output/input ratio of the ecological ditch reached 3002.5 ± 340.7 RMB and 1.53 ± 0.18, respectively. Furthermore, the results indicated a negative correlation between the biomass of V. natans and the concentrations of TN (r = −0.51) and TP (r = −0.46) in water. The study also revealed significant negative correlations between the biomass of V. natans and the concentrations of TN (r = −0.70) and TP (r = −0.48) of sediments. Additionally, The biomass exhibited a positive correlation with both the DO (r = 0.86) concentration in the water and the organic matter content in the sediment (OM_S) (r = 0.95). These findings reflect the tendencies and transformation pathways of TN and TP within the ecological ditch. These findings highlight the potential of ecological ditches as effective tools for mitigating ANSP while providing economic benefits to agricultural systems.