Investigation of agricultural nutrient removal by ecological ditches using meta-analysis

Excessive nutrient export from agricultural areas is a growing threat to surface water bodies and aquatic ecosystems. Ecological ditches have been proposed to eliminate agricultural pollution. Numerous studies have demonstrated the efficiency of total nitrogen (TN) and total phosphorus (TP) removal by ecological ditches, but the removal rates vary greatly. It is vital to evaluate and quantify the impact of the relevant factors influencing nutrient removal. In this study, the synthesis of TN and TP removal rates by eco-ditches was conducted using 115 groups of data derived from 66 articles sourced from Web of Science and Scopus. Overall, eutrophication risk was obviously reduced by ecological ditches, with TN and TP removal rates of over 40 %. Therefore, further analyses were conducted to identify the effect of plants, ditch lining, temperature, and hydraulic retention time on nutrient removal. Subgroup meta-analysis revealed that plant presence and plant combinations were important for water purification. With plant group optimization, partially lined eco-ditches were found to have similar effects to ecological soil ditches in latitudes between 25°N and 35°N. Temperature was a vital factor influencing N and P retention. The generalized additive model analysis indicated the optimal HRT for TN and TP retention was 24–48 h. The areal removal constants of a first-order model were obtained to estimate nutrient removal in different ecological ditches. Overall, ecological ditches have great potential for TN and TP removal of agricultural pollution, and the results of this study will help optimize ecological ditches designed to purify nutrient-rich agricultural runoff.