Water purification capacity of ecological ditch: A systematic review and meta-analysis of influencing factors

Agricultural non-point source (ANPS) pollution, a primary contributor to rural surface water pollution, poses a significant threat to both aquatic and terrestrial ecosystems. Ecological ditches (EDs) have gained widespread usages in addressing ANPS pollution due to their low construction costs and simplicity in operation and maintenance while the removal efficiency of ANPS pollutants in EDs has shown significant variability. In this study, we conducted a meta-analysis using a database containing 1001 data points from 40 peer-reviewed publications to illustrate the impact of various factors (i.e., influent concentration, plant diversity, seasonal variation and temperature, hydraulic retention time (HRT)) on the removal rates of ammonia nitrogen (NH4+-N), total nitrogen (TN) and total phosphorus (TP) in EDs. Our findings indicate that EDs exhibit substantial removal efficiency, with combined effect sizes of 65.2%, 45.8% and 50.1% for NH4+-N, TN and TP, respectively. Most EDs achieved the highest removal efficiency for NH4+-N, TN and TP when influent concentrations fall within these ranges: 8–16 mg/L, 20–40 mg/L and 0–0.4 mg/L, respectively. Plant diversity plays a crucial role in pollutant removal. EDs with more than two plant species are less effective compared to those with a single species. In the winter, wilting plants can even become sources of pollutants, therefore, prompt mowing is essential to prevent secondary pollution. A significantly (P