Reduction of COD and nutrient runoff losses by eco-ditch with embedded nutrient interception and sediment trapping tank

• Eco-ditches with embedded NIST tanks significantly improve the removal efficiency of nitrogen and phosphorus. • The integration of NIST tanks enhances the pollutant interception capacity of eco-ditches, making them effective in mitigating agricultural non-point source pollution. • The inclusion of NIST tanks increased algal diversity in sediments, contributing to a improved nutrient bioavailability. • This work offers practical insights for improving water quality in lowland agricultural regions. Eco-ditches, as nature-based infrastructure, have gained growing interest in agricultural non-point source pollution control. However, their effectiveness is highly dependent on specific design configurations. This study introduces a novel eco-ditch design that integrates nutrient interception and sediment trapping (NIST) tanks to enhance the removal of carbon and nutrients from agricultural runoff. We compared three ditch types: Class A (eco-ditch with NIST tanks), Class B (eco-ditch without NIST tanks), and Class C (conventional ditch) in reducing carbon and nutrient runoff losses in a paddy plain during the rice growing season. Results showed that Class A ditches achieved 18.1%–26.1% higher reduction in COD and nutrients – total nitrogen (TN)/phosphorus (TP) compared to Class B and Class C. Additionally, 31 P nuclear magnetic resonance spectroscopy and 18S rRNA sequencing analysis revealed significant increases in phosphorus bioavailability and algal diversity in Class A sediments. These findings suggest that integrating NIST tanks into eco-ditch provides a cost-effective, scalable solution for improving water quality management in lowland agricultural regions, with important implications for the design of sustainable agricultural drainage infrastructure.