Can vegetated drainage ditches be effective in a similar way as constructed wetlands? Heavy metal and nutrient standing stock and removal by ditch plant species

Authors: MATHIEU, NSENGA KUMWIMBA - Sun Yat-Sen University; ZHU, BO - Chinese Academy Of Sciences; Moore, Matthew; WANG, TAO - Chinese Academy Of Sciences; LI, XUYONG - Chinese Academy Of Sciences

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2021
Publication Date: 4/12/2021
Citation: Mathieu, N., Zhu, B., Moore, M.T., Wang, T., Li, X. 2021. Can vegetated drainage ditches be effective in a similar way as constructed wetlands? Heavy metal and nutrient standing stock and removal by ditch plant species. Science of the Total Environment. https://doi.org/10.1016/j.ecoleng.2021.106234.
DOI: https://doi.org/10.1016/j.ecoleng.2021.106234

Interpretive Summary: In developing countries such as China, rural domestic wastewater often combines with agricultural runoff to impact downstream water bodies. Vegetated ditches are being promoted as a management practices for nutrient and pesticide reduction; however, little is known of their ability to treat components of domestic wastewater or impacts of the contaminants on the vegetation itself. A field ditch was monitored for two years in four places to study reductions of nutrients and metals. Successful contaminant reduction occurred, and a biomass harvesting plan was determined based on peak contaminant retention. This study demonstrates the effectiveness of vegetated ditches as a management practice to reduce contaminant concentrations before they enter downstream rivers and lakes.

Technical Abstract: Agricultural runoff impacts rivers and lakes on a global scale, while in developing countries (e.g., China), rural domestic wastewater is often an additional source of pollution. Scholars and policy makers are now promoting the use of agricultural vegetated ditches (VDs) as a potential supplemental management practices for nutrients and pesticide reduction from agricultural sources; however, information on the efficacy of these systems for the treatment of rural wastewater loaded with nutrients and heavy metal(loid)s (HMLs) removal and standing stock in aquatic plants growing there is rare or unknown. To address this knowledge gap, the present study deals with SS of ten HMLs in ten plant species growing in a VD receiving raw rural domestic wastewater, with the intention to revealing an appropriate period for ditch plant harvesting to maximize HM removal. Mean reduction efficiencies amount to TN (60.62%), NH4-N (63.29%), NO3-N (48.13%), TP (58.45%) and PO4-P (51.98%), with favorable treatment performance during the summer season. Furthermore, the annual average reduction amounted to Ni (50.6 %), Cu (56.1 %), Cr (63.3 %), Zn (79.3 %), Cd (67.5 %), Pb (80.1 %), As (60.3 %), Fe (52.6 %), Al (19.8 %), and Mn (24.3 %). Plant uptake and sediment retention were the major contributors for nutrient mitigation within the vegetated ditches, with subsequent bacterial interaction and transformation of pollutants. Overall, SSs of most HMLs in plant species were greater in either stems or roots than leaves. Based on the seasonal fluctuation of the accumulated HMLs in different plant species, the approach of harvesting plant biomass in order to effectively target HMLs in August or early September is recommended. Overall, reported results suggest that VD is an effective ecosystem to mitigate pollutants from raw rural domestic wastewater in a similar way as constructed wetlands, noting the potential incorporation into local best management practices.