Mitigation of herbicide runoff as an ecosystem service from a constructed surface flow wetland

Ecosystem services provided by wetland systems presently play a pivotal role in intensive cropland as water purification from agricultural pollution. A field trial was conducted in 2014 to evaluate herbicide runoff reduction and retention using a 0.32 ha constructed surface flow wetland (CSFW) at the outlet of a 6 ha agricultural basin. To simulate an extreme pulse contamination, the CSFW was flooded with a runoff contaminated with metolachlor, and terbuthylazine and two other subsequent floods with pure water were applied 21 and 65 days later. Results show that the CSFW can reduce runoff concentration of metolachlor and terbuthylazine by a factor of 45-80 even in extreme flooding conditions. Herbicides retention in the CSFW was reversible, and the second and third floods mobilized 14-31 and 3.5-7.0% respectively, of the amount detected in the first flood. The CSFW performs a high buffer capacity for herbicides, capable to provide water purification service, protecting downstream surface water. Moreover, mitigation capacity of a CSFW for a heavy runoff from a 10 ha basin is 90% for every 50 m in length of a 15 m wide wetland. This confirms that the implementation of CSFWs in agro-systems can improve the sustainability of agricultural production.