Pesticide retention in two small constructed wetlands: treating non-point source pollution from agriculture runoff

Abstract

Pesticide losses to the environment are undesirable because of possible environmental hazards. Loss of pesticides is likely in watersheds where pesticides are used. Small constructed wetlands (CWs) in first- and second-order streams can reduce the loss of pesticides, since water-purification processes are stimulated. Four herbicides and three fungicides were applied on arable soil on two watersheds in Norway. The two CWs are situated in western and eastern Norway. The CWs cover 0.15% and 0.4% of the watershed, respectively. This study presents the pesticide retention obtained in the two CWs. All applied pesticides were found in the streams, with the highest concentrations being found immediately after spraying. The pesticides added to the watersheds decreased on average, through the whole sampling periods, from 3 to 67%. The retention increased with the size of the wetland. In many cases, the CWs reduced the peak concentrations to values regarded as non-toxic for aquatic life.