Efficiency of Three Aquatic Macrophytes in Mitigating Nutrient Run-off

Ditches lining agricultural fields are used to convey runoff water and are typically mowed to reduce vegetative growth. If agricultural ditches are viewed as a wetland, ditch vegetation might be utilized to remove excess nutrients in runoff water. It was hypothesized that particular species of ditch vegetation would be more effective at removing nutrients in runoff water. Replicate 379 L Rubbermaid® troughs (132 cm ×70 cm × 66 cm) were planted with individual species of soft rush (Juncus effusus), yellow primrose (Ludwigia peploides) and cutgrass (Leersia oryzoides), common wetland macrophytes found in Mississippi agricultural drainage ditches. Nutrient-enriched water (target concentrations = 5 mg L!1 nitrate, 5 mg L!1 orthophosphate, and 5 mg L!1 ammonia) was pumped in at a 4 h hydraulic retention time at one end of the tub and discharged at the far end. Water samples were collected from discharge at 1 h intervals for 9 h and analysed for nutrient concentrations. Nutrient removal rates were compared for all plant treatments and unplanted sediment-water controls. Results indicated that no single species was most effective at removing both nitrogen species and orthophosphate, although all three plant treatments lowered nutrient concentrations in water relative to unplanted controls. Ammonia and nitrate concentrations in water were most decreased in Ludwigia peploides tubs (83±3% and 40±8%, respectively) and total orthophosphate was decreased most by Leersia oryzoides (29±7%). Leersia oryzoides was least effective at removing nitrate and ammonia concentrations. By determining specific plant retention of various nutrients, improved planning can be accomplished for best management practices and remediation techniques such as constructed wetlands or vegetated agricultural drainage ditches. Key Words: Nitrate, Ammonia, Orthophosphate, Phytoremediation.