Influence of Three Aquatic Macrophytes on Mitigation of Nitrogen Species from Agricultural Runoff

Agricultural runoff containing nitrogen fertilizer is a major contributor to eutrophication in aquatic systems. One method of decreasing amounts of nitrogen entering rivers or lakes is the transport of runoff through vegetated drainage ditches. Vegetated drainage ditches can enhance the mitigation of nutrients from runoff; however, the efficiency of nitrogen removal can vary between plant species. The efficiency of three aquatic macrophytes, cutgrass (Leersia oryzoides), cattail (Typha latifolia), and bur-reed (Sparganium americanum), to mitigate dissolved and total nitrogen from water was investigated. Replicate mesocosms of each plant species were exposed to flowing water enriched with ammonium and nitrate for 6 h, allowed to remain stagnant for 42 h, and then flushed with non-enriched water for an additional 6 h to simulate a second storm event. After termination of the final simulated runoff, all vegetated treatments lowered total nitrogen loads exiting mesocosms by greater than 50%, significantly more than unvegetated controls, which only decreased concentrations by 26.9% (p ≤ 0.0023). L. oryzoides and T. latifolia were more efficient at lowering dissolved nitrogen, decreasing ammonium by 42 ± 9% and 59 ± 4% and nitrate by 67 ± 6% and 64 ± 7%, respectively. All treatments decreased ammonium and nitrate concentrations within mesocosms by more than 86% after 1 week. However, T. latifolia and L. oryzoides absorbed nitrogen more rapidly, lowering concentrations by greater than 98% within 48 h. By determining the nitrogen mitigation efficiency of different vegetative species, plant communities in agricultural drainage ditches can be managed to significantly increase their remediation potential.