Potential for Phosphate Mitigation from Agricultural Runoff by Three Aquatic Macrophytes

Phosphate from agricultural runoff is a major contributor to eutrophication in aquatic systems. Vegetated drainage ditches lining agricultural fields have been investigated for their potential to mitigate runoff, acting similarly to a wetland as they filter contaminants. It is hypothesized that some aquatic macrophytes will be more effective at removing phosphate than others. In a mesocosm study, three aquatic macrophyte species, cutgrass (Leersia oryzoides), cattail (Typha latifolia), and bur-reed (Sparganium americanum), were investigated for their ability to mitigate phosphate from water. Mesocosms were exposed to flowing phosphate-enriched water (10 mg L−1) for 6 h, left stagnant for 42 h, and then flushed with non-nutrient enriched water for an additional 6 h to simulate flushing effects of a second storm event. Both L. oryzoides and T. latifolia decreased the load of dissolved phosphate (DP) in outflows by greater than 50 %, significantly more than S. americanum, which only decreased DP by 15 ± 6 % (p ≤ 0.002). All treatments decreased concentrations inside mesocosms by 90 % or more after 1 week, though the decrease occurred more rapidly in T. latifolia and L. oryzoides mesocosms. By discovering which species are better at mitigating phosphate in agricultural runoff, planning the community composition of vegetation in drainage ditches and constructed wetlands can be improved for optimal remediation results.