In situ and microcosm investigations into the phytoremediation of hydrocarbon-contaminated lagoon sediments using Phragmites australis

A phytoremediation study was undertaken at a disused fire training runoff lagoon at an ecologically sensitive area in England. The sediments in the semisaline lagoon were highly contaminated with over 145,000  mg/kg dry weight diesel range organics (DRO). Initial microcosm studies indicated that Phragmites australis and Typha latifolia were able to grow in this sediment, and P. australis was subsequently used for test planting in the lagoon. In situ DRO and microbial populations were investigated over a 15-month period. Results were difficult to interpret due to highly variable DRO concentrations in the sediment and varying water levels. Overall DRO concentrations fell but with no significant differences between planted and unplanted sites. DRO and bacterial numbers were related to moisture content. Hot weather, combined with low water levels, gave the lowest DRO levels. Destructive testing of the microcosms after 3 years also showed no difference in DRO between planted and control; however, elevated microbial numbers were observed in P. australis planted systems. Therefore, longer-term studies are recommended to evaluate the potential of phytoremediation in such environments.