This project investigates phytoremediation at a disused fire training runoff lagoon at an ecologically sensitive area in Southern England called Horsea Island. The sediments in the semi-saline lagoon were highly contaminated with over 145,000 mg/kg Dry Weight (DW) Diesel Range Organics (DRO) and were classed as carcinogenic and unsafe for human exposure. Phytoremediation was attractive as an inexpensive and in situ remediation method. However there were limited field studies examining such extremely contaminated conditions. Initial mesocosm studies indicated that both Phragmites australis and Typha latifolia were able to grow in this sediment without the need for additional nutrients and P. australis was subsequently used for test planting in the lagoon. Ex situ greenhouse microcosms as well as an in situ full scale trial was carried out and the response of DRO and microbial populations were investigated over a 15 month period. Using a novel colourmetric plate test developed during this study, planted sediments in both the microcosms and Horsea lagoon showed not only an increased diversity but also an increased number of hydrocarbon-degrading bacterial isolates when compared to unplanted sediments. However, although the overall DRO concentrations fell in both the in situ and ex situ systems in times of hot weather and low water levels, there were no significant differences between planted and unplanted sites. There was also no difference between microbial numbers in planted and unplanted sites in either the microcosms or Horsea lagoon however, the mesocosms that had been growing for three years showed significantly higher numbers of bacteria, hydrocarbon-tolerant bacteria and hydrocarbon-tolerant fungi as well as elevated numbers of fungi in the planted sites. This indicates that phytoremediation may require a longer period of time to enhance degradation in such conditions.
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