Oil Penetration and Vegetation Recovery in Lajas Creek Marsh, Puerto Rico
ABSTRACT In September 1998, during Hurricane Georges, 5,000–10,000 gallons of No. 6 fuel oil were released from a refinery, oiling freshwater marshes along Lajas Creek near Bayamon, Puerto Rico. Aggressive cleanup actions were taken to protect downstream areas including placement of fill material to access the marsh, limited mechanical scraping and excavation of vegetation and sediments, cutting of oiled vegetation, and dragging of sorbents across the marsh by hand. It was thought at the time that oil would not penetrate the marsh sediments and that the vegetation would recover within 3 months. During irregular site visits from October 1998 through July 2000, the authors checked for the presence/absence of subsurface oiling and made simple field observations of vegetation establishment. Fresh black oil was found in creek levee sediments down to the water table, as deep as 60 cm. The oil penetrated the sediments through root channels, animal burrows, and perhaps desiccation cracks in the clay soils. In wetter, nonlevee sediments, oil was mixed into the substrate, possibly by foot depressions, to 15 cm below the surface. A buried layer of fresh oil also was found under fill material. Penetration of oil into marsh sediments likely was related to the type of marsh and geomorphic features present at the site. In January 1999, revegetation from seed was underway in some areas, although the visual appearance of plant cover and height was less than that observed in nonoiled areas and several large areas lacked vegetation. By July 2000, the vegetation appeared recovered in terms of visual appearance. Though plant recovery probably took more than twice as long as predicted, vegetation recovery time was relatively normal, perhaps even rapid, compared to temperate zone marshes.