Restoration of an Oil-Contaminated St. Lawrence River Shoreline: Bioremediation and Phytoremediation

Abstract

ABSTRACT The purpose of this field study was to evaluate bioremediation and phytoremediation in restoring an oil-contaminated freshwater shoreline. Weathered Mesa light crude oil was released intentionally onto small plots in the upper intertidal zone of a study site located along the St. Lawrence River. Treatments were established to examine the effect of nutrient addition and the role of plants (Scirpus pungens) on the removal of oil constituents from the contaminated plots. Fertilizers under evaluation included sodium nitrate, prilled ammonium nitrate, and triple super phosphate. Composite core samples were collected after 0, 1, 2, 4, 8, 12, 16, and 21 weeks for identification of remaining oil constituents by gas chromatography-mass spectrometry (GC-MS). To account for differences because of physical washout, all oil constituents were normalized to the conservative biomarker hopane. Although bioremediation and phytoremediation treatments achieved slightly better degradation of hydrocarbons than natural attenuation, no statistically significant evidence of stimulation through addition of nutrients or biodegradation enhancement by vegetation was observed. After 21 weeks, reduction of target parent and alkyl-substituted polycyclic aromatic hydrocarbons (PAHs) averaged 32% in all treatments. Reduction of target alkanes was of similar magnitude. The pattern of disappearance of hydrocarbons was characteristic of biodegradation: namely, the lower molecular weight alkanes declined to a greater extent than the higher carbon-number alkanes, as did the lower molecular weight PAHs compared to the higher molecular weight PAHs. Since there was little evidence supporting enhancement of biodegradation by nutrient addition with and without vegetation, it was concluded that oxygen limitation most likely dominated the persistence of oil hydrocarbons on the oil-contaminated plots.