Effects of bioremediation agents on oil degradation in mineral and sandy salt marsh sediments

Although bioremediation for oil spill cleanup has received considerable att ention in recent years, its satisfactory use in the cleanup of oil spills i n the wetland environment is still generally untested. A study of the three most often used bioremediation agents, fertilizer, microbial product and s oil oxidant, as a means of enhancing oil biodegradation in coastal mineral and sandy marsh substrates was conducted in controlled greenhouse condition s. Artificially weathered south Louisiana crude oil was applied to sods of marsh (soil and intact vegetation) at the rate of 2 l m(-2). Fertilizer app lication enhanced marsh plant growth, soil microbial populations, and oil b iodegradation rate. The live aboveground biomass of Spartina alterniflora w ith fertilizer application was higher than that without fertilizer; Applica tion of fertilizer significantly increased soil microbial respiration rates , indicating the potential for enhancing oil biodegradation. Bioremediation with fertilizer application significantly reduced the total targeted norma l hydrocarbons (TTNH) and total targeted aromatic hydrocarbons (TTAH) remai ning in the soil, by 81% and 17%;, respectively, compared to those of the o iled controls. TTNH/hopane and TTAH/hopane ratios showed a more consistent reduction, further suggesting an enhancement of oil biodegradation by ferti lization Furthermore, soil type affected oil bioremediation; the extent of fertilizer-enhanced oil biodegradation was greater for sandy (13% TTNH rema ining in the treatments with fertilizer compared to the control) than for m ineral soils (26% of the control), suggesting that fertilizer application w as more effective in enhancing TTNH degradation in the former. Application of a microbial product and a soil oxidant had no positive effects on the va riables mentioned above under the present experimental conditions; suggesti ng that microbial degraders are not limiting biodegradation in this soil. T hus, the high cost of microbial amendments during bioremediation trials may not be warranted in coastal marshes where oil-adapted microbes occur. Thes e results support the conclusion that bioremediation with inorganic nutrien t addition has potential for promoting oil spill cleanup in coastal wetland s.