While catastrophic spills of hydrocarbons are environmental disasters, a more important threat to the health of nearshore ecosystems is diffuse, low-concentration runoff of anthropogenic hydrocarbons from urban areas. The first phase of this research monitored intact sediment microcosms for three months and showed that they were stable, as well as sensitive enough to exhibit changes within the microbial community when weathered hydrocarbons were added. The second phase of this research used these intact sediment microcosms to compare the effects of Orimulsion (a novel fuel product) and fuel oil #6 on the microbial community. The sediment microcosms did not show any changes in the microbial community from addition of Orimulsion. Fuel oil #6 increased the number of bacteria, reduced oxygen penetration into the sediments, and increased hydrocarbon metabolism in the bacteria. The third phase of this research investigated the effects of clay and humic acids on microbial phenanthrene respiration in marine sediment bacteria. This research continues work that was started in pure cultures and expands it by using enrichment cultures and natural sediment communities of bacteria. Cultures enriched with phenanthrene or fuel oil #6 demonstrated a 10–40% increase in phenanthrene respiration in the presence of humic acids or humic acid-clay complexes. Native, unadapted assemblages of marine sediment bacteria exhibited a 30–490% increase in phenanthrene respiration in the presence of clay and humic acid-clay complexes—a far larger increase in phenanthrene respiration than has been demonstrated previously. Increased respiration of phenanthrene in the presence of clay and humic acid is not just a property of a few rare types of bacteria but rather an important characteristic of naturally occurring sediment microbial communities.
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