Evergreen Trees and Marine Bacteria

Alaska's coastal waters contain unexpectedly large populations of hydrocarbon-eating bacteria. This fact comes to light through studies of how petroleum is biologically removed from sea water.

Higher life forms cannot metabolize carbon-hydrogen compounds. But many species of microorganisms--certain bacteria, yeasts, and fungi--can gain energy by eating simple hydrogen-carbon compounds, such as those which petroleum crude is composed of.

However if hydrocarbons are introduced to marine bacteria not accustomed to metabolizing the hydrocarbons, it takes time for the bacteria to adapt to the new foodstuffs. So it came as a surprise to discover that marine bacteria in southern Alaska's waters would immediately attack and begin digesting introduced petroleum.

We have found equally abundant populations of hydrocarbon eating bacteria in Port Valdez, where small amounts of oil are regularly discharged, and in Resurrection Bay near Seward where such discharges are not made. Seeking an answer to this puzzle we searched inland to the forests, where we suspected that rainwater might be washing hydrocarbons from trees and that these compounds were being regularly delivered to the coastal waters by runoff.

Rainwater falling on trees either runs down the stem of the tree or flows outward over the limbs and foliage. Because of their downward sloping branches, evergreen trees are mostly washed by this so-called crown flow. As the water runs down over the bark and needles it dissolves hydrocarbons produced by the tree, among them are the volatile compounds called terpenes. Our laboratory tests have shown substantial quantities of terpenes in the wash water from spruce, an abundant coastal tree.

Apparently the terpene-rich water runs off into the sea where it whets the appetite of the marine bacteria and keeps them in the mood to consume hydrocarbons from any source, including oil spills. Here is yet another example of the interplay between marine and land ecosystems and a warning that what happens to change one may affect the other.