THE PHYSICAL, CHEMICAL, AND BIOLOGICAL EFFECTS OF CRUDE-OIL SPILLS AFTER 15 YEARS ON A BLACK SPRUCE FOREST, INTERIOR ALASKA

The effects of two large experimental crude oil spills conducted in th e winter and summer of 1976 in a permafrost-underlain black spruce for est of interior Alaska were assessed 15 years after the spills. Effect s on permafrost, as determined from measurements of active layer thaw depths and of the total amount of ground subsidence, were far more pro nounced on the winter spill due to a larger surface-oiled area. The wi nter spill also had a more drastic effect on the vegetation. Where the black, asphalt-like surface oil was present, black spruce mortality w as 100 % and there was very little live plant cover except for cotton grass tussocks. Changes in oil chemistry varied with depth; surface sa mples had signs of microbiological degradation, whereas some subsurfac e samples taken just above the permafrost had no evidence of degradati on and still contained volatile fractions.