Experimental crude oil spills were made in 3-m2 cylinders in open water, and in submerged moss, horsetail, and sedge communities of a small subarctic lake in the Mackenzie Valley, near Norman Wells, N. W. T. Studies were made of the effects of crude oil on phytoplankton, periphyton, and attached macrophytes in terms of population composition, seasonal succession, and biomass. The presence of crude oil (15 liters m−2) had no significant effects on phytoplankton composition or abundance throughout the growth season but had a marked inhibitory effect on most members of the periphyton. One notable exception to this observation was a considerable growth stimulation of the blue-green alga Oscillatoria angustissima.
Laboratory studies on the effects of aqueous crude oil extracts on growth and photosynthesis of algal cultures isolated from the lake showed strong inhibition under most combinations of light and temperature. The inhibition of both growth and photosynthesis appeared minimal when the algae were grown under optimal conditions of light and temperature. The effects decreased with time in open culture systems, i.e. when evaporation was freely allowed.
Crude oil caused an immediate reduction in chlorophyll content of macrophytes upon contact, and significant decreases in biomass were evident in follow-up studies of experimental oil spills in macrophyte communities.