Bruce B. von Borstel

Two sand beaches on McNabs Island, Nova Scotia, were sampled on a grid pattern in the intertidal zone to examine sediment-oil interaction. Sediments were taken from 15 cm intervals down to the ground water table (90 cm maximum). Oil was extracted from the sand with n-hexane and analyzed by fluorescence analysis. 40 to 60 sediment samples per day could be analyzed inexpensively with this method.

Oil is dispersed through the sand beach as oil-sediment particles and as sand grain coatings. Oil concentration was greatest at depth within the beach and on the upper foreshore. Particulate oil which is removed from the beach concentrates in the offshore sediments; in this environment the oil content is inversely proportional to the sediment size.

Oil particles with settling properties equivalent to quartz silt are removed from the beach in suspension. Oil particles equivalent to quartz sand are moved to the upper foreshore. The high intensity turbulence of the lower foreshore winnows particulate oil. Oil is less easily winnowed by the low intensity swash-backwash flow of the upper foreshore.

Storm waves remove oil particles with the swash bar. The sand is returned to the foreshore after the storm but without the lighter oil particles.

The entire beach surface is exposed to winnowing. The deeper sand is winnowed only during storms. The frequency of storm erosion is low, hence, beach disturbance decreases with depth. As a consequence, surface sands are negatively skewed, but become progressively less skewed at depth.

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Supervisor: D. J. W. Piper