Oil Spill Effects 391 



estimate of the quantity is 395 kg remaining of the 680 kg added (this is 

 150x2 + 190x0.5). 



During the remainder of 1971 and in later years, the location and 

 general appearance of the oil did not change and there was no further 

 effect on the timing of the freeze and melt. Occasional oil slicks and small 

 patches of floating oil were seen in 1972 and 1973; and in June, 1975, oil 

 was visible in the Carex beds on the west side of the pond as a low ridge 

 several centimeters high in the sediments. Although the surface of the 

 ridge was covered with a brown scum and organic detritus, any mechanical 

 disturbance caused a renewed oil slick to well up from the ridge. 



Spill on Pond Omega, 1975 



The experimental spill in 1975 was made on Pond Omega, a 260 m^- 

 pond located several hundred meters from Pond B (see Miller et al. 1978a 

 for exact location). The 0.24 liter m" dose on 10 July was about one- 

 tenth the amount added to Pond E. The initial movement of the oil slick 

 was controlled by the direction of the wind and within 24 hours after the 

 spill, the oil had collected in the Carex beds around the pond. This was 

 similar to the 1970 oil spill. 



PHYSICAL AND CHEMICAL MEASUREMENTS 



Temperature 



There was practically no change in the physical regime of the ponds as 

 a result of the oil spill. The water temperature of Pond E did increase by 

 about 4°C for 3 days after the spill but returned to normal after the oil 

 moved into the pond margin and after this was exactly the same as the 

 temperature in Pond C. As long as the floating oil covered a large area, it 

 is likely that there was a microstratification of temperature both 

 horizontally and vertically. For example, 7 days after the spill the range of 

 temperature beneath the oil was slightly higher than in a similar location 

 in Pond C (Figure 9-2). Evaporation in Pond E was about the same as in 

 the control Pond C as shown by their similar water levels (Figure'9-3). 

 Finally, it was possible that the oil could change the heat budget of the 

 sediment through a decrease in albedo or an increase in heat conduction. 

 Again the similarity of the depth of thaw (Figure 9-3) to that in the control 

 pond indicates that any changes were too slight to measure. 



