Oil Spill Effects 405 



may have become trapped in the oil on the plant stems and in the floating 

 oil. Snow and Rosenberg (1975a) reported similar entrapment of insects in 

 the surface film of a Mackenzie Delta lake. At Barrow, recovery must take 

 more than 6 years as many of the insects were still absent in Pond E in 

 1977. 



The chironomid larvae were virtually unaffected by the oil spills. The 

 numbers present in the sediments did vary a great deal from pond to pond 

 but the highest and lowest numbers occurred in the control ponds J and G 

 (Table 9-8). Emergence was affected by the oil, however, and the 

 metamorphosis of Tanytarsus was strongly reduced after the spill in Pond 

 Omega (Figure 9-10). This genus of filter feeders did not recover in Pond E 

 either and was also strongly affected in Mackenzie Delta Lake 4 (Snow 

 and Rosenberg 1975a). 



These observations on the aquatic insects indicate that the oil-induced 

 changes are on the species level and that such measures as secondary 

 production and carbon flux are virtually unchanged. For example, the 

 emerging cohort of Chironomus in 1977 presumably hatched in the year of 

 the spill in Pond E and yet its numbers in Pond E were the same as in the 

 control Pond J (Mozley and Butler 1978). These authors conclude that a 

 light spill such as these reported here might best be treated by merely 

 attempting to absorb floating oil onto inert materials and possibly by 

 flooding the ponds to float oil away from the littoral plants. 



SUMMARY 



Crude oil from Prudhoe Bay was added to Pond E in 1970 (1.6 liter 

 m"^) and to Pond Omega in 1975 (0.24 liter m"^). The wind moved the 

 floating oil to the edge of the ponds and some oil floated for about a 

 month. By the end of the summer all the oil was trapped along the pond 

 edge and much had sunk. No oil left the pond during runoff the next spring 

 but oil was still visible at the edge. After several years, at least half the oil 

 was still present and was covered by debris and organic matter; it still 

 welled up and created a scum when disturbed. 



The only physical-chemical change caused by the oil was a slight 

 decrease in the oxygen concentration of the shallow pond margins. This 

 was likely the result of reduced diffusion and water movement. There was 

 no change in the pH, alkalinity, or nutrient concentrations. 



At least half of the oil was lost during the first year after the spill, 

 mostly by volatilization and chemical degradation; there was also a small 

 effect of biological degradation. In Pond E, for example, the oil remaining 

 after five years had virtually the same chemical composition, but there was 

 some loss of those hydrocarbon compounds with fewer than 13 carbon 

 atoms (presumably from biological degradation). 



