392 



R.J. Barsdate et al. 



FIGURE 9-3. Depth of thaw and of the water level 

 in Ponds C and E, 1970. 



Oxygen 



The only measured chemical change was in the oxygen concentration. 

 There is normally a decrease in oxygen near the pond margins caused by 

 the high rate of sediment respiration (Chapter 8), by the shallow water 

 containing a small absolute amount of oxygen, and by the restricted 

 circulation and mixing in the shelter of the emergent plants (Pond C in 

 Figure 9-2). This decrease is intensified by the floating oil which not only 

 drastically restricts water movement but also reduces the diffusion of 

 oxygen through the water surface. These data are for a single date and 

 there is every possibility that oxygen could be lowered even further on 

 warm days or at night. If so, then the benthic animals may be affected. 



Nutrients and Water Chemistry 



There was no detectable change in the inorganic chemistry of the 

 water after the oil spills in 1970 and 1975. We measured pH, alkalinity, 

 Ca, Ha, K, Mg, Fe, and conductivity as well as nutrients (Table 9-1). In 

 fact, the oil itself contains by weight 0.23% N and 0.82% S (Thompson et 

 al. 1971) so the amounts added are large (20 mg N and 70 mg S liter "^ of 

 Pond E) . Also, the organic matter added can change the systems as 

 Brunskill et al. (1973) found anaerobic conditions and H2 S beneath the ice 

 of Lake 4 (Mackenzie Delta). However, in Ponds E and Omega the strong 

 reducing conditions did not develop and evidently the N remains tied up in 

 the heavier fractions (Ball 1962). 



