98 R. T. Prentki et al. 



saturation, and Watson et al. (1966a) always found undersaturation in 

 Cape Thompson ponds. Both Hutchinson (1957) and Kalff (1965) suggest 

 that chemical oxidation likely maintains oxygen undersaturation in highly 

 colored waters. Our data (see Chapter 8) suggest that high rates of benthic 

 respiration rather than chemical oxidation is the dominant force causing 

 undersaturation in the Barrow ponds and, by analogy, in other shallow 

 ponds. 



The summer oxygen regime of shallow arctic lakes is similar to that 

 of oligotrophic temperate lakes, but the winter regime is strongly modified 

 by the extreme arctic winter. In Ikroavik Lake, exclusion of oxygen during 

 formation of 1 .6 m of ice in a water column only 2.4 m deep was the major 

 process, producing a 20% to 40% supersaturation by early December and a 

 74% supersaturation in early June (Barsdate et al. cited in Hobbie 1973). 

 The opposite effect, severe deoxygenation, can also occur in shallow arctic 

 lakes underneath ice; Lake 5 at Cape Thompson, for which zero oxygen 

 was recorded in April 1961 by Tash and Armitage (1967), is a good 

 example. Presumably, the degree of snow cover and its effect on 

 photosynthesis, the water depth, and the respiratory rate of each individual 

 lake dictate its position between these two extreme winter oxygen regimes. 



Deep arctic lakes have an oxygen regime that is similar in almost 

 every way to that of temperate oligotrophic lakes. They are saturated with 

 oxygen throughout the open water season except when the rates of cooling 

 are so rapid that the oxygen influx, and thus the percentage of saturation, 

 cannot keep up (Hobbie 1962). In some cases, the long duration of the ice 

 cover allows the decrease of oxygen caused by under-ice respiration to be 

 quantified (Welch 1974). 



Sediment pH and Eh 



Eh and pH are factors of importance in sediment chemistry, 

 particularly as they influence the iron-phosphorus relationships discussed 

 later in this chapter. Three Eh and pH sediment profiles in Pond J on 11 

 July 1971 were measured in situ with a combination pH and reference 

 probe modified for immersion and a platinum wire redox electrode 

 (Fenchel 1969). Calibration and calculations for E-, the potential that 

 would be observed at pH 7 and 25°C, were made according to Golterman 

 (1969). On 19 July 1973, nine additional redox profiles were measured 

 with a multi-electrode probe similar to that of Machan and Ott (1972). 



The sharp negative changes in pH seen in the 1971 profile (Figure 4- 

 11) at the interface between oxygenated and anoxic sediments may occur 

 as the result of oxidation of ferrous iron with the formation of a FeOOH 

 (geothite): 2 Fe^"^ -I- 1/2 O2 + 3 H2O -^ 2 FeOOH -I- 4 H + . The 

 oxidation potentials indicated that sediments were oxidized only to a depth 

 of 1 to 2 cm in the deep water location but to considerably greater depths 



