Chemistry 81 



FIGURE 4-3. Concentrations of major 

 ions in Pond B, 1970. 



Barrow ponds increased 10-fold between the time the permanent ice cover 

 formed and the time the ponds were frozen solid. Similar concentration 

 increases in major ions and conductivity would be expected. The excluded 

 ions are forced into the sediment as the water column freezes and the 

 freezing front penetrates the sediment (see Chapter 3). The following 

 spring, the water from the melting pond ice still has a considerable amount 

 of ions, even though most of the electrolytes were frozen out. In fact, the 

 conductivity of this meltwater is 5 times higher than that of water from 

 precipitation or snow. Later, as the snowpack melts and runoff water 

 floods the ponds, the resultant flushing produces almost uniform ion 

 concentrations and conductance in all ponds (Figure 4-4). After the period 

 of flooding, two processes, evaporation of the water and re-solution of the 

 ions concentrated in the sediment the previous fall, contribute to an 

 increase in the concentration of ions in the ponds. In the intensively 

 studied ponds, this increase can be as much as 4-fold; in smaller and 

 shallower ponds, such as Pond F, concentrations can increase even more. 

 However, in very wet years, such as 1973, the ponds may be concentrated 

 less than 2-fold during the summer (e.g., Kalff 1965). 



