Chemistry 169 



quantities of non-living detritus were present. We really do not know 

 which is cause and which effect here. Is the zooplankton grazing reducing 

 the POC or is the low POC allowing high zooplankton production? 



SUMMARY 



Sediments 



Because of the high ratio of sediment surface area to pond volume, 

 the pond chemistry is controlled by the events in the sediments. These 

 sediments are highly organic at the surface, are up to 80% organic in the 

 top 4 cm, and are as low as 18% organic matter at 8 to 9 cm. The surface 

 layers are dark brown, unconsolidated material containing some remains 

 of grasses, sedges, mosses, etc. Mean particle size is 500 nm and bulk 

 density is 1 60 mg cc " ' . If organic carbon is 40% of organic matter, then a 

 square meter slice 1 cm thick contains 300-500 g C. There is some mixing 

 of the top 4 cm as a result of animal activity. 



Inorganic Ions 



The pond water is a dilute salt solution with Na and CI the major 

 ions. The concentrations of Na, Mg, Ca, CI, and HCO3 are controlled by 

 abiotic processes, mainly by dilution during rainfall and runoff, and by 

 concentration during evaporation and freezing. During freeze-up, ions are 

 excluded from the ice and are eventually forced into the sediment when the 

 water all freezes. Dilute meltwater fills the ponds in the spring but 

 evaporation of the water and re-solution of ions from the sediments 

 increase the concentrations of ions as much as 4-fold by late summer. The 

 chemistry is a little unusual, as the chloride is higher in concentration than 

 bicarbonate, but this is typical of ponds near the sea; most ponds in the 

 Arctic have more bicarbonate than chloride. In any event, this dominance 

 of the chloride has no practical importance because pH and buffering 

 capacity are still a function of the bicarbonate at all times. 



Other ions have more complicated seasonal cycles than the above. 

 Potassium is highest during runoff, presumably due to leaching from 

 vascular plants and lemming feces. Iron is low early in the summer, 

 reaches a maximum in July, then declines. The concentrations are 

 correlated with DOC, so some complexing or chelating process is at work. 

 Iron concentrations increased after rain too, perhaps as a result of soil 

 leaching. Silica concentrations are very low; the level is always below the 

 concentration supposedly needed for diatom growth and, in fact, there are 



