22 J. E. Hobbie 



1. Arctic lakes and ponds seldom warm above 10°C and almost 

 never stratify. 



2. Arctic lakes and ponds shallower than 1.7 to 2.0 m usually 

 freeze completely. 



3. Ponds and lakes less than 2 m in depth do not contain fish. One 

 consequence of the lack of predation is that the zooplanktonic 

 crustaceans are almost all large species in ponds and shallow 

 lakes. 



4. The ice cover is 1 to 2 m thick and lasts for 8 or 9 months. 



5. Arctic lakes and ponds usually contain low amounts of available 

 nutrients and low total dissolved salts. However, as in the 

 temperate regions, the total inorganic ion concentration is dif- 

 ferent for drainage basins in different types of bedrock. 



6. Oxygen is usually present in saturation concentrations in open 

 waters but becomes depleted to some extent near the end of the 

 under-ice period. In shallow lakes the exclusion of oxygen during 

 the freezing of the ice may result in super-saturation (200%). 



7. The biota of shallow freshwater lakes and of ponds are subjected 

 to strong physiological stresses as the ions may be concentrated 

 30-fold during freeze-up, while the water immediately after 

 the spring melt may resemble distilled water. 



8. Only nannoplankton are found in arctic lakes and ponds. These 

 usually bloom beneath the springtime ice of lakes but total 

 primary production is low and lakes and ponds are oligotrophic. 



9. With a few exceptions, each species of zooplankton has a dor- 

 mant phase in its life cycle. 



10. Fish are very slow-growing, but large fish may live for 40 years. 



1 1. There are no benthic animals that graze on aquatic plants or that 

 shred large organic particles or leaves. 



12. The number of animal species is small and some groups — for 

 example, sponges, Notonectidae, Corixidae, Gyrinidae, Dytisci- 

 dae, and Amphibia — are rare or not present. 



13. Decomposition rates are slow and large amounts of energy and 

 nutrients are tied up in dead organic matter. 



It is obvious that this list of characteristics was obtained from largely 

 descriptive studies. Recently, two IBP projects were carried out that were 

 designed to add experimental studies to the descriptive observations in , 

 order to gain an understanding of controlling factors and environmental 

 interactions. These projects, one at Resolute Bay, Canada, and one at 

 Barrow, Alaska, were located near airfields and studied only a single lake 

 (Char Lake) or a small group of ponds in a single area (Barrow). 



Some of the results of the Char Lake project have been published. A 

 general description (Rigler 1972) indicates that the lake is ice-covered until 

 early August, has a moss cover over 30% of its bottom, and has low 



