Introduction and Site Description 23 



quantities of nutrients. Phytoplankton began to increase beneath the ice 

 cover in February and reached a peak in May (Kalff et al. 1972). Morgan 

 and Kalff (1972) found a maximum of 2 x 10 ' bacteria ml ' with peaks of 

 glucose uptake in July and October. Zooplankton had low populations 

 with Limnocalanus macrurus as the dominant form (Roff and Carter 

 1972). Most of the population hatched, grew, reproduced, and died 

 between December and October, although a few adults were present 

 during the entire winter. Finally, the long period of ice cover allowed the 

 lake to be used as a sealed vessel respirometer to measure respiration of 

 the ecosystem by changes in oxygen concentration (Welch 1974). 



Northern Alaska 



It was possible to carry out the IBP aquatic program only because of 

 the experience and information provided by previous research in northern 

 Alaska. Thus, even before the IBP aquatic project began, we knew such 

 things as the primary productivity of the phytoplankton, the basic cycles of 

 water chemistry, and the life cycles of many of the zooplankton species. 



There are seven types of freshwater habitats in northern Alaska: deep 

 lakes, shallow lakes, ponds, large rivers, small rivers, streams, and springs. 

 The deep lakes, located in the mountains, were formed mostly behind end 

 moraines that dam narrow valleys. These lakes are rather rare and may 

 number only 20 or 30. Shallow lakes, very abundant (many thousands) on 

 the flat coastal plain, were formed mainly by melting of the ice-rich 

 permafrost. These are only a few meters deep and many will freeze to the 

 bottom each winter. The area of these lakes can be large, with lengths 

 reaching up to 10 km or so. Ponds are extremely abundant (tens or 

 hundreds of thousands) in the coastal plain region, particularly in the old 

 lake beds. Here, the growth of ice wedges has pushed up networks of small 

 ridges that contain small (50 m on a side), shallow (10 to 50 cm) ponds. 

 Most of the limnological investigations have been carried out on lakes and 

 ponds; little is known about the flowing water systems. However, there are 

 a number of large rivers in northern Alaska and parts of these rivers are 

 deep enough to allow fish to survive. Small rivers and streams, in contrast, 

 cease flowing completely each fall. Because of the flat landscape and small 

 amount of total precipitation, the drainage is poorly developed in the 

 Barrow area and sizable amounts of flow occur only during the melting 

 period. The final habitat, springs, occurs only in the mountain and foothill 

 area. Although some ten or twenty springs exist, they are a very minor 

 part of the entire aquatic scene. The fact that they flow year-round, 

 however, allows a rich fauna to develop and illustrates both the potential 

 production of arctic water and, by contrast, the strong stresses on 

 intermittent streams. 



