Fresh Water

It is difficult to segregate terrestrial from aquatic habitats, especially in the Arctic where the most biologically productive areas tend to be wet meadows. Freshwater bodies in the Arctic range from small pools to large and deep lakes, to small rills to major rivers.

Arctic rivers and streams fall into three major categories: those that drain from lakes, those that flow from glaciers and ice caps, and those that flow from snowmelt. Some of the world's longest and largest rivers flow from lakes, some of which are south of Arctic regions. The Mackenzie River is notable, with its origins in Great Slave Lake. Such rivers support a rich diversity of wildlife, including resident and migratory fish, muskrat, and other mammals, birds, and many invertebrates. As some of these rivers flow to the sea, they drain a series of lakes connected by stretches of fast flowing water. Others are more continuous as rivers with frequent or infrequent rapids. Rivers flowing down glacially carved valleys are often braided networks of fast flowing streams. Where the rivers slow, especially at estuaries, silt and sand are deposited in deltas. Streams flowing to lakes and the sea form similar features at smaller scales. Streams flowing in courses where soil has accumulated may become beaded as the water flows along the lines of polygon edges and polygon joints where pooling accentuates the beaded appearance. Arctic streams tend not to support much fish life because they often dry up in summer and freeze solid in winter, but they are home to many invertebrates.

Much of the Arctic landscape is characterized by vast numbers of lakes and ponds. Over huge areas, such lakes and ponds are similar in that they mostly freeze to the bottom in winter and have steep banks on the windward shores because of the push from windblown floating ice in spring and summer, but gently sloping, vegetated banks with some aquatic vegetation on lee shores. Deeper lakes may have similar general appearances. The complex of life in the lakes depends very much on whether or not they are deep enough for fish to survive. Shallow lakes without fish are often seething with crustacea in the summer, and are a highly productive habitat for many birds. In deeper lakes, the fish are voracious predators on invertebrate life and on each other (see Trophic Levels). The huge Arctic lakes, such as Great Bear Lake (Northwest Territories), Nettiling Lake (Baffin Island), and Lake Hazen (Ellesmere Island) have unique characteristics that reflect their sizes, the bedrock, and their locations.

Below a certain size, about 2500 m2 perhaps, ponds are too small to show obvious characteristics from aeolian effects. They freeze solid in winter and are underlain by permafrost. During the summer, they teem with invertebrate life. Often, along the edges of such ponds, and associated with the small pools around polygons, clouds of nonbiting midges (Chironomidae) emerge (see Freshwater Ecosystems).

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