A glacier might cling to a winter snow a hundred years and turn it to
ice, a blue tool to rasp and pluck at rocks, before letting it go.
Lingering summer snowfields might delay its passage for a time. But the
water always wins at last, becoming, in one decisive instant, liquid
again, and beginning its long journey to the sea. Plants and dry air
will intercept some of its molecules, sending them back into the
atmosphere to bloom as fog and cloud; but as rain, snow, or dew, these
are soon commissioned to the land again.
Water is so familiar to us that we seldom think about it. We know that
fish swim in the lower lakes, and we are vaguely aware of the
bewildering assortment of life-forms abounding in a pond. But life
begins in the streams.
Even cups of cold meltwaters, scooped out of a rivulet only a few meters
away from its snowbank source, contain some life. Snow algae, which grow
on the snowbank surface, often sufficiently dense to give the snow a
distinctive red complexion, are released into the meltwater. In summer,
small invertebrate life can be discovered in the standing pools of even
the highest cirque.
But conditions are not good for the development of complete aquatic food
chains in the streams and lakes of higher elevations. Alpine lakes, or
tarns, support little visible life. Often flanked by high ridges and
peaks, many tarns receive scant direct sunlight during the day. Since
these lakes occupy basins that capture tremendous amounts of snowfall,
the snowbanks persist in the mountain shadows, and summer makes little
progress in warming the water. Iceberg Lake, for example, is seldom free
of floating ice, and its temperature never rises above 4° C in summer,
even at the surface.
Moving out of the cirque lakes, water is soon churning again, dashing
downward many hundreds of meters to the valleys below, in rapids,
cascades, and breathless waterfalls. Not surprisingly, few plants and
animals are adapted to life in fast-moving water.
Algae can be found covering streambed rocks and stranded, water-polished
tree trunks. Securely attached by holdfasts, these small plant forms
survive the rigorous stream flow that would destroy the larger vascular
plants. Several species exist, from microscopic forms to branched
filamentous algae whose long hairlike strands wave in the current.
A surprising number of insects live on the stream bottom, finding a
measure of protection from the current in the jumble of rocks.
Underwater beetles live under the gravel or among the debris at the
stream-edge, or cling to stones and sticks. Scurrying and creeping among
the rock-crannies are the larvae of stoneflies, mayflies, and
caddisflies. These and the small fish that venture up from lower lakes
are the food of the water ouzel, a creature that loves the places where
the waters thunder.
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The noise of the water is overpowering. A slip into this boiling rage
would mean quick death. Looking 10 meters across the dim, mist-slippery,
water-scoured canyon, I see a young water ouzel peering out of its
unique nest, on the lookout for its parents. Clouds of spray keep the
nest of living moss continually wet; but this bird is waterproofed with
an oily plumage and keeps its vigil at the nest opening. Peering into
the torrent below, then upstream and downstream, it awaits patiently the
delivery of the next meal.
With the approach of one of the adults, three other heads crowd the
opening, begging yellow mouths agape. Flying low, the ouzel parent zeros
through the heavy spray, alighting on a slippery boulder below the nest
ledge. Preparing to fly up to the nest with its load of insect larvae,
the ouzel spots me across the water. At its sharp _jigic, jigic_ alarm,
the bills of the young snap instantly shut. Nervously the bird regards
my close presence, dipping its entire body rapidly up and down, as if
keeping time with the surging torrent.
Discovering no danger, the dusky blue-grey bird bobs more slowly. The
other adult, returning from an upstream forage, alights on the same
rock, occasioning a new outcry from the fledglings. Each in turn, the
parent birds fly up to feed their young, beating their wings to maintain
their position at the perchless nest. Not pausing to regard me further,
they split the stream between them again, one flying upstream and one
down, to continue the hunt. Blinking and shaking the collected mist from
its bill, the single young sentry renews its watch.