Streams of Life

How Streams Provide Many Different Environments

By Ron Divelbiss

Less than one percent of the world's water is fresh river water. Yet in this tiny portion of the biosphere lives a great variety of animals and plants. It is estimated that 640,000 microscopic animals, weighing in total some 45 pounds, drift past the Andrew Britten overlook every 24 hours. The flowing water continuously replenishes oxygen, carbon dioxide, and nutrients, providing river plants and animals of all sizes with the basics of life. Along their lengths, streams present wildlife with many opportunities and challenges.

Flowing downstream, along with the detritus, are tiny worms, snails, and insect larvae carried along by the current. But as the stream widens and deepens, the current slows sufficiently for plants to take root. On their leaves grow algae, which are eaten by snails and other invertebrates. Plants provide not only food but also shelter for river animals. They add to the ecological niches available and to the complexity of the ecosystem. Along the riverbanks, vegetation provides another niche, inhabited by birds such as redwing black birds, and mammals such as carnivorous raccoons.

Detritus-eating and herbivorous invertebrates are hunted by fish and carnivorous insect larvae, and these hunters themselves fall prey to predators: larger fish, turtles, and birds. Down on the mud - or in it - are worms, snails, and crayfish, feeding on organic material, and in turn providing food for bottom-feeding fish.

In early spring the waters are often very muddy with the sediment they carry. It becomes more and more difficult for animals to find their way through the water. Streams are vital for wildlife - and for people. We must treat these ecosystems with respect so they retain their value and their fascination for us.