Stream Ecology

Streams and rivers are living, breathing, and ever-changing! Stream ecology is the study of these flowing freshwater ecosystems. As lotic (flowing water) ecosystems, streams and rivers have three defining characteristics that distinguish them from still water ecosystems:

Open systems—
Strongly connected with the surrounding landscape, greatly influenced by what’s happening upstream, and simultaneously influencing what’s happening downstream.

Reliant on allochthonous inputs—
External inputs (outside the stream or river itself), like leaves falling from trees, are critically important.

Transporting and transforming energy and materials—
Materials are moved downstream and transformed in transit.

There are huge variations in river ecosystems from headwaters to mouth. The headwaters are often defined by abundant canopy cover from trees, little light getting through, lots of allochthonous inputs (leaves, etc.), macroinvertebrate populations dominated by shredders and collectors, and not a lot of fish.  In midstream segments of the river, there is some canopy cover, more light getting through, smaller organic matter (leaves have been broken down into smaller pieces and transported downstream), macroinvertebrate populations dominated by collectors and grazers, and small- to mid-sized fish.  In lower reaches of the river, approaching the mouth, the river’s channel is very wide, contains deeper water, open canopy, much more light, and larger fish.

Stream ecology is all about interactions—how animals, plants, and microbes interact with one other, how light and temperature impact the ecosystem, and how the whole ecosystem responds to changes in its environment, including land use change, climate change, pollution, and other human impacts.

Video Resources

Troubled Waters – Iowa State University | Iowa Learning Farms

Enhanced Learning Activities

A Culture of Conservation Activity Booklet (Grades 6-12)

Additional Resources

Rivers and Streams: Life in Flowing Water – Nature Education

Iowa Benthic Macroinvertebrates – Iowa Department of Natural Resources