North American Prairie Streams as Systems for Ecological Study

Abstract

The Great Plains and Osage Plains of interior North America included vast prairie regions before settlement by western man. Prairie streams that exist today are ecologically interesting for their unstable flow regimes and harsh fluctuations in environmental conditions. How much extant prairie streams have changed from their pre-settlement conditions is unknown, but writings of early explorers suggest that then, as now, mainstream flows were highly variable. Although historically, some prairie rivers were turbid, the siltiness of others has increased with agricultural expansions, and some mainstream biota (fishes) are known to have disappeared. Small streams in these regions have probably changed even more; although they were clear 100 years ago, many are now highly turbid. Differences in ecological conditions among streams of the prairie region may be as great as those between prairie and nearby upland streams. For example, streams of the southern plains are characterized by irregular flow and substrates of small particle size, whereas streams of the northern prairies are more consistent in flow and many have cobble substrates. For some prairie streams, published studies exist of many ecological features, such as hydrologic regimes, productivity, respiration, organic matter processing, and composition of the biota; however, such basic features are unknown for most streams of the interior plains. Limited measurements suggest that typical central or southern prairie streams differ from streams of nearby uplands or northern forested regions in functional properties and biotic composition. Community structure and ecological functioning of many prairie streams appear strongly influenced by physicochemical limitations resulting from irregular flow regimes and environmental harshness, such as major disturbances due to drought and flood. Despite the above conditions, numerous examples suggest that prairie stream faunas are also influenced by biotic interactions, including those due to multi-trophic level effects. A relatively new approach in stream ecology applies the analysis of complex hydraulic parameters to questions concerning distributions or adaptations of the biota. This approach may be profitable in prairie streams, but needs modification to include the sometimes lengthy periods of low or no flow in these systems. As a result of the discussions giving rise to this paper, numerous specific topics are suggested for future investigations. These can be generalized in four categories: (1) basic description and comparison of biotas, processes, or rates; (2) biotic adaptations; (3) controlling mechanisms; and (4) comparisons of prairie stream ecosystems with those of other kinds of temperate streams in North America. Streams of the Mississippi Embayment, Interior Highlands, the Rocky and Appalachian mountains, and the prairies of our inland plains provide a contrasting array of study sites at a similar latitude for consideration by ecologists desiring a broad comparative or experimental approach to questions in stream ecology.