Biological interactions in streams involve a complex physical setting as well as a wide array of food resources and consumers. Food resources are basically the result of the elaboration of organic material by photosynthesis occurring in both the aquatic and terrestrial ecosystems. Within the stream, the organisms that accomplish this are broadly classified as algae, mosses, and rooted angiosperms (macrophytes). Leaves, twigs, branches, and grasses that reach the water are among the contributions from the terrestrial environment. Dissolved organic material is a third source of energy, but less well understood. Different consumers in the river ecosystem utilize these food resources in various ways. Of interest to ecologists are not only what consumers eat (herbivores, carnivores, omnivores, detritivores), but also how they obtain their food. Feeding categories are called functional feeding groups and include shredding, grazing/scraping, collecting (filtering and gathering), and predation. Exploring food web interactions using the latter categories provides a much better understanding of the biological interactions in riverine ecosystems. The most widely used model to explain the structure and function of entire lotic ecosystems is called The River Continuum Concept. This model provides a description of the changes that occur in a stream/river continuum from its headwaters to its mouth in terms of the changes in physical characteristics, energy resources, and functional feeding groups. Several other corollaries have been proposed to further the usefulness of this model and include studies of patch dynamics, nutrient spiraling, river–floodplain interactions, and the involvement of the hyporheic community.

Contributors Foreword Preface Acknowledgements 1. Background and Approach 2. Atlantic Coast Rivers of the Northeastern United States 3. Atlantic Coast Rivers of the Southeastern United States 4. Gulf Coast Rivers of the Southeastern United States 5. Gulf Coast Rivers of the Southwestern United States 6. Lower Mississippi River and its Tributaries 7. Southern Plains Rivers 8. Upper Mississippi River Basin 9. Ohio River Basin 10. Missouri River Basin 11. Colorado River Basin 12. Pacific Coast Rivers of the Coterminous United States 13. Columbia River Basin 14. Great Basin Rivers 15. Fraser River Basin 16. Pacific Coast Rivers of Canada and Alaska 17. Yukon River Basin 18. Mackenzie River Basin 19. Nelson and Churchill River Basins 20. Rivers of Arctic North America 21. Atlantic Coast Rivers of Canada 22. St. Lawrence River Basin 23. Rivers of Mexico 24. Overview and Prospects Appendix: Common and Scientific Names for Plants, Vertebrates, and Selected Invertebrates Glossary Index

This introductory chapter provides a brief description of the water resources of North America. Rivers are one of the most dramatic features of a continent. The North American continent contains a tremendous diversity of river sizes and types. Several factors determining the characteristics of different rivers—the early human history; physiography, climate, and land use; geomorphology, hydrology, and chemistry; river biodiversity and ecology; human impacts and special features are presented. The character of a river is primarily determined by features of its drainage basin, the land area within which it and its tributaries flow. Impacts to rivers are grouped into three major categories: pollution, flow regulation, and water extraction. A fourth significant impact has come from both intentional and accidental introduction of nonnative species. In spite of human alterations, each river is or was unique. There is a great need for major new research initiatives that can lead to better scientific understanding, wider appreciation of their importance, and wiser management of the rivers.

This chapter examines a diverse group of smaller invertebrates, collectively called the meiofauna. This chapter also includes two groups of crustaceans that, because of their size and habitat, are usually included with the meiofauna in ecological studies rather than with their larger cousins. These are the harpactacoid copepods and ostracods, which are important members of the community dwelling among the interstitial waters of the stream bottom. Dwelling within this matlike community, a wide range of meiofauna forms can be found—protozoans, rotifers, worms, and others—that function importantly in the transformation of energy within the stream ecosystem. A wide diversity of meiofauna also occurs within the interstitial waters among the rocks, gravels, and other materials composing the stream bottom. Although members of the meiofauna are small, it does not mean that they are unimportant in terms of production of organic matter for other members of stream ecosystems. Many of them have extremely high reproductive rates, and this, coupled with the very high numbers that may be present, results in significant secondary production—food for other consumers.

This chapter explores the small streams and rivers of America's heartland, most of which originate at low altitude and have low gradients. Long runs and pools predominate, but shallow, gravelly riffles can be found where the geology and gradient combine appropriately. Cascades, waterfalls, and boulders are rare. Substrate varies from place to place; however, often includes sand, silt, and mud. Water temperatures are cold in the north; however they grade into cool and warm waters as one proceeds south. This chapter begins by describing the setting, which is always more complex and heterogeneous than our mental image. It takes a look at the River Continuum Concept, because the understanding of the functioning of forested headwater streams has been greatly advanced by studies in this region. In addition, for those whose vision of a stream is a cold, stonybottom trout stream, it may be interesting to contrast warmer, slower streams that often have sandy and muddy bottoms. Finally, rivers of this region have been greatly modified by human activities. This chapter concludes with a lesson on river history and an examination of the threats and opportunities that confront the mankind today.