Preface to the Second Edition

The diversity of running water environments is enormous. When one considers torrential mountain brooks, large rivers of lowlands, and great rivers whose basins occupy subcontinents, it is apparent how location-specific environmental factors contribute to the sense of uniqueness and diversity of running waters. At the same time, however, our improved understanding of ecological, biogeochemical, hydrological, and geomorphological processes provides insight into the structural and functional characteristics of river systems that brings a unifying framework to this field of study. Inputs and transformations of energy and materials are important in all river systems, regional species richness and local species interactions influence the structure of all riverine communities, and the interaction of physical and biological forces is important to virtually every question that has been asked. It seems that the processes acting in running waters are general, but the settings are often unique.

We believe that it helps the reader, when some pattern or result is described, to have some image of what kind of stream or river is under investigation, and also where it is located. Stream ecology, like all ecology, depends greatly on context: place, environmental conditions, season, and species. This text includes frequent use of descriptors like "small woodland stream,'' ''open pastureland stream,'' or "large lowland river," and we believe that readers will find these useful clues to the patterns and processes that are reported. For most studies within the United States we have included further regional description, but have done so less frequently for studies from elsewhere around the globe. We apologize to our international readers for this pragmatic choice, and we have made every effort to include examples and literature from outside of North America.

Some locations have established themselves as leading centers of study due to the work of many researchers carried out over decades. The Hubbard Brook Experimental Forest in New Hampshire, Coweeta Hydrologic Laboratory in North Carolina, and some individual streams including Walker Branch in Tennessee, Sycamore Creek in Arizona, Rio las Marias in Venezuela, and the Taeri and Whatawhata in New Zealand are locations that appear frequently in the pages that follow. Knowing what these places are like, and how they may or may not be typical, in our view justifies the frequent use of place names and brief descriptions. The names of organisms also appear frequently and may at first overwhelm the reader. It may be easiest to pay them little attention until they gradually become familiar. Ultimately, it is difficult to really comprehend the outcome of a study without some appreciation for the organisms that were present.

As is true for every area of ecology at present, the study of streams and rivers cannot be addressed exclusive of the role of human activities, nor can we ignore the urgency of the need for conservation. This is a two-way street. Ecol-ogists who study streams without considering how past or present human modifications of the stream or its valley might have contributed to their observations do so at the risk of incomplete understanding. Conservation efforts that lack an adequate scientific basis are less likely to succeed. One trend that seems safe to forecast in stream ecology is toward a greater emphasis on understanding human impacts. Fortunately, signs of this trend are already apparent.

We have organized the flow of topics in a way that is most logical to us, but no doubt some readers will prefer to cover topics in whatever order they find most useful. For this reason, we have striven to explain enough in each chapter so that it is comprehensible on its own. This leads to a certain amount of intentional repetition, which we hope will provide clarification or a reminder that will benefit the reader's understanding.

We are extremely grateful to the many colleagues who shared ideas, provided references, and reviewed chapters in draft form. Space does not permit us to thank everyone who answered a query with a helpful explanation and suggestions for source material; however, we do wish to acknowledge the persons who carefully read and improved our chapters. Any remaining shortcomings or errors are the authors' responsibility, but hopefully these are few, thanks to the efforts of Robin Abell, Brian Allan, Fred Benfield, Barb Downes, David Dudgeon, Kurt Fausch, Stuart Findlay, Alex Flecker, Art Gold, Sujay Kaushal, Matt Kondolf, Angus Mcintosh, Peter Mclntyre, Rich Merritt, Judy Meyer, Pat Mulholland, Bobbi Peckarsky, LeRoy Poff, Brian Roberts, Doug Shields, Al Steinman, Jan Stevenson, Jen Tank, Paul Webb, Jack Webster, Kevin Wehrly, and Kirk Winemiller. All were generous with their time and knowledge, and we are indebted to them.

We also wish to thank those who provided helpful reviews of chapters in the first edition of this book, including Fred Benfield, Art Benke, Art Brown, Scott Cooper, Stuart Findlay, Alex Flecker, Nancy Grimm, David Hart, Chuck Hawkins, Bob Hughes, Steve Kohler, Gary Lamberti, Rex Lowe, Rich Merritt, Diane McKnight, Judy Meyer, Bobbi Peckarsky, Pete Ode, Walt Osterkamp, ML Ostrofsky, Margaret Palmer, LeRoy Poff, Karen Prestergaard, Ike Schlosser, Len Smock, Al Stein-man, Scott Wissinger, and Jack Webster.

Others provided invaluable assistance with important aspects of manuscript production. Jennifer Allan, Mary Hejna and Jamie Steffes did extensive proofreading and arranged all the figure permissions. Haymara Alvarez, Susana Martinez, and Dana Infante assisted with production of figures, and Jesus Montoya did a superb job of taking figures made in many different styles and redrafting them to a common style and high quality. Funding for MMC release time and travel to Michigan was provided by Dirección de Desarrollo Profesoral of Universidad Simon Bolívar, and the Horace H. Rackham School of Graduate Studies of the University of Michigan. We also wish to thank our editors at Springer, Suzanne Mekking and Martine van Bezooijen, and our prior editor Anna Besse-Lototskaya, for their support, encouragement, and patience. It has been a pleasure to work with them all.

Lastly, our deepest thanks go to our families for their love and support, and especially for their help and understanding during the time this edition was completed. David wishes to express his appreciation to Susan for the unflagging encouragement that has been a constant throughout our lives together. María Mercedes wishes to thank her parents for their unconditional support in the development of her career. It has been an enjoyable experience for both of us, and we hope that this edition will serve as a useful guide for the next generation of stream ecologists.

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