The hyporheic zone is the area just below a river where constant mixing of groundwater and river water occurs. At this intersection between two sources of water, with different organic carbon and nutrient contents, complimentary pairing of electron donors and acceptors occurs, causing elevated rates of microbial metabolism. Due to these constant changes in electron acceptor and donor availability and because of microbial oxygen consumption dynamics, redox cycling process are constantly occurring and changing within the hyporheic zone. Iron oxides are theorized to play an important role in protecting sediment organic carbon from microbial metabolism through the formation of organo-metal aggregates. This thesis document outlines three related experiments investigating how different sources and forms of organic carbon found in freshwater river and groundwater systems effects hyporheic zone microbial metabolism rates. These studies revealed that deposition of autochthonous and allochthonous organic carbon to the riverbed sediment matrix (i.e. hyporheic zone) was correlated with release of labile dissolved organic carbon. Photosynthetic periphyton biomass (i.e. autochthonous epilithic biomass) was identified as a key source of organic carbon, which lead to highly elevated rates of aerobic respiration, anaerobic respiration, and methanogenesis. The presence of small pockets of anaerobic respiration and methanogenesis was observed within predominantly aerobic metabolizing sediment batch reactors; this shows that hyporheic zone sediment microbial community structure is highly heterogenous with patches of flexible metabolism occurring, depending on electron donor/acceptor availability. Iron bound organic carbon content was correlated with the presence of reactive iron oxide minerals, and these organo-metal aggregates were not biodegraded due to preferential metabolism of more labile pools of carbon such as fresh periphyton POM and DOC. The increase in microbial activity associated with fresh periphyton biomass deposition shows that in freshwater river systems periphyton biomass is a major contributor to ecosystem respiration as well as gross primary productivity. Understanding how natural and anthropogenic inputs of organic carbon, nitrogen, phosphorous and sulfate cause changes in periphyton growth and hence changes in hyporheic zone microbial metabolism is on ongoing challenge to modeling the global carbon cycle.

Overviews of the source, supply and variability of DOM, surveys of the processes that mediate inputs to microbial food webs, and syntheses consolidating research findings provide a comprehensive review of what is known of DOM in freshwater. This book will be important to anyone interested in understanding the fundamental factors associated with DOM that control aquatic ecosystems."--BOOK JACKET.

A hugely important text for advanced undergraduates as well as graduates with an interest in stream and river ecology, this second, updated edition is designed to serve as a textbook as well as a working reference for specialists in stream ecology and related fields. The book presents vital new findings on human impacts, and new work in pollution control, flow management, restoration and conservation planning that point to practical solutions. All told, the book is expanded in length by some twenty-five percent, and includes hundreds of figures, most of them new.

Streams around the world flow toward the sea in floodplains. All along this transit, there is exchange of water between the stream itself and the surrounding sediments which form the floodplain. Many chemical, biological, and geological processes occur when water moves back and forth between streams and these flood plain sediments. Streams and Groundwaters focuses on the consequences of water flow between streams, their underlying sediments, and surrounding landscapes. Certain to appeal to anyone interested in stream ecology, the management of stream ecosystems, or landscape ecology, this volume should become a oft-opened reference.