This book offers an overview of the geochemical processes in aquatic sediments, with an emphasis on conceptual understanding and quantitative analysis. Suitable for graduate and upper-undergraduate coursework, it may also serve as a concise reference for researchers and advanced students seeking a quick introduction into sediment biogeochemistry or a review of the commonly used topics.Core topics include the physical, chemical, and microbiological processes in sediments that regulate the transformations and transport of substances and their exchanges with overlying waters. Separate chapters focus on the elemental cycles of carbon, nitrogen, iron, manganese, phosphorus, and sulfur, and the sediments' role as archives of environmental history. The book also covers the mathematical and modeling frameworks for describing sediment processes, with emphasis on making quick estimates of fluxes and rates and inferring quantitative information from geochemical data.Distinct from earlier marine-centered texts, this volume offers expanded coverage of freshwater systems and integrates exercises and problem sets throughout to reinforce learning and encourage cross-topic synthesis.