This publication presents the application of isotope techniques as a powerful tool for evaluating nutrient dynamics in river systems. Nutrient assessment and management in river systems has been an important part of water resource management for the past few decades, but the provision of appropriate and effective nutrient assessment and management in water resource management still remains a challenge due to the diversity of sources, pathways and transformations of nutrients. The topics discussed in this book show that the application of isotope techniques could enable or facilitate the examination of sources, pathways, transformations, and fates of nutrients in river systems, contributing to integrated water resource management.