Major advancement in the U-Th measurement techniques since the 1990's have resulted in new opportunities for the use of these nuclides to probe into aquatic processes in greater detail. This volume provides state-of-the-art reviews on the applications of U-Th series nuclides to "time" and "tag" in a variety of processes occurring in aquatic systems. * this book provides state of art reviews on the applications of U-Th Series nuclides to 'time'and 'tag' key processes occurring in aquatic systems. * the book is self-contained, each chapter presents nuclide source functions, processes regulating their distributions and models used to describe them. * the book emphasizes current thinking in the field and future directions.