Biogeochemical cycles provide the basic framework for investigating global change and its implications for life on earth. This book presents, in an integrated format, two essential elements of the study of biogeochemical cycles--resolving the intricacies of the biological and abiological processes that form closed chemical cycles, and simulating the cycles using mathematical models. The book includes a DOS-based computer program developed by the authors, entitled BOXES, which provides a user-friendly framework for constructing sophisticated numerical models of biogeochemical cycles ranging from the eco-system to global scale.