Water is, perhaps, the single most important substance on earth. It forms the basis for life as we know it. Organisms, including human beings, can only survive if there is an adequate supply of water available. In addition, the water must be of the proper quality to support life. The living world has evolved and adjusted over hundreds of millions of years to the variation in the natural distribution and chemical composition of water at the earths surface. Water Quality Trends and Geochemical Mass Balance provides an overview of the tracking of water quality changes, through both trend analysis and geochemical mass balances. This volume will serve to extend our understanding of those processes and encourage innovative applications of these data analysis techniques for the study of environmental systems. Also, one should not discount the continuing need for quality environmental monitoring data to provide the basic building blocks used for the trend and mass balance assessments presented herein.