The book is the first comprehensive, integrated synthesis of available information on the current and potential effects of acidic deposition on lakes and streams in geographic regions of the United States having significant numbers of low-alkalinity surface waters. It presents and evaluates data for entire regions and is national in scope. The authors have collected the results of diverse studies of aquatic ecosystems. The authors stress the current status of water chemistry and the processes important in controlling water chemistry. Authors of case study chapters have characterized these processes on a regional basis by using, assessing, and comparing high-quality data sets. A major conclusion demonstrated by these regional comparisons is that there is substantial diversity among regions with respect to the nature of surface waters and the processes affecting them. The most important contributions of the book are the descriptions of intra- and inter-regional variations in surface water chemistry and its controlling factors, and the assessment of the significance of these variations to our understanding of the acidic deposition phenomenon and its implications for public policy decisions.