Knowledge in the field of acidic deposition is expanding rapidly, and both ex perts and non-experts are challenged to keep up with the latest information. We designed our assessment to include both the basic foundation needed by non experts and the detailed information needed by experts. Our assessment in cludes background information on acidic deposition (Chapter 1), an in-depth discussion of the nature of soil acidity and ecosystem H+ budgets (Chapter 2), and a summary of rates of deposition in the Southeastern U.S. (Chapter 3). A discussion of the nature of forest soils in the region (Chapter 4) is followed by an overview of previous assessments of soil sensitivity to acidification (Chapter 5). The potential impacts of acidic deposition on forest nutrition are described in the context of the degree of current nutrient limitation on forest productivity (Chap ter 6). The results of simulations with the MAGIC model provided evaluations of the likely sensitivity of a variety of soils representative of forest soils in the South (Chapter 7), as well as a test of soil sensitivity criteria. Our synthesis and recommendations for research (Chapter 8) also serve as an executive summary. A complementary volume in the Springer-Verlag Ecological Studies series should be consulted for information on European forests. This volume, Acidic Deposition and Forest Decline in the Fictelgebirge, edited by E.-D. Schultze and O.L. Lange, also provides greater detail on the physiologic responses of trees than we present in our regional assessment.

Inhalt

Introduction.- Purpose of the assessment.- Structure of the assessment.- Background on why this has become an important topic.- Lakes versus forests.- Concerns over effects on forests.- Pathways of acidic deposition impacts.- The uncertain nature of truth in ecosystem studies.- 2. The nature of soil acidity and H+ budgets.- Weak acid behavior of soils.- Changes in soil acidity involving the dynamics of weak and strong acids.- Sulfur, nitrogen and H+ budgets.- Loblolly pine case studies.- 3. Magnitudes and patterns of nitrogen and sulfur deposition in the South.- Sources of acids in the atmosphere.- Anthropogenic emissions of sulfur and nitrogen.- Modes of deposition.- Atmospheric deposition in the South.- Trends in deposition rates.- 4. Forest soils of the South.- Climate.- Regional geomorphology and soils.- Coastal Plain.- Mississippi River Valley.- Piedmont.- Blue Ridge.- Ridge and Valley.- Appalachian Plateaus.- Interior Low Plateau.- Ouachita Uplands.- Ozark Plateau.- Central Lowlands.- Importance in soil acidification.- 5. Previous evaluations of sensitivity of southern soils.- Site-specific studies.- Previous regional assessments of soil sensitivity to acidic deposition.- Critique of criteria for gauging soil sensitivity.- 6. Nutrient cycles and nutrient limitations in the South.- The nitrogen cycle.- The sulfur cycle.- The nutrient cation cycles.- Cycles of other elements.- Nutrient limitations on forest growth in the South.- Conclusions.- 7. Simulation of the potential impacts of acidic deposition on forest soils in the South.- The MAGIC model.- Our approach.- Simulation results.- Discussion of simulation results and implications.- Conclusions from simulations.- 8. Synthesis and recommendations.- References.