Acid precipitation effects on soil pH and base saturation of exchange sites

Abstract

The t y p i c a l values and probable ranges of acid-precipitation a r e evaluated i n terms of t h e i r t h e o r e t i c a l e f f e c t s on pH and c a t i o n exchange equilibrium of s o i l s c h a r a c t e r i s t i c of t h e humid temperature region. The extent of probable change i n s o i l pH and t h e time required t o cause such a change a r e calculated f o r a range of common s o i l s . Hydrogen ion i n p u t by a c i d p r e c i p i t a t i o n i s compared t o c a t i o n inputs from n u t r i e n t cycling and o t h e r sources. For example it can be calculated t h a t 100 years of acid p r e c i p i t a t i o n (10,000 cm a t pH 4.0) could be expected t o s h i f t t h e percentage base s a t u r a t i o n i n t h e top 20 cm of a t y p i c a l midwestern f o r e s t s o i l (cation exchange capacity of 20 meq/100 g ) downward 20%, thus lowering t h e pH of t h e A 1 horizon by approximately 0.6 u n i t s , i f t h e r e a r e no countering inputs of b a s i c materials.

The Role of Environmental Filtering in Structuring Appalachian Tree Communities: Topographic Influences on Functional Diversity Are Mediated through Soil Characteristics

“…Cation exchange capacity is enhanced with increasing clay and organic matter contents of soils, which also contribute to greater water-holding capacity of soils. Soil pH is also linked to CEC, where greater soil acidity leads to the occupation of cation exchange sites by hydrogen ions and contributes to nutrient leaching [64,67]. Given the importance of soil moisture and soil fertility in our path models, we expected CEC to be a significant factor as well.…”

Ecology of streams draining forested and non-forested catchments in an area of central Scotland subject to acid precipitation

“…Increased cation leaching and uptake by trees could reduce the base saturation of forest soils (McFee 1977 ;Nihlgard 1972), and the effects of the elimination of ground vegetation, due to canopy closure, should be investigated further .…”

Patterns of Life

“…It has been calculated that at a pH of 4.0 and average annual precipitation of 100 cm that a typical Midwestern forest soil of North America (cation exchange capacity of 20 meq/l00 g) would undergo a 20% reduction of base saturation in the top 20 cm, thereby lowering the pH of the Al horizon by about 0.6 units (McFee et al 1976). Under the most unfavorable combinations, even low-elevation streams have had major changes in chemical properties during the 1960's and 1970's.…”