Soil, acidity neutralization capacity

Acidification the decrease of acid neutralizing capacity in water or base saturation in soil caused by natural or anthropogenic processes. 

Acid deposition is of greatest concern wherever there are large amounts ol lossil fuel combustion upwind of an area. Eastern North America, large areas of Europe, and eastern Asia all receive acidic deposition. Acidic deposition is especially a concern when poorly buffered soils, with little acid-neutralizing capacity, are impacted. In North America, large areas of eastern Canada, the Adirondack Mountains of upstate New York, and sections of New England all are considered acid sensitive areas, where resistant bedrocks and thin soils prevent significant neutralization of acidity. 

Soil solution equilibrium. Soil solution equilibriumis based on the quantification of acid-neutralizing capacity, ANC, which has been defined as ... 

Acid deposition can cause acidification of soils and waters. Acidification can be defined as a reduction of the acid-neutralizing capacity of soils or waters. The acidneutralizing capacity is also known as alkalinity (AUc) and indicates the sensitivity of a water system toward acidification. It can be expressed as [9] ... 

Based on a study comparing N-Viro soil physical properties with those of mineral soils, the physical characteristics of N-Viro soils suggest that chemical characteristics (such as high initial pH, acid neutralizing capacity, and high soluble salt content), rather than physical attributes, are likely to limit the use of these materials as soil substitutes. 

The general sequence of the calculations in PROFILE is given in Fig. 7.12. The acid neutralization capacity (ANC) of soil moisture (the alkalinity minus the acidity) and the soil pH are com-... 

Critical leaching of Acid Neutralizing Capacity of soil solution—ANCie(crit)... 

Solids mineral identification mineral abundance cation-exchange capacity (CEC) extractable Mn and Fe oxides soil pR acid-generation potential acid-neutralization capacity... 

Whenever complete chemical analyses are provided for soil extracts or irrigation waters, the sum of major cations (mmol(+) L-1) should approximately equal the sum of all major anions (mmol(—) L-1). Repeated exact agreement, however, indicates that one ion is being determined by difference. This is usually sulfate for recent analyses, or sodium for older analyses. Also, reported concentrations of carbonate should be negligible at solution pH >9. In the water-supply literature, Ca plus Mg concentrations are reported as hardness, the chemically equivalent quantity of CaC03 in milligrams per liter. Concentrations of bicarbonate plus carbonate may be reported -as alkalinity, the equivalent acid-neutralizing capacity of the water. 

In a first step, nutrient-depleted soils with low buffering capacity are identified to a,s,sess regions with potential for destabilization of forest ecosystems by acid deposition. Becau.se the acidity neutralization capacity of. soils (ANC) cannot be accurately determined from the global data, a simple approach based on the Soil Map of the World (FAO, 1995) is carried out. To evaluate the buffering capacity of the top.soils, the CEC data (cation exchange capacity) and the base saturation data (Na, K, Mg, and Ca) are combined with a map of the global distribution of forests (WCMC, 1997) to obtain the measures for fore.st soils with low buffering capacity. 

These experimental test procedures, together with calculations of the acid-producing potential (APP) and acid-neutralizing capacity (ANC), are characteristic tools for the medium- and long-term prediction of metal release from all types of waste materials. Application of such prognostic tool will become even more important, when the rate of waste material utilization/ recycling is enhanced (in Germany up to 100% by the year 2020), and will intensify the contact of the secondary products with the soil environment. 

Figure 3.10. Time series of predictions with the acidification model PnET-BGC of changes in stream chemistry at Hubbard Brook to changes in past and potential future emissions of sulfur dioxide and nitrogen oxides, including the 1990 Amendments of the Clean Air Act and moderate and aggressive emission control scenarios. Shown are model-predicted stream concentrations of sulfate, nitrate, acid neutralizing capacity, pH and dissolved inorganic aluminum, and soil percent base saturation. Measured values are indicated for comparison...

When a forest system is subjected to acid deposition, the foliar canopy can initially provide some neutralizing capacity. If the quantity of acid components is too high, this limited neutralizing capacity is overcome. As the acid components reach the forest floor, the soil composition determines their impact. The soil composition may have sufficient buffering capacity to neutralize the acid components. However, alteration of soil pH can result in mobilization or leaching of important minerals in the soil. In some instances, trace metals such as Ca or Mg may be removed from the soil, altering the A1 tolerance for trees. 

Equation (3.70) for the electrical neutrality of the solid, with changes in acidity in the solid related to changes in pH with the soil pH buffer capacity ... 

Though water acidification is one of the most important aspects, one would certainly not expect significant changes in water acidity in all exposed areas. The effect is highly dependent on bedrock geology and the nature of the overburden. No acidification of fresh water is to be expected in areas with appreciable amounts of calcareous rocks. The most well known susceptible areas are those with shallow overburden and quartzbearing bedrock. Acidification can occur in catchments with highly weathered sandy soils with low neutralization capacities. 

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