Soil buffering capacity

Notes on the calculation. A full explanation of soil buffer capacity and derivation of the above factors is given by Rowell (1994, pp. 171-172). 

Figure 5.12. General relationship between soil pH (a measure of acid intensity) and quantity of acid or base added. The inverse of the slope of this curve provides a measure of soil buffer capacity.

FIGURE 3 Distribution of exceeded forest soils buffering capacity, (a) today (1980-1990) and (b) (2040-2050). Red areas show forest soils with an exceeded buffering capacity while the green areas show the not-affected areas of acid sensitive and nutrient deficient forest soils. See also color insert. 

Eastern North America. Again, in absolute numbers Eastern North America shows the largest distribution of forest areas with an exceeded soil buffering capacity and high nitrogen deposition, followed by Southeast Asia, China, and Europe. 

Bedrock, including clays, influences soil buffering capacity according to its hardness. The more easily weathered a bedrock, the faster is the release of buffering metallic cations, and the stronger its resistance to acidification. Lime-rich rocks such as limestone, marble and marble slates are very easily weathered. Much of Scandinavia, parts of the UK (particularly Scotland) and the eastern part of N America have bedrock which is much more resistant to weathering generally. 

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. 

Between various wood species great differences can occur in pH as well as in the buffer capacity. Even within the same wood species, differences might occur due to seasonal variations, portion of the wood substance under investigation, pH of the soil, age of the tree, time span after cutting, drying and processing parameters. 

During the lifetime of a root, considerable depletion of the available mineral nutrients (MN) in the rhizosphere is to be expected. This, in turn, will affect the equilibrium between available and unavailable forms of MN. For example, dissolution of insoluble calcium or iron phosphates may occur, clay-fixed ammonium or potassium may be released, and nonlabile forms of P associated with clay and sesquioxide surfaces may enter soil solution (10). Any or all of these conversions to available forms will act to buffer the soil solution concentrations and reduce the intensity of the depletion curves around the root. However, because they occur relatively slowly (e.g., over hours, days, or weeks), they cannot be accounted for in the buffer capacity term and have to be included as separate source (dCldl) terms in Eq. (8). Such source terms are likely to be highly soil specific and difficult to measure (11). Many rhizosphere modelers have chosen to ignore them altogether, either by dealing with soils in which they are of limited importance or by growing plants for relatively short periods of time, where their contribution is small. Where such terms have been included, it is common to find first-order kinetic equations being used to describe the rate of interconversion (12). 

The low pH of acid precipitation can destroy forests and kill fish. Some lakes and streams lie in soil that has the natural ability to buffer the increased acidity of acid rain, usually because the soil contains a high amount of lime. Other lakes and streams, however, have no such buffering capacity. The pH of the water is not the main problem—at least not directly. The problem lies in the amount of aluminum compounds that are leached out of the soil surrounding the lake or stream at lower pHs. Aluminum is toxic to many aquatic species. 

Many lakes also suffer from a phenomenon called episodic acidity. Episodic acidity means that most of the time the lake has a pH within acceptable levels. But occasionally, the pH of the lake becomes much lower when heavy rainstorms or snow melts bring in large amounts of runoff. Episodic acidity sometimes results in large fish kills. The Northeastern part of the United States and Canada are especially hard hit due to the poor buffering capacity of the soil in those areas. 

Ecologically, accidental releases of solution forms of hydrochloric acid may adversely affect aquatic life by including a transient lowering of the pH (i.e., increasing the acidity) of surface waters. Releases of hydrochloric acid to surface waters and soils will be neutralized to an extent due to the buffering capacities of both systems. The extent of these reactions will depend on the characteristics of the specific environment. 

Microbial activity, which is often stimulated during bioremediation projects, can alter the external pH. For instance, the anaerobic degradation of chlorinated compounds produces organic acids and HC1 and the pH may drop to acidic values if the soil has a low buffering capacity. In this case, control of the external pH will be required in order to maintain biodegradation activity at... 

Soil has very high buffering capacity at this point because the added acid is decomposing the inorganic components in soil. This means that a large amount of add is needed to decrease the pH of soil to a point where all metals are solubilized and can be leached out. 

Soil solutions can also be titrated to obtain information about both their pH status and their buffering capacity. Chapters 9 and 10 give a more detailed discussion of electrical and titration methods applied to soil. 

It is the chemical buffering system which contributes significantly to the carrying capacity of a soil [ 17]. In general, any soil cannot completely adsorb all the pollutants from the liquid solution. There is an equilibrium between solvent and solution phases. The amount left in solution gradually increases as the buffer capacity of the soil is approached. 

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 ... 

Kuo, R.J. Matijevic, E. (1980) Particle adhesion and removal in model systems. III. Monodisperse ferric oxide on steel. J. Colloid Interface Sci. 78 407-421 Kuo, S. Jellum, E.J. (1994) The effect of soil phosphorus buffering capacity on phosphorus extraction by iron oxide-coated paper strips in some acid soils. Soil Sci. 158 124-131... 

Bacteria of the genus thiobacillus attack sulphur in the presence of moisture, oxygen and warmth (except thiobacillus denitrifleans which grows without oxygen) The acid produced may cause long term problems close to the concrete if the buffering capacity of the soil is low (7). Damage to specimens is usually restricted to the surface. 

Acid rain primarily affects sensitive bodies of water, that is, those that rest atop soil with a limited ability to neutralize acidic compounds (called buffering capacity ). Many lakes and streams examined in a National Surface Water Survey (NSWS) suffer from chronic acidity, a condition m which water lias a constant low (acidic) pH level. The survey investigated tlie effects of acidic deposition in over 1,000 lakes larger than 10 acres and in thousands of miles of streams believed to be sensitive to acidification. Of the lakes and streams surveyed in the NSWS, arid rain has been determined to cause acidity in 75 percent of the acidic lakes and about 50 percent of tlie acidic streams. Several regions in the U.S. were identified as containing many of the surface waters sensitive to acidification. They include, but are not limited to, the Adirondacks. the mid-Appalachian highlands, the upper Midwest, and the high elevation West. 

Streams flowing over soil with low buffering capacity are equally as susceptible to damage from acid rain as lakes are. Approximately 580 of the streams m the Mid-Atlantic Coastal Plain are acidic primarily due to acidic deposition. The New Jersey Pine Barrens area endures the highest rate of acidic streams in the nation with over 90 percent of the streams acidic. Over 1,350 of the streams in the Mid-Atlantic Highlands (mid-Appalachia) are acidic, primarily due to acidic deposition. Many streams in that area have already experienced trout losses due to the rising acidity. 

The presence of acidic functional groups, mostly carboxyl and phenolic OH groups, in the molecular structure of soil HS renders them major players in the acid-base buffering capacity of soils and in the fate, bioavailability, and physico-chemical behavior of macro- and micronutrients, toxic metal ions, and several xenobiotic organic compounds in soil (Ritchie and Perdue, 2003 Senesi and Loffredo, 2005). Consequently, the effects of amendment on the acid-base properties of soil HAs and FAs is a subject of considerable interest. 

Microbial-driven mineralization of organic matter can also contribute to acidification of the rhizosphere (Badalucco and Nannipieri, 2007). It should be noted that pH variations in the rhizosphere depend also on the soil s buffering capacity... 

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