Soil: acidification

The concern over ecological consequences of the atmospheric input of oxidized and reduced nitrogen centres on soil acidification by the oxidized nitrogen directly, and by the reduced nitrogen following its transformation in the soil into NO/ or due to its uptake by vegetation (Figure 5). ... 

Plants may be affected by indirect modifications of the environment. Soil acidification, for example, can cause the leaching of nutrients, and the release of toxic aluminum. These effects may operate together to produce nutrient deficiencies or imbalances to plants. High soil concentrations of aluminum may prevent uptake and utilization of nutrients by plants.Increased availability of aluminum in soils has been implicated as a cause of forest declines in both Europe and the United States, possibly through the toxic effects on small feeder roots 14),... 

Acid Rain A National Sensitivity Assessment, Inland Waters Directorate, Environment Canada, Ottawa, Ontario, Fact Sheet and maps, 1988. Berden, M. Nilsson, S.I. Rosen, K. Tyler, G. Soil Acidification Extent, Causes, and Consequences, National Swedish Environmental Protection Board, Rept. 3292, 1987, pp 164. 

N. S. Bolan, M. J. Hedley, and R. E. White, Processes of soil acidification during nitrogen cycling with emphasis on legume based pastures, Plant and Soil 134 53 (1991). 

Similarly to N, most S pools are found in organic form in forest floor and soil humus. However, unlike nitrogen, there are important abiotic processes, especially sulfate sorption processes, which play a critical role in regulating sulfate dynamics in forest ecosystems. An example of this type of exposure pathway was shown in the Habbard Brook whole-tree harvesting experiment, where the decrease in sulfate output from the watershed was attributed to sulfate adsorption, which was enhanced by soil acidification from nitrification (see above). 

Satsangi, G. S., Lawrence, A. J., Lakhani, A., Taneja, A. (2003). Assessment of the Potential for Soil Acidification in North India using the critical load approach and locally derived data for acidic and basic inputs. Chemosphere, 53, 1011-1021. 

BREEMEN, N. van. 1982. Soil acidification from atmospheric ammonium sulphate in forest canopy throughfall. Nature Volume 299, October 1982. 

Apart from the economic significance of such loss there are potentially adverse effects on the environment arising from acidification of rain and soil. Ammonia may react with hydroxyl radicals in the atmosphere to produce NOx contributing to the acidification of rain (4). Wet and dry deposition of NH3/NH4+ inevitably contributes to soil acidification through their subsequent nitrification. This effect can be accentuated in woodland by absorption of aerosols containing NH4+ within the canopy followed by transport to the soil in stem flow (5). In more extreme cases, NH3 emission from feedlots, pig and poultry... 

Ammonia has a lifetime of only a few hours to a few days in the atmosphere. It and its reaction products are transported through the atmosphere and deposited on terrestrial snrfaces elsewhere. It is the main gaseous alkaline species in the atmosphere and neutralizes a large part of the acid produced in oxidation of sulfur and nitrogen oxides, probably up to a half though its dry-deposition is much faster than that of NO and SO2 (Dentener and Crutzen, 1994). Dry- and wet-deposition of ammonia contribute to soil acidification because 2 mol of H+ are produced in the nitrification of Imol of NH4+. Also a large part of the ammonia deposited on moist forest soils may be re-emitted as N2O (Section 8.2). 

Johnston AE, Goulding KWT, Poulton PR (1986) Soil acidification during more than 100 years under permanent grassland and woodland at Rothamsted. Soil Use Manage 2 3-10 Kahn SU (1982) Bound pesticides residues in soil and plant. Residue Rev 84 1-25 Kan AT, Chen W, Tomson MB (2000) Desorption kinetics from neutral hydrophobic organic compounds from field contaminated sediment. Environ Pollution 108 81-89 Kang SH, Xing BS (2005) Phenanthrene sorption to sequentially extracted soil humic acids and humans. Environ Sci Technol 39 134-140... 

Although NH3 is not one of the greenhouse gases, NHs-emissions cause negative environmental effects through soil acidification and uncontrolled nitrogen re-circulation. The latter is due to ammonia losses from organic and mineral fertilisers and re-import from the atmosphere to soil by precipitation. 

Bergkvist, B., and L. Folkeson. 1992. Soil acidification and element fluxes of a Fagus sylvatica forest as influenced by simulated nitrogen deposition. Water, Air and Soil Pollution 65 111-133. 

The contribution of root and microbial respiration to rhizosphere acidification depends on the amount of C02 released, the amount of organic material oxidized to C02, and the initial pH of the soil (Hinsinger et al., 2003). However, since the first pK of H2CO3 is 6.36, the contribution of these processes to soil acidification will be significant only in neutral and alkaline soils. 

The adverse effects of this chain of events can include direct damage to vegetation, acidification of soils, and acidification of surface waters with attendant impacts on flora and fauna. In the case of managed (agricultural) soils, soil acidification effects may be overcome through use of lime. Liming has also been used to control the pH of lakes. 

Fe 5.0 Not toxic to plants in aerated soils, but can contribute to soil acidification and loss of availability of essential phosphorus and molybdenum. Overhead sprinkling may result in unsightly deposits on plants, equipment and buildings... 

A process that leads to low soil pH and soil acidification is hydrolysis. The metal most commonly associated with soil acidification is Al3+. Aluminum ions on mineral surfaces hydrolyze to produce H+, which in turn attacks the clay surfaces to produce more acidity. The process is demonstrated below ... 

Adjusted SAR, 419 Soil acidification, 160-164 Aluminum, 160 Carbonic acid, 30-32, 83-87 Nitrification, 258, 334-336, 472 Organic acids, 135-137 Sulfides, 260-271 Soil treatment, 499 Thermal, 500... 

Other modeling efforts include soil acidification models of the macroscopic type that account for the process of S04 sorption in different ways. These approaches, which assume equilibrium conditions to prevail, include the adsorption isotherm, solubility product, and anion exchange. Prenzel (1994) discussed the various limitations of the above approaches in their capability to account for changes in pH. Recently, Fumoto and Sverdrup (2000) used a constant capacitance approach to describe the pH dependency of S04 sorption isotherms in an andisol. Other modeling efforts of S04 isotherms were reported by Gustafsson (1995) in a spodosol. Such isotherm models are of the equilibrium type and include linear and Temkin types of models. 

Finlay, R. D. (1995). Interactions betweeen soil acidification, plant growth and nutrient... 

Danielsson, R. M. Visser, S. (1989). Effects of forest soil acidification on ectomycorrhizal and vesicular-arbuscular mycorrhizal development. New Phytologist, 112, 41-7. 

In addition the runoff should be considered with respect to effects of vegetation and ion exchange. The roots take up various cations and release resulting in a soil acidification. 

The withering of sycamore plants on sandy soil seems to be more likely the result of soil acidification and nutrient deficiency than that of direct impact of air pollutants. Final confirmation of this hypothesis will only be provided by more detailed soil and root investigations as well as by fertilizing experiments. 

Plate 19. Heavy injury on leaves of sycamore (Acer pseudoplatanus L.) maple showing marginal necroses which are not due to fluoride pollution because of low fluoride contents in leaves. Lack of magnesium as a rc.sult of soil acidification by acid rain may be the reason. Haard Forest, North to Recklinghausen, W. Germany, 1982. 

Red spruce (Picea rubens Sarg.) has shown an unexplained die-back in the coastal mountains of North East America which is supposed to be a result of regional soil acidification caused by air pollution (Tomlinson, 1983). 

Soil acidification causes the mobilization of cations, such as calcium, magnesium, potassium and aluminium, followed by lixiviation of metals cadmium, copper, zinc and lead. 

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