Soil, acid sensitivity

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. 

Plants are highly sensitive to soil acidity because many equilibria involving plant nutrients are affected by pH. Phosphorus is a primary example. This essential element for plant growth occurs in soils mainly as phosphates, which are subject to phosphate-hydrogen phosphate equilibria. Consequently, phosphorus is... 

The colors of flowering plants such as hydrangeas are highly sensitive to soil acidity. At pH > 6.5, these showy flowers are deep pink, but at pH < 5, the blossoms are vivid blue. The chemistry of these changes involves complexation of aluminum by pigments that have acidic groups, as the structures show. 

Choose alkaline formulations for products designed to remove oils and organic soils or to treat acid-sensitive surfaces such as marble. 

Based on the mineralogy controlling weathering and soil development, sensitivity of ecosystem to acid deposition is assessed with a comprehensive consideration on the effect of temperature, soil texture, land use and precipitation. The results show that the most sensitive area to acid deposition in China is Podzolic soil zone in the Northeast, then followed by Latosol, Dark Brown Forest soil and Black soil zones. The less sensitive area is Ferralsol and Yellow-Brown Earth zone in the Southeast, and the least sensitive areas are mainly referred to as Xerosol zone in the Northwest,... 

Figure 5.12 depicts a hypothetical soil pH-buffer capacity curve. It is clear from this relationship that the soils most likely to reach very low pH and toxic Al solubilities even with modest inputs of acidity are those with low inherent buffer capacities (arising from the lack of carbonates, clay, or humus content) or those whose buffers have already been expended in neutralizing past acid inputs. These are termed acid-sensitive soils, and are typically acid soils with little clay and humus. They are the most likely soils to reach extremely low pH (<4) on exposure to acid rain or other sources of acidity. Since primary and secondary aluminosilicate mineral dissolution is very pH sensitive, phytotoxic concentrations of soluble AP" are increasingly likely as the pH lowers. 

Based on the mineralogy controlling weathering and soil development, sensitivity of ecosystems to acid deposition is assessed with the comprehensive consideration on the effect of temperature, soil texture, land use and precipitation. The results show... 

In relation to add input from 1980 to 1990, the buffering capacity of 1.8 Mio km or 15% of the acid-sensitive forest soils tends to become saturated in the next 25-100 years. Under the assumptions of the IS92a scenario, this share more than doubles and increases to 4.0 Mio km or 34% between 2040 and 2050. For 1980-1990, the mean buffering capacity of these sols based on our methodology is supposed to last for 65 years more. Under changed inputs this period tends to decrease for 2040-2050 to... 

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. 

Nitrogen Deposition in Nutrient-Deficient and Acid-Sensitive Soils... 

Greatest changes in aerial distribution and increase of concentration will occur in the Asian region (see Fig. 4). Regions with acid-sensitive soils and high N-depositions are concentrated to China and Southeast Asia, Western and Central Europe, and... 

Until recently, understanding of the effects of acidic deposition on soils was limited. However, current research has shown that acidic deposition has chemically altered forest soils with serious consequences for acid-sensitive ecosystems. Soils compromised by acidic deposition lose their ability to neutralize continuing inputs of strong acids, provide poorer growing conditions for plants, and extend the time needed for ecosystems to recover from acidic deposition. Acidic deposition has altered and continues to alter base-poor forest soils in three important ways. Acidic deposition depletes available calcium and other nutrient cations (e.g., magnesium, potassium) from soil facilitates the mobilization of dissolved inorganic aluminum into soil water and increases the accumulation of sulfur and nitrogen in soil. 

MacAvoy, S.E. and Bulger, A.J. (1995). Survival of brook trout (Salvelinus fonti-nalis) embryos and fry in streams of different acid sensitivity in Shenandoah National Park, USA. Water Air and Soil Pollution, 85, 439—444. 

The focus of the research just described utilizing the cucumber-nutrient culture and the cucumber-microbe-soil model systems was to identify and characterize what happens to phenolic acids once they enter the soil environment and how in turn this may influence the behavior and processes of phenolic acid-sensitive seedlings. The research was thus hypothetical, theoretical, and process oriented and not designed to answer speciflc questions related to actual field observations. When choosing any model system for study one hopes and assumes that the model system chosen is not unique but that the relationships and processes observed for the system chosen are representative of a broader array of other systems and hopefully relevant to field systems. 

Boron. The principal materials used are borax [1303-96-4] sodium pentaborate, sodium tetraborate, partially dehydrated borates, boric acid [10043-35-3] and boron frits. Soil appHcation rates of boron for vegetable crops and alfalfa are usually in the range of 0.5—3 kg/hm. Lower rates are used for more sensitive crops. Both soil and foHar appHcation are practiced but soil appHcations remain effective longer. Boron toxicity is not often observed in field appHcations (see Boron compounds). 

A variety of shale-protective muds are available which contain high levels of potassium ions (10). The reaction of potassium ions with clay, well known to soil scientists, results in potassium fixation and formation of a less water-sensitive clay. Potassium chloride, potassium hydroxide, potassium carbonate [584-08-7] (99), tetrapotassium pyrophosphate [7320-34-5] (100), and possibly the potassium salts of organic acids, such as potassium acetate [127-08-2] (101) and formate, have all been used as the potassium source. Potassium chloride is generally preferred because of its low cost and availabihty. 

The documentation of regional level terrestrial consequences of acid deposition is complicated. For example, forested ecosystems m eastern North America can he influenced by other factors such as high atmospheric ozone concentrations, drought, insect outbreaks and disease, sometimes from non-native sources. However there is a general consensus on some impacts of acidic depositon on both soils and forests m sensitive regions. 

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