Ecosystem acidification, nitrogen deposition

In the plains, Cambisols place the most drainage areas. These soils occupy the hilly plains and low mountain belts up to the 500-700 m elevation, where they coincide with the Broadleaf and Coniferous-Broadleaf Forest ecosystem types. In the most continental parts the oak forests are dominant. For instance, at the slopes of the Sikhote-Alin range Cedar-Broadleaf Forest and in Korean peninsula, the Oak-Maple Forest ecosystems are predominant. In Japan Beech Forest ecosystems are the most abundant. Heavy precipitation rates during wet season (up to 1000-1200 mm with P PE equal to 1) favor the increasing base saturation in the Luvic Cambisols. These ecosystems are characterized by a moderate rate of organic matter turnover with mean values of Cb equal to 2.5 C, is 0.67 and Cbr is 1.7. Such moderate rates are favorable to soil acidification with deposition input of sulfur and nitrogen acid forming compounds (NIES, 1996, Bashkin and Park, 1998). This process can be especially enhanced in... 

The level of acidification caused by sulfur and nitrogen deposition is affected by several processes, including base cation uptake, nitrogen uptake, and base cation deposition. Acid deposition affects the soil-plant system and, via soil solution, also the surface waters and groundwater. Leaching plus harvesting reduces soil and biomass Ca, and leads to a significant acidification of ecosystems. The soil base cation status decreases. 

What became popularly known as acid rain is a complex set of physical and chemical phenomena by which gases—especially sulfur dioxide (SO2) and nitrogen oxides (NOJ—are created and emitted, mostly by industrial processes, transported through the atmosphere, transformed into acidic compounds, and deposited onto land and water surfaces, often with serious negative effects for aquatic and terrestrial ecosystems. Acidification of lakes... 

The maximum critical load for nitrogen acidity represents a case of no S deposition. The value of CLmaxN not only takes into account the nitrogen sinks summarized as CLminN, but consider also deposition-dependent denitrification as a denitrification fraction /de. Both sulfur and nitrogen contribute to acidification, but one equivalent of S contributes, in general, more to excess acidity than one equivalent of N, since nitrogen is also an important nutrient, which is deficient in the most natural ecosystems. 

Acidification Release of oxides of sulfur and nitrogen (SOx, NOx) Chemical oxidation and deposition of acid compounds Acidic precipitation and lowering of pH in lakes and soils Ecosystem changes and plant/animal death Acidification Potential (AP)... 

Critical load of nitrogen This is normally defined with respect to eutrophication, and not to acidification. The critical load of nitrogen is the maximum deposition of nitrogen compounds that will not cause eutrophication or induce any type of nutrient imbalance in any part of the ecosystem (Table 3.8). 

Gundersen and Rasmussen (1988) have suggested that the deposition of nitrogen should not exceed the uptake by plants (5-15 kg N ha" 3T" in Nordic coniferous forest ecosystems) in order to prevent acidification of the soil. Rosen (1988) calculated critical loads on the basis of the capacity of woody biomass to accumulate nitrogen and also the increased depletion of base cations from the soil in response to Increased groAvth rates. The critlced load set in this way varies with site quality emd for Scandinavian forests will probably vary between 5-15 kg N ha yr. ... 

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