Critical load of nitrogen

As long as the deposition of both oxidized and reduced nitrogen species, Ncicp, stays below the minimum critical load of nitrogen, i.e.,... 

Figure 15. Critical loads of nitrogen on the ecosystems in the Russian Northern Asia (Bashkin and Kozlov, 1999).

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). 

Liljelund, L.-E. and Torstensson, P. (1988). Critical load of nitrogen with regard to effects on plant composition. In Critical Loads for Sulphur and Nitrogen (ed. by J. Nilsson and P. Grennfelt), Mlljffrapport 1988 15, pp. 363-74. Nordic Council of Ministers, Copenhagen. 

Calculate the critical load. This step includes the calculation of critical loads of sulfur, nitrogen and the total acidity in a steady-state situation for the receptors of choice or for all receptors in all cells of EMEP or LoLa grid (150 x 150 km 50 x 50 km 25 x 25 km 1 x 1°, 10 x 10, etc.) of a region using a GIS (to produce critical load maps). 

Critical loads of sulfur and nitrogen, as well as their exceedances are derived with a set of simple steady-state mass balance (SSMB) equations. The first word indicates that the description of the biogeochemical processes involved is simplified, which is necessary when considering the large-scale application (the whole of Europe or even large individual countries like Russia, Poland or Ukraine) and the lack of adequate input data. The second word of the SSMB acronym indicates that only steady-state conditions are taken into account, and this leads to considerable simplification. These models include the following equations. 

All deposited N is consumed by sinks of nitrogen (immobilization and uptake), and only in this case CLmaxS is equivalent to a critical load of acidity. 

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. 

Therefore, no unique acidity critical load can be defined, but the combinations of Ndep and Sdep not causing harmful effects lie on the so-called critical load function of the ecosystem defined by three critical loads, such as CLmaxS, CLminN, and CLmaxN. In addition, the critical loads of nutrient nitrogen should be also included, CLnutrN. An example of such a trapezoid-shaped critical load function is shown in Figure 2. 

Consequently, risk assessment process is the obligatory continuation of the process of quantitative calculation and mapping of critical loads of sulfur, nitrogen and acidity at various natural and agricultural ecosystems. This is connected with numerous uncertainties a priori included in the computer algorithm for CL calculations ... 

Figure 1. The 5th percentiles of the maximum critical loads of sulfur, CLmaxS, and of the minimum critical load of acidifying nitrogen, CLminN (Posch et aL, 1999).

Latest calculations showed that critical loads of nutrient nitrogen will be exceeded in 35% of the ecosystem area in 2010 even after implementation of the Gothenburg Protocol (Table 1). 

Table 1. Forecast for exceedance of critical loads for nitrogen in accordance with planned increase of gas production.

Table 1 shows also that at planned volume of gas production of 115 billion cubic meters per year, the critical loads for nitrogen will be exceeded and this exceedance will be about 3 kg/ha/yr or about 200 eq/ha/yr in year 2015. 

Craenen, H., Ranst, E. V., Tack, F. M. G., Verloo, M. G. (2000). Calculation and Mapping of Critical Loads of Sulfur and Nitrogen in Flanders, Belgium. The Science of the Total Environment 254, 55-64. 

Figure 8. Exceedances of critical loads of sulfur and nitrogen Jor terrestrial ecosystems of Ukraine in 1992 deposition.

Here we should stress also that the higher level of asthma and chronic bronchitis morbidity took place in recreational zones (Yalta, Alushta) of South coast, where the calculated exceedances of critical loads of a two technogenic sulfur and nitrogen compounds were the greatest among the whole area of the Crimea Dry Steppe biogeochemical region of the biosphere. 

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