The critical load concept

Both ratio of the base cations to aluminum and the aluminum concentrations are used as indicators for steady-state geochemical and biogeochemical processes. By assigning established critical loads to these indicators (for example, the concentrations of aluminum in soil solution should not exceed 0.2 meq/L and the base cations to aluminum ratio should not be less than 1), it is possible to compute the allowable acidification for each ecosystem. An extensive overview of critical values for the ratio of base cations to aluminum for a large variety of plants and trees can be found in H. Sverdrup s papers (Sverdrup H. and deVries W., 1994). 

CRITICAL LOAD VALUES OF ACID FORMING COMPOUNDS ON ECOSYSTEMS OF ASIA 

The experimental data obtained in various countries of East Asia allow us to consider the applicability of methodology of critical loads related to an assessment of ecosystem sensitivity to acid rains. The critical load (CL) and Environmental Risk 

At current rates of atmospheric deposition, 88.0% and 72.7% of ecosystems in North Asia have no or small ( 50 eq/ha/yr) exceedances of CL(N) and CL(S), respectively (Table 1). 

However, atmospheric deposition in excess of calculated critical loads of N and S are exceeded for 10% and 20%, respectively, of the studied ecosystems in this region. 

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The critical load concept is intended to achieve the maximum economic benefit from the reduction of pollutant emissions since it takes into account the estimates of differing sensitivity of various ecosystems to acid deposition. Thus, this concept is considered to be an alternative to the more expensive BAT (Best Available Technologies) concept (Posch et al., 1996). Critical load calculations and mapping allow the creation of ecological-economic optimization models with a corresponding assessment of minimum financial investments for achieving maximum environmental protection. 

In spite of almost global attraction of the critical load concept, the quantitative assessment of critical load values is connected till now with some uncertainties. The phrase significant harmful effects in the definition of critical load is of course susceptible to interpretation, depending on the kind of effects considered and the amount of harm accepted (De Vries and Bakker, 1998a, 1998b). Regarding the effects considered in terrestrial ecosystems, a distinction can be made in effects on ... 

The critical load concept was applied to eastern Canada for two reasons, mainly ... 

Bashkin, V. N. (1997). The Critical load concept for emission abatement strategies in Europe a review. Environmental Conservation, 24, 5-13. 

Cresser, M. S. (2000). The Critical Loads Concept Milestone or Millstone for the New Millennium The Science of the Total Environment, 249, 51-62. 

Present the definition of critical loads and critical levels. Discuss the pros and cons of the critical loads concept in comparison with BAP approach to emission abatement strategy. 

Describe the basic biogeochemical principles of the critical load concept. Characterize the main advantages of using biogeochemical cycling parameterization to set environmental standards. 

Outline the applicability of the critical load concept for setting environmental standards for heavy metals. 

Modern studies have already documented the occurrence of acid rains over Northern Thailand due to the increase in use of lignite as an energy source. Based on the critical load concept, Kozlov Towprayoon (1998) have shown that the critical load values of sulfur for terrestrial Tropical Rain Forest ecosystems of the region are rather low (less than 500eq/ha/yr). As a result of both the high SO2 emission rate and high sensitivity of ecosystems, the excessive input of acidity was calculated for more than 75% of the area considered (see also Chapter 15). 

The critical load concept provides a way of setting a deposition standard based on environmental effects and criteria. There are, however, limitations to this approach and these relate to dose considerations, considerations relating to response and identification of the target units, and also to operational disadvantages of the concept. 

One explanation for the effect is the critical loading concept of Muschelk-nautz. We refer to om discussion of the Muschelknautz method in Chap. 6, and give here only a brief outline of the hypothesis. This concept sprang from a model for horizontal pnemnatic conveying of powders. The idea is that the... 

As an alternative to the critical loading concept, Mothes and Loffler (1984) put forward the idea that the improvement of cyclone efficiency with solids... 

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