The Use of Dynamic Models to Set Target Loads

• Published in: Ambio 1992-08, Vol.21 (5), p.369-376
• Main Authors: Per Warfvinge, Maria Holmberg, Posch, Maximilian, Wright, Richard F.
• Format: Article
• Language: English
• Subjects: Acid soils; Acidification; Dynamic modeling; Ecosystem models; Forest soils; Freshwater; Soil acidification; Soil chemistry; Soil water; Surface water; Watersheds
• ISSN: 0044-7447; 1654-7209

The concept of critical load addresses the level of environmental stress that will not harm ecosystems in a long-term perspective. Methods used to calculate critical loads do not take the time scales of acidification and recovery into account. Therefore, the environmental consequences of different emission reductions can not be fully assessed using only the empirical and steady-state methods used to calculate critical loads. Using dynamic chemical models, the change in key chemical parameters in three Nordic ecosystems were predicted for several deposition scenarios. Target loads for S deposition were set, using 3 different dynamic models, under the condition that the chemical criteria should be met by 2037. For catchments with shallow soils, the target loads for S in surface water, calculated with all models, were similar. All models indicate that the S deposition at Birkenes in southern Norway must be reduced to < 0 meq m-2yr-1to meet the chemical target, ANC in run off greater than 20 meq m-3. For a catchment with deep soils, Yli-Knuutila in Finland, the calculated target load ranged from 250 meq S m-2yr-1calculated with a multi-layered model to 1500, determined with a one compartment model. The calculated target loads for soils show similar differences between models, indicating that for soils deeper than the rooting zone, the choice of model largely determines the estimated target load. For acidified sites, the nearer into the future the target year is, the lower the target load. Systems not yet damaged can be protected for the future, if the load is lower than the critical load. The longer the system is to be protected, the lower the target load.