Development and application of the FAB model to calculate critical loads of S and N for lakes in the Killarney Provincial Park (Ontario, Canada)
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- NIVA-rapport 
In Sudbury, Canada, large reductions in sulfur emissions have resulted in reduced critical load exceedances and partial recovery of many lakes in the Killarney Provincial Park. The First-order Acidity Balance (FAB) model to calculate critical loads (CLs) for surface water includes the potential acidifying part of nitrogen, and takes into account the retention of nitrogen in both the terrestrial and aquatic part of the catchment. We have applied the FAB model to Killarney-lakes, and critical load functions for 43 lakes in the Park have been calculated. The model has been modified to include in-lake retention of nitrogen in upstream lakes in the calculation of CLs. This resulted in increased aquatic retention of nitrogen, giving higher CLs and thus making lakes in chains less sensitive to nitrogen deposition. Including upstream lakes in a simple manner increased the estimate of in-lake N retention by 47% on average and the lake-system method increased this estimate by 73% on average. Critical loads for nitrogen vary substantially within the Park, from 49 to 2472 meq m¯² yr¯¹. On the average N retained in the lake/sediment system (Nlake) was 57% of N deposited according to the modified model.