Exceedance of critical loads for lakes in Finland, Norway and Sweden: Reduction requirements for nitrogen and sulfur deposition

Abstract

The main goal of the present study was to evaluate the different ways of computing the exceedances and the reductions needed for N and S depositions. Two models for calculating the steady state critical loads for N and S acidity were applied to Finnish, Norwegian and Swedish lake data bases. The first model was used for calculating present exceedances from the critical loads of acidity and the second for assessing also the future situations. The critical loads of N and S deposition are interrelated, and therefore, one cannot be looked at without makong assumptions about the other. The question which pollutant has to be reduced in order to achieve the critical load was approached by investigating the present N and S deposition for each lake with respect to the critical load function. Secondly, the reduction required was assessed separatly for S deposition by fixing N deposition to the present level. Only in southern most Norway strong measures to reduce sulfur is not enough, strongest possible reductions of nitrogen depiosition is also required.