A national critical loads framework for atmospheric deposition effects assessment: IV. Model selection, applications, and critical loads mapping

Abstract

ABSTRACT/The critical loads approach is emerging as an attractive means for evaluating the effects of atmospheric deposition on sensitive terrestrial and aquatic ecosystems. Various approaches are available for modeling ecosystem responses to deposition and for estimating critical load values. These approaches include empirical and statistical relationships, steady-state and simple process models, and integrated-effects models. For any given ecosystem, the most technically sophisticated approach will not necessarily be the most appropriate for all applications; identification of the most useful approach depends upon the degree of accuracy needed and upon data and computational requirements, biogeochemical processes being modeled, approaches used for representing model results on regional bases, and desired degree of spatial and temporal resolution. Different approaches are characterized by different levels of uncertainty. If the limitations of individual approaches are known, the user can determine whether an approach provides a reasonable basis for decision making. Several options, including point maps, grid maps, and ecoregional maps, are available for presenting model results in a regional context. These are discussed using hypothetical examples for choosing populations and damage limits.

Estimation of Critical Loads of Acidity for Lakes in Northeastern United States and Eastern Canada

“…Comparison of SIGMA/SLAM, IAM and SSWC results obtained for the Quebec lake dataset showed similar results and spatial patterns, thus confirming that critical load estimates for NEG/ECP lakes were representative. Holdren et al (1993a) did similar comparisons and came to the same conclusion: that different models generated similar CL. Lokke et al (2000) advocated that critical loads should be considered as separations between deposition levels with different risk or probability of damage, instead of being regarded as thresholds.…”

“…The effectiveness of the SSWC model was also confirmed at a 1999 critical loads workshop in Copenhagen (Lokke et al, 2000). Holdren et al (1993a) also showed that the SSWC model ranked among the best in its category.…”

The science and policy of critical loads of pollutant deposition to protect ecosystems in New York

“…The Clean Air Act (CAA) of 1970 and its subsequent amendments led to National Ambient Air Quality Standards (NAAQS) in the United States to protect human health. Scientists wanted similar standards to protect natural communities and hoped that CLs would help to provide them . Progress has been made on both the science and the policy and management aspects of CLs …”

Measuring nitrogen and sulphur deposition in the Georgia Basin, British Columbia, using lichens and moss

“…Acidification due to industrial S emissions have been a great concern in eastern Canada, where ongoing initiatives have led to development of critical loads for S deposition (Holdren et al 1993;Jeffries et al 1999). While coastal British Columbia is not burdened with high industrial S emissions of eastern Canada, the area is particularly vulnerable to acidification due to highly resistant and acidic bedrock geology, which greatly limit potential buffering of incoming acid deposition (Wiens 1987).…”