Effect factors of terrestrial acidification in Brazil for use in Life Cycle Impact Assessment

Abstract

In Life Cycle Impact Assessment, atmospheric fate factors, soil exposure factors, and effect factors are combined to characterize potential impacts of acidifying substances in terrestrial environments. Due to the low availability of global data sets, effect factors (EFs) have been reported as the major contributors to statistical uncertainties of characterization factors and they are the focus of this study. We aim to develop spatially differentiated EFs taking Brazil as case and explore new methodological ways to derive them. EFs are calculated based on a comprehensive database reporting observations of approximately 30,000 plant species at biome and ecoregion levels. Species richness distributions as function of soil pH are developed and translated into potentially not occurring fraction (PNOF) of species, which can be equated to the more commonly used potentially disappeared fraction of species, to assess effects of changes in soil hydrogen ion concentration on terrestrial plant species. Potentially extinct fraction (PXF) of species is proposed as a complementary metric for LCIA models based on distributions of range-restricted species (species only occurring in one ecoregion of Brazil). Different approaches for determining EFs from the species richness distributions are evaluated. Area-weighted EFs are explored to determine potential effects when considering both acid and alkaline sides of species richness curves, thus integrating potentially positive effects of acidification on biodiversity. Spatially differentiated EFs are provided for 6 biomes and 45 ecoregions composing Brazil. Comparisons with previous EFs demonstrate that data availability might significantly influence regression analyses, and the use of more representative data can lead to more consistent EFs. Moreover, consideration of the entire species richness curves yields positive and negative EFs. Adding acidifying substances onto specific soils in Brazilian ecoregions may therefore be associated with increased species richness if the pH approaches the optimum pH from the alkaline side of the curve. The meaningfulness of species richness as indicator of acidification stress is discussed based on this finding, as is the inclusion of the metric PXF, highlighting species whose loss could cause irreversible damages to the environment. We recommend the calculation of area-weighted EFs to be integrated into characterization models for terrestrial acidification, and we therefore advocate that similar work be done for other regions in the world than Brazil to enhance the consistency of the EFs and reduce their uncertainties. We additionally recommend that LCIA method developers further explore the application of PXF for other impact categories than acidification.