Assessment of land use impacts on soil ecological functions: development of spatially differentiated characterization factors within a Canadian context

Among other regional impact categories in LCA, land use still lacks a suitable assessment method regarding the least developed “soil ecological quality” impact pathway. The goals of this study are to scope the framework addressing soil ecological functions and to improve the development of regionalized characterization factors (CFs). A spatially explicit approach was developed and illustrated for the Canadian context using three different regional scales and for which the extent of spatial variability was assessed.

A model framework based on the multifunctional character of soil and the ecosystem services defined by the Millennium Ecosystem Assessment is suggested. This framework includes land use impacts on soil ecological quality evaluated regarding the change in soil capacity to fulfill a range of soil ecological functions. Four impact indicators, namely erosion resistance, groundwater recharge, mechanical, and physicochemical filtration, proposed by the functional method of Baitz (2002), were used to assess three major degraded regulating services: erosion regulation, freshwater regulation, and water purification. Spatially differentiated CFs were calculated based on the principles proposed by the UNEP/SETAC Life Cycle Initiative for two Canadian spatial models (15 ecozones, 193 ecoregions) along with a non-spatial one (one generic). Seven representative land use types were tested.

Using the ecozone-based scale, an overall result comparison between the non-spatial and spatial models indicates significant differences between ranges across land use types and results up to four times larger than what the generic scale can capture. This highlights the importance of introducing a regionalized assessment. When considering the impacts from a specific land use type, such as urban land use, generic CFs fail to adequately represent spatial CFs because they tend to be highly dependent on the biogeographical conditions of the location. When comparing all three resolution scales, CF results calculated using the ecoregions spatial scale generally show a larger spread across each land use type. Interesting variations and extreme scenarios are revealed which could not be observed using a coarser scale-based model such as the ecozone resolution scheme.

This work demonstrates the accomplishment of developing spatially differentiated CFs addressing impacts of different land use types on soil ecological functions. For a large territorial area spreading over many biomes, such as Canada, accounting for ecological unit boundaries proves to be necessary since the generic scale is not sufficiently representative. An evaluation of the extent of spatial differentiation emphasized the influence on the variability of regionalized CFs.