Spatial variation in the ecological vulnerability of freshwater invertebrate assemblages to chemical stressors

Most current ecological risk assessments of chemicals adopt a single threshold approach. However, the single threshold approach has been criticized for being rather general. Natural assemblages may vary their sensitivity to a chemical, and spatial variation in assemblage recovery is not considered. Therefore, it is necessary to evaluate the impact of spatial variation in sensitivity and recovery on ecological risk assessment. Ecological vulnerability to chemicals consists of external exposure, intrinsic sensitivity, and recovery potential, and this thesis focused on spatial variation in the latter two elements. The thesis has three principal objectives: to assess spatial variation in the sensitivity of freshwater invertebrate assemblages to chemicals; to relate spatial patterns in assemblage sensitivity to river typology descriptors and land use; to investigate spatial variation in the recovery process of freshwater invertebrate assemblages. There is spatial variation in the sensitivity of species assemblages to chemicals, with the magnitudes of variation to specifically acting chemicals being greater than general acting chemicals. There is an association between the similarity in species composition and the variation in assemblage sensitivity to chemicals. The river typology descriptors and land use significantly impact spatial variation in assemblage sensitivity to some chemicals. The recovery potential of species assemblages also varies spatially and exhibits certain patterns. Spatial variation in assemblage sensitivity and recovery potential was considered to develop a spatially defined ecological vulnerability framework. Considering the spatial variation in assemblage sensitivity to chemicals, the current environmental quality standards are protective of biodiversity for most of the chemicals investigated; for many chemicals, the standards are very conservative; potentially unnecessarily restricting the use of chemicals that provide significant societal benefits. Spatially defined ecological vulnerability analysis suggests that spatial variation in assemblage sensitivity and recovery potential can exacerbate or mitigate chemical risks compared to using the single threshold approach.