Validating species sensitivity distributions using salinity tolerance of riverine macroinvertebrates in the southern Murray-Darling Basin (Victoria, Australia)

Species sensitivity distributions (SSDs) are commonly used in risk assessment and in setting water quality guidelines, yet their predictions have not been validated against loss of species with increasing pollutant concentrations in nature. We used a rapid toxicity testing method to determine the acute salinity tolerance (72 h LC50 values (concentration of salinity lethal to 50% of individuals)) of 110 macroinvertebrate taxa from the southern Murray-Darling Basin in central Victoria, Australia, and construct an SSD. This SSD was compared with loss of riverine macroinvertebrates species from increasing salinity in Victoria. Macroinvertebrate species richness per individual sample, when salinity was <9.9 mS·cm-1, was invariant of salinity. However, when species richness was calculated across multiple samples above about 0.3-0.5 mS·cm-1, it declined with increasing salinity. This decline was predicted from the SSD after application of a variable safety factor calculated from an exponential or quadratic equation. Our findings confirm that SSDs can predict the loss of freshwater macroinvertebrate species from increases in salinity. This suggests that SSDs may be useful more generally for other aquatic organisms, other stressors, and toxicants.