Macroinvertebrate Responses to Conductivity in Different Bioregions of Victoria, Australia

The use of field data to derive guideline water quality trigger values is likely to be more environmentally relevant than laboratory estimates. In the present study, macroinvertebrate responses to conductivity (specific conductance at 25 °C) within 5 bioregions in Victoria, Australia, were derived from 19 yr of macroinvertebrate field data. Varying response to electrical conductivity (EC) occurred among taxa. Ninety-five percent extirpation concentrations (XC95) for EC were calculated for each genus and species and ranged from 25 to 23 600 µS/cm. Hazardous concentration 5th percentiles (HC05) were calculated for each bioregion from species sensitivity distributions developed using genus and species XC95 values. Genus HC05 values varied substantially between bioregions: bioregion 1 (29 µS/cm), 2 (78 µS/cm), 3 (143 µS/cm), 4 (1068 µS/cm), and 5 (2226 µS/cm). No substantial differences in HC05 values were shown between genus- and species-level calculations in bioregions 1 to 3 and 5; however, a decrease of approximately 300 µS/cm was shown for bioregion 4. The substantial differences in HC05 values between bioregions supports the need for region-specific determination of effects of EC. We explore the use of HC05 values as water quality guidelines across a bioregion gradient and provide a comprehensive analysis of macroinvertebrate responses to changes in EC, with important implications for waterway management. Environ Toxicol Chem 2019;38:1334-1342. © 2019 SETAC.