Macroinvertebrate tolerance across a range of conductivities in the Isaac River catchment (Central Queensland)

Sensitive and tolerant species of macroinvertebrate were present at wide range of conductivity concentrations in the Isaac River Catchment in Central Queensland; indicating the need for further ecological studies in the field to underpin the development of regionally-tailored guidelines for conductivity levels. The Isaac Catchment has naturally high levels of conductivity, but there is also increasing pressure to ameliorate saline mine water discharge. Recently, catchment management efforts have included a revision of the broader Fitzroy-specific water quality guidelines. These include the use of macroinvertebrates as indicators of ecosystem health. Studies of macroinvertebrate tolerance to conductivity in southern freshwaters, as well as in laboratory-based ecotoxicological tests conducted in Queensland, suggest that ranges exceeding 1000 µS/cm are likely to have negative impacts on survivorship of all taxa. However, these results may not be transferable to natural populations of macroinvertebrates from the Isaac, where the naturally high-conductivity water may allow the opportunity for adaptation. To test this, macroinvertebrate assemblages were examined at a series of sites in the upper Isaac River catchment at the end of the dry season in 2012. Patterns in the assemblages were examined together with water quality parameters, in order to gauge the ability of macroinvertebrates to survive at conductivity concentrations exceeding 1,000 µS/cm. The specific conductance of the field sites ranged from 477 µS/cm to 9791 µS/cm and a total of 39 Families from 13 Orders were identified. Species richness was not significantly different between sites of differing conductivity. Macroinvertebrate populations were dominated by Dipterans as well as the traditionally more pollution-sensitive families Ephemeroptera and Trichoptera. There was an absence of any correlation between conductivity and species richness (P > 0.050), suggesting that macroinvertebrate taxa richness occurs independently of conductivity, in this cohort of mining and/or grazing influenced ephemeral systems in Central Queensland.