Assessing The Ecotoxicology Of Salinity On Organisms In Seasonally Flowing Streams In The Fitzroy Catchment

Stage One Report: Development Of Ecosystem Protection Trigger Values For Sodium Sulfate In Seasonally Flowing Streams Of The Fitzroy River Basin

Coal mines in the Bowen Basin have reduced freshwater consumption by implementing water re-use in operations. This has resulted in overall increased salinity of water stored on sites.  Sulfate is often associated with this water but few studies have elucidated the impacts of sulfate on aquatic organisms making it difficult to set criteria for mine water discharge.  There are currently no ecosystem protection trigger values for sulfate in Queensland or elsewhere in Australia. This study has developed the first locally relevant ecosystem protection trigger values for sulfate in the Fitzroy River Basin.

The surface water chemistry present in the Fitzroy River Basin was analysed to define a representative water type for toxicity assessment. A standard suite of toxicity tests were used to assess the potential toxicity of sulfate and a species sensitivity distribution was derived from this data to define protective concentrations. The concentration of sulfate that should theoretically be protective of 95% of species in the receiving ecosystem was estimated to be 770 mg/L and the concentration of sulfate that should theoretically protect 99% of species in the receiving ecosystem was estimated to be 620 mg/L. This study provides a significant advance in scientific understanding of the potential environmental impacts of sulfate in the Fitzroy River Basin and will help improve licensing and water quality management.

Stage Two Report: Assessing The Ecotoxicology Of Salinity On Organisms In Seasonally Flowing Streams In The Fitzroy Catchment

The level of salinity that various aquatic organisms can tolerate without incurring any adverse effects is dependent on several environmental and evolutionary factors. These factors might include, for instance, the relative concentrations of different types of dissolved salts in the water that makes up their habitat, the regimes to which organisms are exposed to waters of differing salinity levels (including naturally derived variations), the degree to which an organism's life history stages have adapted to salinity, an organism's ability or behaviour to avoid adverse levels of salinity, and an organism's capacity for osmoregulation. When dissolved in water, various types of salts exist in the form of anions and cations, and the composition of all ions in the water is referred to as ionic composition. As a consequence of environmental and evolutionary factors, it can be expected that different taxa can exhibit a wide range of potential responses to changes in salinity. In addition, the relative sensitivity of organisms belonging to the same taxon to salinity may vary even on a regional basis, adding a further level of specificity to the issue. Consequently, while the currently available information on salinity-related toxicity can be applied to broadly limit the impacts of saline mine water releases on freshwater ecosystems, there is insufficient specific information that considers the ionic composition of waters to develop guidelines appropriate for numerous distinct regions. Mine waters can be of different ionic compositions and different EC's which in turn can have bearing on their toxicity.

The primary aim of this project was to produce data and gather information on the tolerances of freshwater macroinvertebrates from Fitzroy Catchment to saline mine water, that could potentially be utilised for developing guidelines for mine water discharge in the Fitzroy Catchment. The secondary aim was to assess the influence of ionic compositions on saline mine water toxicity, and to use the information to consider possible amelioration of toxicity in mine water discharge.

The objectives of the study were:

· To conduct acute toxicological tests to determine the tolerances of aquatic macroinvertebrates from a section of the Fitzroy Catchment, to saline solutions those were representative of ionic compositions of mine waters;

· To undertake acute and chronic toxicity tests on representative mine waters ionic compositions using a standard suite of commercially available taxa;

· To determine if ionic composition influenced the toxicity of mine waters.

To achieve the first stage of the study, macroinvertebrates were sourced from Nebo Creek, located in the north-west section of the basin. The two main families tested included Leptophlebiidae and Baetidae (Class: Insecta; Order: Ephemeroptera). The tests were conducted using two representative mine water types diluted with an artificial creek water. The commercial testing experiments were conducted according to the testing procedures recommended in the national water quality guidelines. For both testing regimes mine water compositions were based on a survey of mine water from ten mines in the Fitzroy Catchment. To assess the influence of ionic compositions, the salinity tolerances of taxa were compared using two different types of artificial mine waters.

A significant data set was obtained describing the sensitivity of macroinvertebrates to mine waters. Comparison of salinity tolerance of various macroinvertebrate families showed one artificial mine water type being slightly more toxic than the other. Further comparison of artificial mine water tolerance to marine salts, showed mine waters to be more toxic. However, the comparison between mine salts tolerance and marine salts tolerance may not be sufficiently valid as the macroinvertebrates tested with marine salts were not from the same location or region as those tested with mine salts. No previous experiments have been conducted using marine salts with macroinvertebrates collected from the Fitzroy Catchment.  While some past studies have reported that salinity tolerance of the same taxon from separate locations can be different, one recent study showed that tolerance to sulfates were similar in macroinvertebrates from Fitzroy Catchment and south-east Queensland.

The differences in toxicity between the two mine water types (and possibly marine salts) could be attributed to the different ionic compositions. Even though toxicity is influenced by ionic composition and interaction between ions, the measure of salinity would continue to be an effective guideline, as it is easy to measure in the field and easily used to monitor the water conditions in situ. Hence, a salinity based trigger value remains useful.

The 95% ecosystem protection toxicant trigger value calculated from species sensitivity distribution derived from the commercial tests was estimated to be 2.0 mS/cm. For the protection of 99% of the species the salinity has to be reduced by more than 50% to 0.9  mS/cm. These trigger values are consistent with the lower range of previously published toxicological and other effects data on relevant aquatic species. This is with the exception of biomonitoring studies in southern Australia which have demonstrated declining macroinvertebrate taxa richness when salinity increases above 0.5 mS/cm (for macroinvertebrates) or above 0.05 mS/cm (for PET taxa - Plecoptera, Ephemeroptera and Trichoptera). The disparity between indices of short-term toxicity obtained in toxicity tests and indices of taxa richness obtained in field monitoring warrants further research to better understand how increases in salinity affects ecosystems as a whole.. The trigger values determined from toxicological testing should be compared to biomonitoring data as more field data becomes available.

The toxicant trigger values derived from this study can be used to inform the regulation of mine water releases where aquatic ecosystem toxicity from salinity is the primary issue of concern. This could be particularly relevant for management of mixing zones and near-field impacts (such has traditionally been the case with Transitional Environmental Programs (TEP's)) and where cumulative impacts on aquatic ecosystems or other environmental values are not a major concern.

An e-newsletter has also been published for this project, highlighting its significance for the industry.