Effect of spatial variation on salinity tolerance of macroinvertebrates in Eastern Australia and implications for ecosystem protection trigger values
Introduction
Salinisation is one of Australia's most serious environmental issues. Although dissolved salts are natural components of freshwater and some inland aquatic systems have naturally high salinity levels, it is now well recognised that impacts from excessive anthropogenic related increases in concentrations of dissolved salts can have profound and measurable effects on freshwater aquatic ecosystems (Hart et al., 1991, Williams et al., 1991, James et al., 2003, Kefford et al., 2003, Marshall and Bailey, 2004, Dunlop et al., 2005). In Australia, an estimated 5.6 million hectares of land is at high risk from induced dryland salinity and by the year 2050, estimates indicate that 17 million hectares of land may be salt affected (National Land and Water Resources Audit, 2000). In areas already affected, salinity has resulted in social, economic and environmental impacts (Land and Water Australia, 2002). It is therefore clear that there is an urgent need to manage salinity impacts in Australia.
Establishment of trigger values (guidelines) for salinity can provide a basis for its management but there are currently no widely acceptable, biologically based guidelines applicable at local or regional scales. Probabilistic risk assessment techniques can be used to determine salinity concentrations or trigger values protective of particular taxa or a proportion of taxa (Hart et al., 2003). This can be achieved by modelling a distribution of laboratory derived salinity sensitivity values (species sensitivity distribution (SSD) or taxa sensitivity distributions (TSD)) from which a percentile, or ecosystem protection value (trigger value) can be calculated to ensure the protection of a pre-defined proportion of taxa. Salinity sensitivity data can be derived from either concentration–response laboratory experiments (resulting in ≤96-h LC50 values) using a standard composition of dissolved salts and/or the maximum salinity at which taxa have been observed to occur in the field (resulting in Fmax values). Laboratory experiments provide a direct causal link between a concentration of exposure and a measured effect (Goetsch and Palmer, 1997, Berezina, 2003, Kefford et al., 2003, Kefford et al., 2004) and are preferred for use in the determination of water quality guidelines (ANZECC/ARMCANZ, 2000). Despite a clear need to determine biological effects based ecosystem protection values, there is limited salinity tolerance information available from freshwater organisms in Australia, and in particular there is a lack of such data in Northern Australia as most studies have been conducted either outside of Australia or in Southeastern Australia (Kefford et al., 2003, Kefford et al., 2005a, Kefford et al., 2006a). It is also not known whether the existing salinity tolerance information provides adequate representation of the variation in salinity tolerance in Eastern Australia. This study evaluates the sensitivity of a broad range of macroinvertebrates in Northeast Australia to a standard synthetic marine salt and compares these tolerance values with those observed across Eastern mainland Australia.
Section snippets
Methods
Macroinvertebrates are an important component of freshwater ecosystems forming vital links in aquatic food webs. Macroinvertebrates are known to respond at the community level to salinity impacts (Horrigan et al., 2005) and some are known to be salinity sensitive (Kefford et al., 2003) and are thus useful indicators of salinity impacts. For these reasons macroinvertebrates are an ideal taxonomic group to assess broad geographical trends in salinity sensitivity. To assess macroinvertebrate
Salinity tolerance of macroinvertebrates in Northeast Australia
Sufficient data was available to determine 102 estimates of 72-h LC50 values. The acute salinity tolerance of macroinvertebrates was highly variable between those tested ranging from 6.9 to >55 mS cm−1. Modelled sensitivity values with their respective lower 5th and upper 95th percentiles are shown in Table 2 and non-modelled, assigned 72-h LC50 values are shown in Table 3. The number of individuals tested is given as an indication of the confidence in the estimate. The mean of all recorded 72-h
Conclusion
Freshwater macroinvertebrates in Northeast Australia were found to have variable responses to salinity with 72-h LC50 values ranging between 6.9 and >55 mS cm−1. This range in tolerance is consistent with previous studies in Southeast Australia by Kefford et al., 2003, Kefford et al., 2006a. The large variation in the salinity tolerance observed in freshwater crustaceans and molluscs may be attributable to their classification as either freshwater or marine. The distinction between freshwater
Acknowledgements
This study was funded under the National Action Plan for Salinity and Water Quality State level Investment Program. The program has input from the Queensland Environmental Protection Agency and the Department of Natural Resources, Mines and Water. BJK appreciated the supported by Land and Water Australia and the Murray Darling Basin Commission under the National Rivers Contaminants Program (LWA project No. RMI 12) and from the Queensland Department of Natural Resources, and Water. The authors
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