Impact of secondary salinisation on freshwater ecosystems: effects of contrasting, experimental, short-term releases of saline wastewater on macroinvertebrates in a lowland stream

Abstract

In Australia, secondary salinisation of land and water resources is a serious environmental problem. We conducted two field experiments to examine the effects on macroinvertebrates of increased salt concentration (approximately 1000 and 2000 mg L–1 total dissolved solids (TDS)) and mode of salt water release (continuous press release approximately 1500 mg L–1 and four, separate pulses of approximately 3400 mg L–1 TDS). The abundance of the gastropod Ferrissia tasmanica, the mayfly Baetis sp. 5 and scraper and predator functional feeding groups were significantly reduced at 1500 mg L–1, with the effect exacerbated in pulse release channels. Moreover, the pooled abundance of Oligochaeta, Copepoda and Acarina was significantly reduced at 2000 mg L–1 and the number of drifting animals in the pulse treatment channels significantly increased following commencement of salt water release during daylight hours. In contrast, the abundance of 49 other macroinvertebrate taxa, collector–gatherer functional group and species diversity were unaffected by salinity or release schedule. We conclude that much of the existing macroinvertebrate fauna appears to be halotolerant. However, the abundance of halosensitive species will be reduced at 1500 mg L–1. Delivering short pulses of high salt concentration is more detrimental than delivering the same salt load at a low concentration over a longer period of time.