Thermal pollution in Australian freshwater ecosystems: ecological consequences for fish larvae and juveniles
- Publication Type:
- Thesis
- Issue Date:
- 2020
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Large dams provide reliable water supply for critical human needs including drinking water, agriculture and electricity. Although they provide essential services, large dams can have numerous ecosystem impacts. For example, large dams can substantially alter the downstream thermal regime of rivers resulting in thermal pollution. When scaled to large river basins, such as the Murray-Daring Basin where up to 2700 km of river length is affected, large sections do not have adequate water quality to support physiological and biological processes in fish. The overall objectives of this thesis were to 1) quantify the extent of thermal pollution in an Australian freshwater river and explore practical solutions to mitigate this, 2) assess consequences of chronic exposure to reduced water temperatures in Australian freshwater fish larvae and 3) assess consequences of acute thermal pollution (cold shock) in Australian freshwater fish larvae.
Water temperature downstream of a large dam in Australia’s Murray-Darling Basin was affected by different release mechanisms in use, and acute thermal pollution occurred when releases were interchanged between different mechanisms. The magnitude of chronic (cold) thermal pollution was strongly linked to dam storage volume, which could alter water temperatures downstream within a range of 10°C. Monitoring data informed thermal exposures used in experiments to assess how chronic and acute thermal pollution may affect native Australian fish larvae. Silver perch (Bidyanus bidyanus), trout cod (Maccullochella macquariensis) and golden perch (Maquaria ambigua) larvae experienced reduced somatic and otolith growth when exposed to chronic suboptimal temperatures (ranging from 13°C to 24°C) for 30 days. When exposed to acute thermal pollution, Murray cod (Maccullochella peelii), silver perch and golden perch larvae experienced mortality and reduced swimming ability, their sensitivity was related to both the magnitude of cold shock and their age.
This study demonstrates the utility of engineering solutions in mitigating thermal pollution. If thermal pollution is not addressed in Australian freshwater ecosystems, a range of lethal and sub-lethal impacts may be experienced by native fish species at a critical life stage. Understanding how fish are impacted by thermal pollution that originates from dam and industrial operations will aid in the management of freshwater ecosystems for the benefit of their populations. The current study identifies critical life-stages and sub-lethal traits that need to be considered in the remediation of freshwater ecosystems. Management techniques are outlined that could be adopted to aid fish conservation, threatened species recovery and environmental remediation of aquatic ecosystems.
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