Author:Dean Olsen, Louis A Tremblay, Joanne Clapcott, Robin Holmes
Source:Auckland Council Research, Investigations and Monitoring Unit, RIMU
Water temperature affects all aspects of freshwater ecosystems, from primary producers through to fishes. Altered water temperature regimes can alter the physical habitat conditions (e.g. algal blooms) and cause a wide variety of behavioural and physiological responses with the most dramatic being death (Carveth et al. 2007; De Vries et al. 2008). Consequently, maintaining suitable thermal conditions is critical to achieve instream management objectives, such as the conservation of freshwater species. Management of water temperatures for the protection of aquatic species should consider more than just the critical thermal limits and should be based on the thermal requirements of all life stages of the species in question.
This report reviews the existing water temperature criteria for aquatic life, with emphasis on setting thresholds for effects. It includes the following:
1. A review and critique of field and laboratory methods used for setting temperature criteria for freshwater biota, highlighting information gaps necessary to determine environmental temperature thresholds for native freshwater biota.
2. Comments on the application of these criteria to native freshwater biota, including physiological effects, in relation to both point source (e.g., thermal inputs) and passive (e.g., loss of shade) thermal effects. We consider the relevance of criteria to:
i. effects over long and short time scales (including temperature fluctuations),
ii. effects of temperature in combination with other environmental stressors (i.e., cumulative effects), and
iii. effects associated with modified biotic (e.g., competition/predation with introduced species) and food-web (e.g., heat stress rendering native species more susceptible to predation) interactions.
3. Based on the above, we recommend appropriate environmental temperature criteria for aquatic life in streams and rivers, and/or describe the studies required to determine these.
Auckland Council technical report TR2012/036