Thermal artesian springs are characterised as having a minimum discharge water temperature of 36.70C. However, the often high temperatures measured at the ‘vent’ decrease by convection as water flows outward. This natural gradient of water temperature from a thermal spring vent as it flows out into a spring-fed stream provides a unique opportunity to investigate the influence that temperature can have on aquatic biota. In such rare situations most other drivers of ecosystem patterns and processes (e.g. flow regime, riparian cover, substrate composition etc.) remain constant while temperature alone varies. Therefore, this represents a natural analogue for the effects of temperature increase from global warming and permits predictions to be made of the effects of this on stream ecosystems.
This study investigated the relationship between the aquatic macroinvertebrate communities and a gradient of water temperature associated with outflows from Talaroo spring complex in North Queensland. Over 170 m of stream length the water temperatures ranged from 47.90C near the vents to 26.00C downstream closer to the confluence with the Einsleigh River. Sixteen macroinvertebrate samples were collected along the stream length. A total of 41 different taxa of macroinvertebrates were recorded. Taxa richness ranged between 1 and 21 at sampling locations along the gradient, with a generally progressive loss of taxa as temperature increased. The normal tolerable temperature limits for multicellular organisms is approximately 450C so it was surprising to collect specimens of ostracods, hemipterans and dragonflies at locations with higher water temperatures. Analyses of macroinvertebrate assemblage data showed a significant relationship with water temperature. The changes and general loss of taxa with increasing temperature are likely to be associated with their thermal tolerance limits
The results suggest increases in water temperature from climate change may cause a measurable reduction in taxonomic richness.