Importance of water temperature
River temperatures are rising globally and are expected to continue to rise under climate change. This has important implications for aquatic life because water temperature controls the metabolism of animals and the photosynthesis of plants. Temperature is important in controlling the activity, behaviour, growth and development of animals, particularly cold-blooded organisms such as fish and invertebrates. At extreme levels, temperature stresses organisms and can eventually prove fatal. Temperature is also linked to water chemistry; for example, high water temperatures lead to lower dissolved oxygen levels that can also impact aquatic life.

Mayfly phenology with Dr. Nick Everall and Dr. Cyril Bennett
Dr. Nick Everall has been routinely monitoring populations of the mayfly Ephemera danica in the River Dove catchment since 2007. E. danica hatch underwater and live for two years as an aquatic larvae, after which they emerge in a terrestrial form. We assessed the variability in mayfly emergence between Beresford Dale and Dovedale over the period 2007 to 2013.
 
There was a strong association between the emergence cycle of E. danica and water temperature at each site. Following warm summers in Beresford Dale, E. danica emerged after only one year in its aquatic form in comparison to two years after 'average' summer temperatures. E. danica began reverting back to this bi-annual cycle after the particularly cool/wet year of 2012. In Dovedale, which has a more consistent temperature seasonally and inter-annually due to substantial groundwater inputs, E. danica maintained a two-year cycle throughout the monitoring period despite the phenology changes observed 8 km upstream (for more information see Everall et al. 2014).
 
Bi-annual mayfly populations are less vulnerable to adverse weather conditions because there is an over-wintering population, whereas cohorts with a one-year cycle are more vulnerable as the whole population will be in terrestrial form at the same time. This study suggests that habitats near cool groundwater may provide important refugia for populations of insects, potentially delaying permanent shifts in phenology under climate change. 
 
 
Mayfly
Top: an adult E.danica
Bottom: a larval E.danica used courtesy of Cyril Bennett