Modelling the possible impacts of climate change on the thermal regime and macroinvertebrate species of a regulated prairie river

The thermal regime is a key consideration for instream flow management as the ecological integrity of river ecosystems relies on the natural dynamics of temperature range and spatiotemporal characteristics. Climate change can alter thermal regimes and influence water temperatures. This study aims to investigate probable impacts of climate change (predicted changes in meteorological forcing variables) on the thermal regime and macroinvertebrate species of a regulated prairie river. A 2D laterally averaged CE-QUAL-W2 hydrodynamic thermal lake model for Lake Diefenbaker was coupled with a Water Quality Analysis Simulation Program Version 7 (WASP7) river temperature model and applied to the lower South Saskatchewan River in Canada. Three decades, 2001-2010, 2041-2050, and 2081-2090, were modelled using atmospheric forcing data (relative humidity, dew point, daily mean near-surface wind velocity, near-surface air temperature, total cloud fraction, and surface air pressure) from the Canadian Centre for Climate Modelling and Analysis experiments (CORDEX). To estimate future climate change impacts on the resident macroinvertebrate species, the known temperature tolerances of various macroinvertebrate species were compared with modelled temperature regimes. The WASP model calibration (2011-2012) and validation (2013) outputs produced an acceptable visual fit, whereby predicted values overlap sampled values, to observed water temperatures at Clarkboro and Muskoday sample sites. Major effects on the thermal regime were simulated due to the increase in water temperature induced by Gardiner Dam, which in turn indicated a possible effect on macroinvertebrate species. Gardiner Dam was also shown to be highly sensitive to inflow variations as well as to temperature changes. These findings contribute to the understanding of how future climate-induced river water temperature changes may influence macroinvertebrate species in temperate river systems. This valuable information can inform further laboratory studies of temperature impacts on current macroinvertebrate communities and the development of future mitigation strategies.