Temporal variability of streamflow and plant species abundance on islets as they relate to ENSO events downstream from an inversion-type reservoir

The goal of this study was to analyse the impacts of the sequence of 1 El Nino (2009–2010) and 2 La Nina (2007–2008 and 2010–2011) events on the interannual variability of daily streamflow during the growing season (April to September) and grass species abundance downstream from the Taureau reservoir (4,070 km2) on the Matawin River (Quebec, Canada). This reservoir has inverted the natural annual cycle of streamflow: Maximum flows occur in winter and minimum flows in springtime during snowmelt. Comparison of daily flows over the period from 2006 to 2011 using various statistical tests revealed a significant increase in flows released downstream from the reservoir during the 2 La Nina events, with a particularly large increase in the growing season (April to May) during the 1st La Nina event (2007–2008). In contrast, during the El Nino event (2009–2010), streamflow decreased significantly. As far as the abundance of plant species is concerned, the total number of obligate wetland species increased significantly after the 1st La Nina event and then decreased after the El Nino event, along with the total number of terrestrial species. The study shows that relatively intense El Nino Southern Oscillation events can have significant implications for the management of flows released downstream from reservoirs in Quebec and hence affect plant species abundance on islets.