The Impact of “Man-Made Hydrological Drought” on Plant Species Abundance in the Low-Flow Channel Downstream from the Matawin Dam, Quebec

Ali Assani,Émilie Simard,Édith Gravel,Stéphane Campeau,Ghassen Ibrahim

doi:10.3390/w5030875

Abstract

The interannual variability of streamflow affects the composition and species richness of vegetation in low-flow channels and alluvial plains. Although climate conditions in 2003 and 2004 were nearly identical, large differences in streamflow were observed downstream from the Matawin dam. These differences resulted in numerous days without flow (no water release) during the growing period (May to August) in 2003, leading to man-made hydrological drought. While this drought had no effect on abiotic variables (grain-size distribution and nutrient concentrations in sediments), a significant decrease in the number of terrestrial species was observed in 2004 (year without drought) relative to 2003 (drought year) on three sand bars studied. This decrease is interpreted to result from prolonged submergence of the sites in 2004. Principal component analysis highlighted the effect of individual sites (first principal component) and of the interannual variability of streamflow (second component) on the number of species. The study suggests that, from a flow management standpoint, it is advisable to release enough water downstream from the dam during the growing season to prevent low-flow channel colonization by invasive terrestrial species.

Highlights

Hydrologic variation plays a major role in structuring the biotic diversity within river ecosystems as it controls key habitat conditions within the river channel, the floodplain, and hyporheic zones [1].According to [2] “flow variations regulate taxonomic composition and abundance of aquatic organisms”.many studies deal mainly with lentic natural and man-made settings
These results reveal that there is no statistically significant difference between the two years
A significant difference is observed that is due to the fact that three floods occurred in 2004, while there were none in 2003 (Figure 4)

Summary

Introduction

Hydrologic variation plays a major role in structuring the biotic diversity within river ecosystems as it controls key habitat conditions within the river channel, the floodplain, and hyporheic zones [1].According to [2] “flow variations regulate taxonomic composition and abundance of aquatic organisms”.many studies deal mainly with lentic natural and man-made (fluvial and non-fluvial) settings. Hydrologic variation plays a major role in structuring the biotic diversity within river ecosystems as it controls key habitat conditions within the river channel, the floodplain, and hyporheic zones [1]. In North America, these studies have shown that fluctuations in water levels are the dominant factor controlling the composition and succession of coastal wetland vegetation in the Great Lakes [3,4,5,6]. This conclusion was confirmed for other parts of the world. In New Zealand, for instance, [7]

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