To deal with hourly and seasonal changes in energy demand some hydro-electric dams change the flow of water through the dam. This is called hydro-peaking, and high energy demand results in peaks in river flow during the day. At night however, when everyone is asleep, discharge from the dam is reduced. Along with flow, water level changes, and habitats that are underwater at sunset may dry out overnight.
A recent study by Kennedy et al. (2016) decided to find out what that means for aquatic insects that lay their eggs in the rivers affected by hydro-peaking. They recruited rafting groups to set up light-traps at sunset to catch egg-laying adults. The use of “citizen scientists” was necessary to obtain the amount of data they needed as the river in question, the Colorado River in the Grand Canyon, is very difficult to access and so very expensive to sample by conventional means.
Kennedy et al. (2016) discovered that the effect of hydropeaking on aquatic insects depended on their egg-laying strategies (see figure). Aquatic insects that tend to lay their eggs near-shore like caddisflies, were essentially absent from the river except where traps were set up near tributaries. These sections of the Colorado River have become “sinks” for river-edge egg-layers, their mere existence is maintained by individuals moving from “source” populations in tributaries. Aquatic insect species that lay their eggs in the open water, like black flies, were not affected by hydro-peaking. Aquatic insects that use both river-edge and open water laying strategies, like midges, had high abundances where the timing of their egg laying matched the lowest daily flow. When the timing of low-flow and egg-laying match, the eggs are protected from drying out because the water doesn’t go any lower after the eggs are laid.
In Ontario, we have a few hydro-electric dams that practice hydro-peaking including two dams on rivers flowing into Lake Superior, the Magpie and the Michipicoten. Hydropeaking on these dams causes large changes in the amount of water in the rivers and the amount of habitat that is exposed at different times of the day (see figure, Bond & Jones 2015). Both of these rivers support recreational fisheries for resident and migratory trout. However, with the possible effects the changes in water level may have on aquatic insects, we may see cascading effects on the trout populations.
This study points out just how valuable data collection by every-day people can be. At a much broader scale, the Map-the-Hatch survey hopes to collect similar information to determine how regional level differences in the environment can affect aquatic insects and will only be effective if there are many entries. So keep that in mind the next time you are out on the river and see a hatch, take a picture and take part in citizen science.
Amanda Caskenette, PhD
Kennedy, T.A., et al. 2016. Flow management for hydropower extirpates aquatic insects, undermining river food webs. BioScience. Advance publication.
2015), Spatial Distribution of Fishes in Hydropeaking Tributaries of Lake Superior, River Res. Applic., 31, pages 120–133, doi: 10.1002/rra.2720 Full Textand (