Effect of Intermittent Flow Regulation on Temperature and Macroinvertebrate Distribution and Abundance in a Michigan River

During times of average and low river flow, Prickett Hydrostation ceases operation at night and on weekends. To determine the effect of this intermittent mode of operation on downstream conditions, data on benthic macroinvertebrates, temperature, current velocity, width and depth were collected for 13 months at 5 sites along 15 km of the Sturgeon River immediately downstream from the hydrostation and at an upstream control site. During station operation, current velocity increased 2.6 times 200 m downstream and 1.2 times 10 km downstream, while depth increased 75 cm and 35 cm, respectively. Depending on stream morphology, width increased 0 to 10 m during operation. Maximum temperatures observed were 22°C upstream, 24.5°C immediately downstream from the station and 23°C 10 km downstream. When the station was shut down, temperature fluctuation patterns were similar above and below the hydrostation. During operation, temperature fluctuations were reduced downstream. At the site 200 m below the hydrostation, invertebrate biomass averaged 6.9 times greater than at the upstream site and 2.5 times greater than 10 km downstream. The average number of taxa collected 200 m below the station was 12% less than at the upstream site and the site 10 km downstream, and included 6 genera of stoneflies, 9 genera of mayflies and 10 genera of caddisflies. Intermittent operation of this hydroelectric station did not have a severe adverse effect on downstream benthos and produced downstream temperature fluctuation patterns more like those upstream than would continuous operation.