Author: Bridget R Deemer, Ph.D. Research Ecologist (USGS)

Designation: 

Description:
Aquatic primary production serves as the foundation of many river food webs.  Dams and associated flow regulation change the physical template of rivers, often driving food webs towards greater reliance on aquatic primary production. Still, the effects of specific dam flow regimes on primary production are not well understood.  Hydropeaking is a common management strategy on many large dams and involves hourly changes in water releases proportional to fluctuations in energy demand. This flow regime leads to an artificial tide, wetting and drying channel margins and altering river depth and water clarity, all processes that are likely to affect primary production.  Here we use a state-space metabolism model to estimate spring (May and June) gross primary production (GPP) in 11 reaches over two years on the Colorado River ranging from 120-400 km below Glen Canyon Dam, AZ.  We capitalized on an experimental flow regime to compare GPP rates during steady-low vs. hydropeaking flows. Across all reaches, GPP during steady-low flow days was 38% (95% CI: 2-86%) higher than on days with hydropeaking flows, mostly owing to reduced turbidity during steady-low flow days.  Over 8 years of measurements at a subset of 4 sites, weeks with two days with steady-low flow increased GPP by 23% (95% CI: 8-39%) relative to weeks with hydropeaking only—an effect that was independent of the mean weekly discharge.  Thus, we show how hourly fluctuations in flow arising from hydropower generation altered sediment-transport dynamics and lowered riverine productivity for hundreds of kilometers downstream.

Category: Scientific Program Abstract > Special Sessions > SS35 Controls and limits on freshwater productivity