Experimental reductions in sub-daily flow fluctuations increased gross primary productivity for 425 river kilometers downstream
Aquatic primary production is the foundation of many river food webs. Dams change the physical template of rivers, often driving food webs toward greater reliance on aquatic primary production. Nonetheless, the effects of regulated flow regimes on primary production are poorly understood. Load following is a common dam flow management strategy that involves sub-daily changes in water releases proportional to fluctuations in electrical power demand. This flow regime causes an artificial tide, wetting and drying channel margins and altering river depth and water clarity, all processes that are likely to affect primary production. In collaboration with dam operators, we designed an experimental flow regime whose goal was to mitigate negative effects of load following on ecosystem processes. The experimental flow contrasted steady-low flows on weekends with load following flows on weekdays. Here, we quantify the effect of this experimental flow on springtime gross primary production (GPP) 90-to-425 km downstream of Glen Canyon Dam on the Colorado River, AZ, USA. GPP during steady-low flows was 41% higher than during load following flows, mostly owing to non-linear reductions in sediment-driven turbidity. The experimental flow increased weekly GPP even after controlling for variation in weekly mean discharge, demonstrating a negative effect of load following on GPP. We estimate that this environmental flow increased springtime carbon fixation by 0.27 g C m–2 d–1, which is ecologically meaningful considering median C fixation in 356 U.S. rivers of 0.44 g C m–2 d–1 and the fact that native fish populations in this river are food-limited.
Citation Information
| Publication Year | 2022 |
|---|---|
| Title | Experimental reductions in sub-daily flow fluctuations increased gross primary productivity for 425 river kilometers downstream |
| DOI | 10.1093/pnasnexus/pgac094 |
| Authors | Bridget Deemer, Charles Yackulic, Robert O Hall Jr., Michael Dodrill, Theodore Kennedy, Jeffrey Muehlbauer, David Topping, Nicholas Voichick, Mike Yard |
| Publication Type | Article |
| Publication Subtype | Journal Article |
| Series Title | PNAS Nexus |
| Index ID | 70232345 |
| Record Source | USGS Publications Warehouse |
| USGS Organization | Southwest Biological Science Center |
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Gross primary production estimates and associated light, sediment, and water quality data from the Colorado River below Glen Canyon Dam
Bridget R Deemer, Ph.D.
Research Ecologist
Charles B Yackulic, Ph.D.
Research Statistician
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Gross primary production estimates and associated light, sediment, and water quality data from the Colorado River below Glen Canyon Dam
These data were compiled to model the effects of flow regime and bed grain size distributions on rates of gross primary production (GPP) in the Colorado River below Glen Canyon Dam, AZ, USA. The objectives of our study were to quantify daily and weekly scale effects of an experimental flow regime on GPP in the Colorado River. The experimental flow was conducted at Glen Canyon Dam from May-August i - Connect
Bridget R Deemer, Ph.D.
Research EcologistEmailCharles B Yackulic, Ph.D.
Research StatisticianEmailPhone