TY - JOUR
T1 - Experimental reductions in subdaily flow fluctuations increased gross primary productivity for 425 river kilometers downstream
AU - Deemer, Bridget R.
AU - Yackulic, Charles B.
AU - Hall, Robert O.
AU - Dodrill, Michael J.
AU - Kennedy, Theodore A.
AU - Muehlbauer, Jeffrey D.
AU - Topping, David J.
AU - Voichick, Nicholas
AU - Yard, Michael D.
N1 - Publisher Copyright:
© The Author(s) 2022. Published by Oxford University Press on behalf of the National Academy of Sciences.
PY - 2022/7/1
Y1 - 2022/7/1
N2 - 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 subdaily 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 nonlinear 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 US rivers of 0.44 g C m-2 d-1 and the fact that native fish populations in this river are food-limited.
AB - 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 subdaily 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 nonlinear 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 US rivers of 0.44 g C m-2 d-1 and the fact that native fish populations in this river are food-limited.
KW - dam
KW - eco-flows
KW - hydropeaking
KW - hydropower
KW - load following
KW - primary production
UR - http://www.scopus.com/inward/record.url?scp=85178061393&partnerID=8YFLogxK
U2 - 10.1093/pnasnexus/pgac094
DO - 10.1093/pnasnexus/pgac094
M3 - Article
AN - SCOPUS:85178061393
VL - 1
JO - PNAS Nexus
JF - PNAS Nexus
IS - 3
M1 - pgac094
ER -