COLORADO RIVER BENTHIC FOODBASE STUDIES

IN GLEN AND GRAND CANYONS

Lawrence E. Stevens, Joseph Holway, and Courtney McDaniel 

Biology Department, Museum of Northern Arizona

and

Craig Ellsworth

Western Area Power Administration

-
Colorado River Aquatic Foodbase at the Mouth of Tapeats Creek,

Grand Canyon National Park, Arizona

L.E. Stevens, J.H. Holway, and C. Ellsworth
WHY TAPEATS CREEK?

Hofgnecht Transition (1981): 

• Difference in BMI diversity between tributary 

and mainstream (esp. EPT)

• Marked riverward decline in species richness at 

stream confluences in Grand Canyon

Tapeats Creek is a water quality analog to Glen 

and Grand Canyons

Question: 

Can the rich BMI assemblage of Tapeats Creek 

be recreated in the regulated Colorado River 

tailwaters below Glen Canyon Dam?
• 

UCR ..... 
Hess, drift, and experimental basket 

sampling to evaluate seasonality, 

water quality, flow variation, 

sedimentation, and habitat on 

benthic macroinvertebrates (BMI)
June-July transition Upper Outflow Channel (2017)

Low (~8,000 cfs) vs High (~17,000 cfs) 

10:00 a.m. on 29 May 2017 17:00 on 3 June 2017
Mean Velocity and Substrate Among Zones
BMI Composition and Abundance Decreases 

Strongly from Tapeats Creek to the Mainstream

Circle size reflects density/m2

TC 

uoc 

Stc,neflv·O', 

r lidge 78°, 

a Blaclflvn •. 

• Elmidaeo.s•. 

• Other 3~. 

uvc 

LCR 

• Blaclflv10°, 

• Elmidae0.3°, 

• Other 2. 6°, 

StoneflyO~. 

t11dge86', 

• Blaclflv2°, 

a Elm1dae4.5° • 

• Other4 °, 

UCR 

l,1idge69°o 

a B1aci'1"1 f H 0 , 

• Ehrndae 0.9°, 

a Other 3°, 

St onefl·,0° • 

r•.11dge94°o 

• B1adJ"ly2°, 

a Elm1dae1•, 

• Other 4°, 
Spatial Variation of BMI 

Among Zones
Tapeats Creek benthos (TC/UVC/DOC):

Little embeddedness
Colorado River benthos (UCR/LCR):

High embeddedness, swash zone
EXPERIMENTAL

BASKET

SAMPLERRESULTS

• BMI and EPT abundance/L in the LCR was 

essentially equivalent to those in TC

• The proportional number of EPT species/L of 

substrate were slightly higher (17%) in the LCR 

than in TC (14%). 

Mean BMI Species Richness/

L of Rock

N = >6
CONCLUSIONS

• Tapeats Creek: High densities of EPT and other BMI

• Water quality conditions similar to mainstream in Glen & Grand Canyons

• Larval BMI (esp. EPT) strongly decrease in abundance and richness from Tapeats Creek

into the mainstream

• Decrease occurs independent of daily fluctuations

• Adding suitable LCR habitat ds from confluence  EPT colonization ~equal to TC

• Absence of EPT in the mainstream due to limitations in habitat (sedimentation, 

embeddedness, flow direction and velocity), rather than egg desiccation

• Model for lack of mainstream EPT in mainstream: 

= Larval habitat limitation (embeddedness, anoxic substrata)

> Egg desiccation (flow fluctuation)

> Water quality (temp, DO, pH, SC, other geochemistry) 
Thanks to WAPA, Argonne NL, 

especially Kirk Lagory and Mario 

Salerno, and to MNA. We could not 

have accomplished this project 

without the logistical support of the 

commercial recreational community, 

particularly Arizona Raft 

Adventures, Canyoneers Inc., Hatch 

River Runners, OARS Inc., and Tour 

West Inc., and their extraordinary 

staff. Special thanks to Louise Fuchs, 

Sam Goddard, and David Sinclair for 

their assistance, athleticism, and 

enthusiasm for this project. 

Acknowledgments