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

This work was funded by Western Area Power Administration to address foodbase research not funded in the GCDAMP TWP in an effort

to broaden our understanding of possible mechanisms that affect the foodbase condition below Glen Canyon Dam. 
SCOPE OF WORK:

Year 1: Benthic Hyporheic Anoxia (BHA)

Year 2: Hofgnecht Transition in Tapeats Creek

CO

AZ NM

UT

Glen Canyon Dam *

Lees Ferry *

BHA Study Sites
BENTHIC HYPORHEIC ANOXIA (BHA)

LAWRENCE E. STEVENS, COURTNEY MCDANIEL, AND JOSEPH HOLWAY

Objectives:

• Distribution

• Seasonal monitoring 

• Experimentally 

investigate 

development rate and 

contributing factors

• Effects on EPT

• Effects of the 2016 HFE
Distribution: BHA omnipresent 

up to lowest stage

....-... 

E 

~ .._... 

C 

0 

I 

,1-1 

re 

> Q.) 

w 

Dry, nonBHAZone 

Seasonal BHA 

Development Zone 

BHA ??? 

Ephemeral and permanent 

aquatic macrophyte cover 

Seasonal Maximum Stage ..... !!!!!!!!!!!!111 _11111111!!!!!!! --· 

Minimum Annual Stage 

Distance (N 101 102m) 
Geochemistry and Macroinvertebrate Responses

• BHA and non-BHA water column 

geochemistry is ~similar

However

• BHA LD50 - Heptagenia 18.3 hrs

• Non-BHA LD50 - Heptagenia 562 hrs

y = -47.609x + 111.19

R2 = 0.9097

y = -23.644x + 115.04

R2 = 0.7369

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5

% Survival

Log10 Time (hrs)

HA treatment

Control

CR water: BHA water

+ Sediment

CR water,

No Sediment
CONCLUSIONS

• Located above and below Glen Canyon Dam

• Limited to above Paria River w-expansion downstream unlikely 

• Contributors: 

• TH2O 

• Q stability

• Low DO

• Chara

• Minor impacts to water quality (water column)

• Detrimental to sensitive macroinvertebrates (EPT) 

• Limits aquatic macroinvertebrate assemblage 

• Conceptual Model:

Predam Qflux+ Sedflux --> Dam -->

Daily Qflux& High PAR --> Cladophora --> 1996 ROD -->

MLFF Flows --> Chara dominance --> BHA

BHA Conceptual Model
Possible mitigation options to 

reduce the impact of BHA on EPT

• Increase mainstream 

DO concentration

• Decrease mainstream 

temperature 

• Increase scour or 

drying of substrates 

(flow or mechanical)

• Increase mainstream 

turbidity (limit Chara) 

• Other?

Report and publication: 

Spring 2018
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): 

• Discrepancy between tributary and mainstream 

benthic macroinvertebrate (BMI) biodiversity 

(esp. EPT)

• Marked riverward decline in species richness at 

stream confluences in Grand Canyon

Tapeats Creek is a water quality analog to Glen 

& Grand Canyons

Question: 

Can the rich BMI assemblage of Tapeats Creek be recreated in the regulated Colorado River 

tailwaters below Glen Canyon Dam?
• 

UCR ~ 

0 25 50Meters 
Hess, drift, and substrate 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
BMI Composition and Abundance Decreases 

Strongly from Tapeats Creek to the Mainstream

Circle size reflects density/m2

TC 

uoc 

• Caddi.sfly5°'o 

St onHly0.2% 

r.1iilge37° . 

• BlackflV40% 

• El rn I clae 0.7~. 

• El1nidae0.8.% 

• Dther3l?, 

uvc 

LCR 

• BI aclJ lv 10~ 

• ElmidaeJJ . .1% 

• Other 2.~~-. 

Stonefl 0% 

filiclge86°; 

• B1ackflv2% 

• Elm1 dae4.5~. 

• Oth.er4 "'• 

UCR 

• B1ackfly140,o 

• Elrnidae 0.9~. 

• Other 3% 

• Mcl\lflyo•;, 

• Caddisfly0% 

Stoneff'{0% 

Midll/:94% 

• Blacl1'1yc2% 

• Elm1dc1e1"., 

• Oth.:r4i. 
Spatial Variation of BMI 

Among Zones
Mean Velocity and Substrate Among Zones
Tapeats Creek benthos (TC/UVC/DOC):

Little embeddedness
Colorado River benthos (UCR/LCR):

High embeddedness, swash zone
BASKET SAMPLER RESULTS

• BMI and EPT abundance and diversity

• Mainstem = Tapeats Creek

• Quagga colonization
CONCLUSIONS

• High densities and diversity of EPT and other BMI

• Hofgnecht Transition observed

• Transition occurs independent of daily fluctuations

• Water quality similar to mainstem

• Providing suitable habitat in the mainstem allows for colonization equal to Tapeats 

Creek

• Absence of EPT in the mainstem appears to be due to limitations in larval habitat 

(sedimentation, embeddedness, flow direction and velocity)

• Model for lack of EPT in the mainstem : 

Larval habitat limitation (embeddedness, anoxic substrata)

> Egg desiccation (flow fluctuation)

> Water quality (temp, DO, pH, cond, 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