Improving the Lake Powell CEQUAL-W2 Water Quality Model 

Bryce A. Mihalevich1,2, Bridget R. Deemer2, Charles B. Yackulic2 

1U.S. Bureau of Reclamation, Interior Region 7 - Upper Colorado Basin, Salt Lake City, Utah 

2U.S. Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring & Research Center, 

Flagstaff, Arizona 

“This information is preliminary and is subject to revision. It is being provided to meet the need for timely best science. The 

information is provided on the condition that neither the U.S. Geological Survey nor the U.S. Government shall be held liable 

for any damages resulting from the authorized or unauthorized use of the information." 

U.S. Department of the Interior 

U.S. Geological Survey bmihalevich@usbr.gov 
 

Recent Water Quality Trends 

Currently 3565 ft 

Glen Canyon Dam

"Preliminary 

InformationSubject to 

Revision. Not 

for Citation or 

Distribution." 
 

 

Wahweap Temperature Variability 

Current Depth 

Summer 2023 

Higher SD = More 

difficult to predict 

"Preliminary Information-Subject to Revision. Not for Citation or Distribution." 
 

 

 

Updated Model Evaporation Rates 

• Estimated evap. coefficients based on USBR study 

• Impacts surface heating and mixing 

• Represents seasonal trends well 

• Overshoots in summer 

(Padre Bay) 

"Preliminary Information-Subject to Revision. Not for Citation or Distribution." 
 

 

How are model predictions looking? 

• Improvements are being seen 

• But still some work to be done 

"Preliminary Information-Subject to Revision. Not for Citation or Distribution." 
 

 

 

 

Dissolved Oxygen Dynamics in

Lake Powell and Glen Canyon 

Bridget Deemer, Tom Sabol, Caitlin Andrews, Robin Reibold, Charles Yackulic 

U.S. Geological Survey, Southwest Biological Science Center 

Glen Canyon Dam Adaptive Management Program 

February 28, 2024 

Photo Credit. David Herasimtschuk, 

©Freshwaters Illustrated 

Escalante arm of Lake Powell 

Campsite for Lake Powell quarterly trip- March 9, 2022 

This information is preliminary and is subject to revision. It is being provided to meet the need for timely best science. 

The information is provided on the condition that neither the U.S. Geological Survey nor the U.S. Government shall be 

held liable for any damages resulting from the authorized or unauthorized use of the information. 
-

7 

Preliminary 

Information 

Subject to 

Revision. 

Not for 

Citation or 

Distribution 

2009-2021 

2023 

2022 

Danger Zone 

Dissolved Oxygen 

Temperature 

Turbidity 
How Low is Low? 

The low oxygen in dam releases last year were unprecedented in both 

magnitude and duration 

8 

- 

 

 

2005 

2023 

The colored lines and shaded regions depict daily trends from 2009 to 2021 as the 10th, 50th, and 90th quantiles. 

The thick black line represents 2023 and the dashed line represents 2022. Data collected after 6/01/2023 is provisional. 

Preliminary Information Subject to Revision. Not for Citation or Distribution 
 

 

 

 

 

What Can The 

Historical Dataset 

Tell Us? 

Lower average late summer/fall 

dissolved oxygen in the metalimnion 

when: 

1. Reservoir spring elevation is low 

2. Spring inflow is large 

3. Age/elevation interaction 

Lake-wide low dissolved oxygen events 

will be increasingly common when lake 

elevation is below ~3620 ft. 

3526ft 

3628ft 

3530ft 

3572ft 

3602ft 

3704ft 

Preliminary Information- Subject to Revision. 

Not for Citation or Distribution 

9 
- 

 

Side Channel Habitats vs. 

Main Channel 

>1 mg/L 

departures in 

DO between 

main channel 

and 

macrophyte 

beds 

Chronic Invertebrate LC-50 

Coldwater Fishes EC-10 

Preliminary Information Subject to Revision. 

Not for Citation or Distribution 

10 
 

 

 

 

 

 

 

 

 

Project F update: 

Leaf decomposition, bat monitoring, aquatic insects 

Ted Kennedy1, Eric Scholl1, Anya Metcalfe1, Jeff Muehlbauer2, 

Charles Yackulic1, Morgan Ford1, Cheyenne Szydlo1 Carol Fritzinger1 

*This information is preliminary and 

is subject to revision. It is being 

provided to meet the need for timely 

best science. The information is 

provided on the condition that 

neither the U.S. Geological Survey 

nor the U.S. Government shall be 

held liable for any damages 

resulting from the authorized or 

unauthorized use of the information. 

1-US Geological Survey, 

Southwest Biological Science 

Center, Grand Canyon 

Monitoring and Research 

Center, Flagstaff, AZ 

2-US Geological Survey, 

Alaska Cooperative Fish and 

Wildlife Research Unit, 

Fairbanks, AK U.S. Department of the Interior 

U.S. Geological Survey 
-

 

 

 

Decomposition Study Background: 

• Decomposition of organic matter 

represents a fundamental ecosystem 

process in rivers 

• Changes in decomposition alter how 

energy and nutrients move through 

aquatic and riparian food webs 

Food webs of the Colorado 

River circa 2006 2009. 

From Kennedy and others, 

2014 USGS Fact Sheet 
 

 

 

 

Decomposition Study Background:

Drivers of decomposition are rapidly 

changing in the Colorado River 

From Scholl and others, in press, Ecosphere 

Biological invasion Biocontrol Water nutrients Temperature 

Objective: Compare decomposition of cottonwood, willow, and saltcedar to a 

1998 experiment (Pomeroy et al. 2000) that was conducted in context of: 

-cooler temperatures 

-lower mudsnail density 

-saltcedar litter not affect by biocontrol beetles 

-higher phosphorus concentrations 
• Leaf packs put in river at Lees Ferry

and collected on days: 1, 2, 7, 24, 46,

84, 142 (April 4th – Aug 24th 2022)

Saltcedar 

Cottonwood Willow 

 

 

 

Water 

temperature 

Leaf 

chemistry

(% nitrogen) 

Water 

phosphorus 

1998: cool 

2022: warm 

Mudsnails 

1998: low 

2022: high 

1998: low 

2022: high 

1998: high 

2022: low 

67% decrease 

Prediction: Saltcedar decomposition 

will show strongest response owing 

to warming and higher leaf nutrient 

content associated with herbivory 
 

Results: 

Saltcedar decomposition rate more than doubled. 

From Scholl and others, in press, Ecosphere 

No change in other leaf types (decrease in P offset ↑temp).

1998 

2022 

k = decay rate 
 

 

2023 Light Traps 

2023 Community Scientists 

Collector #samples Collector #samples 

GCY 60 WilliamsK 23 

RatayR 51 KennedyT 17 

FadeleyB 47 MansfieldL 16 

LouvierM 43 AllenK 14 

RoussisO 43 MetcalfeA 14 

LokeyE 42 SellerP 14 

BurchR 38 SiemionG 14 

KristjonsdottirS 37 SzydloC 9 

LowryM 35 TownsendJ 8 

SeabaughC 35 CatlettJ 6 

TankersleyG 35 PettyJ 6 

MagnificoS 32 PalmquistE 4 

GantertJ 27 StalveyA 3 

Thank you guides, GCY, and others!! 

Freshwaters Illustrated 

Kennedy and others 2016, Bioscience In a nutshell 

Community science monitoring started in 2012 

~700 samples of adult aquatic insects per year 

Robust dataset for quantifying insect population response to Bug Flows 
2023 Light Traps - New species of caddisfly detected 

Smicridea fasciatella 

Photo Credit: Kim Beubauer 2022 

• 12 individuals detected in 3 light trap samples in August 

between river miles 216 and 222 

• Considered to be excellent prey for fish, birds, and bats 

• 3x larger than most common Grand Canyon 

caddisflies 

• Common and not known to be a nuisance species to 

boaters in Cataract Canyon 

• Species of management concern in lower Colorado 

River Basin 

• considered a nuisance by residents (large hatches) 

• do not bite or sting 
 

 

 

 

Result 

193/hr w/o Bug Flows 223 per hr w/ 

Bug Flows 

 Caveat~46% of samples 

processed (312 out of 680) 

 2023 

 58% decrease in midges 

 75% decrease in caddisflies 

 Statistics 

Very strong model support for positive 

Bug Flow effect 

 Midges, deltaAIC: 27.6 

 Caddisflies: deltAIC: 36.2 

 Note: deltaAIC >8 considered strong support 

26/hr w/o Bug Flows 91/hr w/ Bug Flows 

Provisional data, subject to change. 

Estimates of annual average from mixed effects model 18 
 

 

Conclusions 

Drivers of decomposition are changing 

 

quality) 

 But low phosphorus likely offset warm temperatures for other 

leaf species 

Decomposition of saltcedar was 2x faster than in 1998 (↑litter 

Preliminary result: strong model support for Bug Flow

effect on aquatic insects 

From Scholl and others, In Press, Ecosphere 

Provisional data, subject to change.