U.S. Department of the Interior

U.S. Geological Survey

Lake Powell as a Regulator of 

Downstream Water Quality and 

Ecosystem Productivity 

Glen Canyon Dam Adaptive Management Program 

Annual Reporting Meeting, January 13, 2020

Bridget R Deemer

In collaboration with: Charles Yackulic, Ted Stets, Bob Hall, 

Ted Kennedy, Jeff Muehlbauer, Nick Voichick and others
Project Information, slide 1

 Project E: Nutrients and Temperature as Ecosystem 

Drivers: Understanding Patterns, Establishing Links and 

Developing Predictive Tools for an Uncertain Future

 Project Element E.2: Linking Temperature and Nutrients 

to Metabolism and Higher Trophic Levels

 Project Objective: Determine drivers of ecosystem 

metabolism (including primary production and 

respiration) throughout the Cre

 LTEMP Resource Goals Addressed or Studied: Natural 

Processes

 Restore, to the extent practicable, ecological patterns and 

processes within their range of natural variability, including the 

natural abundance, diversity, and genetic and ecological integrity of 

the plant and animal species native to those ecosystems.
Project Information, slide 2

 Project Title: Lake Powell Water Quality Monitoring Program

 Project Elements: 

 Revisions to Existing Program

 Characterizing Nutrient Dynamics During Experimental Flows

 Historical Data Analysis

 Project Objectives: 

 Determination of water-quality status and trends in Lake Powell and GCD releases

 Documentation of the effects of the structure and operation of GCD on the quality of water in 

Lake Powell and GCD releases

 Integration with GCDAMP information needs and downstream monitoring programs

 Documentation of the density structure and associated nutrient distribution in the water 

column at the GCD forebay and other locations in the reservoir to determine the quality of 

water available for release from GCD

 Funding Amount and Source: $196,904.91 for CY 2018, 5 Year Interagency 

Agreement R18PG00108

 Cooperators: Bureau of Reclamation, National Park Service
Project Information, slide 3

 Water Quality Knowledge Assessment Completed 

January 7, 2020

 Team: Bridget Deemer, Peggy Roefer, Todd Tietjen, 

Robert Radtke, Charles Yackulic

 Status and Trends:

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow temperature and dissolved oxygen in support 

of Rainbow Trout

 GOOD CONDITION, INCREASING TREND: GCD 

outflow temperature in support of Humpback Chub

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow phosphorus concentrations in support of 

ecosystem productivity
Project Information, slide 4

 Water Quality Knowledge Assessment Completed 

January 7, 2020

 Team: Bridget Deemer, Peggy Roefer, Todd Tietjen, 

Robert Radtke, Charles Yackulic

 Status and Trends:

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow temperature and dissolved oxygen in support 

of Rainbow Trout

 GOOD CONDITION, INCREASING TREND: GCD 

outflow temperature in support of Humpback Chub

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow phosphorus concentrations in support of 

ecosystem productivity
Talk Outline, slide 1

 Gross Primary Production and the Food Web

 Drivers of Gross Primary Production

 Soluble Reactive Phosphorus as a Control

 Flow as a Control
Gross Primary Production (GPP) and 

the Food Web

 Total amount of oxygen produced during 

photosynthesis in the river

 Some of this carbon is available to higher 

trophic levels, some of it is consumed by 

bacterial and autotrophic respiration
Oxygen Data for Modeling GPP

 Lees Ferry (two station)

 30 Mile (two station)

 60 Mile

 Bright Angel

 National Canyon

 Diamond Creek

Appling & Yackulic et al. 2018 JGR Biogeosciences
Gross Primary Production and the 

Food Web

 GPP has been linked to aquatic 

insect densities– suggesting some 

Unpublished data, subject to bottom-up control on the foodbase

change, do not cite.
Talk Outline

 Gross Primary Production and the Food Web

 Drivers of Gross Primary Production

 Soluble Reactive Phosphorus as a Control

 Flow as a Control
Is Primary Production in the 

Colorado River below Glen Canyon 

Dam Nutrient Limited?
Semi-mechanistic Modeling

 Light (PAR)

 Clouds

 Turbidity

 Temperature

 Discharge 

(Hydropeaking)

 Soluble Reactive 

Phosphorus 

(SRP)

Approach based on Hall et al. 2015 L&O
Light, SRP, and Flow 

Unpublished data, subject to 

change, do not cite.
SRP Control GPP

Unpublished data, subject to 

change, do not cite.
Talk Outline, Slide 2

 Gross Primary Production and the Food Web

 Drivers of Gross Primary Production

 Soluble Reactive Phosphorus as a Control

 Flow as a Control
Soluble Reactive Phosphorus as a 

Control

Unpublished data, subject to 

change, do not cite.
TP Loading is a Strong Predictor of P 

availability at Dam

Total 

phosphorus 

loading 

explains ~55% 

of the variance 

in penstock 

SRP 

availability

Unpublished data, subject to 

change, do not cite.
Biological Processes in the Reservoir

Deemer et al. 2020 L&O
Significant Calcite Precipitation in 

Lake Powell

 Lake Powell reduces salt transport to the 

lower basin by an average of ~2000 metric 

tons of salt per day

 These salts can bind phosphate 
SRP is 

difficult to 

measure

Unpublished data, subject to 

change, do not cite.
Talk Outline, Slide 3

 Gross Primary Production and the Food Web

 Drivers of Gross Primary Production

 Soluble Reactive Phosphorus as a Control

 Flow as a Control
Less Hydropeaking= More GPP

Unpublished data, subject to 

change, do not cite.
Weekday and Weekend GPP In 

Bugflow and Non-Bugflow Years

Unpublished data, subject to 

change, do not cite.
Low Water= Higher GPP at 60 Mile

Unpublished data, subject to 

change, do not cite.
Many Factors Influencing GPP- Lack of Synchrony 

Through the River
Project Information, Slide 4

 Water Quality Knowledge Assessment Completed 

January 7, 2020

 Team: Bridget Deemer, Peggy Roefer, Todd Tietjen, 

Robert Radtke, Charles Yackulic

 Status and Trends:

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow temperature and dissolved oxygen in support 

of Rainbow Trout

 GOOD CONDITION, INCREASING TREND: GCD 

outflow temperature in support of Humpback Chub

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow phosphorus concentrations in support of 

ecosystem productivity
Project Information, Slide 5

 Water Quality Knowledge Assessment Completed 

January 7, 2020

 Team: Bridget Deemer, Peggy Roefer, Todd Tietjen, 

Robert Radtke, Charles Yackulic

 Status and Trends:

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow temperature and dissolved oxygen in support 

of Rainbow Trout

 GOOD CONDITION, INCREASING TREND: GCD 

outflow temperature in support of Humpback Chub

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow phosphorus concentrations in support of 

ecosystem productivity
Challenges of Predicting Interflow 

Limnology & Biogeochemistry

Unpublished data, subject to 28

change, do not cite.

~Penstock

depth

Pocket of low dissolved

oxygen water above penstocks

(minimum DO = 2.6 mg/L)
Project Information, Slide 6

 Water Quality Knowledge Assessment Completed 

January 7, 2020

 Team: Bridget Deemer, Peggy Roefer, Todd Tietjen, 

Robert Radtke, Charles Yackulic

 Status and Trends:

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow temperature and dissolved oxygen in support 

of Rainbow Trout

 GOOD CONDITION, INCREASING TREND: GCD 

outflow temperature in support of Humpback Chub

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow phosphorus concentrations in support of 

ecosystem productivity
Acknowledgements

 Lake Powell Monitoring Group: 

Nick Voichick, David 

Goodenough, Robert Radtke, 

Kristin Lewis, and Keri Stout

 GPP modeling/data: Charles 

Yackulic, Bob Hall, Ted 

Kennedy, Jeff Muehlbauer, 

David Goodenough

 Logistics & Lab Support: Carol 

Fritzinger, Dave Foster, and 

Seth Felder, Amy Stephenson, 

Ann Marie Bringhurst

 Mass Balance Modeling: Ted 

Stets, Charles Yackulic
Questions