U.S. Department of the Interior

U.S. Geological Survey

The role of nutrients in Colorado River ecosystem dynamics

Annual Reporting for FY16

January 24, 2017

Charles B. Yackulic (U.S.G.S. – GCMRC)

email: cyackulic@usgs.gov

With lots of help from Bridget Deemer, Michael Yard, Theodore Kennedy, Bob Hall, and many others
Are these just coincidences?

• Rainbow trout populations crash at the 

ferry...and all the way through Marble Canyon.

• Large-bodied native fish get skinny.

Preliminary data. Do not cite.
It was food! 

Preliminary data. Do not cite.
But, what caused the decline in the foodbase?

Let’s consider the usual suspects,

Biotic 

interactions

Flow

Temperature

Turbidity
We know density dependence and 

interspecific interactions matter.

Reach I

0

5

10

15

20

25

Apr2012Jul2012Sep2012Jan2013Apr2013Jul2013Sep2013Jan2014Apr2014Jul2014Sep2014Jan2015Apr2015Jul2015Sep2015Jan2016Apr2016

Reach IVB

0.0

0.2

0.4

0.6

0.8

Apr2012

ul2012

ep2012

an2013

Apr2013

ul2013

ep2013

an2014

Apr2014

ul2014

ep2014

an2015

Apr2015

ul2015

ep2015

an2016

Apr2016

But how can density dependence explain declines separated by 70 

river miles, and where densities vary by an order of magnitude? Also 

can a drift feeding fish really drive invertebrate populations down?

Preliminary data. Do not cite.

Rainbow trout Abundance (x1,000)
Korman and Campana, 2009 Cross et al., 2011

Flow management also 

affects the Colorado River 

ecosystem. But this 

particular decline doesn’t 

neatly line up with any 

clear changes in flow.
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Lake Powell

Navajo Reservoir

6 °C

18 °C

30 °C

 

 

Water temperature 

also matters, and 

may change 

dramatically in near 

future. 

But temperatures 

were not that 

anomalous in 

2014.

Preliminary data. Do not cite.

Preliminary data. Do not cite.
Hall et al., 2016

Tributaries also play important roles, as a 

spawning ground for native fish and sources 

of food and turbidity. But Lees Ferry is 

relatively free of tributary influences.
Biotic 

interactions Flow

Temperature

Turbidity Mr. P

Wait, I didn’t notice that guy over there, who is he?
If our primary producers in the Colorado River are 

nutrient limited, phosphorous is a prime suspect.

N - limited

P - limited

Preliminary data. Do not cite.
Reservoirs, remove P from water.

The CR has low and variable P.

Soluble reactive phosphorus (SRP) –

phosphorous that is readily available to plants

Preliminary data. Do not cite.
R2 – an aside

 Proportion of variance explained by one or more 

predictors

 0 – doesn’t explain anything

 1 – perfectly related

 What is a good R2 depends on the question (i.e., may 

expect to explain more variance when dealing with a 

simple system).
R2= 0.66

R2= 0.97

Seasonal estimates of gross primary production just 

above the LCR (~70 rm below the dam) are highly 

correlated with SRP at the penstocks.

Preliminary data. Do not cite.
And gross primary production is linked to bugs.

Preliminary data. Do not cite.
And native fish 

condition (fat/skinny).

Preliminary data. Do not cite.
Mr. P, what else might you be responsible for?

Preliminary data. Do not cite.
P vs. bugs in Glen Canyon

Near -4 rm

2012 – 2016

April

June/July

Sept

Jan

Preliminary data. Do not cite.
P vs. bugs in Glen Canyon

At Lees Ferry

2008 – 2016

June/July

May

But what about RBT?

Preliminary data. Do not cite.
Lees Ferry RBT recruitment model

 An attempt to 

combine NO, 

AZGF, and 

RTELLS data 

in a relatively 

simple model 

focused solely 

on recruitment.

8

6

4

2

0

Recruitment (x100,000)

2000 2005 2010 2015

Preliminary data. Do not cite.
Annual 

Volume

Hydropeaking

Flood

Antecedent conditions 

(catch of RBT > 150 mm)

Mr. P

Mr. P

+ AV

Mr. P +

Antecedent

Mr. P + AV

Antecedent

All Flow

predictors

Preliminary data. Do not cite.
So what causes variation in SRP at 

penstocks?

 Inflows (strength, timing, and how they travel 

across Lake Powell)?

 Penstock location?

 Other factors?

Preliminary data. Do not cite.
Take home messages

 While many factors likely drive ecosystem responses, the role 

of nutrients has been understudied in our system, and 

phosphorous is the most likely nutrient to be limiting.

 Recent declines in gross primary production, invertebrate drift 

biomass and native fish condition near the LCR all line up with 

trends in P.

 Invertebrate drift at two sites in Lees Ferry also line up with 

trends in P since 2008.

 The combination of existing rainbow trout populations and P 

can explain much of the observed variation in recruitment since 

2000.
Future steps

 More modelling of existing nutrient, gross primary production 

(DO data), inverbrate drift biomass, and fish condition or 

demographics to test potential role of Phosphorous.

 Research into and improved monitoring of nutrients, especially 

P, in the Colorado River over time and space.

Not GCDAMP, but worth considering

 Maintaining (and potentially) expanding nutrient (especially 

SRP) monitoring and research in Lake Powell will likely aid our 

understanding of trends in the Colorado River ecosystem.

 Development of models to predict SRP outflow will likely 

improve our ability to predict CR ecosystem responses.
Acknowledgements

 Bureau of Reclamation, Nick Voichick, Bill Vernieu, Mark 

Anderson, Glen Canyon National Monument and others for 

maintaining reservoir monitoring.

 Bridget Deemer, Michael Yard, Theodore Kennedy, Bob Hall, 

Jeff Muehlbauer , Mike Dodrill, Josh Korman, David 

Rogowski, Clay Nelson.

 Glen Canyon Dam Adaptive Management Program.